How To Build and Operate
Shaker Tables
Part – II Table Fabrication By Gary Weishaupt
Rev 12-16-2009
Shaker Tables
Table Fabrication Introduction In Part-I of this article we covered the history and development of Shaker Tables in general. We then looked at a variety of different table suspension systems and alternatives for drive systems. We built several small mockup prototype tables and reviewed ways to build some of the component parts for the drive mechanism but now we need to take what we learned in Part-I and scale it all up into the construction of a full-sized working wooden prototype table. From the feedback I’ve received so far it appears that the greatest amount of interest is for building tables that utilize the flexible-strip type of suspension system so we’ll be designing and building a carriage that can use this arrangement but still be adapted to almost any of the other systems we’ve reviewed. We have elected to continue using wood for the prototypes but have designed the assembly so that dimensionally it can easily be fabricated using steel structural members. It’s very tempting to go from the small-scale mockups to the final table carriage bypassing the full-size prototype stage but this can be more costly in the long run than spending the little extra time and a few dollars to make the prototype to begin with. One of the biggest reasons for building the prototype is to check that all of your hardware components will fit into whatever space you allocate for the carriage and that you can easily fit wrenches and screwdrivers inside the frame to service those components. This is also the time to verify that your drive system and its geometry actually functions properly. Sometimes great designs on paper don’t work worth a hoot when transferred into reality. More often than not however most full-sized prototypes will perform quite well and can actually be used for at least one or two seasons and this will give you not only a working Shaker Table but also an opportunity to refine and improve your design based upon actual field conditions as opposed to mere theories. People rarely want to hack up a nice finished table to make modifications and changes but won’t hesitate to cut up a somewhat rough prototype creation since its an ongoing project to begin with. One of the primary objectives of these articles is to provide people with a variety of fundamental information about Shaker Tables so readers can take that information and apply it to their own uniquely customized piece of gear.
1
Shaker Tables
Full-Size Prototype Fabrication Materials Material for the carriage frame is 1x2 nominally dimensioned wood with a finished size of 3/4”x1-1/2”. For a steel frame a builder can substitute 1-1/2”x1-1/2” square tubing which is readily available or the harder to find 1”x1-1/2”x.120” rectangular tubing. For the prototype we’ll be using Poplar since it’s very cheap but for a finished wood table I strongly suggest the builder use good cabinet quality Maple. Needless to say all wood materials need to be hand selected for straightness and free from knots or any other defects. This isn’t as easy as it sounds as the quality of wood at most building supply companies leaves a lot to be desired and you may have to visit several yards before you get enough quality stock. For the carriage and associated bits and pieces you’ll need about 32 lineal feet of material. I usually buy a lot more so I can be picky and only cut out pieces from the best section of any length of raw stock. The biggest drawback with using wood for the frame is that unless its extremely well sealed it will eventually start to break down over time in the constantly wet environment these tables operate in. As I mentioned in Part-I regular old shellac as a sealer with a good quality marine grade paint finish should do the job but if you want a table to last for more than about 5 years try using some of the marine penetrating epoxy finishes. For fasteners use stainless steel deck screws or nails or at least something with a zinc coating. I use a small pneumatic finish nail gun with coated square brads for a lot of the connections and these don’t rust and the connection is every bit as tight as you’d get by using screws. I also use biscuits or dowels at most of the joints in the frame pieces and these add a significant amount of strength to the assembly. Needless to say all connections need to be glued and that glue has to be the waterproof variety. Not all glues are created equal and some of the popular brands actually perform pretty poorly. I’ve added the links below to some glue tests that I found interesting. http://koti.kapsi.fi/hvartial/glue/glue.htm http://www.woodenboat.net.nz/Workshop/Workshoptips/Holdfastfolder/Gorillaglue.html I personally don’t care for Gorilla glue and some of the newer space age glues and have found that regular old ‘Weldwood Titebond II’ (not the new III) works extremely well and is completely waterproof even though the label has a warning not to use it below the waterline on boats. Maple and even Poplar are both hard to glue since they have a very closed grain structure and most glues can’t penetrate very deeply so I’ve found that roughing up the connections with a wood rasp and then slightly dampening the areas to be glued will help in getting the adhesive deeper into the wood. I made up a small dummy butt connection 2
Shaker Tables from some Maple scraps glued with ‘Titebond II’ and had to bash it pretty good with a small sledge hammer to get it to break and when it did the most of the glue joint actually held up but the wood fibers tore apart so I’ll continue to use this stuff. Shaker Table frames take a tremendous beating over time due to the constant ‘bumping’ and secondary vibration so they really do need to be strong but not necessarily heavy and one way of adding strength to the frames once they’re completed is to add some removable 1/4-inch plywood shear diaphragms to the sides and bottoms with small closely spaced wood screws.
Carriage Design The table suspension and drive carriage we’ll be building in this article isn’t any revolutionary design concept and in fact most tables are the types of things where form follows function and come about primarily because the mechanical parts and components dictate the design. Basically all we need is a small rectangular frame that’s big enough to contain the mechanicals and allow room for the suspension to move through its motion cycle. The frame we’ll be making making is very similar to that found on the old flywheel flywheel type Gemini tables and other brands that used similar drive systems. It’s a fairly standard structural arrangement. The area where our prototype does differ from conventional tables however is in the use of a separate suspension frame that the table deck is fastened to. The reason I like this system is because it allows you to build one carriage that can be fitted with a variety of different deck styles, designs and sizes. I personally think the design we’re using is extremely easy to construct with limited tools and limited financial resources. It is modular in nature so the major components can easily be removed for storage in cramped spaces, relatively lightweight and much smaller than the pictures would lead you to believe. No special tools are required for this project though thoug h it is strongly suggested that you gain access to a drill press to bore the holes for the bushings and bearing block mounts. There are no fancy miter, dado or mortise type connections and all cuts can be done using a cheap miter box to make 90-degree square cuts, which do need to be accurate. The use of biscuits in the joints is optional and you don’t need a doweling jig as the dowel holes can be drilled with a hand drill. If you have enough room in your shop to lay out the parts of the sub-assemblies as the glue dries you can build the entire carriage frame and deck suspension frame in a single weekend so this not a very time-intensive type of project. You’ll very likely spend more time rounding up the materials and hardware parts than you will in actually doing the fabrication work.
3
Shaker Tables
Budget This particular table design is also relatively easy on the wallet but the final cost will be in direct proportion to how resourceful and creative you are. Many of the component parts can be picked picke d up in used condition at garage and a nd yard sales. Some of the parts you may already have laying around in your garage or shop. The following table lists the frame parts and their costs as of 11-14-09 here in Napa California and all were purchased at either the Home Depot or our local Ace Hardware store. These figures include sales taxes.
1x2 Poplar and Maple Wood Chicago Casting Pillow Block Bearings V-Belt Pulleys Bronze Bushings Shoulder Bolts Nuts, bolts, washers, and screws 5/8” steel shaft (36” long) 5/8” shaft collars V-Belts Hinges Springs Caster Wheels 2” plastic 5/8” steel plate (scrap) Hole saw Saw Blades Glue Sealer Motor
$49.70 48.75 22.80 27.15 24.12 16.31 11.10 13.65 12.25 6.42 7.45 12.80 18.50 8.75 5.56 8.50 6.17 Surplus
Total Cost
$279.70
I was fortunate enough to have an old surplus motor in the shop that I could use for this phase of the work as new motors are pretty expensive but as I’ve mentioned sometimes you can buy an entire piece of used equipment for next to nothing and then salvage the motor to save some cash. You can also temporarily ‘borrow’ a motor from some other piece of gear you yo u might have at home already. You can c an always reinstall it back when you have enough money to buy a replacement. To me, the money I spent seems cheap in comparison to what I have so far, when you consider how much a small lab sized Shaker Table costs so I’m surprised when people email asking if they can build a table for around a hundred dollars. I think you probably can do that if you’re a good scrounger and improviser and buy used parts.
4
Shaker Tables
Table Structural Components This particular table design is pretty simple and has very few structural parts. The major components of the entire finished table are shown in the exploded-view schematic isometric sketch below.
Figure 1
Keep in mind that the’ carriage’ and the ‘stand’ can be incorporated into a single unit. I personally prefer to build b uild them separately and bolt them together but you can build bu ild it any way you need to for your particular requirements. I will not be describing construction of a separate stand in this article as I think it’s fairly self-explanatory. We do need to look at some basic dimensions however that have an effect on the overall size of a finished table unit before going much further. 5
Shaker Tables Figure 2 illustrates two critical dimensions that more or less control the vertical measurements for a typical table setup.
Figure 2
Measurement ‘H1’ is the overall height of the deck surface from the shop floor and is usually in the neighborhood of 36-inches. Measurement ‘H2’ is the overall height to the uppermost opening of the material feed hopper and is typically 42-inches for most setups. Both of these measurements are basically set by the operator’s ability to easily reach all the way across the width of the table from either side and to see into the feed hopper without having to use a stepstool.
Deck Sizes This article is specifically concerned with small tables suitable for the more serious week-ender or small-scale mining operation so deck sizes need to be relatively small but still effective. The term ‘effective’ unfortunately has wide interpretation and some table manufacturers will wildly exaggerate their table’s performance claims in order to gain a wider buying audience. The size requirement of the working deck is in direct proportion to the amount of raw material that you plan to be running. The carriage frame we’re building here can handle decks as small as 17”x36” to a s large as 30”x60”. It is especially well suited for the Gemini deck as used on the Model-60 which is about 36”x48”. From my perspective as a previous table user I’d say that decks much smaller than around 17”x36” are strictly in the home-hobbyist class and not really worth bothering with even as a starting point. Keep in mind that most small testing labs are using tables 6
Shaker Tables with decks that are 24”x48” and they are doing fairly significant work with these tables, processing in the neighborhood of 400 pounds of material per hour which equates to around 30 gallons (dry) of classified gravels per hour. For the average small operator a deck size of between 20x40 to 24x48-inches is ideal. If your operation grows larger it is more cost and time effective to run two small tables rather than one large one. We’ll talk about decks in more detail in later sections but for now having a rough idea of what size you want to build is more than enough information to begin with.
Carriage Construction I usually start construction by culling out the best pieces of material purchased at the lumberyard and start laying out my cut marks to take best advantage of the stock on hand. Always use the straightest pieces to cut the long members and then cut the smaller members from the remainder. Remember that all we’re building at this stage is the carriage assembly as shown below. b elow.
Figure 3
If you decide for whatever reason you’d prefer to build a carriage with an integral stand the assembly might look like the illustration in Figure 4. The construction techniques for either unit are very similar.
7
Shaker Tables
Figure 4
I have to confess that I am in no way a carpentry type of guy so the construction scheme I’ve come up with is the simplest I could contemplate that required the fewest number of special woodworking tools. For this reason you should feel free to improve on it in any way that you can as long as the dimensions remain constant.
A detailed set of large-scale plans for the carriage can be found at these links: http://64.172.168.34/neatstuff/st1-1.pdf http://64.172.168.34/neatstuff/st1-2.pdf http://64.172.168.34/neatstuff/st1-3.pdf
Other drawings will follow and I will post updates at the discussion forum when they are finalized and ready for publication. You can have these sheets printed at almost any office supply type of store that has a large format Hewlett-Packard plotter. The sheets are 30”x42” in size.
8
Shaker Tables The component parts of the carriage frame are shown on sheet ST1.1 as shown in Figure 5, which is a small-scale reduction. There is a cutting list for the various parts on that sheet.
Figure 5
I am refining and improving the basic table on a daily basis so the photographs in this article may not show the latest refinements I’ve decided to make in the design but the drawings will always show the most up to date information so make sure you have downloaded the most recent release of the plans.
Part Cutting and Assembly I usually start by cutting and assembling the pieces needed for the cross-members since I like to start with the smaller parts and work up to the large pieces primarily because I have a very limited work space. These parts do need to be cut accurately and for most parts of the table carriage I personally think that you need to be within 1/32” on any cut cu t and ‘spot-on’ is much to be 9
Shaker Tables preferred. Quite often I use the belt sander to make the final dimensional adjustments that are to fine to do with a saw.
Figure 6
Each cross-member is built-up from two separate parts and they need to be secured together into a monolithic unit. You can simply nail the pieces together or use biscuits or dowels or screws to hold the parts together as the glue dries. If you want you can build the cross-members from solid stock and saw cut the notches notch es at the ends.
Figure 7
10
Shaker Tables After the cross-members have dried I’ll usually put together togethe r the two large side frames.
Figure 8
Figure 8 shows one of the frames in the clamps. Needless to say you do need to put a square on the frame as it’s being clamped down to insure that the corners are at perfect right angles. Once the frame has cured I’ll drill the holes for the suspension links if that’s the suspension method you decide to use. If you’re building a flexi-table the bores for the link bushings aren’t needed. Once the individual parts have cured it’s time to put the frames together but you have to take precautions that the parts are assembled perfectly square and plumb, as the least bit of misalignment can be disastrous. I usually use two carpenters’ squares and a couple of small adjustable squares during the assembly process to keep everything square and plumb. I typically like to make a ‘building-bed’ on the workshop tabletop by screwing down a standard carpenters square right to the table surface. I use this as a ‘stop’ that I push the parts into to insure that they’re at right angles to each other as they are being worked with. If you look closely at Figure 9 you can see the framing square I’ve used to set up my frame assembly area. I’ve screwed this square to the tabletop and use it as ‘stop’ for the assembly process. 11
Shaker Tables
Figure 9
The hardest part of putting a table together, no matter what the design may be, is in insuring that the overall assembly is perfectly square and plumb and that all the holes for the various connection points, mount points and other associated accessory mounts are perfectly aligned. A sloppy frame will only provide sloppy performance so if you can’t build a square and plumb table carriage you will be plagued with sub-par performance from the final product no matter what plans you’re building from. I try to build temporary jigs or fixtures to hold the various pieces in alignment as they are glued and fastened and also to accurately position any hardware mounting holes that are drilled by hand instead of in the drill press. This extra step does ads to the workload but it greatly speeds up the fabrication process if you’re building more than one table carriage. In fact it’s really a good idea for several people to go together on projects like this and build multiple tables since you can usually get some pretty good discounts by buying parts in quantity. Sometimes you might be able to pay for your first table by selling off a second table or renting time on it to club members. Figure 10 shows the carriage while the side frames are being installed. Notice the long pieces of steel rod used as guides so the link pivot point holes are perfectly aligned from side to side. 12
Shaker Tables
I cannot overemphasis how important it is to have everything square and plumb. Quite often you might be tempted to use a piece with a slightly skewed cut thinking that the glue will fill the gap but it will payoff many time over to re-cut something in order to have a perfect fit-up.
Figure 10
The next pieces to add to the assembly are what I call the upper and lower inside rails. When I was putting together the first prototype I just screwed these rails down on the cross members as seen in Figure 11. The red arrow points to one of the eight connections. This ended up being a bad idea and a weak point in the design so for the final product I’ve decided to set these rails down inside, and next to, the main side rails and let the ends lock into the lap-joint pockets on the cross members. The inside rails are then glued and screwed to the side rails for their entire length which adds a tremendous amount of rigidity to the overall assembly. This is much stronger connection method and also allows you make the frame assembly an inch and half lower in height if desired.
13
Shaker Tables
Figure 11
Note that the upper upp er cross members are set back away from the ends of the carriage. This is to allow room for the suspension strips or links to move back and forth during operation and to permit the suspension frame to be adjusted fore and aft to change the stroke length.
Figure 12
Figure 12 shows a mockup for the preferred way to make the connection between the inside and outside side rails, the cross-member and the upright frame legs. This is the
14
Shaker Tables method illustrated in the large-scale plans. This is lower rail connection but the upper is similar. Once the basic carriage assembly is complete it’s time to add any additional blocks or other members that may be needed to install the mechanical parts. In Figure 11 you can also see that I’ve added additional cross members on the right hand side of the frame where the motor will be sitting and some ‘stiffener’ blocks between the side rails and inner rails. At this point I want to digress a little and talk about the hardware components since they determine to a significant extent how this particular design evolved.
Hardware Bearings
On this prototype I didn’t want to spend a lot of money so I bought cheap pillow block bearings made by Chicago Die Casting. These are the bearing assemblies most hardware and building supply stores sell internationally. They do not contain roller bearings but instead are filled with a bronze bushing and the body itself is just a pot-metal casting. These units cost about 60% less than a good roller bearing unit but they can last for decades if you occasionally oil the bushings.
Figure 13
15
Shaker Tables Figure 13 illustrates our lower bearing and shaft assembly in place. The problem with type of bearing assembly is that it cannot tolerate any misalignment or the shaft will bind and prematurely wear. If you use this type of assembly it is likely that you’ll have to shim the bases and shift the mounting holes slightly to get a perfectly free spinning pulley shaft. More expensive pillow blocks use bearings mounted in a spherical housing that permit the bearing assemblies to be misaligned yet allow the shaft to rotate properly. Figure 14 shows one of these spherical bearing removed from the housing and you can see how much the bearing can be misaligned when I twist the shaft off-center.
Figure 14
This particular situation is extreme and in most cases the amount of misalignment will be impossible to detect with the naked eye. Unfortunately this type of pillow block assembly is relatively expensive but much to be preferred if you can afford to do it. The next critical factor in selecting a bearing is the height of the shaft centerline relative to the base of the housing, The greater this dimension is, up to a point, the better off you will be.
16
Shaker Tables I normally use bearings with a height of 1-3/16” which is just one of many standards in the industry. A typical sleeved bearing having this height is shown in the cut-sheet from McMaster-Carr.
Figure 15
If you need a ‘taller’ housing so that a large pulley will clear the extremities of the frame you can make some aluminum or steel spacers from 2” wide by 1/4” or 3/8”thick material placed over a wood strongback.
Drive Shafts
I always use 5/8” diameter drive shafts and on wider tables I’ll go up to 3/4” but on a small table like the one we’re building the 5/8” material will provide plenty of resistance to bending. Standard shaft collars are used to secure the shafts between the bearings and to secure the drive cams or eccentrics to the shafts. McMaster-Carr sells a shaft material that has a ‘flat’ milled along its length, which provides an a n excellent e xcellent shelf for the shaft collar co llar setscrews to seat sea t on. You can always just grind a small ‘flat’ on cheaper shaft material once you get all the cams and pulleys into their final arrangement.
17
Shaker Tables Pulleys
Like most manufactured parts not all products are created equal and V-belt pulleys are no different. On our prototype we’re just using cheap die-cast pulleys and the larger ones are significantly out of round and also skewed around the perimeters. At the slow speeds we’re operating with this isn’t much of a problem but the belts will start to wear prematurely. Good steel or o r aluminum pulleys are more expensive exp ensive but the entire machine will operate much smoother with less vibration and the belts should last for several years between replacements. We talked about pulley size and speed relationships in Part-I of the article so there isn’t a lot more I can add except that the configuration shown on this prototype will be fairly typical for most applications. This particular table is presently configured to provide 214 impulses per minute using a motor that spins at 1725rpm. We’re running a 2” pulley on the motor that drives a 4” pulley on the jackshaft, which in turns runs another 2” pulley up to the cam drive shaft that is fitted with an 8” pulley. For running fine materials you need to get the impulses to around 300 per minute and to do this on our table we will swap out the 4” for a 3” and change the 8” to a smaller 6” and then we be running at 287 rpm. Pulleys are available in almost every conceivable diameter so it is possible to really fine-tune your deck speed but of course the ultimate setup is to use a variable speed motor to begin with. Multi-sheaved pulleys also make it easier to change speeds without having to remove the shafts.
Belt Tensioning
I had originally thought about using belt-tensioning pulleys to handle the problem of keeping the belts tight but after I welded up a test assembly it just seemed to be more trouble than it was worth and really made the whole unit much more complicated than needed. After I made a mounting base for the motor from some scrap 3/4-inch plywood it occurred to me that I could handle the belt adjustment problem by simply making ‘sliding’ bases for both the pillow block bearing arbor and the motor. The upper primary drive shaft is always stationary so all that is needed is a means of providing tension on the belt between the motor and jackshaft and then between the jackshaft and drive shaft. If you have a router you can always just route some slots for the fasteners at your hardware mounting points and simplify things tremendously. You generally won’t need much more than about 1 to 1-1/2” of adjustment at the most and in most cases just 3/4" is all that’s needed to change a belt.
18
Shaker Tables
Carriage Finalization
To finish up the carriage all that is need at this stage of the construction is to add some reinforcing gussets and stiffener blocks at the corners of the frames and where the various pieces of hardware mount to the frame. We’ll cover the finer points of adding adjuster screws to the belt-tensioning sliders, springs and other elements later. We’ve posted three videos of the prototype fitted with two different drive arrangements at Youtube, which you can see at the following links: http://www.youtube.com/watch?v=vEDXzXwbKG4 http://www.youtube.com/watch?v=rLZ4dYErsko http://www.youtube.com/watch?v=hNAXDrrk154 Keeping in mind that we’re still in the development and refinement stage of this project the feedback from viewers has been positive but most people think the machine is far larger than it actually is. I think this is an illusion created by having the carriage sitting on top of a workbench that’s 46” high instead of on a more conventional stand of some sort. The unit is actually fairly small being only 30-inches long by 16-inches wide and 12inches high. As I’ve mentioned elsewhere you can always build it smaller depending on the size of the motor you’re going to be using.
Figure 16
19
Shaker Tables Figure 16 is a snapshot of the carriage sitting on the floor and I think you can get a better idea of its mass when you compare it to the size of the 24-inch cabinet drawers and the propane bottle. I left the table running after we installed the suspension frame and so far it’s been in continuous operation for about 57 hours and there are no signs that any of the frame member connections are experiencing any type of undue stress. To be honest the unit is operating far better than I had ever expected considering the crude methods we’re using in its construction. Since the frame isn’t bolted down to anything residual vibration does make it move around a bit but after 12 hours it had only moved about an eighth of an inch from its original position on the workbench. One of the problems with small tables like this that use flexible strips as both the suspension members and tension springs is that they vibrate horribly. Using rigid suspension links as we have done here completely eliminates this problem. Just out of curiosity I decided to find out exactly what kinds of stresses were being placed on the drive mechanism but having no strain gauges of other sophisticated measuring instruments I just stuck my finger in between the eccentric and the roller as I hand-cycled the drive belt and found that the pressure is only around 20 static pounds. That’s about the same force an old fashioned wooden clothespin puts on your finger. In actual operation the dynamic load is probably about three times greater which is still far less than the force used to drive a nail with a hammer.
Suspension Frame
Most Shaker Tables have the surface decks mounted directly to the suspension members, which makes it difficult to install various types and sizes of decks to a single carriage. On this design we use a separate suspension frame that can accept a wide variety of different deck sizes with different types of riffles for different types of raw materials. As mentioned earlier this carriage can accept decks as small as 18x36-inches to as large as 32x66-inches and also handle decks similar to the popular little Gemini Model 60. This feature gives this table design tremendous flexibility that shouldn’t be underestimated if you’re operating on a limited budget but expect to increase the size of your production operation over time. For a less complex table you can always build the suspension frame and deck surface as a single unit. In fact using a taper jig on a table saw you could build the frame with built-in slopes on the structural members. Regardless of which method you decide to use keep in mind that the deck and deck frames are structural elements and when the table is loaded the assembly can have a
20
Shaker Tables significant amount of weight on it so we need to design the assembly to handle this weight without distorting. If we were using steel or aluminum for the members there wouldn’t be much of a problem but wood isn’t as stiff so we have to be more cautious in how we build these structures. The first thing to consider is the total ‘dead load’ of the assemblies. That is the total weight of the deck surface, deck frame, launders, edge boards, water piping system and anything else attached to the deck. In our particular example we’ll be building for a deck having 8 square feet of surface area, basically a 24x48-inch deck. Using 1x2 maple for the structure of the deck frame will give us a weight of 7.29 pounds and using 3/8-inch plywood for the deck adds another 8.28 pounds. The launders add another 6.48 pounds and the water supply system is another 5-pounds for a total deck assembly dead load of 27.05 pounds. Lets round this up to 30-pounds. Now we need to consider the ‘live load’ placed on the deck by the weight of the slurry and wash water. I did some desktop figuring to come up with a number here based upon a slurry that was composed of 20% gold, 20% heavies and 60% quartz sands, well saturated and with a stream of wash water one eighth inch thick and the results were a slurry and wash water weight of about 12 pounds per square foot. Just out of curiosity I took a cookie sheet and filed it with my typical concentrates to a depth of one-quarter inch and then saturated this material until it had about an eighth of an inch of water cover. I weighed this test sample and it only came in at 8.7 pounds per square foot. To my way of thinking I feel confident that if I use a value of 10-pounds per square foot as a live load I’m probably in the ball park and if anything erring towards the heavy side since the slurry is never level but trapezoidal as it’s being processed. A more realistic figure might be in the neighborhood of 6-pounds per square foot in the real world. Using the value of 10-pounds per square foot for the live load, 80-pounds, added to the dead load of 27.05-pounds we need a suspension frame that can support a total operational load of 107.05-pounds. This might sound like a lot of weight but keep in mind that this is a distributed load spread out over the surface of the deck. Since our particular suspension frame is basically a 4-foot long rectangle with two primary beams, each beam must be able to carry one-half of that load, divided by their length, or 13 pounds per lineal foot. You can use some of the online beam calculators to check your member sizes and in this cases we are well below the limits for a pieces of 3/4x1-1/2” maple.
21
Shaker Tables If you don’t want to do a bunch of math you can just build a ‘test’ beam that you plan on using for the suspension frame and pile weight on it until you begin to see some deflection and that’ll tell you when you’re getting into the ballpark on material size. This may sound like a pretty rude, crude and non-scientific way of doing things but it produces results that are sometimes better than can be calculated on paper.
Figure 17
Figure 17 is a snapshot of our suspension frame with some weight placed in the center of one of the side beams. I used an old 10-pound dumbbell and five 3-pound lead ‘ducks’ to load the beam up to 25-pounds in the center and still could not see or measure any deflection in the beam so I’m pretty confident that this frame will meet our requirements. For small projects like this one common sense and gut intuition will usually serve you pretty well so I wouldn’t get carried away with trying to fine-tune every single component of the table, especially if you’re building it out of wood as it is a very ‘forgiving’ material. On the other hand if you’re looking to develop something that you want to build and market to the public then you really do need to test almost every single component in any way that you can possibly imagine before committing to a final design concept. Even then you need to test run your product idea for several seasons before thinking about offering something to potential buyers. I wish manufacturers of mining equipment did far more product research than they typically do as most of us end-consumers are in this business for the ‘long-haul’ but 22
Shaker Tables much of the gear being sold is designed for short-term applications, about one to three years until it simply falls apart and needs replacing. I suppose this is akin to the automaker philosophy of ‘planned-obsolescence’ as we’ve all come to know it. This is one reason I prefer to build my own equipment. Figure 18 depicts the suspension frame mounted on the carriage using the ‘link’ method. We’ll describe how to implement a ‘flexible-strip’ suspension later on in this article. Normally I would build the suspension frame to where it is wider and bolts ‘outside’ of the link connections but this particular frame is designed for a somewhat unusual deck arrangement.
Figure 18
On wider suspension frames you can mount the links on the outside surface of the carriage uprights but I prefer to keep them inside for safety reasons. An example of a wide suspension frame is shown in the sketch of Figure 19. Note that there are intermediate members that serve as the link mount points. I can’t go into a lot of specifics about the suspension frames because a lot of their design depends on what size your deck will be, how much weight it has to carry and what type of suspension and drive systems you decide to use for your particular application. Never the less I think that what little we’ve shown here and what’s included on the plans will be more than adequate to assist in your projects.
23
Shaker Tables
Figure 19
This type of suspension frame can be extremely strong if you connect the members using half-lap joints so each piece is a continuous length of wood from end to end. Now that we’ve built the suspension frame it’s time to look at how to connect it to the carriage frame.
Link Suspension System
A link suspension system is probably one of the easiest to implement and they work extremely well and provide a lot of flexibility as to how you decide to handle not only the entire drive system but also the tension and rebound spring systems as well. Links are used in many large commercial tables but no small tables that I am aware of. I think the reason for this is because it is more expensive and time consuming to build a link system as opposed to a ‘flexi-strip’ suspension system. I prefer the link system so we’ll discuss how to set this up before we address the installation of a flexi-strip system. First of all you have to build the links themselves. If you’re building with wood you really do need to use good quality hard Maple that’s perfectly flat and straight. I use 1x2inch (nominal) material that has a surfaced dimension of 3/4”x1-1/2”. The length of links will vary from design to design but for this particular table the measurement between pivot point centers is 10.375-inches. We’ll be using bushings that have an outside diameter of 5/8-inches so bore the holes with a sharp bit and use a backing board so there isn’t any split-out on the bottom side of the cut. Figure 20 shows the links after the first pivot point holes have been drilled. 24
Shaker Tables
Figure 20
Whenever you’re making parts that need to have identical dimensions or identical holes it’s a good idea to temporarily fasten them together with clamps and do the cutting and boring at one time.
Figure 21
25
Shaker Tables Figure 21 shows the links with some 5/8-inch drill rod in the pivot holes. In practice you drill through all four links while they are clamped together and then insert a rod into the first bore to hold alignment while the second hole is being drilled this way you know for sure that all four pieces are exact duplicates dimensionally. Once the links are finished they need to be unusually well sealed otherwise the bushing holes will begin to deteriorate from moisture intrusion. Urethane is a good product to use as it will build up a slight ‘thickness’ on the insides of the holes which will insure that the bushing are a good tight press-fit into the bores.
Link Bolts
To attach the links to the frames it is customary to use ‘shoulder bolts’, sometimes called ‘shoulder screws’ by some vendors. These fasteners are specifically designed to act as bearing shafts on parts that need to rotate and they come in stainless steel as well as mild carbon steel. For most application bots with a 1/2-inch diameter shaft are more than strong enough for tables up to around 30”x60” but beyond that it is better to use bolts having a 5/8-inch shaft. Shoulder bolts can be purchased in 1/4-inch shaft length increments and for our tables that use 3/4-inch thick frames and links, plus 1/4-inch spacers and washers we need a length of 2.25-inches. Since material is seldom perfectly accurate in its manufactured condition a shoulder bolt is designed to be lengthened or shortened with special shim washers that come in a wide variety of precision thickness.
Figure 22
26
Shaker Tables Figure 22 shows a typical shoulder bolt alongside the different shim washers. The larger washers on the left are ‘shortening’ shims and the washers on the right are ‘lengthening’ shims. By using a combination of shims you can control the amount of tension on the bolt and the fastened pieces to insure a tight but ‘movable’ connection.
Figure 23
Figure 23 shows the bolt with three ‘shortening’ shims installed on the shaft.
Figure 24
27
Shaker Tables Figure 24 illustrates the ‘lengthening’ shims installed on the threaded shank of the bolt that in effect adds length to the smooth shaft. Regardless of whether you’re building with steel or wood shoulder bolts are designed to run in bushings fitted through the joining members. In steel construction we’d be using bronze bushings b ushings but since these bushings are impregnated with oil we can’t use them on wood structural members otherwise the lubricant would just leach into the wood fibers. For wood construction we need to use nylon or delrin bushings. Figure 25 illustrates various types of bushings and thrust washers in both bronze and nylon.
Figure 25
The two bronze bushing in the uppermost portion of the picture are called ‘flanged’ bushing and I personally prefer to use this type but I did not have any of these in nylon on hand when I was working on the table. All of this material is available from McMaster-Carr and other online industrial suppliers as well as the better local hardware stores. The objective in creating a bushed connection with shoulder bolts is to securely fasten the movable members together tight enough to prevent any lateral play or slop in the joint yet not have so much compression that the members cannot rotate. Figure 26 shows a mockup of a typical link connection using nylon bushings and thrust washers with a standard mild steel shoulder bolt. b olt.
28
Shaker Tables You can’t really see it in this snapshot but the shoulder bolt uses a pair of jam nuts so the tension can be precisely adjusted yet kept from loosening as the bolt rotates.
Figure 26
Ideally you want the connection to be tight enough so that a little pressure is required to actually rotate the parts. Three to four pounds of mild hand pressure is fairly typical for this type of application. It will lessen slightly over o ver time as the bushings wear down. The nylon bushings usually will last for a couple of years before needing to be replaced in wood members but the bronze bushings in steel can last for decades if kept lubricated. Once the suspension frame is attached to the carriage with the links we can start to look at the construction of the drive system, sometimes called the ‘motion-system’.
Drive System For this particular table we’re using a drive system that consists of an eccentric cam mounted to the drive shaft that ‘bumps’ against an off the shelf caster wheel. At first glance it’s a fairly rude and crude drive arrangement but in application it is extremely efficient, effective and very easy to build on a tight budget. So far I’ve had the table running 24 hours a day using this arrangement and we’re now just under 500 hours of continuous operation and none of the components are showing any wear or stress so I’m confident that the system works even when using less than optimum parts.
29
Shaker Tables Eventually I want to change out the cheap plastic caster wheel to a better quality hard rubber wheel primarily to cut down the noise level more than anything else. The plastic wheel actually works very well but it creates a lot of noise since it doesn’t have any bearings on its very loose axle shaft and the wheel surface is extremely hard.
Drive Components
The drive components consists of what I call the ‘drive-bar’ which is secured to the suspension frame, the roller ‘brackets’, the eccentric cam mounted to the drive shaft and the tension/compression springs. The drive-bar is simply a piece of 1x2 laid on the flat that is secured underneath the suspension frame as seen in Figure 27 highlighted with the arrow.
Figure 27
The ‘roller brackets’ that hold the caster wheels are attached to this bar. For a large table it is a good idea to add a strong-back on the topside of the bar to act as a stiffener to prevent deflection under load. The roller bracket I made for this table was pretty simple and most fabricators can probably come up with a more elegant design but this one works but it’s something I want to improve on down the road.
30
Shaker Tables Figure 28 is a snapshot of the roller bracket we ended up using to mount the cheap 2” plastic caster wheel assembly.
Figure 28
Figure 29 is a shot of the bracket attached to the drive-bar.
Figure 29
31
Shaker Tables In hindsight I should have made the reinforcing wedge extend past the lower caster mount screw holes but even this unit has held up just fine so far in the project. Figure 30 is a picture looking up from below the table frame towards the drive-bar and the roller bracket.
Figure 30
This snapshot also shows the relationship between the drive eccentric and the roller wheel when the table is in what I call the ‘neutral mode’. It’s not to clear in this snapshot but there is 3/8-inch of clearance between the eccentric and the roller wheel when the machine is in the ‘neutral mode’.
Flexible-Strip Flexible-Strip Suspension System Before we move on to Part-3 that will cover Table Deck construction I wanted to briefly describe the ‘Flexible-Strip’ type suspension system, which seems to be very popular today and is used on several different brands of tables. We covered the basis concepts of flexi-strips in Part-1 of this series but on a full sized table we need to build a little more robust arrangement as in use there is a significant amount of force being applied at the mounting points of the strips.
32
Shaker Tables For this reason I prefer to make the strip mounting brackets from steel instead of wood but I suppose that you could use wood components on a small table. To rig up a flexible strip suspension on our prototype table you start out by cutting 4 pieces of steel angle stock into 9-inch long sections. In this example we just used 1.5x1.5x.125-inch angles but on a production table you should use 1/4-inch thick material. Along with the section of angle iron you cut 9-inch long strips of steel strap stock to serve as the outer clamp bars. The pieces are shown in Figure 31.
Figure 31
The angles and clamping bars are drilled for 5/16-inch machine bolts. I typical use 4 bolts per unit. These pieces are normally thru-bolted into the wood frame cross members so drill holes for these additional fasteners as well. For the strips themselves you can use pretty much any relatively thin and flexible material such as plywood, nylon sheeting and even sheet metal. We’re using a piece of scrap 16-gauge steel on this table. I personally prefer to use marine grade plywood but everybody will have his or her own preferences. Besides being flexible the strips also have to be stiff enough to carry the weight of the suspension and deck frames plus the load on the deck when the table is in operation.
33
Shaker Tables Attach the angle sections to the carriage cross members using 5/16” flat head machine screws with the heads toward the bottom of the members so they can be countersunk. Figure 32 shows one of the angles in place on the lower cross member. Keep in mind that when using the flexi-strips that the suspension links, show in this snapshot, are not used. I was just to lazy to un-bolt them for this series of pictures.
Figure 32
On this particular table I ended up using a piece of 1.5x2-inch angle for the upper brackets since it worked out better with the location of the compression/tension spring rod. Figure 33 illustrates the finished flexi-strip mounted in place. I didn’t do a detailed layout for these brackets since they were made purely to illustrate the concept of mounting the brackets so I just drilled the holes by eyeball, which is why the spacing isn’t perfect, but I think you can see how this system is fabricated and installed. Again, remember that if you’re using this suspension system the links are not used and the strips can be wider or narrower than what we used here. It is important however to have everything well bolted and secured. For some people this suspension will be easier to fabricate than links while for others links will be the simpler method so try both systems when you’re building your first prototype tables.
34
Shaker Tables
Figure 33
The strip of sheet metal is ‘clamped’ between the angle iron and the flat bar with four 5/16-inch machine screws. We’ll have a drawing showing the specific details of this suspension system in the final set of building plans.
Wood Verses Steel Construction So far we’ve only been documenting wood table construction and it performs extremely well and a wood framed table can last for several seasons if it’s well built and well sealed from moisture but there are drawbacks to using wood as structural frame. Even though wood is more than strong enough for table construction it has the disadvantage, due to its low density, of acting somewhat like a large shock absorber so much of the impact force imparted by the drive mechanism is dampened slightly compared to what you would experience if the frame were made from steel. For most applications this shouldn’t be a problem but if you want a table that performs to the maximum extent then you should seriously consider building the carriage and suspension frame from steel. This change actually only raises the material costs by about $150 dollars if you have welding experience. Unfortunately if you have to hire somebody to do the welding the cost can triple that amount but its something to consider if you have a lot of high quality material to process.
35
Shaker Tables
Large Scale Plans We’ve prepared a set of large scale building plans to accompany this article but keep in mind that this project is a work in progress so the plans basically document what we’ve done during the construction of this particular table design. We’ll be making changes and refinements as we go. If time permits I’ll be updating the plans as we make improvements so each drawing contains a revision date. Be sure you have the latest edition of any sheet. The plans are in Adobe pdf format and the sheet size is 30x42-inches. These can be printed at almost any office supply business that has a large format HP printer/plotter. In a pinch you can print them at home on a regular printer by using ‘tile-mode’ which will break the sheet down into small 8.5x11-inch sections, which can be taped together. The best way to download the plans is to simply right-click on the following links and select the ‘save-as’ option instead of actually loading the drawing into your web browser and then saving it to disk. These are the links to the drawings we’ve prepared so far. We will be adding new drawings as they are completed so check back.
http://64.172.168.34/neatstuff/ST1-1.pdf http://64.172.168.34/neatstuff/ST1-2.pdf http://64.172.168.34/neatstuff/ST1-3.pdf http://64.172.168.34/neatstuff/ST1-4.pdf http://64.172.168.34/neatstuff/ST1-5.pdf http://64.172.168.34/neatstuff/ST1-6.pdf http://64.172.168.34/neatstuff/ST1-7.pdf http://64.172.168.34/neatstuff/ST1-8.pdf
Part-II will be continued………………. If you want to contact me my email address is
[email protected] [email protected]..
Happy Prospecting, Gary 36
