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Work Holding 5

A Universal Work Holder

Mark3 version to be found at the bottom of the page.

For some time now I have been mulling over a satisfactory  way of holding smaller work flat up under the plate. This is to make small box lids etc. I have not so far been 100% satisfied with tables held in the WoodRat fences as I always seem to get some small movement of the piece or irritated with the time taken to fix everything down. After some experimentation I believe I have now got a very quickly set and flexible system that works far better than I dared hope. This design has been made out of scrap that I had to hand and the sizing of wooden parts is not critical. Pictures explain things best so see what you think.

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The whole thing comprises of two sections: the first or left fixed wooden fence with plywood cheek and the right side or sliding part with plywood cheek. On the inside of each cheek are set simple and adjustable MDF work-holding pieces designed to be sacrificial. The sliding side is fixed to an accurately made part inserted into the travelling carriage and can be held into place in the usual way with a cam-lock. Only one cam-lock is required and both the normal fences are removed. This system holds the work really firmly and allows for through cuts.

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The first thing I made was a replacement fence. The dimensions are not important but it must be square. Use a good stable hardwood. I used  mahogany but oak would be good. Mine measures 1 and 3/4" by 1 and 1/2" by 12" long. If in doubt make the fence  face the same size as the 'Rat one. Also carefully drill the 8mm mounting holes to match those of the carriage. I drilled the upper hole at 8.5mm to allow for some adjustment for vertical when fixed.

Don't neglect to rebate the channel side as shown or the fence will bind and prevent tracking of the carriage.

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I used good 22mm plywood for the fixed fence cheek which measured 9 inches high by 5 1/2 inches deep. Clamp the cheek to the fence and mark up the positions of the 8mm fixing bolt holes on the fence and cheek. I made the holes on the drill press to that they were vertical. I screwed 8mm inserts border="0" into the plywood as shown and used 8mm by 50mm stainless cap head allen bolts for fixing. The other 8mm hole is for screwing on the sacrificial cheeks.

Fence and cheek all mounted. Stainless steel 50mm long countersunk 8mm bolts were perfect to attach the fence. There is no reason why hex or allen bolts couldn't be used though.

Take time to set the fence and cheek square  to the channel in the usual way before tightening down. The 8.5mm upper mounting hole permits this.

 

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The next part to make is the slider insert. Now this part is the heart of the system and it is essential that it is an excellent smooth and slop free fit to prevent any torsion or movement when tightened up. I made the first one from Tufnol but it wasn't very accurate. Next up was this one made from a piece of 12mm thick kitchen chopping board. It was better and slid like silk but still permitted a bit of play when the cam was locked. A third and  revised one from two pieces of acrylic was much better and finally used. The choice is yours and suggest that nylon 66 would be the best choice. I made my slider 7 and 1/2 inches long which is a good compromise between anti-twisting length and work-holding width.

 

This is the revised and much more accurate two piece, acrylic slider. The red piece is 5mm thick and is a good slop free fit in the carriage grooves. The black part is 6mm thick and sits in the outer part of the carriage. The white gunk is dry PTFE sprayed on as lubricant. The plastic is packed off the ply by two card shims so that the ply just clears the channel face without any play. The two part route is certainly easier to make compared to cutting accurate rebates. I placed the parts in the carriage and super-glued them together to keep an accurate relationship between them before drilling and counter-sinking the fixing holes in the drill press.

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border="0" This is the white plastic slider screwed to the rear of the right side sliding fence which was abandoned in preference to the one shown on the left.

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The revised slider  attached onto the 22mm (8" by 9") plywood back-plate with wood screws.

The sliding cheek is held square to the back-plate with an oak corner piece. ( sorry- shown upside down!) The curved recess is to give clearance for the inner cheek fixing knob.

Of course you could use triangular fillet pieces top and bottom instead if you prefer which would give even greater stiffness.

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This shot shows both cheeks in position. With a good fit of the plastic runner in the carriage there can be no twisting or torsion of the sliding part when locked onto the work.

Next little job is to make two sacrificial work holding parts to match the plywood cheeks in size. These parts must be square. I made mine from MDF  but plywood would be OK. These need rebates cut on the upper edge. Clamp them in the cheeks and tight up under the plate and run the router bit down the centre in the normal WoodRat way to get them equal. The slots are 1/2" wide and centred on the previously drilled holes in the plywood cheeks. I fashioned two plastic Tee nuts from some nylon6 and drilled and tapped them with 8mm threads to accept the Trend knobs. These parts are so simple and quick to make that they really are disposable items. The idea of plastic nuts was so that the MDF would slide up and down easily when setting up but I suspect alloy ones would work OK.

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The Tee nut in place.

Here is the inner cheek held in position by the Trend knob.

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These are the replacement bolts which are standard sizes available from your local fixings shop.

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Click on the thumbnails below to see how versatile this system is.

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Normal holding.

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Table with extra clamp

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Mitre box

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Horizontal table

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Two way mortise rail

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Large work holding.

 

    Drawing produced in Sketchup by Dave R. 

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 When reverting back to the two fence system on the 'Rat I shall keep the wooden fence in place. When setting the inner cheeks in place to hold the work push them back against the channel face and this will ensure that there is no "rattle". So far I have been very pleased with the results as the larger cheeks give a good firm grip on the work and an extra clamp can be used as shown above. I now rarely use the 'box', mitre box or worktable  as this does the job of all three.

I have found the work to be very firmly held without having to put much pressure on with the cam-lock but the perfectionist could arrange that the cheeks instead of being parallel to each other had a very slight taper so that the vertical edges nearest to you met first. i.e.  rather like a bench vise. There are several ways to hold the adjustable inner cheeks in place so use what you have. I will make alloy Tee nuts instead of plastic ones to try.

I hope you find this of interest.

Some Updates

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Here is a slightly updated version. This exploded diagram is not to scale or perfect but shows that I reduced the size of the sliding base-plate to maximise travel but kept the same carriage slider. I used fillet pieces for stiffness. Now use alloy retainers instead of plastic ones.

Here are some ideas how to modify the sacrificial fences to hold various work.

A. Horizontal cylindrical. N/S

B. Horizontal cylindrical or angular. N/S

C. Vertical round. N/S

D. Vertical angular or round. N/S

E. Small rectangular pieces as in Burr Puzzles E/W

F+G. Circular or angular. E/W

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There are three PKZIP files of Sketchup 5 drawings for you to download here, here and here. These drawings are fully 3D and you can rotate them to your heart's desire.

MK3 revision border="0"is available in a fully scaled Sketchup drawing from which you can take the measurements that I used on this link, RevisedUWH1.zip. Download, unzip to a folder and use Sketchup program or viewer for the 3D version. On the slider part I have reduced the back board to 100mm  wide. The slider part for the rail is longer than the back part and can slide behind the fixed fence when closed. This maintains the torsion resistance when locked. An 8mm nut sits in the adjustment slots in the sacrificial fences to accept the locking knobs. when held tight nothing protrudes beyond the sacrificial fence faces. All bolts are now cap head allen versions with no countersink heads used at all.

I have experimented with different types of wood sliders to fit in the rail but find it difficult to machine the exact size required. So far the two part acrylic is by far the easiest to make. 5mm and 8mm thick sheet are standard.

Any one else made one yet?


Here is one made by Alf

"Not a thing of beauty (I don't have such posh off-cuts!) but it does indeed work a treat. I decided to butcher the existing stop rather than make a wooden one, 'cos it's solid enough and my 'Rat's got more holes in it that a string vest anyway. Need to do something instead of the wing nuts, but they work well enough for the time being."

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Alf made one. She fixed the left cheek to an alloy fence. When question if there was any flex in the cheek when mounted that way her reply was:-

"No flex so far, in fact it's surprisingly rigid. But I've not used it that much yet.. I thought I may try the easy way first, assuming I'd end up making a wooden one eventually anyway.

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The sliding part is a couple of bits of foam board(?) cadged off a sign-maker (planes beautifully, by-the-by) stuck together with superglue and screwed on the back. Well and a couple of washers to get the fit right. Not sure how long the foam board will last, but there's plenty more and it doesn't take long to run up another if required. Not-a-good-picture here."


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