Mods 13

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An "Anti-Rattle" Experiment

There have been a number of designs of little gadgets made up to remove the tiny amount of fore and aft movement that can occur in the carriage with reference to the channel. This movement happens because of slight flexibility of the plastic carriage runners. In use the carriage needs to be pulled forward to remove this "rattle" when mounting tables or camming up your work.

Over time I have tried to think up other ways to reduce this play. I have mulled over brass, nylon or P.T.F.E. strips, bearings and packing pieces but discounted them all.

On my 'Rat the channel runner grooves measured 6.3mm wide and in a search for something that thick to replace the plastic with, I stumbled across some 6mm M.D.F. sheet. When checked I found it to be 6.35mm and good firm fit in the grooves. I have been running with this M.D.F. as a replacement for the U-Shaped plastic for three weeks now with no apparent wear and more importantly no "rattle" at all! More time will be needed to decide if this will be a permanent cure but for those who wish to try this is what I did:

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First search through your local DIY emporium to ensure that you have M.D.F. of the correct tolerance. I used some which was 6.35 mm thick.

I set the bandsaw up to cut a strip of M.D.F. the same depth as one of the U-shaped plastic runner pieces.

Cut off enough for one carriage length. For ease of fitting I chose to cut the full length in half. These pieces will be for the carriage underside strip.

I made the top strip very slightly lower than the full height of the plastic U-channel. A full depth strip caused the carriage to jam.

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I tapered the ends of the strips to simplify fitting.

I used a foam sanding block to clean up the strips and gently round the edges. This was to prevent any possible jamming.

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Gently tap in the M.D.F. strips in the same manner as the plastic ones. I strongly advise you to fit the lower ones first. Ensure the denser faces are on either side with the cut edge upwards. The strips must be fully seated but be careful as distorted strips won't slide!

Fit the slightly smaller runners to the upper grooves. It is much easier the adjust the height of these to get a slop free carriage.

Once the strips are inserted I gave them a good spray with a dry P.T.F.E. spray. The M.D.F. will swell a very tiny amount to give a really good fit yet the carriage still travelled smoothly. No judder, jamming or play at all but it did squeak a bit.

There are alternative teflon lubricants that have some oil content that could be used.

I think the secret is not to allow too much swelling but still keep a good fit with no jamming.

I have not tried silicone based lubricants.

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So far, after several weeks, it has been working just fine with no apparent wear at all. Even if it does wear then it is so cheap and easy to replace that it is not a problem. The only concerns that I have are if the M.D.F. absorbs any water and swells in damp weather but time will tell.

The search for a better material continues but M.D.F. does work. Why not give it a try and report back?

Update

Lewis Stepp from TheCraftsManGallery recently visited me and brought with him a strip of castNylon6 plastic. The idea being to try it for carriage runners. Well like most others have found, the tolerance on stock plastic is quite wide and it was too thick to fit the 6.3mm carriage slot. Now, not being one to be easily defeated I concluded that there was nothing to be lost in trying to machine it to size. This proved to be much easier than I thought........

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I cut a flat piece of wood to fit between my new fences upon which I place the strip of nylon. This table was set flat up under the plate so that it could be passed through the cutter and manually held against the channel.

A view from under the plate showing the supporting table. The wood needs to be stiff so that it doesn't sag.

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I used a solid carbide 1/2 inch up-cut spiral bit with the router set at a low-ish speed and carefully took shallow cuts until I got very close to the 1/4inch required thickness. The nylon machined very smoothly with no problems at all.

 

This shows the first raw cut. I gradually enlarged the rebate until it was wide enough so that I could band-saw off two strips. One each for the top and bottom.

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I discovered that it was simple to scrape and  plane to a very smooth finish. In fact I found that to get the exact fit that I wanted in the carriage grooves it was best to scrape, test, re-scrape and test before finally fitting. It was apparent however that the carriage recess was not perfectly even throughout its length. This no doubt, is because it is an extrusion and not a machined groove. I believe that this could well be the reason why Martin Godfrey specifies the flexible U-shaped strips for runners.

The fences were taken off and the carriage removed from the channel to install the runners. After a little fettling I was satisfied with the final fit. This photo was taken before the final edge trimming was done. The most difficult thing was re-installing the drive wire!

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Here is the right hand side. I found the nylon to give a very smooth and jerk free feel to the carriage and there is no 'rattle' at all. I did give it an extra spray with  dry PTFE but in truth it was not required.

So the answer is not to be defeated by trying to find plastic the correct thickness but to buy a thicker piece and machine it. Where you obtain the plastic; well that's a different matter......................


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