Official Luthiers Forum!

A few years ago I built a rim sander ala Proulx and McKnight. It is essentially a shaft that protrudes above the surface and had a set of "dogs" that spun a radius dish which sat on a lazy susan bearing. I use my rim sander a lot as I make radius dishes on the cnc and use the rim sander to finish sand the dishes. So I didn't really like the lazy susan bearing, it was load and they wear out fairly quickly in the high dust environment I was exposing them to. So I removed the lazy susan bearing and had the 5/8" shaft welded to an 18" diametre 1/2" steel plate and then placed 4 cup bearings to support the edge. I felt better about that but the machinist couldn't really get my centre hole bang on and that bothered me. Also, I felt that the cup bearings were only marginally better than the lazy susan bearing. Then Brad Way posted the nice sander he made and I have been lusting after it ever since! So I finally bit the bullet and just started all over again and now have something I think that will last me some time! Now this is not your inexpensive version by a long shot, but as I said I use it a lot and I wanted it accurate. So the heart of the project was the plate that I had made up in a machine shop. It cost me $675 to have this made , but it is robust and true! Here it is:



The centre pops out if I ever want to remove the pin (I can't see needing to do that but just in case.....)

This heavy steel disc just sits on the shaft of 15:1 reduction gear powered by a 1/2 hp 1750 rpm washing machine motor.



The reduction gear and motor are inside an mdf box which is on wheels so I can move the unit around very easily.



The top of the box is a double laminated piece of mdf, 24" by 32".



The steel disc fits on the reduction gear shaft through the hole in the mdf top and just sits there by gravity.



The last picture is with one of my laminated radius dishes (without sandpaper) and shows the area of the top of the box around the dish.



So I still have to mount the door in the front of the motor cover and I will also be moving my go bar deck right on to the rim sander. That is the reason the top is the size it is. I have also begun making guitar moulds and forms and this rim sander will be outfitted with posts that will limit how far I can lower a set of sides onto a dish while they are still in the mould. This will make getting side width for each guitar a thoughtless and accurate process. I will post on that part later when I get it done. So this sander turns at 117 rpm, just about right! The "A" type belt is sitting on 3" pulleys with a one to one power ratio. I can't stop this sander by hand, it is very smooth and much quieter than my other sander. Not only that but it has a smaller footprint and is much more maneuverable with the larger wheels. I was concerned that it would try and roll around on it's own but it is pretty heavy and just feels solid! Total cost is probably about $1000. But that is what you would pay for any other good tool.

Anyway, just more ideas for the 'ole library in case anyone else is thinking about something like this. It could be done for a fair bit cheaper using ebay and if you know a good machinist with a large lathe.

Thanks

Shane

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Canada

Really neat, thanks for that. Nice to see something so well thought out.
I love the re-use of the motor as well.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Very cool, Shane. When I did one of these, I ended up using an old pottery wheel. The wheel worked well as a bearing system, but I hacked it together with hose clamps and stuff. It was finicky and not worth the hassle considering my small space and the very small number I need to sand each year.

Mike

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Mike Lindstrom

When I sand the rims there is very little dust generated. It only spins at 117 rpm so the dust just seems to settle into the middle of the dish (kid of like Chladni pattern dust ). When I am finish sanding radius dishes there is indeed more dust but it is not easily collected and it is MDF so it is heavy and usually says on the dish as well. I have tried dust ports on my last sander and none were that effective. The steel disc is steel.....It weighs probably 40 pounds or so. That just makes the unit nice and stable. A person could build these indeed for a fraction of the cost. My first one still works fine (and will be living at friends house now) and it was probably less than 1/2 the cost of this and still has a steel plate rather than dogs. The dogged version was probably in the $200 range to build.

Thanks fellas!

Shane

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Canada

Shane, does the disc have a keyway to register on the gear reduction motor, and do your radius discs do the same? And who made your gear reducer?

Hi David,

When I make the dishes on the CNC I drill a 3/8" hole in the middle of the mdf disc and drop on it the CNC table where it is otherewise held with vacuum. To finish sand the dishes on the rim sander I just place a router mat (non-skid thing) on the metal plate and use the centre pin on the plate to locate the centre of the dish. (I hope you are following me....). For my own dishes that I actually sand rim sets with I have the centre pin plus two other holes (not visible in the picture because the steel plate was spinning when I took the picture) in the steel plate and a corresponding centre hole and two 3/8" wooden dowel pins on the dishes. So my own dishes are dogged to the steel plate with those dowels. The steel plate fits onto the reduction gear with a sleeve that can be seen on the plate picture where it is off the machine. The reduction gear shaft is 1" and is keyed. That sleeve is about 2"+ and is also keyed. The plate was 3/4" steel and it was machined true after the sleeve was welded on, holes bored and all of that. It is now just over 5/8" thick. That is why the plate was so expensive, it was basically a day's work at the machine shop plus the steel.

Hope that helps!

Shane

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Canada

That is one nice sander! Nice job.

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Brad
Avon, OH