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| Disc/Belt sander speed control? |
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| MetalMuncher:
I have one of these Belt/Disc sanders from Harbor Freight. http://www.harborfreight.com/4-inch-x-36-inch-belt-6-inch-disc-sander-97181.html Have any of you found a safe way to vary the speed on one of these machines? I read some articles on AC motor speed controllers. (I know a Router Speed Control, made for brushed motors, probably won't work. I don't see any brushes on this motor.) The articles provided enough information to confuse me, as the motor data plate isn't very informative regarding the "type" of this motor (shaded pole, PSC, etc.?). It lists 3/4HP capacity, 3.5A. My plan is to try lapping the gib strips for my Sieg X2 mill using the sander. I found a web store named "Econaway Abrasives" that sells custom made sanding belts in various sizes (they have a form to input the dimensions you want) all the way up to 2000 grit, so I have some ordered spanning the full range of what they offer. But I am thinking slower speed on the belt might make things easier for me, as the shape of these strips makes them hard for me to hang onto. I bought a replacement set of gib strips from LMS, to try this project. BTW, if any of you are still using the original gib strips like I am, which have the surface consistency of 000 sandpaper, these replacement strips are WAYYYYY nicer! They actually look machined, and in fact might not need to be lapped at all. But I wanted to try this out to see how well it would work. I had tried manually lapping the OEM strips years ago, but their odd shape, coupled with my fingers, made doing so very difficult, so I gave up. Since this sander has a stop on the belt for abutting the work piece, it may make things much easier for me, and surely require far less elbow grease. :) --- I was just examining the sander and noticed the drive pulley on the motor is a bit larger in diameter than I expected. So perhaps I can try a smaller drive pulley. I don't aim to slow it fantastically, just somewhat, to allow better control while holding the strip. As it is, I'll likely have to make some kind of holder. Maybe mill a slot into a block of UHMW about half the thickness of the strip. |
| Fergus OMore:
Without access to something like a surface grinder or a tool and cutter grinder to accurately grind FLAT gibs, I'd say that your chances of using a belt sander from Harbor Freight or anywhere else is nil. Having said all that, you can remove quantities of unwanted metal but you still will not get something like a blued mating of a gib with perhaps 25 spots per square inch which is what is required in such an application. If I had to tackle the problem, I would file, scrape and blue the offending gib to a flat reference. The process has been covered many times here and elsewhere and provided that you can sharpen and re-sharpen a scraper, it is fairly straightforward. Tedious, long and mucky but each scraping cycle will improve your gib. The cost- apart from effort- is minimal and an old file to convert and blue- Dykem or whatever are all that is needed. Regards Norman |
| Jonny:
Second what Norman said, its asking for trouble. Linishing you will not get it square you will roll the eges no matter how tight the belt is effectively ending up with a large radius. Normal way is to file or scrape, black and keep removing the high spots. Fine 6" three square just the job they have a nice belly if a quality file. |
| MetalMuncher:
Fegus, thank you for the information. However, the actual question posed here is how to slow the sander, not whether my project has merit. ;) It is an experiment, for my own reference. If they turn out as hoped, I'll use the new gibs. If not, I'll continue using the ones in the mill being used for the past 10 years. When I am told I can't do something, I try harder. :D My good friend Ron, a pro toolmaker, when I initially consulted him while buying the Homier lathe and mill, laughed and told me both of these machines would never be useful for anything. I think every member here who uses mini machines knows better. These beasts often fly in the face of "conventional machining wisdom". I have read his textbook "Technology of Machine Tools" which I've had on semi-permanent loan for years. Although it bore some useful information, most of what it specifies are things that often don't apply to these mini machines. Although I can work a file well, I would consider it the least likely to end up with a flat finish, especially on something only 1/2 wide, since only muscle control is all that keeps it anywhere near level. Jonny, thank you for the information. Can you please convert your final sentence to English? |
| BaronJ:
A shaded pole motor is for all intents a fixed rotational speed device. Its speed is locked to the frequency of the AC supply ! Reducing the voltage will appear to slow it down but it will cease to turn as soon as load is applied. If you can find a way of varying the frequency whilst still supplying enough power at the rated voltage. Only then will you be able to change its speed and still drive the load that you want to apply. There are inverters that are intended to drive three phase induction motors with a variable frequency so that the speed can be controlled. So your problem is not insurmountable. |
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