Need help on sizeing custom wheels for belt grinder

I worked in a shop that finished heavy equipment wheels with belt sanders. The idlers were aluminum and when they wore flat the machinist would put a fresh crown across the surface. He used two degrees on the compound of the lathe and left about 3/4 of an inch flat in the center on a three inch wide belt. I have done some myself for a friend and he was not satisfied with such a small taper and I ended up setting the compound to four degrees on a 3 inch wide belt. The large pulley was sent out to a vulcanizing outfit that put a rubber coating on. You can order a variety of hardnesses of rubber. If the rubber is too hard the edges of the belt would cut into the rotating wheel too much. Normally we machined the rubber flat when it was marked up excessively. Our belt grinder/sanders varied from one inch to three inch wide belts. We only crowned the bare aluminum idlers. The rubber coated wheel wheels had the edges slightly radiused but flat across. Hope this helps, Randy

It is heavy cast iron and runs smooth except for the tracking of the belt.

On close inspection it has three plastic wheels for the belt to ride on.

Molded garbage.

I intend to machine up three new wheels but need assistance in the dimensions.

The present wheels are all 31/2" in diameter by an inch across.

How should I finish the surface of the new wheels?

I presume I have to crown them all and should the edges be radiused or sharp?

I intend to use aluminum.

All suggestions appreciated.

david

I think you have the idea - barrel shaped wheels. They could be ribbed - like real barrels - the metal hoops - but small to help grip from side wards motion and improve tracking.

See if they can be adjusted for tracking.

Mart>

My belt grinders only have the drivewheel and idler(on some) with any type of crown. One grinder (Delta) has all plastic wheels and they are over 10 years old, and work just fine. My homemade belt grinder only has 1 1/2 deg crown on the drive wheel (bare aluminum) and nothing on the idler or contact wheel and it has never moved sideways during use, as long as proper tension is on the belt.

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Thanks for all the helpful suggestions.

David

One of the recent Village Press mags had an article on making your own small belt grinder, the guy used laminated wood for the pulleys and had some recommendations for crowning. The mag had a kitchen pump on the cover. I have a book called the $50 Knive Shop where the author used some rubber-tired industrial caster wheels for driving a homemade belt grinder.

I've got an Asian-made Delta 1x42 I bought cheap, it's been a pretty good workhorse and the plastic wheels have given me no trouble. Might be you could recrown what you've already got and make them work for you. What troubles are you having with the tracking? Most of the units I've seen have been almost primitively simple in that area, shouldn't be that hard to fix.

I was over to the HF store the other day, they carry PSA sanding disk adhesive, Franklin brand. I'd never seen it before. If you use 8" disks like that Delta of mine does, the PSA disks are a little hard to find on the shelf. With the adhesive I can make my own from sheets of sandpaper. I don't use the disk sander part much, but it is handy to have from time to time.

Stan

Ok, I'm bored so I'll say waaaay more on this subject than anyone wants to hear.

Most of these things used crowned pulleys because they do track the belt AND they compensate for the fact that the shafting is usually far out of alignment. The greater the crown, the more it compensates for tracking/alignment problems and the more it chews up the belt over time.

Using a crowned pulley on belting causes a problem called an "approach bulge". This bulge eventually causes the belt to wear out and track poorly. The trick is to get as LITTLE crown as possible to avoid the problem, and still be able to track.

Tracking is also a function of belt quality. Crappy quality belting will always drive you nuts. It also sands far worse than good commercial quality belting. the first time I used top quality sanding belting I was flaberghasted at the extended life and fact that it continued cutting almost like new throughout that life. At that time I had only used "off the shelf brands from the home center (hobby stuff) and ordered a box of "ends and pieces" from "the sanding catalog"(division of Klingspor abrasives, I believe). These were ends from fabricating industrial belts. Worth every penny to get the good stuff.

Anyway, back to my ramble to kill a little more time. Assuming that the belting is straight and the pulleys are in perfect alignment, the tracking errors that are seen are generally caused by the outer 20% of the belting. That is, the center of the belt will run true and the edges are where the tracking errors come from. To this end, a pulley called a "Narrow Bodied Roll" is often used. A narrow bodied roll is a pulley that is perfectly flat over the center 60% of the belt width, with the edges turned slightly smaller in diameter under the outer 20% of the belt width on each side. The diameter that is turned down is only smaller by 1/5 of the thickness of the belting. What this does is relieve the pressure under the edges that track poorly so they have less of an effect on tracking.

One really great style of pulley for tracking with no problems was developed by US steel. This pulley is called a Lorrig Type II. Essentially, this is a lagged pulley where small grooves are cut into the lagging at an angle toward the middle of the pulley. When the rubber lagging compresses slightly under the belt, the flexation of the rubber pushes the belt toward the center, causing positive tracking. These things were VERY good. Pulleys cold be waaaay out of alignment and still track the belting. The reason these never came into common use is that they are more costly to make and US steel wanted a little too much to license their patents.

Back to the original question.

Don't crown the pulley, taper it. Taper should be VERY small. The smaller, the better. However, if the shafting is out of alignment or the framework will flex under load and cause misalignment, the taper needs to be increased. 1 degree taper would probably be a good start.

If you can get away with it, only the drive pulley should be tapered. This pulley exerts the greatest force on tracking so is where all the tracking needs to be done. The others should be flat if possible. Often, because the drive needs to be lagged and rubber lagging is hard to taper, it is left flat and tracking is done on the steel pulleys instead. it depends on your machine.

Don't try and overcompensate for bad alignment by using extra taper. Put your time into alignment via the use of good quality bearings in the idlers etc. If it still won't track well, then go back and increase the taper.

Ok, I've rambled and killed enough time. I guess I should actually work.

Koz

Stan Schaefer wrote:

Thanks to everyone.

I think I can now fix this job with confidence .

david