View Full Version : Which plastic?

Black Forest
08-06-2011, 09:30 AM
I want to order some plastic to make the wheels for a belt grinder.

Any suggestion as to which plastic would be suitable?

08-06-2011, 09:39 AM
The plastic should be heat resistant. Linen impregnated bakelite or some other thermosetting plastic should work. Bakelite may be known by other brand names like micarta.

08-06-2011, 09:50 AM
Why would you choose a plastic? Wouldn't aluminum or steel make more sense?

The more heat-resistant a plastic is, the more expensive it is. What diameter are you looking for? Some of the best plastics fro an application like that don't come in large sizes, just smaller rounds and/or sheets.

08-06-2011, 10:26 AM
I assume you are talking about the tracking and drive wheels? I built mine out of aluminum (some are 6 inches in diameter), and have no issues with static buildup, even when using a ceramic backed platen. Size is a function of required SFM and bearing speed. Sealed bearings get hot at speed. My grinder can go up to 6000sfm.

If you mean the contact wheel (where you press against for grinding), that should be rubber, but some use polyurethane. Heat is the enemy, and they can get hot.

One design I looked at used (bored out for bearing cartridges and profiled) the high temperature wheels from bakers oven carts - bascially bakelite.

08-06-2011, 11:25 AM
Use aluminum. Plastic will greatly shorten the belt life because it will overheat the belt.

08-06-2011, 12:03 PM
I built a 2x72 a few years ago. The drive pulley and idler are aluminum; the contact wheel is an old caster which has a rubber over molded tire. I bored out the caster and pressed in two sealed bearings. The idler is on a swivel so the belt will track properly.

Alistair Hosie
08-06-2011, 01:35 PM
Yep Evan is correct use Aluminium it cuts well and can be shaped even on a woodlathe to get accurate shapes etc Alistair

08-06-2011, 01:56 PM
If the plastic overheats the belt,I'm wondering if the little Mylar tape that holds the belt together would come loose? Those belts are pretty violent when they break! You could get a nasty cut if the edge of a belt got you. Cut with grit in it!!

08-06-2011, 03:12 PM
It's not so much that the plastic overheats the belt, it's that the plastic doesn't conduct the heat away like aluminum. While I suppose it could cause the tape to fail what it will do is to melt the adhesive that holds the grit to the belt and cause fast belt wear. Steel is also not a good choice because it is a poor conductor. Copper or silver rolls would be optimum. :D

08-06-2011, 04:20 PM
Another vote for aluminum drums. Al tubing isn't accurately made round, but you'd want to maintain balance. To this end you might press in the end caps, which would also center the axle shaft or hold the bearings, whichever way you need to build it. With the drum mounted on the shaft, fix the shaft to some bosses and arrange to rotate the drum while the OD is machined. This machining can be done on the mill, which would make is fairly easy to get a crown on the drums. Shim each boss up a bit and machine halfway across the drum, then drop that boss back down and shim up the other one before machining that half of the drum. The crown produced would be two tapers meeting at the center of the drum at the high spot- all this done of course after the OD of the drum has been trued.

The ID would be pretty well centered by the end caps, as long as they have their ODs and IDs machined in one fixturing. You'll likely find that the OD is out of kilter ie the aluminum tubing is not an even thickness all around- thus the above suggestion.

If your proposed drums are short compared to the diameter, then it might be simpler to just turn them on the lathe, but if longer, truing them up can be a trouble-prone process. On one hand you have a long tube to true up, but as you mount it it squashes out of 'round'. The hold is not that great, and there's a lot sticking out from the chuck. You can't rely on a steady rest because the surface riding on it isn't round to start with.

Just putting a few ideas out there- I've considered this myself as I develop my own belt sanding machine designs. One will be using a 12 inch wide belt, another will be using a 3 inch wide belt.

Black Forest
08-06-2011, 04:36 PM
I will use billet aluminum!!! I will buy a 200mm rubber covered contact wheel and build the drive and idler wheels from solid aluminum.

08-06-2011, 04:40 PM
I use nylon pallet truck rollers. I wouldn't be a heavy industrial user but occasional heavy use. No issues with heat damage to wheels or belts...


08-06-2011, 04:49 PM
No issues with heat damage to wheels or belts...

How do you know? They might last longer with metal rollers. However, that sander has a lot of space between rollers for air cooling of the belt.

08-06-2011, 06:16 PM
Not meaning to hijack, but just elaborating a bit on my own plans in case someone could use the ideas, or maybe be spurned on by one of them-

One of my designs calls for a section of backing for the belt so that it will remain flat while pressure is applied to the belt. One backing will be cast iron or a piece of ceramic tile or even glass- if I can determine that the belt will ride across that without problems. Another backing will have graphite-impregnated sheet put on it. This will allow smooth, easy operation of the belt, with some resistance to workpiece pressure, but not enough to prevent some gouging, etc. Each has its own benefits and drawbacks.

One of the machines I build will have a zirconia belt on it, and it will be run at a fairly high sfm. The belts I have are only 3x16, so the plan is to make the rollers as large in diameter as possible and still get a 'work envelope' of about 3x3. The rollers could almost touch, and in practice I'd be limited to a roller diameter of about 3 inches. I'm going to see how compactly I can build this one, possibly putting the motor inside one of the rollers. It will be a portable sharpening machine. It would be usable either upright or horizontally. I have a motor and bearing set that came from a vacuum cleaner brush, where the motor was inside the roller- could be an ideal conversion.

The machine I have planned to use the 12 inch diameter belt will be an upright and will probably use 4 or 6 inch diameter rollers. These belts are I believe, 48 inches long, so my work envelope will be 12 by about 14 inches. I would like to make the flat backup plate removable so I can select either the graphite cloth one or a hard surface one. I have the remains of a dust collector system, so if I can make the motor run again, I'll try to incorporate dust collection with the turning of the rollers by the same motor.

These machines will supplement the belt/disc sander I have and the drum sander. Each has their own strong points.