Belt sander contact wheel (long post, sorry)

[jacampb2]

I have a couple of 4x36 3/4hp belt/disc combo sanders from sears. Fitted with norton zirconia alumina belts, they do pretty good for their size. Last year I stretched one of the two sanders to take a 54" belt. This worked great, and I love using this one. The short one pretty much serves disc sanding duties.

Anyhow, they use a cast aluminum contact/idler wheel. I really wanted a rubber contact wheel in a bit smaller diameter than the 2.25" wheel that comes on them. Searching for contact wheels, I came to the quick realization that they were way to expensive! The only stuff I could find in 4" width were far to large in diameter and several hundred dollars. I have found that rubber contact wheels seem to give a better "bite" by the abrasive and that belts tend to last longer.

I use the belt sander contact wheel mostly for cleaning up tubing notches, so you need a wheel close to the diameter of the tube joint you are making. I work most with 1.75" tubing, so a contact wheel of the same diameter would be ideal.

So, since I couldn't find a commercial one that would fit my needs for a reasonable price, I decided to try to make one. I figured I would try 4 hockey pucks bonded together and to a metal hub and see how it does. At $.99 each, hockey pucks are in my price range. I drilled the pucks to .75" on the lathe and turned an arbor to turn their OD on and keep it concentric. Turned them down to close to the correct diameter, and then took the old contact wheel off the belt sander that doesn't see much belt use. I made an arbor for the aluminum wheel and turned it down until I just had the center hub, just over .75" OD. I put a good layer of loctite super glue on the hub, and fed each of the turned down hockey pucks on the hub with glue between each puck as well. With a tight interference fit and the glue, hopefully they wont slip. After that, I turned them on the hub and arbor to the finished diameter.

I tried it out on the little belt sander, and it does give a lot more bite, but it now stalls the motor if I lay into it. I have a couple of 3hp motors around, so that will have to be the next evolution. I am thinking of cutting axial groves in the wheel with a tire groover. The axial groves should add more cooling capacity and even more bite.

Here is what I came up with.



This is the lengthened sander with it's original contact wheel



Here is the new rubber one, ready to go in.

Later,
Jason

[lwbates]

I may be wrong, but I don't believe the belt grinder you have was designed for the aluminum drum to be used as a contact wheel. I think it's just supposed to use the platen area and maybe a slackbelt area on the other side for polishing. What you're doing will make a much more usefull machine out of it. You can experiment around with grooves across the face of the contact wheel at about a 15* angle to the wheel shaft centerline. narrow grooves will make it cut better than the plain face. The wider the grooves in relation to the uncut surface of the wheel, the more agressivly it will cut.

[darryl]

Nice use of some pucks. They're pretty tough, so it should work out ok

Something else that you could have done, if you have a tool post grinder- get a can of that tool handle coating and build up an eighth or so thickness on the original aluminum drum. It would take several applications, timed appropriately so subsequent layers bond well to the previous without stripping the previous layer. The drum would have been well roughened to begin with of course. Then once the coating has fully cured, grind it to a smooth finish. I've done this and it works well. You could get fancy and use one of the epoxy urethanes, where you're able to choose the durometer you want.

Not saying it's any better or worse than your hockey puck idea, just another way it could have been done.

[R W]

A very interesting thread, no need to apologise for the length of it.

[jacampb2]

Thanks for the ideas guys.

Lwbates: It very well may have never been intended to be used as a contact wheel, but I only use the platten for quick chamfers, and I have always used the idler wheel to adjust and clean notches. It works well enough, but is very slow cutting compared to my buddies 1x24 belt sander with a rubber contact wheel. One of the issues is with a new belt it literally strips about half of the abrasive off the belt on the first few cuts. After that, it still cuts, but less grit hits me in the face. I presume I am seriously cutting the life of the belts down by using the aluminum contact wheel, and at about $6 each, it is too expensive to blow through them.

darryl: Thanks for the suggestions, I considered the rubberized coating stuff along with a few other options. The problem with the ruberized coating is that the original wheel was already a larger diameter than I wanted. The outer surface of the wheel was less than .125 thick and supported by vane like spokes. The central hub where the bearings are is about .875 OD, so I would have had to take it down to the central hub, and then built layers up on that, I think it would have taken far more coating than would be reliable. I never considered urethane epoxy, and did not know such a thing existed. I did think about possibly getting some hard rubber fixed casters and machining them to the right diameter, something like shopping cart wheels? Hockey pucks turned out to be the cheapest idea for the experiment, and as far as durometer goes, they are pretty hard stuff. They should stand up to a fair amount of abuse, provided they stay glued in place

RW: It was mostly just a warning to the old timers here. If they saw the need, they would be able to figure it out for themselves. I get carried away with my descriptions, and I cross posted this on some other non machining related forums, so I wanted to keep my explanations detailed and (hopefully) well written for others who may be starting out like me. There is also the hope that if I did something wrong, or could have done something easier, that the old hands will give me criticism.

Thanks,
Jason

[jacampb2]

Well, I made a bit more progress on this belt sander. I changed my stretched sander over from quick release belt change to a screw tensioning setup that should maintain more even pressure on the belt than the old spring loaded setup. Pretty simple design. I have yet to cut grooves in the rubber contact wheel, but even with it smooth, it is proving to be too much for the 3/4 HP motor. It looks like it shouldn't be too bad swapping it over to a 3HP and it should be about impossible to stop with that sucker on it.

Here are the pictures:









Later,
Jason

[jacampb2]

I made a bit more progress today. This is rapidly becoming significantly different from the tool I began with. I knew my 3HP westinghouse motor would not fit in the old sander base, but I thought there might be a slim chance I could get away with it and my same timing belt length by using the motor as part of the frame. I cut a piece of 3/16" plate 15x6. Marked out the motor mounting location and drilled the plate. My intention was to have the motor hanging from the bottom of the plate, allowing me to tension the belt with it's mounting slots. The plate will serve as the top of the new housing. I will add a rectangular tube "leg" to the front and back of the plate, and a plate steel bottom as well. The plate still needs stiffened up, the plan for that is a .75x2 rail along the long (drive) side of the plate.

In the end, I was off by about .5 inches center to center of the two shafts. All my measurements said it was going to work fins with the original timing belt, but once it was all together, the belt was to short. Fortunately for me, XL timing belts are cheap, but I wanted to have it back up and running w/o any special orders. As it is, a 160XL belt will fit it perfectly. I am kind of wishing I hadn't tackled it today though, as I need the sander this week. I still have my little one, and it can go back together pretty easily, so I will probably just throw a belt on it and use it for the time being.

Here are the pictures. Don't mind the Dane, she is an attention whore.





Later,
Jason

[BCtech]

That looks like it should be very effective.

I have a question about the idler, does it have any crown in it? How about the drive wheel?

If not, do you have any problem with keeping the belt centered?

I made a combo 12" disk and 4x36 belt sander out of mdf and the belt will stay centered unless I put any uneven load on it, then it migrates to the side.

Both my idler and drive wheels were made from stacked and glued mdf and as I didn't own a lathe at the time, they were smoothed on the disk sander itself, allowing the disk to spin the hub assembly while holding the bearings.

Using this method and careful measurement, I did put about 3/32" crown in the drive hub but I'm wondering if it actually does much.

[jacampb2]

That is one slick idea! I have never seen a sander made almost entirely out of wood, and definitely not a wood framed one done that well.

As for the question, the drive wheel and contact wheel have no crown. I tested them on a flat surface and they do not rock. The sander has a tracking adjuster on the idler wheel, I have modified it to no longer be spring loaded, for the exact reason you mention. It was quite easy to overcome the spring pressure and have the belt walk, and when it did, it walked to the solid/mounted side of the sander and shredded the belts lickety split on the frame.

The belts will walk a small amount still, but I have to be really laying into it to make it do so. Previously the 3/4 HP motor would stall long before I hit it hard enough to walk the belt off. Time will tell what the Frankenstein one will do. If I have to do anything, I will add a turn a rubber drive wheel and add a slight crown to it.

As mentioned above, it is likely that this sander was never intended to have the idler used as a contact wheel. This is probably why I have had to make some of the mods I did. On the platen I have never had the belt walk regardless of what I am doing. In it's next generation, I may make it take an even longer belt. Belts don't get significantly more expensive for common lengths, so longer belts are more cost friendly and last longer.

Later,
Jason

[Bill Pace]

Very neat work BCtech......nice looking sander,-- is the disk MDF too?---- I sure love my 12" disk, I bet you will too.

Theres probably some figures for crowning out there some where, but I just started playing around with a little 1x42, replacing a couple idler wheels and learned a couple things.... Mainly that it takes VERY little (if any! like Jason says, his has none) and that the more crown I put in, the worse the belt would wander. I ended up just taking a file and and spinning it in the lathe taking a few thou off and got a pretty stable belt. I do believe it would have worked just as well with a flat wheel, but after the third attempt and getting it stable, I let well enough alone.