Thread: Steel Roller Question

I have acquired a seriously solid steel roller, 80 mm diam x 180 mm long with a sealed 1" shaft and bearings from a rail grinding machine.
It seems like it would make an ideal candidate for the idler roller for a 150 mm wide belt sander but have no idea if it can handle the 3000 rpm.
I have mounted it in my Hercus and it spins up to ~1200 rpm very smoothly but it does have some back resistance.
Does anyone know what is inside these, maybe packed with a heavy grease?

A photo would be handy. 3000 RPM is pretty much a leisurely stroll for a 1" ball bearing, so I reckon you should be okay.

If you can read the bearing number look it up on the manufacturer's website. SKF, FAG, NSK etc all give performance data for their products including max rpm.

Thanks Guys.

I will have to open it up to see what the bearing is as the whole thing is very well sealed.

According to skf, their angular contact ball bearing (at 30mm OD) is limited to 30000rpm, though Id suspect thats with air/oil spraying to keep it cool. A bunch of their other bearings have similar upper limits, so I would be prety confident that a 26mm diameter bearing would cope with 1000rpm, no matter who made it.

Unless its one of those chinese bearings that look like a bearing, smell like a bearing but are actually manufactured from the finest surface ground butter. If it was a reputable, well known manu, id be happy to subject it to 1000rpm.

Originally Posted by scottyd

According to skf, their angular contact ball bearing (at 30mm OD) is limited to 30000rpm, though Id suspect thats with air/oil spraying to keep it cool. A bunch of their other bearings have similar upper limits, so I would be prety confident that a 26mm diameter bearing would cope with 1000rpm, no matter who made it.

Unless its one of those chinese bearings that look like a bearing, smell like a bearing but are actually manufactured from the finest surface ground butter. If it was a reputable, well known manu, id be happy to subject it to 1000rpm.

Thanks for the info - I really doubt this is a cheap bearing - it has SERIOUS written all over it with doing any rpm.
I actually need it to run at 3600 rpm, if it was 1000 rpm I would not be worried.
My concern is that it might be packed with a heavy grease which will place too high a load on the motor.
The motor I will be using is a solid 1440 3HP 3Phase unit and using a 2:1 pulley I will get the RPMs up to 2880. Then via VSD to 3000.
The drive pulley is 20% bigger than the idler, so the idler will be running at 3600

Well the timing belt idlers in my rex have bearings of a similar size to what youre describing and they do the same RPM as the engine. Id does 3000rpm plus for extended durations plus the number of wrx's out there doing motorsport work with similar bearings being subjected regularly to 8000rpm and more. Those bearings are under moderate loads and pretty poor conditions (hot engine, dusty environment) and survive just fine. That said, the timing belt replacement interval isnt actually in place for the belt, its there to replace the bearings first and foremost. The logic there is that if the bearing fails and seizes, then the belt will be destroyed in very short order (then valves start meeting pistons and it gets ugly from there). I would assume your bearings should be fine for that sort of speed, but with regular checks for developing play and wear and replacements as required.

Originally Posted by scottyd

Well the timing belt idlers in my rex have bearings of a similar size to what youre describing and they do the same RPM as the engine.

Let me once again say I am not worried about the size of the bearings but what they are bathed it which I think is a heavy grease. While the bearings can be turned by hand but they will not spin freely by hand, not even for a mm.

Clean it out and grease it appropriately? There are specific requirements for the amount of grease to go in a bearing, the manufacturer should have some guidelines. I would say that if they dont spin freely after that, then they are for the bin.

Originally Posted by scottyd

Clean it out and grease it appropriately? There are specific requirements for the amount of grease to go in a bearing, the manufacturer should have some guidelines. I would say that if they dont spin freely after that, then they are for the bin.

Yep that's the plan.

Originally Posted by BobL

I have acquired a seriously solid steel roller, 80 mm diam x 180 mm long with a sealed 1" shaft and bearings from a rail grinding machine.

Bob, Just to clear me up, when you say, rail grinding machine, is that as in train rails? That might explain the heavy grease.

Is 80mm dia large enough for an idler on a belt like that? I tried googling up tech sheets for sanding belts, but come up a blank.

And does the idler need crowning?

Would it be possible to use it as the idler, but sleeve it up to a larger diameter, that would reduce the rotational speed, and give you a larger bend radius on the belt.

If I'm not mistaken Bruce - Abratool, this was his industry.

Regards Phil.

Originally Posted by Machtool

Bob, Just to clear me up, when you say, rail grinding machine, is that as in train rails? That might explain the heavy grease.

Correct and correct!

Is 80mm dia large enough for an idler on a belt like that? I tried googling up tech sheets for sanding belts, but come up a blank.

If you look at hand held belt sander they use quite small rollers with belts/grits that are not significantly different to what are used on linishers.
In fact some of the rollers are amazingly small.

And does the idler need crowning?

I don't think so but it does need an alignment mechanism which I think I have sorted.

Would it be possible to use it as the idler, but sleeve it up to a larger diameter, that would reduce the rotational speed, and give you a larger bend radius on the belt.

Yep - also a possibility but I don't think I will need it.

Originally Posted by Machtool

Bob, Just to clear me up, when you say, rail grinding machine, is that as in train rails? That might explain the heavy grease.

Is 80mm dia large enough for an idler on a belt like that? I tried googling up tech sheets for sanding belts, but come up a blank.

And does the idler need crowning?

Would it be possible to use it as the idler, but sleeve it up to a larger diameter, that would reduce the rotational speed, and give you a larger bend radius on the belt.

If I'm not mistaken Bruce - Abratool, this was his industry.

Regards Phil.

Thanks Phil for the referral on the idler.
The idler in question may have been part of a 3 pulley set up.
That is the primary contact wheel,where the abrasive belt makes contact with the workpiece, usually rubber or polyurethane serrated or plain, & possibly 2 other idlers for tracking & tensioning.
One of the idlers needs crowning to maintain tracking of the abrasive belt.
The narrower the belt the more crown is needed. I think Phils idea of a larger idler pulley is a good idea particularly if only a 2 pulley set up is used.
Small diameter pulleys are difficult to get belts to track well.
Suggest a larger, say alloy pulley could be shrink fitted to the existing pulley, & a crown provided on the OD.
Heres a list of suggested crowns for different diameters.
4" !/8" crown
6" 1/16" crown
10" 1/32" crown
These are a few starting points, a simpler approach might be to purchase a complete Back Stand Idler Assembly, this has the tensioning device, the tracking facility & the crown machined accordingly.
Hope this may be of some assistance.
regards
Bruce

Thanks for the info Bruce - much appreciated.

I measured the crowning on my Makita belt sander on which the belts track extremely well and has 2" diam rollers and it only has crown of ~1/20".
On our 150 mm wide 3m long belt sander at work, which uses an 8" diam roller, it has a 1/16" crown.

I had a chat to my ally welding BIL and he said he can help me make a driving roller using 4" diam ally tube.
I'm looking forward to interacting with BIL as he is a very handy guy and a pleasure to work with.
I will start with a 1/32" crown and see how it goes from there.

I'm still in the process of designing the layout of the sander but have more than enough parts to start.
It's basically a 6" wide, 24" long sanding bed (ie 1220 mm belt), with a 3Ph 3HP 2 speed Italian motor which I will run via a VSD.
I already have all the bearings, shaft, pulleys, motor and most of the steel for the frame.
The only thing I see the need to fork out $$$ for is the VSD ($160), some more steel and some graphite slip cloth ($14).

If there's too much drag I'd be more worried about the sanding belt breaking than the motor overheating.

And those belts get expensive when you do a few in.

I saw a neat design on the web where the guy used a section of RHS as the horizontal belt backing/work support - had a fixed pulley at one end and an adjustable one at the other end.

Another piece of RHS went down at 90 degree to a floor base plate and mounted the vertically adjustable motor on - formed a "T". The belt ran in a triangle.

Simple and good design.

If I wanted a big linisher that's the way I'd go. Lot's of easy designs out there.

Rob