Shop built belt sander / linisher.

[doorframe]

I'm not building one. I've already built two. Both take 6" wide belts. One is about 2 feet long, the other 3 feet. Built them a few years back, and used both extensively. The basic configuration is basically a fixed drive pulley, and an adjustable slave pulley. The slave pulley adjusts left/right for tension and tilts in/out for belt alignment. They are all metal construction. Very solid and very heavy.

So, here's the problem. These are not absolute precision machines, so although I can track the belts to run pretty good, they do drift more than I would like. I didn't have a lathe when I made the original pulleys so they were 'as close as I could get' with an angle grinder, hacksaw, welder and files. The pulleys are now going into my lathe to be 'trued'. This will (I hope) reduce the vibration and help with the tracking.

So, the question. Should either the drive or slave pulley be conical / crowned? Or both? Or neither?

 

[Walney Col]

If you get the adjustment mechanism working finely enough you should be able to run flat pulleys, otherwise I'd just crown the freewheeling one. On a nominal 4" dia pulley 6" long the crowning shouldn't need to add more than 1/8" max to the diameter and possibly as low as half that. On well engineered linishers the crowning on a similar wheel would be 0.015" max.

 

[doorframe]

Thanks WC. The freewheel is also the adjusting wheel.

The wheels are 3" diameter.

 

[doorframe]

The slave pulley has been turned to a slight crown, approx 0.5mm from the centre to each end. Due to the size limitations on my small lathe I couldn't get the cross slide into a position to make a taper fine enough so I had to make steps and finish with emery. Also, as the pulley is permanently welded to the 25mm shaft I couldn't get the tail stock onto the bed so had to faff about making a steady. The steady ended up within 0.05mm of perfect, which is close enough for me.

The step marks are still visible but hardly noticeable to the touch.

The drive pulley was simple as it just needed truing, not crowning.

It's always been a little underpowered, so before final assembly I will add a second motor (identical to the 1st) and join them with a couple of pulleys and a V belt. I haven't got any pulleys suitable for this so the next job on the lathe will be to turn a couple from some large pieces of some 'sort of plastic' which used to be an 18" pulley at the top of an isle crane where I used to work. If it could handle 3 tons it'll handle any stresses I might put it under.

What I also need to know is what belt speed I need to end up with. Anyone?

 

[woodpig]

For what it's worth both wheels on my BDS250 are crowned, and very noticeably so. Once set the belts don't wander.

 

[woodpig]

Looking at the exploded diagram:

http://www.free-instruction-manuals.com ... 821050.pdf

Both pulleys are the same size and I expect the motor to be the usual 1450 rpm.

 

[doorframe]

Thank you WP.

I can crown a bit more if needed, but I am limited by the wall thickness of the tubing used to make the rollers. It was only about 1mm to start with. It's stainless steel so that's making the turning a little harder than it might have been.

The motor is 1450rpm (I believe) and connected direct (through a flexible coupling) to the drive shaft. It's fine when it's up to speed, but struggles to get going from a standstill with the belt under tension, which is why I want to add a second motor (I've got an identicle one in the junk box).

With 75mm diameter pulleys at 1450rpm, my rusty maths gives me approx 6 metres/second belt speed.

 

[doorframe]

Ok, got the motor specs completely wrong. It's actually 2800rpm. So closer to 12metres/second. I think that's too fast.

Plan B. Double pulley on the drive shaft, with single pulley on 2 x 2800 motors. Pulley ratios will slow the speed by approx 50%.

Gave up trying to make pulleys from the plastic block. I don't know what its made of, but it just melts when trying to cut a blank cylinder with a holesaw in the pillar drill. This binds up the holesaw and seizes up the cut. Even at creep speed with plenty of lube. So, made the 2 smaller pulleys from 35mm ply. To stop the ply splitting I've screwed though from both sides and tests show it hold up fine.

Double pulley has been machined to fit the 25mm shaft and the pulleys are on the motors, so next job is to mount the motors with a degree of adjust-ability. The perspective of the pic makes it look like the pulleys are all the same size, but the drive pulleys are approx 50% of the circumference of the driven.

 

[woodpig]

The manual says my BDS250 has a 1HP motor and the belt speed is 517 m/min. Hope this helps.

 

[doorframe]

Cheers WP. That will give approx 8 metres/second.

My 2 x 1/2 horse motors connected as shown will give me 1HP at around 6-7 metres/second, so I think I'm on the right track.