Widebelt sander tensioning

[RSnow]

Hi All,
Right now I am in the process of designing a wide belt sander and I have an idea that I would like to get some opinions on.
For starters I plan on using three air cylinders for the upper idler drum.
One in the middle that will push the drum upwards with stops on both ends. This will take up most of the slack in the belt and will not move once it is fully engaged. The remaining belt tension will be handled by the other two cylinders, one on each end of the shaft. Tracking can be adjusted by increasing air pressure on one side or the other.
In theory “I think” it should work but in the real world it may not as control valveing may not be adequate.
I would like to get some opinions.
Thanks

 

[MikeHalloran]

Tracking is normally done with a subtle crown in a drum... more subtle for wider drums, with very fine resolution on whatever mechanism tilts the axis. The response to axis tilt will be much stronger for wider drums.

So, you need wedges or micrometers, not direct acting air cylinders, for the tilt.

I think.



Mike Halloran
Pembroke Pines, FL, USA

 

[MiketheEngineer]

You might want to take a close look at say a Craftsmen 4'' wide belt sander and see how it works. It uses a simple screw adjustment that works quite well for me.

While this is only 4'' wide - it may be possible to scale it up for your application. You don't say how wide is wide. Craftsmen says this is a wide belt??

 

[MikeHalloran]

Uh, no, 52 inches is wide.

http://www.timesaversinc.com/metal.php

I've seen 'em up close, but not disassembled, so I don't know exactly what they do for belt tracking.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Uh,No, 130" wide machine using hydraulic roll adjusters. Checkout Acme Manufacturing.

http://www.freepatentsonline.com/4021970.html

We have 4 96" wide crown rolls on a non-woven fabric system with the tension controlled by a Rotac.

http://www.rotachydroac.com/index.asp

 

[MintJulep]

The ends of the roller define a line.

Two points are sufficient to fully define a line.

Three cylinders will result in an unstable system as any time one cylinder makes and adjustment the other two will respond.

 

[ornerynorsk]

Commercial widebelts in the wood industry use a single upper drum (crowned), fixed pivot on one side with an air or hydraulic cylinder on the other side, with feedback provided by an electric eye for belt tracking. The system is totally dynamic, adjusting itself on continual basis. There may be other systems, as well, but this is what I have seen.

 

[RSnow]

Thank you guys for your responses. I see that I need to provide some more information.
I’m planning on an 18” wide belt. The center cylinder will push the entire unit up until it hits the stops. The pressure in this cylinder will be far beyond the two outer cylinders so the frame will not move. That way the outer two cylinders can apply the proper tensioning for the belt and also allow for alignment of the drum. For the sake of argument, let’s omit the third cylinder. So my question is with two cylinders on the axel, will it be possible to micro adjust the cylinders in order the correctly position the drums axis???

Almost all of the machines that I have looked at use a single center cylinder for tensioning and use another cylinder to control the oscillation. Tracking is less of an issue in theses machines as they want the belt to drift and they use an electronic eye to monitor belt position. My plan is to move the drum assembly latterly instead of just the belt.

Thanks again!!!