Thread: Steel Roller Question

Hi Bob,
Will this be for timber or steel? In either case I'm fairly certain (maybe Bruce may know) that belt life and efficiency goes up exponentialy with belt length. The longer the belt the more time it has to cool before it has to cut again, and when a belt gets too hot in timber it will start to burn more and on steel the grit adhesives will start to let go.

Edit, missed your last post, timber it is.

Originally Posted by BobL

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).

Bob
The crowns I suggested were for heavy metal removal, anything up to 3HP per inch of belt width.
Lighter duty work as in woodworking & the like & a much smaller crown is fine, in fact I have used a wrap of masking tape a 1/3rd width of the belt & adhered around the centre of an idler to stabilise the belt.
We manufactured hundreds of belt machines in my business, the machine used 1/2HP acoss a belt width of 1/2" the 2 idlers & tensioners were 3/4" dia & had a peaked crown of about .040" These belts tracked well, & were primarily used for metal grinding, portable hand held machines.
So it depends on the application.
Belt speed is a big factor with belt life, & the concept of a variable speed for the belt would be an excellent addition, this is why portable air tools are great for this work, they offer a built in speed control.
Slower belt speeds allows a flexible belt to conform to a shaped contact wheel & get into corner weld grinding, for example using a 1/4" wide belt over a shaped contact wheel.
A starting point for belt speeds
Wood 2000 to 3500 feet per min
Metal 4000 to 6000 feet per min
However as mentioned a variable speed will allow the belt to perform in a different manner. Slow belt speeds & the abrasive generally runs cooler doesnt have a tendency to burn the wood as much, removal rate is less, which is very often desirable.
High belt speeds with metal, particularly grinding stainless steel, & premature glazing will occur. Often lubricants are used to minimise this effect & prevent what is termed "welding" of the metal particles to the abrasive grains resulting in short belt life.
There are many variables, these are a few of them & I hope this may be of some assistance.
regards
Bruce

Originally Posted by Abratool

. . . . . I hope this may be of some assistance.

Yep - thanks - much appreciated.

Bob
When it comes to belts, thats what we made for near 40 years.
I still have roll stock of most grades except #80 #100 & still make a few belts.
I mention this because I can make you belts to suit your machine & seeing its going to be a graphite coated platen supported belt a zero caliper no bump join can be made for you.
This join has proved popular with people making wooden trophies & the like as its smooth running, does not bump or fill at the join area as do conventional belts.
Just lets know if you are interested.
regards
Bruce
ps These are the belts & joins I use on my own H&F 150mm wide by 2260mm belt platen machine for serious hobby work.

Is there any benefits to different profiles for the crowning? Is it better for a spherical face or a straight taper from the centre...straight tapers with a flat spot?

Thanks Bruce I already have a couple of belts to play with - I'll see how I go with these.