72" belt grinder

[steve_s]

Hi Guys

So this is something iv been wanting to make for a while, iv been doing a bit of web searching about belt speed and i have found this doc from 3m regarding belt speeds
http://multimedia.3m.com/mws/media/...mance-for-post-casting-op-incast-july2013.pdf
Now looking at the recommended speeds to run the belt on carbon steel it should run at 6500 surface feet per minute so using http://www.blocklayer.com/pulley-belteng.aspx on a motor running a 2800 rpm I need a 9" drive pulley to run the belt at that speed.

Am I right on this ??????

This is where I have got to at the moment just using stuff I had laying around the main frame is an old weight bench I picked up, just mocked up some wooden wheels as a test the wheels will be made from 50mm aluminum bar, if the drive pulley has to be 9" looks for the time being it will be made from ply wood till i can get a bit of aluminum big enough

 

[vbottles]

How are you planning to control the belt speed? As finer grit belts work better at lower speeds. I use a vfd to control my grinder speed. I use a drive wheel of 8 inch on a 2.2 kw motor 1400rpm so I can set the frequency to 100hz and eat steel or 10hz and tickle it when finer belts.
Going the vfd route costs a bit more but give huge versitility. Just make sure it is in a dust proof enclosure or you will blow it up. If you have cheap step pulleys this will work but drive wheel size will be important.
Andrew

 

[pedrobedro]

I can't see any method of tracking the belt on there, have you allowed for that ? Unless everything is perfectly in line and all your future belts are identical you will need something preferably on the tensioning wheel and a bit of a dome on the wheel as well.

 

[steve_s]

I can't see any method of tracking the belt on there, have you allowed for that ? Unless everything is perfectly in line and all your future belts are identical you will need something preferably on the tensioning wheel and a bit of a dome on the wheel as well.

Not got round to that bit yet still work in progress.
Iv got 2 little gas struts from a kitchen door to try for the tension not sure if they will be strong enough will give them a try if not will look for an alternative a spring probably

 

[steve_s]

How are you planning to control the belt speed? As finer grit belts work better at lower speeds. I use a vfd to control my grinder speed. I use a drive wheel of 8 inch on a 2.2 kw motor 1400rpm so I can set the frequency to 100hz and eat steel or 10hz and tickle it when finer belts.
Going the vfd route costs a bit more but give huge versitility. Just make sure it is in a dust proof enclosure or you will blow it up. If you have cheap step pulleys this will work but drive wheel size will be important.
Andrew

I have a VFD to use but im not sure if it will be compatible with the motor im using got to look up the instructions. The main thing was to try as much as possible to use stuff I had already got.

 

[bigegg]

Id make the drive pulley smaller, and use stepped pulleys to change the drive speeds.
Theres something about a home-cast 9" unbalanced aluminium pulley spinning at 2800rpm that terrifies me!

Ps, direct drive:9" seems about ball park.
9" dia = 2.5ft circ x 2800 = 7000FT/min
Ish

 

[knighty]

if the pulleys are slightly... erm... I can;t think of the word for this... pointy ?

if the flat edge the belt runs on isn't actually flat, but has a curve to it so it's higher in the middle, the belt will naturally track and run on the highest part possible

it's kind of counter to how you would expect it to work

(it's the same way bandsaw blades are setup, you tilt the top wheel and the blade moves to the highest point)

 

[bigegg]

if the pulleys are slightly... erm... I can;t think of the word for this... pointy ?

if the flat edge the belt runs on isn't actually flat, but has a curve to it so it's higher in the middle, the belt will naturally track and run on the highest part possible

it's kind of counter to how you would expect it to work

(it's the same way bandsaw blades are setup, you tilt the top wheel and the blade moves to the highest point)

"crowned"

 

[pedrobedro]

"crowned"

In my post #3 I called it "domed" You still need mechanical tracking to fine tune it.

 

[bricol]

Belt companies, and I guess sanding belt companies, have recommendations for the crown height and shape - just don't get confused like one of our suppliers between diameter and radius of the crown, who rather over-crowned multiple, expensive, pulleys that were designed to be as light as possible.

 

[kevanf1]

if the pulleys are slightly... erm... I can;t think of the word for this... pointy ?

if the flat edge the belt runs on isn't actually flat, but has a curve to it so it's higher in the middle, the belt will naturally track and run on the highest part possible

it's kind of counter to how you would expect it to work

(it's the same way bandsaw blades are setup, you tilt the top wheel and the blade moves to the highest point)

Look at how the pulleys are made (domed slightly) on power take offs on such vehicles as Land Rovers and various tractors.

 

[Screwdriver]

Pulley wheels are crowned. About 1 degree if you're turning it on a lathe.

 

[vbottles]

If it isn't crowned enough just put a few layers of electrical tape one the wheel.
Andrew

 

[steve_s]

So here is an update of this project not 100% finished but in workable condition. Have now got some ali bar to make the pulleys but to be honest the plywood ones I have made work fine I will be making a larger size drive pulley when I come across some more 18mm ply.

 

[KemppiFrog]

Steve, some of the other bits in the links you put up in your first post, could be interesting some on here. Stair calculators was something in a recent post.
And, the 3M link I found useful, as I am planning a linisher, so the belt speed info is just what I need. Probably stepped pulleys for me, think I have pair in the 'spares' bin.