Actual Circumference of a 2 x 72" Belt

JasonSCarter · Apr 9, 2009

Alright guys after much dreaming I've started my grinder (HAWGER) project and will post pics when it's finished.

However, being me I'm approaching it in a very unorthodox manner. A KMG or other name brand was not in the budget so I'm going to build one similar to the one featured on PurgatoryIronWorks youtube video. My intentions is to glue the belt around a 2" x 22.91" flywheel made by stacking, laminating and fastening mechanically 4 - 1/2" x 23.25" hardwood plywood circles. then attaching it to a bearinged shaft via flange, (possibly a 6 lug chevy truck axle

) and running it at 200 rpm netting me 1200 sfpm (low, but safe) I'll run it in to the proper diameter by useing a wood lathe gouge to remove what is not needed while it is running.

so my question is this how consistent is the 2x72 belts in being actually 72 linear inches every time?

72" linear = 22.91" circumference
1725 rpm 1" pully to 8.625" pully = 200 shaft rpm
200rpm x 22.91 Dia x pi / 12 = 1200SFPM

Jason

stephanfowler · Apr 9, 2009

JasonSCarter said:
so my question is this how consistent is the 2x72 belts in being actually 72 linear inches every time? within 1/2" or so

72" linear = 22.91" circumference don't you mean diameter
1725 rpm 1" pully to 8.625" pully = 200 shaft rpm
200rpm x 22.91 Dia x pi / 12 = 1200SFPM

Jason

MOST of the time belts are very consistent, every now and then you'll get an odd batch

I just finished going through a batch of Klingspor 80g JFlex that was mysteriously larger than my other belts, and if I didn't remember to reset my tool arm it would come flying off at me..... good times

but that's the only time I've seen that in almost 2 years of grinding

James_Terrio · Apr 9, 2009

I've seen that video and I think it's VERY cool. That guy has several interesting vids.

Re: using store-bought 2X72's... To err on the side of caution, I woyld make the flywheel smaller and build an idler wheel behind it on an adjustable or spring-loaded arm, so you can compensate for slight differences in actual belt lengths. Half an inch is more than you think. Otherwise you may find that some belts fit perfectly, some won't go on at all, and some are dangerously "sloppy". I've never built a grinder but I have a lot of experience with web-fed printing presses, and I'll tell you without a doubt that the ability to adjust for tension is ALWAYS a good thing. That could also give you the option of putting a platen in there somewhere if you want, while still having a pretty large contact wheel for hollow grinds.

On the other hand, you could build the flywheel to whatever circumference you want, and use 2" shop rolls of abrasives to wrap it with, as described in that video. I'm not sure if you can get shop rolls in the grits or types you may want, though.

Regardless, I agree with your thoughts about running it slow if the contact wheel is homemade from plywood. Use the best shaft and bearings you possibly can. BOLT the plywood wheel together, don't just glue it, and use big washers on both sides. You may have to twiddle with the bolts/nuts to get it balanced and run true. Spinning round things that aren't true are very sloppy and dangerous.

JasonSCarter · Apr 9, 2009

Thanx for the info hmm I was hoping they were fairly consistant guess i could cut and glue to make them fit.

Stephen
[Qoute]"72" linear = 22.91" circumference don't you mean diameter"[Qoute]

No, but I may be wrong, but by my logic, becuase I'm taking something that was linear and wrapping it around something that is round then it is a circumference, not a diameter.

Jason

stephanfowler · Apr 9, 2009

JasonSCarter said:
Thanx for the info hmm I was hoping they were fairly consistant guess i could cut and glue to make them fit.

Stephen
[Qoute]"72" linear = 22.91" circumference don't you mean diameter"[Qoute]

No, but I may be wrong, but by my logic, becuase I'm taking something that was linear and wrapping it around something that is round then it is a circumference, not a diameter.

Jason

72" is the circumference of the belt, I.E. if you cut the belt it will stretch out 72"

James_Terrio · Apr 9, 2009

JasonSCarter said:
Thanx for the info hmm I was hoping they were fairly consistant guess i could cut and glue to make them fit.

That's an idea worth exploring. That would allow you to buy any kind of belt you want and suit it to your wheel. Make the wheel a bit smaller to allow for trimming as needed.

StephanFowler said:
"72" linear = 22.91" circumference" ...don't you mean diameter?

Stephan's right. For your original idea, you would need a wheel that is 72" in circumference (all the way around the outside of it). Circumference of a circle = PI x diameter, where PI = 3.141592... OR, Diameter = circumference divided by pi. (it works out the same either way.)

In your case, the desired circumference of the wheel is 72". 72(circumference) divided by 3.141592(pi) = 22.918(diameter). Your numbers are right but your nomenclature was wrong.

JasonSCarter · Apr 10, 2009

James_Terrio said:
That's an idea worth exploring. That would allow you to buy any kind of belt you want and suit it to your wheel. Make the wheel a bit smaller to allow for trimming as needed.

Stephan's right. For your original idea, you would need a wheel that is 72" in circumference (all the way around the outside of it). Circumference of a circle = PI x diameter, where PI = 3.141592... OR, Diameter = circumference divided by pi. (it works out the same either way.)

In your case, the desired circumference of the wheel is 72". 72(circumference) divided by 3.141592(pi) = 22.918(diameter). Your numbers are right but your nomenclature was wrong.

Thanx James and Stephan :thumbup: I see what you mean :foot: That happens alot with me, I know what I'm saying but I confuse the heck out of those around me.

Jason

James_Terrio · Apr 10, 2009

Don't feel bad, I had to google it to make sure I was explaining it right.

Steven Penner · Apr 10, 2009

It seems to me that if you want to do that, you could just start with "shop roll" abrasive material and skip the pre-made belts altogether.

It would make switching grits more difficult and you may see some advantage in having multiple machines, or wheels made up. Just move to a different machine, or swap out a different wheel...

AcridSaint · Apr 10, 2009

I didn't watch the whole video, but I think I have a good enough idea from skipping through it.

I change belts many times during the making of a knife, I also use slack belt, wheel and platen at different junctures, sometimes switching back and forth. I feel that you'll be limiting yourself by making a machine that you have to glue abrasive to, unless you also plan on making a slack grinder and a disc grinder. Even then, I do a lot more belt changing than I feel would be comfortable or convenient.

For what it's worth, a person could take the idea presented there and pretty easily make it into a two wheel grinder by adding a bit more hardware, probably less than $50 worth. That would be a much better solution in my opinion.

JasonSCarter · Apr 10, 2009

Thanx guys I see your point, I guess I should have added this is not my first or only grinder, I also have a 4x106" Glaziers wet belt I use for flat platten, and slack and general polishing. This thing is AWESOME as there is no heat build up to deal with. also I have a small craftsman 4x36 with a 6" disk attached for slack and flat platten also. so switching back and forth is still an option. The shop roll route looks to be the way I'm gonna go as I get almost 3x the belt for less than the average price of a 10 pack of 2x72 belts.

Jason