Grinder belt speed question?

flatgrinder

flatgrinder

Joined
Dec 20, 2005
Messages
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Hi,

If you could only have one belt speed for your grinder, what would it be?

1750 or 3600 SFM? Any other recommendations? Is 1750 too slow -or would it be a good "all rounder" for all belt grits.

If you're not sure how to calculate the belt speed, here it is for a direct drive:

Motor RPM x ((2 x 3.142 x Wheel Diameter/2) / 12)

(I'm building a fixed speed, 2 wheel grinder -using a 14" contact wheel, with a 3.5" drive wheel (maybe?), and trying to decide on a speed for it). I'll be making some hollow grinds.

Thanks!
 
Why fixed speed? If you're building the thing, why not ferret out a nice 3-phase motor and VFD? I'd say it's worth the trouble.

If you CAN'T do that, I'd go with the faster option. I usually do hollowgrinding with a BIII running 3600 rpm on a large drive wheel (I think it's about 7 inches or so) with a non-serrated 12-inch contact wheel. [I also grind edge up, with a very effective fixture that's not easily explained. It's very fast, very precise. Mister or cold-air gun for cooling.]

I do turn it down about half speed for finer grits.

Really, the variable speed will enhance the usefulness of your tool immensely. I would urge you to go that route.
 
I do all of my grinding with a 1750 RPM 14" drive wheel, somewhere around 6000 SFM if I don't miss my guess. Not a lot of room for finesse unless you have a good touch for grinding.
 
In terms of SFM, if I only had one speed, I think I would want about 3000-3500 SFM. This is not terribly fast...but 1700 is just too slow for performance belts especially with more aggressive grits such a 36-80.

Of course, this can be debated and this is just my opinion.
 
I would really recommend NOT direct driving a 14" wheel.At 6500 SFM the belt will be screaming,and any imbalance in the wheel or drive could be catastrophic.I would make a 8-10"" drive wheel and run the belt slower, or make the drive wheel fixed at 6" and the contact wheel changeable (like a Bader).The best solution for you would be a variable speed motor.
Stacy
 
I've got a Grizzly G1015 two wheel grinder rated for 3600 FPM. I wanted the larger radius of a 10" contact wheel. The byproduct was that I've increased the speed of the unit, but not to the point that it's in any way uncontrollable for me.
 
If there is any way to go variable speed, and you can do it with single phase in 110V or 240V with a NEma controller to DC motor, do that....also would recommend a reverse switch for sharpening running away from you.
I run as slow as 150-200 SFM on a 10" wheel and on a platten. and as high as 3500 SFM or about 1/2 of available speed on the controller and a 2500 RPM rated DC motor. Only time I ever exceed that is hogging rough outlines on 416 that is un-heat-treated for liners/bolsters...but still grind barehanded to avoid excess heat. I usually grind Titanium slow enough to avoid sparks and thereby minimizing Ti fire probability.
I grind all my blades and springs after heat treat so need to keep the steel cool enough to not change the Rc with grinding heat....also always grind barehanded so if my fingers warm up on the steel, dipping time...
Good Luck
 
Stacy 14" drive wheels turning at 1750 RPM are standard in the metal finishing industry and have been for over 50 years.

The industry standard is also 3"X132" for belts for best belt life. The extra length is considered necessary for belt cooling and best belt life.

Buffing wheels in the range of 14" to 20" diameter are also the norm.

I admit that walking up to a 20" buff at 1750 RPM can be intimidating but for commercial polishing it sure works well.
 
First off, I just re-read the post.
Flatgrinder is using a 3.5" drive wheel.I thought that he said it was a direct drive on the 14" contact wheel.My mistake.Most two wheel units I have seen were driven at the contact wheel,with a tracking second wheel.If the drive wheel is constant,then the contact wheel is the same SFM regardless of how big or small it is.
At 1600 SFM his unit will be a bit slow for some work,but that's a good general all purpose speed.He could switch a 5" drive wheel,but a variable speed motor would be the best solution.Two wheel grinders can be a bit tricky to track at high speed.

George, I agree that there are commercial units built for industry to run 3X132 (and larger) belts at 6000SFM. Flatgrinder was asking a question from a hobbyist point of view,about a unit that will be HOME BUILT to run 2X72" belts.The least bit of imbalance or warp can be deadly at high speed.
About 35 yeas ago I used a 12" industrial grinder occasionally. It scared the He!! out of me just to turn it on.I would let it run for at least one minute before I would step in front of it.I have seen what a big wheel unloading can do. A new wheel went off like a bomb .It tore the whole pedestal out of the floor,and took out a good chunk of the wall.Luckily no one was in front of it when it unloaded! We have all heard the horror stories of grinding wheel accidents.A broken belt (usually from too much tension and too high speed) can put you on the floor, too.
Safety is more important than speed in my book - Stacy
 
Get some step pulleys and make yourself a variable speed unit, Rob Frink sells them. the ones I used were for air commpressor pumps and a auto fan belt:D . thats what I have had on my COOTE grinder for 8 plus years.I set the grinder on the end of the bench, Then I drilled set holes in the work bench for each speed level, and then clamp it down with a c-clamp and a tad of inner tube:thumbup: so there is no vibration. it is really worth the extra hassle! when you want to slow things way down to work different hardwoods and snythidics ETC
 
My Bader runs about 3,500 sfm (7.25 drive dia. with 3600 rpm) at top speed via VFD. This speed arrangement was recommended by Dan at Bader some years ago. They seem to advocate faster speeds for better belt efficiency and performance.
I have not found that speed particularly hazardous (so far). Of course, I don't make my own contact wheels out of old inner tubes or use roller-skating bearings in turned hardwood hubs or do other wacky cheapskate things to get myself maimed as some folks seem to advocate from time to time.
 
Thanks for the replies!

Some real good info here. Stacy's warning has been noted, the inertia from a 14" contact wheel flying off at high rpm will sure knock the wind outta ya -if not more. I'll be careful, that's another reason I was considering the slower speed for such a big wheel.

I had a thought this evening about converting my Grizzly to a 3 wheel grinder, basically replacing the 8" wheel with a 4" drive wheel from sunray, then locating a tooling arm in front of it with a 14" idler wheel acting as the contact wheel at the end and running a longer belt (maybe a 2" x 132") -that way I still have the ability to track the belt via the adjuster at the top of the Grizzly.

I'm going to give it a go, and let you guys know how it works out. I'm going to try a couple more ideas too. May take a while as I'm kinda busy these days ... but thanks again for the info! :thumbup:
 
Rhinoknives,

We were evidently posting at the same time (didn't see your post before posting mine). As such, I WAS NOT referring to your idea of using inner tube for vibration isolation when listing some of the "Wacky Cheapskate" stuff I've hear people do and advocate regarding grinding equipment.

Rather, I was remembering someone that was turning hubs in scrap hardwood, using some questionable 'found' bearings and, I think it was supergluing the contact rubber or using Shoe Goo or something.
Try running that thing at 4000 sfpm for a while and see what happens to you!
 
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