Broken Belts

U

unky_gumbi

Joined
Aug 28, 2009
Messages
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For all of you that have true 2X72" grinders, how often to you deal with grinding belts breaking or chunking out? I was grinding the bevel in a knife yesterday on my crappy tire 1X30 grinder and the belt chunked out at the seam and pulled the blank out of my hand, but first it pulled my little finger into the moving belt and ground off a bit of the tip and dislocated it. the damage to me was minor and nothing to worry about, popped the finger back into place cleaned up the tip and went to the hospital to make sure I got the finger back in right. Its not like I haven't popped my fingers back in place before with playing sports and the freeride mountain biking I am use to that sort of injury.

I chalk the broken belt up to the little grinder is really a sander and meant to be used for wood not steel, and it runs fast with no speed adjustment, but it got me wondering how often do belts break on the big purpose built grinders
 
For me...I don't have belts break very often. Maybe once every couple years.

There's actually 2 scenarios:

1.) The 100% break

2.) The flapper!

The "100 % break" is usually just a loud pop that scares the bejeezus out of me...then the belt falls harmlessly on the floor.

The flapper on the other hand is when you snag an edge or partially tear the belt such that a flap of belt whips the day-lights out of you before you can get clear. For me...there is ussually some warning....it's a slight ticking sound when I grind near the edge. Once I'm aware of it.....I ussually toss the belt with the idea that belts are cheap compared to the potential consequences.

Flat grinding on the platen is brutal on belts and this is where I'm more careful. The belt seam really takes a pounding when it get pinched between the workpiece and the platen plate.

For me, I think I can avoid broken belt issues with some basic "shop sense"...or "common sense". If the belt is really worn, or has tears...or the seam is in bad shape...then toss it.

But occasionally....you'll get bitten.

Be safe!

-Rob
 
i always try to check the seams of my belts regularly. if a belt gets loose in the middle, they tend to snake side to side which is a good sign its going to break soon. i have used superglue to mend a belt before so i could finish up a knife if that belt was the only one i had in the grit i was using.

i have heavy plastic sheeting around my bench to contain dust and i had a belt shoot through the plastic which was interesting. i bet it would have left a mark if it had hit me.
 
My thoughts/reply would be the same as Rob's! About the only time I break a belt is when I do something dumb, or occasionally you will get your hands on a bad batch of belts.

I once had an order of 50 grit Blaze belts where the first 5 I put on the grinder broke at the joint withing 30 seconds of turning on the grinder. That's where purchasing belts from a reputable source comes in. I contact my belt dealer (Tru-Grit), and they sent a UPS call tag for the whole batch, and had replacements to me before the old belts ever arrived back to them.
 
I had about 4 belts break all at once on me right after starting to grind on them as Ed experienced. All of them were the 100% breaks that Rob mentioned, and it sounds like someone fired off a pistol right in front of you. The good thing for me is that it happens so fast that I don't have time to get scared and drop my work :D. You just kind of end up standing there holding a knife to a platen with no belt running over it and wondering what just happened. Occasionally they will slap you, though.

I think that run of bad luck was probably a bad batch of belts or belts that had been on my shop shelf too long (they were all the same brand/grit and were purchased at the same time).

I've also had belts chunk out on me or turn into flappers. This is usually because I am being too miserly and pushing the belt long past its useful life. I don't do that much anymore, and my techniques have changed over time so that I am much less abusive on belts now that I used to be.

--nathan
 
I think all of Rob's observations are spot on. The one thing I would like to add is, do not present a sharp edge to the belt if possible. That is a 90 degree edge. After profiling the knife, grind a 45 degree chamfer on what will be the edge (edge down). It helps to scribe the centerline and 2 lines 30 thou or so apart. Now when you present the side of the blade to the belt (edge up) there is a lead in ramp. This extends the life of the belt by not stripping off the abrasive, and won't cut the belt.

~Alden
 
The glue used to bond the mylar lap to the back of butt jointed
belts will degrade with time......Older belts come apart alot more
often.
 
Ed Caffrey said:
My thoughts/reply would be the same as Rob's! About the only time I break a belt is when I do something dumb, or occasionally you will get your hands on a bad batch of belts.

I once had an order of 50 grit Blaze belts where the first 5 I put on the grinder broke at the joint withing 30 seconds of turning on the grinder. That's where purchasing belts from a reputable source comes in. I contact my belt dealer (Tru-Grit), and they sent a UPS call tag for the whole batch, and had replacements to me before the old belts ever arrived back to them.
Click to expand...
I had the same thing happen with a batch of 36 grit blue Nortons. One got me in the forehead.:eek:
 
The belt that broke on me this time was a Klingspor 120 it had a moment of ticking and as I heard it the blade was being ripped from my hand, not even enough time to register what was happening. This thing runs at 3400rpm so Not much time to react when things pop. It was a new belt, but its not the first one that has broken or chunked out. I don't blame the belts, its just that the machine isn't meant to be used for knife making. I had one let loose with out the little top guard on and the belt flew off and over my head when it broke. All I had done was turn on the machine to center the belt. After that I started just turning the drive wheel by hand to center the belt and then putting all the guards back on before turning it on, and I never stand in front of it any more now.

I only have a couple more weeks till I am laid up till Christmas so during that time I will be building up a real grinder. Even though they still snap belts it seems like they aren't as drastic at the little 3400rpm machine. I could just go back to files and sandpaper, then all there is to worry about is blisters:p
 
FWIW, the batch of new belts that broke on me were Klingspors. Otherwise, I hadn't had issue with them.

--Nathan
 
It's nice to have a square wheel grinder when belts break.
I once bought some "cheap" belts off e-bay, and they came apart quickly.
I don't think I have ever had any belts I bought from Pop come apart.
As has been said, old belts will tend to come apart more than the new ones. I have some old micron belts and I have experienced a lot of breakage with them.
Often a belt will sound different right before it breaks. If you listen for the sound you can stop the grinder and avoid the break.
 
Using an old (the original, not the Wilton clone) 2"x72" Square Wheel and the blank down on the table, I snapped three 60-grit belts in a row in my ignorance by stupidly presenting the square edge to the belt. Quit using a table, grind a bevel first, no troubles since. I get Norton belts from www.Acutabove.com
 
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