What did I do wrong - belts breaking at joint

D

DarrenW

Joined
Dec 8, 2013
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13
Have been reading about using scrapers (sen) to profile blades and read a few threads, one by Don Fogg was the best, and decided to make one from a Nicholson file I had.

I used my belt grinder to remove the teeth on the wide side being careful to not ruin the heat treat - all well and good. Started to grind in a 30 degree bevel on the thin side and cut the belt only a few seconds in. Put on a new belt, boom same thing. Put a third belt on being careful on how I was grinding and almost immediately heard the thunka thunka of a belt about to break. Looked at the belts and they all failed at the joint.

I've never had this happen before. Is there something about grinding a file that is any different from grinding on a knife blade, hardened or otherwise?

Ended up using a my 1 x 42 to finish, it survived, then touched up with sharpening stone.

Why did the 1x42 work and not the 2x72?

Just confused is all. Wondering if anyone can enlighten me.

Thanks
Darren

PS just tried it and don't know why I've not heard of it before!
 
The same thing happened to me with a couple of j flex belts. I forgot where I bought them so I was stuck. The tried to repair them with postal tape but it didn't work out. I went on grinding and never had another problem. I can only guess that the belts were somehow defective because I have used dozens of each kind of belt ever since with no breaks.
 
From a machinists point of view I would suspect the belts are being run with a bit too much tension. The joints are the weak point and as they go over the wheel there will be a slight bit more tension. I kept all the abrasive belts no matter how smooth they got cause an intact belt is still better than a strip of abrasive material. yrmv
 
I just made another sen last week. Grind them edge down and you'll be fine. Make sure your belts are running in the right direction(if applicable). It is just a vulnerable approach angle(30-40deg, edge up), I guess.

Incidentally, my "happy" geometry for a sen is 1.25" wide, 35deg edge with a 32" dia hollow grind on the backside. Here is a pic of it in progress...
 

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One other thing that comes to mind, is if the belts had gotten damp or wet and then dried out appearing good for use. (personal experience with this one :) )
 
jdm61 said:
How OLD are they?
Click to expand...

That would be my question... anytime that I have belts "explode" on me is when they are really old and I used the edges of the belts more than the entire width of the belt.

Scary as hell when it happens.
 
I have one of those Jancy Radiusmaster grinders that I do not really use anymore since I got my KMG. I had a bunch of stuff to do a while back and not enough heavy grit belts for the KMG, so I fired it up. The belts I had were at least 5 or 6 years old and they blew up at the joint after just a few minutes of use. These were old belts, but they had not been used, so they were not worn belts. Mike at Sheffield supply told me that the age was likely the cause as the tape, etc can get brittle. I had one batch of allegedly new Norton blue Norzon 36 grit belts do that to me a few years back too.
TheWeatherman said:
That would be my question... anytime that I have belts "explode" on me is when they are really old and I used the edges of the belts more than the entire width of the belt.

Scary as hell when it happens.
Click to expand...
 
jdm61 said:
I have one of those Jancy Radiusmaster grinders that I do not really use anymore since I got my KMG. I had a bunch of stuff to do a while back and not enough heavy grit belts for the KMG, so I fired it up. The belts I had were at least 5 or 6 years old and they blew up at the joint after just a few minutes of use. These were old belts, but they had not been used, so they were not worn belts. Mike at Sheffield supply told me that the age was likely the cause as the tape, etc can get brittle. I had one batch of allegedly new Norton blue Norzon 36 grit belts do that to me a few years back too.
Click to expand...

Ah... good clarification. Mine were just used heavily.
 
Awesome Guys, thanks for the input.

I think this may be a function of almost all of your hints. The belts are old (just ordered 30 Norton Blaze belts today) and were used to grind a previous blade with lots of water dunking to keep it cool - was prehardened. Also I was also originally grinding into the blade edge when one went then flipped it as I thought the same thing.

All done now and works well! So glad I tried it.

Once again the collective knowledge of the Blade Forums to the rescue.

Take care all.
Darren
 
I wanted to jump in on this as it relates to Norton Blaze. It seems that my 120 and 150 grit get weak pretty quick in comparison to my 40-80 grits belts. I am going to pay attention to the tension from now on.
 
I have a few boxes of new Norton belts that have been under my bench they been under there for a few years. I found them started using and they brake at the seam. tape is dried and brittle. what to do with them? can they be fix? I have a few boxes of them all new
 
I've discovered that the glue joints are only good for a few years. After that, they're quit likely to break at the glue joint as soon as you put them on your grinder and tension them.
 
Some of the joints aren't that great to begin with.
Bootstrap Bill said:
I've discovered that the glue joints are only good for a few years. After that, they're quit likely to break at the glue joint as soon as you put them on your grinder and tension them.
Click to expand...
 
I have a few boxes of new Norton belts that have been under my bench they been under there for a few years. I found them started using and they brake at the seam. tape is dried and brittle. what to do with them? can they be fix? I have a few boxes of them all new-------Reeves, I've tried every industrial adhesive known to man to repair the failed glue joints with absolutely no luck. I wish I had better news for you. I have several large crates of new old Hermes belts that are unusable for the above mentioned reason. Bummer
 
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