Disc sander run out

REK Knives

REK Knives

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Knifemaker / Craftsman / Service Provider
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Just got my 9" disc sander set up and the outside rim of the face is running about 4 thou difference... Is this something I should try to fix or is it good enough? What's 'normal'?
 
razor-edge-knives said:
Just got my 9" disc sander set up and the outside rim of the face is running about 4 thou difference... Is this something I should try to fix or is it good enough? What's 'normal'?
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Probably depends how you're using it. I liked to lay blades on the disk flat and polish them freehand, so as long as it didn't feel weird it'd be ok. OTOH if you're using a table it may not be good enough.
 
Thanks guys. Well I got a disc sander because I wanted perfect flatness on certain things and the run out doesn't help hehe.

I checked the spindle/Arbor and it has about .001" run out... You think this would translate to .004" at the outer face of the rim of the disc?
 
If you bought a hub and discs it's possible they are fine and your motor connection is causing the run out. .004 isn't much.
Frank
 
HSC /// said:
is the keyway and key sloppy,?
the .004 is likely from the fit onto the shaft
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No, it is very tight... I have to hammer the hub on lol. I played around w/ tapping the out and in part on the hub to no avail... I have it seated all the way onto the shaft.

Frank Niro said:
If you bought a hub and discs it's possible they are fine and your motor connection is causing the run out. .004 isn't much.
Frank
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Thanks Frank... yeah I got the hub and discs from Rod and I'm pretty confident those aren't the issue, I am wondering if the .001" run out in the shaft could cause the .004" on the outer rim. Going to call the motor company tomorrow and see if they will replace the motor.
 
I've been running 3 different discs for 7 years or so--- with varying small degrees of runout. With that being
said I fortunatley got one of Nathan's when he still had a few. The days of riding the hump are over.
Ken.
 
If it's got .001 at the shaft the further away from the shaft you get the more run out you will have.
 
Absoultly if the shaft runs out it will affect the edge by a greater deg. Quick way to test is put your indicator on the face of the shaft and mesure there with the indicator as close to the edge as possible. Then take your disk diamater and devide by your shaft diamater and times it by the runout you measured. This assumes the face is square to the OD which it should. But is the shaft run out tapered or square to the axis. Meaning does the turn out get less as you mesure closer to the motor. If it does then it would affect disk run out. If not then the disk should run flat but the OD will be out .004.
 
JTknives said:
Absoultly if the shaft runs out it will affect the edge by a greater deg. Quick way to test is put your indicator on the face of the shaft and mesure there with the indicator as close to the edge as possible. Then take your disk diamater and devide by your shaft diamater and times it by the runout you measured. This assumes the face is square to the OD which it should. But is the shaft run out tapered or square to the axis. Meaning does the turn out get less as you mesure closer to the motor. If it does then it would affect disk run out. If not then the disk should run flat but the OD will be out .004.
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Thanks JT, yeah the run out seems to get much less the closer to the center of the disc. I contacted the company I got my motor from (Automation Direct) and they are sending me a replacement... outstanding customer service. It's amazing that they are even letting me keep the old motor, they just need the name plate off of it! Now I can use it as a back up motor for my Wilmont belt grinder.

Hopefully I'll get this issue sorted out! I hate skipping!
 
I would expect about .004" run out on a 4.5" radius disk mounted to a shaft of 1" or less in diameter with .001" run out. The math is pretty much a straight ratio, although sometimes you get lucky and something else in the system is slightly off in the opposite direction.

.001 run out on a shaft isn't much, for a lot of applications the motor would be acceptable. So check your replacement motor before bothering to mount your disk, it may not be much better. If it tests OK, don't pound the hub on. At a minimum you'll "Brinell" the bearings (machinist slang for "leaving tiny round dents in the bearing races") and it is possible to bend the shaft and cause run-out again. Get a local machine shop to heat/ press the hub on for you
 
When I made my disk for my grinder I ground the surface flat with the disk mounted on the motor and it spinning.
 
JTknives said:
When I made my disk for my grinder I ground the surface flat with the disk mounted on the motor and it spinning.
Click to expand...

That's a great idea man, I bet it's PERFECT now huh?
 
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I would be sure of any changes you make to the hub or discs of a Neilsen disc grinder. They are manufactured to very fine tolerances Hammering the hub on doesn't sound like a good way to maintain the accuracy that was originally machined in. I know that a surface grinder isn't going to make them better. They are already far better than that in their make up as we received them.
Frank
 
Frank Niro said:
I would be sure of any changes you make to the hub or discs of a Neilsen disc grinder. They are manufactured to very fine tolerances Hammering the hub on doesn't sound like a good way to maintain the accuracy that was originally machined in. I know that a surface grinder isn't going to make them better. They are already far better than that in their make up as we received them.
Frank
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Thanks for the pointers Frank, When I said hammering the hub I meant that I would either lightly tap the center (only) with a brass hammer but if I was going to put more force into it I used a 1" piece of ABS as a buffer and still right over the center.


Mahoney said:
I would expect about .004" run out on a 4.5" radius disk mounted to a shaft of 1" or less in diameter with .001" run out. The math is pretty much a straight ratio, although sometimes you get lucky and something else in the system is slightly off in the opposite direction.


.001 run out on a shaft isn't much, for a lot of applications the motor would be acceptable. So check your replacement motor before bothering to mount your disk, it may not be much better. If it tests OK, don't pound the hub on. At a minimum you'll "Brinell" the bearings (machinist slang for "leaving tiny round dents in the bearing races") and it is possible to bend the shaft and cause run-out again. Get a local machine shop to heat/ press the hub on for you
Click to expand...

hmmm that's a good idea I didn't know that was possible!
 
When the new motor comes in, try holding a heat gun on the disc hub for a minute, and then sliding it on. If it still seems like it'll be tight, you can lightly polish the motor shaft by (carefully) holding a piece of emery paper against it while the motor is turning.
 
knife to a gunfight said:
When the new motor comes in, try holding a heat gun on the disc hub for a minute, and then sliding it on. If it still seems like it'll be tight, you can lightly polish the motor shaft by (carefully) holding a piece of emery paper against it while the motor is turning.
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You guys are full of good information! Thanks will do!
 
It takes a bit more than a minute with a heat gun to expand a hub by a couple thousandths. A proper motor repair shop will have an induction heater to do the job. If you are determined to DIY, you could try heating in an oven or a heat treat kiln. You are on your own for the research to decide how hot to go, it'll depend on the metal the hub is made of and it's coefficient of thermal expansion.

I would not do more than lightly chamfering the end of the shaft with the emery paper if you go that route. If you are not very careful when polishing the shaft, it's possible to sand in a tiny taper that will introduce run-out.

Other possibilities at the local machinists or motor shop if you can't get the hub on easily, turning down the motor shaft or boring out the hub. Either can be done accurately with the proper equipment.
 
Mahoney said:
It takes a bit more than a minute with a heat gun to expand a hub by a couple thousandths. A proper motor repair shop will have an induction heater to do the job. If you are determined to DIY, you could try heating in an oven or a heat treat kiln. You are on your own for the research to decide how hot to go, it'll depend on the metal the hub is made of and it's coefficient of thermal expansion.

I would not do more than lightly chamfering the end of the shaft with the emery paper if you go that route. If you are not very careful when polishing the shaft, it's possible to sand in a tiny taper that will introduce run-out.

Other possibilities at the local machinists or motor shop if you can't get the hub on easily, turning down the motor shaft or boring out the hub. Either can be done accurately with the proper equipment.
Click to expand...

Thanks for the warning! I will keep this in mind!
 
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