New Disc grinder

D

DukeHarley

Gold Member
Joined
Apr 11, 2014
Messages
644
Just purchased a new 9” Disc Grinder and when I unboxed it I gave the disc a quick spin and saw there was some run out. Grabbed my Indy and checked the outer edge. The run-out was .023”…….is this acceptable? I was told when I talked to them they allow them to go out with .015-.030 run out. I can’t see getting anything square with it that far out or using it on kitchen blades for thinning. Being a machinists Im totally capable of truing it up but…….

Anyway my question is how much run out is acceptable for knife shop use?
 
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Totally NOT acceptable. Runout should be a one or two thousandths at most. The shaft was bent in shipping. Contact the seller. Who did you get it from?
 
AMK and he told me that .015 to .030 is acceptable. I’m not real impressed with my phone call with them either. VERY DISAPPOINTED!

My intent was to build one but time constraints didn’t allow. Now I have a machine I can’t use for its intended purpose until I fix it.
 
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DukeHarley said:
Just purchased a new 9” Disc Grinder and when I unboxed it I gave the disc a quick spin and saw there was some run out. Grabbed my Indy and checked the outer edge. The run-out was .023”…….is this acceptable? I was told when I talked to them they allow them to go out with .015-.030 run out. I can’t see getting anything square with it that far out or using it on kitchen blades for thinning. Being a machinists Im totally capable of truing it up but…….

Anyway my question is how much run out is acceptable for knife shop use?
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Disk was ON motor when you received it , or you installed it ?
 
Natlek said:
Disk was ON motor when you received it , or you installed it ?
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It was mounted. There was not visible box damage and unit was packed well. He literally told me these are shipped and allowed to be between .015 and .030 run out. If you’re making a grinder for knifemakers how do you justify that much run-out in your product?! Kinda bummed I must say…….
 
DukeHarley said:
It was mounted. There was not visible box damage and unit was packed well. He literally told me these are shipped and allowed to be between .015 and .030 run out. If you’re making a grinder for knifemakers how do you justify that much run-out in your product?! Kinda bummed I must say…….
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Is it the disk or the output shaft of the motor?

have you taken the disk on and off? How is it's fit? I t should be a tight/slip fit. Not loose and sloppy.

are there multiple set screw fastening it down to the shaft?

You being a machinist you probably know all this stuff. I just have lots of questions :/

Sucks.
 
First, it occurs to me to ask which runout you are referring to. Is it on the perimeter of the circle or the face of the disc? If it is the roundness, then the tolerance you state is OK. The roundness can be trimmed by a file while running if it causes any vibration. If it is the face wobbling, it is totally unacceptable.

Craig has my next questions.
Take the disk off and check the shaft. If the shaft is bent call the seller and send it back. If the disk is a sloppy fit to the shaft send it back.
If it is OK, re-install the disk carefully and lock down all set screws. Test the tolerance again. If it still has a lot of runout, you can call the seller for another chat or true the disc yourself. As a machinist you will know how to true the disc. I would true it on the lathe first and then check if you need to do more while spinning on the sander once remounted.
 
Stacy E. Apelt - Bladesmith said:
First, it occurs to me to ask which runout you are referring to. Is it on the perimeter of the circle or the face of the disc? If it is the roundness, then the tolerance you state is OK. The roundness can be trimmed by a file while running if it causes any vibration. If it is the face wobbling, it is totally unacceptable.

Craig has my next questions.
Take the disk off and check the shaft. If the shaft is bent call the seller and send it back. If the disk is a sloppy fit to the shaft send it back.
If it is OK, re-install the disk carefully and lock down all set screws. Test the tolerance again. If it still has a lot of runout, you can call the seller for another chat or true the disc yourself. As a machinist you will know how to true the disc. I would true it on the lathe first and then check if you need to do more while spinning on the sander once remounted.
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I checked run out on the outer edge of machined face of the disc, where the paper sticks. I used my Interapid Indicator and Starrett mag base. Set dial on low at 0 and slowly spun and high spot read .022”.

I may just do it myself as I’m a 30 year machinist/toolmaker. My issue is I’m swamped with knives and a home renovation……that’s why I bought vs build.

Now I have a machine I can’t use until I go into my work some evening and use the lathe when it’s not in use. Just kind of defeats the whole purpose. Im really not trying to be a Karen but I’m gonna be honest when I was told the sell them with up to .030 runout and feel this is acceptable for Knifemaking equipment…..I’m really concerned with the whole unit for $1000. Just sayin……
 
I may just fix it myself as it seems to be the most logical way to resolve…..but had I known I would have ordered another brand…..Hard Core or Tru Grit. Kinda regretting my purchase.

Ill probably tear it apart tonight and try to turn the face this weekend before sending back. I’m pretty sure it’s the face of the disc and not the shaft but I need to verify. I don’t want to send back as it seems like a solid machine otherwise. I just keep going back to him saying……”.015-.030” is acceptable for a $1000 machine. The Harbor Freight 12” at work is .018”. Seems a better buy at $149.99. 😂😂😂

I appreciate the reply’s guys. I need to find time to get on here more often.
 
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Best way to true is disk mounted on shaft .Make shaft of exact dimension as one on motor , lock down all set screws and put in lathe chuck .............
 
DukeHarley said:
I checked run out on the outer edge of machined face of the disc, where the paper sticks. I used my Interapid Indicator and Starrett mag base. Set dial on low at 0 and slowly spun and high spot read .022”.

I may just do it myself as I’m a 30 year machinist/toolmaker. My issue is I’m swamped with knives and a home renovation……that’s why I bought vs build.

Now I have a machine I can’t use until I go into my work some evening and use the lathe when it’s not in use. Just kind of defeats the whole purpose. Im really not trying to be a Karen but I’m gonna be honest when I was told the sell them with up to .030 runout and feel this is acceptable for Knifemaking equipment…..I’m really concerned with the whole unit for $1000. Just sayin……
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Can you please clarify a little more. I'm curious since I own one of these.
Is the run out the surface of the disc moving towards and away from you as you hold work against it, or the edge of the disc that you are not contacting?
 
I have trued a disc with a big file. Lock everything down tight and mount the grinder solid to the bench. Spray the face with DyeChem.
Turn on at slow speed, set the file on the work table, and bring the file slowly into contact with the full face. Stop the machine and look at the marks. It should show the high and low area. Turn back on and run at full speed. Repeat the file contact as many times as needed to remove al the DyeChem. Spray again and make sure it is true. On an out of round disc perimeter edge, I just bring the file against the spinning disc and it will true up pretty fast. This isn't a critical area unless it is causing vibration.
 
I’m checking runout on the face where the abrasive is stuck to. I’m not concerned about centrifugal measurement…..which I can easily fix with machine running. Im saying…….the disc should run flat so the disc is continuously making contact with my workpiece. It will not. If I run an indicator on the FACE of the disc and spin it one revolution it will go from .000 to .020/.022 on the working surface. This will
not work for squaring materials for handles and will not work for cleaning up flats and thinning kitchen blades.
 
Stacy E. Apelt - Bladesmith said:
I have trued a disc with a big file. Lock everything down tight and mount the grinder solid to the bench. Spray the face with DyeChem.
Turn on at slow speed, set the file on the work table, and bring the file slowly into contact with the full face. Stop the machine and look at the marks. It should show the high and low area. Turn back on and run at full speed. Repeat the file contact as many times as needed to remove al the DyeChem. Spray again and make sure it is true. On an out of round disc perimeter edge, I just bring the file against the spinning disc and it will true up pretty fast. This isn't a critical area unless it is causing vibration.
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.020 with a file? That’ll take a minute or two. I’ll try to get it removed and get to the shop tonight. The lathe should be open and I’ll blue it up and see if I can turn it. Our 3 jaw is crap so I’ll probably just indicate in a 4 jaw…..probably better anyway. I’ll keep you guys posted. So appreciate the replies guys!
 
DukeHarley said:
I’m checking runout on the face where the abrasive is stuck to. I’m not concerned about centrifugal measurement…..which I can easily fix with machine running. Im saying…….the disc should run flat so the disc is continuously making contact with my workpiece. It will not. If I run an indicator on the FACE of the disc and spin it one revolution it will go from .000 to .020/.022 on the working surface. This will
not work for squaring materials for handles and will not work for cleaning up flats and thinning kitchen blades.
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That is ridiculous and unacceptable. Mine is essentially perfect.
 
Richard338 said:
Can you please clarify a little more. I'm curious since I own one of these.
Is the run out the surface of the disc moving towards and away from you as you hold work against it, or the edge of the disc that you are not contacting?
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Richard338 said:
That is ridiculous and unacceptable. Mine is essentially perfect.
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Unusable as far as I’m concerned!

I just checked motor shaft and it wasn’t even .0002” out so we’re golden there……

Then rechecked face of disc and it is out .023 give or take .0001”.

Took video but don’t have host any longer.
 
I was a toolroom machinist in a former life......
I was able to get a real nice 1 degree disk. I wanted it Flat.

I figured it was going to be an easy fix, right?
my lathe is older than dirt, and spinning that large of diameter on it had it's own set of challenges.
It Sung like the dickens.... howling, and screaming!
All the different speeds, I had issues preventing chatter. I had to do some creative, and sketchy things to get it to all work out.

What I'm saying is Be Careful!!!
keep us posted. :D
 
If you've been dealing with the irascible owner, try speaking with the production manager. May not get any farther but he's a lot easier to deal with.
 
Richard338 said:
I would call them again. I don't see how you can market a disc grinder with a straight face saying that much runout is acceptable.
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So after talking with you guys I got to thinking…….if you guys aren’t gettin my point as to what’s wrong then maybe I’m explaining myself wrong and possibly the guy at AMK is confused. I sent him some video and he called me again. We re hashed out what the issue was and he thought I meant concentricity was out but it’s the but perpendicularity of the unit between shaft and face of disc. We got it hashed out and a new disc will be on its way.

I did some more measurements…….shaft is .625 on the money but bore in disc is .628 and I believe either not bored perpendicular or tapers slightly.

Anyway cooler heads prevail and it’s worked out. Some issues with articulation on my part I believe. Sorry guys!
 
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