9" disc grinder- getting it perfect?

S

StuNY

Joined
Feb 16, 2014
Messages
152
Just built a 9" disc grinder based on watching the Nick Wheeler videos and must say this is going to change everything in making my kitchen knives! I can't believe how flat my flat grinds are turning out. I ran a couple of rejected blades across it and found my 2x72 work had left a number of peaks and valleys that I didn't even know were there. Surely going to save me a lot of time in the hand sanding stage. I was able to share my belt grinder KBAC-27 with it based on some great posts here.

Question though... while the disc I got from USAKnifemaker is nicely balanced and spins well up to full RPM, I notice there is a very slight wobble in the disc. Doesn't seem to affect the finish, working well, but it would be nice to true it up a bit. In searching other threads I saw a reference to Nick Wheeler addressing this in a post but can't find it here. Anybody know of a link, or have advice on how to get the wheel to run perfectly? I sure don't want to mess up the balance of course!

Thanks,
Stuart
 
I'd add some additional sets screws and very thin shims and use a dial test indicator to dial it in.

One limitation of using the output shaft of an electric motor (rather than a real spindle) is there are limits to the precision you can get because runout can change depending on temperature and speed.
 
Nathan the Machinist said:
I'd add some additional sets screws and very thin shims and use a dial test indicator to dial it in.

One limitation of using the output shaft of an electric motor (rather than a real spindle) is there are limits to the precision you can get because runout can change depending on temperature and speed.
Click to expand...

Thanks Nathan- I didn't even think about using shims- great idea! Was thinking I needed to machine it somehow but that is an easier approach for sure- and I get to use some of that leftover shim stock I got for tramming my mill!
 
stainless steel heat treat foil works for a shim and aluminum foil is ~ .0005 and malleable and works for adjustments
 
Wow! Thanks so much Nathan- two pieces of heat treat foil did the trick, running .004" at outer rim now- what a difference! Was .025" when I started. So much smoother grinding now. Much appreciated!
 
what rpm you running at? I am thinking about a 9" disc and wondering if I can get away without putting it on a vfd and spinning it up to 1800. Or do you prefer more control at lower speed(s)?
 
My motor is 1hp running at 1800 rpm. But with the VFD it doubles that to 3600 rpm. With that said, I don't think I will be running it at full speed from what I have done so far. It shares the VFD with my belt sander which I do run at the full 3600 though so that is why I leave it set there. From experimenting a bit yesterday it looks like on an already heat treated knife with 80 grit paper about 60% is about right, but at 220 grit going down to 30-40% works best. Too fast at finer grits and it heats up fast, risking ruining the temper.
So yes, I think the lower speed control is pretty important. You could probably get away with your 1800 rpm motor without the VFD for a while but once you add the VFD you will wish you did it sooner! Oh, and of course having it reversible is pretty much essential. I got the 1 degree angled disc and like it very much so far.
 
I spray a spritz of windex on my disc. It seems to help with paper life and heat issues. It does make a bit of a mess though.
 
great job Op! And that's a great idea nathan, didn't even think about adding another set screw...

J. Hoffman said:
I spray a spritz of windex on my disc. It seems to help with paper life and heat issues. It does make a bit of a mess though.
Click to expand...

That's a good idea but yeah I can see it making a mess... my problem w/ disc grinding so far has been how fast the sandpaper wears out compared to a belt, and its much more of a pain to switch out!
 
razor-edge-knives said:
... my problem w/ disc grinding so far has been how fast the sandpaper wears out compared to a belt, and its much more of a pain to switch out!
Click to expand...
I am pretty impressed how easy it is to switch between papers on the disc using the 3M Feathering Disc Adhesive (per Nick Wheeler's video). The adhesive stays with the disc, not the paper and I already stacked up three different paper grits that I have been swapping between. I'll bet I even switch out papers faster on my disc than changing belts on my 2x72 grinder.
Good tip on the windex! seems to work better than dry and doesn't make much of a mess if the rpm's are low. I am looking into adding a Kool-Mist kind of setup to both the disc and my belt sander. Submersible pump, spray nozzle and foot switch are looking promising!
 
I have been looking at getting one of these too. What disc is preferred the flat or the beveled disc?
 
I got the beveled disc just because Nick Wheeler was using it and had a strong rational for the benefits over flat. With that said, there seem to be differing opinions here one vs the other and I am sure people more experienced than me can provide insights into which is better for your needs.
Stuart
 
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