Are Disk Grinders Really That Awesome?

J. Keeton

J. Keeton

Joined
Nov 15, 2005
Messages
1,201
I think I may know the answer to this one....

Who here loves their disk grinder?! And what's your favorite part about having one?


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I'm thinking of building one... Is a 1725 RPM, enclosed, 1HP motor with a VFD the ticket? Do they need to be reversible? 9'' 1 degree bevel disk from KMG?


Cheers Yall,
James

Edit: My primary intended use is for cleaning up blade bevels.

Edit #2: This video from the legendary NickWheeler NickWheeler is what got me thinking about getting one -
 
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All I know about disc grinders, is that my 2 x 42 belt grinder has one on the opposite side, and I've rarely used it, and whenever I have, I just ended up going back to the belt for it anyway. - and thanks for the etching machine tutorial, mine has been going strong over a year now!
 
1 hp is more than enough for a disk grinder, and YES you do need VFD which gives you reversible. They are very handy for cleaning up bevels.
 
Yes on reverse. I use mine for every handle I make. Not for blades.

Edit: I realise I use it on blades, for long straight spines and roughing up the tang for glue up.
 
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weo said:
Some say yes, some say no. I (currently) prefer a flat disc to the bevel.
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I haven't touched my bevel disc (and therefore don't use a disc grinder) in months, due to the hollow factor we discussed at length before. It does seem to make hand sanding harder. You tried to warn me, but I had to see it for my self.
 
I have a little and cheap 5" disk sander from Menards. It has variable speed control from 0 - full, 1700ish rpm? I love it. The work rest is nice and accurate and it runs super smooth. As a slip joint knife maker I really only use it for initial cover profiling currently. Other than that I don't see why I would ever need to have one of the bigger and more expensive units for slip joint making. I either hand flatten handle material on a stone or mill to my desired thickness. I made a custom hardened platen with a back bevel of 45* for doing things like back square shaping. I've invested heavily in making my 2x72 basically a one stop grinder station and I'm extremely happy with the performance. Maybe that is the relevant question here? As these 2x72's continue to be made so versatile are they making other more specialized grinders obsolete for makers just starting out?
 
I'm planning on putting a 1/2 hp motor on the same VFD as my belt grinder. Saves a good chunk of money. Then I just need a disc grinder plate to attach. The motor is less than $150 and the disc is like $90. I think all the wiring and switches would be about $40 total. It's the cheapest way I've figured so far, but I haven't gotten it all together yet. Good luck with yours
 
Case_D said:
I'm planning on putting a 1/2 hp motor on the same VFD as my belt grinder. Saves a good chunk of money. Then I just need a disc grinder plate to attach. The motor is less than $150 and the disc is like $90. I think all the wiring and switches would be about $40 total. It's the cheapest way I've figured so far, but I haven't gotten it all together yet. Good luck with yours
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I'm not sure if putting motors with different HP on the same VFD is a good idea.
 
I ‘d hate to do without mine for slippies and kitchen knives.
 
I used to have a small disc grinder attached to my old Craftsman 2x42 and didn't find myself using it all the time, mostly because it was way too fast. Now I have a full size disc grinder attachment for my Brodbeck 2x72 which gives me plenty of HP and variable speed, although it's not reversible. I haven't needed that feature yet though. I use the heck outta mine, mostly for cleaning up handle material or flattening my grinds before moving to hand sanding. Mine is a flat disc, and although I like the idea of a beveled one, I think it's probably mostly user preference. I would highly recommend setting it up so you can use it vertically or horizontally though. I've found that to be a useful feature, as it allows you to get different angles for the best view.
 
I use mine all the time. I can't imagine not having VSD on one because they need to be used at slow speeds. It really shines for flat sanding flats on bevels before hand sanding. I use mine to flat sand handle scales also. I use a flat disc and not the bevel but I'd love to try both for a comparison. But I'm totally happy with my flat disc grinder.
 
Reversible is amazing. I mostly use mine for handles as some said above. I haven’t had the light bulb moment on flattening bevels yet. I have both flat and bevel disks. I have the Nielsen system but just have the one of each. Not a whole set of each as was intended with them. The bevel disk is for longer blades that cross midline. I run both off my 1 vfd. I have a female receptacle wired off the back with both motor having a male plug. Just swap to whichever I need at the time. I made my work rests (square tubing with set screws on top to adjust depth and placement and have a 90* one and 45* bevel one.
 
I never used to use mine that much, until I learned how to use it properly. Really helps for identifying and removing any low spots before hitting hand sanding. 10 mins on the disk saves me an hour of hand sanding at least.

I 'use a flat disc, and use reverse often
 
Variable speed, reversible, adjustable table with miter guide and the game changer is the Nielson Disc system.

Is it necessary? Not for fixed blades.

For slipjoints knives it really speeds up the process and keeps things square and allows you to remove the smallest amount of metal at a very controlled process.
 
Case_D said:
I'm planning on putting a 1/2 hp motor on the same VFD as my belt grinder. Saves a good chunk of money. Then I just need a disc grinder plate to attach. The motor is less than $150 and the disc is like $90. I think all the wiring and switches would be about $40 total. It's the cheapest way I've figured so far, but I haven't gotten it all together yet. Good luck with yours
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1/2 hp should be more than enough, I think I have a 3/4 hp on my disk grinder. The cost difference between 1/2 and 3/4 hp wasn't enough to worry about.

The idea of running the 1/2 hp motor from your 2X72" (2 hp?) will work just fine. Do remember the 2hp VFD settings won't protect the 1/2 hp motor, but I've never seen any need to protect the motor with VFD anyway. I spent the extra $70 for a Chinese VFD and it works just fine. Disk grinding doesn't produce enough steel dust to worry about, and drop a cover over disk grinder VFD when not in use.
 
So if I’m thinking about this right… I need to source:

~1HP enclosed 3 phase 1800RPM motor that runs on 110… with a 5/8 shaft

And a VFD that takes 110 single phase wall power to a 110 3 phase output

Then of course a disk from someone like Jantz or KMG or Nielson
 
J. Keeton said:
So if I’m thinking about this right… I need to source:

~1HP enclosed 3 phase 1800RPM motor that runs on 110… with a 5/8 shaft

And a VFD that takes 110 single phase wall power to a 110 3 phase output

Then of course a disk from someone like Jantz or KMG or Nielson
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110V 3 phase motors don't really exist (yes, there are a few out there, but the vast, vast majority of 3 phase motors are 230V/460V). I'd recommend getting a VFD that outputs 230V 3 phase power like the KBAC-24D. A TEFC (totally enclosed fan cooled) motor is what you really want for longevity. While it may not see as much dust as a belt grinder, it will still accumulate some over time and a properly sealed motor will survive in those conditions indefinitely.

Edit: You'll want a frame 56 or 56C motor; they are the only NEMA motor frame sizes that have 5/8" shafts.
 
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