What parts to build a disk grinder

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pso

Joined
Oct 29, 1998
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I am considering building a disk grinder. What recommendations can those who have disk grinders make regarding:

- motor ratings (HP and rpm)
- usefulness of variable speed
- how to change grits easily
- source for disks
- work rests

Knifemaking is a hobby for me, and will remain so, so it is hard for me to justify a large budget (otherwise, I would place an order with Ron Frink immediately). I am still only working on my second knife using files and sandpaper. I live in a townhouse and have no shop or garage space. The grinder would probably get mounted on a dolly and get pushed out into the communal carport when in use. I have several ex-prototype 3-phase drives from my last job so the variable speed is basically a matter of extra wiring. I will see if I am able to scrounge a small enough motor from work since they make motors (mostly big) on the other side of the plant. If not, I would find a used one, probably 3-phase.

Am I better off finding a disk sander at a garage sale?

Thanks in advance.

Phil
 
I use a couple of 1 HP on mine. But I have seen others using 1/3-1/2, on up. You want to make sure that the motor has a minimum 1/2" shaft.

Variable speed is great, if you want to spend the $$.

You can get "economy" discs from Grizzly, or Sears parts. Just tell them you need the 9" disc for a 6X48" belt sander.
They should be in the range of 10-20 bucks.

Edited to add: I would recommend 1750 RPM if you're going with AC single speed.:D
 
I use one of Rob Frinks disc,it has a slight taper on the disc i use it to taper tags,I do not get an kick back if I go past the center of the disc.
I have a 1hp Lesson 1725 with a drum switch to change directions.
works slick;)
 
From what I can tell, there's no easy way to change grits. Rob Frink (I think, middle-age memory) told me to use a heat gun to loosen the adhesive. I'm accumulating parts for one too. I bought Rob's tapered disk, it's a fine thing. :D

Dave
 
Dave,

There's something about that tapered disk I don't understand. I'm sure it works, but it seems to me that it will only make one point of contact on the blade. You know? It would never be flat.

In my mind it would be like a spinning cone. Ummm, picture it this way: if I have the tip in the center and the tang on the outside edge, then it would only be making contact along one line from tip to tang. If I make this line near the spine then the edge would be off the disk, no?

Maybe the slant is so slight it doesn't matter, but if it is enough to keep the blade from touching the opposite side of the disk (to prevent catching) then wouldn't it be sloped enough not to make a flat surface?

Don't get me wrong Frink is the man and I've never seen one of these. It just puzzles me.

Steve
 
Originally posted by ddavelarsen
From what I can tell, there's no easy way to change grits. Rob Frink (I think, middle-age memory) told me to use a heat gun to loosen the adhesive. I'm accumulating parts for one too. I bought Rob's tapered disk, it's a fine thing. :D

Dave
Click to expand...

Dave, I use 3M feathering disc adhesive. It is available in spray or tube. You can get it from K&G, or any body shop,auto paint supply store.
If you get the tube(it lasts longer), apply it to a hand spun disc in a concentric fashion. Use an old 80 grit or heavier abrasive disc to smear the stuff out flat. Let it set up for 10 minutes aprox., or until it is tacky to the touch, but will not transfer to your finger. You apply your 9X11" abrasive sheet now, and trim it.
You should be able to get a few changes out of this before you have to strip and reapply adhesive.
The spray works the same, just somewhat easier.
To remove the stuff and clean your disc, you can use laquer thinner(which I found works best), acetone, or adhesive remover, also available from K&G.
http://www.knifeandgun.com/catalog/adhesive_186655_products.htm

Edited to add: You simply peel off the old disc, and stick on another with this method. It's very easy, no scrapping etc.
 
Steve,

Yes! you are correct. In theory, the beveled disk is a cone and consequently will produce a hollow grind rather than a true flat. When you work the math out to determine how much hollow grind it goes something like this:

Say the blade is 2" tall from spine to edge. In theory the hollow generated at about 4" radius on the disks works out to be a depression of about .00008". That is to say if you lay a straight edge across the blade, from edge to spine, to measure the hollow grind, you should be able to slip a .00008" feeler under it. This measurement was generated from a solid CAD model that was sectioned at the 4" radius. I cannot measure this small in reality. Truly not scientific but an exercise that I did just to get an idea of what was happening.

Also, it should be noted the the hollow radius changes from the edge of the disk to the center of the disk. Or from the base of the cone to the tip of the cone. The hollow radius goes to zero at the center...in theory.

Aside from the technical-smechnical stuff.....the beveled disks outsell the flat disks about 3:1.

For some guys, the hollow grind idea is unacceptable and resort to the flat disk. The trend is: beveled disks for flattening big blades (Bowies, Camp knives)...flat disks for small full tang fixed blades and folder parts.

Another comment about disks....John Leitch wrote and article in Knives Illustrated winter time last year about his disk system. A great system! He has interchangeable plates that fasten to the main disks. this way when he changes grits, he simply changes the plate. His wall is full of different plates made from different materials...with different grits ready to use. No waste from using a sheet one time and tossing it. When done, just hang it on the wall untill needed again. I'm not sure what issue the article came out in....but it was over a year ago and I believe it was cold and snowy hear in Ohio when I read it.

Take care,
Rob
 
to measure the hollow grind, you should be able to slip a .00008" feeler under it.
Click to expand...


hahhahahaha, I dream of getting a flat grind that flat.

So a 1" wide blade would be .00004 at it's deepest point. That's pretty close to 1 micron. Which, I think, is the depth of 2000 grit.

OK it not an issue. Maybe I need one of these.

Thanks Rob,

Steve
 
>>How to change grits easily

I use spray adhesive to fix 9X11" abrasive sheet and I trim it after.
You can use Permanent or repositionable spray adhesive.

To remove them, I use a heat gun to loosen the adhesive and peel of.
The heat gun trick are verry usefull when you use "adhesive sanding disc"
because the adhesive are verry strong and hard to remove. (Sometime, for
coarse grit I use Home-Depot 9" adhesive sanding disc) To decrease the
adhesive force I put some talc on it before, it is easier to remove thereafter .


Alain M-D
 
Ok all, what I want to know is what is the preferred way to mount the disc? Do you mount it horizontal with the motor below it or vertical with the motor behind it? I would think the safe way would be horizontal so if it threw a blade it would fly away from you instead of at your feet and legs. But if it did kick back towards you it would be going to vital area, instead of your feet and legs. I am talking a flat disc because I have one on an old 6x48 I don't mind stealing. :D
 
Personally, I would mount the disc(s) vertically, for the very reason you mention. I would rather take a hit in the foot/leg, than a knife in the intestines, or worse.
Even the leg/foot danger is minimized if you just watch where you put your feet while using the disc. I just don't put my feet directly under it.
I know there must be a reason for mounting a disc horizontally, but I don't know what it is.:confused:
 
I have 2 disc grinders mounted horizontal. They both have forward and reverse. Mounted horizontal I can use both hands on the blade and grind it, just like on a platen. For the mark side you would want the disc turning clockwise, going into the blade edge first. For the backside you would want the disc going counter clockwise into the edge. For safety sake and control of the speed, I have added a foot switch or deadman switch. I use the disc grinders in my shop, more than any other power tool. Hope this adds a little light on the subject. Another reson I like the disc grinder horizontal, I have to grind sitting down.

Ken Beatty
 
Ideally you'd be able to switch it from vertical to horizontal. Vertical to do stuff like dovetail bolsters and scales; horizontal to flatten tangs and blades.

I'm pretty sure no one here has built one that would flip up and down, or they'd have posted a pic already. ;)

Since I'm at the point now of actually mounting all the hardware on something, I'd sure like to have some input on how one might go about building it such that you could do this. Even if one of you guys has an idea how to go about it and the Photoshop skill to draw it...

Yeah I know I'm fishing here but I've been procrastinating building this thing because I want it both ways of course! :D So who has an idea? I think Bruce Bump was asking about this the other day too.
 
Dave, some guy did that and posted photo's at CKD. You'd have to search for it, but I distinctly remember it.

I still don't see the need for it though. I've been using single speed one way vertical disc grinders for many years, and have never felt the need for horizontal.

I am however in the process of replacing one of mine with a DC variable speed motor. That, I think will be a big improvement. :eek: :D
 
Thanks Mike, I'll go looking. Do you do your flattening vertical too then? I guess I don't see any reason it can't be done, so maybe it's not so big an issue.

Yeah I'm lucky to have a VS DC motor too, thanks in large part to Roger Linger for fixing my eBay-special controller. It was a good deal all right - with no guarantee. :rolleyes: One of the greatest parts of this forum for me has been meeting people who can - and will - help. So thanks Mike, I'll go find the article you mentioned. I owe Roger big time but haven't been able to find a way to help him back. :)

Dave
 
sorry to drag out an old thread but i'm tired of searching, can someong point me in the direction of a good 6" disc, aluminum or steel, i've found many 9" and 12" but i'd like my horizontal ones to be 6".

Thanks
 
If you can find them on their site, you could call Grizzly, customer service, and order a replacement 6" disk for their combination belt/disk sander.

I just tried to find one on their site, but have never had ANY luck using search features. They say they can't find belt sanders, or grinders in their catalog. :rolleyes: :confused:
 
3M feathering adhesive sold by most of the knife supply houses is the way to go. One application and you can change your sandpaper (back and forth) around 4 or 5 times. Then clean it off with the 3M adhesive cleaner. Very easy. Much easier than using permanant adhesive and removing with the heat gun. The tackiness is something a bit stronger than a 'post it note' to give you an idea.

I use one of Rob's beveled disks and I can not measure the hollow. I've tried. You can use the slight bevel to help get a tough scratch out here and there. I asked Tom Mayo about vertical vs horizontal, he said that was easy, go with vertical.
Here's mine. A 3/4 VFD 3phase motor with the drive (converter) just above the motor. It runs on 220v single phase input and converts it to 3 phase to run the motor. Adjustable speed with full torque 1140rpm to just 4rpm, forward and reverse. The work table is home made telescoping square pipe with tightening nuts/screws. This work table is 45 degress for doing dovetail bolsters, just out of sight is the flat work table. I always wanted to design it so that it be both horizontal and vertical. After using it with just a vertical mount, I never felt the need for horizontal.
Hope that helps.
diskgrinder.jpg
 
I have a bunch of disk grinders for different things. I made most of the platters but found recently that Woodcraft has them for 15.00. I have a couple now and like them. One day when I get off my butt, I'm going to order one of Rob's beveled disks.

John Leitch wrote and article in Knives Illustrated winter time last year about his disk system.
Rob, I tried this and have a problem with it. On very slow finish grinders it works OK but on my faster grinders, it launches a spinning steel Frisbee at me.

Anyway...I try to stay with 1 hp and larger motors just because I like big motors and scrounge them, I have enough grinders so I can switch grinders and grit without changing disks. I am going to try the 3m feathering adhesive. I have had a running battle with adhesives on the faster grinders,
 
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