9" Disk Grinder

D

Dennis Paish

Joined
Jan 3, 2007
Messages
302
Greetings,
After watching a Nick Wheeler video I noticed he did not have any backing on his 9" disk grinders. I use 0.125 gasket cork and I see others sell a rubber disk.

So the question is why is... with or without backing.

Looking forward to your responses.

Regards,

Dennis Paish
 
Dennis, I'm no expert but I use a Neilsen Magnetic Disc system with multiple discs and I tried them with and without cork backing and I took the cork backing off. I have not tried the rubber backing but the reason given is that the gasket allows a tiny bit of "give" and helps smooth the transition from edge to flats. The main reason I use the 9 inch is to make things really flat like bolsters and the flats on my ricasso and above my hollow grinds. Now after using my flat platen on the 2x72 I put some layout blue on my blades and true them to flat on the disc. It is amazing that what you thought was flat is full of "lakes" or low spots as I call them. The disc is the only way to get blades really flat before grinding and after heat treat. Maybe its in my head but I think the gasket will not give me the true flat surface that I want and for that reason I also sold my 1 degree offset disc and only use truly flat discs. I believe that Nick Wheeler says the same thing but I will not put words in his mouth. I will buy another 1 degree offset disc but only use it to square up longer pieces of stock but not to flatten blades. Just my opinion. I even use 3m spray adhesive on fine grit thin paper because I think the feathering adhesive is too thick and makes a less even surface for the paper...I could be nuts though. Larry
 
Karl, Well, Thanks very much for bringing it up that I don't have room for a surface grinder in my 630 sq.ft. shop/ garage which I have to share with the wife's Toyota! You are 100 % right though. Larry
 
Hard to use a surface grinder on the bevels. It is much easier to get a good flat bevel with a disc. Also once you become proficient with a disc it is possible to achieve flat ricasso within .001. Setting up the surface grinder can take a lot of time to do the same thing. I have 2 discs, one with and one without backing. I use the thinnest cork gasket material I was able to source locally. It is 1/16 and I only use it for fine grits to 400. Then I go to hand finish from there. I could take it further just prefer the control I get from hand finishing.
 
Why is a disc grinder needed if a flat platen is available? I know that a 2x72 flat platen can grind the ricasso to within a few thousandths of an inch.

Maybe I haven't gotten my disc grinder technique perfected, but I still find that the belt grinder flat platen is more effective for me in flattening surfaces.

If I can't realize the benefit of my disk grinder this year, I will be selling my variable speed 1 HP, reversible, 9-inch disk with Rod Nielsen magnetic disk system.

Mike L.
 
Good timing for this topic, as I recently built myself a variable speed, reversible disc grinder. My experience with it so far has been limited but very good, and I can already see where a second disc with a thin backing would be beneficial right around 320/400 grit. I was thinking a 1/16", 70 durometer rubber backing might be the ticket. Like Mr. Richards, 400 grit is likely as high as I'll want to go in grit before moving to my hand finish. If I go with a rubber backing, is there a specific rubber I should be looking for? In doing a search, I'm seeing different types of rubber mentioned (neoprene, viton, epdm, etc.) but I don't know much about the differences. Any thoughts on this?
 
The belt can work. What is easier to use get to get steel flat, a 2" wide piece of sandpaper running loose over a flat platen Which has the tendency to build up in front of the blade, or a 9" wide flat rotating piece of steel with the paper securly attached? Yes they can both accomplish the same thing and both take practice. I did not get a belt for 18 years so I worked out many of the problems you are having. I am just having them with the belt. I found i hog on the belt and finish on the disc. I do not fully finish on a machine. I will take it to 400 and then hand finish.
 
Mike, I stared at my disc setup for two years and only used it to make flat bolsters and smoothing the spine on new blades. I could have done without it altogether and like you I used the flat platen on my KMG to flatten blades and true them up again after heat treat. Now I use the disc on every knife at one point. In my opinion it makes the blades flatter with less effort and I do not have problems keeping the two sides parallel to each other when taking the blades to a fine grit finish like I had once in a while. Once you start using it you will probably begin to rely on it. Maybe you will never need it but it might be a good idea to keep the setup in case you do want to try some different finishing techniques. I also bought a Beaumont table for the my disc sander and it helps me make real neat dovetailed bolsters. Larry
 
Larry
Can you post a picture of the Beaumont table? I have ordered my motor and drive for my disc grinder. I'm looking forward to getting true flats and bolsters on my blades. I hope its worth it.
Thank you
David
 
David, Here are two photos of the table. Guess where the excess green chrome compound from my buffer goes? Well, It was shiny and beautiful when I got it. The closeup shows the tables edge chamfer and the stop for setting the table quickly to a 45 degree angle which is really neat for dovetailed bolsters. I thought the table was a little expensive when I bought it but it is such a quality fixture that I use it every day. I have not seen a better disc sander table anywhere. You will not be sorry if you have one. Larry


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logem said:
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If I can't realize the benefit of my disk grinder this year, I will be selling my variable speed 1 HP, reversible, 9-inch disk with Rod Nielsen magnetic disk system.

Mike L.
Click to expand...

I have a reversible disc setup but without variable speed. If you do want to get rid of your disk setup list me know what you want for it. Any idea if the Beaumont table would fit the face?
http://www.beaumontmetalworks.com/shop/item.aspx?itemid=7

Thanks
 
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Well a couple of things. If you do not have speed control then you will not receive any further help. I find that about 3o%-40% output is what is needed to get a better or as good a finish as you would with the flat belt and a granite sanding table. As well I believe the rubber gasket is a mistake for sure. A 1/16 quality automotive CORK gasket works fine and does give FLAT at about 35% speed output. I have found that no gasket seems to be needed for 60 grit but sure does for 120. I have used 4 different discs running full speed with no success to make it worth while. As well the non magnetic set ups are even more expensive to use.
Frank
 
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