Surface grinder attachment mag chuck protection?

S

StuNY

Joined
Feb 16, 2014
Messages
152
Just finished up my surface grinder attachment build following all the great posts here! Very impressed with how accurate these things are! Per usual I milled slots in an aluminum bar for the magnets to sit down in. I may have gone overboard with the magnet spacing because it takes some real effort to get a blade off once on there. I notice the sharp steel edges of my knife blanks are scratching/shaving the aluminum flats some with all the effort. I have started covering them with blue painters tape to protect them and while it works without compromising accuracy, it is usually pretty tedious to remove once I have finished grinding. Anybody have any solutions they are using? I was thinking of just putting a piece of paper on there but wasn't sure if that was dangerous?
Thanks!
Stuart
 
I have a Reeder SGA and they state that it is not necessary to have all magnet slots full of magnets. I tend to use just three or four on a nine inch knife. I have also used a thin (1/16 or 1/32) thick steel sheet over top of magnets. It is a sacrificial surface that I grind true to save me having to keep grinding the steel mag-chuck.

If you are happy with paper, then that will work a bit, but its not great protection. Problem with tape, appart from the inaccuracy of having glue, is that if it gets picked up by the blade being scraped past, it leaves a bump for the next blade, unless you swap it every time, which would be a pita

I am curious that you used aluminum for the chuck with grooves. That isn't going to work as well as steel, except for removing heat from the blade through higher conduction. Aluminum will tend to be gummier to grind true to the belt, and the chuck will need to be trued every so often unless you have a sacrificial face. The magnets in a steel chuck attract the blade to themselves, and themselves to the chuck, hence holding the blade. With aluminum chuck you have to rely on glue or shaped grooves to capture the magnets, neither seems that great. And, as you have found, the aluminum gets gouged.
 
Try a sheet of .03 G10 liner. Nice and flat, smooth surface, thin enough that the blade doesn’t move when magnetized and sitting on top of it (at least for me).

Disclaimer: test before grinding so you ensure the magnetic pull is strong enough and you don’t send your blade flying. Good luck!
 
Cliff Carter Knives said:
Try a sheet of .03 G10 liner. Nice and flat, smooth surface, thin enough that the blade doesn’t move when magnetized and sitting on top of it (at least for me).

Disclaimer: test before grinding so you ensure the magnetic pull is strong enough and you don’t send your blade flying. Good luck!
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Ah... perfect- thanks! I have it already in my shop and will give it a go. I was thinking of using brass shim stock but this is better since it won't deform and mess with accuracy.
 
I too recommend a thin sheet of G10, just wider than your mag plate.and it's nice and easy to lift your blades and other parts off.
 
I did switchable magnets for my chuck. Much easier to clean off the surface and add/reposition blades! It was more expensive up front, but I did 1/4" aluminum angle iron and then a 1/2" aluminum plate as the chuck. I can add spacers between the angle and plate if needed as it wears/gets dressed down, or replace the 1/2" thick face fairly easily and quickly, too. I put in 4, 150 mag switches, and have 2 more for the far ends of my 24" long chuck, but I tried a blade with a single 150 magswitch, a 120 grit belt and around 25% on my VFD and the blade didn't move or slip. When I eventually rebuild the chuck, I will probably go with 2 mag switches in the center and then space the other 2 out farther. I may also build a shorter chuck since most of my stuff is in the 7-15" range, but I do have some pieces coming up with 18" long blades, which was the reason for the big chuck!

Most people do aluminum for the chuck and mill it for the magnets and epoxy the magnets into the grooves. They typically recess the magnets slightly so they can true the chuck to the contact wheel. I don't think I have seen a steel homemade chuck assembly or one that the magnets aren't epoxied/locked into somehow? I did a magnetic switchable platen face with steel platen, rare earth magnets and then steel platen backers and I had to use double sided tape to secure the magnets to the original steel platen or they would slide around a lot.
 
I specifically went with a surface grinder with switchable magnets, I highly recommend it. Otherwise spacing the magnets or, like has been said above, use G10.
 
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