View Full Version : grinding magnetic parallels

09-17-2014, 02:27 PM
I finally got my 6x12 Walker magnetic chuck ground and I have some used 1"x2"x8" magnetic parallels I would like to clean up. I have checked them and they are all fairly the same size (within .004") in height and width. I would like to clean them up an make sure they are the same thickness and height by grinding them on my Harig 6x12 grinder. I am currently using a Norton 46J grit 6"X1" wheel. Because they are steel plugs in an aluminum block I have some concerns grinding the aluminum. Is this possible and if so what concerns should I take?


09-17-2014, 03:55 PM

Magnetic parallels being .004" out of parallel is like a mile out. Leave them as is until you need to use them for a grind job. That is how they are supposed to be used.

As to keeping the wheel from getting loaded up, you can either dress your wheel a little more than usual or use bees was to keep it from getting loaded up.


09-17-2014, 04:34 PM
I'd be inclined to to grind them now so when I really need them they're ready to go. I won't have an extra step or worse yet forget they're not the same height. Yes aluminum can clog the wheel but chances are you'll want to rough them once to size, dress the wheel, let everything cool off for a couple hours and then take a light finish grind anyway.

Forrest Addy
09-17-2014, 08:15 PM
Grinder parallels off by 0.004? That's like landing your airplane beside the runway. They should be within 0.0001" of common size and parallelism.

Grind them. It's a wet grinder tight? Add a little coolant concentrate only if the wheel seems to load with aluminum. Thing about aluminum/steel parallels is the steel cleans the aluminum smears from the abrasive grains (or something like that) so loading isn't much of a problem.

If you were grinding straight aluminum you would soon see those little scuffs. Go ahead and grind them but allow me to nag: dress the wheel when it needs it.

09-17-2014, 10:01 PM
Someone probably only needed one of them for some setup and ground that one only to be parallel to the chuck. More than once.

Dunno about others, but that kind of approach always annoys me. A friend of mine described another mechanic of his acquaintance as "He's the kind of guy who will change seven spark plugs because the eighth one is hard to get at." Do things right.

09-18-2014, 02:53 AM
Put a piece of paper .004 thick on top of the low parallel. The magnetic flux will pass through the paper.


09-18-2014, 08:25 AM
They are made to be re-ground - if required - but if they are good enough they don't have to be re-ground.

I'd use a well-balanced coarse grade aluminium oxide wheel - which should be re-dressed often to save the wheel clogging up with aluminium or whatever the non-magnetic material is.


09-18-2014, 01:01 PM
I've done this and not had a problem using flood coolant and very light cuts.

Spin Doctor
09-18-2014, 05:13 PM
I grind mine every time I use them. its the eay I was trained. The whole idea is by grinding them you are estblishing as flat a surface as the grinder can produce. Plus once you grind them do not remove them from the chuck. and do not turn off the magnet. As to coolant. On a wet grinder use it. On a dry inder I spray on a film of WD-40, LPS, Oilzum or some other light spray oil. IMO about all they are good for aside from cleaning surfaces