Surface Grinder

residual means left over magnetism. But that switch is prolly the demagnetizer that removes the residual magnetism.

I got that part of residual, when you turn the chuck off it gets rid of the magnetism. Still don't get it.

db

It turns off power to the magnet without causing a demag cycle to occur--this allows for a small amount to holding power to remain--it's mostly used during spark-off for instance to allowa thin plate to partially relax a bit in order to help compensate for some minute warpage on the opposite surface.

Where as in full holding mode, your magnet coils are powered with DC....and if you simply shut off the DC then a small amount of magnetism still remains, ( commonly called "residual magnetism" )......in order to get rid of this "residual", AC ( or a relatively low frequency DC square wave in which the polarity reverses at each pulse) is applied to the coil and then is slowly but gradually reduced to zero. ( commonly called "demag cycle" )

Thanks appreciate the reply.

db

The electro mag chucks I used, residual was for varying the magnetic strength buy rotating the percentage knob? - IE: to take the warp out of a thin plate w/o pulling it flat down.

hell sometimes I grind w/o magnet on - blocked by a super flat parallel that's stuck magnetically to hold your warped piece- just taking a tenth / pass max.

Big plate grinding trick so not to pull middle down: lay 1 -2 sheets of newsprint on chuck -wet paper put plate on grinder belly up - using variable - find % that hold's plate - grind'er flat!

the newspaper "cushion's" it so the outer edges of the plate smush & less smush in the middle. kind of a variable shim stock- use with water -wet paper first.

Oh, the flatest- "paralell" grinding can only be achieved by direct contact with chuck- that goes for non Ferris & graphite.

Have you ground your chuck lately?

No prob.

Also, generally speaking you will almost always want to run a demag cycle before finally taking your work out of the chuck or else it will remain slightly magnetized which causes the inconvenience of having stray chips and fine filings etc wanting to stick onto it......and if I recall correectly, the lower carbon steels will retain more residual than most other alloys esp if they're in an annealed condition.