surface grinder magnet

Brown and Sharpe 824 with a Walker electric chuck. About 40 - 50 years old. We got it from another plant about 25 years ago and I doubt the magnet was ever removed.

A couple months ago it was grinding a taper. (.005 in 8") So I reground the magnet and it was good for .0002 in 8".
Well it is tapering again, .0008 in 4" . ( taper is on the 8" direction)

Pulled the mag off and it was ugly with rust. Hopefully the rust was causing the movement and not something harder to fix.

I ground the bed and it was off .0005 or less.

The magnet is next, but I'm concerned that the bottom plate joint may also be a problem. Is it a bad idea to remove the bottom plate? 30 some screws and they are rusted badly also.

I plan on putting the magnet on upside down with low power and clean it up, then ink it up to see if it is close to a match to the bed.

I can't make it too much worse, its going bad on its own. I imagine the rust is from the coolant getting out of balance.

Side note: does anyone remove their magnet on a regular basis to stem rust?

Dave

One can grease, oil, lay a sheet of mylar at the area under the chuck to make the fit free from rust for a greater number of years. Some say grind the set pad and some say grind the chuck bottom.. It depends...Grinding the set pad is ok/good but If you burn the grind you set stresses in the table (very bad). For .0005 it's not a good idea but OK done is done.
I hone a set pad to make it darn near dead flat. Hone my chuck bottom for the same result. I have greased the chuck bottom with out-of-a-gun, not from a dirty can. Have oiled the bottom with heavy clean oil, back in the 60s I use Mylar under,,,All with good results.
Chuck should be removed every few years preferably at chuck skim time,
ink it up is good.

Rescraping a machine you may find more set pad error and so perhaps good to tickle the pad.

Good to one hand draw down the chuck hold nuts, three finger pull is plenty but first feel the nut and thread past the set place to know the threads are smooth well past the hold position. The hold foot needs to angle down to it is not pressing on the outer edge of the chuck hold down lip. always wet grind the set pad and the chuck with a course wheel. I like a 46 k some like to use a 36 grit because the surface finish is not as important as Not Burning the Chuck. (A burn can be the ruin of a chuck, it may never be the same after a burn) The chuck is likely the biggest thing you will grind so heat can sneak up on you and mess up the job. A pause off the chuck is better than trying to do it fast with little go-off at the ends. Well off at ends and pause is Good.

For grinding it's good to use the whole chuck not just center at the front rail. So have some flats to hold work at the 2nd half out.

the set pad was actually out less than .0005. Lot of high crusty stuff even after using a wire wheel on it. This grinder uses a 14" (46 grit) wheel and in a maintenance shop we are trying to grind everything with one wheel. The wheel is about 10" currently and grinds better than at 14.

I will find out tomorrow how flat it is now compared to my granite plate, possibly scrape to match the mag bottom.

The mag is maybe 5" thick so upside down with low mag it shouldn't distort.

Thanks for the response.
Dave

46 white AO is my favorite all around wheel... j-k-l

After removing, cleaning, reinstalling and regrinding the magnetic chucks on 3 surface grinders(18"-28"), I found corrosion buildup after removing those some 6-7 years later. Eventually I cleaned it all again and very thinly coated the tables and chuck bases with Dow Corning Silicon Grease 976V. Investigating one machine after some 8 years showed no rust. The grease is very good at water repelling and staying attached to the metal.

Most people don't mount chucks correctly. Watch the torque and note that it's different at each end.
http://www.walkermagnet.com/Collateral/Documents/English-US/chuckinstall.pdf

thanks for that link. I wasn't aware of the torque requirements.
The original bolts were very tight but also rusted up and partialy eaten away. and I made new ones out of stainless.

Pulled one bolt from the chuck bottom and I do not have long enough bolts to replace them so I didn't split the bottom open. It does seem sealed.

After grinding the bottom and inking it, no high pct of contact. So I started scraping to match. Be lucky if I finish tomorrow.

Dave

I don't have coolant on my home grinder, but it's been about 5 years and should probably check it this year. Manual grinder and not fun to regrind the chuck.

Dave

A very simple chuck test is to set a small block at the chuck center but at the far right side and give it a tickle grind with looking at you down dial number. Then set the block at center chuck touching against the back rail. .001 difference and likely time to skim the chuck.

Most say to skim/grind chuck with mag on. I do it that way

Good to hang coolant a gravity bucket / use a simple hand spray bottle / buy a simple pump so pumping out of a bucket for when coolant would help.

winger said:

Brown and Sharpe 824 with a Walker electric chuck. About 40 - 50 years old. We got it from another plant about 25 years ago and I doubt the magnet was ever removed.

A couple months ago it was grinding a taper. (.005 in 8") So I reground the magnet and it was good for .0002 in 8".
Well it is tapering again, .0008 in 4" . ( taper is on the 8" direction)

Pulled the mag off and it was ugly with rust. Hopefully the rust was causing the movement and not something harder to fix.

I ground the bed and it was off .0005 or less.

The magnet is next, but I'm concerned that the bottom plate joint may also be a problem. Is it a bad idea to remove the bottom plate? 30 some screws and they are rusted badly also.

I plan on putting the magnet on upside down with low power and clean it up, then ink it up to see if it is close to a match to the bed.

I can't make it too much worse, its going bad on its own. I imagine the rust is from the coolant getting out of balance.

Side note: does anyone remove their magnet on a regular basis to stem rust?

Dave

Click to expand...

If you are referring to the bolts on the bottom plate of the magnet- DO NOT take this apart. These would only be disassembled if you are repairing the magnet.

In a perfect world it would be nice every couple years to pull the magnet, clean the bottom/chuck, re grease it and reinstall. sometimes int he production world this is not the case.

Possibly the best, and longest thread about this subject-

https://www.practicalmachinist.com/...or-under-chuck-324747/?highlight=horror+chuck

My instagram post when I pulled my magnets-

The Kinetic Co., Inc. on Instagram: “Oh, you think everything is rosy under those magnetic chucks?

#thefunbegins #thatsmell #11yearslater”

Scraped the bed to match the magnet bottom.(took most of the day, not a pro at this.)
Used the torque spec and loctited the nuts. With only 15 lbs. I also put a block in the other 2 t-slots so it can't start to move.

Finished grinding the mag top at the end of shift and no time to try it. Suprisingly it only took .002 to clean up. The key will be if it stays in another month or if it has more serious problems.

Dave

Many years ago in the toolroom I'd occasionally regrind a chuck if it needed it. I'd read somewhere a suggestion to remove some of the periphery of the wheel with notches to reduce heat buildup. So I took an older wheel over to the snag grinder, ground out some notches freehand, mounted, dressed the wheel and dressed the chuck. I shudder now thinking about it but I got away with it. Maybe I should have noticed when all the older toolmakers scattered?

Here find an Ok chuck grinding instruction..Couple of things I do differently..someday I may write a simple book The Apprentice Guide to Surface Grinding.

Note when you see the spark trail changing that often means the chuck is heat expanding, and so the chuck will not be dead flat.
Watching the trail is called counting sparks.

YouTube

I notice he does one thing that I wouldn't. Either he has absolute confidence in circumstances or it was a shortcut for the video. He's exploring where he first touches the chuck and once he knows the territory he stops and says he's going to set the vertical. The place he stops has the wheel still over the chuck. Apparently he's confident that he NEVER turns a handle the wrong direction. I've set my head to only stop and make changes when the wheel is clearly off the chuck, (or workpiece) end or side. This might go back to an actual event I no longer remember clearly but is seared into the subconscious.

Most guys who work in a shop with machines shared with many others will have seen a chuck with a little divot on it somewhere that tells someone else's story of "Oh shit".

Hi Dave,

When I received my Sanford 6 x 18 grinder, the bed was pretty rusted around the chuck, I assumed it would be a nightmare under the chuck. But when removed, I found it to be pristine. It had been greased with some kind of clear grease. I was surprised at this.

Not sure if this will work for you, but I will be greasing mine again when I replace the chuck.

Best Regards,
Bob

Agree with TGTool, that is why I say OK method and Couple of things I do differently.… not a good or best method.

I use heavy oil or grease not WD
I hand feel the chuck with a parked/dressed wheel a few places to know where my Down Dial number will hit.
I indicate the front not the back, because you grind the back rail in place. Its more difficult to true the front rail.
He doesn’t tell how tight to make the hold downs.
He uses one shot of lard. and no coolant. (soapy water hand spray is better}
Touches with a running wheel with not knowing the down number, I come to skin a slip of paper to know I am .002/3 away.
I would never/ever stop travel on a chuck
He uses a short over travel (1/16), so no time to cool part and the machine not rested between come-backs so any vibration from travel shift or other machine quirks are not settled down.
Think he says course wheel but should be more specific, perhaps suggesting 32 to 46 open wheel, perhaps J through L..
I keep a slip if masking tape with a marked line on it and slip it on the down dial number for if I have to leave the job for a time.
OH, and I warm up the machine perhaps 5-10 minuets before a chuck grind.

michiganbuck said:

Agree with TGTool, that is why I say OK method … not Good.

I use heavy oil or grease not WD
I hand feel the chuck with a parked wheel a few places to know where my Down Dial number will hit.
I indicate the front not the back, because you grind the back rail in place.
He doesn’t tell how tight to make the hold downs.
Uses one shot of lard. and no coolant. (soapy water hand spray is better}
Touches with a running wheel with not knowing the down number, I come to skin a slip of paper to know I am .002/3 away.
I would never/ever stop travel on a chuck
He uses a short over travel (1/16), so no time to cool and the machine not rested between come-backs so any vibration from travel shift or other machine quirks are not settled down.

Click to expand...

OMG I just watched the video. HE DOES use WD!!! Unbelievable. I used WD once on a set of parallels. Guess what happened? Every parallel that touched another was rusted. And Fast. NEVER use WD40 for rust prevention!!

It's ok for working ops like stoning or tapping or cutting or cleaning. But never as a protectant. Hope this helps.

Best Regards,
Bob

TGTool said:

I notice he does one thing that I wouldn't. Either he has absolute confidence in circumstances or it was a shortcut for the video. He's exploring where he first touches the chuck and once he knows the territory he stops and says he's going to set the vertical. The place he stops has the wheel still over the chuck. Apparently he's confident that he NEVER turns a handle the wrong direction. I've set my head to only stop and make changes when the wheel is clearly off the chuck, (or workpiece) end or side. This might go back to an actual event I know longer remember clearly but is seared into the subconscious.

Most guys who work in a shop with machines shared with many others will have seen a chuck with a BIG divot on it somewhere that tells someone else's story of "Oh shit".

Click to expand...

During my apprenticeship I did this to a brand new grinder! Man was my boss pissed.

Many a guy with bringing home his first surface grinder will make grinding the chuck his first job.. big mistake.

Much like the guy who wants to tear down a his first lathe to make it zero/zero...another big mistake.

I haven't gone back to look at the vid so this is just what I think I saw. He took off the back rail, and I thought it was just a plain bar, thus necessitating the careful alignment of the chuck. In my recollection all the grinders I used had a back rail that was L-shaped and overhung the chuck with a small gap. That allowed you to also dress longitudinal alignment which might need it more often than chuck dressing. I guess we never had rails on the end. If the part or setup was iffy you just blocked it in with something. If (knock on wood) you sailed something right off the chuck, that's what that big upright sheet metal part on the end of the table was for.