Thoughts On When To Dress Magnetic Chuck

[mikey553]

JL,

I understand your reluctance of taking the chuck off. If you have a decent long straight edge or parallel, you can use it to check the chuck surface, but you will not get the exact measurement.

There is nothing wrong with dressing the top of the chuck, but if your ways are worn, you are just fooling yourself. After the dressing the top of the chuck will replicate the ways. If they are curved (like on my grinder), so will be the chuck. And you may indicate it on a machine all day long and not see more than .0001", but it does not mean it is flat.

Mike

[JoeLee]

Mikey,
I really hate to take the chuck off. I did indicate the table after I restored the machine and it was pretty much dead on. It still had the fancy patter KO puts on it. I'm guessing it was ground in place after they assemble the machine as it wold be pretty hard to get it dead nuts any other way. Not sure where it is now but either way dressing the surface should take care of any small discrepancies in way wear shouldn't it??

JL...........

[mikey553]

If you really want to check the grinder and the chuck, take the chuck off and check it on the surface plate. Also indicate the table surface under the chuck. If it is still original (ground in place when the machine was new), this test will show you the condition of the ways.

[JoeLee]

Doozer,---- My experience as well !
Rich

Mine still has plenty of gripping power, that's not the issue. The lever moves with the same amount of force as it always took to throw it. Has not got tight, sticky or hard to move.
The slight rise in the center of the chuck when the magnet is on is what has me confused. Usually the chuck surface is pulled down, not pushed up.
As far as the outer ends, that could just be wear in the table or saddle ways?

JL..................

[Rich Carlstedt]

Just a point of reference, because it was mentioned here....
Every Brown and Sharpe mag chuck I have used was very weak.
Either the magnets were never that strong or the lost some jam over time.
.........................................--Doozer

Doozer,---- My experience as well !
Rich

[JoeLee]

I indicated the chuck with my Interapid DTI. Not sure if magnetism has any influence on it. Maybe someone else can answer that.

This is the instructions from KO Lee on dressing and resurfacing the chuck. I believe I followed this when I first dressed it 20 years ago. https://leblondusa.com/wp-content/up...esurfacing.pdf

JL...................

[wierdscience]

That's what I did when I dressed it in. Now I have a mister that I think I will use this time. I wouldn't ink the entire surface because as thin as that ink is too much of it will load the wheel. Maybe draw some circles around the areas where the difference is and it can be watched that way.

JL..................

What grit wheels are you running?

Rich also has a good point about the magnet influencing indicators. My Starrett Last word (mostly steel) indicators show influence, but my Teclock stainless ones don't

[JoeLee]

Just a point of reference, because it was mentioned here....
Every Brown and Sharpe mag chuck I have used was very weak.
Either the magnets were never that strong or the lost some jam over time.
I have an O.S. Walker mag chuck, an older one. The pre-ceramics branding.
Anyhow, I am always impressed how strong it is for an older mag chuck.
Back to the grinding question...
A friend of mine was having a heck of a time grinding in a Brown and Sharpe
chuck. The solder around the poles kept loading the wheel before he could
get across the chuck. He talked to a Norton rep and he sent my buddy a
7" grinding wheel, black in color. Not sure if it was AO or SC, the word is that
it worked well for the job.

--Doozer

I wanted to replace this chuck after I restored the machine, but the Walker chucks were around 2K at the time if I recall. I also thought of Suburban. Don't want anything with leaded segments. Brass would be better and stainless better yet, at least for dressing issues.
The B&S chuck has plenty of gripping power for stuff over 2" long or so, as long as you span a couple segments it'll hold. It's small parts that tend to get pushed forward sometime.
That's where a fine poll is nice, and that's what I would get.
The other small problem I have with this is residual magnetism after I turn it off. It's hard to take large stuff off of it, like my tool makers vise for example. I have a couple 3/8" sq. aluminum bars that I use to gently pry it off the surface. It's always been that way as far as I can remember.

JL:...............

[mikey553]

Joe,

If your grinder is that old, maybe it would make sense to check the ways. I have a 6 x 12 grinder, which was used in a toolroom for many years. When I checked the ways, they were worn and no longer straight. If you dress the chuck with worn ways, it will check very good with an indicator, but your parts will not be flat. You will have a mini-copy of your ways in the part. The bigger the part, the more effect it will have on accuracy.

My ways are worn to the point I have to mill them first before scraping. The highest point is in the middle, the ends drop down from that point. I believe it is a natural wear on this inexpensive machine with poor lubrication and gravity trying to change the shape of the ways. Years ago I was making a telescope concave mirror using the same technique. When you are rubbing two surfaces against each other, the top surface becomes concave and the lower - convex.
Mike

[JoeLee]

Joe
Many years ago when I used manual grinders with lead chucks, I was taught to wipe the table first with paraffin wax to prevent
the wheel from loading when resurfacing.
be careful of indicator movement/deviations caused by the magnet being on
Rich

I'll keep that in mind when I dress this, but the idea of using wax is now to me.

JL................

[Doozer]

Just a point of reference, because it was mentioned here....
Every Brown and Sharpe mag chuck I have used was very weak.
Either the magnets were never that strong or the lost some jam over time.
I have an O.S. Walker mag chuck, an older one. The pre-ceramics branding.
Anyhow, I am always impressed how strong it is for an older mag chuck.
Back to the grinding question...
A friend of mine was having a heck of a time grinding in a Brown and Sharpe
chuck. The solder around the poles kept loading the wheel before he could
get across the chuck. He talked to a Norton rep and he sent my buddy a
7" grinding wheel, black in color. Not sure if it was AO or SC, the word is that
it worked well for the job.

--Doozer

[Rich Carlstedt]

Joe
Many years ago when I used manual grinders with lead chucks, I was taught to wipe the table first with paraffin wax to prevent
the wheel from loading when resurfacing.
be careful of indicator movement/deviations caused by the magnet being on
Rich

[JoeLee]

When I install mine I first check the fit of the table to the chuck with blue then carefully ground it in with flood coolant and a long labourious spark out. There after when I just have to be sure, I grind a parallel in place. That to can trip you up....i after several poor results trying to get something flat I discovered I had a garbage made in India parallel that I could actually twist in my hand!

Anyway, assure a full contact fit to the table, spark out with flood and grind in a parallel when it really matters are the take aways.

After I restored the machine I did indicate the table before mounting the chuck. There was no rust on the table. Coolant was never used on this machine. It was dead flat all over. I had the chuck ground at a local shop on a big grinder. They ground top and bottom sides, the top had some imperfections in it that I wanted removed. When I mounted it on the machine I dusted the top. Didn't need to take much off, maybe a couple tenths overall.
It's been good ever since, until recently I noticed these discrepancies.

JL...................

[JoeLee]

If it's been that long since being surfaced I would think it's time. Trick I picked up from an old toolmaker is to soak down the surface of the magnet with WD-40 between passes. The WD keeps the lead and brass damping from loading the wheel up and also reduces heat input.
It also helps seeing where the highs and lows are while grinding. I do that by coating the surface with a fat black marker before the spark pass.

I've got a 6x12 B&S magnet very similar to that one, the magnets in it are nearly completely dead. The one I have just uses steel bar magnets.

That's what I did when I dressed it in. Now I have a mister that I think I will use this time. I wouldn't ink the entire surface because as thin as that ink is too much of it will load the wheel. Maybe draw some circles around the areas where the difference is and it can be watched that way.

JL..................

[Doozer]

How much rust is under the chuck?

-D