Magnetic chucks and fixturing on a grinder

I’m fairly new at surface grinding, and one of the things I really don’t have a good feel for is how to safely use a magnetic chuck for grinding. My grinder is a Harig 612 with a Walker 6x12 magnetic chuck.

Should all work be blocked to stop it from slipping on the mag chuck? I.e. the chuck has a couple of fences for that purpose, but what if you are grinding thin work or small work like shims or washers, or if the work overhangs the ends of the mag chuck?

What if the work needs to be supported or blocked off the grinding table, how to do it? I.e. there are no t-slots on the grinding table for clamps or t-nuts. I have some parallels that are for a mag chuck, but how do I determine whether enough magnetism is transmitted through the parallels to hold the work securely.

Can a magnetic chuck be drilled without damage to the magnetism? I recently bought a 5x10 chuck that I plan to mount on a 5x10 sine table that hinges on the 5 side. The chuck has a fence on the 10 side, but none on the 5 side, and I want to add a fence so that I can grind gib stock.

The magnetic transfer parallels will work just fine for holding your work up off the chuck. It doesn't matter a whole lot if they weaken the field a little, just block in behind your workpiece with those blocks mounted directly on the mag chuck. You ought to always block thin work. On those parts with larger surface area and/or thicker cross sections you can sometimes get away without blocking in. You can generally use a scrap piece of thin steel or even some washers to block in thin stuff. Be careful not to overheat (to the point of burn marks especially) your work or it may warp and then the chuck will have even less holding power.

When grinding super thin stuff like shims you might be best off with something like double-sided tape - even more important to keep the work cool though. As far as drilling the mag chuck, you ought to be able to, but watch out for crossing the poles if they are in a direction that they will be crossed by a fence and don't put a hole in that hits in between poles, put it solidly in one or the other. Steel crossing the poles may weaken the field near the fence. Some chucks I've seen have those side fences made of aluminum if they cross the poles.

Here find a video of the inside of a magnetic chuck. Few are this bad, likely yours is not.
Mag Chuck Restoration - YouTube

I think it is a very, very poor practice to drill a chuck top. The chuck top is not very thick and bolting to it will distort the top plate and so lose all the accuracy of the surface grinder.
A flat part with a 3” bottom, 2” tall, and 2” wide is a stable part on the chuck because high grinding pressure will make it slide not tip over. Stand it on end so 2” on the chuck and 3” tall it becomes an unstable part and so might be clamped to an angle plate. The angle plate's broad base makes the part stable. A part with two clamps holding is more stable than most work held in a vise.

Knowing what parts need fixturing is an important skill a grinder operator must learn.
Block-in blocks, angle plats, clamps, and the like. One might say block-in and fixturing on a mag chuck is liken to using the steady rest on a lathe. A tall part on a grinder is like a long part on a lathe. There is so much about holding on a magnetic Chuck that I could not tell it all here.

One thing is that you should block a part to high on the part at the go direction. Just setting a block-in at the front may not actually block-in very well because that block-in block or the part may not be square (a true right angle). Likely it would take quite a number of pages and photos to explain holding on a magnetic chuck.

I have read many/most grinding books and none does justice to holding parts on a mag chuck..it just takes about two lifetimes to learn it all.

QI OP: [but how do I determine whether enough magnetism is transmitted through the parallels to hold the work securely.] My old trick is-> if I can push over a set-up with two fingers it is a chancy setup and so needs more blocking or caution.

Parallels placed in front and behind do little to reduce tipping, a block-in at the Go Direction is a better hold.


Parallels placed in front and behind and the bump smack with the likes a brass knicker, or a hammer handle to make a little tighter.

QT eKrets When grinding super thin stuff like shims you might be best off with something like double-sided tape - even more important to keep the work cool though.

A hand spray coolant bottle might keep thin parts cooler, keeping the wheel fresh dressed, travel one way, more time off the part at the end of long travel...perhaps a bigger grit more open white AO wheel

Fully agree with the above suggestions. Almost every grinding job warrants giving careful thought to how it should be held on the chuck unless it's in a spin fixture. I almost always try to situate the work so I'll have the shortest grind path, less time the wheel is in contact with the work. This often means angling the workpiece to have it all on the chuck. Yes it means more cross feed cranking but it keeps heat in the workpiece lower. I've also used double sided tape with good results I'm just don't feel a lot of confidence in the adhesion where heat and coolant are involved. I prefer blocking in (Just my preference) and using a sacrificial piece of steel when possible. I'll also use a magic marker at the edge of where the workpiece/blocking/vise and the chuck is so that IF something moves I have an immediate visual reference that it's moved. Thin materials are always iffy so I reduce my depth of grind-per-pass. Sometimes that means .0005 or less to ensure it doesn't move and/or cause the workpiece to "bow" up. I'll use a coarse grit that still ensures a decent finish to keep the heat down. A spray bottle has already been mentioned. I've used clay walls to hold coolant that helps avoid over-heating. Some materials are not magnetic enough (D-2 tool steel for one) and I'd rather spend the extra time setting it up in a grinding vise to ensure it's not going to launch off the chuck. Work too big for the chuck is almost a whole topic by itself with grinding strategies and fixtures so I won't attempt that here. Just know that the longer/thinner the workpiece is the greater the chance for warp due to ground/un-ground sections and stress from the mill and/or heat treating. I'm not the last word on grinding and these are just my opinion.

With any machining operation always ask yourself, "What's the worst possible thing that could happen?" Then take whatever steps are necessary to insure it can't. The one that scares me with the SG is grinding tall narrow parts. Lots of leverage to pull it off the chuck, then it could wedge and blow the wheel. That's where proper blocking is essential. Thin stuff is always a problem because it wants to warp. I block very small parts with strips of strapping. Heck, I've even made shims out of strips of strapping. Most people over dress their wheels. Dress fast and coarse. The surface finish will still be good but there'll be less chance of burning. I'd never drill a chuck. That's just wrong, especially if you've priced fine pitch chucks recently. Any vise or sine plate can be held magnetically just fine. BTW, make sure the end guard on the table is present. I think most of us have blown at least one small part off the chuck. I like to put a rag on the guard for padding, but be careful it doesn't catch fire from sparks.

I'm 99% certain that he meant to drill the side of the mag chuck for a fence where the original manufacturer didn't. That was the intent of my post anyway. I agree with both Buck and Conrad and would never drill into the top surface of a mag chuck unless I had pulled it out of the scrap bin and didn't intend to do any precision grinding on it.

It is good to have multiple respondents to questions like these, as I can never think of all the intricacies at once. Reading all of these guys' posts, I see things that make me think "Oh yeah, should have said that, and that, and..."

Bump rail screws/bolts should be kept in new condition and go deep into the threads so as to keep from stripping them out, Tightening should be about two fingers on a short wrench.

Thanks for suggestions. Re: books on grinding, any recommendations on books or videos or websites that have good information on this subject? I would love to see some setup photos. E.g. right now I don’t have a good example of how to block high.

Re: using clamps. My angle plate also does not have t-slots or holes. It also does not transmit magnetism to the top, hence the need for another mag chuck. Perhaps I need to get creative here and make a fixture plate with threaded holes or t-slots?

The 5x10 chuck I bought is this one:
Fine Pole Permanent Magnetic Chuck 5" X 10" N45 Magnet Material Neodymium 871248493684 | eBay

As you can see, there is no fence on the 5 side. So the question is can I drill the 5 end for screws to attach a fence?

rimcanyon said:

Thanks for suggestions. Re: books on grinding, any recommendations on books or videos or websites that have good information on this subject? I would love to see some setup photos. E.g. right now I don’t have a good example of how to block high.

Re: using clamps. My angle plate also does not have t-slots or holes. It also does not transmit magnetism to the top, hence the need for another mag chuck. Perhaps I need to get creative here and make a fixture plate with threaded holes or t-slots?

The 5x10 chuck I bought is this one:
Fine Pole Permanent Magnetic Chuck 5" X 10" N45 Magnet Material Neodymium 871248493684 | eBay

As you can see, there is no fence on the 5 side. So the question is can I drill the 5 end for screws to attach a fence?

Click to expand...

Yes, absolutely. The poles don't go anywhere near that end.

QT Op [right now I don’t have a good example of how to block high.]

If you have a tippy part, say 5" tall and only 1" x 1" setting on the mag, and the part's shape does not offer a straight side to be C clamped or parallel clamped to an angle plate or clamped to a 123 block you might set a 2" high block on the go side of that part to give a little resistance to it being pushed over with the pressure made by the grinding wheel.

But if you blocked that part high, perhaps a ^bump-block-in that is 4 7/8" tall the part being ground would be more securely held in place.

The major go side is the direction the wheel motion would push the part.

A minor go side might be the side in the direction the crossfeed might be traveled if incrementing across the part.

These forces are the same as on a milling machine and where the cutting tool would induce a force to the part in a certain direction.

A ^bump block might be a rectangle of steel, an angle plat, a parallel or bar double C clamped to a solid object set on the chuck ..

Yes, a bump-block and a block-in-block are much the same.

Note: standing alone the part would be easily pushed over with two fingers, but with the bunp block in place it can not be pushed over.

If you intended to incremental cross the part you might place two bump blocks on the part to resist force in two directions,

A simple C Clamp might provide 2,000 pounds of pressure, most good setups use two C Clamps.

Here are light-duty C Camps as one would use on a surface grinder.
Light duty up to 1,800 lbs

Regular duty C ClampS
Regular duty up to 9,300 lbs, deep throat

One clamp or two depends on the setup.

toolmaker clamp/parallel clamp is also very common for surface grinder use.
Tesa Brown & Sharpe 599-754-20-2 $43.55 Toolmakers Clamp, 6.25" L x 4.625" W | Zoro.com

ekretz and Buck, thanks for taking the time to answer my questions. Buck, I have a much clearer idea of what you mean by blocking and blocking high. Makes sense.

I started this thread because I managed to launch a workpiece off the grinding table a few days ago, and knew I was doing something wrong.

The workpiece was a tapered gib that I had just brazed an extension on, and it picked up enough momentum to knock a 2" hole through the aluminum dust chute. Probably I had it wrong in several ways. For one, as the gib moved in the go direction, it raised up into the wheel. i.e. the tilting table should have had the tilt axis on the left not the right. Second, I had the newly brazed on piece hanging off the end of the table, because it needed to be ground on both sides, and the gib would not sit flat. Third, my clamp was not strong enough. I had a piece of steel spanning the gib, clamped to the tilting table on each side.

Most of not all grinder hands have had accidents. A long, slender and thin part like a gib is tough for sure.
Grinding long ways one might have to stop and change feed direction on the part, that can be a bugger.
Grinding short-way one often gets impatient and rushes the job.
We could make an enjoyable thread on gib grinding methods.

One method I have used for a tapered part like gib that was longer than my chuck was to grind long-way with angle dressed to the wheel with low flat block-ins at the far and close side. Down feeding only on the right and grind up to stopping on the part. At each pass, I placed another space at my travel stop so as not to bump the wheel stop radius from the last pass. Stop drop-ins were just cuts of band stock. Yes, running wet with a coarse wheel.

Much better would have been a screw adjustable long travel stop like a Cincinnati #2 has to stop travel feeding long travel to the left

Or, if you're a chicken-s like me, you might mill it and scrape it.

One thing about magnetic parallels. If you have a fine-pole chuck, you need fine-pole parallels. And the parallels transmit magnetism much more efficiently if their laminations are aligned with those of the chuck.

There is some seriously excellent knowledge in this thread, thank you all!

metalmagpie

Conrad Hoffman said:

Or, if you're a chicken-s like me, you might mill it and scrape it.

Click to expand...

It should be scraped anyway, even if it is ground, so probably doesn't save a huge amount of time to grind anyway as long as you can mill it and keep it fairly flat.

And yep, I have launched a few parts myself. I have done parts longer than the chuck by angling them and grinding half at a time, that works pretty well. See attached sketch.