Sometimes I set up a long-throw dial indicator on my lathe for doing shoulders or locating other longitudinal features. I've always wished I had a mag base for this that was machined just to sit on a V-way. Aren't most V-ways the same angle? Wonder why no one makes such a thing. Anyway, I don't know anything about strong magnets or how to get them or fix them into a machined base. Whenever I go to buy magnets what I get will barely pick up a paper clip or two and I want something about fifty times stronger than that. If it came in a usable shape I could just epoxy it into an aluminum base.
Nope -- it varies between manufacturers. I've had to modify things like a mount for a turret carriage stop to fit the angle of my Clausing. It may have been built for a South Bend or something else.
Tear apart a recent bad hard disk drive with voice-coil servos. They often use a rare-earth magnet, which can be strong enough to be dangerous as you bring it close to some steel. (Or go to a hamfest, and you'll usually find someone selling them -- often from the same source.
First off -- the way the magnets in the dial indicator bases are usually set up is that there is a cylindrical hole into the side of a composite base. Most of the base is mild steel, but bisecting the cylinder -- or with a dogleg, if it is designed to grip on a side as well as the bottom -- separating the two pieces with a non-magnetic material -- probably brass. I'm not quite sure how that thick a layer of brazing is done, but certainly there is some way. Probably more difficult with silver solder from what I read.
Anyway, the magnet is shaped to fit into the cylindrical hole, with two pole pieces pointing out from the center of rotation. When it is rotated so one pole is adjacent to one of the mild steel halves, and the other is adjacent to the other half, the field routes through the two halves, and through whatever they are adjacent to (if also a magnetic material).
If you rotate the magnet so both poles are equally touching the two halves of mild steel, then the magnetic circuit stays almost entirely within the body of the base. It is short-circuited, so it can't get to the outside world.
The nasty part of this is that if you remove the magnet from the base, it loses a large chunk of its strength, unless you slide it out of the base and into a cylinder of the same size bored into mild steel to act as a "keeper". this makes it more difficult to get a strong magnet which is not already built into a base -- with the exception of the rare-earth magnets mentioned above from disk drives. With some of those, you could make a two-piece slug which encloses the rare-earth magnets, and acts as your cylindrical magnet with the poles facing to the sides. Probably a good idea to use some LocTite or something similar to secure them in the proper position, so if you drop it it does not become jammed.
Most often, such dial indicator mounts are designed to clamp onto the ways, instead of depending on magnets, since the force is in the direction in which they would most easily move (sliding along the ways).
I know next to nothing about magnets *so I'll jump right in here with an uninformed answer, RCM, style*. I think that the newer "super magnets" are alloyed with rare earth material, one of them being neuobium (sp). They are quite strong and can be dangerous if not handled carefully. Before super magnets, the field of most all DC motors were electromagnets. Now, as I understand it PM motors, (starters?) are now mostly all made PM.
Bob (can't resist a post) Swinney
PS: Before some sharpie corrects me on this - I know that telephone magnetos and some others were made of ordinary material but their permanence was not good and they had to be stored with a "keeper" bar to retard demagnitization. Such is not the case with rare earth magnets.
I would not bother with trying a magnet. The way I did this was to machine a small holder out of 1/2 by
1/2 aluminum bar stock, with the upper one having a V cut out of it to match my SB 10L's upper way, and the lower one flat, to match the underside of the bed.
It's held in place by a small screw with a captive tommy-bar, that can slide back and forth to clear the tight spots. The ends are pressed on ball bearings. The bottom is keyed to the top with a slot and a tab to keep it from rotating when the screw is tightened.
This can be located at any spot on the bed and gives 0.001 length readout, and if you are willing to stop and re-set and re-position it, it will go longer than that.
Photo, where the indicator can be dimly seen in front of the QC gearbox:
Whoops. Double post. Sorry!
Jim
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This must be a specially alloy of niobium and neodymium.
:)
I think the newer magnets use samarium and cobalt.
Jim
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What you want is called a "rare earth magnet" or NIB (neodymium iron boron) look on the web for an outfit called wondermagnets or bust open a few junk hard drives. There are always ads on ebay These magnets are strong enough in bottle cap size to pinch a good blood blister into your fingers. Lee Valley has them also.
The magnets on the last of these web pages are finger biters. One is relatively safe but they jump to each other from maybe six inches away. Someone took my pair, but I am sure they got a few blood blisters.
I made mine using a rectangular ferrite magnet about 2" x 1" x 3/8"
You can get very strong, small, inexpensive supermagnets from
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but I would not recommend that. It would be nearly impossible to remove steel swarf from them. The ferrite magnet works fine and I can blow swarf off of it with compressed air.
Maybe if you buried a little supermagnet or two in aluminum you could de-swarf it with compressed air. If you stick a supermagnet directly on a piece of thick steel you about can't pull it off -- have to slide it or pry it off.
Bob Swinney is right, supermagnets do not need keepers. Neither do ferrite magnets. Alnico magnets do.
(clip) Anyone done this? Ideas? ^^^^^^^^^^ There must be something wrong with this, or one of you would have mentioned it already. I have a magnetic dial indicator base with a stack of laminated iron plates. With the lever in the "off" position, you can put it on a piece of pipe, or any other non-flat surface, and then turn the lever to "on." This energizes the magnets, but also, at the same time, locks all the plates. It is very secure. It would not, however, keep the mast at a particular angle. When released, everything moves around.
Grizzly sells a flat magnetic base for dial gages. They also have a nice and inexpensive 2" ($20) gage to mount to it. Of course it's flat-backed so you have to lay it on the flat side of the way. I then eyeball it parallel to the bed, which is good enough for anything I do. But it sure would be nice to have one that fits on the v way. That way it would automatically be aligned. I'm thinking of perhaps milling a magnetic base with the on/off switch to fit the V-way. Not sure if this would interfer with the rotary action of the switch or not.
John
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That's a good idea, but I noticed that your way extends to the left of your headstock? Mine doesn't so it would be nice if the gage could easily be unmounted from the machine to get it out of hte way if need be. How hard is the one you have to unmount?
John
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Good eyes. Actually the clamp will not pass by the right end of the tailstock, so it does limit the travel of the carrige to the farthest right.
Because of the design, all one has to do is loosen the clamp screw a bit more than usual, and the tab that prevents the bottom from turning disengages from the top, so the bottom will rotate 90 degrees and the entire clamp and indicator assembly slips right off. No tools required.
As another SB 10L owner once mentioned here, the company actually sold a specialized item, which is basically a short section of bed prism, that bolts to the front of the bed near the gearbox, so you can mount indicators or the micrometer carriage stop, in such a way as to work very close to the headstock.
Jim
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piggybacking... A good source of strong magnets at a reasonable price is American Science & Surplus - The site navigation could use some work, so here's the direct link to the magnets -
I already *have* a clamp-on-the-ways micrometer head. I also have a 2" round permanent mag base for a dial indicator which I use with my 4" travel Federal dial indicator. That one is pretty handy, but I wanted the easy-on attribute of the magnetic DI holder combined with the precision locating of the milled-to-the-ways clamp style.
What I want to do is a milled-to-the-ways permanent magnetic DI holder. No off-on switch. Nothing fancy. I just need to know how to get magnets to glue into the base of the (probably aluminum) holder. I think I have my question answered.
BTW, I also have one of those clamp-anywhere mag bases that are made of a bunch of sliding plates. Those don't work worth beans on the ways of a 9" South Bend or a 15" Cincinnati. Trust me.
There you go, why would anyone need anyting more than a pocket T and jeans :^)? My drawer is full of them too. I've got a nice suit too but it's also only for funerals/weddings.
John
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