Magnetic Drill Vise

[Dunc]

I have a few microwave transformers looking for a job. There are many build it articles on the web (for eg, https://www.youtube.com/watch?v=jSxOtDPh9Ew&t=333s) that are based upon them. More recent microwaves seem to be using smaller transformers (switching power supplies instead of "brute force" using 60 Hz?). While the videos give the basics, in general, to achieve maximum magnetism how important is transformer iron mass (are bigger transformers better)? Should multiple transformers be identical? How should they be wired (series, parallel or...)? Should the transformer(s) be tightly packed inside the case? Does the material thickness (mild steel) of the Base & walls matter - does thicker increase magnetic force? Would a cover (mild steel plate) increase/decrease/have no effect on the magnetic strength? Builders seem to favor DC. While AC (120 volt) might be acceptable I don't want to go where I know nothing.
How many pounds pull makes an acceptable vise? How could I measure it or is "management by result" suitable?
Any other thoughts appreciated. Thanks!

[danlb]

Your post brought to mind that many magnets have more holding power in a vertical direction than they do to horizontal motion. In short, great for tension, not so great for shear. Since drilling is an action that causes the work to spin if the drill jams, would a mag chuck have trouble holding the work?

Dan

[Doozer]

Mag drills work perfectly.

-D

[Bob Engelhardt]

...In short, great for tension, not so great for shear. ...

Yes - magnets are not very good at shear. So, not very good at holding the work while drilling, but good for holding the drill. 'Cause the magnet is offset from the bit/torque by 6" or so. I.e., at the end of a lever.

[Bob Engelhardt]

There was a long discussion of MOTs as electromagnets in the "Should I use pot" thread:

https://bbs.homeshopmachinist.net/forum/general/1839236-should-i-use-pot

[Dunc]

Hmmm... going to rethink this. The drill press vise I already have certainly clamps well enough.

[Bob Engelhardt]

I can also point out that it depends upon the material thickness, a lot. A piece of 3/4" thick bar will be held much, much better than a piece of 16 ga sheet.

[nickel-city-fab]

Well, they do make magnetic chucks for lathes. Pretty expensive tho.

[danlb]

You could probably take a page from the surface grinder mag chucks. They often have a ledge up against the work that keeps it from moving in that direction. Dogs / fences are used in drill presses the same way, so a fence on the table may be all that's needed to keep the vise from moving, and a ledge on the top of the vise may keep the work from spinning.

[Paul Alciatore]

Some of my thoughts on this:

DC would be better because AC would, at least potentially, introduce the possibility of introducing vibration at the AC frequency or twice that. This could have an effect on surface finish. Of course, that may not be a concern at a drill press as the inside of a drilled hole is not going to have a very nice finish anyway.

Transformer Mass: I am not sure I can produce the equations off the top of my head, but generally speaking when a given amount of power is to be transformed, lower frequency transformers need to have more mass in their cores than high frequency ones. This is why aircraft originally did not use 50 or 60 Hz which are common on the power grids. Higher frequency allowed transformers and motors that had less mass in their cores. It is also much, if not all of the reason why switching power supplies are smaller, lighter, more efficient, and less expensive than the linear ones. The 50 or 60 HZ power line frequency requires larger, more massive transformers than the higher frequency switching supplies use. That higher frequency is often thousands or even tens of thousands of HZ.

Now, this may not be as important in an application where the gripping power or magnetic field strength of the magnet is of prime importance. In fact, those larger, low frequency magnets may be able to support a larger magnetic field than a smaller, high frequency one would. And a DC magnet would definitely work.

Resisting Shear or Rotational Forces: I would think about a thin layer of a substance with rubbery properties. This could be a painted on coating or a thin sheet attached with adhesive. This could greatly reduce an tendency to move sideways or rotate. Even a sheet of paper would help.

[Franz©]

With only limited experience building a magnetic broom for chip harvesting, I'll throw this in.
DC on the coil lifts chips and hangs onto them. AC applied to the coil demagnetizes the core and drops the chips. That ends the magnetic portion of that brainfart. I will add operation requires IQ higher than that of the average shop sweeper and ability to follow directions as well.

Be careful when applying either DC or AC to a coil of wire. There MUST be iron in contact with the coil to absorb the flux created or the coil will cook and do so fast. Flux can sufficiently heat mercury in a glass tube to use the Mercury as a timer of good accuracy. We did a lot of that before Mercury killed the planet and millions of kids showed up with heads 180° out of alignment. You could easily see it under mercury vapor lights called fluorescent lights.

Now I'll return to pondering use of an ancient Mark IV air conditioner clutch as a magnetic drill anchor.

[J Tiers]

.....

Be careful when applying either DC or AC to a coil of wire. There MUST be iron in contact with the coil to absorb the flux created or the coil will cook and do so fast.....

What you need in an AC coil to limit current, is "inductance". Many turns of fine wire on a small core, or fewer of heavier wire on a large coil.

Inductance is not much help with DC. There, it takes resistance to limit current. BUT, you do need the core to focus a magnetic field to do things like mag drill bases, or relays and solenoids.

[JRouche]

I like the idea of a mag chuck on a drill press. I did something similar and posted the electrical device I use to power it.

Mine is a 12x24" walker mag chuck I scored at an auction. No power supply included.

I didnt want to fry the coil so adherence to the 1 amp label on the chuck was used.

I use mine as a final cclamping down deal. I clamp the part in a large iron DP vice and slide it around on the mag vice till I am under the drill point then hit the power button on the device and it locks the DP vice down very tight. I also included a degaussing switch to do that. JR

[J Tiers]

Good idea.

Not having a mag chuck, I just put an x-y on the DP, and the DP vise on that. The mag chuck is faster and easier than cranking on the x-y.

[The Metal Butcher]

I like the idea of a mag chuck on a drill press. I did something similar and posted the electrical device I use to power it.

Mine is a 12x24" walker mag chuck I scored at an auction. No power supply included.

I didnt want to fry the coil so adherence to the 1 amp label on the chuck was used.

I use mine as a final cclamping down deal. I clamp the part in a large iron DP vice and slide it around on the mag vice till I am under the drill point then hit the power button on the device and it locks the DP vice down very tight. I also included a degaussing switch to do that. JR

JR, what you describe is sort of what I was thinking might be nice. Having something like a cam lock drill press vise and a mag vise upside down, bolted to the vise, then you could slide the whole unit. Lots of weight though, so it probably wouldn't be very friction free. Your method would be better for that. I haven't found the need yet on my big drill press, typically I just slide parts around and bolt them down or move the table. Maybe someday I'll try it.

But I don't think holding small parts on a magnetic chuck alone is a good idea like the original question.