Electromagnetic Drill Press Vise!

[Frank S]

Something seems a bit off in a couple of statements about the laminations being insulated from each other in transformers. Every EI transformer I have ever cut open had the I welded to the E unless they were EIEI meaning the E parts were interlaced with the I's filling the voids then bolted or riveted together. Never have a seen a transformer that had the individual laminations insulated from one another in any way shape form or fashion not even varnish.
It is correct however that factory made magnetic chucks used a lot for holding parts on a surface grinder have what appear to be separated laminations with magnetic and nonmagnetic materials. generally, these are made of made of FE-Si steel with stainless sandwiched between them pressed tightly together and welded around the perimeter to prevent separation then ground on all sides magnets are then made up in a pack with Seperators corresponding in the same way the chuck table top is laid out to switch the magnet off there is a lever which moves the magnet pack out of alignment Other chuck tables which may have both permanent magnets and electro magnets in them use the electro magnets to release not for the holding. Then there are pure electromagnetic chucking tables where it looks like the coil is a copper bar woven between the laminations in a continuous zig zag pattern from one end to the other.
I have 2 6inch diameter electromagnets that are made out of a solid bar trepan bored with a coil potted in the cavity they have about 600 lbs pull each using 120vac @ 6 amps

[bainbob]

Something seems a bit off in a couple of statements about the laminations being insulated from each other in transformers. Every EI transformer I have ever cut open had the I welded to the E unless they were EIEI meaning the E parts were interlaced with the I's filling the voids then bolted or riveted together. Never have a seen a transformer that had the individual laminations insulated from one another in any way shape form or fashion not even varnish.
It is correct however that factory made magnetic chucks used a lot for holding parts on a surface grinder have what appear to be separated laminations with magnetic and nonmagnetic materials. generally, these are made of made of FE-Si steel with stainless sandwiched between them pressed tightly together and welded around the perimeter to prevent separation then ground on all sides magnets are then made up in a pack with Seperators corresponding in the same way the chuck table top is laid out to switch the magnet off there is a lever which moves the magnet pack out of alignment Other chuck tables which may have both permanent magnets and electro magnets in them use the electro magnets to release not for the holding. Then there are pure electromagnetic chucking tables where it looks like the coil is a copper bar woven between the laminations in a continuous zig zag pattern from one end to the other.
I have 2 6inch diameter electromagnets that are made out of a solid bar trepan bored with a coil potted in the cavity they have about 600 lbs pull each using 120vac @ 6 amps

OK Frank, Maybe you need to take a closer look or go to a manufacturer's web site. If you've never seen shellac on laminations in a transformer you just weren't paying attention. First, I happen to be a design engineer (last 41 years). If you don't insulate the laminations (especially for a/c transformers) eddy currents WILL flow between them and ruin your transformers efficiency (hense high current draw). For a d/c electromagnet it's not as big a deal (no flux reversals). When it comes to what's inside an electromagnetic chuck, there is no copper band. It's WIRE. In fact it's pretty small gauge because they're designed to run on high voltage DC. Since they get their power from a wall outlet it starts as 120 volt a/c and after rectification it peaks at 170 volts DC. Obviously that's NOT going into a copper band. The gauge of the wire depends upon its length, which depends upon the chuck size. On some of them they use separate electromagnets, on others they use a common core and criss-cross as they transition to the next one. In all cases (talking electromagnetic, not permanent magnet chucks) the cores meet with the top plate, not the bottom. The whole thing is then potted to seal it up (precision grinding is almost always done wet - flood coolant at high volume). Unless you had a massive chuck there's no way it drew 6 amps. The 12x72 chuck on my Mattison only drew 4 amps. Check out a scrap yard crane. It only requires 5 amps to lift thousands of pounds. It's all about flux density. The wires to that crane magnet are only 16 gauge, and that's only to avoid the voltage drop in that long run. By the way, the separator plates are not stainless. They're either brass or lead (poured lead). The mild steel plates do not run to the steel chuck body. They stop well short of it on both sides. Lead and brass are both non-ferrous so they are not susceptible to magnetic fields. I have never heard of a chuck that uses both permanent and electro magnets (possible but doubtful because they're already pressed for space inside the chuck body and using an electromagnet to counteract the permanent magnet would surely weaken it over time. On a permanent magnet chuck they use a cam (on the handle) to pull the magnet pack away from the top plate (it doesn't take much separation to disengage it since flux falls off as the square of distance). Hopefully this helps explain my points. I am certainly not trying to insult you. What you did is pretty clever. I think I might have just bought some door latch electromagnets instead (easy) as they're very strong and have a nicely machined face with poles.

Bob Bain

[Jon]

Congratulations Marsh - your Electromagnetic Drill Press Vise is the Homemade Tool of the Week!

There is a lot of utility and cost savings in homemade electromagnetic workholding devices, and this is a good example of both.

Some more good builds from this week:

Pipe Louver Die by Frank S
ER40 Collet Chuck by LEOtech Austria
Lathe Tool Post by LEOtech Austria
Garden Dibber by Mazay
Anvil Pipe Saddle by Frank S
Proximity Sensor Wiring by GBWM
Bandsaw by rep
Trolley by ttmrj
Cylinder Anti Crush Plug by Frank S
Box Cutter by diy creative crafts
Pipe Drilling Base for Mag Drill by orioncons36
Tripod Handles by Guy Marsden
Pulley Shaft Key by Frank S
Pruning Shears Extension Handle by orioncons36
Circular Gasket Cutter by olderdan
XZ Limit Switch Setup by tonyfoale
Pantograph Torch Burn Table by Frank S


Marsh - we've added your tool entry to our All Homemade Tool of the Week winners post. And, you'll now notice the wrench-on-pedestal award in the awards showcase in your postbit, visible beneath your username:



And, you'll be receiving a $25 online gift card, in your choice of Amazon (US-only), PayPal, or bitcoin. Please PM me your current email address and award choice and I'll get it sent over right away.

Nice work!

[Floradawg]

Actually the secondary winding on a microwave transformer wouldn't work. The voltage on that winding is very high so you'd need a lot more than 120 volts to do anything, even if you unwrapped half of it. The reason it draws (and needs) so much current is because of the eddy currents. Those are caused because the laminations are shorted together by his welds (and the saw cuts). The laminations are insulated from each other when the transformer is manufactured (either by paper or shellac). One other thing to note is that it won't release cleanly because there is no provision to demagnetize it when you turn it off. This is normally done by applying reverse polarity pulses, done by a magnetic chuck controller.

The voltage is very high because that is the voltage designed in the microwave oven. When that coil is removed one can apply whatever voltage that is desired. If I understand you, the reason his chuck requires very high current is because he sabotaged the project by shorting the laminates and thus requiring high current to overcome the increased eddy currents. I think in a carefully designed project a microwave transformer secondary coil could be used. How much voltage and current required, I don't know but I don't think it would necessarily require a very high voltage.

[old kodger]

OK Frank, Maybe you need to take a closer look or go to a manufacturer's web site. If you've never seen shellac on laminations in a transformer you just weren't paying attention. First, I happen to be a design engineer (last 41 years). If you don't insulate the laminations (especially for a/c transformers) eddy currents WILL flow between them and ruin your transformers efficiency (hense high current draw). For a d/c electromagnet it's not as big a deal (no flux reversals). When it comes to what's inside an electromagnetic chuck, there is no copper band. It's WIRE. In fact it's pretty small gauge because they're designed to run on high voltage DC. Since they get their power from a wall outlet it starts as 120 volt a/c and after rectification it peaks at 170 volts DC. Obviously that's NOT going into a copper band. The gauge of the wire depends upon its length, which depends upon the chuck size. On some of them they use separate electromagnets, on others they use a common core and criss-cross as they transition to the next one. In all cases (talking electromagnetic, not permanent magnet chucks) the cores meet with the top plate, not the bottom. The whole thing is then potted to seal it up (precision grinding is almost always done wet - flood coolant at high volume). Unless you had a massive chuck there's no way it drew 6 amps. The 12x72 chuck on my Mattison only drew 4 amps. Check out a scrap yard crane. It only requires 5 amps to lift thousands of pounds. It's all about flux density. The wires to that crane magnet are only 16 gauge, and that's only to avoid the voltage drop in that long run. By the way, the separator plates are not stainless. They're either brass or lead (poured lead). The mild steel plates do not run to the steel chuck body. They stop well short of it on both sides. Lead and brass are both non-ferrous so they are not susceptible to magnetic fields. I have never heard of a chuck that uses both permanent and electro magnets (possible but doubtful because they're already pressed for space inside the chuck body and using an electromagnet to counteract the permanent magnet would surely weaken it over time. On a permanent magnet chuck they use a cam (on the handle) to pull the magnet pack away from the top plate (it doesn't take much separation to disengage it since flux falls off as the square of distance). Hopefully this helps explain my points. I am certainly not trying to insult you. What you did is pretty clever. I think I might have just bought some door latch electromagnets instead (easy) as they're very strong and have a nicely machined face with poles.

Bob Bain

Sorry old chap, you might be a cutie when it comes to designing stuff, but you've clearly NEVER looked at a microwave transformer. The laminates are welded together (shorted) OUT OF THE FACTORY.
Another transformer I have here, from out of a welder also has the laminates strip welded on two sides. So either the manufacturers are complete numb-skulls, or there's something you don't know about transformers.

[bainbob]

Sorry old chap, you might be a cutie when it comes to designing stuff, but you've clearly NEVER looked at a microwave transformer. The laminates are welded together (shorted) OUT OF THE FACTORY.
Another transformer I have here, from out of a welder also has the laminates strip welded on two sides. So either the manufacturers are complete numb-skulls, or there's something you don't know about transformers.

OK, I'm getting tired of the BS from people without a clue. Microwave transformers are basically cheap junk. They have to be competitive so they cut every corner they can. Many don't even use copper wire - they use copper coated aluminum wire instead (just like the modern penny). The cores are built differently than you think. The inner cores are actually shortened so they won't contact the outer edges. They weld it just to prevent 60Hz buzzing while in operation, not because it doesn't cause an increase in eddy currents. Since the inner laminations are smaller they aren't actually welded, which helps. Google it and go read about transformers before you post a other smart-alec remark and show your ignorance. And yes, the laminates ARE insulated with paper, shellac, varnish, or something else or the huge eddy currents would cause extreme losses. Welding across the perimeter is bad but not anywhere near what uninsulated laminates would be.

[old kodger]

"Smart-alec remarks"? hark at the pot calling the kettle black. I have taken many microvave transformers to pieces (impirical evidence), and I promise you the inner laminates are NOT shorter than the outer ones. As to copper coated aluminium windings, again you've clearly never taken one to pieces.
If there's one thing that pisses me off, it's university education that presumes that it is superior to actual world evidence.
I also tire of bullshite.

[bainbob]

Obviously you can type (with minimal brain cells). Go to Google and type "why there is welding on some iron transformers core". Read it and understand what a moron you actually are.

[old kodger]

Obviously you can type (with minimal brain cells). Go to Google and type "why there is welding on some iron transformers core". Read it and understand what a moron you actually are.

Typical, when all else fails demean the messenger. As a result of your kind advise I did go look at google, only one of several sites even mentioned eddy currents and then only with regard to higher frequencies, but there is one other potential issue here, THIS GUY ACTUALLY MADE SOMETHING, please point me to ANYTHING you have posted as a home-made tool (apart from yourself).
Be aware,We must agree to differ, and in that regard I shall not respond to any more posts from you.

[Floradawg]

OK, I'm getting tired of the BS from people without a clue. Microwave transformers are basically cheap junk. They have to be competitive so they cut every corner they can. Many don't even use copper wire - they use copper coated aluminum wire instead (just like the modern penny). The cores are built differently than you think. The inner cores are actually shortened so they won't contact the outer edges. They weld it just to prevent 60Hz buzzing while in operation, not because it doesn't cause an increase in eddy currents. Since the inner laminations are smaller they aren't actually welded, which helps. Google it and go read about transformers before you post a other smart-alec remark and show your ignorance. And yes, the laminates ARE insulated with paper, shellac, varnish, or something else or the huge eddy currents would cause extreme losses. Welding across the perimeter is bad but not anywhere near what uninsulated laminates would be.

Modern U S pennies are zinc alloy plated with copper. I just thought I'd take the risk. Might regret it.