Help designing electromagnet pick up tool(pen)
Help designing electromagnet pick up tool(pen)
(OP)
I am a total newbie to electromagnets. I am a Machinist and need a way of cleaning metal chips out of T-slots on machines. I could not find a tool to buy (I did find one listed from Spap-on but it has been droped for some time). So I am trying to build one. I would like to use 2 AA bateries (pen light design) and keep the overall width of the electromagnet under .5" so that it can fit in the T-slots. Length is not an issue and I am not sure what is more important,pull or area for the chips to attract to. Any help to where I could buy the tool,just the electromagnet, or tips on the design would be greatly appreciated. Just keep in mind I am a Machinist...so keep the words simple! Here is a link to all I could find for off the shelf electromagnet in .5". But it is 12V...will it work for me @ 3V?
http://www.newmantools.com/magnets/emr.htm
Myles
http://www.newmantools.com/magnets/emr.htm
Myles





RE: Help designing electromagnet pick up tool(pen)
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and wipe off the swarf?
They are certainly available, I bought one recently.
The problem with an electromagnet is that it will retain some magnetism when you switch it off so the swarf will tend to stick to it anyway. But don't let me put you off though if you are determined to see it through!
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
Just wanted to pass along one suggestion a machinist gave me once: Wrap the permanent magnet with a plastic bag, inside out. Use it to pick up the particles and when done, unwrap the bag so as to capture all the particles.
As long as the particles aren't too large, they'll easily come off the magnet and you'll never get your hands dirty. For sharp particles, I've resorted to thicker bags.
Regarding the electromagnet idea, you might just want to wrap a large nail with many turns. Power it up to pull the particles then turn it off while over a garbage can. Most of the particles will fall off, you can then unwrap the windings and just throw the nail away.
Regarding your question about batteries, I tend to doubt a pair of AA batteries would be sufficient, a higher voltage is generally required to push enough current through the many windings.
Good luck!
Mike
RE: Help designing electromagnet pick up tool(pen)
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RE: Help designing electromagnet pick up tool(pen)
How about a camera battery (or two)? Some of them are similar in diameter to a AA battery and many of them have higher voltages. The higher the voltage, the more amps you'll be able to pump through the wires (especially one as thin as #30).
Admittedly, they do cost more but they ought to provide enough power.
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
The total of turns x amps will be your magnet strength. Exchanging one for the other has no impact.
There are ways to optimize this, but trial and error will get you close.
Are you builing this with the outer shell as the magnetic return path?
I'll try to figure out how to describe the geometry that I am thinking of.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
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RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
Increasing the length would help, but it wouldn't be nearly as effective as getting more coil turns & amps into the electromagnet. That's why I'm suggeting higher voltage batteries, to increase the amps.
Given that you need a very small diameter, I think it'll be difficult to have an outer shell return path. Having a return path would help alot, but not if you lose many windings. You might have to experiment. As EdStainless mentioned, trial and error will get you close.
The return path outer shell can be threaded (if you can accommodate one).
The windings will be much more effective inside the cavity.
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
Picture a short spool, solid center post with one end larger diameter than the other. You wrap your coil around the center. You may need finer wire.
This fits into a can. The large end of the spool should be snug. The gap between the can and the small end of the spool is your air gap.
Let's say the can is 0.500" od x 0.050" wall.
The spool will have a center diameter of 0.150" (same area as the can). One end will be 0.400" and the other will be 0.300". The air gap will 0.050". The gap needs to be filled and sealed.
The can can be as long as you want, the excess height doesn't hurt. That will be your battery housing.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Help designing electromagnet pick up tool(pen)
1.75 watts
3 VDC
0.58 amps
5.143 ohms
613 turns total
358 ampturns
This assumes a pretty well done winding. Nice and even, not random wound. Don't think a couple of AA's will be lasting too long this way.
RE: Help designing electromagnet pick up tool(pen)
I ran a couple of coil designs. Using some of Ed's assumptions, 0.15"ID, 0.40"OD and 3 watts per square inch of surface. Ed - I think a double wall tubing might be available and stay within your dimensions. That would allow this to be cleaned easier. Like the plastic bag suggestion earlier. 0.050 is a lot thicker than necessary. Of course if Myles' is hitting it to clean it then he will be building magnets pretty regular 0.05 or not.
At 3 watts/ square inch this IS NOT continous duty. I'd say leaving it in the coolant between uses would be a good idea. And VPI potting to keep out moisture.
I used #30 copper wire again.
2" length 3" length
watts 9.9 14.7
VDC 12 18
ADC 0.83 0.82
Turns 1994 3012
lbs wire 0.042 0.064
Total NI 1645 2459
OD 0.39 0.39
Maybe I'll get back and calculate some fields after lunch.
Ed - Why the taper on the coil? I didn't in my design calc's.
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
Working from batteries requires delicate balance between current and battery life.
Sounds like you have a bad battery.
I didn't mean to infer tapering of the coil.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Help designing electromagnet pick up tool(pen)
Myles,
If you used #26 wire and the same other dimensions you had much lower resistance. Magnetic field is generated by your ampturns (NI) #26 wire would have given you many fewer turns and lower field strength. Higher current as well. Both results as you observed.
Maybe one of your batteries is shot.
I assumed the shell to be non-magnetic. Perhaps that's not what you all have been thinking.
RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
Pull is an easy measurement one can make with a magnet however that is not all that is going on. Notice how a magnet with more 'pull' still only picks up chips on it's edges.
RE: Help designing electromagnet pick up tool(pen)
The original design of #30 copper wire, on a 1/4 inch bolt, 5 layers, and 1.25 inch coil height should operate as follows.
1.75 watts
3 VDC
0.58 amps
5.143 ohms
613 turns total
358 ampturns
I added a .001" thick burr .01" away from the pole face so I had something to calculate the attraction on. I used 1010 cold rolled steel material properties for the bolt and burr. Without any outer shell, it produced .06 N attraction. With an outer shell .030" thick and a .125" thick end cap, also 1010 CRS, the attraction on the burr increased to .2 N. Too bad there is no way to attach files on this site or I could give you a nice flux distribution plot.
RE: Help designing electromagnet pick up tool(pen)
Here is a workaround that might be worth considering for uploading that flux distribution plot:
FAQ559-1177
RE: Help designing electromagnet pick up tool(pen)
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You have to click on the little words "click here to download" in the center of the page surrounded by a bunch of advertising. I have a .5" Dia head X .5"long press fit to a 1/4" Bolt(with the head machined off). A plastic nut whitch leaves me with a 1.5" long coil of #30 copper magnet wire. How would you suggest I attach a outer shell and end cap? I never tried but if the site allows me to upload exe files I could upload a model that you can rotate around and look at.
RE: Help designing electromagnet pick up tool(pen)
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RE: Help designing electromagnet pick up tool(pen)
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RE: Help designing electromagnet pick up tool(pen)
RE: Help designing electromagnet pick up tool(pen)
http
RE: Help designing electromagnet pick up tool(pen)
For better battery life you may want to go to finer wire and more turns. Just a single gage number will make a significant difference because the resistance/length goes up and the length of wire goes up. The total number of amp-turns will decrease only slightly, mainly because there is less total copper and more insulation in the winding window with the finer wire. You don't really need any heat shrink (assuming you are using enamelled magnet wire) but it will help keep things in place. Or you could varnish the wound coil.
RE: Help designing electromagnet pick up tool(pen)
I would wind with very fine wire and keep the coil as close to the center pin as possible. Coat the windings with resin (urethane or epoxy) and shove it all together. Make sure that the air gap at the working face is sealed.
You could put a thin piece of Al or brass on this face to protect it, but keep it very thin.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm