Help designing electromagnet pick up tool(pen)

[myles240]

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

 

[UKpete]

Myles, I dare say you have already considered it, but why not use a permanent magnet "magnetic pen" such as this:

http://www.theysoundgood.co.uk/web pages/details.htm

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!

 

[myles240]

Yes, I have been using a permanent magnet for 18 years now. I just have gotten fed up with trying to get sharp metal slivers off the magnet without getting one in my hand. Sometimes we bang off the chips, but it does not work very well. Many times I am conitously cleaning out a slot that I am machining and your hands are wet from coolant for hours. On an enclosed CNC the flooding coolant will wash away the chips, but on a small CNC knee mill that amount of coolant would give the oferator a bath! But thanks for the obvious solution. I dont want a very strong magnet because it will be hard to pull away from the piece you are maching.

 

[MagMike]

Hello Myles,

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

 

[myles240]

I am cycling this operation every 10 seconds for sometimes an hour at a time...so I need somthing easier. I have made one with roughly the same magnetism as my permanent magnet from a 1/4" bolt and #30 magnet wire with about 5 layers and about 1.25 long. I was wondering how I could get a little more power from it. I tried running 4 wires parallel but it didn't seem to work for me. Here is a link to one that runs of 1.5V...I just need a small version.

http://www.sciencefirst.com/vw_prdct_mdl.asp?prdct_mdl_cd=20030

 

[MagMike]

Hello Myles,

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.

 

[myles240]

Just my first thought would be they wont last very long and the expense. I can use thicker wire...#30 is just what I tried first.

 

[myles240]

Sorry about my last post...I thought you wrote Watch not camera.

 

[EdStainless]

You wound a coil, now try it at a higher voltage. You can use the shorter bateries and stack 4 or 5.
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.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[myles240]

To get more strength can I just go longer,as I have already reached my maximum Diameter? No, I dont have an outer shell return path. To make it fit I would need to put less turns. Would this be better? Also can the return path outer shell be threaded on instead of trying to wrap the wire inside a cavity?

 

[MagMike]

Hello Myles,

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.

 

[myles240]

Thanx I'll try an outer shell.

 

[EdStainless]

What is the resistance fo your coil? I want to play a little.

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

 

[MJR2]

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
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.

 

[MJR2]

Ed, Myles,
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.

 

[myles240]

Tried a thread on shell last night...scraped the windings putting it on...oops. I used #26 wire. Since it was junk I tried without the shell. It was weaker than my one with #30 wire...then I tried it with only one battery and it was stronger???...But the wires got hot in a hurry.Not what I expected. I'll keep trying.

 

[EdStainless]

Field strength is proportional to total of amps x turns.

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

 

[MJR2]

Okay I just ran the one with a 3" coil. We get about 630 gauss right on the surface of the 0.05 sleeve on the end on centerline. It drops to about 250 at 1/4 inch. This should pick up something, not much but something. Oh the core only gets up to about 5000 gauss. No where near saturation.

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.

 

[myles240]

I was assuming that the outer shell had to be steel.What should it be? Can the end of the magnet(bolt head)be a press fit or does it have to be made out of the same piece of steel. Also I am finding that surface area is more important than strength. A pemanent magnet at the end of a scriber with little pull almost picks up as much chips as a magnet with about 4 times the pull???

 

[MJR2]

My thoughts were in keeping a SS tube around the outside of the pen magnet. This would make it easier to clean and sealed from coolant getting in. However a steel tube without an end or perhaps a SS end cap and a steel pin for a core is substantially stronger than what I described earlier. Although none of these could be described as strong magnetic devices.

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.