# Magnetic chuck for holding brass sheet stock?



## SilverWorker (Aug 29, 2013)

I have some brass sheet stock (about .030 inch thick) that I'm cutting little parts (about 1/4 X 1/4 inch) out of, about a 100-200 pieces in one go using a cnc mill with a little 1mm endmill. I'm using double sided tape to hold the parts and trying to avoid having to leave tabs on them to hold them down as I really don't want to finish all those tabs off by hand. Problem is the sticky double sided tape tends to come loose, parts shift and get messed up. 

I'm a neophyte to machining so I'm just scratching my head trying to figure a way to hold all these sheets and was reading about magnetic chucks- I know that it's not going to hold a sheet of brass down, but maybe can you put a magnetic top layer over the brass that can get machined through, that will provide enough force to hold those little parts down? Never having actually used or seen a magnetic chuck I don't know if its far off base. Wondering if there's something that would be easy to machine through, maybe sheet metal or that kind of plastic refrigerator magnet material.  Don't have any idea of the holding force that could be generated, but guessing there's not too much force needed considering the size of the cut & endmill, and the fact that double sided carpet tape is almost doing the job...


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## 4GSR (Aug 29, 2013)

The brass will stop the magnetic gauss from penetrating through it and magnetizing the steel for holding.  Now it may not stop it totally but will reduce the gauss to a lot less holding power if any at all.


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## ScrapMetal (Aug 29, 2013)

Possibly something like a vacuum chuck?  

http://www.nemi.com/vacuum_chuck_packages.htm

http://www.datrondynamics.com/Vacuum_Chuck.htm

I don't know much about there capabilities of if they'd fit your application though.

-Ron


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## Charley Davidson (Aug 29, 2013)

Try contact cementing the stock to a piece of cabinet grade plywood be sure to use a roller to get the brass sheet down tight & flat.


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## jamie76x (Aug 30, 2013)

Why not use than cnc mill and and make a die to cut the pieces out?
Or have them laser cut. Seams like a lot of wasted time with a lil end mill and trying to hold the pieces down.


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## samthedog (Aug 30, 2013)

x2 for the laser cutting.  I don't think milling is worth the frustration nor is the costr of a vacuum / magnetic chuck.


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## SilverWorker (Aug 30, 2013)

Thanks all, I'm going to try the contact cement as it's the cheapest and quickest alternative I've got available. I checked into a vacuum table with one company already but I was advised that the size of the pieces would greatly reduce the ability of the vacuum to hold them. Jamie, I would love to learn how to make a die to cut them out, can you point me to any resources that would help a beginner get started? I'll look into laser cutting services as well.
Thanks again!


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## dickr (Aug 30, 2013)

Not to sure of your shape but you might try sandwiching them between alum sheet if your end mill is long and strong enough.
dickr


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## pdentrem (Aug 30, 2013)

Been doing similar stuff for the last 14 yrs.
I use 3M 77 Spray glue to hold thin materials at .001" to .030" on a backer board of laminate. See here http://www.mscdirect.com/product/63408017 . This board is fairly flat and not affected by mineral spirits used in the removal of the glued up parts.

Running the spindle at 24K on the one machine with a 11 ipm feed and .020" 2 flute endmill. The other machine spins at 60K and 30 ipm with the same bit. The second higher spindle speed machine is much better and the tool life is twice the slower machine on average. Note the tooth load is only .00022"! Your spindle speed may not be this high but the small endmill and tooth load is the key for success for this type of operation.

The first three sides will cut just fine. It is the fourth side that you will run into trouble. At times the part will move at the last little bit to finish the cut and leave a tit/nub as the endmill plows through. In my experience a surface of .250" should not move if using a new sharp end mill.

Two ways to fix this.
1. Cut only 3 sides first on a matrix of parts and then using GOOD tape, tape down the parts. Be sure to use your fingernail to press the tape into full contact or use a rubber laminate roller. Better using the fingernail. Now using a NEW endmill just cut the fourth side. In my experience a surface of .250" should not move in this situation but it can and will happen. For example when cutting .030" thick .600" OD parts out of PT there is movement at the last of the cut. In this case I use high strenght Hot Glue and still tape for that last cut. If using Hot glue, temperature needs to be controlled. Use a cold air gun like this http://www.mscdirect.com/product/77314375?fromRR=Y but it is expensive! Yes I have one of these as well but rarely use it with my current method.

Option 2.  If you cannot do #1, use a flat surface to place the finished part with the edge that needs to be touched up facing a 600 to 1200 grit sanding disk. A faceplate with a sheet of said paper works well for this. You do not need a lot of speed to remove that nub. I setup a spare chuck mounting plate and glued 600 grit paper on the outside edge and just placed a flat plate in the tool holder at the center point of the disk and ground off the offending nub. You can either use a holder or just your fingers in this case. Use a magnifier to locate properly your edge to keep things square etc.

I have tried flowing hot glue into the first set of cuts but found the tape method works the best due to being quick and easier to clean up in the end.

Pierre


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## Snugrat (Aug 31, 2013)

Why not try a foot stomp shear cutter.?
               snugrat  :thinking:


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## pdentrem (Sep 5, 2013)

Here is a picture of part of a milled piece using the method I suggested. No it is not the smallest I have done, but it is one of the most elaborate to date.
Pierre


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## SilverWorker (Sep 6, 2013)

*Thanks Pierre!*

That looks beautiful. What material is it? Do you have any recommendations for the "Good" tape?


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## rdhem2 (Sep 6, 2013)

Mr. pdentrem;

Very fine looking gizwichie in your last photo.  How thick is the material and how did you manage such sharp inside corners if not punched?


Always curious in the great PNW.    :thinking:


_*Russ *_


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## 4GSR (Sep 6, 2013)

Boy! You weren't kidding about your part being small.)


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## SilverWorker (Sep 6, 2013)

Ken, I was thinking about what you said about the magnetic field not going through the brass, and was curious- did a little reading and a little experiment. I was able to hold a thin sheet of brass to the fridge with a kitchen magnet, which was not too powerful, so it seems maybe there is enough field getting through to be useful. My reading suggests that brass behaves like air or paper with respect to static magnetic fields, it has a low magnetic "permeability", so it shouldn't block a static magnetic field, but it is a conductor, so it will block oscillating electro/magnetic fields as they will just set up eddy currents in the brass. I'm wondering if you know if the magnetic chucks use static permanent magnets or electrically generated oscillating magnetic fields?


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## lrsglory (Sep 6, 2013)

samthedog said:


> x2 for the laser cutting. I don't think milling is worth the frustration nor is the costr of a vacuum / magnetic chuck.



x 3 for laser cutting. Larry smith here


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## churchjw (Sep 6, 2013)

I have a project where I need to cut some parts out of thin stock (<.030") Nothing as detailed as these parts. I tried to get some quotes for having it laser cut.   But they want $2 a piece and I need 80 of them.  More than I can put into the project.  I tried making a die to cut them but sheet stock that thin is hard to shear to shape.  Never could get my tolerances right.  Does anyone know of a good source to get metal parts laser cut? I think I may try gluing some to a board and milling to see if that works for me.  Thanks for that wonderful idea. 

Jeff


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## pineyfolks (Sep 6, 2013)

dickr said:


> Not to sure of your shape but you might try sandwiching them between alum sheet if your end mill is long and strong enough.
> dickr


2 Pieces of lexan might work to sandwich them also.


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## pdentrem (Sep 6, 2013)

*Re: Thanks Pierre!*



SilverWorker said:


> That looks beautiful. What material is it? Do you have any recommendations for the "Good" tape?



It is a copper silver braze material. What I use for tape, a good new roll of quality true masking tape, not the low stick stuff. The trick is it can not be old as the glue gets to be not as sticky and dried out. Once heat or humidity gets to the tape the likelihood of movement is higher. I have not tried the new Gorilla tape as of yet.
Pierre

- - - Updated - - -



rdhem2 said:


> Mr. pdentrem;
> 
> Very fine looking gizwichie in your last photo.  How thick is the material and how did you manage such sharp inside corners if not punched?



It is .002" thick and was milled using a .012" end mill at 60k rpm. Used a CNC mill of course.
Pierre


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## Tom Griffin (Sep 6, 2013)

Pierre,

You might try MEK to dissolve the 3M 77, it'll likely cut the adhesive much faster than spirits.

You are right about the RPM's for those small end mills, it amazing fast they need to spin to keep the chip load down. I had to mill a .010" square hole in a sheet of brass once with a .005" end mill and the CNC mill I had could only manage 4000 rpm. I had to do the work under a microscope and could see the mill flexing as it fed around the frame. Luck was apparently on my side because I got it on the first attempt.

Nice job on the parts.

SilverWorker: I have a lot of experience with both permanent and electromagnetic chucks and can say with certainty that you won't be able to hold a piece of brass sheet with a piece of steel sheet firmly enough to mill. They barely have enough holding power on thin steel parts for grinding. You would also need a spacer between the brass and the chuck so you don't mill the chuck which would only make matters worse. The spray adhesive is definitely your best option.

Tom


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## metalman (Sep 6, 2013)

My first thought was to cut strips the width of the part. Make a punch  and die of one row of holes and punch the four rows of holes. Then shear  the part off to length. With this type of stamping the distance between  holes and between the holes and edge can be as small as one and a half  times the thickness of the material. If the clearances are smaller than  that another possibility is chemical maching or ECM.


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## OldMachinist (Sep 7, 2013)

SilverWorker,
I used to make lots of thin plastic and brass parts using Mitee-Grip. http://www.miteebite.com/products/mitee_grip_e.html

I still have a roll, I can send you a small sample and the instructions if you'd like to try it.


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## pdentrem (Sep 7, 2013)

OldMachinist said:


> SilverWorker,
> I used to make lots of thin plastic and brass parts using Mitee-Grip. http://www.miteebite.com/products/mitee_grip_e.html
> 
> I still have a roll, I can send you a small sample and the instructions if you'd like to try it.




That looks interesting. I will have to get the boss to get some to try on Monday. Thanks for that.

I have tried a paper based product, it is double sided and washes off in water. Works but expensive in a production environment. I also tried the crystal wax stuff where you use a heatgun to flow the wax and then place your part in position. I have found that the wax style stuff is problematic if trying to maintain flatness. The spray glue is thin enough to not cause issues that way. We called 3M to see what works best to remove/dissolve Spray 77 and they said mineral spirits was best.
Pierre


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## SilverWorker (Sep 8, 2013)

*Thanks, Don*

Thanks Don, I will be happy to give it a try. I haven't set up a coolant system yet though so I guess that should come first.


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## OldMachinist (Sep 8, 2013)

Send me a PM with your mailing address and I'll send you a piece.


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## george wilson (Sep 9, 2013)

I'm not sure about brass.030" having much part in reducing flux strength. I say this because there are millions of magnetic guitar pickups out there that have brass covers that thick. Some nickel plated,chrome or gold plated. Many have no holes at all to let the magnet adjustment screws stick up through. The Gibson Johnny Smith pickup has no openings. The Fender Telecaster bridge pickup has none at all.

Do you know that everything,even water IS magnetic if you have a strong enough magnet? I saw a program where this scientist has a mega strong electric magnet with a hole through the center. He even suspends small frogs magnetically in the hole!!

It seems that gravity,magnetism and (I think)light,or it could be electricity are made of the same stuff. They haven't figured out what that stuff is,yet.



I make lots of brass or silver parts for jewelry casting models. I just SUPER GLUE the parts down. For Pete's sake, DON't use some rubbery stuff like contact cement!!! To get parts loose,a little heat will melt the super glue. Then an acetone soak will get the rest off. I clean my gluing surface with a wood working chisel. Super glue is RIGID,which is what you need.


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