press fit for a magnet...
press fit for a magnet...
(OP)
Howdy folks
I have a simple (but not so) problem. We are in production with a solution that is not ideal. We need to attach a small magnet (diam.100"+/- .002, cylindrical) to the end of a stainless rod (.050"+/-.000005, seriously).
the solution that the previous engineer went with was to machine a brass socket, where the rod presses in one end, and the magnet is glued into the other end. problem being the magnets are highly polished and dont adhere well, and that gluing in production is not ideal for several other reasons.
we want to press fit the magnets also, using plastic for the socket. the difficulty is that with the magnets tolerance, I am having trouble finding a plastic that will not yield at the worst case tolerances. we are not doing volumes that would justify molding these parts. of course, creep is also a concern.
so the question is: is there a machinable plastic I should look at that could handle ~.005" diametrical press fit at .100" while maintaining a hold on the magnet over time? UHMW looks good on paper, but I cant find any info on creep resistance, and knowing how "unstable" it is, I do not have warm fuzzies spec'ing it.
thanks!
I have a simple (but not so) problem. We are in production with a solution that is not ideal. We need to attach a small magnet (diam.100"+/- .002, cylindrical) to the end of a stainless rod (.050"+/-.000005, seriously).
the solution that the previous engineer went with was to machine a brass socket, where the rod presses in one end, and the magnet is glued into the other end. problem being the magnets are highly polished and dont adhere well, and that gluing in production is not ideal for several other reasons.
we want to press fit the magnets also, using plastic for the socket. the difficulty is that with the magnets tolerance, I am having trouble finding a plastic that will not yield at the worst case tolerances. we are not doing volumes that would justify molding these parts. of course, creep is also a concern.
so the question is: is there a machinable plastic I should look at that could handle ~.005" diametrical press fit at .100" while maintaining a hold on the magnet over time? UHMW looks good on paper, but I cant find any info on creep resistance, and knowing how "unstable" it is, I do not have warm fuzzies spec'ing it.
thanks!





RE: press fit for a magnet...
have you concidered an extended lenght, undersize brass socket and then deforming to expand?
RE: press fit for a magnet...
Some nylons when conditioned to 50% relative humidity have quite large elongations but they are going to relax if the temp is too high. A small amount of glass fill (~13%) will reduce the elongation but help with the high temp.
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RE: press fit for a magnet...
Why not a snap fit?
Maybe a 2-piece plastic socket that is welded together to contain the magnet?
Maybe mold the magnet right into the socket?
RE: press fit for a magnet...
I (think I) need a low modulus material to accommodate the wide range of press fit interference possibilities. plus low creep. the glass fill will accomplish the latter, but will it accommodate the former?
RE: press fit for a magnet...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: press fit for a magnet...
Kenat, good point, I am looking for it's COF now... may just test it insitu empirically. I just dont have time to let it sit for years to make sure creep performance is ok...
I just had a thought of using a soft "film" instead of the glue (teflon tape, parafilm etc) thus retaining the brass piece.
might be more labor than manufacturing wants to deal with tho...
will test after lunch!
RE: press fit for a magnet...
Tunalover
RE: press fit for a magnet...
Look at:
https://www.kjmagnetics.com/blog.asp?p=sticky-busi...
http://www.cyberbond1.com/adhesive-solutions/magne...
You need to make sure the thickness of the adhesive film is large enough to take the shear load from differential expansion.
The most likely adhesive problem is lack of cleaning, but there are some retaining compounds designed to tolerate oil contamination. You might contact MasterBond and 3M and Henckel-Locktite.
Too bad manufacturing is stick in the mud over modern technology.
RE: press fit for a magnet...
RE: press fit for a magnet...
Just throwing out a thought. I had a mechanic show be the "trick" to using super glue. I can't remember the locktite designation, but the trick is to use 70% rubbing alcohol to clean, then once the two pieces are together (with glue), use a misting sprayer and lightly wet around the joint. the wicking of the alcohol carries the water the super glue needs to set.
I used this to attached ground key stock to polished harden hydraulic stems (outside the working stroke of course) for taking terst measurements.
RE: press fit for a magnet...
Maybe talk to a loctite/henkel sales rep or the technical service department?
RE: press fit for a magnet...
RE: press fit for a magnet...
another day in paradise, or is paradise one day closer ?
RE: press fit for a magnet...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: press fit for a magnet...
Han primo incensus
RE: press fit for a magnet...
another day in paradise, or is paradise one day closer ?
RE: press fit for a magnet...
RE: press fit for a magnet...
http://www.solvayplastics.com/sites/solvayplastics...
RE: press fit for a magnet...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: press fit for a magnet...
RE: press fit for a magnet...
If it is not practical to produce a suitable interference fit between the magnet and a non-ferrous housing, the next best option is to use some type of anaerobic adhesive to secure the magnet in a non-ferrous metal housing.
RE: press fit for a magnet...
Bruce
http://accuratus.com
RE: press fit for a magnet...