[MFchief]

All;

I know this isn't really a Tormach question, but I don't post on that many forums, and this is about as close as I could get.

I need to place some small magnets ( 3/8") into bores in polycarbonate, and I'm looking for advice as to the best way to do it.

My initial thought is a light press fit, but I have very limited experience with polycarbonate, and I'm concerned that this may cause micro cracks to develop over time and lead to failure.

Is this a valid concern? My next thought was to epoxy the magnets in place.

Any advice would be much appreciated.

Terry

[nitewatchman]

I use lots of small magnets in 3D Printed Assemblies.

I find that a snug fit, as in finger tight with water thin ACC adhesive works very well. I would share your concerns with a press fit.

I also print polycarbonate, makes very durable assemblies.


Gary

All;

I know this isn't really a Tormach question, but I don't post on that many forums, and this is about as close as I could get.

I need to place some small magnets ( 3/8") into bores in polycarbonate, and I'm looking for advice as to the best way to do it.

My initial thought is a light press fit, but I have very limited experience with polycarbonate, and I'm concerned that this may cause micro cracks to develop over time and lead to failure.

Is this a valid concern? My next thought was to epoxy the magnets in place.

Any advice would be much appreciated.

Terry

[MFchief]

Thanks Gary, I like your approach, think that I will try that first.

I am milling one part that will be held in place magnetically to another one that I had planned to print in PLA. I've never used a polycarbonate filament before. Any advantages over PLA? I assume that the poly filament will work with standard printers, temps, diameter, etc.

Terry

[Sir John]

Have you considered epoxy?

[MFchief]

I have, that was my second thought after the press fit.

I just finished milling the first piece and the fit of the magnet in the hole is very close, I suspect I will have better luck on this one with the CA, because I don't believe I can get enough epoxy between the magnet and the poly to create a decent bond.

Terry

[Sir John]

I have, that was my second thought after the press fit.

I just finished milling the first piece and the fit of the magnet in the hole is very close, I suspect I will have better luck on this one with the CA, because I don't believe I can get enough epoxy between the magnet and the poly to create a decent bond.

Terry

CA does not bond well to smooth surfaces. see this article.

https://www.starbond.com/tutorials/w...dhere-well-to/

[toyshop]

Fractures usually start around drilled holes. I use a propane torch to melt the edges of acrylic or plexiglass to head off later fractures. Lexan has a very fine point between melting the edge and burning. I don't know if any type of glue will prevent this.

Rough drilling and boring may give a better surface finish that will not fracture.

Dave

[MFchief]

I have read various accounts that most common adhesives don't play well with polycarbonate, CA's and epoxies included. The stress relief of the torching sounds like it could help.

I have room to put a plug behind the magnet, and plan to leave a small thin lip in front of the magnet to keep it from pulling out to the other magnet it faces. I hope that will do the job, it's not a super critical situation, so I think that will work.

Terry

[jwatte]

I haven't glu3e to PC, but I have glued to that really-slick stuff: acetal!

The adhesive that works there is "show goo," which is made to waterproof hiking shoes. But ... it also bonds pretty well.

Sounds like you have something that works, but if you need to experiment more, I'd recommend that!

[SCzEngrgGroup]

CA will work just fine, just make sure you don't over-do it, as it will make a mess of ANY surface it touches. Gorilla brand "Super Glue" is, by FAR, the best I've found for gluing to Acrylic and PolyCarbonate, and is thick enough to fill any small gaps. Many others will not stick at all. Applied to a machined surface, you will never be able to get the magnets out, without destroying the Poly.

Regards,
Ray L.

[nitewatchman]

PC prints well but requires much higher temperatures. Usually 260 to 300 C for me but it is good stuff, about the same or a little better strength than nylon BUT more difficult to print.

PC prints well on a PEI bed with the bed temps between 100 - 120 C.

PC absorbs water and must be throughly dried. It also wants t
o shrink and curl up on the bed. Requires planning and good design but it is good stuff for strength.

Thanks Gary, I like your approach, think that I will try that first.

I am milling one part that will be held in place magnetically to another one that I had planned to print in PLA. I've never used a polycarbonate filament before. Any advantages over PLA? I assume that the poly filament will work with standard printers, temps, diameter, etc.

Terry

[MFchief]

Thanks for the tips Gary, I'm going to get some and play around with it.

I have some Gorilla brand CA, that's what I plan to use, I'll let everyone know how it comes out. It will take a few days, Cura says it's going to take 20 hours to do the print I need, and I'm still fiddling with the CAD for the part.

Terry

[maker of things]

I affixed rare earth magnets into bores in Delrin with 3m VHB tape with good success. The magnets are 1/2" dia about 1/8" thick. I cut squares of the tape and applied to magnet, then removed the backing and trimmed overhanging corners while trying to not touch the back of the tape. Both magnet and plastic were cleaned with alcohol in advance. The bores need not be tight for this application. Previous attempt with CA glue met with magnets releasing from plastic.

tape https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[MFchief]

Thanks, if I can't get the glue to work, I could probably try the tape by sticking it to the plugs.

Terry

[hersh]

If the design allows, you could also, spot the bottom of the hole with a drill, just deep enough to leave a dimple for epoxy to sit in.

[MFchief]

On one half of the joints, I do have room for that, thanks.

Terry

[mbarnett]

You can press the magnets into a pocket and it will stay. I do this all the time. Just make a pocket about 0.005" smaller than the magnet. For instance I use 1/2" x .125 magnets and make a pocket of 0.495 x 0.130 deep and then press in the magnets. They do not fall out or cause cracks. I use 1/4" Poly. Just be sure to get your polarity correct because there is no taking it back without damaging the material.

Mike

[MFchief]

Hi everyone.

Just wanted to close out this thread that I started a while back.

As usual life got in the way of finishing this project and I just wrapped it up today. I 3D printed the dust boot which took 16 hrs, and naturally the first one messed up and I had to re-do it.

But, I did finish it up today, and to the point of the original post, I ended up sizing the magnet pockets in the polycarbonate arms, and the associated pockets in the printed PLA body for a light press fit. It seems to be working fine, but time will tell if cracks start to develop. Good news is, with our hobby/business, I still have the files, so if need be, I can make new parts pretty quickly.

As you can see in the attached pic, the boot is held to the arms just by the magnets, in order to facilitate quick bit changes on the router.

Thank;s to everyone for your suggestions and ideas.

Terry

[nitewatchman]

Cool!

Very nice looking job, what material was used to print the boot?

Gary

Hi everyone.

Just wanted to close out this thread that I started a while back.

As usual life got in the way of finishing this project and I just wrapped it up today. I 3D printed the dust boot which took 16 hrs, and naturally the first one messed up and I had to re-do it.

But, I did finish it up today, and to the point of the original post, I ended up sizing the magnet pockets in the polycarbonate arms, and the associated pockets in the printed PLA body for a light press fit. It seems to be working fine, but time will tell if cracks start to develop. Good news is, with our hobby/business, I still have the files, so if need be, I can make new parts pretty quickly.

As you can see in the attached pic, the boot is held to the arms just by the magnets, in order to facilitate quick bit changes on the router.

Thank;s to everyone for your suggestions and ideas.

Terry

[popspipes]

Attached ThumbnailsVery professional looking job, congrats!!