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DavidF wrote:sometimes its just about repetition.... once you set up a toggle clamp clap press, it may take a couple of times to hit dimension. But once you do it will be repeatable... Thats what I'm trying to say, simple, repeatable... I also feel overmolding would be simple and accurate, Maybe thats just me but so be it...

Run of the mill neodymium magnets can not handle the heat of an overmolding process. They would have to be remagnetized after the molding process which is not an inexpensive or reliable process at best. SmCo can withstand the process, but size would need to be increased for equivalent strength and cost increases considerably.

If you want to encapsulate a neodymium magnet, ultrasonic or friction weld a cap in place. Machinable epoxies may prove durable enough for the application as well depending on the configuration.

ccavanaugh wrote:

DavidF wrote:sometimes its just about repetition.... once you set up a toggle clamp clap press, it may take a couple of times to hit dimension. But once you do it will be repeatable... Thats what I'm trying to say, simple, repeatable... I also feel overmolding would be simple and accurate, Maybe thats just me but so be it...

Run of the mill neodymium magnets can not handle the heat of an overmolding process. They would have to be remagnetized after the molding process which is not an inexpensive or reliable process at best. SmCo can withstand the process, but size would need to be increased for equivalent strength and cost increases considerably.

If you want to encapsulate a neodymium magnet, ultrasonic or friction weld a cap in place. Machinable epoxies may prove durable enough for the application as well depending on the configuration.

A very vaild point.....I totally forgot about magnets loosing their strength when heated.
I think it is still worth a try as the plastic cools very quickly in the mold and the heat may not soak in enough to have detrimental effects especially with N42SH magnets.

I just got to say... David you read my mind!
Some time ago I made this jig using a push toggle clamp, with an adapter for holding the magnet.

I couldn't go further with the magnetic arms because the aluminum rods were not perfectly flat.
Carbon fiber tubes are a rare item here. I did manage to find fiberglass tubes, but the weight might be an issue.

[img]https://c2.staticflickr.com/2/1568/2412 ... a587_z.jpg[/img]
[img]https://c2.staticflickr.com/2/1598/2352 ... 1f77_z.jpg[/img]
[img]https://c2.staticflickr.com/2/1467/2385 ... abe7_z.jpg[/img]
[img]https://c2.staticflickr.com/6/5754/2352 ... 76e5_z.jpg[/img]

Fiberglass is decent as an arm material, I used to have fiberglass arms on my rostock. They weren't that straight though, and they aren't that stiff either. Metal tubes (like thin walled brass) work great, even though they are dense.

CF tubes have excellent straightness and stiffness, plus they are as dense as plastic. And no thermal expansion either!


Here is my arm jig;
Notice how the balls are stationary, and the cups are to be slid into place before being locked around the arms. There are no moving parts on this jig. This means you can rough cut the tubes to approximate length rather than having to keep the length exact across all arms. But the ball to ball center distance is always maintained. If I were to make another jig, I'd keep it the same except replace the aluminum T slot with a CF square tube. Then thermal expansion would be near zero and the jig would be as perfect as possible without a metrology machine.

Hi guys, quick question:
How good related to friction wear is a glass-epoxy molded part?

I was thinking of making the boom ends using this material. I know I can get a very smooth rod-sphere contact but the wear issue is something to consider.