Friday, 4 July 2014

Magnetic Joint Improvements

posted 2 May 2014 12:46 by David Taylor

For those of you that have been following along, you would have known that my original tool end contained 6mm gutter bolts, with Neodymium magnets on each end, covered with heat shrink. This worked well for a while but then the heat shrink seemed  to get a bit loose, causing some of the balls to move around a bit. This caused wildly inconsistent prints. I tried to give the balls a seat by adding hot glue and while that improved things, the heat shrink would sometimes actually come off the tips of the gutter bolts. Cable ties over the heat shrink improved things a little more, until the ball just popped out of the hot glued seats.
So it was time to find a real solution. I drilled a 2.5mm hole in each chrome ball, threaded it to 3mm, and locked each one in place with a lock nut.

How to drill into a chrome ball bearing

You have to grill your balls. ;-) I tossed mine into the braai (Barbeque for you non-South African's). A normal charcoal braai. Drop them in, make sure they don't fall out of the hottest bit of the fire and continue cooking your food as usual. Leave them in the hot ash until the next night (The idea is to let them cool down slowly). Some people suggest heating them until they are white hot and then putting them into hot sand to cool over 24 to 48 hours. Looks like a normal braai works just as well.
They do however come out quite hard still. I broke 3 taps threading 6 balls.
They also loose there nice chrome shine, but the end result should be a solid, consistent connection, which weighs a bit less due to the lower volume components.
106 grams (3.7 ounces)71 grams (2.5 ounces)
The fact that I have magnets on the bottom and top of the balls also wasn't a good idea. The magnets seemed to interact with each other at certain angles reducing the holding power randomly. Getting rid of the bottom magnets in this case should also improve things.
Next steps: Testing, and then do the same with the trucks at the other end of the diagonal rods.

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