Sunday, January 18, 2009

Acetal on the lathe

I started turning up the flanged nut for the X axis on the table mill. The current nut is made of UHMWPE (aka a piece of plastic cutting board), but it was made on a drill press, and it's accuracy is low enough that it binds fairly easily.

The new nut is made of Delrin (aka Acetal). This is my first time maching acetal and overall it was very pleasant. The only negative is that is grabs very easily. I got a little carried away and the autofeed was a little fast, and thus the piece of 50mm rod made contact with the ceiling. Oops.

Taking slightly lighter cut made everything good. The plastic machines to a very nice finish, and appears to hold it's shape very well. I just faced the rod, did a skim cut to true it, narrowed one section and then cut it off with a parting tool. Very easy!

I'll definitely be using this more.

The other thing I did was something I've been been meaning to do for a while. After tapping a thread into a hole, there's frequently small shards of metal et al which are difficult to remove. Just running a bolt into the hole tends to mash the splinters into the thread making a bit of a mess.

So took a normal M6 bolt, and used the ginder to put a groove up the side of it (cutting across the threads). Screwing this into the hole nicely removes the splinters of metal (they collect in the groove). This is akin to just running the tap in, but the bolt is a looser fit, and doesn't risk further cutting of the thread. Worked better than I expected.

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