Shed Party

John and Peter came over for a bit of a roadtrip, we went to Jaydees and Hare and Forbes. John and Peter showing remarkable fiscal restraint.
Hey, it's only money right?
Pete's whole family is apparently crook, and he was under the weather by the time we got back from Hare and Forbes. John and I had to work hard to catch up, but we were soon there. As a result, productivity dwindled as the afternoon progressed but good fun was had. Mostly we spent our time, noses pressed against the polycarbonate, watching the NC router make a part for Peters dads drill press that John broke.

Anodising sorted

The anodising tank has been playing up of late, At first I thought it was some dodgy metal that Keith gave me, but we had a bit of a shed party the other day and another job screwed up. I'd put some fresh acid in for it too. I spent nearly all of yesterday trying to figure the bloody thing out. Turns out that one of the electrode clips had corroded ALMOST to the point of being open circuit and was dropping enough voltage that the part was still anodising, but the current density was so low that no dye would stick to it. (Pore size is a function of current density).

It actually only took me an hour or so to figure this out, but murphy and a nasty hangover from the shed party ganged up on me and the fault was masked by a bunch of other things going wrong. Still, got there in the end. Apologies for those who've been waiting on jobs, I'm working through the backlog.

Router spindle speedup

For background, here's the CNC router I built. More here

The previous evolution of the spindle involved a timing belt drive, which worked OK, but was a bit inherently noisy and had (due to it being recycled) one pulley bore just a little off center. This resulted in some low (motor RPM) speed vibration that reverberated in the enclosure.

Since Keith did such a good job on the v-pulleys for the X2 conversion, I got him to make up a set for me. I made the decision to go for a bit more speed and changed the drive ratio from 2:1 to 3:1 while we were at it.

I haven't clocked it, but it should be doing something like 9KRPM now.

The improvement in noise was as expected. A little more high frequency noise, a lot less low frequency noise and about 50% louder when cutting metal. Happy with that.

The problem I had now though, was high frequency chatter. The finish on the part was terrible. At first I thought it might be the belt slipping, there isn't much wrap on that little pulley. I tweaked the mount to get some more serious tension but it didn't make a lot of difference. I concluded that the new speed must be exciting some resonant mode in my machine and made up the new spindle nose collar you see in the second pic. Always hated the little one I originally made; too thin and only two slots for the C spanner. The new one weighs about 4 times the old and has two more slots.

Anyhow, this made all the difference. Cuts at 50% more feed rate (600mm/min) now looked really nice. In fact I get reasonable cuts all the way up to 1000mm/min! The extra mass at that speed gyroscopically stabilises the spindle, compensating for the flimsy gantry, bonus!

PK