The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

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awemawson:
No, that was just the clip. (And no violence was involved!)

charadam:
Serious question Andrew - is this something you should print, to ensure the material quality you need?

awemawson:
The wall thickness of the switch body is the problem I think as its under 1 mm with threads in it as stress risers. I don't think I could print in the detail required.

I did however yesterday print a tubular spanner in ABS to make fitting the next one easier. Just a castellated tube. I'll pop in a picture when I'm on a proper PC not this iPad.

Later edit: photos added

awemawson:
The replacement key switch body arrived in the post this morning and was fitted without drama :thumbup:

awemawson:
I'm still chasing the occasional 'wrong indexing' of the turret when changing tools, so have been chasing my tail looking at the turret servo system in some details.

There are three Siemens Simodrive servo systems in this lathe, all the same except that the drive cards have different current capabilities. X is a 20 amp, Z is a 30 amp, and the turret is a massive 40 amp. It came as a surprise that the turret was the biggest.

Having yet again pulled the covers off the turret to take a picture of the servo motor specification plate,needless to say in the most inaccessible place! I've been able to compare the settings on the card to the Siemens manual, and they correspond exactly. Then I thought that I was on to something. The same servo motor that indexes the turret also drives the powered tooling, and I thought that I had noticed some discrepancies in actual speed (measured by a reflective rpm gauge) and the commanded speed.

So this mornings job was to tabulate the errors and try and work out what was going on.

I had a reflective sticky tab stuck on an ER32 collet nut. 100 rpm gave 350, 200 rpm gave about 400, 1000 rpm gave approx 1600 - what the heck?

Then, in a flash of inspiration I wrapped brown insulation round the collet nut, and stuck the reflective tab onto that. Guess what:
100 =100, 200 =200 etc etc up to 2000 rpm - absolutely spot on all the way through the range. But this itself is rather peculiar, as I've been fiddling with the Tacho scaling pot so I'd not expect it to have been so accurate :scratch:

The main issue seems to be getting the twelve tools on the turret properly balanced - apparently unbalance is more of a problem than total weight (45kg) of the tools I'm told.

I was going to try and make up a spreadsheet of the various tool weights and try shifting them about to get a balance, then I realised, as the geometry of the tools differ, the point at which the weight acts also differ.

Then I was going to make an analog of the tool disk in aluminium plate with a central bearing, and manually shift tools about until it balanced, rather like balancing a grinding disk.

Then I thought . . . this is getting silly . . . .go and have a cup of tea . . . . :coffee:

. . . so that's where I am now :clap:

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