A couple of general design questions - ball-screw thread length, stub-shaft etc.

[Wal]

Hi Mitch,

Cheers for your post - you'll be happy to know that my mill was built just under a year ago now..!

Forgot I posted this topic TBH, but since it's been bumped back up I have a few observations of my own to add.

I fretted for a while about measurements, how precise tolerances needed to be etc. - it got to the point that it stopped the project going forward because I was over-thinking how things would piece together. Now that I've been through the process I can see that super-exact measurements aren't necessarily mandatory - sure getting things as close as you can should be your goal, but once all the bits are to hand you soon realise that the motor-shaft that fits into the coupler will have a bit of slide-room, as will the machined end of the screw - likewise, that floating bearing at the other end has plenty of room to slide around inside the support block. What I'm saying to the casual reader of this who might be worrying that things aren't going to fit if they're 0.1mm out, is design it knowing that there will be a bit of wiggle room, get your hardware machined according to how you've designed it to fit together, but rest assured that there's a bit of room for manoeuvre (which is also something you should aim to build in to your design too.)

Jazz warned me off the TBR20's a while ago, and on future builds I'd certainly go with profile rail, but you know, so far they've been alright - yep, the bearings need a bit of adjustment from time to time, but hey, twice a year ain't bad. To answer my own question - the TBRs came un-drilled - Clive S kindly drilled mine out for me on his Warco. Once again, worries about how far apart holes were spaced along the length proved meaningless - I spaced them sensibly on the rail mounts and then placed the holes on my alu plates accordingly. The clearance holes can be up to a mm bigger to give you that extra bit of wiggle room when lining stuff up later.

Cheers, and a happy New Year!

Wal.