[Runner4404spd]

the 9x20 lathe is an extremely flexible package and by that I mean not rigid. there are ways of making it stiffer. I have in the past taken way more than your cutting on my 9x20 lathe however there are plenty of areas that need to be addressed.

1. spindle preload. make sure you preload the spindle really well. if its flopping around you will have no hope of cutting anything
2. carriage stiffness. make sure that the carriage clamps are tightened and that its not flopping around
3. cross slide stiffness. this has a pretty crappy gibb, so make sure that you tighten all the screws and they are making good contact.
4. make sure your spindle is aligned to the ways and not cutting a taper.
5. make sure your tool nose is on center of just below.


these are just a few of the areas that I have found that need to be addressed. also I didn't see what HP vfd and motor you have, but your spindle belt maybe slipping under higher load.

[jakemestre]

Update:
I bought a spindle. It's bigger than the lathe.

It's a D1-4 with a 55mm bearing surface in the front, and 50mm in the back. I've come up with a design for a new lathe that will machine a 11"dia x 10" and fit inside the existing enclosure.


I have a couple of questions though:
The first is about bearings. I've been reading the cncbookbook miniblog on belt drives and I've landed on grinding my own duplex bearing set out of plain angular contact bearings. Mostly because I can't afford a $1500 set of bearings. I don't really know how to figure out what the preload should be and then the amount to grind to achieve it. You'd think that in mechanical engineering school they'd go over things like tolerances or preload, but no.
Second question; What ABEC rating to go with. The current lathe only spins up to 4000rpm so the bearing rated speeds are well above that. How much will an ABEC 3 bearing change the quality of the lathe over ABEC 7?
And one more: Aluminum or Steel for the headstock? I was thinking of making the spindle into a cartridge but two bearing supports line bored isn't sounding all that bad. Thanks to everyone lending a helping hand.
Jake