9x20 lathe conversion, pointers wanted

[m_c]

1) 4 or 5 will be good enough.
2) Use whatever you can get that suits your budget. You won't be pushing for every last bit of performance, and the neglible amount of play in a belt isn't going to matter in the grand scheme of things.
3) It will cause racking, especially if you're gib isn't adjusted correctly, however you just compensate for it in either via tool offsets, or the part g-code.
4) Measuring is pointless unless you already have ballscrews on. My last lathe used a 1.47nm stepper directly coupled to a 12x4mm ballscrew on the Z-axis, and it could sink a 8mm drill into aluminium, but would only mark steel. My current lathe has a 750w servo connected at some stupid ratio (about 1.3:1 IIRC) to a 16x5mm ballscrew, and it'll knock the turret out of alignment before it'll stall the servo!
Personally, I'd say go for some of the good quality high torque NEMA 34 steppers combined with good drives and see how you get on with a 2:1 reduction. You can always change ratio later.
5)On a lathe, backlash isn't really an issue, as you're nearly always cutting from a single direction with each tool, so you can compensate pretty well. It's not like a mill, where backlash can cause havoc when trying to cut with the cutter digging in and moving in the backlash. Do some searching on ballscrews. Generally you get them already assembled and from the same supplier.
6) QCTP, Gangtooling, or a combination of both are the cheaper options.
7) Whatever. They're all a much of a muchness in terms of performance on a lathe. It all comes down to how much you want to spend.
8) That will depend on what EMC will accept. I use Mach3 and my old lathe only had a single pulse opto slot sensor connected to a smoothstepper, and it threaded perfectly well even though it only had a 750w DC motor.

[Clive S]

8) That will depend on what EMC will accept. I use Mach3 and my old lathe only had a single pulse opto slot sensor connected to a smoothstepper, and it threaded perfectly well even though it only had a 750w DC motor.

Short Vid what EMC can do on a lathe. ( Don't what to get into the old debate re Mach v EMC) I use both but EMC can be a pig to set up but on a lathe its hard to beat.

https://www.youtube.com/watch?v=TDUv0kKAfH0

I have converted mine but not done the encoder bit yet. Happy New year. Clive

[Stupoty]

Short Vid what EMC can do on a lathe. ( Don't what to get into the old debate re Mach v EMC) I use both but EMC can be a pig to set up but on a lathe its hard to beat.

https://www.youtube.com/watch?v=TDUv0kKAfH0

I have converted mine but not done the encoder bit yet. Happy New year. Clive

happy new year :)

i've done a bit of reading and it seems a 1 pulse per rev for positional info and a slot encoder with either one or two sensors (depends if you want to know what way your turning) is whats good wih emc.

i have a bit of experiance with emc for controling some cnc camera rigs etc. so i'm fairly comfertable with it.

i'm hopeing to be able to do off round shapes. Like latheing hexes etc.

I will mostly be machining steel.

Stuart

[m_c]

Don't what to get into the old debate re Mach v EMC

Why not? ;D

Quite a few of the external motion controllers can manage that (apparently Mach4 and Darwin/PP can manage it, but Mach4 turn isn't commonly available yet), but for the vast majority of users, they won't be able to tell the difference between a thread cut with a single slot sensor and one cut with a quadrature encoder. I only used my old lathe as an example as it worked perfectly well.
My current lathe has a quadrature encoder connected to a KFlop/Kanalog, so it's capable of the Z-axis tracking the spindle perfectly and even reversing back, but it's got no major benefit during normal threading.

[Stupoty]

Why not? ;D

Quite a few of the external motion controllers can manage that (apparently Mach4 and Darwin/PP can manage it, but Mach4 turn isn't commonly available yet), but for the vast majority of users, they won't be able to tell the difference between a thread cut with a single slot sensor and one cut with a quadrature encoder. I only used my old lathe as an example as it worked perfectly well.
My current lathe has a quadrature encoder connected to a KFlop/Kanalog, so it's capable of the Z-axis tracking the spindle perfectly and even reversing back, but it's got no major benefit during normal threading.

Hello,

I can see that threading at higher rpm should be fine with a single pulse per rev as the temperal error will be low and thus spacial error also low, how does this compair with tasks like machining a square section on a shaft?

Stuart

edit "i had a typo"

[m_c]

If you're needing to interpolate moves on different axis, then you'll need to use a proper quadrature encoder.

However, do you realise you won't be able to turn a sharp cornered square using this method?
I'd even question the ability to produce a reasonable quality square using this method, given the cutting angles that would be involved.

[Stupoty]

If you're needing to interpolate moves on different axis, then you'll need to use a proper quadrature encoder.

However, do you realise you won't be able to turn a sharp cornered square using this method?
I'd even question the ability to produce a reasonable quality square using this method, given the cutting angles that would be involved.

hello,

yeah i would imagine their would be some inacuracy in tool paths, i plan on going for many slots on the encoder just not sure how many i nead, i can always experiment wih this.

i'm not building it with anything perticular in mind it's just i cant have another lathe sitting around :) (i have my first lathe on a shelf in the bedroom it's a piece of art and i'm a bit attached to it)

at the moment I'm aiming highh and seing how far it can go :)

even if i end up with not as much capability as I would like it will be an interesting journey.

A mostly flat surface could be handy for easy finishing on a mill for example. Less nead to index part for hex heads for example.

thanks for the input I am taking it all in and i prommis i'm not going to try and run before i walk and all that.

Stuart