motor vs spindle rpm, pulley ratio questions

11 Jan 2024 13:02 #290422 by warwickben
 i tried searching this but was not sure if i was using the right terms.    i had started to convert a hobby lathe in the past and it worked with manual control of the spindle. had put two encoders on it so i would be able to thread etc, blew it up when i tried to control that spindle tho lol.

any ways im starting to make a lathe more from scratch.  using a atlas head stock i got from ebay. wanted a bigger thru bore and i have chucks i can use on.

i was just gonna use a vfd and a 1-2 hp motor since i have setup a few cnc routers with a vfd  and did not blow any thing up.
if my pulleys on the spindle and motor are the same size , that is easy enough to setup.
is there a reason not to run it 1 to 1? 
if i use different different size pulleys what area in the docs, link to post etc  how do i handle telling the vfd to spin the motor at the right speed to get the spindle rpm i want    i was gonna use rs485 and a huanyang vfd since i have one already. 

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11 Jan 2024 14:04 #290428 by andypugh
Start with the size of work you intend to make, the material and the tooling. That will (after a fair bit of calculation) tell you want RPM range you need to cover.
Also, in your case, there is probably a limitation on the maximum speed imposed by the spindle bearings of the Atlas headstock.

It's more annoying to not have enough torque to turn large parts than to not have the speed for small parts. as you can still make the small parts, just not as efficiently.

Does the Atlas lathe headstock include a back-gear? If so, keep it...

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11 Jan 2024 14:59 - 11 Jan 2024 15:14 #290429 by warwickben
Thanks for the response . 
I figured I’d play around with the back gear and pulley sizes etc . Cause I figured 1-1 would be to easy lol . 

I’m just confused how I go about having LinuxCNC  handle the ratios and vfd. 

I’m smart enough to know what I don’t know.    I don’t know what terms to use to search for the info.    Like on my tormach 770,  has a button for low or hi for the spindle pulley .
I don’t know how to go about having that feature in Linuxcnc gui/ how to set the  pulley/gear ratios etc and it tells my vfd what speed to run the motor at so my spindle rpm is right . 

Or am I over thinking this , since I’ll have the two encoders for threading rpm/postion. Will linuxcnc just read that and tell the vfd what todo ?  
Last edit: 11 Jan 2024 15:14 by warwickben.

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