Centroid Community CNC Support Forum

For some reason the plasma manual has me confused.

First is says: The Plasma Machine Gearing ‘sweet spot’ for mechanical design is so that the machine operates with 1.5 to 2.5
turns of the axis motor yielding 1” of travel for the X- and Y-axes. 750-1250 motor rpm.

Next is says: Arrange the
mechanical parts to be in the 1.5 to 2.5 inch range of travel per one revolution of the Axis Motor. 333 to 200 motor RPM

Looking at the graph shown after this paragraph and I seen posted here by Kieth it aligns with the first sentence.

I am in the 1.5" per motor shaft turn of the second sentence. Been running like this for 10 years with steppers and Mach3. Upgrading to Acorn Plasma and closed loop. Now is time to make any changes. Z axes is 8:1. Not sure why it's so hard to figure out, or is there a mistake in manual?

As long as you are in the 1.5 to 2.5 range you'll be fine. Motor RPM doesn't really come into play unless you have a high reduction ratio. Especially on the Z axis as it needs to be "snappy" if you have THC enabled. If your X and Y have a high gear reduction and you plan to cut thin material only you'll want high RPM motors to get the necessary IPM of travel to cut thin material. What ratio do you have on the X & Y axis? Typical gear reduction sacrifices speed for torque.

What is your current turns ratio for the Z axis? You say you have 8:1 on the Z, that is an odd ratio and with a high reduction like this you'll want a fast motor here for sure.

Focus more on the turns ratio and be sure you are in the sweet spot, especially for plasma.

But I think his question was, 1.5 to 2.5 what?

If you search the plasma manual, you will find three places where it recommends "1.5 to 2.5 turns of the motor per inch of travel", and the one place where it says "1.5 to 2.5 inch range of travel per one revolution of the Axis Motor". The latter is an error.

cncsnw wrote: If you search the plasma manual, you will find three places where it recommends "1.5 to 2.5 turns of the motor per inch of travel", and the one place where it says "1.5 to 2.5 inch range of travel per one revolution of the Axis Motor". The latter is an error.

Yes this was my question or cause of confusion.

My Z is directly connected to the lead screw. I think it is 8 threads/inch, one turn moves 1/8". Looks like i need to change or gear up. The X is chain drive with one turn of motor moving the axis 1.5". The Y axis is a rack and pinion, again 1 turn moves axis 1.5". IMO after 15+ years it moves fast enough to do any cutting I have done. Usually on thin material I used the slow fine cut parameters. I may have to make changes, so while I am at it I would like to try to bring things closer to the "sweet spot"

Well then I guess the manual needs to be cleaned up and I now see his confusion. I assumed the OP knew that all this referred to the "overall turns ratio" set in the wizard where it does say "turns/in or rev/deg" under "overall turns ratio", that's my bad and yes, confusing. That one line in the manual is odd as it contradicts ALL the other wording in the manual that reference "turns per inch".

Thanks for pointing this out Guys, Pg.3 and 9 of the Plasma Manual has been updated.

You can find the Updated manual here
https://www.centroidcnc.com/centroid_di ... manual.pdf