Pulley and Pinion sizing advice

[ClarKent101]

I'm attempting to size a pinion and pulley for my Y axis and eventually the gantry X axis. Can someone who knows better cast an eye over this and see if this makes sense?

Using a MOD1 rack and pinion

3:1 Ratio with a belt reduction from pinion to T5 pulley

T5 Pulley size: 15 teeth
Pinion size: 44 teeth

Other info:
Plasma cutter: Powermax 45xp
Steppers: Nema 34
Belt width: 20mm
Linear rails: HGR25 (HWIN)
Machine operating speed: 1,270 mm/min (55 ipm)
Moving / jogging speed: 6,350 mm/min (250 ipm)

Is there anything else I should be taking into account here?

[robertspark]

suggest the use of a 20T pinion
https://www.apexdyna.nl/en/why-does-the ... e-20-teeth

my gear driven 3:1 reduction drive uses 60:20T

I used mod1 but some believe mod 1.5 or 2 to be optimum

a nema34 on mod1 rack... bit big imo,

I run
NEMA 23, 4.2A, 3.2mH, 3.1nm / 439oz in holding torque
mod1. 20T with a 3:1 gear drive reduction and get 600ipm at 0.6G comfortably.... it can go a LOT faster + higher acceleration before stall... but no point

do you have a sketch of your design?

do you have more info on the NEMA 34 motors

[ClarKent101]

Hi Rob,

I've attached a few pics of what I have so far. I've been trying to ensure that I maintain a certain amount of accuracy, using some of the parameters given on the Hypertherm site, they recommend around 0.25mm for travel (rail and traverse axis).

https://www.hypertherm.com/learn/artic ... r-xpr300/

So if my stepper motor is 1.8 deg = 200 steps per rev.
Linear distance: Pi x Pitch Diameter
3.142 x 50mm = 157.1mm linear travel per revolution
157.1mm / 200 steps/rev = 0.75mm linear travel per step.
0.75mm/0.25mm = 3

So my gear reduction should be 3:1 to get that accuracy of 0.25mm. Is this correct?

Also, big gear on pinion mating with rack, small pulley on stepper?

[robertspark]

I am confused, how did you get:
3.142 x 50mm = 157.1mm linear travel per revolution

where did 50mm come from?

https://www.linearmotiontips.com/differ ... of%20teeth.

you have a MOD1 rack and a 44T pinion.

1 MOD x PI (3.142) x 44T = 138.23mm of linear travel per pinion revolution

Stepper motors are SELDOM run at 1:1, and are normally run at a higher microstepping resolution for smoothness. I set my drives at 10 micro steps (this has a LOT of different opinion .... choose what you feel is correct!)
Below are some of my choices in why I used 10 microsteps and no more.... but I'm also running a metric setup so the numbers are easier (5:10 etc) than 4:8:16:32 etc which tends to align better with parts of an inch (1/4; 1/8th; 1/16th etc)
https://www.geckodrive.com/support/step ... ution.html

https://e2e.ti.com/blogs_/b/industrial_ ... -confusion
https://www.faulhaber.com/en/support/te ... realities/

so if your machine was mine:
~138.23mm / (200 full steps x 10 microsteps x 3 (the drive reduction ratio))
= ~0.0230 mm / step

I'd still look at a 20T pinion as that is what seems to get used by most setups + for the reason I posted earlier

These may help you for ideas:
https://www.avidcnc.com/pro-rack-and-pi ... p-227.html
https://www.finelineautomation.com/prod ... ion-drive/

I designed and made one very similar to this using standard gears and parts with laser cut plates:
https://www.ebay.com/itm/132994274061?h ... xyiRlScaKM