Help Selecting Rack And Pinion

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EverydayDiesel
Posts: 59
Joined: Sun May 31, 2020 11:46 am

Help Selecting Rack And Pinion

Post by EverydayDiesel » Tue Jul 28, 2020 1:16 pm

Most of you are alot smarter then me when it comes to this kind of thing and I have spent days trying to figure this out and just seem to be running in circles.

I am using teknic servos and have the following choices in rpm (each has plenty of power and will not be a problem)
840 rpm
1,770 rpm
2,370 rpm
3,180 rpm
4,150 rpm

I will be using a 10:1 gearbox for better resolution

Where I get dizzy is in picking out a rack and pinion appropriate for (lets say 1200 ipm rapids)
http://www.apexdynamicsusa.com/lanotatt ... ion_1_.pdf

Can someone please look at this document and tell me which one would be appropriate for my setup?

Rodw
Posts: 462
Joined: Sun Aug 21, 2016 1:49 am

Re: Help Selecting Rack And Pinion

Post by Rodw » Thu Jul 30, 2020 5:23 am

The rack is not really critical in terms of the design. I have found helical racks run more smoothly than straight cut racks.
But the pinion diameter deserves a bit of attention. Choose a pinion that gives you around 20mm to 30mm travel per motor revolution with your gearbox reduction.

So then pick a motor rpm that has good torque at your maximum cutting speed and still has enough top end to get to your chosen rapids

EverydayDiesel
Posts: 59
Joined: Sun May 31, 2020 11:46 am

Re: Help Selecting Rack And Pinion

Post by EverydayDiesel » Fri Jul 31, 2020 7:04 pm

Thank you so much for the reply.

So if I choose the 1700rpm with a 25mm per inch gear and a 10:1 reduction I should get 177ipm rapids?

If that is the case then I am using 1,383 oz teknic servos


They also make a 2,370rpm (1,047 oz) motor if I benefit from faster rapids.
(I am building it so that it can support a heavy gantry since it will also be a cnc wood router which will have 3 spindles) I plan on swapping the z-axis attachment (one for wood and one for metal)

Rodw
Posts: 462
Joined: Sun Aug 21, 2016 1:49 am

Re: Help Selecting Rack And Pinion

Post by Rodw » Fri Jul 31, 2020 9:37 pm

Forgive me for metric units but:
25mm diameter pinion gives 79mm linear travel per pinion rev
5:1 gear box with 30 m/min rapids ( 1180 ipm) Will give you a 1948 RPM. 20 m/min (800 pm) is well within reach
Going to a 10:1 gearbox and 12m/min rapids (470ipm) = 1533 rpm which might be doable (about 10% under max)

It kinda shows that the design parameters for plasma and routers are mutually exclusive. Router needs the bigger 10:1 reduction for better torque and plasma needs more velocity and acceleration so would be better with 5:1 reduction

EverydayDiesel
Posts: 59
Joined: Sun May 31, 2020 11:46 am

Re: Help Selecting Rack And Pinion

Post by EverydayDiesel » Fri Jul 31, 2020 11:55 pm

So I might be better suited going with a 3180rpm motor
https://www.teknic.com/model-info/CPM-S ... voltage=75

I like the idea of having motors that are quicker then needed since most of the metal I cut will be thin gauge

Rodw
Posts: 462
Joined: Sun Aug 21, 2016 1:49 am

Re: Help Selecting Rack And Pinion

Post by Rodw » Sat Aug 01, 2020 3:04 am

If you were going to spend that sort of money, I'd get Clearpath to go over the engineering with you.

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