Overall turns ratio, advice.

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avp
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Overall turns ratio, advice.

Post by avp »

Hello All,
I currently am running nema 34 open loop steppers on my router. with a 2:1 reduction on rack and pinion. So my overall turns ratio for X and Y are currently .63662
The machine runs and cuts pretty smooth, rapids are set to 1000 ipm. For what I do my main profile cuts are at 600 ipm.
For a while now I wanted to get my overall tuns ratio in the sweet spot to make it even better. After doing some calculations I came to realize that with my current steppers and leadshine drives I will not be able to get into that range. There is not enough rpm to do it with steppers. I wanted to go to a 10:1 gearbox with a little larger pinion. I was looking as either a little over 2 or a little over 3 for my overall turns ratio. I cant remember the exact numbers that I calculated. My question is, it is worthit to switch to clearpath servos to get the higher rpm. I have an 70v DC power supply at present.
Any recommendations on this would be appreciated.

Thank you
Bill
Last edited by avp on Sun Aug 27, 2023 3:49 pm, edited 2 times in total.
Ken Rychlik
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Re: Overall turns ratio, advice.

Post by Ken Rychlik »

A machine that runs and cuts smooth is hard to complain about. I have had axyz and muticam's running .08 steps and they do it all day every day. I have not used those servo's, but I'm sure someone will chime in that has. I thought about setting 1600 steps in the wizard and 3200 on the drives so I could lie to the turns ratio, but I have both on 3200 and they do very well. It seems a touch smoother than when they were on 1600.
Ken
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Re: Overall turns ratio, advice.

Post by cnckeith »

Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
ShawnM
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Re: Overall turns ratio, advice.

Post by ShawnM »

A faster motor, stepper or servo, has zero effect on the gear ratio. I'd suggest a 5:1 gearbox for your current setup. And just so you are aware, the faster you run a stepper the less torque it has. It falls off QUICK.
avp
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Re: Overall turns ratio, advice.

Post by avp »

A faster motor, stepper or servo, has zero effect on the gear ratio. I'd suggest a 5:1 gearbox for your current setup. And just so you are aware, the faster you run a stepper the less torque it has. It falls off QUICK.
Yes, I am aware of that. So in order to keep my 1000ipm rapids and 600ipm cutting speed or go even faster, and get my overall turns ratio higher say into the 2's the current steppers do not have enough rpm to use a gearbox they will simply loose torque and stall at their rpm limit.
avp
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Re: Overall turns ratio, advice.

Post by avp »

Hello,
I just want to verify that I am calculating this correctly. I am upgrading to helical rack & Pinion and clearpath servos.
So I am designing with the ability to switch out 3 different size pinions if need be. The largest one I can use is a 32 tooth pinion that has a pitch diameter of 2.0051"
So 2.0051/Pi = .63824 Then .63824 x 5 through a 5:1 gearbox would give me an overall turns ratio of 3.1912 for a starting point. Is my math correct?
Thank you
Bill
Last edited by avp on Sat Dec 09, 2023 11:01 pm, edited 1 time in total.
cncsnw
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Re: Overall turns ratio, advice.

Post by cncsnw »

No, your math is not correct. You have the pinion diameter in the numerator, when it belongs in the denominator. A larger pinion results in fewer motor revolutions per inch of travel.

If you have a 2.0051" diameter pinion, then its effective circumference is 2.0051 * pi = 6.2992 inches per revolution.
The reciprocal of that would be 0.1588 revolutions per inch. Then 5:1 gear reduction would bring that up to 0.7938 revs/inch.

You want the smallest pinion you can fit. That will increase the revolutions per inch. You probably will also want more than 5:1 reduction. Maybe 10:1, combined with the smallest pinion, would get you into a favorable zone.
avp
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Re: Overall turns ratio, advice.

Post by avp »

Thank you,
I knew something did not seem right. I will rework this design. Probably go with the 10:1 gearbox with the 1" pinion. That will get me into the zone at roughly 3.1831 The only concern I have with that is retaining my high rapid rates. At least 1000 ipm.I am using a max 2380 rpm clearpath servo. Using that overall turns ratio, how would I calculate what rpm the motor would turn at, at 1000 ipm. I know it's simple I just can't think of it at the moment.
Ah, sometimes too simple. 3.1831 x 1000 = rpm.
Bill
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