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  #1  
Old Tue 16 January 2007, 09:09
fabrica
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Understanding & Selecting gear pinions - setting the steps per mm[inch]

Gerald, What do they mean by the diametrical pitch and how does it relate to the distance travelled per revolution. My pinion has a diametrical pitch of 20 as per Boston gear specs.


********************************************

For those trying to follow this thread, please do not mix:

- inches, diametral pitch, DP, steps per inch

and

- millimeters, module, steps per mm

they are not compatible with each other

Gerald
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  #2  
Old Tue 16 January 2007, 09:19
Gerald_D
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It means that 20 teeth make a precise diameter of 1 inch. I suppose your pinions do have 20 teeth and so you are on the "standard" number of teeth for the 1 inch diameter. The distance travelled will be Pi times diameter, equals 3.1416 X 1, equals 3.1416 inches (X 25.4 = 79.79645mm)

What is your gearbox ratio?
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  #3  
Old Tue 16 January 2007, 09:38
Gerald_D
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If you had a 20 tooth DP20 pinion direct to motor with no gearbox, Mach3 will want a "Steps per mm" setting of 2000/79.79645 = 25.06377.

If you have a 3.6 : 1 ratio gearbox with that pinion then Steps per mm becomes 90.22957

Etc.
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  #4  
Old Tue 16 January 2007, 21:43
fabrica
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Thanks for your explanation. My pinion does have 20teeth as you guessed and the gearing ratio is also 3.6 : 1 and the motor rotates .5 Deg per step.
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  #5  
Old Tue 16 January 2007, 22:19
Gerald_D
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Okay, if you are setting up Mach to work in millimeter, the magic number you need for calibration is 90.22957 steps per mm.

Just to explain a little further....
Most stepper motors have 200 full steps for one revolution (1.8o per step). Your motor has a 3.6 reduction gearbox on it therefore the output shaft is 0.5o per step. In other words, the motor must receive 720 full steps before the shaft will make one turn.

The Gecko driver employs 1/10th micro-stepping....meaning that the Gecko must receive 7200 full steps from the computer before it will produce 720 full steps to the motor, before the shaft (pinion) will make one turn and move the machine 79.79645mm. Divide 7200 by 79.7964 and you get your calibration value.
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  #6  
Old Wed 17 January 2007, 05:02
Hugo Carradini
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Hello Fabrica.
¿What is the difference in performance between using motor direct to the pinion and working with a motor with gearbox?
Thanks for your answer
Hugo Carradini
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  #7  
Old Wed 17 January 2007, 20:53
fabrica
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I think by using a gearbox you get a better torque and also a better finish on the cuts that you make.
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  #8  
Old Thu 18 January 2007, 09:38
Hugo Carradini
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Hello fabrica. I understand that but you also reduce speed . ¿Do you have and estimate off the IPM you can archived with your actual configuration and the IPM going direct to the motors? I am getting ready to start buying my stuf and want to have everything clear in my head . Thanks for your time.
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  #9  
Old Thu 18 January 2007, 09:42
Gerald_D
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Hugo, maybe you want to look at this thread: Selecting motors for the MechMate
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  #10  
Old Thu 18 January 2007, 10:43
fabrica
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Hugo, With modern software like Mach3 you could increase the RPM of the motors by taking advantage of their in built higher pulsing speeds. These RPM increases of the motor through higher puilsing sppeeds adequetly compnsate for the lost speeds due to gearing. You have a win win situ here. Higher torques at the same cutting or jogging speeds which you had earlier. With higher torques you have better cutting or engraving quality. No lost steps on steppers.

If you need furher info on this issue you could follow the links provided by Gerald.
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  #11  
Old Thu 18 January 2007, 18:03
Hugo Carradini
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Thanks fabrica and Gerald.
I am just getting use to the order of the deferents links.
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  #12  
Old Mon 26 February 2007, 19:21
reza forushani
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As you know, I got movement. Now I am studying the Mach3 and Vcarve. Can somebody help me with numbers to plug in for English system (inch)
Thanks
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  #13  
Old Mon 26 February 2007, 22:00
Gerald_D
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Reza, I've forgotten the gear ratio of the motors you ordered? are you using 20 teeth pinions?
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  #14  
Old Mon 26 February 2007, 22:23
reza forushani
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3.6 and yes.
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  #15  
Old Mon 26 February 2007, 23:08
Gerald_D
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20 teeth make a precise diameter of 1 inch. One turn of the pinion makes 3.1416 inches of linear movement.

With the 3.6:1 gearbox, 3.6 turns of the motor make 3.1416 inches of linear movement.

The Geckos need 2000 pulses to make one turn of the motor, so you need 7200 pulses to make one turn of the pinion, to make 3.1416 inches of linear movement. That gives a value of 2291.8 pulses per inch to be set in Mach.
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  #16  
Old Mon 26 February 2007, 23:19
reza forushani
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Thanks Gerald. On the Calibration screen, it's asking for other stuff. Where do I plug this number in (2291.9) Thanks again
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  #17  
Old Mon 26 February 2007, 23:45
Gerald_D
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In Mach, you first do the Config > Select native units, and I am sure you picked inches there.

Then you do Config > Motor Tuning, and at bottom left there is a block "Steps per", it actually means "Steps per selected native input", which in your case is "steps per inch" or "pulses per inch"...

For the rest, you can play with any value on that screen, because you pick the final speed and acceleration values once the whole machine is moving.
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  #18  
Old Tue 27 February 2007, 00:23
reza forushani
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Got it boss. Thanks a million $$$
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  #19  
Old Sun 20 May 2007, 11:41
Hugo Carradini
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Pto. Ordaz
Venezuela
Hello Gerald and friends.
I have been reading different opinions and get a little confused. I got my motors with a 7.2 : 1 ratio gearbox . ¿What is the optimum numbers of teeth for my pinions and the magic number for setting Mach3 in steps for mm? I just don't want to make a mistake with the calculations, and don't want to end with an incorrect pinion. I all ready got my racks 1/2 /side like Gerald suggest and need to get my pinions.
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  #20  
Old Sun 20 May 2007, 12:24
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The popular choice of DP20(1/2"Wide) pinion for the motors with 7.2:1 gearbox now seems to be the 30tooth. Doc Tanner, and all the latest ShopBots, are going with that choice. (for the 3.6:1 gearbox, or direct-drive, the American DP20 choice is 20tooth, and the metric M1 choice is 24teeth)

Hugo, I am a bit lazy to fetch my calculator now, but this is more or less how you can calculate it....

A 30tooth DP20 gear will have an effective diameter of 1.5". One full turn of the output shaft will make that gear roll a distance of 1.5 X Pi (about 5" ?) along the rack (You must calculate this exactly with a calculator)

The number of steps needed to make that gearbox turn one full turn is 2000 x 7.2

So, take 2000 x 7.2 and divide it by 1.5 x Pi (My memory has Pi = 3.1416, or you can also use 355/113.....the old schoolboy 22/7 is not good enough )

Last edited by Gerald D; Sun 20 May 2007 at 12:27..
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  #21  
Old Sun 20 May 2007, 12:36
Hugo Carradini
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Pto. Ordaz
Venezuela
Thanks Gerald.
Very precise.
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  #22  
Old Mon 28 May 2007, 15:15
Hugo Carradini
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Pto. Ordaz
Venezuela
Gerald I will have my pinions made here. Before I go to the turner I want to know if the "effective diameter" is measure from the bottom of the tooth or the top of the tooth.
Thanks
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  #23  
Old Mon 28 May 2007, 21:01
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
It is near the middle of the tooth.

I used the words effective diameter, but the guys who work with gears all day call it the Pitch Diameter, or the diameter of the Pitch Circle.
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  #24  
Old Mon 23 July 2007, 14:15
bbreaker
Just call me: Mickey
 
Galgan
France
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ok now can anyone tell me, i whant to go to metric and i have a 7.2:1 gearbox, how many teeth can can my pinion have, if gerald know.

thank's

i'm on the forum, from a moment but i start my Mechmate now
Michel from France
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  #25  
Old Mon 23 July 2007, 23:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Hi Mickey, I presume you are going to use metric Module 1 gears. If this is the case, then I suggest a 35 tooth pinion to go with the 7.2:1 gearbox.

*** The following added at top of thread as well *******

For those trying to follow this thread, please do not mix:

- inches, diametral pitch, DP, steps per inch

and

- millimeters, module, steps per mm

they are not compatible with each other
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  #26  
Old Tue 24 July 2007, 00:27
bbreaker
Just call me: Mickey
 
Galgan
France
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thanks gerald. ok i search now the good number for Mach.
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  #27  
Old Tue 24 July 2007, 23:54
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Now that everyone understands how to calculate these things . . . .


. . . . and the zipped spreadsheet where you can play with your own values in the green area: Gear Speed Steps Freq Calculator.zip
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  #28  
Old Wed 25 July 2007, 00:19
bbreaker
Just call me: Mickey
 
Galgan
France
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Thank's a lot gerald, not a problem for everyone now.
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  #29  
Old Wed 25 July 2007, 05:57
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Gerald,
Thanks for the spread sheet. I'm assembling the "kitchen project" and learning the Mach program at this time.

Greg
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  #30  
Old Thu 24 January 2008, 13:41
Gato Richy
Just call me: Richy
 
Chillán
Chile
lost in gears

Congratulations for this excellent forum.

I have tried to read every thread concerning to gears. Unfortunately, I got lost in the woods.

I trying for more than a year to finish this plasma cutting machine, and I'm stuck right now, just when I've got little more time for it.

My "FAQs" are:

1. if I chose PK299-01AA motors I should use it directly (no reduction). If no reduction, What gear should I use? 30 or 35 teeth 20 DP in all 4 motors?

2 if I chose PK296A1A-SG7.2 (or 3.6)...what gear should I use? 20 teeth 20DP in all 4 motors. What about the G203V problem?

As my cnc will be use for cutting, is it necesary to reduce on all axis?

Thanks

Richy

Chile
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