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Author Topic: Quantifying A-axis rotary  (Read 5142 times)

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Offline Keith

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Quantifying A-axis rotary
« on: December 15, 2005, 06:18:26 PM »
Hi,I'm just getting my feet wet with my 4th axis,rotary table.I did a 'g1' a(value).I just put in 360 as the value not thinking anything about degrees,just as a starting point.Did the move.My question is, 'in finding a value for where you want to wind up',is this value strictly an 'inch per minute' number? ...and if I calculate the proper ratio for the worm gear to 'pulses per',will this put me where I want on some point ,on some circumference?
Thanks,Keith

Offline Graham Waterworth

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Re: Quantifying A-axis rotary
« Reply #1 on: December 16, 2005, 05:11:31 AM »
Hi Keith

the a axis indexer should be set up so that one full rev of the indexer is 360 degrees (0 to 359) that way all calculations for movement are decimal degrees.

what you have to watch out for is feed matching (G01) if you want to mill a slot at 45 degrees round a 1 " bar over a 90 degrees length round the bar the command G01 X19.95 A90. F100. would give a slot at 45 deg on a 1" dia bar.

WHAT! I here you cry.

If you take the top and bottom off a been can, then cut the tube down the length, opened it up and rolled it out flat the rectangle you are left with is the circumference of that dia can (less the cut width).

If you then draw a line on that rectangle at 45 degrees from the cut edge to 1/4 of the way up the length that is what you would get on a round bar of that diameter.

so a formula

bar dia 1"
45 degree slot running from right to left over 90 degrees

1"*25.4*PI  = 1*25.4*3.1415 = 79.7941

90 degrees is 1/4 rotation so 90/360 = .25

79.7941*.25 = 19.9485

So the X axis movement is 19.94mm

G00 X0 A0
Z1.
G01 Z-.2 F50.
G01 X-19.94 A90.
G00 Z25.

If the feeds are not matched then the slot will not be at 45 degrees.

I hope this helps

Graham.

Without engineers the world stops

Offline Keith

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Re: Quantifying A-axis rotary
« Reply #2 on: December 16, 2005, 09:27:05 AM »
Awesome Graham ! I woke up thinking "of course it is resolved in degrees..." I mean the increments on the 'table' are in degress ! but still had the equations and 'steps per whatever'  in my brain's limbo.
That's the whole kit and kaboodle you laid out for me. My first xmas present. Very appreciated ! 'Cut','Pasted' and 'Saved as...'-Keith
PS-Since starting my CNC knowledge 6 months ago (I'm actually an electronics person)and when it comes to learning all this,I rarely say "what?" anymore ; my "whats?" have become reserved for the supplier of my system's bold and erroneous suggestions at solutions,that I later ,empirically prove wrong.

Offline Keith

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Re: Quantifying A-axis rotary
« Reply #3 on: December 16, 2005, 03:20:35 PM »
One more thought about all this not clear; how to set up the units in the motor tuning section of mach2:my rotary table's motor is 400 steps per and the worm gear requires 72 turns to complete a revolution that makes 28,800 steps to make the table turn 360 degrees.Since I am using inches as a unit in mach2,do I use the diameter of the rotary table(4") to calculate the steps per unit,in the motor tuning of mach2 for the a-axis?-Thanks for all your help,Keith
Re: Quantifying A-axis rotary
« Reply #4 on: December 16, 2005, 04:28:31 PM »
The unit is  degrees so you are going to have steps per degree... The vel of the axis will be in Deg per min... The feed rate is also in DegPerMin or (DPM). This can be hard for people to understand... But Art has added in the Rot Dia that will make it so you can run in IPM because the controle is looking at the circumference and calculating the DPM.

Hope that helps
Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com

Offline Keith

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Re: Quantifying A-axis rotary
« Reply #5 on: December 16, 2005, 04:55:44 PM »
That is hard to comprehend unless what you're saying is : if I place the number of steps per unit in the a-axis window which represent one full rotation of the rotary table,Mach2 offsets that for it to be represented in degrees. If this is true then am I placing the 400 steps per unit of the stepper motor(one full stepper revolution) or the 400*72(28,800,one full rotation of the table)) for the number of stepper motor pulses times the worm gear ration,into the motor tuning,steps per unit window?-Keith
Re: Quantifying A-axis rotary
« Reply #6 on: December 16, 2005, 06:38:31 PM »
The Steps per unit Box is going to have 400*72(28,800)/360 You have to divide by 360 because One unit is a "Degree"

Hope that helps
Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com

Offline Keith

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Re: Quantifying A-axis rotary
« Reply #7 on: December 16, 2005, 06:41:49 PM »
Ah-ha! Thanks so much.Think that's going to do it.Voila!
Re: Quantifying A-axis rotary
« Reply #8 on: December 20, 2005, 11:33:32 AM »
The Steps per unit Box is going to have 400*72(28,800)/360 You have to divide by 360 because One unit is a "Degree"

Hope that helps
Brian


Brian as I was reading this thread I bagan to worry that I had set my units per up wrong, but your explaination put that to rest.

Mike

Offline Keith

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Re: Quantifying A-axis rotary
« Reply #9 on: December 20, 2005, 11:41:31 AM »
I'd just like to add to all this,if anyone is using a stock Sherline package for this rotary business that although the motors are 400 steppers,the microstepping feature requires you to double this 400 steps to 800 within Brian's equation to achieve the desired resolving.I set mine up this way and 'bingo' ,works like a charm.Thanks for everyone's input.-Keith