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A axis not matching actual angle.
« on: March 17, 2011, 01:29:32 AM »
hi,
I am trying to set up to use a 4th axis. It turns but the DRO reads 4 or 5 or so when it has gone 360 degrees. I have the General Logic Config set for A axis to angular. What else am I missing?
Thanks,
Dwight.

Offline Tweakie.CNC

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Re: A axis not matching actual angle.
« Reply #1 on: March 17, 2011, 08:41:31 AM »
Could it be the 360 deg roll-over ?

Tweakie.
KEEP SAFE !
Re: A axis not matching actual angle.
« Reply #2 on: March 17, 2011, 10:51:18 AM »
I don't think so but not sure. If I enter A0 into the MDI input line it just goes round and round, 4-5 complete turns and it is only at 24 or 25.
Re: A axis not matching actual angle.
« Reply #3 on: March 17, 2011, 11:30:19 AM »
Hi Dwight,
   What do you have for "steps per" in motor tuning for A ?
How is it set up ... microstepping and/or gearing.
Sounds like your Steps per Unit is possibly not right .
Russ
Re: A axis not matching actual angle.
« Reply #4 on: March 17, 2011, 10:12:22 PM »
Thank you Overload and Tweakie. The steps per is set to 3200, the same as the X and Y axes which work perfectly. The actual device is a Sherline 4th axis about 10 years old. The native units is inches and I use G21 command to operate in MM. It behaves as though it is in inches instead of degrees.
Re: A axis not matching actual angle.
« Reply #5 on: March 17, 2011, 10:22:30 PM »
Edited,
the native units are inches, I use G21 to run in MM. I start in MM with the 4 axis at 0. I type in G20 into the input line and the DRO reads 340.2587. G21 and it goes back to 0.
« Last Edit: March 17, 2011, 10:32:49 PM by rolexmechanic@comcast.net »

Offline Hood

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Re: A axis not matching actual angle.
« Reply #6 on: March 18, 2011, 03:16:38 AM »
The unit for a rotational axis is degrees so if one revolution is 3200 steps your steps per unit for that axis will be 3200/360 =8.88888888889

Hood
Re: A axis not matching actual angle.
« Reply #7 on: March 18, 2011, 10:54:11 AM »
I'm confused. If each step, which is in reality very small, read on the DRO as 8 degrees then wouldn't it have moved only a very little when it reads 360? Instead it is just the opposite.  A full 360 on the axis reads only a few degrees on the DRO.

If I zero the A axis DRO in inches (G20) then go to mm (G21) it changes to 357.4285 degrees. Zero in mm and switch to inches it reads 340.2587.
Re: A axis not matching actual angle.
« Reply #8 on: March 18, 2011, 01:06:07 PM »
It's not units per step, it's Steps per Unit.
For example:
Your motor is 200 steps per revolution.
Multiply that by whatever microsteppin you might have ... say 10 which would = 2000 steps per motor revolution.
Multiply that by whatever reduction you have in the mechanism .. say 4:1 would = 8000 steps per table/chuck revolution.
 8000 / 360 = 22.22222222222 Steps per Unit
Re: A axis not matching actual angle.
« Reply #9 on: March 18, 2011, 05:24:47 PM »
Could you double check my math on this? I think the motor is a step motor with 1.8 deg. so a full turn would be 200 steps. It is 1/4 step, so is that multiply by 4? which would be 800. The sherline website lists a worm 72-1 ratio so that would yield 800x72=57600. Divide by 360, so steps per should be 160?
Does that sound right?
Thanks so much for being patient with me while I figure this out.
Dwigh