A axis speed

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A axis speed

Postby RichardV48 » Sun Nov 08, 2015 9:05 pm

I have a question about a lathe I converted for cnc. I created a rounding tool path for a piece of 2 inch square stock 6 3/4 long using a 1/4 end mill to cut it. The problem I ran into was that once I started running the file the rotary axis rotates at one degree per second, took 54 minutes to round the part. When it rapid moves it is much faster. Is there a way to control the speed of the rotary axis or does the software control it based on the feed rate of the X asis? I'm new to rotary but having watched some Youtube videos they seem to run much faster when they cut.
Thanks,
Richard
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Re: A axis speed

Postby 4DThinker » Sun Nov 08, 2015 10:38 pm

Unfortunately your A axis is converting/using inches per minute as degrees per minute. Mine does the same thing. To overcome this I edit any toolpaths that will become A tool paths (rotational) to a much higher value, say 5000. You can do some math to know how high to get an equivalent feed speed on your A axis. If your cylinder is 2" diameter, the circumference is 2pi or 6.28 inches. If you desire a feed speed of 100ipm then you'll want 100/6.28 or 15.9 revolutions every minute. 360 (degrees in one revolution) times 15.9 equals 5,730. Put in a feed speed of 5,730ipm for any tool path that becomes A axis moves for a 100ipm performance.

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Re: A axis speed

Postby NormanAlbert » Sun Nov 08, 2015 11:32 pm

To add to what's been said so far, don't forget as the diameter gets bigger the loads on the rotary drive get higher. If missed steps become an issue, that's probably where the problem is. Norm
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Re: A axis speed

Postby IslaWW » Mon Nov 09, 2015 4:15 am

Richard...
Which control software are you using? Most have a way to provide a proper rotary feedrate based on XY feeds. ShopBot and WinCNC via some PostP math and Mach from an onboard calculator.

In any event, the simple formula for rotary feeds (in degrees) that match surface feed rates (in inches per minute) is: 115 * [XY feed in ipm] / diameter
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Re: A axis speed

Postby RichardV48 » Mon Nov 09, 2015 4:28 pm

Thanks for the responses.
When you talk about editing the tool path, what exactly are you editing? I went back and looked at the rounding tool path but I dont see any feed rates for the rotary. I had the motor tuning for the rotary axis set at 5000. I have doubled it and notice no difference in the speed of the rotary axis. The only time I see a slight improvement is by increasing the X feed rate but it is barely noticeable.
This is a home made conversion, so to get really good quality I am stuck running at slower feed rates.

I am using Mach for the controller.

Thanks again for the feedback.
Richard
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Re: A axis speed

Postby TReischl » Wed Nov 11, 2015 12:53 am

If you are using mach. Search through this forum and you will find information on how to set up mach. Trust me, you are not stuck with slow feedrates.
http://www.tedreischl.com

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Re: A axis speed

Postby TReischl » Wed Nov 11, 2015 12:56 am

Find the. "Use radius for feedrate" setting in mach.
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Re: A axis speed

Postby RichardV48 » Wed Nov 11, 2015 2:13 pm

Thanks, I will check that out.

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Re: A axis speed

Postby RichardV48 » Thu Nov 12, 2015 10:33 pm

I found the problem! When the code for the rounding tool path was generated a G94 code was inserted. This is a feed per minute mode. I changed it to G95 which is a feed per revolution mode and the A moves as it should. I went back and looked at the options for a rounding tool path and did not see where you can select the G95. G94 must be a default.
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Re: A axis speed

Postby dealguy11 » Sat Nov 14, 2015 1:45 pm

The advice above regarding an option in Mach to use radius for feed rate is the way to go. I don't use Mach any more, but when I did and that option was selected I didn't have to mess with G94 vs G95 issues. There is another parameter in Mach to automatically convert from feed rate to radial rate given a specific diameter of the part that you enter in Mach. It's been a couple of years since I used it, but look for it - it's there.
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