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Synchronise Rotary axis feed with X and Z feed
« on: January 05, 2010, 06:15:35 AM »
Hi, I have my rotary axis setup for some time now.

The problem I have is: Ratio is 7:1 Microstep is 8, so 8 X 200 X 7 = 11200 steps per revolution and 31.1111 step per degree.

To get a decent feed rate with the rotary, must input at least a feed of F1000.

And a feed of 1000 is way too much for a router table.

How could I overcome this in configuration, is there other way to calculate my step.

Thanks for any advice.

Jeff 

Offline Hood

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #1 on: January 05, 2010, 06:29:17 AM »
Have you looked at the Rotation  Dia DROs on the Settings page, think that may help you but as I have never used a rotary axis I cant be sure. Greolt is the guy to talk to about them.
Hood

Offline RICH

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #2 on: January 05, 2010, 08:28:49 AM »
Jeff and All,
In Mach Mill, Settings (Alt-6) Tab you will see Rotation Radius for the A/B/C axis.

Look in the Mach2MIll_6.11 Manual, 6.2.12 and you will find a very brief explaination and here it is:

" As described in the Feedrate control family, it is possible to define the approximate size of a rotated workpiece so the rotational axis speed can be correctly included in the blended feedrate. The relavent diameters are entered in the DROs of this family"

Anybody want to provide a simple explaination?
My guess on this:
 If the A axis was linear and had the same steps per units along with velocity and accel as the other axis then a point along / around a circumference  would be linear sych'd with the other axis exactly for only one specific diameter.

If the A axis was linear and didn't  have the same steps per units then the above would no longer be true  
for a given feedrate.

So by inputting the diameter that will be cut , Mach modifies the feedrate such that the linear moves will be
"APPROXIMATELY" snch'd for a commanded feedrate.
  
What formula is used for calculating the combined inch/degree feedrate( blended feed rate) ?

Does Mach read the diameter in the program and adjust the feedrate for a different diameter and adjust accordingly?

Based on what diameter....ie; define linear steps per unit based on a diameter of 1 in motor tuning?

RICH

BTW,you will not find those DRO's  a modified  lathe screen....Yet!  ;)
« Last Edit: January 05, 2010, 08:31:22 AM by RICH »

Offline RICH

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #3 on: January 05, 2010, 08:52:38 AM »
Is the following formula applicable in Mach?
Any comments on use?

RICH

Offline ger21

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #4 on: January 05, 2010, 09:20:46 AM »
Set your steps/unit per degree. Enter the diameter of your part in the DRO on the settings page. Go to Config>Toolpathand check "Use Diameter for Feedrate".

There was a bug where the Diameter DRO actually wanted the radius. It's supposed to be fixed in the latest version, or the next one. Not 100% sure, so you may need to try both and see.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Synchronise Rotary axis feed with X and Z feed
« Reply #5 on: January 06, 2010, 12:39:30 AM »
Hi, just did what you said and it work great, much easier to build program

Thanks's again.

Jeff

Offline Greolt

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #6 on: January 06, 2010, 05:09:21 AM »
As of Version R3.042.033 this has been, not quite fixed, but greatly improved.  Previous versions it was buggy.

The DROs on the settings page are now labelled "Rotation Radius" which is now correct.  Previously they were labelled "Rotation Diameters" which was partly right and partly wrong.

When "Use Radius for Feedrate" is checked in toolpath setup and you have a number greater than zero in the appropriate "Rotation Radius" DRO this turns on the rotary axis feedrate compensation.

The compensation system takes the value of the "Rotation Radius" DRO and the value of the Z axis DRO and adds them together to ascertain what diameter the cutter is at.

Then it compensates the rotary axis feedrate to keep the tool cutting at the called for feedrate. (within motor tuning parameters)

So if you are using the centre of rotation for Z zero (which I always try to do) then have a near zero number (0.01) in the "Rotation Radius" DRO and the Z axis DRO value will be used for the calculation.

If on the other hand you have Z zero at the outer circumference of the job, enter that radius in the "Rotation Radius" DRO, then this value plus whatever Z DRO is, will be used for the feedrate calculation.

I said "not quite fixed" because Brian was going to fix the issue of a "Rotation Radius" DRO value of zero turning the compensation system off, but he must have forgotten.

That is why you must use a near zero value in the "Rotation Radius" DRO and not zero.

Hope this is clear and helps.

Greg

« Last Edit: January 06, 2010, 04:15:37 PM by Greolt »

Offline RICH

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #7 on: January 06, 2010, 08:55:58 AM »
Greg.
"Hope this is clear and helps."

Thanks for the reply and plain explaination and it does help. There are a lot of different postings  on Rotation DRO and 4th Axis and one would need to do a lot of reading / searching and filtering of the discussions to sort it out.

"have a near zero number (0.01)"
Art posted, back a few years ago  / before my time of using Mach, that a value of .0001 as a Rotation Radius will cause the feedrate to default to the linear axis feedrate. Just found that last night. Unless one is aware of rotary use along with the development over time, a user applying rotary to do something will end up with some basic questions. Thus finding answers can be difficult.

Exploring use of rotary in a limited different manner ;)
RICH

Offline ger21

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #8 on: January 06, 2010, 09:02:32 AM »
Thanks for that info, Greg. So, the radius entered is really the location of Z zero relative to the axis of rotation?
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline RICH

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Re: Synchronise Rotary axis feed with X and Z feed
« Reply #9 on: January 06, 2010, 10:54:12 AM »
So the feedrate will not vary on the fly for multiple diameter changes? .....It's a fixed feedrate relative to a single diameter  .....Otherwise you would have electronic gearing / feedback such that a turn of the spindle will slave the Z  to the rotary movement which is currently not available. Now if the A axis is linear, and say an arc is broken into line segments, then all would be in synch?

OOPS,  ignore the above as i'm doing rotary control on the lathe.
 
I can confuse myself when i think,  ;D
RICH
« Last Edit: January 06, 2010, 11:09:20 AM by RICH »