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> How to flip 4th axis rotation and set max Z depth for rotary machining?
charlie brumfiel...
post Jul 4 2013, 01:06 AM
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So SprutCAM want to to turn the axis toward the back of the machine (Clockwise if you are looking at the t-slot face of the rotary table). I'd really like it rotate towards the front of the machine so i can keep and eye on the part as it's being machined. I am using a rotary machining process along the x axis (linear) using the both option under machining type.

Also how do I set a maxmium Z depth? I do not want the bit to plunge past Z0.000. SprutCam insists that it plunge to the other side of the work piece when it get to the end of the part.

Thanks in advance.

Charlie
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Sprut_UK
post Jul 4 2013, 06:42 AM
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Hi Charlie, welcome to the SprutCAM user forum.

The selected machine configuration in SprutCAM dictates the direction of the rotary axis. If you are using '4-axis milling machine (A)' and you change this to '4-axis milling machine (-A)' the direction of the A axis will be reversed.
The direction of the A axis in SprutCAM must match the direction used on the machine itself. This may mean that you have to alter the rotary axis direction on the actual machine too.
If you are using a specific machine configuration (e.g. Tormach), then you can temporarily alter the A axis direction by changing the scale factor to -1 (see attachment). If you do this you will have to manually alter it for each new project, or speak with your SprutCAM supplier about getting a revised machine configuration created for you.

You don't say which operation you are using that you need to restrict the Z depth? I will assume that you are talking about the 'Rotary machining' operation. You will need to add a fixture(s) to restrict the machining to / from an area (see attached images).

I hope this helps?

Dave






Attached File(s)
Attached File  04_07_2013_07_16_13.png ( 23.89K ) Number of downloads: 13
Attached File  04_07_2013_07_29_20.png ( 78.02K ) Number of downloads: 16
Attached File  04_07_2013_07_44_32.png ( 87.48K ) Number of downloads: 7
Attached File  04_07_2013_07_45_07.png ( 129.94K ) Number of downloads: 7
 


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charlie brumfiel...
post Jul 4 2013, 05:31 PM
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yup that's exactly what i was looking for. guess i'll just add the support (fixture) to my model then. we're running a tormach 1100, a tormach 770, 3 taigs, and a legacy CNC router off of sprut cam. So far i'm liking it. though the a axis rotations are unduly slow. It runs at about half the speed deskproto does for axis rotation. i think it has to do with sprut cam calculating the feed speeds for every a axis movement instead of letting mach 3 do the calculations.

charlie
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Sprut_UK
post Jul 4 2013, 06:09 PM
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Thanks for the update.

The Tormach post will most probably be outputting 'inverse time' feedrates to the Mach controller (G93 inv. time feed / G94 feed per min.) for the rotary axis moves.
Is the Deskproto running with inverse time feedrates or is it capable of converting linear feedrates to rotary / rotary + linear feedrates on the fly?

I'm not sure.

Dave


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charlie brumfiel...
post Jul 5 2013, 06:11 AM
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Actually Deskproto does not calculate the feed speeds for a-axis rotations independently. It just uses your feed speed specified for the rest of your machining ops. this allows Mach 3. if configured correctly to, (and that is a big IF) to calculate the degrees per minute of rotation based off of the Z axis height above the 0 line (center of a axis).

tormach does NOT configure their machine controllers (mach 3) to do this. instead you can specify a height above 0 offset on the setting page of mach 3. we use 1 inch on the tormachs as we machine 1 inch bar stock.

my taig's however will calculate the degrees per minute of rotation based on the z axis height.

anyway, i think there is a bug in sprutcam's post processor for tormach as no matter what feed speed i specify the a axis rotation is always WAY slower that what it actually needs to be / can run. which makes spiral and circular rotary machining out of the question.

Example: tormach's 8" rotary table will turn at 3-4 rpm, sprutcam when set to feed speed of 135 ipm run's the rotary table at about 1 rotation per minute and a half (according to my stop watch). where as the following code with a 1" offset in mach 3, will make tormach's rotary table spin at the full 3-4rpm.

G0 A0.0
G1 X0.0 Y0.0 Z1.0 F135
G1 Z0.25 A360.000

I've also used a bit of regular expression to remove all F words that follow an A word from a sprutcam generated spiral rotary machining path and it did result in MUCH faster machining times.

Again this is ALL done with the 1" a axis offset on the Tormachs. I have yet to test it on the Taig machines with their automatically calculated speed based on Z height.
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charlie brumfiel...
post Jul 5 2013, 06:19 AM
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and yes your are correct sprutcam is outputting a g93 command for A axis feed speeds. see example below.

QUOTE
N15270 G93 A0.564 F14342.1



i'm really not a machinist so i'm still murky on g93 vs g94. i think g94 is the more common unit per minute feeds. where as g93 is units over time maybe? or is it units per spindle rotation? not sure off the top of my head.
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Sprut_UK
post Jul 6 2013, 04:40 PM
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Inverse time feedrate is preferred when working with combined linear and rotary moves because it uses the amount of time that it takes for a combined move, for the feedrate. Historically this has always been done using 'inverse' time.

To test this you can create a rotary axis move to machine around a 1" diameter bar at a feedrate of 3.14", which will take 1 minute (1 rpm). Simply draw a line from X0 Y0 to X0 Y3.14 and use 2D Contouring with a 'Base Surface' of 0.5" radius and 'Curves projection method' of 'Map to UV domain' (see attached). When machining this way the depth (Bottom level) becomes an incremental distance and should be set to 0 for this test (see attached).
This test is for the Tormach postprocessor. It should produce a feedrate of F1 which should take 1 minute to do.

Please let me know what the results are so that I can investigate the postprocessor problem, thanks.

Dave

Attached File(s)
Attached File  06_07_2013_17_29_31.png ( 21.09K ) Number of downloads: 10
Attached File  06_07_2013_17_35_22.png ( 46.33K ) Number of downloads: 6
Attached File  06_07_2013_17_43_59.png ( 85.01K ) Number of downloads: 5
 


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Sprut_UK
post Jul 8 2013, 08:18 PM
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I contacted Eric from Tormach today and he ran a couple of tests for me to check the Tormach postprocessor output for rotary and combined rotary / linear machining, and the (inverse time) feedrates worked correctly.

Let me know the results of the test and we can then try and find out the cause of your machines rotary axis feedrate troubles.

Dave


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charlie brumfiel...
post Jul 11 2013, 04:14 PM
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maybe it's an issue on my end then. i can run the test above on monday or tuesday. my rotary tables for the tormachs are at a local machine shop having some fixture work done right now.

thanks again for looking in to this.
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