Bevel cutting

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cnc_freak
Posts: 17
Joined: Fri Apr 20, 2018 5:36 am

Bevel cutting

Post by cnc_freak » Sun Jul 28, 2019 6:36 pm

Hello all.
I recently retrofitted an old tube profiling machine with 5 axis. The machine uses a oxyfuel torch to cut the tube profile.
The machine will cutting mostly saddle pipe profiles in order to weld them on.
In order to weld the pipe a bevel is needed, not only the saddle profile to be cut.
Normally the cam software will handle that but unfortunately, the cam post processor and the cam manufacture can't do that.
So one option is that the A axis "the bevel axis" will be handled by the Kmotion.

After some calculations the A axis "the bevel" is depended from the X axis, which is the rotational axis. So roughly A axis, goes from 0 to
60 degrees or more, depended also from the thickness of the pipe, but lets stay , for making the things simple, to a max angle of 60 degrees.

For a complete cut of the saddle profile the X axis do a complete circle 0 -> 360 degrees. When the X is from 0 to 90 degrees the A axis should go from 0 to max (60 degrees) and when the X goes from 91 to 180 the A should go from max (60 degrees) to 0.

So to conclude i think a more flexible solution is to make a look up table for the A axis, which will be different for each cutting thickness.

The problem is i don't now how to do something like that.
A look up table with 36 entries will be ok, 360/36 = 10 degrees.

When the X axis is between 0<X<10 the first entry of the lookup table should be A axis output, when X is between 11<X<20 then the second
entry and so on.

I read in wiki about the kinematics, but i don't now how to accomplish something like that.

Any help will be appreciated.
Attachments
tube_outside.txt
The profile in dxf, rename the extension, to .dxf
(40.32 KiB) Downloaded 4 times
tube_outside.txt
The Gcode of the profile
(2.56 KiB) Downloaded 4 times
PHOTO_2.jpg

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TomKerekes
Posts: 512
Joined: Mon Dec 04, 2017 1:49 am

Re: Bevel cutting

Post by TomKerekes » Mon Jul 29, 2019 4:29 am

Hi cnc_freak,

I think the first step would be to get the kinematics to work to correct for the yz motion as the A axis rotates.

There is an existing CKinematics5AxisGimbalAB.cpp file that might work if you change some parameters and re-compile it. Try the steps here to see if you can compile the libraries.
Regards,

Tom Kerekes
Dynomotion, Inc.

cnc_freak
Posts: 17
Joined: Fri Apr 20, 2018 5:36 am

Re: Bevel cutting

Post by cnc_freak » Tue Jul 30, 2019 3:44 pm

Ok i managed to change the post processor and i have the A axis output as i want.
Now another problem came out. The post processor has an output of feed lets say 300mm/min.
When the machine moves all three axis A,X,Y then it goes very slow, when the A axis has reached the target then the X and Y axis go very fast.
I understand that the KMotion has to calculate and slow down the axis in order that all three reach the target simultaneously, but why the A axis goes so slow?
I attach the gcode and the init file, of the machine.
Attachments
S 10-10_90 STD40 OUTSIDE-60.txt
The gcode
(4.25 KiB) Downloaded 3 times
Init5Analog.c
The init c file
(11.7 KiB) Downloaded 1 time

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TomKerekes
Posts: 512
Joined: Mon Dec 04, 2017 1:49 am

Re: Bevel cutting

Post by TomKerekes » Tue Jul 30, 2019 4:11 pm

Hi cnc_freak,

So you decided to not do the kinematics as I suggested? If not it seems to me you will need to have your CAD do the Y and Z compensation somehow as A changes.
Now another problem came out. The post processor has an output of feed lets say 300mm/min.
When the machine moves all three axis A,X,Y then it goes very slow, when the A axis has reached the target then the X and Y axis go very fast.
I understand that the KMotion has to calculate and slow down the axis in order that all three reach the target simultaneously, but why the A axis goes so slow?
How do you have the A Axis configured in the Trajectory Planner? If configured as degrees with Radius of 0 then it should not be considered into the feedrate calculations unless its maximum velocity or accelerations are exceeded. See also here.
Regards,

Tom Kerekes
Dynomotion, Inc.

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