Need Help Cutting my first 4th axis gear

[Bbrault]

Hi
I need your advice on cutting my first 4th axix gear.

I designed a 3/4 spur gear and I generated the G-Code.

I have a Taig Mill with a rotary table running Mach-3.
I am using a feedrate of 6IPM and a PLunge Rate of 3IPM.

The problem is with the A axis G1 code. (Root wall and Tangentials)
It is feedrate remains at 6 Degree per Minute therefore executing these combined (XYZ and A) motions way too slowly.

I did not anticipate this problem but it makes sense since the units for XYZ are different from A

Your help is appreciated.
Thanks

[ArtF]

Hi:

In Mach3, you set the A radius to the radius of the gear. Since to do a 4th axis gear you zero at the top of the gear,
Mach3 doesnt know the diameter so it can figure out the A axis speed on the circumferance. Mach3 has a DRO for A axis radius
so it can figure out how fast to move on a A axis motion. Without it, it will assume degrees mixing with units, that makes it
awful slow. Set that DRO to the radius of your gear.

Art




   

[Bbrault]

Thanks Art
I got it.
Its now rotating at the correct feed rate.
I just need to make the actual cut!

[Dan Mauch]

Is that dro the one in the settings window?
Dan

Hi:

In Mach3, you set the A radius to the radius of the gear. Since to do a 4th axis gear you zero at the top of the gear,
Mach3 doesnt know the diameter so it can figure out the A axis speed on the circumferance. Mach3 has a DRO for A axis radius
so it can figure out how fast to move on a A axis motion. Without it, it will assume degrees mixing with units, that makes it
awful slow. Set that DRO to the radius of your gear.

Art




     

[ArtF]

Dan:

  I believe so, but my only mach3 unit is in my cold cold workshop, so I cant boot it up to see.
I use Auggie in my basement dungeon, ( it has a similar DRO ), but I cant recall top of head where I put it
in Mach3.. I suspect its on the jog tab for some reason..

  ( Sad , isnt it, I wrote the damn thing and cant tell you where the DRO is top of head..Too much
code has gone by and its been several months since I cut on my garage machine. Next time Im out there
Ill take a snap and post it for archival purposes.. )

  In expanation, if you zero the Z at the center of the 4th axis, you can allow m3 to determine radius is equal to Z,but if you zero on a gear, you need to put the radius in that dro so m3 can add it to the current Z so it
knows the outside circumferance, this is also what you need to do in lathe op's to keep constant cutting speed.
I rememebr I labeled it as A Axis radius..

Art

[ArtF]

Thx to YaNvrNo for sending me a photo of the setup screen, the DRO is labeled A Axis Diameter. I used
the setting rarely enough to forget its location..


  Heres a snapshot, all rotations axis may be set this way..

Art

[Bbrault]

Hi Art
I am glad that my first gear cut was in Delrin...
I did work out the feedrate but something went terribly wrong between the rot wall and the tangential and it appears to be with the generated code itself:
Below is a sample:
The root wall appears to have the correct angles around 5degree but the following tangential shavings are way off with 17 and 23...
I am back to my project to try to figure out what went wrong.
Its probably an obvious mistake.

( Root Wall Begins. )
G0 Y-0.033  A5.146 
G1 Z-0.116  F2.00
G1 X-0.174  F6.00 
G1 Y0.033  A-5.146 
G1 X0.174 
G0 Z0.250 
( Tangential Shaving Begins. )
G0 Y-0.035  A5.403 
G1 Z-0.077  F2.00
G1 X-0.174  F6.00 
G0 Y-0.113  Z0.000  A17.711 
G0 Z-0.092 
G1 X0.174 
G0 Y-0.148  Z0.000  A23.163 
G0 Z-0.104 
G1 X-0.174 

[ArtF]

Hi:

  Make SURE your A axis is turning the correct direction. In almost every case of this complaint,
the A axis is turning backwards. Its not unusual at all. There is almost no case where you'd notice except in gear cutting,
where the direction is very important. If your A Axis is moving A++ direction, looking at it from up axis, ( from X++ direction
back to the chuck, it should spin CCW. ).

    When tangental shaving begins, it isnt unusual to see numbers such as you show, the Y axis moves sideways to make the tool hit the edge, and that edge must be tangent, so it turns a fair amount at times. That having been said, the Y doesnt appear to be moving much
but is dependent on the tools diameter so I can never tell from a quick look at the code.

  Look to the simulation though, it is created from the GCode internals, so its is always accurate as to the design. Slow
it down and look at the first few moves, Does the A axis move to 17 and then 23 degrees in the sim? If so, and the sim
is not showing the tool cutting off anything important, then almost certainly the axis is rotating backwards.

  I have found that most people with a 4th axis have never actually checked the direction for a standard direction,
which is CCW when view from the front of the chuck when rotation A0 to A++ direction.. Mine too was backwards when
I started cutting gears, after several years of Mach3 cutting on it, I just never noticed.. :)

  The symptom of this is the teeth get cut off or cut very very thin..

Art

 

[Bbrault]

Art
You are correct, I changed the Rotary Table to X-- and everything works fine now and it all makes sense.
Thank You for your help.

[Dan Mauch]

Hmmm. shouldn't the screen say radius like mine? But am not sure why or how I was able to set it to radius.

Dan Mauch

Thx to YaNvrNo for sending me a photo of the setup screen, the DRO is labeled A Axis Diameter. I used
the setting rarely enough to forget its location..


  Heres a snapshot, all rotations axis may be set this way..

Art

[ArtF]

Seems to me there was a couple versions of that screen Dan, you may have an older ( or newer ) one..

Art