Z axis starting point

[danmauch]

I have made a lot of gears using my laser cutters but I now need to make  my first 17 tooth gear with a .944 OD on my Milling machine using the A axis. Using Gearotic Thought I had it generate the G code.  I have run into a problem. In the video you show the tool bit at Z 0.00 tangent to the centerline of the x axis on the blank to be cut. I zeroed the display for the X,Y and the Z after setting it up. When I ran the part it cut too deep  because of where I started the Z axis. I'm using a .037"D endmill and looking at the G code it look correct. Is that correct that Z zero should be with the tool bit just touching the blank?
Dan Mauch

[ArtF]

Dan:

  Yes, the Z should be zeroed center of blank top dead center. Any idea when it went screwy? ( Also, make sure its a recent download, I just fixed a couple problems in 4th axis and nice looking gears were produced a week or two ago on that new version.

If it is going too deep, can you turn on just rooting with no root wall selected and try it, let me know what that
does and we'll see whats up Dan..

Art

[danmauch]

Yes I checked that I have the latest development version although when I click on about it says GT 2.00
I have two other problems  that I also have .
1. When I take a snap shot using the built option no picture is taken.
2. When I take a video  using that option I get a message Unable to create compressed screen.
Today I machined another blank to the correct OD of .944 for a gear that has 17 teeth
Here is a short video of the machining https://www.youtube.com/watch?v=Y6HV2cA ... e=youtu.be

It's hard to see because of the white delrin but again it is cutting off the tops of the teeth. I only have .002" vertical backlash on the Z axis.
I set the tool just touching TDC and set Mach3 Z=0.0 and the tool is centered on the centerline of the chuck.
I can email you my G code that GT produced if needed.

TIA Dan

[danmauch]

Here are two photos that show that most of the teeth are being cut off.

[ArtF]

Dan:

  Looks like the A rotation is backwards from GM's expectation. Can you reverse the direction bit so the A axis is reversed and give it another shot. When the Axis moves to the Y++ direction, the rotations should also be to the same direction.. I cant tell from the video which flank your on
so I cant tell if GM is wrong or you are, but Im pretty sure thats going backwards to the executing code.

  Sorry about the video Dan, Im finding some machines can, and others just cant capture the openGL double buffered shots.. though I was hoping those troubles went away with last update. Which compression mode did you choose? I also find most work for me, but some not at all..

Let me know what that does..

Art

[SkyMoBot]

Or send us a picture of your setup and your config screen.  I cut A-Axis gears all the time and have had great results.  Using a probe tool to get the exact offsets has been a life saver for me.

[ArtF]

>>Using a probe tool to get the exact offsets has been a life saver for me.

  It can be picky its true, thats just the nature of this type of 4th axis work,
but Dans cuts look completley backwards to me, the tool appears to moving to the Y++ while the
a axis rotates to the ++ instead of to -- direction. I suspect reversing it will make things much clearer unless
the video is fooling with me :)

ARt

[danmauch]

Thank you O Supreme Grand Master of all gearheads! That did it . I reversed the A axis direction and just cut a nice looking gear. I need to make another one as the face width wasn't quite right but since it was a test that's ok. I can fix that. I have attached a couple photos that hopefully show the involute teeth. There are some burrs on the end of some teeth. Otherwise the gear fits the circular rack perfectly. This saves me about $1070 because that's what Mercedes Benz wanted for a replacement windshield wiper transmission.  They say they don't make replacement gears so  you have to buy a new transmission. There are no after market replacement gears. It's interesting how it works. On My S320 the windshield wiper not only moves back and forth like most but unlike most it extends and retracts  during a portion of the travel so that the driver side windshield is completely wiped without hitting anything..

Thanks again.
Dan Mauch

Dan:

  Looks like the A rotation is backwards from GM's expectation. Can you reverse the direction bit so the A axis is reversed and give it another shot. When the Axis moves to the Y++ direction, the rotations should also be to the same direction.. I cant tell from the video which flank your on
so I cant tell if GM is wrong or you are, but Im pretty sure thats going backwards to the executing code.

  Sorry about the video Dan, Im finding some machines can, and others just cant capture the openGL double buffered shots.. though I was hoping those troubles went away with last update. Which compression mode did you choose? I also find most work for me, but some not at all..

Let me know what that does..

Art

[ArtF]

Hi Dan:

  The teeth on that gear look thinned ( but I cant see them clearly enough).. perhaps the bit is a touch too large in diameter..or the blank was a touch too small. ( The blank diameter is pretty sensitive and the tool diameter isnt great at reporting if its too large..

  Glad to see its working though. I tihnk Im going to bump up the priority of a 4th axis simulator. As soon as the 2.5D workbench is out to
allow better 2.5D work, I think Ill do the new 4th axis. Seeing it work is the best diagnostic I think, most of us have trouble thinking
in 4th axis, so it'd be great to have a visual way to verify what we're doing..

Art

[JustinO]

"...burrs..."

I've been cutting ABS with a single straight flute 1/16" carbide router bit. No burrs. It cost $6.

[danmauch]

I'm using a .0375D EM. The blank is .944D and there are 17 teeth. I looked under a magnifying lens at the old gear and the new gear  does look thin. The information I have is that is the correct diameter and the CNC portion of the program doesn't have an issue with the .0375D EM  The root measures at .070 which is more than the cutters width. It seems like the program is making the root wider than the bit and thus is thinning the teeth.  While it's difficult to measure the old gear teeth at their widest point is ~.092 and the new gear measures ~.072. So you think I should increase the diameter? How much should I increase the diameter? You best guess is fine.
Thanks again
Dan

Hi Dan:

  The teeth on that gear look thinned ( but I cant see them clearly enough).. perhaps the bit is a touch too large in diameter..or the blank was a touch too small. ( The blank diameter is pretty sensitive and the tool diameter isnt great at reporting if its too large..

   Glad to see its working though. I tihnk Im going to bump up the priority of a 4th axis simulator. As soon as the 2.5D workbench is out to
allow better 2.5D work, I think Ill do the new 4th axis. Seeing it work is the best diagnostic I think, most of us have trouble thinking
in 4th axis, so it'd be great to have a visual way to verify what we're doing..

Art

[ArtF]

Dan:

  Id try setting the bit size as .04 ( 7% increase for a 7% loss in width) and see what it does.
Id be interested to know....

Art

[danmauch]

In the cnc module I increased the EM size to .04 however the teeth are still thin and not quite right. Here are some pictures. I measured the root and it was still oversize in that the width of the new gear root was .078. The original gear root width is .06.
Any help is appreciated. BYW I can upload another video of this latest gear being machined.
Dan Mauch

[danmauch]

My apologies I just went out to double check the diameter of the end mill with my tenth mike and found that the cutter is .061D not.0375 . I most  have forgot to zero my caliper when I first checked it.. I'll redo the G code and see if that works better.
dAN

[ArtF]

Dan:

  Happens to all of us. :)

Im betting it looks better next run..

Art