Sharp Corners in Plating

[John T]

Hi Art,
I know that the corners in plating cannot be any sharper than the curvature of the bit being used, however the corners do not appear to be as sharp as they might be.  Its almost as if the machine is "getting ready" to make the corner and actually starts ahead of time.

What settings will give me the sharpest possible corners?

John

[ArtF]

Hi John:

  You mean outside corners? They should be perfectly sharp.. 
  On the other hand you probably mean an inside corner of the tabs? Show me a photo and Ill try to figure out whats up.
Your right that an inside corner will never be sharper than the radius of the bit itself, but if the bit size is proper for the
Gcode that was made, it shoudl be a perfect radius of the bit itself. You DO have to measure any bit though, its not unusual
for an .125 to be found when measured to be .13 or a metric equivalent size, which means the Gcode generator didnt make the
code to an exact match, and just about the only place youd notice is in an inside corner. I use a laser on my plates and havent had any
trouble with them , but then Im going from a dxf to the laser directly with a compensation kerf added , Id like to see whatever effect your
seeing just to make sure we're speaking of the same thing. :)

Thx
Art

[John T]

Hi Art,
Unfortunately even the outside corners are rounded off.  Here are a set of photos that hopefully will show what's happening better than I can describe.  The bit being used is a 1/16" and the hole in the center of the cut was cut with the same bit as the rest.

As you will see from the screen shots everything looks good until the cut is made.

PS  The tab size won't go under 0.5"  - is that normal?

[ArtF]

John:

  Ive just uploaded version 4.87 to correct a problem I found in plateing and a display bug for opengl..

This will not solve your issue though. ( Though it will help with the plating changes being properly updated when
you change them).

  Now to your problem....

  I checked here and I get square corners. Your rounded ones can be caused by a couple things..

The most important things to check is firstly, when the gcode loads in mach3, do the corners look square on the
toolpath screen? An outside corner which looks square in the toolpath should be square when cut. Think about the tool
bit as it moves, if it does a 90 degree direction change, the result is a square 90 degre outside corner..

  So if your path looks 90 degrees on the outside corner, then the path is good. SO the thing most likely if thats
the case is your setting of CV in Mach3. CV ( constant Velocity) concatenates linear motions to make things run fast.
It does this by blending two motions together using the acceleration setting for those axis. So if you use very low acceleration,
you get a much rounded corner. Raise your accel and the rounding goes away. ( OR use exact stop mode for a plate cut)..


Let me know if this seems the case, or send me a photo of the toolpath, if it doesnt have square corners then perhaps I
have a bugt Im not seeing..)

Thx
Art

[John T]

Hi Art,
Problem solved.  The corners are really sharp ie to the limit of the bit.  I never even thought that the acceleration in Mach3 might be causing this.

[ArtF]

excellent...

  ( Good thing I wrote Mach so Id know..lol )

Art