Milling Tight Inside Corners???

[Frogblender]

Hi... I wish to cut a "square" hole in a sheet of 1/8" 6061, with the corners of the square hole having a radius as small as possible (ie. .015"); I don't want to resort to EDM/punching/broaching/hand-filing/crazy rhohedral bits etc.

My plan is to:
- rough the square using a .125"dia endmill, which'll give .062" corner radii.
- Then use a .031"dia endmill (or perhaps even smaller?) for finishing, which'll give .015" corner radii - which should be tight enough.

But I need a gcode generator to create the multiple light cuts (.002" each?) so the small endmill doesn't break. In another post someone called this "trichordial" cutting, but I can't find any such tool in Mach3. Can anyone steer me in the right direction?

[jalessi]

Frogblender

Set the post processor or (tool path) in your cam software to the step over the tool requires not Mach3.

Jeff...

[Frogblender]

Frogblender

Set the post processor or (tool path) in your cam software to the step over the tool requires not Mach3.

Jeff...

I misspoke - I meant BobCad with Fanuc post proc - not mach3

[mcphill]

I misspoke - I meant BobCad with Fanuc post proc - not mach3

You set the stepover (your .002" cut depth) in the BobCAD machining step. What version are you using? Can you post the file?

[ryansuperbee]

I might have the wrong idea here. But could'nt you program and run a small drillbit on all the corners and then run your endmill between the holes? just a thought.

[Frogblender]

I might have the wrong idea here. But could'nt you program and run a small drillbit on all the corners and then run your endmill between the holes? just a thought.

Unless the endmill is the same dia as the drillbit, you won't get a clean square- there'll be little concave triangles sticking out.

[Andre' B]

Just open up notepad and whip up a little macro program.

[Frogblender]

Just open up notepad and whip up a little macro program.

That is a very nice and educational little picture there. Thanks! It seems like that macro clears only 3 corners? But I get the idea.

The only issue with that macro is the tiny endmill will be running along the long edges of the hole - edges which have already been roughed out - greatly increasing machine time. The macro I need a) just concentrates in the corner, b) ideally has fancy sine/geometry stuff to evenly remove the material the roughing bit couldn't reach, c) approaches the material from the side (ie. the end of the endmill never gets touched) - the tiny bit will flex much less if you stay away from its end.

[Andre' B]

It only clears one corner. As written it would be for using a 1/16 endmill to clear out a corner left by an 1/8 endmill.
Edit:Edit: It is written for a 1" square centered on zero so the first G0 move puts the tool 0.01 away from the start of the arc left by the 1/8 tool.

Would need 3 more subs for the rest of the corners or make one sub that is much more complicated.

Improvements would be to add arc in and out moves, and get rid of the Z move up and down at each level (safe but it takes time and should not be needed here).

Edit:
I have found that for very small end mills small Z level steps tends to be more forgiving then side milling.

[Grifftek]

I took a stab at the program, you can see some snapshots and a tool path simulation here!

On the last picture there is a small movie camera icon, click on it for the simulation video.

if you need the posted code, let me know and I can email it to you.

Bill Griffin

[BurrMan]

If your like me and just want the softwrae to do it:

In BobCad I just drew my square then drew squares the size of the bit selection in each of the 4 corners so I could break the geometry then create a contour. I could then create a profile on the 4 contours. Many lead and pass options. In this screenshot I used a circular lead in and out. This shows all in one shot but I think BobCads Profile feature can do "Spring Passes" so you can take .002 swats at it or whatever the material/amount calls for.

[mmc005]

Burr,
Like you, I always want to have the software do the work for me. I like the idea of the macro but it's not needed for this type of profile. There are many ways to attack this issue, I would break the profile before and after the radius then use the spring pass feature(if it works) to generate the moves for me, I would also create a line 90 degrees to the wall. I would also use a vertical lead in/lead out unless you need the G41/G42 code for your program.