Hello Guest it is May 23, 2019, 04:11:39 PM

Author Topic: Radius Experiment  (Read 3520 times)

0 Members and 1 Guest are viewing this topic.

Radius Experiment
« on: January 01, 2008, 09:00:48 PM »
Hello all,
Here is a simple example of problems I am having with radiusing and tool tip offsets.
If anyone would care to try this, I'd like to see YOUR results.
M3Turn
Run the attached code with t0 uncommented.. all is perfect.
                  "                     t0101         "        both X and Z offsets are "IN" the material, not away.
I changed the tip direction to 4 and the Z offset is correct but the X offset is into the material.
Then try either G41 or G42. Mine goes totally nuts.
Just interested if yous does the same as well and if you see something I'm missing.
This is really beating me down.
Thanks,
RC
« Last Edit: January 02, 2008, 08:10:24 AM by Overloaded »

Offline jimpinder

*
  •  1,233 1,233
  • Wakefield, West Yorks, UK
    • View Profile
Re: Radius Experiment
« Reply #1 on: January 02, 2008, 12:09:28 PM »
Overloaded - I am not sure what you are saying. Are you saying that you are wanting to put a radius on the end of a bar i.e. a 1 inch bar with a rounded end at 1/2 inch radius.

I do not see how you can achieve this with a sharp pointed tool which I take is a straight V shape. You need, for the picture you are showing, a tool that is cranked left, and I would suggest, a smooth radius tip of at least 90 degrees. Unles your toolholder moves as it describes an arc, then a different part of the tool must come in touch with the workpiece as it moves around.

I generally cut mine the other way, from the centre, outwards, and the tool first makes contact on its left hand side, and then as it works round, the point of contact gradualy moves to the top of the tool, to the right of centre.

Unfortunately, without some very sophisticated (sorry Art if you have done this) calculation, the result will not be a perfect circle, because you start at the true radius (the side of the tool touching the end of the work at X0 Z0), then as you come round to the side of the work the width of the tool tip comes into play and the radius is short and the tool cuts into the bar.

The answer is (I think) say with a tip of 0.125 radius is to start round from X0 Z0 - with the side of the tool touching the work, but add on the tool tip width when writing the code -  I.E. CALL THE START POINT  X0 Z0.125. The code would then be, from that start point  G2  Z-0.5 X0.625 R0.625. The radius of the arc the tool describes is always the radius you want, plus the tool tip radius.  I have used a large radius tool tip here to better illustrate the point.

As long as you use a cranked tool, the offset radius is always equal on both axis, so you could, I suppose, use an offset for the tool tip when cutting arcs. You would have to change tools to cut arcs in other directions, of course.

You could add the offsets in when calculating your offsets for the tool table, but this would be difficult to remember to add the tool tip offset on every cut. Perhaps the easiest wat would be to use T0101 for a lefthand crank tool, and then T01nn when using it to cut an arc and include the larger offset in a second offset slot.



Not me driving the engine - I'm better looking.

Offline jimpinder

*
  •  1,233 1,233
  • Wakefield, West Yorks, UK
    • View Profile
Re: Radius Experiment
« Reply #2 on: January 02, 2008, 12:11:54 PM »
I think g41 and g42 are designed for the offsets to take into account the thickness of a milling cutter - not to add thickness to a lathe tool
Not me driving the engine - I'm better looking.
Re: Radius Experiment
« Reply #3 on: January 02, 2008, 01:02:27 PM »
Hi Jim, and thanks for taking the time.
The tool is ground and positioned so as to face and turn.
 If I am understanding the manual correctly, (no guarantee), using G41 or G42 along with T# and OS# automatically compensates for the tool nose radius and takes care of the calculations, mainly for angled cuts but seems it would work on a radius as well.
Maybe the part rad. is driving it nuts.
 

I'm going through the manual ONE more time.

Thanks Jim,
RC
« Last Edit: January 02, 2008, 01:07:50 PM by Overloaded »

Offline jimpinder

*
  •  1,233 1,233
  • Wakefield, West Yorks, UK
    • View Profile
Re: Radius Experiment
« Reply #4 on: January 02, 2008, 08:52:42 PM »
I apologise profusly to Art if he has done it, but I seem to remember a post in the past that says these are NOT implemented in Mach 3 turn becasue of the amount of maths involved.

I know it works in Mill, becasue I use it to add cutter compensation, I have tried in Turn, but never suceeded. The next time I have the machine as a lathe, I will try.

I did some handrail stanchions for a miniature railway engine not too long ago - basically a vertical pole, with circular knobs at the top and middle. I had a difficult job to make the curve of the knob the same on both left and right hand sides. In the end I used a fairly sharp tool at 90 o to the work (on brass), but it still left flats.
Not me driving the engine - I'm better looking.
Re: Radius Experiment
« Reply #5 on: January 02, 2008, 10:17:08 PM »
Thanks Jim,
It's definetely some "BUGS" about it. Maybe big as them Oklahoma CRICKETS !   :o   :D
I have been informed that it is on the "TO DO" list.
 
RC    ;)
« Last Edit: January 02, 2008, 10:24:30 PM by Overloaded »