Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Keith on June 12, 2006, 03:08:25 PM
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Not sure why but after a few different attempts and different sizes,the 'circular pocket' wizard seems to construct a small 'flat' at the extreme 'Y' positions (it may be doing this throughout the spiral but not sure. Looking at the code all looks well but I wonder if it is because the 'R' command is used in place of a g interpolation; I had heard that the 'R' command works out better for arcs than it does for complete 360 degree moves but I can't substantiate that. Regular circles work fine on my machine. Also,an 'H' command comes up,I'm unfamiliar with this command.-Keith
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Hi Keith,
The flat could be cutter flex or backlash.
For your information :-
Circular holes can be cut very easy with the following commands.
Hole is at X0 Y0 with a radius of 1.000"
G00 X0 Y0 (move to start)
Z-.1 (move to Z depth)
G01 G41 X1. D(offset number for tool rad) F5. (move X pos+radius and use compensation)
G03 I-1. (do a full circle cut)
G00 G40 X0 Z1. (rapid to X start and Z safe)
M30 (end)
Graham.
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Hmmmm...right...backlash. My machine has a enough to go round. It's a Sherline and despite many attempts,I'm plagued by it (although it mostly gets thrown off by 4-5 thousandths or so,I still go nuts seeing the numbers off...I always make myself look at exactly what a thousandth is when bummed).Although why does it cut a circle properly but not a pocketed circle?(yeah I use g03/02, that you posted).-Keith
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Doing a normal circle you only have 4 direction changes, with a spiral pocket this is multiplied by the number of arcs cut, so the backlash is highlighted. Also the cutter can be pulling and pushing the table at varying amounts as the circle gets bigger.
Graham.
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Try:
G13 I.5 F10
IF you have the flats it is time to start working on the mill :( Check your gibs and see that you have good nuts on the screws.
Hope we can help!
Brian
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The gibs look okay,my concern is exactly how to adjust the backlash screws. Documentation on that is mighty slim in the Sherline documentations and talking to people there usually winds up with my pet peeve of everyone answering questions qualified by a pause and then..."I think". I've looked at that documentation so many times without really being able to figure it out. Anyone with a Sherline that has(fiured it out),please do enlighten me.
And hey,thanks for G13,I've been so engrossed in writing code 'long hand' that I never realized there was a direct call for any kind of pocket!-Keith
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Posting for Graham who says:
if you modify your nut like this you can remove most of the backlash.
By putting two grub screws into the small holes and nipping them down
you can adjust the lash.
(You can view image here,I can't seem to be able to insert and image on the post):
http://www.lightlink.com/keith/Nut.JPG
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I have this EXACTY same issue. Nice little flat areas. I've tried almost everything possible. Making the cuts as small as .005 at a time. Different size end mills. Still makes me a nice flat spot on the extreme X positions. Very frustrating. I don't know if it's me, my router, or my code.
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Is the flat always the same length independent of the circle diameter, if it is then it sounds like backlash or movement in the gibbs, if it varies then it could be cutter pull/push.
If you use very high helix cutters this can help reduse pull.
Graham.
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I haven't tried the high helix cutters. Good suggestion.
I think your right on with cutter push pull. The gantries on routing tables don't like alot of torque applied lateral. Not the most rigid for sure.
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Hi,
I have had great success with 60 and 75 degree cutters, they transmit the cutting force more in the Z then in the X & Y.
The only thing to watch out for is that you have a good hold on them or they pull down in the chuck.
Graham.
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I just successfully 'knocked out' my 'flats by a little bit more attention to 'back-lash' if that gives anyone some hope.-K
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Excellent news Keith, theres hope for all.
Graham.