Cutter Comp Applied on Arc Move

[Randy Morton @ Clem Industrial]

I hate this error. It annoys me. It also annoys me because I cannot seem to formulate a reason why sometimes I have absolutly no issue using it and other times every instance that has wear gives me this error.

 

In this instance, I am doing a simple 2d contour. Using a 5/8 endmill to circle mill a bore. Easy enough? Apparently not. The contour starts and ends @ the 12 oclock position and then leads in or out. All looks normal on verify. Going with ccw arcs to climb mill and I get this aggravating error.

 

Lead in/out settings are set as such;

 

Line = 0%/Tangent

Arc = 100%

Enter & Exit at midpoint in closed contours is checked

Gouge check entry/exit motion is checked

 

All others are unchecked.

 

Could someone pleaes explain this to me so I dont have deal with it again? Grr...

 

Thanks

[dgriffiths]

I hate this error. The way I fix it is I enter a small value in the line lead in/out. This way it picks up the cutter comp on the line move and should do away with the error. HTH

[Zoober]

Randy, you need a perpendicular entry then you can arc in/out. without it, the post will try to put G41 or G42 in a G2/G3 line, which is illegal.

 

Instead of.....

quote:

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Line = 0%/Tangent

Arc = 100%

Enter & Exit at midpoint in closed contours is checked

Gouge check entry/exit motion is checked

---

try...

Line = 100%/perpendicular*************

Arc = 100%

Enter & Exit at midpoint in closed contours is checked

Gouge check entry/exit motion is checked

 

HTH

[Randy Morton @ Clem Industrial]

Sound logic to a simple problem. I added a 10% line lead in/out and it eliminated my problematic error.

 

Sage advice I will hopefully always remember. Thanks guys!

[Zoober]

[Thad]

quote:

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I added a 10% line lead in/out and it eliminated my problematic error.

---

I hope you also took Robert's advice and used a perp move instead of tangent. If you didn't, you may end up with other problematic errors down the road.

 

Thad

[Smit]

If the bore is small you can set an entry point to the center of the arc and check the use entry point in the in/out dialog. This will give you a short line move automatically. Just be careful your arc entry doesn't gouge the bore.

[Guest]

Changing your start point to somewhere else that does not have the lead in/ lead out happening on an arc is a quick fix as well

[Randy Morton @ Clem Industrial]

Thad,

 

I gave the perp entry vs the tangent entry a try, and maybe, since my lead is not very big, I cannot really see any difference. I posted both ways out and the has obvious differences, but the cimco backplot looks pretty much the same for either way. What kind of problematic errors could one run into by continuing to use tangent?

 

Smit,

 

I have used that in the past and still likely will on occasion for things but the problem I run into is that the operators say 'I dont understand what its doing'. It starts on XY Zero, then move to (for example) X.625, Y.9475, arcs in, circle bores, arcs out to X-.625, Y.9475 and then moves to XY Zero again. To me it makes perfect sense, but even the people who 'claim' to have years of experience complain that they do not understand why it needs to make so many moves and how the moves are accomplished. As such I try and avoid the XY Zero confusion if possible, but I would personally rather use it on small bores.

 

Related Question: Lead in/out Overlap. I see the obvious benefits to this, read the help file about it, but I dont understand what units the overlap is in. Is it percentage of the diameter? The cutter? Often, if I wanted to ride the cutter all the way around a second time I would have to put in like 300 or 400....but I have no idea what this means and am just going off the backplot 'looks'.

 

Thanks!

[cadcam]

or sorry to say by a fadal they support cutter comp on an arc.

At least the old ones.

[gcode]

Tell your operators to man up and run the damn code

 

as for the overlap, it is a distance.

If you insert Pi*D in the overlap field you'll get a full circle

[Randy Morton @ Clem Industrial]

Thanks Gcode!

[jeff]

Someone posted this handy tip a while back:

((hole dia - tool dia) /2 )) x .4142

put the result in your lead in/out for your tangent line length AND your arc radius, and then use 135 degree for your sweep.

Your tool will now start and end in the center of the hole.

[Zoober]

The reason for all of this is pretty simple. When a control has to calculate cutter comp, it must be able to position itself tangent to the current and next moves to be able to stay comped for the profile. When you turn on comp on in an arc move, where on the arc must it become tangent to the next move?

I have always been taught to turn comp on perp to the next move, and turn comp off perp to the previous move. that way, it will ALWAYS do what you expect, and NEVER gouge.

 

Example:

[crazy^millman]

Funny Robert, I have seen the Oi controls not like the direct move in they will not apply the cutter comp till the 2nd move. I always put a 1 to 5 deg arc move in and solves the problem. Most machines work just fine, but these Oi controls act weird.

[Zoober]

Ron, I haven't seen that(not saying you're wrong , I just haven't seen it). We have two 0i controls, and I have never had a problem with the direct move approach as long as the approach move is >.0002 larger than the largest amt that will be in the wear offset table. This works on our 15, 16i, 18i, and 0i's. Even works on our Siemens 840D and cough:Fadal:cough

I will be looking out for it tho. Thanks.

[crazy^millman]

Well it is the weirdest thing I have ever seen. Our Mazaks, Okumas, and older Fanuc does it with no problem but these 2 machines, by different builders with the Oi control do it. Not that big a deal only 2 extra lines of code for ever comp move.

 

Is what I did for about 2 days on some parts till I figured it out. The code looked Flawless, but I finally sat there and watched it run this 3 hour program and when it started moving the Y axis along a long cut to start applying the Wear comp they were using is when I caught it. We were only talking about .0034, but it was throwing the parts out of print and we could just not figure out why until I added a X move to the Straight in Y move then it was fine.

[Thad]

quote:

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What kind of problematic errors could one run into by continuing to use tangent?

---

Probably an occasional gouge, or comp error at the control (cutter radius too big blah blah blah). Yes, it *can* be done and you may go a long time without errors, but the best (least problematic) way to do it is to use a perp move. I doubt you'd find a text book, reference manual or online source that *doesn't* recommend using a perp move to turn comp on and off. Lastly, I'll bet there are some controls that can't use an arc move to turn comp on and some that can't use a tangent move to turn comp on...but they'll ALL be able to use a perp move to turn comp on. It's just "the right way."

 

Thad

[P_Scott]

Randy@SFI,

 

A sure way to get those bores without having to mess with Lead In/Out and comp errors is to use the Circle Mill toolpath instead of a Contour. The Circle Mill has parameters for things such as "Start at Center" and "Perpendicular Entry". Usually I set the "Start at Center" by default and ignore the "Perpendicular Entry". The other thing you can do with Circle Mill is if you pick the arc itself you don't have to input the size of the circle to mill. Or you can simply pick a point and that gives you the option to type in the hole size you want. HTH

[Guest CNC Apps Guy 1]

quote:

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...It's just "the right way"...

---

Indeed... 100%, ALL THE TIME EVERY TIME.

 

Why SETTLE for might, possible, etc... when you can have 100% guaranteed every time?

[MotorCityMinion]

This may work as a quick fix:

Machine type, control definition, cutter compensation, SELECT: Start and end cutter compensation above part. This may also limit your options for start point positioning. This was an option in the MPMASTER.control and may not apply to your control definition.

 

WE have a few Fadals, I run the Haase's and Makinos and whenever I need to run a program that was posted for the Fadals, there's a high probability that it comps on the arc. GRRR. I then add comp (manually) to the first move out of the gate, and cancel comp after the last Z move. I consider this a less than polished technique but it makes chips none the less.

 

When all else fails, I manually program a cutter path that produces a parachute, or ice cream cone shaped cutterpath using a 45.deg straightline move prior to ramping on the circle. I exit the cut using the same technique.