Author Topic: making parts to size on customer prints  (Read 6559 times)

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Offline SDConcepts

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making parts to size on customer prints
« on: November 23, 2008, 11:17:31 PM »
i am new to using mach 3 and was playing around with cutter comp on my cnc mill.  i am currently trying to cut an arc with cutter comp and it doesn't seem to be working.  i would hope that i could ultimately use cutter comp to be able to run the job with multiple different sized endmills.   so far though i haven't had any luck and i've had to go back and manually fix the parts because the cutter just wouldn't take enough material.  i guess is was lucky that it was not enough and not too much.  i'm just wondering how good of luck people are having making parts to print? 

Offline jimpinder

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Re: making parts to size on customer prints
« Reply #1 on: November 24, 2008, 03:59:18 AM »
Cutter compensation is one of those subjects that comes up very regularly.

Yes, you are quite right. Using cutter compensation yOu should be able to program the machine to cut as per the drawing, and the machine should then make allowance for the width of the cutter, according to the tool table.

If you search this forum, a complete explanation with diagrams was given by Graham Waterworth as to how it should be applied, i.e. left or right hand, depending on what result you wanted to achieve.

Having said that - and I am sure someone will tell me - HAVE WE LOST THAT WHEN WE UPGRADED THE FORUM - ANYBODY?? :-\
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Offline jimpinder

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Re: making parts to size on customer prints
« Reply #2 on: November 24, 2008, 04:12:24 AM »
If you are experimenting, you must remember that Mach 3 must run into cutter compensation, In other words, it is no good lining up your work, then switching on cutter compensation and expecting Mach 3 to jump to one side or the other to apply the compensation.

If you are cutting, say, a circle in a plate, then start at the circumference of the circle (without cutter comp). Your first move should be to apply cutter comp - G41 or G42. The second move is move round the circumference of the circle a short distance - say a quarter turn G2 or G3. This is the move that Mach uses to apply the compensation. The third move should be then to cut the circle, drop z, then   - G2 or G3 Bear in mind that the tool table must have the cutter diameter, and the correct tool must be selected.

G41 and G42 depends on whether you are using G2 or G3 (which direction your tool is travelling) and whether your tool is inside or outside the circle.

Try replacing your cutter with a felt tip pen, and drawing it out on a sheet of paper, you will be able to see the different paths, particularly if you try doing the circle first, then using compensation. The way Graham drew it, I am quite sure he has it in his head as a fixture, but to us lesser mortals, it could be a good reminder to then pin the diagram on the workshop wall.

« Last Edit: November 24, 2008, 04:17:15 AM by jimpinder »
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Offline RICH

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Re: making parts to size on customer prints
« Reply #3 on: November 24, 2008, 07:10:02 AM »
I have done many pieces to size using cutter compensation. Let me make a few points without getting specific on programing  or the tool tables and such. A lot of my mills are regrinds done by me on a Darex end mill sharpener.
I measure the end mills using 3 or 5 flute anvil micrometers to determine the endmill diameter. I think one should do some testing of their machine to see just how well it can hold dims. Try milling an outside circle as a test and maybe at
 a few different diameters or an inside circle. That will quickly tell you what to expect as it takes into account
the "whole system" ie; tool, depth of cut, feeds /speed, table movement, material, cutting fluid  etc..  If the system doesn't have the ability in movement or cutting to begin with you can't expect software to make up for what is lacking. With some testing done and knowledge of what can be expected, you can appropriately try to make up for those shortcomings to some tolerance.
In summary do some testing and apply to your machining.
RICH



Offline SDConcepts

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Re: making parts to size on customer prints
« Reply #4 on: November 24, 2008, 07:46:59 AM »
ok a little back ground on me... i have run mills in the past so i'm familiar with lead ins for cutter comp.  i guess what i'm really after is the limitations of the software.  i have an IH mill and with that i have cut plenty of circles using the wizards and they were right on within .0005 of the actual diameter.  the current print i'm working at needs me to put an arc at the base of the part.  basically i need to remove about .100 of material and then throw an arc profile on the part so it can be welded onto a tube. 

in mach when starting cutter comp is it necessary to have both an x and y move?  or will just one of them suffice set cutter comp? 

Offline jimpinder

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Re: making parts to size on customer prints
« Reply #5 on: November 24, 2008, 02:52:27 PM »
I will put my hand up and admit, that after I wrote my last post, I went into the workshop to try it, with a pen in the spindle chuck. No matter what I put in, in what order, I was still getting the pen to describe the arc, circle, or line, without any compensation. I am at a loss.

If you look on the GCode tag on the milling 1024.set, there is now a description of many of the  codes, including 41 and 42

Rich - gives us a clue in what order to put the code in. Does it only work in a GCode program, or can you access it from the MDI line. The codes at the top of the display change as you enter them.

Are there any settings in Config that I am missing.
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Offline SDConcepts

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Re: making parts to size on customer prints
« Reply #6 on: November 24, 2008, 03:12:04 PM »
i agree this is a serious problem with Mach 3.  i am having doubts of running customer parts on what i have to believe to be hobby equipment now.  even with tool paths generated in a cam program, how does it offset correctly?  what if your using reground end mills?  what if your end mills aren't spot on the diameter?  how can you compensate for this?  i've run a few jobs on this setup and basically all of them i had to rewrite the path when i swapped end mills.  this really should not be the case. 

Offline RICH

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Re: making parts to size on customer prints
« Reply #7 on: November 24, 2008, 08:06:52 PM »
You can cut my head off on this one!
I used a different control program and controller for many of those pieces that were made. So stupid me 
just ass..u..me..d it worked the same way in MACH. You had to have a move before the compensation
and the compensation lagged one move in the program before it was implemented as it needed to know how long the next move was before it compensated for it with the same amount applied for all the next moves until canceled.
So just forget what i just said as it may not apply to how MACH implements it.

I also found that things worked better if i just let the CAM program generate compensated code rather than use compensation. So in using Mach i continued to used that system.  Which is fine if almost everthing you make is a onezy like me, but would be a PITA for a lot of parts to do and tool wear was involved.

I may have saved Graham's post as it was a good one. Let me look rather than confuse.
RICH

Offline RICH

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Re: making parts to size on customer prints
« Reply #8 on: November 24, 2008, 08:25:58 PM »

Offline SDConcepts

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Re: making parts to size on customer prints
« Reply #9 on: November 24, 2008, 11:08:04 PM »
I may have been a little to hasty...  i sat down and looked through my programs, it looks like mach is trying to compensate, but i can't tell without actually running a part.  i will try draw some tool paths tomorrow using cutter comp with different sized tools as per the tool table.  i am also under the impression that the wear offsets don't work.  is this correct?  ultimately i'm not that worried about it, but its just good to know.

thanks

Jerry