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Issues With Parts Coming Out To Size

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native34

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#1
Hello, i am having an issue where my parts are not coming out to size. The problem seems to be only with the outer profile. everything else is coming out within .0005". Where the outer profile is coming out exactly .010" over sized. I have tried several different parts and several different cam programs, and nothing seems to help. it is always coming out with these dimensions. I have re calibrated the mill several times. The backlash is around .0001-.0003 in x/y and .002 in Z. This is very repeatable. I have been pulling my hair out for a few weeks now trying to figure this out, with no progress. Has anybody else had an issue like this?
 

TomS

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#2
Hello, i am having an issue where my parts are not coming out to size. The problem seems to be only with the outer profile. everything else is coming out within .0005". Where the outer profile is coming out exactly .010" over sized. I have tried several different parts and several different cam programs, and nothing seems to help. it is always coming out with these dimensions. I have re calibrated the mill several times. The backlash is around .0001-.0003 in x/y and .002 in Z. This is very repeatable. I have been pulling my hair out for a few weeks now trying to figure this out, with no progress. Has anybody else had an issue like this?
Have you measured your cutter diameter? It could be under size. Thinking out loud.

Tom S.
 

native34

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#3
yes i did. i used the same cutter for both the inside and outside ops. I als performed spring passes on both as well. They were also climb cuts. This is one of the wierdest things i have seen and doesn't make any sense to me.
 

JimDawson

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#4
An interesting problem.

Are you running the insides as pockets or profiles? It sounds like something is adding a tool offset into the outside profile. You have eliminated calibration and CAM as the problem. Which leads me to conclude that something in the controller is handling the g-code incorrectly. G41, G42 being turned on when it shouldn't????? Maybe issue a G40 to turn all comp off?

Look at the g-code and do the calculation to figure where the tool should be, then compare that to the actual tool position when cutting. The easiest way to do this is to make about a 4 inch square with an inside 3 inch pocket, then run that. Try a profile on both inside and outside and see what happens. To check tool position vs. g-code you can just run an air cut and look at the DRO.
 

native34

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#5
Yes Jim my final op on both inner and outer is a profile op using the same tool and using computer for cutter comp. the part I machined tonight was just that. A rectangular blank that I machined a rectangular pocket inside and outside. Both roughing ops were 2D adaptive pocketing ops. Followed up by a 2D contour for finishing op, with a final spring pass.i have done several of these different type of practice parts using different machining and drilling ops while calibrating my mill, but the results are the same. All features and hole placement comes out to spec, except for the outer profile.
 

JimDawson

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Whatever is going on I'm 99.9% sure the problem is not hardware. Your machine must be calibrated correctly and the encoders are reading correctly or else the other dims would be off. So the only thing left is software/firmware.

One thing that comes to mind is run the outside profile as a separate op and set a negative (-0.005?) roughing clearance in the CAM program, see if it comes on size. Worst case this might give you a workaround. If this works, then it might point to a direction to look.
 

derf

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#7
Before you beat yourself up too bad, sometimes it pays to look in the simplest places. I had a similar experience, and when it got right down to it I confirmed the machine was good, the tool was good, the program was good, but the guy measuring wasn't.:dejected:
 

native34

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#8
Jim, I will give that a try. Derf I fully understand where you are coming from, and would tend to agree with you, but I have measured these part using, digital height gauge, CMM, calipers, and mics. They all tell pretty much the same story. I found a post on one of the boards that I need to follow up with regarding a bug in Mach and g28.1, g92, causing this guys parts to come out slightly oversized on outside and slightly undersized on inside profiles. The difference between my issue and his is it is only happening on the outer profile to me. Everything else is coming out to spec.
 

native34

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#9
Ok, Jim. I changed my cam op I made the tool .005" smaller than it was in the previous op and cut the outer profile again. The part measurement went from 2.110x1.610 to 2.1035x1.6035. So basically what I found out is that I have to lie to the system and tell it the tool is smaller than it actually measures. To me this doesn't seem like a good solution but one I may have to live with, until I can pinpoint the real problem. I really think the problem is with mach3 but because they stopped supporting it. My only solution is to either buy mach4, buy new hardware and change to either uccnc or linuxcnc, as neither of those two are compatible with the ehternet smoothstepper.
 

JimDawson

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#10
That's strange. I have never seen that problem before. I wonder if there is some setting that is ''stuck'' in Mach3. I have seen Mach3 do some unexpected things. When it is cutting oversize, does the DRO agree with the G-code, I would expect to see a difference given the problems.

Does your CAM software not have a roughing clearance setting for each op? I use CamBam, and it has roughing clearance for pocketing and profiles. It will take a negative or positive number. On an outside profile, a negative number would cut a smaller part. I use that for cutter comp, rather than do it in the controller software.

With the cost of hardware and time spent, purchasing Mach4 might be the least expensive option.
 

native34

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#11
I'm using fusion 360, so I'm not sure if it has that setting. Im pretty new with fusion. Still trying to figure it out, I'm used to using Mastercam and bobcad. I had the same problem with them as well. I just found something on the warpt9 site that says that there are some. It's with .066 version of Mach and the recommended fix is to revert back to .062 release of Mach and the latest version of ess driver. It doesn't specifically mention my issue but it is worth a try at this point.
 

native34

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#12
Ok, here is the latest. I removed Mach 3.043.066 and installed 3.043.062, re-setup the part and ran the programs. I'm happy and sad to say that there were no chips produced. Happy that my mill has so little backlash that it is able to reposition to a great degree of accuracy, and sad to say that it didn't have any affect on my problem. The outside profile is still to large. I really at a loss on this one. I opened up a support ticket with machsupport. Hopefully they will have some insight into what is going on.
 

JimDawson

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#13
I'm at a loss too. The only machine I have here with Mach3 on it is Alloy's Shizouka. I guess I'm going to have to fire that up and make sure that it is not doing the same thing, we never really checked it out for accuracy. Maybe I can find something. I'm glad I'm not having that problem, I couldn't sleep until I figured it out.
 

derf

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#14
Why don't you write a simple program , without tool cutter comp and see if the sizes jive?
 

tmarks11

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#15
sounds like a CAM problem to me. Draw a simple box and CAM the outside with one pass. Look at the g-code and see if the XY coordinates are where they should be. I am betting they are not.

Look in the CAM menu where you are defining the cut. One of the tabs has a selection for "stock to leave" like you would do on a roughing cut. Maybe this is the problem. I don't use Fusion360, but I use HSMWorks, which is the same CAM program.
 
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