Rotary machining reference question...

[PeterM]

This is tricky to describe and maybe this is more of a machine related question but I will try.....

I am using VCarve Pro 9.5 to generate g-code to rough mill and then finish mill some wood handrail fittings. I create 2 separate files - 1 for rough machining and the other for the finishing pass. I am confused about something....
After successfully referencing the machine on it's X,Y,Z,A & B axis, I load the material into my Legacy Artisan CNC and and then machine the part with with the rough machining pass. If I then re-reference the machine without removing the rough machined part, I notice that the stock doesn't rotate back to the spot that it originally was orientated at in the beginning - it looks maybe 15% off from it's original position even though the machine has been successfully referenced again. Would anyone know why this is so? I am very confident that the various parts of the configuration that hold the part are very tight and haven't allowed the part to rotate by accident. My stock is solidly affixed with multiple screws through a 4 pronged plate. I'm concerned that if I start the finishing pass, that I'll somehow be off from the correct orientation....
Thanks,
Peter

[TReischl]

I would be concerned too.

Obviously referencing is all about tripping the switch next to the plate fixed to the chuck.

First question: I do not see a reference mark anywhere in the picture. So how do you actually know that it has not returned to the correct location other than your eyeballs are not happy with what they are seeing?

Second: Is the switch moving at all?

Third: The plate used to trip it, is it secure? Looks secure to me, but pays to check it.

Fourth: Is it possible the chuck has rotated on the spindle? Easy to check that too, better not be loose at all.

This is kind of an ugly situation because you are in the middle of a project, otherwise you could put a test piece up and do some testing to see what is going on.

Had this happen to me a while back:

I use a big honking 5 inch 4 jaw self centering chuck on my rotary. It gets taken on and off regularly. It is mounted to a 1-8 TPI spindle. There I was, in the middle of a long project and things started to go wrong, real wrong. Cutting in the wrong places. YIKES! Investigation revealed that the chuck spun loose, probably during a rapid rewind. This chuck does not have a tapped hole for a grub screw to prevent that from happening.

Lost steps would not cause the problem you think you have because you are referencing to a mechanical switch, so no worries there.

BTW, I like the reference switch setup you have going there. May have to check into implementing that on my machine. That will take some investigation into Mach 3 since I do a lot of turning with commands like G1 X10 A45000 which would cause the switch to be activated many times during the cutting. Obviously have to set it up as a home switch only, not a limit.

[PeterM]

Thanks for posting a response....
To answer your questions,

1. It's not visible in the picture, but I have diagonal lines forming an "X" on both ends of the stock from when the stock was square. I made a point to mount the stock,plates,etc so the orientation was all up and down and side to side if you understand what I mean. Also, when I had everything set up in the beginning, I had the 4 pronged mounting plate (which is attached to the end of the stock) oriented straight up and down and side to side, but as seen in the picture it is rotated a bit to the left even though the machine is referenced.

2. The switch is not moving at all.

3. As mentioned in the first answer, the plate is very secure.

4. I don't believe anything has rotated in the spindle. I have that tightened down well.

Part of the problem is that this has occurred a number of times before. I have to think this is an operator issue. There is something simple that I'm not getting, or probably not doing right. I'm waiting to speak with the CNC manufacturer who uses VCarve....I think they might know.

I resorted to going back to bundling both roughing and finishing into one file and then ran everything successfully. I had to start over with a new blank. I just would prefer to run 2 separate files so that if something goes wrong in the process, I wont have to start the entire program over again from the beginning. I've had 50/50 luck with starting the program somewhere in the middle of the g-code.

Thanks,
Peter

[IslaWW]

Peter...
When you speak to them, see if there is a restart option. Most control softwares allow you to painlessly restart a file at where you left off or any other operator selected line.

[TReischl]

If you suspect that you are losing steps there is an easy way to check that is very accurate:

But a blank in, make a witness mark.

Enter an MDI command for 360000 degrees. This will cause the chuck to rotate ten full times. If this does not show an error then the next step is to put a real program in the control, run it without doing any cutting and see if it stops at the mark.

I hesitate to bring this up. . . . . .

A friend and I collaborate on designs. I run Aspire 4.5 and he runs 10 something or other. I sent him a CRV3D file of a complex rotary design, it has elements that crossover the 0 degree line. Lo and behold the edges did not match up, by a lot, like .06 on a 4.00 diameter. Well, we created a simple test program that merely engraves a line around the diameter to see how that worked out. It works fine on mine. It doesn't on his. So then he created the same design from scratch on his, same result, ends did not match up.

It is easy to see this in the program files. Mine has the commands A0.000 and A360.000. His? Something like 359.6 and .4 something or other. Huh? What? Since I am not running 10 I have not posted the issue because I do not have an issue with 4.5.

Thought I would mention this before you run into that problem too. Things like this cause us to get nuttier by the day.

[gregk]

If you suspect that you are losing steps there is an easy way to check that is very accurate:

But a blank in, make a witness mark.

Enter an MDI command for 360000 degrees. This will cause the chuck to rotate ten full times. If this does not show an error then the next step is to put a real program in the control, run it without doing any cutting and see if it stops at the mark.

I hesitate to bring this up. . . . . .

A friend and I collaborate on designs. I run Aspire 4.5 and he runs 10 something or other. I sent him a CRV3D file of a complex rotary design, it has elements that crossover the 0 degree line. Lo and behold the edges did not match up, by a lot, like .06 on a 4.00 diameter. Well, we created a simple test program that merely engraves a line around the diameter to see how that worked out. It works fine on mine. It doesn't on his. So then he created the same design from scratch on his, same result, ends did not match up.

It is easy to see this in the program files. Mine has the commands A0.000 and A360.000. His? Something like 359.6 and .4 something or other. Huh? What? Since I am not running 10 I have not posted the issue because I do not have an issue with 4.5.

Thought I would mention this before you run into that problem too. Things like this cause us to get nuttier by the day.

Would you be so kind to attach the test file that does not cut correctly for your friend?

Greg K