What if.... I need to change a bit in a very long project?

I designed the Aluminum part on Inventor and created the tool paths on MeshCAM. I import from meshCAM into easel. I have worked out most of the upgrade bugs in using Aluminum and things are going moderately well (using X-controller, a Super-PID speed control on my Dewalt 611, Nema 23’s all around, and a rail clamping system). I even fashioned a vacuum on my router and the aluminum I am cutting is absolutely cool. However in my 20th hour of this job I am beginning to wonder how long this cheap 1/8" bit will last. I have been pausing the job at night and that works fine, but if I pause the job and move the spindle; will it work like my 3d printer and find the last place it was working to restart? Or is it relying on me to find the last place I was working?

I have never done anything this complex before and can’t help think about the what ifs. Any ideas on bit changing?

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If the machine loses it’s position you are done, Changing the bit in the middle of a job is not something that is normally done. I really don’t see how that could work. Since you would need to rezero the Z axis and then be sure the next gcode command positioned the Z height were it left off. If the X or Y moved before the Z was set correctly damage could occur.

I don’t think I would even attempt it. Especially if I was 20 hours into a project

I’ve done it on several jobs. Use the grbl setting to keep the motors powered at all times, be careful not to move it while changing the bit, then zero the z-axis. If you do move the X or Y axis, you definitely need to have homing switches or a 3 axis touch plate.
A touch plate should help immensely, but I didn’t have one at the time I was doing this.
-Kelly

He seems to be talking about changing bits in the middle of the same job.

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As in the same g-code file.

That’s what I thought he was saying, pause in the middle of a the currently running gcode file and change the bit, then try to pick up where it left off.

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That scares the daylights out of me, in fact even changing from a roughing bit to a fine bit mid-job is something I can’t do well. Even with the motors powered I wind up, while trying to loosen the collet, moving one way or the other on the Y axis just a few steps of the motor.

Is there a way to actually lock the motors, or is powered-on the only option?

I’m honestly considering replacing the 611 with a 618 just so I can go with a 1/2 collet since there are easy-swap collets for 1/2 but nothing for 1/4…

Any suggestions?

What size steppers are you running? With my Nema 23s I change bits all the time on my dewalt without moving the spindle.

23s… Maybe I’m cranking down too hard.

Really wish they had a two wrench system for the 611.

Just make it tight, my guess is you are cranking way too hard.

I think you’re right. I had a bit fly out of a plunge router years ago, so I’ve been overly cautious ever since…

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Me? Typically 40in\min and .0625in DOC. 611 set on 1.5. Nothing fancy.

Maybe you could split your toolpath into 2 or more toolpaths. You would end up with 2 or more g-code files and you could choose to change the bit between g-code files or keep going if it looks good. You should not lose your zero if the motors are powered when changing bits. Also, I have homing switches. Even if something catastrophic happens I can re-home and my zero is remembered from the last run.

The easiest way I have found to do this, is making a copy of your project in easel. Then remove the parts of your drawing that need the second bit. After finishing the first part, move the machine to a comfortable position to change the bit ( with powered stepper motors ) then make a second copy of your project removing the parts of the drawing you’ve already cut. Use the function "use previous home position " when you start the new cutting process in easel. Your tool should travel to the initial point you used before.

Right, changing the bit in the middle of the job. To put it in perspective; I am bringing in my code from MeshCam and using it as is.

That is what I did before using Inventor and MeshCAM. I am trying to prove a point with my students that I can go from CAD drawing to metal. If I use the drawing elements of Easel, it doesn’t illustrate my point.

You folks have helped quite a bit:

If the machine loses it’s position you are done,
Absolutely, and that is one of the issues with importing Code.
That scares the daylights out of me, in fact even changing from a roughing bit to a fine bit mid-job is something I can’t do well. Even with the motors powered I wind up, while trying to loosen the collet, moving one way or the other on the Y axis just a few steps of the motor.
Very True. My issue is that unless I start smelting my Aluminum waste, I must be very careful.
What size steppers are you running? With my Nema 23s I change bits all the time on my dewalt without moving the spindle.
I also have NEMA 23’s and I need Clearance to change bits. To do this I must move a locked Z axis.