Tool measurement - missed opportunity

I just made a mistake in my last milling session: I inserted the tool too deep and did not let enough out to mill the bottom of the part. I.e. the part was too deep for the cutter.

Since Carbide Motion measures the tool length, it would be cool if it warned the user that the cutter is too short for the job.

Hi Fred,

What you’re suggesting here would actually be quite difficult, because the g-code doesn’t necessarily include information about the stock and other positional data, and the path is calculated with the tool-length “baked-in” in MeshCAM or other CAM package.

What could be done is a measurement comparison between the programmed tool length and the actual tool length when measured in-machine. By comparing the “overall length” in MeshCAM or “body length” of the tool in other CAM packages, to the measured length, it could at least raise a warning if it’s substantially different.

I agree with you it is non trivial. Maybe printing the measured tool length and asking the user to confirm before actually milling would help a lot. Could be made an option on CM to help beginners; experts can always disable.

That would save beginners from ramming the spindle into the stock.

I learned my lesson; lucky I was peeping at the job. :smile:

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While reading about similar mistakes, I think I had an idea. What about the ability to “pause and change tool” ? Essentially, pausing, lifting the spindle, replacing the tool and re-measure the tool length before continuing the milling process (keep x and y; offset z by the delta length) ? This would allow changing bits if you notice they do not cut that well, are too short etc. more efficient than resuming from scratch.

I realize this is only useful for newcomers but since this is a market for the 883…

Hi Fred,

At first I read your post and thought “yeah, that could be useful!” but, then I thought about the other risks and issues that it would introduce—it would probably need to be introduced with a group of additional features, which could get to be substantial feature creep…

For instance, if you replaced the tool with the exact same tool, and had it adjust the length by the new measurement, then the net result will be that the tool takes the same tool-path—which doesn’t necessarily solve the reach problem you encountered, as the end-depth of the cut will be the same. The only thing it will have prevented is collisions with the collet-nut, and it didn’t sound like that was your main issue here.

What you’re looking for is a way to have an additional z-height compensation that can be applied at the Carbide Motion level instead of in CAM, but how would you then ensure that your feed-rates are appropriate for the adjusted cut-depth, and that you won’t accidentally jam the cutter into the material too deeply? Or if the tool is lower then when the spindle retracts to go between areas in the part are the retractions still going to pull the tool high enough? If the tool path is being executed at a lower z-height overall, then it’s going to introduce all kinds of new opportunities for “whoops!” without the benefit of a simulation to preview the impact of the changes, like you would have otherwise in MeshCAM or other CAM packages.

Generally, since you program your stock dimensions in accurately prior to generating tool-paths, and then you set your zero positions prior to running the job, that’s when you’ll be ensuring that the tool is going to travel where it’s expected to on the z-axis. The critical part here is setting and checking your zero positions before the job—if your z-zero is floating above the stock, then it’s going to cut air first instead of your material, and then the bottom of the cut won’t be as deep as you are expecting, as you experienced X-)

But, I do think it would be a value-add to have a check of “overall length” and “flute length” of the tool as provided by MeshCAM, or “Body Length” as provided by HSMworks/Fusion360. That would be the opportunity to account for and prevent potential collet/stock collisions.

Thanks for your comments. The use case I described is very related to beginners: I installed a tool but too deep in the collet-nut. I initially asked to have a warning after tool length measurement but I understand it may be difficult (and I think it is really very difficult to do right).

Then I started musing on alternative ways to solve that problem: pause the job and reposition the tool so it would protrude more and, after the machine checks the new tool length (assuming the tool type is unchanged), continues the same toolpath (i.e. shifting up the spindle to account for the new tool length) – I am assuming that “toolpath” here means the path taken by the working-end (the extreme-end) of the flute.

On a second thought, I also figured this could be useful if for instance the tool snaps and, reacting quickly, the operator paused the CNC and replaced the tool with a fresh one - i.e. I just added other problems-to-be-solved to the “solution”.

These was merely me thinking out loud and musing.

It would indeed be nice if we prevented the job to start (or at least give a warning) if somehow the tool was measured to be too short based on some “a priori” knowledge. The pause-change-resume was only another way to try to solve the problem.

I did the same thing a few times and put the tool too deeply in the nut, but the result for me was that I realized I wasn’t going to be able to plunge into the material far enough without hitting the nut, so I realized that after checking the stock dimensions and had to adjust it.

They’re good musings on a solution to that problem–I’m with you on a length check/confirmation and a pause + re-measure for replacing tools. :smile:

yup I learned this one the hard way too. and try finding long shank cutters in sizes under 1/8 …

I’ve found long reach & long-shank small diameter tooling at bits&bits.