Relevant to various discussions of bits cutting deeper than expected, I was watching this amazing woodworker on YouTube accidentally ruin a very expensive project with his CNC machine (not a LongMill - but completely relevant): https://youtu.be/j34KtFaFyQs?si=Z4PrMqcM_3E6tENU&t=1840
The video is timestamped to the exact moment of his big “oops” - where he had an upcut bit pull itself too deep into his workpiece, ruining an expensive walnut slab, and thus his entire piece.
I have in the past theorized that upcut bits can pull themselves into the work (and I have confirmed it when I have had bits clearly pull themselves out of my collets). This video shows the consequences.
Short version - make sure your bits are always tight, and downcut (if it is suitable) won’t pull itself into your workpiece.
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Jikes!
I use upcut a lot for roughing but am conservative on how deep the’ll cut. I have this happened once with a balnose that I believe is an upcut too. I just entered the house to idunno, ask something or whatever, glanced the security feed from the camera above my mill and saw something was off. Cut the power to the garage and found the bit hanging from the collet French kissing my wasteboard. Like, deep.
Luckaly It was not a 15K French kiss. I was happy to have that camera feed and finaly could show the misses why I went trough all the trouble installing it.
Some will say, you must stay at your machine at all time, but I know me and that won’t always happen. Long jobs are long jobs and I won’t pause them when going for a cupper.
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I, too, have left my shop with my Longmill MK1 running, and although I’ve always been careful to tighten the router collet properly, I understand that “stuff” can always happen when you’re dealing with even simple machines. Double, or perhaps triple that when it comes to complex machines such as CNCs.
In the 2+ years that I owned my MK1, I can count on 1 hand the number of times I’ve left it alone for 15 minute stretches, and fortunately, have never had any problems. That’s not to say that a problem won’t ever come up ,as I’d stated above, anything’s possible when using complex machinery.
I now have an AltMill that I’m in the throes of assembly, and will probably continue being vigilant. But I certainly appreciate that it’s a much more powerful and faster operating machine than my Longmill MK1 ever was, and as such, I’ll most likely stick around the shop whenever it’s operating.
Cheers,
Marty from Kingston
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I’m transitioning from the metal side of CNCs to the Longmill and wood. A couple of habits I’m still trying to transfer is cleaning toolholders during tool changes and cleaning new tool shanks.
When I swap out a toolholder on a large CNC I wipe the mating surfaces to clear any chips and feel for any burrs. I have to remind myself that I can’t reach into a collet on the smaller router/spindles so compressed air is my friend to clear the dust out. We also thoroughly clean the shanks of new tools to remove any oils left from manufacturing/shipping to lessen the chance of slippage and that one is a little easier to remember (especially at the rate I’m getting new tools for this new machine in the home shop).
They’re just little things but I hope it helps someone.
James
Dayton, Ohio
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As someone who has only used hobby level CNC machines that tool holder looks ridiculously large! 
Also that’s good advise, especially the part about oil on new bits!
Its called a CAT40 holder, some versions will hold a shank diameter of 1.3". They are what we use on all of our HAAS CNCs in the lab here at school. They make a pretty distinctive sound when you drop one on your foot. 
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Is it high pitched and does it shut the gates to heaven?
If you do it wrong it certainly will get the attention of an entire ZIP code.
That’s it, I need one of them cat40s. Always wanted a large audience!
The Altmill should be a nice addition to your shop and you’ve probably got it up and running by now since your post was a while back.
I can appreciate your thoughts on the added power and speed and hence dangers of the Altmill. I don’t have one but when I’ve watched videos it seems scary fast to me.
I’ve done some things that were not strictly safe with my Mk1, like clearing debris/parts from through cuts that popped out when the mill was headed away from me. I hope that I would be smart enough to not do something like that if I had an Altmill. I know I shouldn’t do it with the Mk1 either as anything could happen, and the safest course would be to always keep my enclosure door shut when the mill is working.
Anyway, stay vigilant Marty and I hope the Altmill treats you well.
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