Upcut vs downcut and crash

I could say I’m not crazy, but that is hard to believe. If I use my .250 2 flute upcut endmill, it run fine. If I use the .250 downcut 3 flute endmill, it will stop and disconnect.

I suppose it is noise being generated by the router and I would have to play with speed and feeds to fix it.

Any other ideas?

Wow. That would be a first (establishing a link between EMI and the type of endmill being used).
How repeatable is it ?
If it is repeatable, does it still happen if you do an air cut (and then, this would be Area51 terroritory…)
The only (very) indirect effect I could imagine is that a downcut will push on the stock, while an upcut with pull. Could this have nothing to do with the endmill but introduce a weird effect where the router has play in the collet/bearing/whatever and when you push on the axle, it rubs somewhere internally to the router?
I like mysteries but there is likely a much, much more down to earth explanation.

It is very repeatable. I will experiment some more like trying an air cut. I was thinking maybe vibrations set up in the router

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I guess I lied to you. It was very repeatable yesterday. Today working fine, but haven’t pushed it as much as I did yesterday

To be sure it’s repeatable, you must do exactly what you did when it happened last time.
Has there been a change in temperature or air moisture?

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I was having the same issue while cutting birch plywood or and plywood and cutting with a compression bit. Turns out it was building up static charge on the rails and z carriage. So, I had to run a ground wire from the z carriage, thru the drag chain to the y rails. Since then, I’ve had no further issues. Carbide suggested you use 14-16 braided copper wire. If you have a multi meter, set it to 2k on the dial to check for isolation. This will help you determine where to run the wiring. Fee free to DM me if you run into trouble or have questions.



While I didn’t use braided wire, I have every rail and the router grounded via 16 ga copper wire. It is wired in a star config, each ground goes to a single point which is then wired to the power ground pin. I have a anti static hose which has a drain wire connected to the router ground.

I almost think that I am getting some chatter with the bit which generates noise on the power line. Once I get back to a repeatable situation, I may try a filter on the router line

An upcut bit could be throwing more dust into your dust collection which could be increasing static buildup. Not sure how “probable” this theory is, but it’s at least “possible”.

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I agree with Robert – I think he nailed it.

My best detailed explanation for what I think is happening:
The electromagnetic interference is from tiny arcs produced when the static charge builds up enough to jump to another material. Think of static shocks, but they’re smaller than you can see/hear and jumping all over the place. The static charge is developed by dissimilar materials rubbing against each other (triboelectric effect, like rubbing a balloon on your hair), whether it be air and plastic or sawdust and plastic. With more dust thrown up by the upcut endmill compared to the downcut, you have a higher surface area for charge to accumulate and more opportunities as the dust moves for arcs to form between the dust and hose.

It sounds like you’ve done a good job grounding things already, but could there be static build-up inside your plastic shop vac, or even in your sweepy?

Do you live in a particularly dry region? One possible reason for variations day to day is the changing humidity. The more humid it is, the more readily the charge can dissipate into the air without arcing – or arcing at a lower potential, radiating less EMI in the process.

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Thanks, I have dust collection hooked up, but don’t use it - too noisy. Maybe today I’ll get a chance to experiment by taking some maple and just doing repeated pockets in it.

I’d go with the power filter on the router next.

It sounds like you’ve already done the basic grounding, if you have a regular router with plastic bearing housings it’s possible you have a static discharge path through the router to the AC inlet which could also be generating electrical noise.

Is your router power cable routed well away from all the Shapeoko wiring?

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Got back to it today. OK, so I’m crazy. Cut 3 deep pockets in maple with the down cut bit and not one disconnect. I think I’ll add the power line filter just for the hell of it. I just have to see if I have one big enough.

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