Comment by dekhn | Hacker News Reader

Comment by dekhn | Hacker News Reader

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I understand you put thought and time into your approach and it was a hobby to learn more abotu the process (and thus you know about MPCNC but decided to make your own). I've also build similar systems and I've learned some timesaving tricks that have paid off in terms of hobbyist enjoyment.

I really like buying the majority of the parts from a place like OPenBuildsPartStore, rahter than assembling frames from channel manually. Time/cost/quality tradeoff is hard to beat here.

I strongly recommend switching to Grbl_Esp32 https://github.com/bdring/Grbl_Esp32 with external controllers (this board https://www.tindie.com/products/33366583/6-pack-universal-cn... with these plugins https://www.tindie.com/products/33366583/external-stepper-mo... and these controllers https://www.amazon.com/STEPPERONLINE-1-0-4-2A-20-50VDC-Micro...). That's what I ended up with because tuning current using the little pots is dumb, and you want a TON of current going to those huge motors. ESP32 + Grbl has a bunch of nice features that aren't in plain old Uno GRBL.

My system has high torque NEMA23 with no gears (same motor for all 3 axes), I can't see any situations where adding more torque to the X or Y axes using a smaller gearer stepper makes sense.

"I can't see any situations where adding more torque to the X or Y axes using a smaller gearer stepper makes sense."

Generally agree. Torque is only needed to a specific threshold. If it requires a lot of torque, then that's probably a good sign to slow the movement down (for the sake of the machine's longevity).

On the contrary, plenty of tools need to move and chip otherwise they'll get dull, cutting speed is a function that increases a machines' longevity. But cutting speed does require a solid mechanical setup, drivers that can source some current and a drive train that does not suffer from over or undershoot ('slop').

"plenty of tools need to move and chip"

Not sure what you mean by that. I dont know all the tools in the world, but generally a chipped tool gets less sharp. Even something like obsidian would get less sharp in regards to the intended use with a random chip as compared to a well knapped tool.

"cutting speed is a function that increases a machines' longevity."

I'm not sure you are using cutting speed the same way I'm talking about movement. Applying too much lateral torque to a router bit is how bits break, bearings wear prematurely, etc. You don't need much torque to move the router.

If you want faster cutting speed, then the RPM of the bit can be increased, or using a different bit design. You can cut faster and it still shouldn't require much torque for the movement.

I suspect he means that you want to move quickly through aluminum, especially if you don't have active cooling. If you move slowly you can get problems like chip welding and everything goes south.

I actually didn't have enough torque to move the router through lots of material until I moved to some fairly serious stepper drivers and configured them to use max current and voltage (IE, I got a 48V, max 20A power supply). Even then, if if accidentally move the router bit while it's not spinning into the work, the motors stall well before the bit breaks (1/4" carbide end mill).

I guess if they're getting welding there's no sprayer set up. Some emulsified oil (10% Ballistol) usually works great for lube and cooling, even in small quantities.

Yeah, that makes sense. That sounds like it's really not that much torque the way you describe - just above functional minimum and no where near too much (eg people forcing it through and breaking bits).

They possibly meant "plenty of tools need to move chips".

A common problem that causes chatter and poor tool life is not taking a large enough chip. Large chips stabilize the tool (the rotation of the tool pulls it into the part) as well as allowing for a more continuous, uninterrupted cut (whereas too small of chips cause the flutes to have to re-engage the cut over and over, and the number of engagements and tool life have an inverse relationship).

True. My point was that it shouldn't take very much torque to match the cutting speed with the movement speed. Even if you increase cutting speed you can keep the same torque (for movement) by increasing movement speed. It should be a balancing act with torque (for movement) being fairly constant in the range to provide continuous engagement, with the cutting and movement speeds changing.

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