Speed and Feed

I’m new to CNC, but I have read enough here to understand there are lots of variables involved in setting the speed and feed. Nonetheless, I’m hoping for a little advice on how to go about finding that sweet spot. For example, let’s say I’m using a 1/4 flat bit. It seems that it’s hardly working at all, but it is leaving a very nice finish. I’d like to speed things up. Do I speed up the XY travel speed, or do I change Z so that it takes a bigger bite? Also, I have a dimmer switch wired into my 660. With only sound to go by, how do you optimize the spindle speed?

Have you checked out the milling basics? Good general advice there.

You can get a cheap laser rpm gauge thing and mess with the speeds to get an idea of where your dimmer switch ends up at different settings, but it may be a “+/- 2000 rpms” deal depending on temperature, switch, etc. Plus, at lower speeds the 660 will bog more and it’s really tough to measure the speed while that bugger is cutting. I tried!

There was a guy on the bobscnc group that cracked the 660 and the laser thing open and rigged the sensor directly to something on the back of the motor. It was really cool but he ended up having to modify a lot because the device cooked pretty quickly under constant use. Might be ok for spot checking, but I don’t recall what all was involved. How did I get off track so quickly? Anyway…

Guessing that you’ve seen the milling basics page and you’re looking for the next step, the short answer is always look at the chips. They should be actual little pieces (unless you’re in mdf). If they aren’t, increase your feed or slow down your router (speed). If the chips look good and you want more, go deeper.

Part of the pid Ryan offers reads the speed I’ll post a link when I find it.:grinning:

1 Like

Where did the development on this end up?

I think Ryan’s insurance people slowed it down. It was working and a couple people were using int

2 Likes

This is still viable, and I am having good luck with it so far. Full disclosure, I’m using an old GRBL CNC Shield v3.00 on an Ardiono Uno, not any of the boards in the store.

I bought the parts bundle available in the store last week. The circuit board for the nano is no longer available, but you could order your own from the info provided in the “board” link in the first message in the topic linked above. I wired it up using some perf board last night based on that same information. I got the on/off working in CNS.js (including setting up the ViPi image for the first time) last night, but I haven’t tested the sensor yet. I was getting a little groggy and decided playing with mains wiring was something best done while well rested.

The most challenging part has been tracking which pin is which between my older CNC shield and GRBL being updated to make best use of the PWM-capable pins, and trying to get 2 additional relays going to control vacuum and possible air assist. None of that is related to the PID stuff from the store. That has all worked as designed with no issues.

3 Likes

Thank you for the update it has not been a very active thread of late. I may get to this and give it a try thanks again and keep us informed.

1 Like