So, I’m setting up for milling out a sterling silver pendant (I could easily saw pierce this out, but since I have the mill, why not try it, right?), and according to my research it looks like if I want to have the RPMs set at 5000 (which appears to be the default setting) then for my 0.01 inch bit, the feed rate should be 0.50 inch. I get this “GRBL Error: Undefined feed rate” error. I’ve had some errors pop up in the past, and usually I’ve found ignoring them seems to be the thing to do… but this is a new one, and also it appears that the work isn’t moving at all, just sitting there. thoughts? Is there a min setting for feed rate (obviously)?
Hi there, GRBL takes all units in mm, so it’s likely that if you entered the feed as a unit-less value, it probably thought you meant 0.5mm.
Also, are you sure that’s the speed you want? with your .01 end-mill, is it a 2-flute? ball or square-end? How are you arriving at that 0.5IPM speed?
This Precise Bits article walks through how to fine-tune your speeds and feeds with micro-tools, and it references this guideline for getting the right feeds & speeds starting point with most metals. With a bit of google digging, it sounds like milling sterling is similar to milling copper, so you could probably get by with feeds and speeds similar to what you can find for 6061 aluminum.
On the other hand, you could mill something in renshape to pull a silicone mold and make lost-investment waxes or mill it straight in jeweler’s wax if you only want one… and I can find a lot of feeds and speeds for wax out there.
I’m sure there is a minimum feed-rate, but I doubt that’s what you’re actually going to need here 
-Jonathan
thanks! I’ve been out of town and now am back to try it. I thought I did all the math correctly… but I didn’t know GRBL takes all measurements in mm, so that is probably what is causing the error. I’m back at the mill, and will find out today.
I am using a 2 flute end mill (square). I’m not so mathy, so I’ll give the aluminum settings I have a try and see what happens.
As far as casting etc… that is something that I am familiar with… a project like this is better suited for saw piercing. I am more doing it to prove I can do it on mill. I lay out and hand saw things like this on a regular basis, so the issue here isn’t “what is the best way…” I could have finished this project a long time ago if that was the case!
I am getting these huge rpm numbers, and when I try and back work the formulas for better rpms, I ended up with those numbers. I think the lesson I have learned here is that I am just going to buy the GWizard subscription.
Thank you for the help and pointing to the guidelines! I’ll post a picture if it works and see how it goes.