So I’ve had my machine for a few months and had zero CNC experience at the time I purchased. I had no idea what end-mills, flutes, feed rates, and other CNC terminology meant or how it impacted my machining. I was pretty familiar with 3D printing, so some of that knowledge did transfer over.
I purchased my Shapeoko XL for the purpose of machine “face plates” for electronics. I’ve been buying cheap bits off of amazon as I didn’t want to break a 20-30 dollar bit in my “learning” stage. The bits all had good ratings and multiple reviews confirmed that they could machine aluminum.
Machine: Shapeoko XL
Stock Material: 1.2mm to 1.6mm 6061-T6
Endmill: 1/8 inch flat/square head & 1/8 inch ball head
Spindle: Dewalt 611
The default settings in Carbide Create for machining aluminum is .254mm depth per pass with a feedrate of 1524mm. In my experience this is WAY too deep per pass. I would break a bit within 10 seconds of the first cut.
To give this post some structure, I’ve broken down what I’ve learned over the last few months. Take this with a grain of salt as I pretty much just learned through trial and error.
Clamps, Clamps, Clamps. I can’t stress this enough. When I first started I would use 4 clamps and just make sure the stock is secure to the table. That simply isn’t good enough. You need to make sure that the entire stock is flush to the table and will not “lift” between spans. What happens is the endmill will go over a span, push down the stock (even just a fraction of a mm) and make the cut. The stock then comes back up to it’s original position. The next time the endmill comes around there is a good chance it will “catch” on the stock because it’s higher than it should be. Your fine as long as the endmill continues to push the stock down but often on the last cut, there may or may not be enough material to push the stock down; you’ll catch the bit on the part of the stock that isn’t flush to the table. Now you broke your bit and you were 95% done with the work. This is frustrating to say the least.
I always run a “test loop” over my stock to make sure I don’t hit any clamps and verify that the endmill is where I think it should be. This is an easy way to prevent losing a good piece of stock or breaking a bit. I’ll normally zero my Z axis about .1mm above the top of my stock (0,0) and run all my paths for 1 iteration. If my endmill touches the stock, I’ll zero the Z another .1mm higher and start over. I originally broke a lot of bits on the first run because the far end of my stock was higher than my 0,0. This caused the endmill to bite off more than it could chew. With my setup now, often times my first few runs over a path don’t even touch the stock. I’m fine with this because it means that I will never cut more than my depth-per-cut.
I like to size my stock about an inch or more around the perimeter of my outermost cut. Too many times I tried to save stock and only leave 1/4 inch (or less) of wasted area. This resulted in the endmill running into clamps, etc. Now I just make sure that this isn’t an issue by giving myself some room.
Stock height. I set my stock height to be about .5 to 1mm higher than it actually is. This gives me some wiggle room if the stock isn’t level or the aluminum gets pressed down into the MDF. Having to break out the dremmel tool or try and make a final cut by hand is normally a disaster.
Depth per pass, feed rate, spindle speed. This might sound absurd, but my current depth per pass is .05mm with the default feed rate of 1524. I can push this to .07 if I’m using cutting fluid or wd40. However, I don’t like the mess it makes in the working area. I set the spindle speed to 1.5 on the Dewalt 611. The downside is that my parts take a LONG time to cut out. The upside is that I can consistently run this setup without the fear of breaking a bit.
I’ve attached some pictures of my clamping jig and a completed part.
I would love for some people with more experience to give me some feedback. If I used a more expensive bit would I be able to do a deeper depth per pass? I’m just afraid of breaking a 20 dollar bit. I have no problem breaking these cheap ones.