Second time I’m complaining about narrow slot bits. This is a SPETools O_flute 1/16 upcut bit. I’m cutting aluminum, 18,000RPM, 0.06 DOC, 15 IPM. I expect the slot to be .0625 wide and it is only 0.053 wide. I sent a query to SPETools and they haven’t answered in a couple of days.
Even though it is upcut, the chips are getting stuck in the slot and have to be scraped out. Probably too much heat being generated. Maybe do a little less DOC or go slower.
Could the end of the bit be vibrating in the slot since it only hits at one point?
My caliper is accurate ( at least much more accurate then the difference I’m seeing ).
Any ideas? Any better recommendations for speeds and feeds - I kinda got those numbers interpolation info on the SPETools website.
My caliper is accurate ( at least much more accurate then the difference I’m seeing ).
this sounds dumb, but did you measure the thickness of the bit with your calipers? If any error in your caliper, it would be translated to the measurement of the bit.
In my experience, SPE is cheap for a reason. It’s going to vibrate and chatter much more than any other premium bit. I’ve also seen them be nearly dull and not nearly as sharp as their competitor counterproducts.
You usually can’t measure a single flute with calipers. The opposite side as the cutting edge is relieved, so you won’t read the full diameter.
There is potentially a little bit of vibration going on, but also deflection. You said you’re taking a 0.06" DOC which is massive. (Did you mean 0.006"?) If you take that big a bite ouf of the material, you absolutely need to run a finishing/spring pass. Just run the toolpath a second time, and see if the cutter shaves any more material off when it’s not slamming through a bunch of material in a high-stress environment.
That tiny a cutter too will also pose chip evacuation challenges. There’s not much room for chips to bounce out of the slot. Chips in the slot will weld to, or otherwise push a small cutter off-course. If you can’t chase the cut with compressed air, consider using a dust boot to help get chips out of the way. Not as good as compressed air, but way better than nothing.
Edit: More info - Clinb vs conventional doesn’t matter in a single-width slot. One side will be cut as conventional, one side as climb. The only thing reversing direction will change is which side of the slot has a slightly nicer finish.
Not necessarily. You’re using 2 different parts of the calipers to measure a slot -vs- the tool.
And as Winston mentioned, it’s kinda tough to measure a single flute tool. If the flute makes a full revolution it can be done, but most of these size tools aren’t that long.
0.060" is a lot. I take up to 0.015" with 1/4", 0.010 or less with an 1/8".
I complained to SPE about this very issue. Their response is that you need to measure the slot, not the bit. It was a condescending (tone, not content) reply and I decided that would be my last purchase. I think they mix up mm with inches somewhere in the process of marketing. They look the same to the naked eye and shipping folks don’t care.
It’s pretty rare to see a tool when slotting actually cut the slot too small. I suppose it’s possible that the tool is deflecting AWAY from both sides.
If you run the path again, does it remove anything? What about peck drilling? You could use a lighter material, like acrylic, tooling wax, or PVC that holds a good edge but won’t deflect the tool much.
I’d try a 2-flute cutter to see if that changes anything. If the cutter is deflecting, I’d expect the opposing flute to eliminate that.
Random anecdote:
When we got our first Haas many years ago, we had a part that kept ending up with triangular holes from a standard drill. In digging deeper, we noticed that triangular holes were not getting spot drilled first, so the drill bit must have wobbled through the part the whole way, making a triangular hole. When we added the spot drill, everything was fine.
All of that to say, a cutter can deflect in strange ways.
I didn’t measure the tool as i can’t really measure a single flute bit.
I don’t think I have a 2 .flute bit to try.
I just changed the DOC to 0.03 and put in a piece of Lexan. The slot after the second pass was 0.53 wide. The Lexan is much softer and shouldn’t stress the bit and cause deflection ( my humble opinion )
BTW, I was using the 0.06 DOC since SPETools said the DOC should be the size of the bit. I didn’t just pick that number out of the air, but I did feel it was a bit much for aluminum.
It look to me that the tool is actually too small. I guess that’s the last SPETools bit I buy.
Many OEM bit S&F are for industrial CNC machines and not the hobby class. An example is Frued bits give fantastically high F&S for their bits for a Shapeoko. So take what the OEM recommends with a grain of salt. If your slots are too small after trying your F&S maybe you will need to make a pocket wider to get the desired with you need. As @WillAdams often says add geometry.