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Milling Thin and Deep Channel on Vertical Mill


Aug 18, 2020
I have to mill a 1/8" thick channel in some long 1018 stock. The channel has to be 1 5/8" deep. I am running this on a CNC vertical mill and I have a couple concerns.

First, how do you prefer to balance speed, feed, and cut depth? I know there is a sweet spot depending on what the tool and machine can handle. I want to get these milled as fast as possible. Considering I have to use a flimsy (and long) 1/8" endmill, I can't imagine pushing much depth before snapping a tool. I know some have used G-wizard for getting these settings.

Second, I do not want to have any shank in contact with cut surfaces. I figured this was good practice even though it could work otherwise. This means I have to source a 1/8" carbide endmill with at least 1 5/8" long flutes. Any tool recommendations?



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A woodruff key cutter, or a slitting saw. Turn the part 90 degrees.
Thank you guys for the input. We actually started trying this on a large horizontal milling machine with a slitting saw, but the results were less than satisfactory. I think this was due to an error when aligning our two mounted vises.

How deep can you typically cut with a slitting saw? What's the formula for optimization?

If you clamp that work piece buried in a vise you will clamp on to the saw blade as soon as you start to cut through. If you hold on to the bottom 1/8 inch the stress in 1018 will most likely cause the 2 vertical legs to splay apart. Or maybe pinch the blade, sometimes it moves extra weird.

I would second making it from 3 pieces. If it must be one piece you might have better luck with a material with less internal stress. 12L14,1144, or hot rolled A36 might work better or at least anneal your 1018 before you start.

Edit: Here's your endmill. Good luck!
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Hi WakelessFoil:
How deep you can cut with a slitting saw depends on the saw diameter, and the arbor diameter.
How deep you can cut in one pass depends on how good your chip evacuation is.
How fast you can run it depends on what material it is (HSS or carbide) what diameter it is and what the stock material is.
Your biggest hazard will come from two places:
1) The stock warps
2) You catch a chip and tear the shit out of the slot and probably bust the saw.

So you want annealed or hot rolled stock, and you want to really blast the coolant at it so you're sure you don't get a chip caught in a tooth gullet.

This is never going to be a fast process so don't be impatient with it.

BTW, if you absolutely HAVE to mill a deep skinny slot with an endmill, buy stubbies and neck them down...don't try to run a skinny cutter with long flutes.
Like this:
necked cutter.JPEG


I did some parts out of 360 brass that had a slit into a bore, as I was getting done with the cut it chomped down on my saw and turned into multiple saw remnants. We ended up making the part out of 2 pieces.
I’m working on this too. Wakeless set this up on the horiz. Mill and it ran fine. He only took off about .300 per pass because we wanted to play safe given the 8” saw on a 1” arbor, and time wasn’t a factor. Some video:
Would a shaper work ? It looks like there is a good sized one to the left of the horozontal mill
Yes technically speaking the 24-in. Shaper is capable, we did think about that briefly but it fell off the chart because we’d have to make a special tool (cutter) and maybe a custom tool holder for it.
Yes technically speaking the 24-in. Shaper is capable, we did think about that briefly but it fell off the chart because we’d have to make a special tool (cutter) and maybe a custom tool holder for it.
You should better rethink that. Assuming that the machine is still in good shape, despite the old say that, with shapers you can do anything but money, the main reason they are still around in several job shops is indeed because you can cut slots and dovetails with minimal (very cheap) tooling.
In this case, a lathe parting tool would have been the ticket.