Question about milling steel

I usually use the shapeoko to mill hdpe, rubber, and a little bit of aluminum. I started experimenting with steel and I’m working on a 1/4" thick 4x6 part that has a couple of pockets and a contour cut. I started with a new bit but quickly burned it up (I had the RPMs set way too high) before I could finish contour cut. I tried my only other 1/4" end mill but I think it was too spent to use on steel.

Before buying a new bit and wasting the cash can the shapeoko cut long passes of 1/4" thick mild steel using the default rates, lowest rpm setting on the dewalt trim router and w40 as coolant and some compressed air to clear the chips.

If so, is the 1/4" endmill carbide 3d sells an appropriate bit for the job?

Thanks for your help.

I have not personally cut steel but I know you can as long as you are very careful and use a small tool. I would look at this for inspiration:

I would probably not use a 1/4" tool for cutting steel. I would look at 1/8" or smaller.

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I often cut steel on the Shapeoko and in fact, I spent most of the day today cutting some 1018 low carbon steel (Ref 1.25 dia). I was boring 5/8" holes in 1.0 inch long slugs and milling a 7/8 C’Bore 1/8" deep. Major cutting tool manufacturers will list the cutting rates for their tools for a general range of material. (HSS, Carbide and Coated Carbide, etc.)

For example, 303 Stainless steel my reference chart says 150-200 SFM. I ALWAYS try use the lower number to start.

So using an online SFM Calculator a 1/16" end mill at 11,000 rpm = 170 SFM.

So this one number tells you the important info. Spindle speed for a particular cutter diameter.

Feed and Depth of cut? I like what I call the 10/10 rule for steels. Feed: 10 in/min. DOC 0.010" (Starting Point)

Following these guidelines, I can easily get a full day out of a cutter, or if I use the higher number…about a half-day. It’s what I’ve use for 40+ years of machining and 5+ years on my Shapeoko.

Questions?

Oh and for the cutter lubricant?.. (Eg: steel and 303 stainless) WD40 using my Drip Can method OR Oil-soluble coolant.

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I appreciate the replies. Will slow things down and try a 1/8” end mill and see if that helps

In the interim does anyone know the rpm speed on the different dial settings with the dewalt trim router?

The speeds for a DeWalt are listed at the bottom of the chart:

I found that I kept chipping the corners off of endmills when trying to slot / contour cut in steel, especially when ramping (at higher DOC and feedrates, anyhow). Corner radius endmills solve that problem if you don’t mind machining .010/.015" into your wasteboard for full depth cuts. I like these ones from Lakeshore Carbide: CORNER RADIUS END MILLS

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Thanks, I’ll look into those bits.

In the interim I ran the operation really slow with a 0.005 doc. This really helped out but other than taking forever I was only able to cut 1 part before the bit got too dull. I think the dewalt router just runs too high of an rpm, even at the lowest setting.