I use a app for spindle speeds & all seems to cut well when rounded to the closest pully I have. I never paid much attention to feed rate since I was hand cranking. I just went by feel. Now that my new mill has a power feed I guess I need to learn how to add feed rate into the equation. I need to get my scales ordered & on so I'll know how fast I'm going.
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Problems Milling 4140
- Thread starter ericc
- Start date
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- Mar 10, 2015
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- 248
What app are you using for spindle speeds, I have been looking for a good one.
https://play.google.com/store/apps/details?id=com.techrds.machiningmatemachiningmate
I mostly only look at RPM for my cutting tool.
I mostly only look at RPM for my cutting tool.
I agree that the RPM's are critical for tool wear but you cannot minimize the effect that too light of a feed rate will also affect tool life especially when the material can work harden. The skin on 4140 will work harden with every pass so it is important to keep the feed rate up at least .001 per tooth. I would feed harder than that in most cases so my cut is below the work hardened surface. Like any other tool, an end mill is made to be used, not babied.
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4GSR
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4140 will work harden??? I cut on a lot of 4130 - 4145 all heat treated in the 30's HRC. I've engineered a lot of stuff over the years using 41xx materials. I don't ever recall any of it work hardening from dull tools light cuts, etc. I use both HSS and carbide endmills on the stuff. I have a Bridgeport type of mill too. The worse that has happen, I've broken off my share of endmills over the years, from running them past the stage of being dull. Occasionally, I'll run across a piece of steel that may be heat treated in the high 50's or higher that will not cut at all. That piece gets tossed! But 4140 work hardening from machining? I guess if you rub on it with great forces with another piece of steel, it might surface harden.
The sub-critical annealed (dull red heat) piece was noticeably softer, so I tried again with a different tool. I used a homemade 5/8" tool holder like a flycutter with a Rex aaa 5/16 lathe tool bit in it. I tried running this at 250 RPM, but it threw blue chips. I backed it off to 160 RPM and 0.7 ipm feed rate. Still got some blue chips on hard spots. This is as slow as the power feed would go. The tool cut at 0.020 and it struggled at 0.030" doc. At 0.040 doc, the y direction slipped and the tool dug a piece out of the side of the slot and the piece slipped in the vise. With Y and Z ways locked, 0.030 barely worked and the machine was obviously straining. Even with a constant spray of soluble oil coolant, things were too hot. The cut was eventually finished (with the dig) and the bit was dull. Fortunately, it can easily be sharpened without buying another end mill.
Someone suggested I try a 1/2" 4 flute carbide end mill, but I am afraid of goofing up one of these expensive things.
Someone suggested I try a 1/2" 4 flute carbide end mill, but I am afraid of goofing up one of these expensive things.
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4GSR
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Any "alloyed" steel will throw blue chips. regardless feed rate, depth of cut, or RPM's when using fly cutters, face mills and such tooling.
Get after it and do some cutting!!!
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Cut 4140 HT all the time, and yes, it will work harden on you. Mostly happens is using a dull drill bit, or when some one in the shop is trying to hard to drill a piece and running too much rpm and no coolant. Have to use a carbide end mill after that to get through the created hard spot.