Basic mill advice for steel...


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  1. #1
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    Default Basic mill advice for steel...

    Just learning milling and CNC and have done a bit of aluminum without any big issues but steel is another story. Having trouble keeping things cool. My latest attempt was cutting down an off brand tubing flare wrench (basically a box end wrench with a slot so it can be put over a tubing fitting). I have a manifold for lube on my mill that has the fittings very close together and the wrench was pretty thick so though I would machine it rather than grind. Took a file to it to check hardness and it filed ok - not soft but the file was definitely taking of material. Mill is Precision Mathews PM25MV. Had HSS and 3 flute carbide 3/8" end mills on hand so chose the carbide one. 600 RPM from a speed and feed calculator. clamped the wrench in a vice with the end sticking out and close to the side. Noticed that the wrench middle section seemed straight but when in the vice it didn't clamp tightly near the end so put some thin aluminum sheet on both sides of the vice to get a solid grip - that worked well. Used tapmagic in a manual oil can for lube. Got it done but by the time I finished things were too hot. I did the depth of the wrench in one pass - about 3/8". The chips were very small - about the size of coarse hair.

    I think several things contributed to the heating and want to get some feedback. Probably too cautious on the feed and didn't feed fast enough resulting in some rubbing rather than cutting. Flex in the end mill and the part. The mill has a shield that hangs down in front of the spindle and to keep it from hitting the vise I had to hang the end mill about 3" out of the spindle. The end of the wrench also had some spring to it. So with flex I got more rubbing at times when I stopped feed to put a bit of lube on it or take a better look at where I was at. Trying to adjust X and Y for the curve caused some slowdown. Would probably have been better to move X in steps and run Y in and back away for each cut so I was always cutting and not rubbing. Then smooth the finish with a file.

    Could have done this with a grinder but wanted to try this by milling. Looking for advice and tips so I can improve my skills.

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  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Basic mill advice for steel...

    I'm not sure what ''too hot'' means. Machining generates heat and without flood coolant things are going to get hot. Conventional cutting generally generates more heat than climb cutting due to the cut geometry. But climb cutting is normally only done on CNC machines or sometimes very light climb cutting on manual machines without ball screws. Trying to climb cut on an acme screw machine just doesn't really work because the tool tries to pull into the work and there is no way to control it against the backlash.

    Maybe taking a little bigger bite would be helpful in that it would move more of the generated heat into the chip. The tougher the material the more power it will take to remove material and thus more heat is generated. Having a part too hot to touch is not unusual when not using coolant, I've been burned a few times when I wasn't thinking. Believe me, the work can get hot.

    If the chips weren't coming off blue you weren't pushing the tool hard enough, but this is limited by the machine mass and HP and the PM25MV is a pretty light machine. Sometimes it is what it is, and you work within the limitations of the equipment.

    Overall if the part or the tool bit were not glowing red, then I would say that your experience was normal and you were doing just fine. It's not uncommon to have red hot chips coming off of a carbide tool bit especially when cutting tool steel.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Basic mill advice for steel...

    The carbide end mill was discolored when I was done and it was throwing a few sparks/yellow hot very small bits briefly at one point but the part wasn't glowing red. Think I wasn't pushing the tool hard enough and I could have done more without bogging down the spindle.



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Basic mill advice for steel...

Basic mill advice for steel...