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Machine Tools/Chip depth per tooth


QUESTION: I'm knew at CNN milling. I have BobCad/Cam software that generates Tool Paths/speeds and feeds for a given end mill or face mill dia. My program gives me SFM, RPMs, CLF (Chip load per flute/tooth)etc. The one bit of information it doesn't provide is how much material to remove with each pass. What I don't understand is how does chip load per tooth relate to depth of cut. I'm removing .121 material off of a .75 wide 1018 steel using a 2" face mill/3 flute. I've been using about .015 per pass and I'm not sure if I can go deeper until the finish pass. With a manual mill you can feel it, but with a CNN you can only watch and then stop it if it doesn't seem to be cutting ok. I hope you can give me some guidance. I would really appreciate any help you can provide. Thank You

ANSWER: Try thinking as little different. You part is only .75 wide. You are cutting it with a 2 inch shell mill. There is only 1 tooth in the material at any given time. That's not enough. It will just beat the inserts to death. Try using a high performance endmill. I use a V Carb endmill made by SGS all the time. For an example I cut 304 STST with a .500 endmill at 2407 RPM, 13.5 IPM with a .500 depth of cut. Yes that is .500 on the depth. You will be able to do what you want in 1 pass. Most CAM programs generate speeds and feeds for you but that is only for conventional cutters. It is up to you to override those to compensate for today's high performance tooling.

The biggest problem I  have is keeping the parts in the vice.

Also make sure your coolant mixture is correct. This is just as important as the tools you use.

If you do make the switch ask your tooling vendor to show you how to run the tool. I do this all the time. Have a rep come out and let you try some samples. They want to make the sale and need to stand behind the tools they sell.

If you are determined to stick with the face mill try changing to a smaller one and check with the manufacturer of the inserts for a recommended depth of cut.

Good luck.

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QUESTION: I'm doing a counterbore in machine steel. The counterbore is for a 1/4" Cap Screw. The counterbore dia is .414 and the pilot is .281. what size hole should I bore before I use the counterbore. I used a K drill, which is .281 dia. Is the pilot of the counterbore suppose to fit easily into the pre-drilled hole or is it designed to open up the hole at the same time it is counterboring. I tried this operation with the parameters describe above and it seemed like the pilot portion was binding in the pre-drilled hole. This is the first time I've used a counterbore and I wasn't very successful. Your advice would be helpful. The counterbore is a HSS Keo.

The pilot should slip into the drilled hole. It is only there to guide the counterbore. Use a low RPM and a slow feed. No pecks just plunge all the way to the depth you need. From your previous question you have access to a CNC mill. You would be better off to cut the counterbore with an endmill. You will have a better hole, less deburring, and possibly 1 less tool change in your program if you have another tool already setup to do another operation.

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machine tool setup and operation,selection and use of cutting tools, welding and metalfabrication methods, machining of plastics and metals,cad/cam,cnc,workholding and all related questions regarding metalworking and finishing


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