Cast iron milling

I am using a mini mill to mill the lead screw mount bracket for a mini lathe. The bracket appears to be cast iron, although I have no way of finding out what type. I have tried 2 straight center cutting flutes, 4 straight, slow and high spiral center cutting flutes. I have tried them at slow speed and slow feeds, slow speed and high feed and fast speed at high feed. Duh, it still always tries to gouge into the work either at the start or end of the cut. Slow speed means about 400 rpm and fast is about 1700. Feeds where either 5 or 10 IPM. The cutters are all 3/8" shank and cutting diameter. Some are HSS some are carbide coated and non coated.

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Cast iron is not a material to try taking "skin" cuts because of the hardness of the surface scale (usually has a lot of residual sand in it also). The rule of thumb (I've heard) is to "bury" the cutter and use a heavy feed.

Your description sounds like a combination of two factors:

Lack of rigidity in the machine and/or setup is allowing the cutter to raise and ride on the surface until the end of cut where less contact is present and consequent digging in.

The corners of your endmills are almost immediately broken down when hitting surface scale and either cause or add to problem described above.

Good Luck!

Reply to
Ace

Perhaps a dumb question, but are you locking the Z axis? If it's a Chinese mini-mill, it will always tend to suck itself downward. This is due to the slop in the Z-axis feed. You *must* lock the Z-axis every time. If plunge cutting, feed with one hand and apply pressure to the locking lever with the other. This gives you some a way to add friction while you are plunging. When you reach final depth, lock it.

-G

Reply to
Greg

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