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Subject: Milling grey cast iron

Date: 12/01/00 at 12:37 PM
Posted by: David Heath
E-mail: dmheath@telocity.com
Message Posted:

I don't have a lot of experience with machining cast iron other than drilling and tapping. I have a 11"x6"x1.75" plate I was milling to size. I used a 5.5" face mill with 8 carbide inserts. It has a 7 pos. rake and 11 clearance angle. The machine is a Bridgeport Series 1 VS.

I squared up the block and sized the length and width without having to remove much material, but I had to machine the thickness down to 1.412". I ordered the plate as 1.5" and didn't realize the raw casting would be that much thicker.

Anyway, that's a lot of material to remove. I started removing 0.050" doc by about 60% of the tool width at about 1ipm feed rate and 200fpm. The machine chattered and shook quite a bit. My machine is in very good shape and didn't expect that sort of behavior out of it. So, I increased and decreased the surface speed without much effect. I couldn't imagine feeding any slower, so I increased that to about 2-3ipm. That solved that problem.

I figured 0.050" x 6 passes wouldn't be too bad for the rough cutting then finish it to size. Well, now when I'm taking the light cuts (2-5mils), it starts to chatter every now and then. So, I backed the feed back down to 1ipm (not unusual for finish cutting). That helped, but still acts like it wants to chatter ever so lightly here and there.

I managed to finish the plate very nicely, but am still concerned about my procedure. Other than getting a plate closer to thickness next time, does anyone have any suggestions as to what I am doing wrong? Also, I started off squirting cutting oil on to cool and lubricate, then stopped to see what would happen and it seemed to cut better without. Wrong cutting fluid maybe?

Thanks for any help,
Dave


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