Back plate fix

L

Larry$

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Several years ago I bought an 8" 3 jaw chuck and turned a back plate for it. My first experience with cast iron. It seemed to fit snug but there was runout. I attributed that to the chuck not my poor attack on the cast iron. I've been on a campaign to get my tools improved. I just finished aligning the head stock on my lathe. This morning I did a series of tests and concluded it was as good as I was likely to get. I took the back plate off the chuck. D1-4 spindle. Put my Mitutoyo dial test indicator on it. Not good! I needed to take a shave on it. Tried HSS, total failure. Got out a tool with a CCMT insert, dull. Turned the insert around, much better. I turned the back plate a little thinner to get a new ledge to fit the chuck to. Each time I got to the new ledge there was resistance to cutting and then the tool would jump forward and chips would fly. Not a good way to approach and exact fit. I sharpened a HSS tool on the tool & cutter grinder. Gave that a try, no go, trashed the edge instantly. Back to the inserted tool and jumps. I got lucky and got a very tight fit. Many trials.

Time to test the results. I put a piece of 1 1/2" aluminum in the chuck and turned it smooth. Turned it around in the chuck and using the same tool position turned up to the other cut. Much to my surprise an near perfect mach. That chuck is better than I thought. Once again luck trumped talent.
 
Wow, sorry to hear about your difficulty cutting the cast iron. I used a cheap Chinese barbell weight, and as soon as I got through the skin, HSS cut it just fine. It produced a fine dusty powder that got on everything. The machining went great, though. Good to hear that you were successful in the end. Did you use a pre-made blank, or did you source repurposed cast iron? I've heard that the better quality material is more uniform and easily machinable. Still, I have had decent luck with broken drain covers, junk weights, etc. I stay away from window weights, though. They just look too nasty.
 
It would seem that you likely turned the CI with HSS at way to high of SFM if it did not hold up; before carbide was invented, folks managed to cut hard cast iron with HSS, and even carbon steel if appropriate cutting speeds were used.
 
ericc said:
Did you use a pre-made blank,
Click to expand...
Yes, I got the ready-to-machine D1-4 back plate blank from Grizzly. I tried to ease an edge with a file. File wouldn't touch it, damaged the file.
 
That doesn't sound like cast iron? Damaged a file? Weird, never seen that
-Mark
 
A chill spot in cast iron can damage a file. It can be really hard. Also, lower carbon inclusions in cast iron can get hard. This can be demonstrated by dotting a piece of cast iron with a few arc welding beads. I have done this experiment with mixed results. Some get worse than others.
 
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