Thread: Boring head cutting unwanted taper.

I’m using a boring head to open out a 16.5mm hole to 18.0mm in 25 thick 1214. I’ve tried to make this part 3 times and I’m consistently ending up with an inconsistent taper of 0.1 to 0.2mm, big at the top small at the bottom.


I can’t see what the problem is, I have the quill locked, head is trammed, 500RPM, brazed carbide tool, Bristol Ericcson tenthset boring head. Any thoughts?


I’m starting to suspect the bearings, I remember Dave J did a write up on replacing the bearings in an HM52 a while ago.

Time to change to HSS I'd say.

Stuart

edge buildup on the carbide making the tool rub and not cut maybe?

My thoughts also. I used a carbide tipped lathe tool in a fly cutter, and it did a similar thing.
Kryn

Another vote for a problem with the brazed carbide tool here. I've never had much success with the cheapo brazed boring bar set I have for my boring head, just don't cut at all well. Best thing I ever did was buy a bar for it that takes TCMT inserts - now my boring head makes far smoother bores than my lathe, and I don't even think I've turned the insert around. No chatter, nice little spirals of swarf every time.

You might be able to try more RPM though? I'd run my insert bar at probably 1200-1500 for that size hole, and that'd still probably be on the slow side compared to recommended cutting speeds.... Maybe try 800-1000?

I agree with the comments about brazed carbide toolbits. They often don't have the right relief on them and scrape rather than cut. The side thrust tends to push the tool away from the work when that happens. You can get a much sharper edge on HSS anyway.

Have you had similar problems in the past when using this?

HSS was the answer, thanks guys.

I made a HSS boring bar as stiff as the job would allow, the hole I was having trouble with is now boring true.