Boring Problem

[Antman]

I have this problem boring in the lathe in mild steel. The swarf builds up ahead of the tool and pushes out at the end of the bore like a small concertinad cylinder. I don't think it's the tool angles as the swarf curls out behind the tool (as I think it should) in the first 1 or 2 mm, only as the boring gets deeper. Especially bad using a slender boring bar in a deepish bore the boring bar gets deflected, pushing all that connected swarf ahead of if and a tapered bore is the result. PLease give some advice.
Thanks,
Ant

 

[Maryak]

Do a couple of passes with the tool at the same setting, this should take out the flex/taper from the bore.

Hope this helps

Best Regards
Bob

 

[Swifty]

If the bore is small and the boring bar is only just clearing the bore, there may not be enough room for the swarf to travel backwards forcing it to go out towards the headstock. If there is plenty of clearance in the part being bored, you may like to up the feed rate and try to break the chips. While long strands of curly swarf may look impressive, it is a sign of speeds or feeds not being right.

In normal machining operations the swarf should break to prevent long strands fouling the machine or injuring the operator.

Paul.

 

[MachineTom]

There is a fix but it isn't cheap. There is a boring bar made by Micro 100 that is carbide with back rake, chips come out the bore as a single almost wire like chip. Works great except for the cost. You didn't say what kind of cutter you are using, Insert, HSS, brazed carbide. changing the angle of cutter to bore to more or less positive may have a effect as well. Negative rake tools tend to make the little balls of chips, more feed tends to stop that.

Try one thing at a time, feed, speed, DOC, angle.

 

[Antman]

Thanks Bob, Paul and Tom. I'll try to put your advice into practice, but I'll be away until next week. Although I'm asking so many questions I am making things with my shaky technique, believe it or not, though not engines yet. Still hoping to get to a level of competence where I don't have to ask such basic questions. Thanks again for your answers and patience.
Ant

 

[rake60]

Every boring cut I take on my hobby lathe is followed by a "spring cut".

If the "spring cut" looks heavy it gets another "spring cut" before I move on.

After the bore is roughed to within .020" of finish size, I will repeate that cut until it no longer makes a chip.

After that, I take .007" on a side twice to check for taper and finish.
Then .007 on a side more on a side twice to confirm the first pre-finish cut results.

At that point it's now or nothing.
Dial in what is left and take the finish cut.
It will never be oversize.
If it ends up undersize, you have to take very light cuts to bring it to size.
The finish will be bad, but that happens...

Rick

 

[Swifty]

Ant, don't be afraid to ask basic questions or what you may think are silly questions. People aren't born with a mechanical aptitude, it comes with experience and the members are willing to share their thoughts on any problems.

Paul.

 

[deverett]

Ant, don't be afraid to ask basic questions ...
it comes with experience ...
Paul.

Good judgement comes from experience.
Experience comes from bad judgement.

Dave
The Emerald Isle