Setting my boring bar

R

raferguson

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I bore infrequently on my 7x12 minilathe. The last time I was boring I struggled, and the chips were not curls, but little tiny particles. At that time, I recall being told that was just wrong, that I needed to produce curly or continuous chips. I recall rotating my bar to get it to produce curly chips. Now I am trying to bore again, and I have tried rotating my bar, but am not having any luck producing continuous chips. Was I just lucky last time? Is there a system that I can use to set up the boring bar?

I read some articles on line about boring, and honestly they were discussing forces and angles and carbide inserts and relatively sophisticated aspects of optimizing boring, but did not seem to give much in the way of hints on setting up my boring bar. I have the usual Little machine Shop Chinese brazed carbide boring bars. I have selected the shortest bar to reduce vibration. I am trying to bore to 5/8" ID for a ball bearing.

Hints would be appreciated.

Richard
 
What material are you trying to bore at what diameter bore and what depths of cut are you trying to take at what RPM?

If you're getting something more like dust than chips, it does sound like you're rubbing more than cutting.
 
Mild steel, 5/8" ID. Depth about 3/16".

I do not know the RPM, maybe 500 RPM. Depth of cut maybe 0.002 inches. But it is not cutting.........
 
Have you checked height, rake angle of the boring bar? have you checked if it is rubbing the bore?

Also, here is a brief explanation of tool alignment by Quin Dunkley AKA "Blondihacks"

 
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Brazed carbide is often not sharp enough to work well on a small machine. I've mostly made my own using HSS blanks. If you have a welder you can tack a hss blank into a slot in the end of a rod, and then cut some relief angles in the cutting tool pretty fast. You can even cut the slot by holding the bar in a tool holder on the lathe and put an endmill in a collet chuck (or a 3 jaw if you don't mind breaking the rules!)

I also have a pre-ground hss boring bar from Accusize Industrial off Amazon that works fine if you don't want to do that work.

A hair above center seems to work ok for internal boring.
 
www.hobby-machinist.com

A Boring Primer

Boring on the Lathe for (New) Hobby Guys A Primer Being able to bore an accurate hole on the lathe is an important skill every hobby guy should have. We may not need to bore a precision hole all that often but when we need to, we should be able to. As we all know, that is easier said than...
www.hobby-machinist.com www.hobby-machinist.com
 
Has your boring bar been sharpened with proper clearances since you bought it? Generally, I set my tools on center, and they have clearance ground on end, front, and back rake, I use insert tools with TPG inserts and for smaller bores I use form relieved Bokum tools, which are sharpened on the top only.
 
I get the idea that these little lathes prefer HSS tooling, I have heard that before. I looked for premade HSS boring bars, but did not find one. Could I buy a piece of drill rod, heat it red, and then give it a little bend, and grind off what I do not need? I am not concerned about that part of the process, but a bit unsure about sharpening...... Would I need to harden drill rod after I heat it red hot? I have a temperature controlled kiln, and I also know how to use color to temper, do I have options there.

What would it take to sharpen a carbide boring bar? Could I do that with my standard bench grinder, or do I need a special wheel?

Richard
 
Check out what micro100 has to offer for boaring bars. They have bars that appear to be well suited for smaller lathes and seem to be highly recommended.

Micro100

www.micro100.com www.micro100.com
 
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