Boring Issues

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freeqgeek

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Evening Guys-

Making my first real attempt at boring something other than aluminum and am running into issues. Hoping someone here with a lot more knowledge than I can tell me where I am going wrong.

I am working with stainless round stock. Diameter of 1” and 6” in length that is running true in the 4-jaw with +/- .002 TIR. I have a 3/8” boring bar with carbide insert installed in the QCTP and hanging out just a hair over 3”, which when I rotate the stainless should allow me to bore the entire length. I drilled out the stock with a 1/2” drill bit and am now attempting to bore it the remainder with a plan of leaving a wall thickness of .01”.

So here is the problem… God awful chatter and a terrible finish. I have tried adjusting the speeds and feeds. Double checked that my tool is on center. Reduced the tool hangout down to 1”. Tried running dry as well as the other extreme end with way too much oil. Swapped the insert for a fresh one. No matter what I try I get a terrible squeal, chatter, and the finish is not even close to usable.

Would appreciate any advice you guys have to offer.

Thanks!
 
What size QCTP? AXA?

What lathe?

What depth of cut? Which type of stainless?
 
The lathe is a PM-1236 running with a BXA tool post, and I have tried everything from .0050" to .0100" depth of cut.
 
You didn't say what stainless you have, and I'm a noob who has only worked one type, so you might try it, but hopefully someone more experienced offers advice.

The stainless I have work hardens easily and you need to take deeper cuts to prevent it. It's counter-intuitive, but cutting about 0.020" worked best for me. And my lathe is lighter than yours, PM-1127. My steel is 304.

If you have scraps available, you should be able to test outside a bore as well with the same boring bar. It might help you dial in the cut before working on your part.

Some tips I was offered when I had some trouble with SS. https://www.hobby-machinist.com/threads/machining-304-stainless.67116/
 
With a wall thickness of only .010 (finished) you are likely to have nothing but trouble; one thing that would help greatly is to switch to 303 stainless; if the part is hanging out of the chuck that far, use a steady rest, but bottom line, the wall thickness is going to defeat any sort of precision job being possible.
 
Think I would have gotten larger stock and drilled then reamed that ID to size . Then use plugs and turn the OD down concentric to the bore . JMI .

AND , I just saw a .010 finished wall thickness ? Better fill that bore with something , lead shot , bbs etc , to help stabilize that wall cuz it will chatter !
 
Indeed. Boring is NOT a boring subject to me. I have only a few boring jobs under my belt, and they were anything BUT!
 
ttabbal said:
You didn't say what stainless you have, and I'm a noob who has only worked one type, so you might try it, but hopefully someone more experienced offers advice.

The stainless I have work hardens easily and you need to take deeper cuts to prevent it. It's counter-intuitive, but cutting about 0.020" worked best for me. And my lathe is lighter than yours, PM-1127. My steel is 304.

If you have scraps available, you should be able to test outside a bore as well with the same boring bar. It might help you dial in the cut before working on your part.

Some tips I was offered when I had some trouble with SS. https://www.hobby-machinist.com/threads/machining-304-stainless.67116/
Click to expand...

Thanks for the link. That is really helpful.

I don't honestly know what type of stainless it is. I managed to dumpster dive at a local shop and pay twenty-five cents a pound for anything I wanted. Found quite a bit of useful material, especially for someone just starting out. Gave me the opportunity to make mistakes without wasting expensive material... :)
 
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