Small boring bar that will break 304?

Comatose · Nov 18, 2015

I have to bore some 304 stainless. The bore is .230 inch and about 3/4 inch long. This particular batch of 304 is really nastily stringy and its eating through my supply of solid carbide boring bars. It won't even break when I plow through the outside with a CNMG 432. Just wraps up andbif I don't pick the stringers off the bar just about each part, snap.

Short of doing a ton of pecks, does anyone have a recommendation for source of solid carbide boring bars with a chipbreaker that will reliably break 304 or a better technique?

Right now I am running 0.015 width of cut, 2500 rpm and 0.003 inches per rev.

Thanks!

iMillJoe · Nov 18, 2015

More speed and more feed.

Mtndew · Nov 18, 2015

What bar are you using now?
We use Sandvik and for the really small stuff we use PHorn

bsmith · Nov 19, 2015

Why not ream it? .015 depth of cut seem a bit much for such a small hole. Drill it closer.

bjorn toulouse · Nov 19, 2015

Mtndew said:
..............for the really small stuff we use PHorn

At work we use PHHorn on 316 & 316L with excellent results.

Rex

Hertz · Nov 20, 2015

Is it possible to switch to 316? I mean the price difference on that small of a part would be almost nothing but will cut much better.
304 is so unpredictable. My experience is I've found it to be different every time I cut it. Get a part, tweak the program, everything runs great. Next time the job comes up, shit just doesn't work. Almost as if someone messed with the proven program.
Back to the original question, I agree with bsmith, if you can, ream it rather than trying to bore. Of course this is if you are not too concerned about concentricity.

SIM · Nov 20, 2015

Hertz said:
Is it possible to switch to 316? I mean the price difference on that small of a part would be almost nothing but will cut much better.
304 is so unpredictable. My experience is I've found it to be different every time I cut it. Get a part, tweak the program, everything runs great. Next time the job comes up, shit just doesn't work. Almost as if someone messed with the proven program.
Back to the original question, I agree with bsmith, if you can, ream it rather than trying to bore. Of course this is if you are not too concerned about concentricity.

Seemed like words from my mouth...although the last part I'd locate and straighten hole with the kiss of a boring bar before reaming.

I have also been know to use an endmill...HSS or Carbide...1,2,3 or 4 flutes and plunge the drilled hole to size or leave a bit to clean with reamer/boring bar depending on whats needed.

I have found 304 to be like cheap aluminum...perfect chips one time and gummy birds nests on the next lot of material.

Dupa3872 · Nov 20, 2015

We do a lot of small stuff just as you described in everything from Titanium to Delrin. Sandvik makes a CXS line of small boring and other I.D tools. Check it out you will need to buy a holder but the tools/system is the best Ive found. Changing a small solid carbide bar is as easy as changing an insert. These tools have saved us tons of time/money.

Make Chips Boys !

Ron

Mr Dean · Nov 28, 2015

Use a replaceable carbide tip drill I recommend a sumitoyo the finish will be better

[uQUOTE=Comatose;2656630]I have to bore some 304 stainless. The bore is .230 inch and about 3/4 inch long. This particular batch of 304 is really nastily stringy and its eating through my supply of solid carbide boring bars. It won't even break when I plow through the outside with a CNMG 432. Just wraps up andbif I don't pick the stringers off the bar just about each part, snap.

Short of doing a ton of pecks, does anyone have a recommendation for source of solid carbide boring bars with a chipbreaker that will reliably break 304 or a better technique?

Right now I am running 0.015 width of cut, 2500 rpm and 0.003 inches per rev.

Thanks![/QUOTE]

Use a replaceable carbide tip drill th finish will be better and you will save a lot of time

Rapid_Tech · Nov 29, 2015

I doubt you'll find any boring bar that can break the chip on a small bore like you have. Drill as close to size as you can, which shouldn't be very hard, and take 1, maybe 2, cuts with the boring bar depending on size and surface finish. Make sure your coolant is fairly rich and that it's getting shot right into the hole. If you're lucky the coolant may push out the chips.

When you say you're plowing along when OD turning what exactly do you mean? If you're not feeding at least .015-.02 per rev, depending on OD size, then you'll never break the chip.

2outof3 · Nov 29, 2015

bjorn toulouse said:
At work we use PHHorn on 316 & 316L with excellent results.

Rex

Yup. Also try to bore from bottom out if you can.

Krovvax · Nov 29, 2015

Rapid_Tech said:
I doubt you'll find any boring bar that can break the chip on a small bore like you have. Drill as close to size as you can, which shouldn't be very hard, and take 1, maybe 2, cuts with the boring bar depending on size and surface finish. Make sure your coolant is fairly rich and that it's getting shot right into the hole. If you're lucky the coolant may push out the chips.

When you say you're plowing along when OD turning what exactly do you mean? If you're not feeding at least .015-.02 per rev, depending on OD size, then you'll never break the chip.

Qell to be honest if you need to push up to 0.015 to 0.020 ipr you realy sont have the good chip breaker for your job. I can start to break chips at 0.008 at 0.100 doc. I usually rought at 0.012 to 0.015 to be honest.

Rapid_Tech · Nov 29, 2015

Krovvax said:
Qell to be honest if you need to push up to 0.015 to 0.020 ipr you realy sont have the good chip breaker for your job. I can start to break chips at 0.008 at 0.100 doc. I usually rought at 0.012 to 0.015 to be honest.

Maybe it's because you Quebecers like to take your time

. We in Ontario like to get things done. The point I wanted to get across was you have to up the feed rate to break the chip. Feed rate also depends on the diameter of the material. If you're turning .5" material you may only need .008ipr to break the chip, 3" material may need .025ipr. Oh, and I do have a good insert for the job, my favourite being Sandvik 2025. If it allows me to rough faster, why wouldn't I?

Krovvax · Nov 29, 2015

Rapid_Tech said:
Maybe it's because you Quebecers like to take your time . We in Ontario like to get things done. The point I wanted to get across was you have to up the feed rate to break the chip. Feed rate also depends on the diameter of the material. If you're turning .5" material you may only need .008ipr to break the chip, 3" material may need .025ipr. Oh, and I do have a good insert for the job, my favourite being Sandvik 2025. If it allows me to rough faster, why wouldn't I?

Ive never said i like to take my time or whatever. The point is alot of people dont use good grade/chip breaker and start bitxhing about 304/316. Yes they can be challenging sometime but there is way harder stuff to work with. I would like to puah my lathe to 0.025 but he dont like it so i go with something that work good and that i dont have to babysit and can make more money somewhere else.

I was not trying to be cocky i was just trying to help.

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