Boring finish troubles

My formal training is graphic design, haven’t done much machining but I’m really enjoying it.
I’m try to bore a 4.5” in 1018 to fit a bearing and my finish has sucked and final size has not been accurate.
I’m running an Haas ST20, I’ve got a Sandvik 1” boring bar with CCMT 09 T3 insert. I think I’m reading the numbers correctly, .012 depth cut and 1550 sfm.
I’m drilling out to 1.4 and trying to finish out to about 4” . The bar is squealing like a stuck pig and the finish is terrible.
I’ve got the bar out about 6”, which I’m going to try and move in today. Not sure I’m using the right cutter to take off that much material? Like I said, I’m pretty green so any help is appreciated.

If you're really running at 1550 SFM, that's too fast. Try 400 SFM to start, move up if it runs well.

Shorten the boring bar as much as you can, but ensure you're not going to hit anything.

Let us know the condition of used cutting inserts, ideally post a clear picture of what the edges look like after use. Same goes for your boring bar mounting method and part chucking, every picture tells a story...

bpfohler said:

My formal training is graphic design, haven’t done much machining but I’m really enjoying it.
I’m try to bore a 4.5” in 1018 to fit a bearing and my finish has sucked and final size has not been accurate.
I’m running an Haas ST20, I’ve got a Sandvik 1” boring bar with CCMT 09 T3 insert. I think I’m reading the numbers correctly, .012 depth cut and 1550 sfm.
I’m drilling out to 1.4 and trying to finish out to about 4” . The bar is squealing like a stuck pig and the finish is terrible.
I’ve got the bar out about 6”, which I’m going to try and move in today. Not sure I’m using the right cutter to take off that much material? Like I said, I’m pretty green so any help is appreciated.

Click to expand...

I thought it was way too fast but that was the manufacturers suggestion. I’ll shorten the bar and slow down.

Always hold a boring bar with its insert to a radius to see perhaps 7*+ clarance under the cutting edge ..and that all the heal is well clear of and getting close to the bore ID.

Yes, look at the starting ID hole size with holding the boring bar assy to the part. eyeball look is close enough.

Agree as short as possible.

For a one-up take your time with a light feed rate and not the fastest RPM.

Consider the bottom of the bore(depth) so not crashing into a full insert cut at bottom of the bore.

QT: [I’m drilling out to 1.4 and trying ...

So you want to hold it to a 1.4 bore and be assured the boring bar and its insert have clearance below the cutting ...held just the way it will set in the machine.

The insert/ bit lead portion needs axial clearance (going forward) and radial clearance (going around) and back taper(edge falling away from the inside at behind the cutting action.

Setting the lip below the center can diminish expected and needed clearance.

Setting high above center can change the rake attitude.

In regards to the title...maybe try to liven things up a bit, nobody likes a boring finish.

Thanks, I'll be here all weekend

plastikdreams said:

In regards to the title...maybe try to liven things up a bit, nobody likes a boring finish.

Thanks, I'll be here all weekend

Click to expand...

"ba-dum-bum-CHING"

Length of boring bar before chatter:
Steel = 3x bar diameter
Carbide = 5x diameter.

Try .02doc, 600sfpm .004ipr