What's with this boring bar? Insert moves(maybe?)..............

david n · Dec 27, 2019

This is the only 55° insert boring bar I have in the shop......5/8"Ø.............DPMT21.51 insert..............don't really use them. Now I have this Ali part that I want to back bore a tight-ish Ø(+/-.0008) and part off..........one op. Super light cuts......one rough at about .05 and then finish around .015 doc.............I have been fiddlin' fartin' with this piece-o-crap for pert-near an hour and my Ø's are all over and the Z depth is wacked too...........AFAICT the insert must be wishy washy in the pocket.......but the screw is snug and I can't really see if it moved............anyone else have problems with this style insert/boring bar? Or is it just the one I have that is cursed? I tried lighter DOC but no go.....I get a few good parts and then scrap.............Adjust the offset and just more of the same................I might just order up a new one.............

fmari --MariTool- · Dec 27, 2019

Yea,
Sounds to me like the insert is moving in the pocket. Pocket walls may be damaged or something just not lighning up. If your in a pinch a little lok-tite will do the trick. Best thing to do is just replace the boring bar, put some red tape on this one and look at it when you have time.

Delw · Dec 27, 2019

david n said:
This is the only 55° insert boring bar I have in the shop......5/8"Ø.............DPMT21.51 insert..............don't really use them. Now I have this Ali part that I want to back bore a tight-ish Ø(+/-.0008) and part off..........one op. Super light cuts......one rough at about .05 and then finish around .015 doc.............I have been fiddlin' fartin' with this piece-o-crap for pert-near an hour and my Ø's are all over and the Z depth is wacked too...........AFAICT the insert must be wishy washy in the pocket.......but the screw is snug and I can't really see if it moved............anyone else have problems with this style insert/boring bar? Or is it just the one I have that is cursed? I tried lighter DOC but no go.....I get a few good parts and then scrap.............Adjust the offset and just more of the same................I might just order up a new one.............

View attachment 273477

do you have the correct screw? I never had problems with min, they are sanviks I think yours is too? do you have the correct insert?
the back side of that pocket looks to be gapped a tad
I never done .050 depth of cut I do max as .020 with them. but on steel. (just saw you said Alum.) shouldn't be a problem however that's the wrong insert for alum in that bar, your chips are building and causing your problems I bet. are you on center?

wrustle · Dec 27, 2019

Delw said:
do you have the correct screw? I never had problems with min, they are sanviks I think yours is too? do you have the correct insert?
the back side of that pocket looks to be gapped a tad
I never done .050 depth of cut I do max as .020 with them. but on steel. (just saw you said Alum.) shouldn't be a problem however that's the wrong insert for alum in that bar, your chips are building and causing your problems I bet. are you on center?

Yeah, my thoughts exactly on the insert. Looks like a molded edge, not ground.

csteen · Dec 27, 2019

likely insert moving yes as others have said. Sandvik has a proprietary insert in that style, not sure if they go that small of IC they definitely reduce the amount of movement in the pocket.

gregormarwick · Dec 27, 2019

I use DCMT all the time, and generally don't have a problem with them.

Negative rake D shape inserts are prone to deforming the pocket if they get pushed in Z, like going a notch too far when touching off against a stationary part - less of an issue with positive rake inserts usually, but it's possible something like that may have happened to your bar.

Or maybe the steeper rake angle of the DPMT makes it locate less repeatably than DCMT, I don't know.

csteen said:
likely insert moving yes as others have said. Sandvik has a proprietary insert in that style, not sure if they go that small of IC they definitely reduce the amount of movement in the pocket.

You're referring to the Coroturn TR system, they have a singe fixed IC of 11mm.

They work very well, but the inserts are significantly more expensive than generic DCMT/VBMT.

Illinoyance · Dec 27, 2019

I am in agreement with those who suspect a deformed pocket in the bar. It sounds like you have enough time invested in this to pay for a new bar. In Ali I think you would want a CCGX insert.

Ox · Dec 28, 2019

Well - you obviously don't need us to tell you that the insert is moving around, but yeah, we can confirm it I guess....

I haven't ran the numbers on your bar, but I think that you should.
I wonder if your bar is not meant to run the metric insert, and you need to get the right insert?

I have been in your shoes on 35* inserts in the same app, only to find that some wrong inserts got mixed in.
They are almost the same, but will result in this wishy worshy experience if going one way.
I'm guessing the other way the insert just wouldn't fit, but not been down that road yet I don't think.

--------------------

Think Snow Eh!
Ox

guest · Dec 28, 2019

That's a Kennametal boring bar, DPMT21.51 is the correct insert.

Dmin is .800", so first pass has to be at least that diameter or it's gonna rub...

CarbideBob · Dec 28, 2019

It should not be moving but the post says back boring which this tool is not great at.
Rough in and then back? All back?
In AL I do not know if insert shift or chip weld, I'd tend towards built up cutting edge giving how it come and goes. In that case a new bar or pocket will not help you.
Bob

michiganbuck · Dec 28, 2019

Shoulder bump at the bottom of a bore can change the direction of cutting forces to push an insert a tad the other way at the start. The far side of the radius intersecting the part before the outer edge is in the cut..I have set a .015 shim at my stop to go .015 less depth with each next pass. Doesn't matter as the part will vb e parted off

doug925 · Dec 30, 2019

IMHO, the SDUPR insert holder is weak!
I have a few of them, for internal profiling applications.
Once an insert is destroyed, or the bar crashed, it is worthless.

The insert pocket wall, rest pads, get smushed, and allow the insert to rotate about the screw.
Your X's & Z's will be off, and continue to change, until the insert hits the opposite pocket wall.
Just my $0.02.

Doug.

CarbideBob · Dec 30, 2019

doug925 said:
IMHO, the SDUPR insert holder is weak!
Doug.

Duh....even if new inserts in a molded IC "M" and brand new bar you can not forward and back bore.
You can not even measure one of thees in manufacturing process with a M, this is why they make ground IC inserts.
Lower cost tools in the pocket will not do what others can. In many cases using the lower cost will work just fine.
Using this locator you run into problems as any wiggle moves the cutting tip a lot.
M inserts do not "fit" the pocket and should only be fed in one direction or force. Yes many do other but it is a crap shoot.
Pin and top clamp are much more successful in such use than screw downs so everyone loves a CNMG.

It is a very unpredictable holder but I do wonder about others as in built up edge mucking with things here.
Despite what seems to be clear this is not a backbore tool.
Bob

david n · Jan 4, 2020

New bar...............works perfect. Inserts weren't the problem. DPMT and DPGT style are both working. Old bar went in the scrap bin.

Search

Largest Manufacturing Technology Community on the Web

Search

What's with this boring bar? Insert moves(maybe?)..............

david n

Diamond

fmari --MariTool-

Titanium

Delw

Stainless

wrustle

Titanium

csteen

Aluminum

gregormarwick

Diamond

Illinoyance

Stainless

Ox

Diamond

guest

Guest

CarbideBob

Diamond

michiganbuck

Diamond

doug925

Titanium

CarbideBob

Diamond

david n

Diamond

Similar threads