# Lae Diy Boring Bar Insert?



## AGCB97 (Dec 15, 2016)

I've found myself doing quite a bit of boring of 2+". I'd like to make a larger boring bar to fit my QCTP. I would make the QCTP holder and drill it to accept the bar. I'm thinking a 1  1/4" bar that will take carbide inserts.

What I would like help with is selecting the inserts before I start making anything.

I turn mostly alloy steel and would like to take deepest cuts at fastest feeds. I have several carbide charts but still feel overwhelmed by the choices.

Probably want 80 degree diamond and a large enough size and thickness to give best longevity and withstand an occasional strike of rear shoulder or cutting through a previously drilled hole in material (my material is mostly cutoffs from machine shops).

I've read that uncoated carbide has sharpest edges. Is there a good reason not to use uncoated for roughing?

Thanks for your time!
Aaron

EDIT: This post did not get the right name. My typo and sick computer


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## Tony Wells (Dec 15, 2016)

CNMG432 is my go-to insert for what you describe. It is available in wide variety of coatings when needed, nose radii, and different matrices for different materials. It can, being an 80° diamond, bore and face square shoulders. It's a tough insert, and if you need larger or smaller IC, they also are available to design around. Just bear in mind that the majority of them are negative rake and will take a rigid bar and a healthy machine to use successfully.

Oh, and I use coated for just about everything. But by far the majority of my work is in various stainless grades. But even for roughing, the coatings can be an advantage in most any material. Typically they are harder or can take higher temperatures than plain carbide and hence gain you higher operating speeds and longer life, particularly in hard to machine materials.


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## AGCB97 (Dec 23, 2016)

Here's what I came up with. It is 16" long, 1  7/16" diameter. CR or better.
The inserts are Mitsubishi CNMG 432 grade UE 6005
I'm holding it with a heavy holder that came with the lathe.
Tried it out on a piece of 2 1/2" ID DOM tube and it cuts well at .035 DOC. My lathe has 1  1/2 HP motor

Thanks
Aaron


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## 4GSR (Dec 23, 2016)

That looks like a home made boring bar.  I've made a couple over the years that uses inserts.  Not too hard to make.


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## carlquib (Dec 23, 2016)

That is a good looking boring bar. How much side clearance did you build in. One of the problems I have is having the chips not cooperate and being pulled between the bar and the work. I have tried multiple boring bars but so far I haven't found one that doesn't have this problem when taking a heavy cut. 

Hello, my name is Brian and I'm a toolaholic


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## AGCB97 (Dec 23, 2016)

I tried to get 5 degrees side and front clearance and 5 degrees negative rake in both front and side


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## AGCB97 (Dec 23, 2016)

If I have good success with this one I'll make one sized in between the 3/4" that I have and this


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## 4GSR (Dec 23, 2016)

If you can get your hands on some of the old tooling catalogs like Valenite or Carboloy, they list the insert angles for the different diameters of boring bars they list.  Be surprised how much angle there is on a insert leaned forward on a 1/2" diameter bar.  Its more than 5 degrees for a negative insert.  Even with positive rake inserts, they get leaned forward in the negative direction on smaller bars too.  Ken

EDIT:  Here's a boring bar I made way back when I could see small things.


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## jdedmon91 (Aug 17, 2019)

In these photos are some larger boring bars that I rescued from my old employer before I retired. There made for a CNC lathe, I machined dovetails and put adjusters in them, I’ve not used them often but occasionally they come in handy. The left hand one I use a an turning tool


Sent from my iPad using Tapatalk


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## Firstgear (Aug 17, 2019)

If you are worried about chips, I would put a hole in the bar with a cross hole and tapped for a fitting that I could put air into it and keep blowing the chips out as it went.....put a regulator on the line so you can find the right setting.  This will also add some cooling inside the hole for the cutter.....


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