MILL BORING HEAD MAKING TAPER

[Swarthy]

My first mill ( Bridgeport series 1 clone with R8 tooling) 3" boring head used with a vertical tool holder ( S12S-SDUCR3 with dcmt 11t308 mt tt8125 insert. Boring a 3" hole x 3" long always makes a taper about 1-2 thou. My finish is great but on long boring jobs it make a small taper ??

Question is it my mill my tooling or me?

 

[mmcmdl]

You . Take a spring cut . The bar is most likely flexing .

 

[Mini Cooper S]

First for more accurate holes I always take 2 or 3 "free cuts" to help remove any flex in the setup. Also keep the work as high as you can, the less that the quill extends, the less quill deflection there will be. One last thing, I don't know how long your boring bar is sticking out of the boring head, but it helps to keep that as short as possible. One more last thing, it may help to tighten the quill lock clamp just a little bit to help take up any clearance ( looseness) in the quill.
Richard

 

[DavidR8]

Tool stickout and quill extension is going to increase deflection. Keep both to the absolute minimum.

 

[mmcmdl]

I hate using inserted tooling with boring heads also . A good HSS or solid carbide are my go tos . I grind a dead sharp point on either with no issues .

 

[benmychree]

I hate using inserted tooling with boring heads also . A good HSS or solid carbide are my go tos . I grind a dead sharp point on either with no issues .

I quite agree with Dave on this issue, most carbide inserts do not have a sharp enough edge to cut freely, and no amount of free cuts is going to remedy that situation.

 

[RaisedByWolves]

First for more accurate holes I always take 2 or 3 "free cuts" to help remove any flex in the setup. Also keep the work as high as you can, the less that the quill extends, the less quill deflection there will be. One last thing, I don't know how long your boring bar is sticking out of the boring head, but it helps to keep that as short as possible. One more last thing, it may help to tighten the quill lock clamp just a little bit to help take up any clearance ( looseness) in the quill.
Richard

And another last thing…..

Make sure the cutter regardless of the material is clocked backwards of the direction of cut 5ish degrees or so.

And as mentioned, spring passes.

I’ll do a couple coming up to size, say .005-.010 away from the final dimension to let things settle in a bit, then a few for the setting that mathematically gives the finished size.

Hint, boring heads don’t always agree with math.

 

[Swarthy]

In review of the answers, I think clocking the cutter and using a hand ground sharp cutter are my favorites. all the others i was already doing. thanks for the help

 

[Dan_S]

In review of the answers, I think clocking the cutter and using a hand ground sharp cutter are my favorites. all the others i was already doing. thanks for the help

do you have hones to make the tool truly sharp, and keep it that way?

imo, people grind to much and don't hone nearly enough.