Problems with a 1.5" dia bore, 4" deep, BP clone, Criterion boring head.

[4GSR]

If your lathe will swing this, drill and bore it in the lathe instead of the mill. Or rig it up and line bore on the lathe.

 

[AlfaGTA]

So too late to make this right, but i would offer some pointers fro future work.
material looks to be cold finished.....Lots of internal stress in that stuff.
Would have drilled a through hole first close to required size.
Then cut the slot for your clamp. drill and tapped for the pinch bolt. fit sims to be tight in the slot...leave the shims long to protrude into the bore.
(this will eliminate having an interrupted cut at the slot when boring) Fit the pinch bolt and snug up....Slot done before the finished bore will eliminate post slot movement that can disrupt the bore.
.I am with the poster that suggested a solid boring bar directly mounted in the spindle, at the vety least a full 3/4" bar with a separate tool bit in a cross drilling for your boring head.
Set size by moving the tool bit, use indicator to gauge....
Best on your BP clone to feed using the knee.....Make a simple driver to fit the elevating crank dog coupling and use a cordless drill to move the knee.....
Sharp tool....Perhaps an Aluminum style positive insert with a very small radius on the nose.

Cheers Ross

 

[Overland]

So too late to make this right, but i would offer some pointers fro future work.
material looks to be cold finished.....Lots of internal stress in that stuff.
Would have drilled a through hole first close to required size.
Then cut the slot for your clamp. drill and tapped for the pinch bolt. fit sims to be tight in the slot...leave the shims long to protrude into the bore.
(this will eliminate having an interrupted cut at the slot when boring) Fit the pinch bolt and snug up....Slot done before the finished bore will eliminate post slot movement that can disrupt the bore.
.I am with the poster that suggested a solid boring bar directly mounted in the spindle, at the vety least a full 3/4" bar with a separate tool bit in a cross drilling for your boring head.
Set size by moving the tool bit, use indicator to gauge....
Best on your BP clone to feed using the knee.....Make a simple driver to fit the elevating crank dog coupling and use a cordless drill to move the knee.....
Sharp tool....Perhaps an Aluminum style positive insert with a very small radius on the nose.

Cheers Ross

Thanks Ross for taking the time.
I've done several bores on my BP clone with similar setups, but not as deep.
Combination of depth, material not consistent, quill extension, and not the best boring tool.
This is not a critical dimension job of course, but still always good to do it right.
Next time, my new-to-me Mazak VTC I hope.
One of these days I'd like to get some DeVlieg Microbore inserts and make up some bars to go in a BT40 holder, but don't quite understand what the bore in the bar should look like for the inserts.
Bob

 

[GregSY]

I'm beginning to feel like a machining genius now that I see that setup. I cant imagine a better job for a reamer/cutter as opposed to a boring bar. All day long.

 

[Overland]

I'm beginning to feel like a machining genius now that I see that setup. I cant imagine a better job for a reamer/cutter as opposed to a boring bar. All day long.

Use what you've got on a one-off job like this.
Do need to get an index able boring bar though.
Bob

 

[JohnMartin]

One reason for bores being larger at the start is that one will typically feed the bar in a short way then pull it out to measure. Expecting a spring pass to bring the entire bore to a constant size after that, especially on a machine with some flex, just doesn't work. And cutters that are less than dead sharp will push off on spring passes.

 

[Overland]

What style of indexable tip boring bar would you guys recommend, for a Criterion 3/4" head ?
I see several with TPG inserts, but I hate them from my experience in a facemill.
Main use would be low carbon steel, on a vertical CNC.
Thanks
Bob

 

[michiganbuck]

qt op (Main use would be low carbon steel, on a vertical CNC.) Fingernail shaving sharp for starters.

 

[mattthemuppet]

What style of indexable tip boring bar would you guys recommend, for a Criterion 3/4" head ?
I see several with TPG inserts, but I hate them from my experience in a facemill.
Main use would be low carbon steel, on a vertical CNC.
Thanks
Bob

TPMT/ TPGT would work well, STFCR is the boring bar code from memory. Front clearance (looking down at the top of the insert) is either 0 or 3deg, so it doesn't leave ridges on the face of the bore like a pointier bar will, if that makes sense. You can get TPMT (molded, for steel/ CI) and TPGT (ground, for alu/ plastics) in all kinds of grades and coatings, they're really common.