Boring head diameter vs bore diameter

Bill D · Jun 24, 2010

Never really used a boring head. I do not find info on head diameter relative to the bore size it can cut. I know the bar can be put in horizontally to make almost infinate size bore. But with say a 3" diameter head and a 5/8 bar what is the largest size vertical bore it can cut. I realize the smallest size is limited by the bar size but I do not find good info on the offset allowed. Or the amount the non centered vertical bar hole(s) is offset from the centerline.
Why buy a smaller head other then cost? As I see the geometry the head can not go into the bore if the bar is vertical. IOW the bore is smaller then the head unless the boring bar is horizontal.
Since most heads on ebay are 2-3 inches I assume that is a good size for a bridgeport.
Bill D.
PS: can you use a smaller bar for a smaller hole if you make a sleeve for it?

joe m · Jun 24, 2010

You can use a 2" head to bore a larger hole but it is best to keep the cutter close to the head for rigidity if holding a close tolerance on a part. I have made sleves to hold a smaller shank bars in a larger head hole with good results. You will need to drill the sleve to align the set screw to grip the bar securly.

I use my 2" head more often to the 3" head. Your applications may be different. But you can never have too many tools in the box.

Dave K2 · Jun 24, 2010

Hows about a 3" head cutting a 12" diameter...

Cast iron cylinder block and the result was excellent. Tip was carbide.
The height was cut in two stages using quill feed and the final cut was made with quill locked and the knee was lifted.

Good fun all round

smdubovsky · Jun 24, 2010

In my limited experience, the only difference is how far over you can adjust them before you have to move the boring bar to the offset hole (plus increased rigidity Im sure.) A 3" head will be able to adjust ~50% more than a 2" head. I only have a 3" head for my BP and have not wished it to be smaller (yet). I've not yet needed to used it like DaveK2 w/ the bit mounted sideways.

I have run into the problem where I've wanted a larger one. Say I had to open a hole from 1" to 2.5". W/ the bar in the offcenter hole, you can't 'back up' enough to start boring the 1" hole, so you have to use the centered hole. Then at some point you run out of adjustment range and have to move the bar from the center hole back to the offset hole. A little bit of a pain in you have to do it a couple times (and you loose the exact micrometer setting when you move the bar!) but nothing impossible. I kept thinking w/ an even bigger one you be able to do it in one shot.

You can use a sleeve to fit a smaller bar. Same way a lathe does it.

Croz · Jun 24, 2010

Phew Dave, is that an R8 taper on that mill?

adama · Jun 24, 2010

Whilst i have a bridgeport i only have a 2" head as it was purchased when i had a old mill drill type "thing" Using the cross hole i have done a fair few at 4" and every thing was stable at that, sorta got the impression i could go a lot further out.

Dave K2 · Jun 24, 2010

Croz said:
Phew Dave, is that an R8 taper on that mill?

Bog-standard R8 spindle vari-speed bridgy, about 1983 i think.

It seemed quite happy but was only taking light cuts of about 0.3-0.5mm i think.

It took a while :rolleyes5:

donie · Jun 24, 2010

This is a bar I made for a larger Criterion square head, for enlarging the cylinder bore for motorcycle crankcases, sometimes over 4".
I like the square boring heads, because they are short and very stiff.
They do have only one central hole. To keep good balance, I make up hollow bars like this and braze carbide in them.
I rotated the cutter 180 so it could be seen in the photo.
Criteion boring head picture by donsmonarch10ee - Photobucket

jabezkin · Jun 24, 2010

Nice work Dave K2;

Still looking for a large bearing race?

winger · Jun 24, 2010

No pictures, but have done 11" bores with a 3" boring head. Rigged up to use a tpg holder from the lathe on the boring head. Even with a 40 taper the cuts were on the light side.
Dave

Dave K2 · Jun 24, 2010

jabezkin said:
Nice work Dave K2;

Still looking for a large bearing race?

Allways looking for stuff

Dave

jabezkin · Jun 25, 2010

I'll nab the next one.
One ol guy here hated to back out of his short driveway. One car, two car garage, one of the big bearings, a few wheels..........he pushes the turntable around by hand, drives out.

Stay healthy.

Did the last one work okay?

Dave K2 · Jun 25, 2010

jabezkin said:
I'll nab the next one.
One ol guy here hated to back out of his short driveway. One car, two car garage, one of the big bearings, a few wheels..........he pushes the turntable around by hand, drives out.

Stay healthy.

Did the last one work okay?

That sound a neat idea.

Yes the last one works a treat, use it often, much appreciated.

Dave

jabezkin · Jun 25, 2010

Dave K2 said:
That sound a neat idea.

Yes the last one works a treat, use it often, much appreciated.

Dave

My pleasure.

Can't stand when they scrap stuff like that................

Let me know.

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Boring head diameter vs bore diameter

Bill D

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joe m

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Dave K2

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smdubovsky

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Croz

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adama

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Dave K2

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donie

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jabezkin

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winger

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Dave K2

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jabezkin

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Dave K2

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jabezkin

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