Boring Head And Bars "?"

[negatronix]

Hi All!

I'm looking to do a bit of boring, and could use a nudge in the right direction for the tooling I would need to get going.

My project is 2 pcs of 3.5" OD .5 wall round steel that are 5" in length.

I want to bore and "true" the centers. This is more of a learning project, that I will want to apply to a real project in a month or so.

My question is/are... What size boring head, 2" is what I am looking at. What size shank, I am considering a 3/4" and 1", but have seen R8 1.5" that threads into the head. What size bar, and should I use a horizontal or vertical setup.. which would be more accurate.

Thanks ahead of time for any help/input!!

-Kory

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[T Bredehoft]

Without knowing your machine capabilities, I'd suggest a lathe operation. 5 inches is approaching the limit (or beyond) of quill movement on a mill and a lathe can easily handle a bore 2" in diameter and 5 inches long. I use use perhaps a bar 3/4 in diameter with an insert to do the cutting, either HSS or carbide. HSS on a smaller (Hobby) lathe the High Speed tooling would work better. In a standard industrial lathe, carbide tooling would be best, especially a solid carbide bar with an insert. The first work would be drilling the opening with perhaps a 1 1/4 in drill.

 

[Grandpop]

+1 on using a lathe. Assuming you only have a mill and need the boring head, I would heavily reccomend using the boring tool horizontal rather than vertical. Any bar hanging vertically out 5" is going to chatter, while the stub hanging out horizontal will be much more rigid. As mentioned above, going to be difficult to find a mill withmore than 5" travel. You want the bit slightly above the top of tube at start, and slightly thru the bottom of the piece at the end. Sounds like would have to bore part way thru, flip end over end, locate off the finished part and bore remainder. Would needs the ends very square for that to work, or need a pretty big vee block!

As for other questions, I keep my boring head and drill chucks on 5/8 straight shanks. Easy to swap between the drill chuck and the boring head that way (same height too). My head is 2" x 3/8 bar hole, and not much that I can't do (have bored 8" in aluminum once). Have used 3"heads at work with 3/4 bar holes when required, but never liked them for everyday work.

Whatever boring head you get, make sure that one graduation equals .001 off the bore diameter. Most of the cheap / import ones will take .002 off the diameter for one grad.

 

[negatronix]

Thanks for the help folks.
My machine is a Grizzly GO755... I should have mentioned that in the original post. The quill travels 5.25, though the specs say 5".

Unfortunately I don't have access to a lathe, and the parts that I will eventually bore out have plates welded on the bottom, and a square tube on the side.

Does the boring head usually travel through the hole, or is the bar the only piece that does.. ie do you use a head larger or smaller than the intended hole with a long bar.

I am looking at a Bridgeport #2, but can't find specs.. is it a 2", 3" etc. If anyone knows please chime in.

Thanks!

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[Grandpop]

On deep bores I've had the best luck when the bore is open on the botom. Helps get rid of the chips too. Can stil be done with a bottom plate like you have, may have to give an air blast or three on each pass.

Do you need to bore all the way to the bottom plate, or can you stop above by some amount? If need to get down to bottom you will most likely have to use vertical bar (bigger dia the better). Any bar hanging out the side hole horizontally won't be able to get all the way to bottom unless you make a special bent one.

Typically using a vertical bar the head wil not go inside the bore, since the wall on the slide offset is bigger dia than the hole. Could get around that by using a bar with a large offset so the cutting edge is out farther than any other part of the head. When using horizontal bar the head typically goes inside the bore since the cutting edge is outside the head diameter.

Will that tube out the side of your part have an open hole in it? If yes, you are going to need fairly heavy duty bar to eliminate chatter when you hit that hole.

 

[4GSR]

......snip.......
I am looking at a Bridgeport #2, but can't find specs.. is it a 2", 3" etc. If anyone knows please chime in.............

A Bridgeport No. 2 head is about 3" OD, may even be 3-1/4". Been too many years since I've used one. BUT it will only hold 5/8" OD tools. It is threaded for an odd balled thread like 1-7/16-16 thread. IT is not threaded for a standard shank like the Criterion type boring heads use.