Home Made HSS Boring Bar

[Al Slitter]

Greetings All;
I want to make a boring bar for my 7" x 12" lathe, my thinking is to make up some small HSS cutters that will be inserted
into the bar and locked in place with a grub screw.
I anticipate the boring bar to protrude 5" or 6 " from my OXA tool holder and have a diameter of 1/2" or 5/8"

First question: The material for the boring bar should it be tool steel or would cold rolled steel be fine.

Second question: The mounting of the HSS cutter should it be 90 degrees to the boring bar or 45 degrees or some other angle.

My intent is to have a general purpose boring bar which will do light cuts only, my lathe is a mini lathe so for the most part I stay with HSS
as I like the fine finish that HSS gives.

Thoughts please

 

[Rbeckett]

Sounds like a great idea and I would go with tool steel and use 1/4 inch pieces of HSS for the tooling. I would cut the slot at 90 degrees and install a set screw or two to hold the bit tight and no chattering hopefully. The 7X lathes do lack a lot of rigidity so light cuts will be the order of the day when you get it cut and all put together. Have fun and don't forget the pics as you go!!!

Bob

 

[Surprman]

I just built a home made boring bar yesterday. I recently made a nice boring bar holder for my lathe that will hold a 3/8, 1/2 and 5/8 diameter ba (there are pictures of it on this forum). I used cold rolled steel for my bar and turned it to 5/8. I have a bunch of 1/8 inch HSS blanks so I drilled two holes in my bar, one at 90 degrees at one end and another at 45 degrees at the other. I then spent a some quality time with a small square needle file to make the holes square to accept the blanks. All I need to complete the bar are the two set screws. I drilled and tapped the holes in the rod to hold the blanks in the center of the bar. In retrospect, I probably should have milled off a flat parallel to the 45 degree slot and drilled and tapped perpendicular to the axis of the blank. I think it will still work the way I have it though. I'll post pictures of it when I am done.

 

[Terrywerm]

I made a boring bar some time back for a specific project, but this one was 3/4" in diameter and uses a 1/4" bit. It is made from a piece of CRS that I had laying around and is 9 1/2" long. I did not square out the tool bit holes however, and it seems to work just fine the way it is. I want to make one or two that are similar, but smaller in diameter, 3/8" and 1/2" diameters. Here are the pics of the way I made my 3/4".

 

[rgray]

I'd suggest starting with drill rod. I have built quite a few bars and started with 1144 stressproof, but have better results with 0-1 drill rod hardened and tempered. If you don't have the equipment to do the hardening they will still work fine and you may have the ability to harden in the future.
I got the square broaches from 1/8"-3/8" but a round hole works to. I also have needle filed round to square (alot of work)
90 deg and 45 deg are probably best I have made a few 30deg for special things.

Pic is of a 3/4" and 1" they are 12" long. 45 deg at one end and 90 at the other.

 

[Al Slitter]

Thank you everyone for all of the information and advise.
I will go with two boring bars a short one out of some medium carbon steel that I have and the longer one out of tool steel.
I have decided to go with a boring bar that will be at 90 degrees to the work and will use a couple of broken end mills as the cutters.
After completion I will harden the tools then anneal the tool to release some of the strain.
My thoughts on going with the 90 degrees is based on using the boring bar as an internal threading bar as well.
I hope that that makes sense, I will take a few images of the process and finished items once complete. I hesitate on showing the work as
compared to others on this site I am just a rank amateur!

 

[John Hasler]

Interesting that you got good results with square cutters in round holes in your boring bar. I've been considering doing just that with one I'm making. How tightly do the cutters fit the holes?

 

[Terrywerm]

They just slide in with just a hair bit of clearance, John. The setscrew seems to hold them in place just fine.

 

[Bishop]

Other than general durability will hardened drill rod make for a more ridged boring bar than normalized rod? If the Young's modulus doesn't change with hardening wouldn't that mean the stiffness would remain the same? Sorry but everything I learn is from reading so I might have that all messed up.

Cheers
Shawn

 

[Al Slitter]

I am happy to see that this thread is continuing on.
First off I want to correct an error I made previously, I had said that after Hardening the boring bars I would Anneal them,
what I meant to say was that I would Temper them. Sorry about the error!

If anyone has concerns about Hardening and Tempering there are two great video's that cover this on U-Tube, the links are listed below:

http://www.youtube.com/watch?v=hw4Rl0uG7ok

http://www.youtube.com/watch?v=1wqbiU5sC30