Setting up for deep boring

[Doug Gray]

Setting up for deep ,deep boring (Moved from what did you do in your shop today)

To day in the shop I started to set up for some deep boring.
I have a job that calls for 6" long bushings. I will use 2 1/2" heavy wall pipe, the od gets turned and the id gets bored , I would like to hold +-.0015 on the bore. Boring 6" deep on my 14/40 lathe is a challenge. I've decide to do away with the top slide and instead mount a piece of 4" x 4" mild steel I have had kicking around for years. I intend to use a piece of 1 1/2" 1045 as the boring bar. I'm thinking I will use 3/8" square hss for the cutting tool. I think the hardest part of the build will be figuring out how to run the hold down bolts thru the 4 x 4. In the pic below I have the bottom of the 4 x 4 bored for the registration nub on the cross slide. Thoughts?
Wish me luck.



I decided to wack some of the corner off to facilitate drilling the mounting holes, the block is a little over 5" tall. I used a number of sketchy setups with my table mounted porta-band and a regular(ish) horizontal band saw.






Matthemuppet mentioned it would be nice to use inserts, which i would love to do especially since there is no provision for adjusting the height of the boring bar. The thought of laying out and milling a pocket for an insert seems very daunting to me for some reason.

 

[mickri]

I would take a different tack with this. I would make a norman style post that would mount on the cross slide and a holder for the boring bar that would mount on the post. This would allow you to adjust the height of the boring bar and to adjust the angle of the boring bar. Something like this.



Excuse the crude drawing. I left out a lot of the details that would be specific to your lathe. These are easy to make. You can make it with your lathe and a drill press.

And I would use a steady rest to support the end of the pipe.

 

[Alcap]

I made my holder wit a V on the lathes centerline with the thought I could use any size round bar . https://www.hobby-machinist.com/threads/1-1-2-boring-bar-used-for-boring-a-atv-cylinder.93275/

 

[Liljoebrshooter]

I had a similar job a couple years ago. The issue I had was getting a straight hole with no taper.
I bought a 3/4" and 1" boring bar for the project. They easily did that depth with light cuts.
Joe

 

[Rex Walters]

I've never actually done it, but for a 6" long bore, might line boring (tool between centers, work mounted to the cross-slide) be easier? You'd have to make a tool with some way to incrementally (and accurately) change the cutting diameter, and figure out how to mount the work rigidly on center, but neither seems that hard.

Boring 6" with a 1.5" dia boring bar and the work in the chuck might hold tolerance, but you're fighting both stick-out from the chuck and boring bar deflection. Definitely a good idea to remove the compound and mount the tool rigidly to the deck if you go that route.

 

[mksj]

Typical issue is rigidity of the lathe and tool post, so on a smaller lathe going to a solid tool post system helps. You will also want to support the work material with a steady rest. Rigidity of the boring bar is a factor the maximum depth for a steel boring bar is 3-4X the diameter, carbide is 8-9X the diameter.

This is the setup I used for deep boring a 4140 steel spider for a 1.59" hole to 8" depth with a 1" carbide boring bar using a CCPT insert. Tolerance was 0.001" end to end. Most boring bars you want a neutral or positive rake insert/cutter so you cut as opposed to push the metal. Vibration and chatter are also issues, although carbide tends have less vs. my steel boring bars. Downside of carbide is brittle and it can snap easily.

 

[Doug Gray]

Typical issue is rigidity of the lathe and tool post, so on a smaller lathe going to a solid tool post system helps. You will also want to support the work material with a steady rest. Rigidity of the boring bar is a factor the maximum depth for a steel boring bar is 3-4X the diameter, carbide is 8-9X the diameter.

This is the setup I used for deep boring a 4140 steel spider for a 1.59" hole to 8" depth with a 1" carbide boring bar using a CCPT insert. Tolerance was 0.001" end to end. Most boring bars you want a neutral or positive rake insert/cutter so you cut as opposed to push the metal. Vibration and chatter are also issues, although carbide tends have less vs. my steel boring bars. Downside of carbide is brittle and it can snap easily.

View attachment 372558

I like this set up, I wasn't considering using a steady rest, but definitly should be.

 

[Doug Gray]

work mounted to the cross-slide

I can't get my head around how to mount the work on the cross slide ... at centre height

 

[Doug Gray]

Work is progressing slowly. The t-nuts in the cross slide are M8 1.25. I have zero M8 hardware so I made my own. 5/16 drill rod is the perfect diam.

I'm leaning now toward using insert tooling. I think I could simply mount a conventional boring bar. Trim the shank on the tool and run the spindle backwards. The I can set up the boring bar and the tool on centre height.

 

[Larry$]

How about using the line boring bar to cut the pocket for the work to ride in? Use a set screw to feed the tooling out and another one@ 90 degrees to lock it.