# Setting up for deep boring



## Doug Gray (Jul 17, 2021)

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.


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## mickri (Jul 18, 2021)

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.


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## Alcap (Jul 18, 2021)

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/


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## Liljoebrshooter (Jul 18, 2021)

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


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## Rex Walters (Jul 18, 2021)

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.


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## mksj (Jul 18, 2021)

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.


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## Doug Gray (Jul 18, 2021)

mksj said:


> 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.


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## Doug Gray (Jul 18, 2021)

Rex Walters said:


> 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


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## Doug Gray (Jul 18, 2021)

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.


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## Larry$ (Jul 18, 2021)

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.


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## mattthemuppet2 (Jul 19, 2021)

good point Larry, that's kinda how I drill the holes for my boring bar tool post holders - set the holder to center it vs. the spindle, make sure the tool post is square and hold the drill/ reamer in the 3 jaw chuck. All the ones I've done so far have come out very true and when I've checked the cutting tip, it's at the correct height.


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## Shotgun (Jul 19, 2021)

Doug Gray said:


> 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.


See my last post in the dividing head group project thread.  I drilled and tapped a piece of 3/4" hot rolled stock and srewed the insert flat to the face.  Worked like a dream.


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## mattthemuppet2 (Jul 19, 2021)

Doug, it's not that tricky to mill the insert pocket, especially if you're going to use a triangle shaped insert. Stick it in the vise pointing up at the right angle (45 deg? bit more maybe?) and side mill the pocket until you hit the right depth (towards the center of the bar) and the center line of the bar. Rotate the bar 7deg (for TCxT inserts) and cut the back wall. Rotate it a bunch more to give chips somewhere to go above the insert. Take the bar out, put an insert in the pocket and mark where the hole is. Drill and tap the hole maybe a thou or two towards the back wall of the pocket, that'll help pull the insert into the pocket tightly.

Then when you set up the bar, rotate the insert tip down until it's on center height, that will give you the clearance under the tip.

It'll take a little while to do, but you'll only need to do it once!


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## Doug Gray (Jul 19, 2021)

I'd like to just shorten the shank on this style of tool, mount it at 90 degrees to normal, so it's cutting on the back side of the bore, and run the spindle in reverse.
Will it cut properly?


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## Doug Gray (Jul 27, 2021)

Work continues on this project. I now have a P.O. for the bushings so this setup needs to happen asap.
Last night after a week of camping I was able to get back on the "tool post" and got it bored to accept the 1 1/4" diameter boring bar.


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## Doug Gray (Jul 28, 2021)

Tonight I

Drilled and tapped four 5/16" setscrew holes in the top of the tool post
Turned down the shank of the tool
Milled a flat on the boring bar
Used that flat to register a hole exactly perpendicular for the actual tool










Above photo shows milling the flat. 1 1/4" face mill, .025" DOC , feed by hand super slow (like 20 min.)


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## Doug Gray (Jul 30, 2021)

Completed setup, ready for work.


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## Rex Walters (Aug 2, 2021)

Doug Gray said:


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


Yeah, without tee-slots on your cross slide it would have been a bit of a hassle.

I note that you successfully created a dedicated toolpost to hold the boring bar on center, though. (Nice work, by the way!) 

I don't think it would have been much more difficult to cobble something together to hold the work. I wonder if you could have drilled and tapped some holes in the back part of the cross-slide to hold a fixture of some sort (maybe some way to hold a grinding vise with shims to adjust the height).

Much bigger work (and bigger lathe!) but Keith Fenner showed some dedicated fixtures he made to hold work for line boring several years ago: 






With that rigid tool-post and chonky boring bar, I'm sure you'll get good results (and have a nice tool for future jobs).

I still want to try line boring on my little lathe someday, though. I like the idea of supporting the boring bar at both ends for long bores. I made a replacement cross slide with tee-slots for my little hobby lathe exactly for this sort of thing.


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## Doug Gray (Aug 7, 2021)

The bushings are ready for drilling, the two holes are 90 degrees apart.




My indexing plates have a 2" opening , too small for this job.... wait Bostic 260 to the rescue. The indexing plate was simply glued to the end of the bushing..








The setup

a plate is locked into the tee slots
vee blocks are up ajainst the plate
the work is slide up ajenst a stop
the indexing plate is squared to the table





How to center the work in the x axis the od is 2.800 so e regular wiggler or centre finder .... so the ball edge finder is put to service.




first hole is drilled then the index plate is used to index the bushing.












 Thanks for looking


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## Rex Walters (Aug 10, 2021)

Hot glue? Really?!

Pretty sure a _real_ machinist would have at least have used carpet tape. ;-)

I really need to make some indexing plates like that. They look handy!  I've been able to get away with just collet blocks so far (I rarely make anything very big) but I'd like to have something like that in my arsenal.

I guess hex and octagon plates should cover almost any indexing need. If you were to remake yours, would you stick with the 2" ID?


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## Doug Gray (Aug 10, 2021)

Rex Walters said:


> Hot glue? Really?!
> 
> Pretty sure a _real_ machinist would have at least have used carpet tape. ;-)
> 
> ...


I sent you a PM Rex.


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