View Full Version : boring

08-16-2003, 05:35 AM
What's a good way to enlarge the inside of a pipe? Here's the specs:
18 in long
i.d. is 1.40 in
final i.d. to be 1.48 in
aluminum pipe is closed at one end
it's req'd to leave the first and last
inch at full wall thickness.

This looks like a job for a boring bar, except for the length. That would be a serious ammount of overhang. The lathe is an 8x18, so there's not enough room to carry the bar that far anyway. Since the pipe is closed at one end, I can't pass anything through the pipe. I do have a fixture to mount the pipe on the crosslide, at center height, if that would be useful. Any ideas?

08-16-2003, 07:03 AM
Chuck one end of the work and support the other end with the steady rest or a live center.

Make a hollow "boring bar" which can pass through the headstock. That would solve the lathe length problem. The bar would be restrained from turning by a fixture to the left of the headstock.

If you made the boring bar with an expanding end which would be opened with a drawbar, it could be inserted into the work, opened, and slowly withdrawn. After it was withdrawn the required distance, the draw bar would be loosened so the tool could be removed.

If you had three or more cutting points on the end of the boring bar, it would be self-centering.

You could try it on a piece of scrap pipe to find out exactly how much to tighten the drawbar to get the required ID.

You'll have to flood it with coolant/lubricant to keep the chips from clogging the clearance between the bar and the ID. The coolant could be pumped through the bar, which is hollow. Some of the fluid is going to come back through the headstock, so it's going to make a mess.

You might even try running a pushrod from the carriage to the boring bar to control its travel.

That's a longshot solution to a tough problem. I hope you don't have many pieces to do.


[This message has been edited by winchman (edited 08-16-2003).]

08-16-2003, 10:56 AM

You are scaring me. Have you actually done this?

Shed Machinist
08-16-2003, 11:02 AM
Sounds like a useful tool.

08-16-2003, 11:26 AM

Assuming that your customer's requirements permit, perhaps the following technique will work.

make three parts:

one inch length of pipe
one inch length of pipe with closed end
sixteen inch length of pipe

Remove the tail stock from your lathe and mount the sixteen inch length of pipe in your carriage fixture. Remove headstock chuck and use a reground (1.48 diameter) morse taper drill in the spindle to drill 8-1/2 inches deep into the pipe. Use power feed and your finest feed rate.

Reverse the length of pipe in the carriage fixture and drill from the other end until the drill meets the previously drilled hole.

Fixture and weld the three pieces together. If necessary, turn the outside weld flush with the pipe. (Use a spider and a steady rest.)

Should the use of a drill be inappropriate, perhaps a morse taper boring tool (with a drawbar) can be fabricated. I would still flip the pipe and bore from both ends.


08-16-2003, 11:36 AM
It ain't gonna line up

08-16-2003, 11:50 AM
Maybe make yourself up a boring bar to fit in the chuck,ditch your tailstock and clamp your workpiece to the carrage,headstock rotates boring bar and carrage feeds workpiece into it,this will be a long bar(19"at least)so maybe make up a support for the end of the bar out of a pillow block bearing and flatbar bracket,just a thought.

08-16-2003, 01:55 PM

Since I also have an 8 x 18 lathe, I'm very interested in how you eventually solve this problem. On my machine, it's not practical to bore an 18 inch pipe in a single setup, for several reasons. Your lathe may have more capability in terms of carriage travel, length of the ways and so forth.

A previous poster noted that alignment would be a problem if the workpiece was flipped end-for-end. I certainly agree and this is why I prefaced my suggestion with "if your customer's requirements permit". Obviously this also applies to the suggestion for making a three-piece assembly and welding.

Please let me know what you come up with, I can benefit from your experience.


G.A. Ewen
08-16-2003, 02:06 PM
Ok since nobody has asked I have to, What the heck are you making? http://bbs.homeshopmachinist.net//confused.gif

Is there a seam on the inside of the pipe?

What is the OD?

[This message has been edited by G.A. Ewen (edited 08-16-2003).]

08-16-2003, 03:03 PM
Usually when someone makes a pipe bomb they cut grooves in the outside so it will make shrapnel. (just kidding)

Having pipe, a lathe, black powder can get you arrested for bomb making materiels.
Don't pee off a policeman, there is always something illegal around.

08-16-2003, 03:06 PM
"You are scaring me. Have you actually done this?"

No, but it was the only way I could think of to do it based on the limitations given in darryl's post.

Didn't mean to scare anyone. What part of the scheme is it that wouldn't work?

Here's another idea. Make the boring bar with "follower pads" to keep it on center as it goes into the pipe. The space between the pads would allow the chips to get out. This bar doesn't expand. Feed it in and bring it out. The ID is now 1.48" all the way to the open end. Swage the end down to 1.35" ID for 1" and then bore it to 1.40.

I'd also like to know what it's for.


08-16-2003, 03:38 PM
Once saw a similar job exactly like this except that there was about 6 inches of concrete cast inside with tungsten carbide chunks in it.

The concrete and tungsten carbide was added to make it harder.

Seriously some schemes for making things don't work.

Make two pieces of equal length but machine a male step on one and a female (internal bore) for a slip fit on the male piece. Size the step and bore to leave a small groove for welding. Make the two 9 inch long pieces and then stick them together and weld it and then trim the weld flush with the OD.

08-16-2003, 09:03 PM
Thanks for all the replies, guys. The customer is me, the pipes will become naptha tanks for a backpackable cooler/stove combo. If you don't know by now, I'm hooked on backpacking, the rumpy-pumpy thing, as I think Allistair once called it. Anyway, space, construction, and tank protection issues led me to use pipe for the tanks, as the length would be no problem, but area and position was. I had end caps installed on the bottom before I realized I hadn't thinned the walls to reduce weight and slightly increase fuel capacity. I don't want to thin the top ends, as valves, fittings, and a pump are to be installed there.
What I've come up with is make a metal disc to fit inside the pipe, mount it on a rod which can be rotated, and mount a cutting edge onto the disc, in such a way that it can be extended beyond the edge of the disc by about .o4o, and clamped there. I could either rotate the rod with this disc on it, or rotate the pipe in the lathe, and feed the rod into it. If I rotate the pipe, using a steady rest, I'll relieve a short section with a boring bar to the req'd depth, then insert the rod/disc/cutter to that point, then adjust the cutter to just hit the relieved part. I'll use a vice grip on the rod, to hold it from turning, and feed by hand. I don't know how well it would work, as it will take out the full .o4o in one pass, and there is no way for a finishing pass. Jamming is high on my list of concerns.

C. Tate
08-16-2003, 10:22 PM
Make in three or four pieces thread and cut grooves for o-ring and simply screw it together. This will allow for easier machining and gives you some flexability. Use only one or two pieces for short trips and add sections for longer trips.

C. Tate

08-16-2003, 10:34 PM
Forget reducing the inner diameter - waste of time, and the reduction in weight is almost nothing. If you are worried about weight, make them out of thin-walled Titanium and have them TIG welded.

[This message has been edited by Thrud (edited 08-16-2003).]

08-17-2003, 02:49 AM
Thanks, Thrud, for the reality check. Sometimes the gain is not worth the time and effort, and that may be the case with this project. I got the job done, shaved a few ounces off the weight, and increased the capacity from 600 mls to 630 mls. Probably insignificant in actual use, though many seasoned hikers swear by the advantages of saving even one ounce. Ecclectic eccentrics, they are. ( but then what am I?) Good thing I'm not epileptic, then I'd be an ecclecticepilepticeccentric. maniac.
I did pretty much as I outlined in my previous post, with the disc fitting the hole in the pipe as a guide, the cutting edge clamped to the side of the disc in a groove, and the rod chucked in the lathe. The pipe I supported in a steady rest, and I held and fed the pipe by hand. When it jammed, which it did several times, I just let go of the pipe, and let it rotate in the steady until I got the power off. Two steadies would have been much better. A refinement of the angles on the cutting edge would have given a better result, but it's done.
Roger, I liked your idea of the 3 point cutter for it's self-centering , but worried about the extra torque it would have taken to turn it. Your 'through the spindle' boring bar idea has merit, I'm going to have to think about that some. The carriage can be made to slide the bar back and forth almost 24 inches on an 8x18, by a simple repositioning of the bar with respect to the carriage. At the center of the workpiece, up to 12 inches away from the chuck, there would be flex in the bar, so there could be chatter and other problems. On my lathe, the maximum diameter that would fit through the spindle is 13/16 in, not exactly a rigid bar when unsupported for 12 inches.
By the way, there is no seam in the pipe I used, that would definitely have thrown the whole procedure out the window.
Lastly, I'm not making a pipe bomb, but I did consider using propane for my fuel, filling these little tanks from a larger barbeque tank with suitably made adapters, paying strict attention to the maximum fill volume (80%) to allow for expansion. The pipe as reduced in wall thickness can handle the pressure with a large safety margin, but two things conspired to sway me away from propane: the illegality of filling or refilling this obviously uncertified container, and the insurance risks of having the apparatus in my, or more importantly, someone else's vehicle.

08-17-2003, 08:54 PM
If you TIG weld the tank out of Titanium you should not need anything thicker than 14 Ga. This will increase the fuel capacity, and make it only a few ounces finished. Think how impressed your hiker friends will be (charge them 3 times what it costs you - trust me)! Have it hydrostatically pressure tested by a propane outlet. DOT requires cylinders to recertified every 5-10 years - the last one I had done cost $25 (canadian) and they replaced the safety blow off and valve.

[This message has been edited by Thrud (edited 08-17-2003).]