How To Bore 1 Meter Pipe

[sanjiv]

I have to bore one meter seam less pipe of diameter 125 mm inside. i have to bore the same to 128 mm. I made a boring bar about 2050mm of dia meter 90 mm. I coulkd not able to bore as there is vibration in boring bar. What should I do?

[WOLOG]

Try using a brazed carbide tool. Sharpen it well and grind a small chip breaker in the carbide. Play with the RPM's and feed and depth of cut. I don't think there is a definitive answer to this. It will be trial and error all the way. I think someone once told me it was part of being a machinist. You may also try a carbide insert with a positive geometry"sharp" A negative geometry insert will cause way more push off and chatter. Good luck.

[Geof]

If you have a lathe with a bed longer than 2m you can try to line bore it.

You fasten the length of pipe onto the saddle of the lathe so it is exactly on center. You need a boring bar with the cutter not quite in the middle. You position the pipe close to the chuck and you put the boring bar through the pipe and grip it with the chuck and have the end supported on a center in the tailstock.

Now you feed the pipe over the boring bar which being supported at both ends is less likely to chatter. You have to adjust the amount of cut by moving the cutter in the bar.

[handlewanker]

Hi Geof, even line boring wouldn't help much.
The length of bore is a metre and the diameter is 128mm, which means you'll get deflection unless you use twin cutters in a balanced boring block on the bar, like on a horizontal borer.
I've seen some queer set-up to prevent deflection, like the one where they had a pair of rollers fitted to the end of the boring bar.
The bore was 9" diam, and about 8 feet long, no way could you hope to stop the bar bending, so the bar was fitted with two hardened rollers on adjustable arms that looked like a Mercedes three pointed star.
The tool pointed down and the two rollers were at the top and 30Deg to each side of the centre line.
To make matters worse the lathe only had 2 feet of saddle movement from the end of the bed to the bore.
They fitted the bar with a bronze bush on it's end and pushed this into the spindle bore at the chuck end as a spindle support guide.
The cutter head was a ring, like a donut, that clamped onto the bar and had an adjustable tool that pointed down, with the two adjustable rollers on shafts that acted like a steady as the boring bar was pushed into the bore.
The first cut was for an inch deep into the bore, and the two rollers were then adjusted to contact the bore on the cut surface, then the boring bar was allowed to push into the bore for the 2 feet it could go.
The bar was held in the tool post on a large split bush and clamped.
When the 2 feet had been bored the saddle was move back and the swarf removed, then the boring bar was re-entered to the 2 ft depth, unclamped at the saddle and the saddle moved back 2 ft, the bar re-clamped and the cut re-started.
Despite all the stop, start and resets, they eventually bored it out to 10" diam or so.
The end of the tube being bored ran in a steady that had ball bearing rollers instead of the normal bronze points.
This particular job ran day and night for 4 days and two blokes took turns at 12 hour shifts each.
Oh yes, I forgot the lathe was one of thos big old flat belt driven jobs with back gear, about 30" centre height and a long bed of 12 feet or so, probably a gun barrel lathe from way back.
If ever there was a heartbreaker it was this one.
Everything was hard to turn and there was no power traverse.
I don't know why but I've only ever seen these lathes painted in a medium grass green colour, except for one that had a bed 30ft long and was cream.
I reckon ole Sanjiv is taking notes on this one, best of luck cobber, you'll need it, and a long bed lathe to boot.
Ian.

[lerman]

You didn't provide specifications: diameter tolerance, finish, material, straightness, etc. What will this be used for?

If instead of boring it, you reamed it, you might have a better chance.

Ken

[Geof]

Originally Posted by handlewanker Hi Geof, even line boring wouldn't help much. The length of bore is a metre and the diameter is 128mm, which means you'll get deflection unless you use twin cutters in a balanced boring block on the bar, like on a horizontal borer......

Provided you maintain a constant feed deflection is less important with line boring; you get the same deflection through the entire length of the cut. When boring a long tube conventionally with a long boring bar you get chatter from both the tube resonating and the boring bar deflecting. With line boring you can clamp the work piece so chatter does not come from there. Then if you have the boring bar rigidly held in the chuck it is far more rigid and any chatter from there is only likely to be excited at high frequencies which is much less likely to occur if the speed is modest. It is also possible to make the boring bar even more rigid by having a steady rest adjacent to the tailstock end.

[sanjiv]

Dear Sirs
The job is for pneumatic cylinders of different sizes. I fix the cylinder ( seamless pipe to be bored) on slide. I made boring bar out of 90 mm dia seamless tube of length about 2040mnm. After boring I have to do honing/ burnishing the same than hard Chrome. But I cant do first operation Boring. I will load the photographs tomorrow.

[Geof]

Originally Posted by sanjiv Dear Sirs The job is for pneumatic cylinders of different sizes. I fix the cylinder ( seamless pipe to be bored) on slide. I made boring bar out of 90 mm dia seamless tube of length about 2040mnm. After boring I have to do honing/ burnishing the same than hard Chrome. But I cant do first operation Boring. I will load the photographs tomorrow.

You say your boring bar is tube. This can deflect much more than solid bar but with tube you can fill it with lead shot and see if this will stop the vibration. Do not pack the lead shot tight it has to have a little bit of space to rattle and move so it can absorb the vibrations before they build up too big.

[DareBee]

Using a solid and hardened H13 boring bar or solid carbide boring bar will help.

If your business is making cylinder tubes you had better invest in a line boring machine immediately or sub contract the tubes that are too long for you to do in a lathe.

[Geof]

Originally Posted by DareBee ......solid carbide boring bar.....

90mm dia. 2040mm long $$$$$$$$$$$$$$

[sanjiv]

Originally Posted by Geof You say your boring bar is tube. This can deflect much more than solid bar but with tube you can fill it with lead shot and see if this will stop the vibration. Do not pack the lead shot tight it has to have a little bit of space to rattle and move so it can absorb the vibrations before they build up too big.

Yes it is also a seamless tube. OD is 90 mm & ID is 70mm. If i made a boring bar from solid rod will it work? can the same boring bar will be used to bore 150 & 200 mm cylinders also?

[DareBee]

Who knows if it will work.
2 meters is ridiculous long.
Like I said, get a line boring machine.
Or pay the price to R&D the process on your own.

One other option is to contact Sandvik, they will custom design and build tooling (in this case a boring bar) on the basis of a performance PO. If they think it will work.

Geof - 1 job I did last spring cost me $7G to develop a custom boring rig and inserts.
BTW they refused to performance PO the unit I made because they figured it couldn't be done