Drilling or boring a barrel. Not for a gun, UK

[Adi]

I have several workshop machines such as decent lathe, mill etc, but never quite figured out how to drill and ream a long bore or say 10 inch or more without going greatly out of alignment. Standard drill seem to wander and may not run true.

Thinking here of bar stock say 5/8" diameter close to a foot long and being able to drill the hole all the way through and still be central at the other end. Then bore/ream it out to size. I do not need any rifling as I need a smooth surface for a piston.

I guess this is a problem you must face on this forum on a day by day basis, so if the moderator allows this post to continue as I am based in the UK, I will ask how this is done, I saw what I think was a gun drill which had a single carbide cutter on the end but the size and length of it could not see it being used for any gun manufacture, so how is it done if it is not giving trade secrets away.

Thanks

Adrian

[Al_Messer]

Drill a smaller pilot hole halfway through. Turn the piece around, and drill until the second hole meets the first one. Then proceed to step-drill completely through until you are just under the finished diameter. Then, PULL the correct size reamer completely through the piece from the Headstock end, using PLENTY of lubricant, slow speed and a light feed.

[GeorgeGaskill]

holes, not just barrels. The real problem with gundrilling using a conventional lathe is the feed rate and the requirement for high pressure oil feed to the drill to flush the chips from the hole.

The normal advance per turn with a gun drill is on the order of .0001" per turn which is at least an order of magnitude smaller than the slowest feed on a conventional lathe. Also RPM is on the order of 5000 although there are some drills designed to work at 3000 RPM.

The high pressure cutting oil is not optional as the chips must be forced down a straight groove on the drill (no twist) and it must happen immediately or the drill will seize and twist off.

And they don't drill a perfectly centered hole anyway. Better than twist drills but not perfect.

If you intend to bore it (a challenge in itself with a 5/8" round and a foot deep hole), that will be your best bet of having the hole centered the whole length.

Maybe you should process the hole first and then support the finished hole between centers and turn the outside concentric with the ends of the hole.

And there is still the issue of the hole itself being straight, although boring should give a pretty straight hole.

By the way, most gunsmiths do not make their own barrels but buy them from specialist barrel makers (who have the proper specialized machinery for barrel making.) See this article from Border Barrels for more info regarding barrel making.

[John]

Why not try a piece of aircraft tube. This is 4130 seamless tube that comes in many sizes and different wall thickness.

[Bryan]

You can get DOM hydraulic cylinder tube down to 5/8" also...

[Adi]

Well I thank you all for your comments and the article that George pointed at was fantastic in giving me an understanding of the gun drill process. It may be beyond what I have at the moment to do that type of drilling as as the job was a one off I can not see myself getting a bigger lathe.


I will have a rethink of my task and see if any long and slender rams ever make it on ebay in the UK.

Thanks again for your comments

Adrian

[Al_Messer]

No one else has suggested it, but why not shop around at your local scrap yard for a piece of thick-walled drawn tubing as suggested. Another though: the steering wheel shaft out of an old VW or similar vintage vehicle.

[jpfalt]

Schedule 80 or schedule 120 pipe in small diameters may suit. Then you just ream and/or hone the bore to final finish. The OD is around 5/8 and the ID is slightly over 1/4".

[Adi]

Lateral thinking, I like it, why make life hard when there is an easier way.

It is just down to finding the answer. Just looked at details on a few rams and the inside of the barrall is not required to be smooth just the ram part. So a length of ground silver steel, and fit an end cap in a tube with a few O-rings to seal against the bar may well do the trick.


Adrian

[Engineeruk1]

You should use a lathe steady to support the material in conjuction with the spraymist system available here.
http://www.hammco.com/accessories.php