Need to enlarge the bore on a pc of bronze stock fron 1/2" to 3/4" the length of the material is a bit over 12". any suggestions on where I can find drill bits and reamer with extra long shanks? any tips on keeping the hole concentric to the OD?
If money is not an object, get a core drill of appropriate length. Try the local tool supplier, or McMaster Carr.
If you gotta do it on the cheap, turn down the shank on a 3/4" drill or use a Silver and Demming type drill, and solder an extension onto it. A little creative grinding and it will have it's own pilot.
12" isn't all that long a hole, in the scheme of things.
Bore the length oversize, fit accurate bushings to the ends, along with wipers to keep the whole inside works clean.
On both size and location to decent tolerances is going to be a right job to do. Never been around one, but it seems a job for a horizontal boring machine, or a similar cobble-up from a lathe with a boring bar between centers.
Have a ten inch atlas lathe, do not want to get into an expensive deep hole drill or high pressure coolant systems, any ideas on a low tech solution to deep hole drilling. any one have a source of supply for extra long drills and reamers?
I'd save the bronze for something else and press flanged Oilite bushings into the ends of a steel tube. You could make a half-round reamer out of 3/4" drill rod and pull it through, so the near end guides the shank while you cut the far end.
Unfortunately, the Atlas lathe in question does not have T-slots on the cross-slide for mounting a workpiece. They are somewhat less common here in the USA than in your locale. The majority of the cross-slide for this lathe is somewhat round topped -- or at best not machined flat and fitted with T-slots.
The best bet for that would be a milling attachment for that specific lathe, which mounts in place of the compound on the dovetailed round projection around which the compound rotates.
Even my Clausing (a somewhat more robust lathe) has the compound mounted by a round boss which projects down into the cross-slide, and it is secured by T-bolts in a circular T-slot in the cross slide surrounding the hole for the boss. Not exactly what you would want for mounting a workpiece on the cross-slide.
Now -- if I had the cross-slide which was a companion to the bed turret (capstan) for my lathe, it would have sets of T-slots.
A Myford, of course, would have the T-slots -- and is probably what you are most familiar with.
Amen! I would say that learning to make a gun drill would be the better approach.
Certainly purchased long drills (aircraft drills are available in 12" lengths) would be highly unlikely to approximate a straight hole. :-)
I'm in Canada. Really. We do pretty much get the same stuff as you guys up here, just less of it. :-)
A bud of mine has a 10 inch Atlas POS lathe in his shop. If a lash-up is required, a lash-up it shall have to be. If I had that lathe and that job, a machined in place bed for the casting, with end grain hardwood between the top of the cross slide (compound renoved) and the casting would be a starting point.
Build a tooling plate (wrong term maybe) to fit onto the compound mount, and reinforce the surface to prevent rocking, with a little epoxy or bondo type body fill cast in place. Use a film wrap or a spritz of cooking oil to prevent it sticking down to the cross slide.
There IS always a way. Sometimes it is not an elegant or easy way, but there is a way. There is a hundred plus years of back issues of Model Engineer magazine out there proving that guys that really WANT to make something with limited tooling CAN.
Depending on the size of the casting, that might be an option. It will also provide one more potential location for the set-up to flex, as well. All trade-offs.
Use the Tee slots to anchor a plate, drill and tap holes wher you need them! :-)
I have a Myford S7 now. Just got rid of a 10 inch Rockwell Delta. Had a beaten up South Bend 9, too. And another Myford, an ML7. The availability of slots had little to do with my reasoning of the method. Just that it is the most secure way to do a job like that on the wrong machine. If it is the machine that is available, then make the best use possible of it!
Yeah! Even a D-bit cutter running in a similar fashion to a gundrill, where it is guided by its own hole, would be a good pick. Slower, but a good pick.
No matter what, the guy is going to have to go slow and withdraw often to clean out and check tooling, etc. He seems to think that all gundrills run with high pressure coolant feeds. Gundrills were in use for hundreds of years before someone thought to drive fluid through them!
No, I figure they would approxiamate one just fine! :-)
They would not make one though.
And the OP needs to drill through 12 inches, so he needs a longer drill than that if he is to be able to hold onto it while it works.
A D-bit reamer. Done by yourself. Needs some trying and fiddling to get it running and make a nice and smooth surfaces. I'm making a variant of a D-bit. I call it G-bit. Looks like a D-bit, except I cut out only one segment (thus the G) and not two segments (the D). The "G-bit" has better support. Not the fastest way to drill a hole. :-)
Shotgun barrels started out with straight sides, and then get the contour put on after the bore is finished. The walls are quite thick enough, if you look at the chamber end. First the hole through, then the reamers up to just below size, then the lapping/polishing out to final dimensions. Some chokes were done using tapered reamers, some by swaging down the outside of the blank after polishing, some are machined in the bore after manufacture.
It is said that Harry Pope, one of the legends of rifle barrel making, used a twist drill on an extension to drill his barrels. His barrels are still sought after. Proof that great work can be done with less than optimal tools!
If you get a chance, find a copy of the video "Gunsmiths of Colonial Williamsburg". It follows through the whole process of building a Flintlock rifle, using a forge welded barrel blank. The interesting thing is to see the drills and reamers used to open and clean up the bore there. Really low tech, but effective stuff.
Another video that covers a lot of the detail, is the Lautard video of Bill Webb's Rifling Machine. It covers a little more modern approach of drilling, with a pressure coolant fed gundrill, and a cut rifling head.
Most barrels these days are button rifled. It is a fast, accurate enough process that leaves a decent barrel in one pass of the rifling cutter, and does not require near the investment that a hammer forging machine requires. The rifling is done by a carbide button being driven or pulled through the barrel by hydraulics, usually.
Modern rifle barrels start out as a large diameter round bar. The hole is drilled, the rifling installed, and the outer contour cut. At least for barrels other than hammer forged, which are a whole different process, that will never be suitable for anything but volume production.