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| Deep hole drilling 101 on lathe? |
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| Lew_Merrick_PE:
Pekka, A true gun barrel drill is designed to drill extremely deep holes with very tight tolerances on diameter and straightness. The business end actually burnishes the bore and has enough contact area (diameter X length) to keep if running straight and true. They usually contact around 270° of the hole's periphery to achieve this. The primary "secret" of a gun barrel drill is that the point is located exactly on 1/4 of the diameter such that the side-acting cutting forces are balanced. It seems like overkill for a drawbar clearance hole to my way of thinking. I drill 30:1 (depth:diameter) holes with fair regularity using only bell hanger twist drill bits. So long as I keep the cutting edges sharp, I can drill such holes with no more than .010 inch (0.25 mm) wander when making gas passages that are typically .094 inch (2.4 mm) diameter X 3.75 inches (95.25 mm) deep in Rc 35-40 4130 steel. ??? |
| PeterE:
Pekka, How deep is the hole you want to drill? If you look into my thread about the pin vice I show that I drilled a 3 mm hole 90 mm deep and it came out well centered in the other end. I did that using a combination of center drill, ordinary jobbers drill and an extra long jobbers drill. To be fairly safe I used new drills to be sure the points were correct. /Peter |
| PekkaNF:
hank you. Actually with that material I have tried many methods. Peck drilling was no-go, work hardening does not work well..Some resharpened SDS long masonry bits worked somewhat, but after it started to chatter, tip chipped and rest you know. Some HSS-co twist drills seem to work and the short trough cooled drill was the only one that worked fine. I would be fine with 25x, if can drill on one go. So trough cooled twist drill or something else...then gun drills wandered my way 20€ apiece and I tought that it might be worth of finding out...I need pressure pump, holder and such anyways. There are some other drawbacks and unknowns on this gun drills anyway, like if I read it right that it is not ideal if the material tends to make long continuous curly swarf and that is what I have. Still some :coffee: to go. Pekka |
| unc1esteve:
Pekka, My need for deep holes was several. A #46 hole one and one half inch deep and a .2180 hole 13 inches deep. I had bought a metal bench that had an old Atlas lathe attached to it. Missing parts, needed a lot of work. I was going to use the bed for something else until I took a close look at it. It was in good shape so I took it apart, replaced the missing parts, cleaned, repaired and painted it. I added a variable speed DC motor and changed the pulleys to achieve 4000 rpm. I checked with Timken, the maximum rpm for the bearings with oil is 7200 rpm. I added a variable DC motor to the lead screw so I could slow down the feed rate. I made a collet system to replace the chuck. (This was also deep hole drilling. Step drilled from both ends, then reamed). I made a pressure vessel to supply air and coolant like the Sterling unit. I then added a high pressure pump from a small pressure washer to increase the coolant pressure. I purchased some carbide 'v' with a through coolant hole from EBay. I bought some 'v' tubing from Drill Masters. I hard soldered a gun drill the length I needed, 18 inches. Ground it to size on the lathe and the T&C G. Hooked everything up and that is where I stopped. I have a few details to finish. I have not made a test hole as of yet, other things got in the way. One thing I am having trouble with is to keep the solder out of the coolant hole. I purchased some anti-flux and have been doing some reading. The material I am drilling is 4140. I am going to purchase some stress proof before I continue so I can see which is better. I believe the stress proof will be. The long, curly swarf is to be avoided. It will jamb and destroy the gun drill. The higher the rpm, the slower the feed rate, the smaller the chip, the more success. Long term project. |
| PekkaNF:
Good work you have done with your drilling machine. Thank you, you gave me some really good info. My needs and drills are not that long, the two drills I have are 10 mm dia and about 350 mm or so, to make 300 mm long hole max. Should have done my reading first :doh: Pressure of the cutting oil didn't surprice me, but rpm of the blank did. Alhough I have one extra lathe body to experiment....but do I want to use time and effort to do it? Great learning experiment no doubt. I read deep drilling parts of the linkked PDF and had some hard time trying to figure out tables and other numerical values that were missing units. Like "500 lbs" sounds to me more like force and not pressure....One table had oil volume, but not units etc....but reading the text of someone doing the production did give some pointters. Later on there was really nice chapter about drilling and reamin and plenty of general machining info. Halfway of the manual many pictures seem to be missing, but that is no problem here. I'm going to track down the orginal drill makers data for this drill to see recommendations, that should give me pretty good idea viability of my idea. Pekka |
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