Gun Drilling

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ttoberer
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Gun Drilling

Post by ttoberer » Tue May 11, 2010 10:43 pm

Im thinking of getting some more gundrills. I am sure my method of using them is not the best, I actually start the bore with a center drill, then hold the gundrill in my hand to feed. This is on the wood lathe. exactly how I do most long drilling. I remember seeing a picture somwhere of someone holding the drill in the toolrest of the metal lathe. I would like to see a picture or get an explanation of a better way to use these. for air I made an adapter out of vinyl hose to slip over the end of the drill. Thanks in advance!

chris bayley
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Re: Gun Drilling

Post by chris bayley » Wed May 12, 2010 12:34 am

Eaxactly what do the only difference being is that I am using a metalworking lathe that literally weighs a ton. Speed used when boring is around 1150 rpm for nicely centered pieces or 850 rpm for off-centered pieces e.g. barrel drone sections and feed speed will vary with the type of wood and how well it is cutting.

On my old and much lighter lathe I used a hollow center to support the work when boring very large and long sections that were off center. With this the biggest problem was a lot of vibration however this waslimited by placing a few sandbags on the frame to dampen it and reducing the speed

The main advantage of holding the dril in the hand is that if you feel the drill running off you can to a certain extent compensate. You can also make up a holder to improve grip.

Chris
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Hillmann
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Re: Gun Drilling

Post by Hillmann » Thu May 13, 2010 6:37 am

Here is a pic of my old gundrilling arrangement on the Myford Super7. The holder was a cast iron gizmo I made which indexes against the cross slide and carriage for ease in setting up at center. It allowed the holder to be run back and out of the way of the tailstock for initial center/twist drilling and then the holder was quickly returned to center with the use of a stop (not in view in the picture) against the rear of the carriage. It worked very well, however a much simpler holder might be made which could screw to the top post. The stock steady rest was bored out at true center to accept bearings of various i.d.'s, thus making it possible to taper the end of a rough square, load the bearing on the taper, and drop into the steady and drive with a 4 jaw chuck, (or rounds in the 3 jaw chuck.) The steady bearings worked well also, and it was well worth the effort of boring the steady, a modification involving clamping the steady to the ways as well as a vertical milling fixture, then loosening it from the ways and feeding it into a fly cutter held in the headstock. The amount of material removed from the steady casting was minimal and it did not affect the use of the bronze steady shoes in the normal manner. A slip of cigarette paper was placed between the mating surfaces of the steady while the fly cutter was introduced, which, when removed, provided a nice snug fit for the bearings. For the air feed, I used a compressor by drilling out and tapping the rear of the gundrill and installing quick change male air fittings on each drill. This is an easy modification to the gun drill and is accomplished by putting the shaft of the gundrill in the headstock spindle and drilling/taper reaming with the tailstock and then tapping with the proper taper tap.

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ttoberer
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Re: Gun Drilling

Post by ttoberer » Thu May 13, 2010 10:37 am

Great ideas, thank you! I feel a little better about my setup, but im always looking to streamline it.

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dirk the piper
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Re: Gun Drilling

Post by dirk the piper » Thu May 13, 2010 6:07 pm

Like some other makers, I use a wood lathe to do the boring. I don't think it's necessarily better or worse than using a metal lathe. However, I just wanted to show one way it can be made to work. The setup that I learned from Tim Britton is to use gun drills that have a side air port, so they can be held in the lathe tailstock with a Jacobs chuck. Then, I slide the tailstock with my hand, so I can still "feel" the drill's action against the wood as it is inserted into the spinning workpiece. In addition, as a suggestion from someone on this forum, I fixed-up a nice dust-collection system around the bit. This method of dust collection gets just about all the dust ejected through the drill bit, even at 100psi. I'm hopeful that this sort of precaution will delay the inevitable allergic reaction to woods like cocobolo... ;-)

-Dirk
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billh
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Re: Gun Drilling

Post by billh » Sat May 15, 2010 5:33 am

I hand feed almost all of my gun drills as well, and make continuous small adjustments to approach of the bit as I bore, as Chris describes - I can feel when the drill is running true. This does seem to improve centering of the smaller, more flexible sizes.

However, the real reason I do this is because it's the only way I can do it, since my lathe is not a long-bed and the spindle isn't large enough to accommodate a chanter blank.

It certainly works fine, and I think it's actually advantageous for thin drills which are very prone to buckling and/or sagging if fed from the end without guidance near the insertion point. For larger diameters - say, over about 6mm, I think there may be advantages to tailstock mounting of the gun drills as described by Mark H. and others.

I couldn't really make out the dust collection system in the photos, Dirk, but it sounds like a good idea. Gun drilling is one of the dustiest activities in the workshop, at least in terms of making the dust airborne. If you're doing feeding quite slowly (as I think is best) then the dust from the gun drill is very fine.

best regards

Bill

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KM
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Re: Gun Drilling

Post by KM » Sat May 15, 2010 6:59 am

Dirk,
I notice what appears to be a filter drier on the air hose. Does this get clogged with oil ( depending on compressor type), stifle airflow, remove much moisture, last long, and are they expensive?
cheers

Hillmann
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Re: Gun Drilling

Post by Hillmann » Sat May 15, 2010 1:59 pm

I used the fine feed tumbler on the Super 7, and although I don't have the lathe anymore, I remember thinking that this was plenty slow enough, and it allowed me to monitor the shaft of the gundrill with my fingertips while the carriage did the work. My feeling at the time was that the lead screw was better at feeding the drill than my shoulder. The important thing in this operation is to begin the hole very accurately, utilizing both the center drill and a sharp twist drill in the tail stock. If the hole is started really truly, the gundrill will naturally wish to follow the path of least resistance, i.e. the dead center of the rotation. If all is not right, the shaft of the gundrill will vibrate, and a bit of "feeling" of the shaft will quickly find the center of the stock. after that, it will want to run true if all else is in-line to begin with. At the finest feed rate on that particular lathe, the "chips" come back like black baby powder. I usually collected the dust with a modified shop vac nozzle attached to the steady rest. Nonetheless, it usually seemed pointless as the invisible plumes of dark talc would fill my nose in short order. In-line moisture traps are very inexpensive, and although there was one supplied with my compressor, they are not really needed for this application.

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dirk the piper
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Re: Gun Drilling

Post by dirk the piper » Sun May 16, 2010 10:06 pm

That filter drier is just cheap insurance against the possibility of spraying water at some nice, dry piece of wood. nothing more. It probably isn't necessary, but the thing came with some other air tools I bought. It also doesn't clog or appreciably reduce the pressure. Then again, I'm using a fairly hefty 30-gallon compressor, and the max pressure at 140 psi is much greater than what I need for this work. I think about 100psi works just fine. My compressor is the oil-lubricated type, and is not too loud.

The dust collection, I found to be much more important (for me... ahh-Chew!) When gun-drilling properly, the dust comes out very fine, indeed. Before using this setup, I tried various other ways to collect the dust with almost no success at all. The high pressure used to just blow the dust past the collection hood. Then, as a result of the following forum discussion, I rigged-up the 4-inch PVC elbow to a dust-collection hose:
viewtopic.php?f=4&t=853&p=6313&hilit=du ... tion#p6313

To do this, I drilled an oblong hole that fits the Jacobs chuck, and another hole for the side air port. This method improved the dust collection quite a bit. Then, after a while, I attached the square flat hood to the open end of the elbow with a couple of brass bolts and some duct tape, and the result was even better. Of course, the above link shows how the same idea was applied in a different manner at McGee flutes for an engineering lathe. If you don't have a dust collector, you could just as easily use a shop vac (and earplugs.) Also, it might just work better to let the elbow slide along the shaft of the bit as in the link. I probably made it more complicated than it needs to be...

-Dirk
I'm a piper, you're a piper, he's a piper, she's a piper - wouldn't you like to be a piper too?

ttoberer
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Re: Gun Drilling

Post by ttoberer » Tue May 18, 2010 8:59 pm

I have one 20 or so inch 5/32 in drill that have been using successfully, if im not careful, it still wanders. I assume it was designed for boring metal, but seems to work fine again if Im not in a hurry. I remember reading that you can find gundrills specifically for wood, but many surplus drills can be had cheap, but I assume they are designed for metal also. Is this a problem? What is everyone else using?

engineeruk1
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Re: Gun Drilling

Post by engineeruk1 » Thu Nov 14, 2013 10:41 am

Gun drills for cutting wood benefit from having a different cutting geometry on them than the one used for metals.

See the link for the specifics- http://hammco.com/gundrills.php

The point position of the tip is changed from being a quarter of the drill tip diameter(d), to d/3.5. There is also no need for the outer secondary cutting facet.

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