How to drill Straight holes in Cannons with Photos

[seacoastartillery]

     Whether you are drilling the cannon's bore or a carriage hole for one of those long bolts, you should be able to drill a straight hole.  Here is a method which will not fail to produce a straight, correctly sized hole. 

                                               A Method for Drilling a Straight Hole
                                                  By the Seacoast Artillery guys

     Ever since I was a kid, I always wondered how a gunsmith could drill a hole of the required straightness to accept a long ramrod under a Kentucky Longrifle barrel.  When Mike and I attended the Colorado School of Trades in  ’76 and ’77, we found out.  A straight hole can be drilled most easily when it is drilled with a bit that is designed NOT TO CUT on it’s sides.  Twist drills cut on their sides and are notoriously ineffective for producing long, straight holes in wood.  In a gundrill, only the material ahead of the drill bit is removed.  The drill, itself, must be straight as well.  Only a “Gundrill” works this way, and it is the tool we always choose when long, straight, precisely located holes are needed.  We measured some of the gundrilled holes we recently drilled in the white oak, upper carriage pieces for the 7” Treble-Banded Brooke Rifle we are currently building.  The results with photos are below.

     First, these holes are .161” Dia. and approx. 10” long, interrupted by a 1.25” gap.  The grain of the separate pieces of white oak drilled is NOT oriented parallel or square to each other, but at a 45 deg. angle.  This grain orientation WILL bend a twist drill

     The matrix below is the result of our surface plate inspection using a transfer stand and a .0005” test indicator.  All the carriage piece-parts sets are numbered to avoid confusion during assembly and to help in data collection for quality assurance.



Part No.   Deviation from .760” +/- .005”  (Deviation from centerline of vertical  pc.)









                 Left……           Middle……         Right…….     

1   .764                    .763                       .762                                 
2   .759                    .763                       .760
3   .764                    .763                       .764
4   .765                    .762                       .763
5   .760                    .764                       .761                                                         .76
6   .761                    .761                       .764
7   .763                    .765                       .762
8   .757                    .761                       .758


     The matrix below is a measurement of the distance from the base of the vertical pc. to the breakout of the gundrilled hole with the front of the vertical support pc.  Measured directly with a 6” Caliper.

Part No.    2.365 +/- .005         (Base to breakout distance)

1   2.365
2   2.360
3   2.364
4   2.367
5   2.364
6   2.361
7   2.361
8   2.366




     Professionally produced, carbide tipped, metal-drilling, gundrills produce holes of incredible straightness; usually, we have found, the 17” to 22” holes we drill in 4150 ordnance steel are from .002” to .003” of the .005” total allowed on our straightness specifications.



     The very large 1.5” gundrill shown in the collection photo was produced in our shop for very long gundrilling in oak and the straightness of those large holes is very consistent at .010” to .020”.  It has a compressed air hole off-center at the tip.



     The odd looking gundrill is a 15 degree per side tapered chamber gundrill which has a small hemisphere at the bottom and a cylinder at the top for the Brooke rifle chamber.

For accurate results you need to orient the parts to be drilled carefully and clamp securely without damaging the wood.  A centerdrill to start the hole is a very good idea.



     The small gundrills were made in our shop from drillrod and are milled carefully to duplicate professional metal-drilling gundrills, although they drill carriage wood, white oak, for us.  The same angles work for metal or wood.


We would be happy to answer any questions you may have.

Regards,

Tracy and Mike

[gulfcoastblackpowder]

Very nice description, though some of your photos need to be fixed (never mind - they just loaded slower).  Having never seen or shopped for a gundrill, I don't know that l'd be able to make one.  Do you have any suggestions on sources or information regarding the fabrication of them?  What's the benefit of the compressed air hole, and is it to relieve compressed air as you're drilling (a through hole) or does it create it (blind).

[seacoastartillery]

    Hi gulfcoastblackpowder.    I can inspect one of our gundrills on the optical comparator, for you old-timers, 'shadowgraph', tomorrow and post a sketch with dimensions and angles Monday evening.  We just milled the angles by eye using on of the Sterling Gundrills as a guide.  The drills we make work great.  The angles are not critical for use in wood.

     The benefit of the compressed air hole for wood drilling is to cool the drill and blow the chips out of the hole.  For metal you need a high pressure oil set-up or a water soluable mister like we use.  Compressed air delivers the air/cutting fluid to the holes bottom, cools the drill and forces chips and ribbons out of the gundrilled hole.  Either blind or thru holes can be drilled with a gundrill using compressed air.

     These are simple tools to make with a milling machine; without one, you would have to have or create a grinding wheel set-up capable of some precision.

Sketch on Monday night,

Mike and Tracy

[Victor3]

"First, these holes are .061” Dia. And approx. 10” long."

 Really

[seacoastartillery]

     Thank you, Victor.  .061" is kind of small isn't it!  Because they are so small, the bolts are made of Swiss Cheeze rods which we find work better that inconel and you don't have that severe work-hardening to overcome.  Properly aged, this type of cheeze works well for making long bolts as long as they aren't over-stressed on the take up.        Chgd. to .161" Dia, thanks to "Hawkeye" from LA.

T&M

[Victor3]

  My proofreading services are always free of charge to the fine folks at seacoastartillery

[Spuddy]

In the photo with the clamps in it there appears to be tin foil behind the wood.  What purpose does it (tin foil) serve?  I wish that I lived closer so that I could do some of the mundane chores around the shop, and maybe learn a thing or two.

[Double D]

Tin Foil, my guess keep wood chip out of the mill mechanism and prevent marring the wood where it clamps to the face plate.  Now lets see the real reason!

[dan610324]

probably to protect the wood from oil stains

[thelionspaw]

I really appreciate how you piece the wood together. Great joining.

rc

[seacoastartillery]

     Well Spuddy, looks like that really sharp, bronze-casting, beer making, Swede just aced our Western moderator out on the reason for the tin-foil!   Dan, You are correct, our Bridgeport mill was made in 1965 and although it has been rebuilt twice, it leaks a couple drops of oil each and every day.  Double D is correct, however, on the need for dent protection.  When we clamp to a slightly rough surface, we use a piece of poster cardboard or two to protect the wood.  In this case we are using a smooth angle plate which is perpendicular to the milling table within .0006" in 10" and the spindle is trammed-in to the table within .0002" so the drill goes straight down through all that wood and comes out darn close to where you want it to!  Thanks Tim, good question.

     Thanks, Richard, coming from you, we consider that to be a very thoughtful compliment.

Regards,

Tracy and Mike

[seacoastartillery]

     As promised, here is a drawing with dimensions for a .866" Dia. Gundrill.  You can scale this down or up by using ratio formulas or proportional formulas to make you own metal or wood cutting Gundrill.  For wood, o-1 tool steel works well (Drillrod).  For steel drilling, you need a tool steel like S-7 or something similar hardened to about 62 Rc. or carbide.  For small drills, like we use for deep holes in wood carriages which are smaller 1/4 thru 1/10 scale, we make the void or lengthwise notch 90 degrees.  the relief angles are not super critical.  Close is good enough.  Any questions will be answered quickly.  Hope it's clear, if not, let us know.

Regards,

Tracy and Mike

[GGaskill]

When gundrilling barrels, the work revolves.  I doubt that you revolved the work when you were drilling the Paixhans base.  You must have some kind of revolving fitting to get the air into the revolving drill.

[seacoastartillery]

     George,  Although we used conventional Fostner type bits and ship auger bits in our Milwaukee heavy-duty hand drill to do the Paixhans Monster mortar base drilling, we have gundrilled very deep, 36" holes, into white oak for other projects before with supplied air cooling and chip evacuation.  I should have included that before with pics for clarity.  You can buy an air bearing fitting for about $225 or make one of delrin like we did for about $10.  A 4" long, 1" Dia. delrin rod was drilled 3.75" deep with a 3/8" Dia drill, then the rod was drilled .02" larger than the Gundrill shaft diameter to a depth of 3.0".  A 1/4" pocket for a 1/4" ball-bearing was drilled in the cap end and a hole was drilled for a standard air fitting 3/4" from the cap end.  To use, you put a light coat of bearing grease inside the delrin tube you just made and put it over the end of your gundrill shaft and place the ball bearing end of the fitting against something solid that won't move.  The shaft is placed in the lathe chuck and tightened.  The work is brought to the drill and advanced into the drill after the air valve is opened.  The air delivery fitting that you made is, in reality, a true air-bearing, meaning that the parts do not contact each other, but rather float on a film of compressed air.

T&M

[GGaskill]

I figured it would be something like that.  Now for the technique for drilling the air hole in the gun drill.   

[seacoastartillery]

   

I figured it would be something like that.  Now for the technique for drilling the air hole in the gun drill.  

     George,   We drill air holes in gundrill bits shorter than 2.5" long with twist drills, after center drilling first.  For longer bits with larger compressed air holes, mostly over 3/16" dia., we use gundrills, so make some small ones first, then you can make the larger ones.  We drill into fully annealed tool steel and heat treat later, after milling the bit's muli-facets and larger chip evacuation groove. 

     Almost forgot, when using a gundrill on steel, you must counter-bore with a center cutting end mill.  The depth, rule of thumb, is one diameter deep.  These drill DO NOT self-center, they must be guided when starting by being placed into a hole only slightly over the gundrill  diameter.  In wood, a center drill pocket is sufficient to guide the start of the gundrilled hole.

Thanks for all that good instruction you past on to Mike and I on how to cast a high quality zinc cannonball in Montana!

Tracy and Mike

[Double D]

A 1/4" pocket for a 1/4" ball-bearing was drilled in the cap end and a hole was drilled for a standard air fitting 3/4" from the cap end.

Can you draw me a picture, my feeble mind can't grasp this concept.  Show me the ball bearing pocket

To use, you put a light coat of bearing grease inside the delrin tube you just made and put it over the end of your gundrill shaft and place the ball bearing end of the fitting against something solid that won't move.  The shaft is placed in the lathe chuck and tightened.

Do you mean the shaft runs through the head stock and the drill is turned by the lathe and the work is stationary?  How about some pictures of the whole set lathe and mill...

I suppose I could tow my travel trail down and park it in your driveway and have you teach me...I'll need electricity, water, sewer connection, wireless internet and a clear view of the southern sky for satellite TV.