Deep Hole Drilling / Cannon Barrel

[BronxFigs]

My problem:

I need to drill a blind hole 1.250" diameter, about 19 inches deep into a piece of round bar stock, 3.00 inches in diameter. I have a .750" drill bit 18 inches OAL. This will give me a pilot hole approximately 17.500 inches long. I could open the pilot hole with larger diameter drill bits, but can't drill/bore any deeper than about 10 inches. (I will be using a 13" X 40" lathe).

Some questions:

Can I extend my reduced-shank, stubby, Silver and Deming (1/2" shank) drill bits by sinking/set-screwing the back end of a 1-1/4" drill bit into a 1.00" diameter X 16" length of steel, round stock? I could easily drill a 1/2" hole - (for the reduced-shank) - into the end of the round stock and drill and tap for set screws to hold the S&D drill bits. Note: When peck-drilling cannon barrel, I cannot spin work slower than 90 RPM. I'll drill a little, then, withdraw the extended bit to clear chips, and will keep bit constantly lubed with cutting oil.

Do you think making/using a drill bit extension is a workable solution? The price of an extra long, 24" X 1.250" drill bit is far beyond what I want to spend for a one-off project. Besides, I have the large diameter, S&D drill bit on hand, and would rather use the tooling that I already have.

If there are other alternatives .... e.g. end mills, D-bits, boring-bars?..... please give me some ideas. Fabricating a drill bit extension rod seems to be the easiest, cheapest, and quickest option....but, I could be totally wrong.

Thanks for the help.


Frank

 

[Dalee]

Hi,

My first thought is a boring bar and as an aside, rebated chamber. A d bit will also be cheap and easy. If maybe a bit slower.

The thing to remember is a round bore is a happy bore. Straight is less important. So think about how to make the roundest hole you can. More than how straight you can get it.

Dale

 

[BronxFigs]

Dale,

Thanks for the suggestions. My first cannon barrel was step drilled, and the final hole was generated using a .750" X 18" OAL drill bit. I was actually astounded that I was able to drill such a deep hole, so easily into steel. So with my success, came the idea to go bigger, and deeper....until I saw the prices of extra long drill bits.

I too, thought about making a long, D-bit from some drill rod/silver steel and, of course, hardening it. Love making cannons, but drilling the deep bores are always a big problem for me.

Frank

 

[kvom]

I would likely try to take a 3/4" boring bar and mount it on a 1" steel extension after pre-drilling (possibly with a 1-1/8 S&D as described.

Obviously the bar would need to be offset from the center of the extension to allow the cutting edge to clear.

 

[Buchanan]

The extension to the reduced shank drill is a very practicle idea. I have often used it. The biggest problem is when the drill binds.
This is often because swarf is trapped by the back end where there is no clearance. You can grind or machine clearance or just clear the chips away often.

 

[Swifty]

I have, in the distant past, taken a suitable steel bar and machined a slot in one end and then soldered a piece of HSS blade in the slot. The HSS is then ground to mimick a drill, it worked but was very slow as you have to keep clearing the swarf.

Paul.

 

[rodw]

My BXA toolpost has a 1" boring bar holder. I'd make a boring bar out of some 1" rod and a carbide insert.

 

[BronxFigs]

Thanks for all the suggestions and ideas for alternative solutions.

Swifty....never thought of that....making a very long spade bit. Thanks.

Using my Silver & Deming drill bit mounted into a long extension seems like a viable option. Once a portion of the 17" deep pilot hole is step-drilled and then opened up to the 1.250" dimension, I could slip the S&D bit into this hole and start drilling deeper, little by little. My biggest fear is binding and galling when the drill reaches near full depth. Will the set-screws holding the drill in the extension, prevent this? If the drill binds badly, then, I got big problems. The drill may pull out of the extension bar and get stuck in the work. How will I get the drill out? This situation, is my biggest fear. I am now wondering if it would be better for me to weld the drill into the extension, and grind away the weld to match the extension diameter?

This may work with peck drilling...a technique which will decrease the chances of chips jamming, and binding the drill inside the hole.

Having never drilled a hole this large and this deep before, it's all new to me. What's the worst that could happen? So if it goes badly, I'll take the work, stuck drill, and extension bar, and toss it all into the scrap bucket. I'll let you know what happens.

Thanks again, for the help.
Frank

 

[Dalee]

Hi,

If jamming the works with chips is a major worry for any kind of drilling. Then a boring bar will be your best bet to avoid that.

It will tolerate working that deep with very minimal chance of things going wrong.

A 1" bar will be stiff enough for the job. Just take lighter cuts and deflection will be minimal.

Dale

 

[bazmak]

If you go with the drill extension then grub screws will not be sufficient
to hold the 2 together.You should drill and pin or use larger grub screws in a deep dimple in the shaft.2 grub screws at 90o apart min
.If you have the length then multiple grub screws offset
YOU MUST step drill in stages,and only cut a couple of mm deep each time
before pulling out the drill full length to clear the chips
If the drill binds up its near impossible to remove
I would also make a large boring bar with a RCT on the end for finishing

 

[BronxFigs]

bazmack...will do.

Thnx,
Frank

 

[petertha]

I've never done anything like this but here are a few links if they are helpful. I would think the gun builder/restoration folks must know a lot about these related issues & tooling.

My only advice is you might need how to 'dead end' the barrel. I've found just drilling through 2-3" long stock requires quite a bit of axial push with bigger diameter bits. Surprisingly stock can move back in the chuck jaws (marring the OD) or push the tailstock rearward giving a false depth reading, even though everything is clamped tight to begin with. Good luck.

https://johnsmachines.com/2016/02/15/making-a-cannon-barrel-is-boring/
http://www.chaski.org/homemachinist/viewtopic.php?t=23391
http://lassengunsmithing.com/html/24pdr8.htm

 

[BronxFigs]

petertha-

Just read your suggestions and read through all your links. Many thanks for the help.....especially for linking me to the information regarding Howell's D-bit.


Frank

 

[Blogwitch]

You can buy very long and large SDS drills nowadays very cheaply, they are masonry drills, but you can grind the tungsten tips to a metal cutting profile and they cut very well once done. The last ones I saw that were in a German supermarket here in the UK a few months ago were less than 10 bucks each.

Get very close to size, then revert to what others have said, either a rigid boring bar or a D-bit for final finishing.

A boring bar will straighten things out even if the hole is bent, but a D-bit will act like a reamer and follow a pre drilled hole, even if it is bent like a banana, but too much bend and jam ups occur. I personally wouldn't go down the D-bit route for anything more than four or five inches deep. Been there many times, sometimes successful, many times not.

What you really need to do is contact a good gunsmith and he might point you in the right direction as to how they get straight barrels, but at the size you are talking about it is more of a howitzer producer rather than a gunsmith. Have a look on Youtube to see if anyone else has produced what you are after, why reinvent the wheel when someone else has been there before.

John

 

[goldstar31]

Oddly, John and I differ somewhat because I can bore almost 13" and an 1/8thbore with a D Bit. I made Northumbrian small bagpipes- years ago.

Nevertheless, much written is valid but my thoughts are 'in line boring' if possible. When you get to something really exciting like boring a Quorn, you will find out.

Stuck with a closed hole, I'd settle for a safer technique and go vertical. Again, if there was room, I'd rather have a cutting tool constructed using a tube. Wrong? read up on lathe alignment.

Norman

 

[Dalee]

Hi,

The more I think about boring the cannon barrel, the more I like a spade drill for the job. A replaceable insert one. The holders are pretty simple to make. Just mill or even hand grind some flutes for chip clearance. Held in a tool post holder, the stickout length can be easily managed.

The inserts are not stupidly expensive, around $20US to $30US and can be had in HSS or carbide. A simple cross screw holds them in.

The advantage is they are very good about drilling straight and round very deeply.

A quick and dirty sketch.

Dale