What would I use to drill a chromoly barrel 16" .410ID

K

KyleH

Moderator
I am a machinist and have access to all kinds of machines, but I have yet to be exposed to anything that could precisely accomplish this task. I would use an 8.5" drill and reamer form both sides of a barrel then thread the barrel onto my receiver correct? The drilling wouldn't actually be .410, I would of course drill and ream it. It is for a 4.10 shotgun shell and will be made out of solid stock.

Heres the project:
http://www.thefiringline.com/forums/showthread.php?t=264042
 
They pointed that out in the other thread, I emailed the ATF for a full list of requirements for a Class III shotgun.

What would I use to drill an 18" barrel .410? If I could get a 1/2" boring bar in there would I maybe have more success? Same question then for .615"/.739"/.775" (20/12/10 gauge)?
 
Drill with a gun drill. Available from Star or one of the other cutting tool manufacturers. Use a lap to finish (the drill will cut between a 63 & 32 RMS finish) or rig a long mandrel if you've got a hone available. Order your drill just a few thousandths undersize, 13/32" or thereabouts will be just fine. A properly sharpened and properly used gun drill is not likely to cut much oversize.

As you've apparently no experience in drilling deep holes I'll outline a simple procedure using an engine lathe:

1: Set up the stock using the chuck and a roller bearing (cam follower) type steady rest.

2. Bore a flat bottomed hole about 3/4 to 1" deep not more than 0.0005" bigger than the measured diameter of the drill- 0.0003" oversize is about optimum.

3. You'll need to rig a splash guard, a coolant pump capable of delivering cutting oil at about 500 psi, and a means of inducing the oil into the drill.

4. Gently insert the drill into the hole so that it's not quite bottomed, start the oil flow and slowly engage the clutch of the lathe. The lathe should be turning at a minimum of 1800 RPM (assuming you're using a carbide gun drill). Gently start the drill cutting. As the chips emerge you'll be able to gauge proper feed- in a steel like 4150 @ 27-32 Rc the shaving should have a crinkled texture rather like crepe paper. You'll be surprised at how freely the drill cuts. Stop just shy of the end of tailstock quill travel. Back the drill off the cut a bit, stop the spindle, cut the flow of oil, extract the drill, thoroughly clean the hole, reinsert the drill and advance the tailstock toward the chuck. Repeat as needed. Never bump the drill.

A 24" piece of stock can be drilled in well under a half hour using this crude setup. A short hole like this (short for a gun drill) will ususally not exhibit more than a few thousandths drill drift (off center at the exit end of the hole). For a fine finish I'd recommend that a beginner use a hone or a lead lap. Modern gun reamers do work but there are many ways for a beginner to go wrong. You could of course use an old style square reamer (a hardened steel tool carried in a hardwood plug shimmed to scrape, not cut) but this is slower than a hone of lead lap.

Bob
 
I should have been more clear. I am a 19 year old mechanical engineering and machining student which is why I have never drilled a precise hole more than 4" deep.

Few more questions:
1)I don't have a roller bearing steady rest, will a brass bearing one be fine?
2)The lathe I usually do work like this on has a coolant pump that simply sprays onto the part, would spraying it into the hole like a normal drill be ok or does this require something special like pumping it through the drill bit? The drill bit I am looking at has the hole for pumping it through, I will have to ask my instructor if we have what we need to get that done.
3)Minimum of 1800 RPM?! I am pretty sure thats a fast as this lathe will go. Did you mean 180?
4) What you say never bump the drill you mean careful not to gouge it because its carbide and breaks easily correct?

Thank you for your help and for answering my questions, I am new. I think I will try a short barreled cannon next week thats .177, if I like it and it comes out decent I will buy a .177 bit and make a long, black powder one, then if that comes out good I will make a full size project.
 
drill

KyleH: Sir; it excites me with your thinking. Sir; without seeming condescending
man first bored things out with rocks, stick, brass, bone, antlers, you get the picture.
It can be done:D proper metal to fit your need; drill bit of appropriate dimension
Drilling speed; slow, without chatter, prevent/control heat, lubricant, flush drilling constantly,
You will end with a piece of pipe. no rifeling: Not unlike a shotgun barrel.
Threading will be the harder part. Take your time and let us know how it turns out. I cannot see; unless you loose sight of what you are trying to accomplish;
a problem. Factor in wall thickness; full threading for receiver, loctite together
Future project; Hone the barrel for finish. Simple
 
KyleH,

3. 1800 RPM. Not 180 RPM. 180 RPM is far too slow to run a common carbide gun drill, at 1800 RPM you're cutting speed is a bit under 200 F/S- this is the low end of the effective machining speed range for cutting medium carbon chrome molybdenum steels with carbide.

1. You'll find it difficult to maintain a lubrication film on the bronze pads of a common steady rest at this speed. Were I forced to try this I'd recommend mixing a bit of litharge into particularly tacky high quality grease, perhaps Lubrication Engineers Alamguard #3752. But it's a simple matter to adapt most conventional steady rests to accept rollers. For limited use you need not use high quality bearings.

2. Gun drills consist of a base which is used to hold the drill and through which coolant/lubricant is fed, a tube which in section looks like the illustration below, and a carbide cutting tip.

tube.bmp


The coolant must be fed to the tip of the drill. There it serves two purposes: to lubricate and cool the tip and to flush the swarf out of the hole. Your pump setup need not be fancy, costly, not durable but you must deliver plenty of volume through the drill at the recommended pressure. Failure to do so will result in a bound or broken drill.

4. "What you say never bump the drill you mean careful not to gouge it because its carbide and breaks easily correct?" Correct.

*****

As Neophyte1 points out you can use older technologies. In order of personal preference:

1. Gun drill with high speed steel tip. I haven't seen one of these in years, I doubt that they're made commercially anymore.

2. Gun drill with a hardened carbon steel tip- I'd select Carpenter's F2 steel for the tip if I had to make and use such a drill. This old fashioned tool steel makes cutters that will significantly outperform cutters made from 1095 or W1.

3. Flat or spade type drill (be sure to remove swarf very frequently in use). Again, not manufactured commercially in the configuration you'll need. Be sure to design the shank to allow plenty of lube/coolant/flushing oil and plenty of room for the swarf to "escape". An ordinary lathe coolant pump will provide sufficient pressure here.

4. Twist drill. It will probably lead off center. How much depends on many factors. Again, I'd prefer to use a twist drill that had coolant holes did I have to use such a drill. Twist drills having coolant holes are available- perhaps not in a long enough length. If necessary you can make a longer shank that will accept oil. An ordinary lathe coolant pump will provide sufficient pressure here.

good luck,

Bob

edit: fixed picture
 
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I will use a carbide drill I found one with a coolant hole for what seems like a very reasonable price.

And yea at even 900RPM it was wearing on the brass steady rest the other times I have used it. Its a sharp lathe...made in Taiwan. :( Works good otherwise though.

I will talk to the instructor and see what he thinks and make a real short one with just a regular HSS .177 number drill, then probably sand the inside. Basically a crude black powder cannon. Then I will make a longer barreled one with a carbide gun drill, and if that goes well and I have the time I will make a very nice one capable of shooting shotgun shells within the rules of the law. Making one 18.25" long and then making the overall length just above the minimum with whatever I use to hold it.
 
410 bbl

Sir:
I'd probably center that bbl blank in my 3 jaw and true it front and back (3 jaw only runs out .0015) get a common twist drill properly ground about .015 or .020 below .410 to be able to ream it and drill using a double flap of denim on drill face to stop chatter, go SLOW not 1800 rpm! and oil frequently upon withdrawall at peoper intervals - drill all the way through and then use a .409 good reamer with oil and slow feed using air to blow chips out both drilling and reaming. You could polish the bore then if needed and cut threads and chamber - do not use water or gas pipe - 4130 or 4140 is great.
Harry B.
 
I have collets up to 1 1/4 would it be better to use maybe 1" material and 1" collet? Denim on drill face?
 
Henry Bonar in his post above is absolutely correct. If you use high speed steel you must slow down- I'd try about 250 to 300 RPM first- you'd need to find a speed at which you can keep your drill from "burning" (overheating which will lead to eroded corners or worse).

Without oil holes through a twist drill you'll have to extract and lubricate frequently, perhaps as frequently as every 1/8 to 1/4" of forward travel.

If you use a carbon steel drill you'd have to go even slower- I'd start at about 125 RPM.

Bob
 
Thats not a problem I can set the CNC to peck and just let it pull out every .25. HSS is the worst bit we have at the shop We have almost exclusively HSS drilling stuff with carbide for everything else except endmills which we have both, mostly HSS.
 
bbl.

Sir:
Denim on the drill face? I take no credit for this - an old smith Dave Taylor told me this. In enlarging a present smaller hole, especially, it really gives you a fine looking hole with NO chatter. Several denim thickneces may be necessary on large holes. It seems to stabilize drill in into virgin steel also.
Yes, as the other smith says, keep that drill speed slow and as he says clean out (blower) and lube often!
Harry B.
 
bbl.

Sir:
Denim on the drill face? I take no credit for this - an old smith Dave Taylor told me this. In enlarging a present smaller hole, especially, it really gives you a fine looking hole with NO chatter. Several denim thickneces may be necessary on large holes. It seems to stabilize drill in into virgin steel also.
Yes, as the other smith says, keep that drill speed slow and as he says clean out (blower) and lube often!
Harry B.
P.S. Don't ever let anyone tell you that in barrel drilling that they drill a STRAIGHT hole through a 36 or 44 inch round stock - check it out! There is ALWAYS some run out at the outboard end.
 
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