# Deep hole drilling “large” stock on mini lathe?



## TTD (Dec 12, 2014)

Hi guys, I have another newbie question for ya…


Note: By “large” stock I mean larger diameter than spindle bore of my particular lathe, which is quite small…just have to put things in perspective…


First, a little background on the project I’m getting ready to tackle - I designed a trick side lever breech for my .25 cal airgun (another hobby of mine) and have pretty much figured out how to go about machining almost everything using only my 7 x 12 mini lathe, but admit that I’m stumped on how to perform the very first step...boring a full length (i.e- 6.5” long), 7/16” diameter hole in some 1” aluminum hex bar.


Now, I know on a bigger lathe you would normally just mount the hex bar in the lathe chuck, put your extra long 7/16” bit in the drill chuck in tailstock and have at it (after center drilling first, of course), but my wee lathe only has a ¾” spindle bore and 10.5” of carriage travel so there goes that idea out the window. I could (theoretically) do the operation in reverse - mount the drill bit in lathe and hex bar in milling attachment and feed the bar into the spinning bit, but I’m afraid the hole will end up veering off-center, effectively making it nothing more than a paperweight with an off-centered hole.


Any ideas, providing it’s even possible on such a small machine??? 


Worst case scenario (and the direction I think I'm heading), I have a machinist/gunsmith buddy who lives about an hour from me who can perform the operation quite easily and quickly on his much bigger 12 x 28 (1.5” spindle bore) so I’m not really stuck, was just hoping to be able to do 100% of the project on my own for a change…kind of a “personal milestone” sorta thing for me…lol


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## MarkStephen (Dec 12, 2014)

Another newbie here and I am going to hold off on saying on how I would do it as it may very well be wrong. What I will mention is some thing I'v been told by "them that know" about drilling long holes, though your hole is not that long. The first thing I was told is, drilling long holes never come out straight. That is to say the exit will always be off axis from the entrance. The longer the hole, the more off axis it will be. Standard twist drills are good at doing this. To reduce this error, the gun drill was invented - GunDrill - for drilling those real long holes. After the hole is drilled, the work is placed between centers and the OD is trued up with the ID so both are on the same axis. So if your OD Must be 1" or real close, use a bit larger hex or round stock to give you enough material to turn it down true with the axis of the drilled hole. 

Now to you more informed readers out there, was this info given to me accurate, or is this in error? 

Mark


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## Wreck™Wreck (Dec 12, 2014)

TTD said:


> Now, I know on a bigger lathe you would normally just mount the hex bar in the lathe chuck, put your extra long 7/16” bit in the drill chuck in tailstock and have at it (after center drilling first, of course), but my wee lathe only has a ¾” spindle bore and 10.5” of carriage travel so there goes that idea out the window. I could (theoretically) do the operation in reverse - mount the drill bit in lathe and hex bar in milling attachment and feed the bar into the spinning bit, but I’m afraid the hole will end up veering off-center, effectively making it nothing more than a paperweight with an off-centered hole.



What makes you think that holding the drill in the chuck and the part on the crossslide is any less accurate than drilling from the tailstock?


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## TTD (Dec 12, 2014)

Wreck™Wreck said:


> What makes you think that holding the drill in the chuck and the part on the crossslide is any less accurate than drilling from the tailstock?



Just the way I was (briefly) taught, I suppose. I'm pretty much green as grass with lathes/milling machines so still LOTS of learning to go yet. I did work/train at buddy's shop last winter for a couple months while I was laid off, but I tried to cram so much info into me in those 2 months that I think a bit leaked out...

Anyways, I was taught (right, wrong or otherwise...) that I would have less problems with a "wandering" bit by having it (bit) held stationary in tailstock and your work piece spinning in lathe. Something about "allowing the bit to follow the path of least resistance", which in my mind made perfect sense so I've been running with it ever since. 

I am certainly open to (and appreciate) any and all suggestions, though!


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## mattthemuppet2 (Dec 12, 2014)

one option - drill undersize from both sides after indicating your stock as true as you can (gentle taps with deadblow, tightening different chuck key holes etc), then make yourself a D bit from drill rod to drill the rest to size (this is from what I've read, never done it myself!). You could try a reamer, but they tend to follow the drilled hole, so that might not help. Lots of peck drilling either way to clear chips so your drill tip doesn't wander.

Does it have to stay hex? If not, the advice above about drilling then mounting between centers to turn the OD concentric to the bore would be the best way.


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## Andre (Dec 12, 2014)

Could you show some pictures of your design? I would like to make a sidelever breach for my Benji Disco.


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## TTD (Dec 12, 2014)

MarkStephen said:


> So if your OD Must be 1" or real close, use a bit larger hex or round stock to give you enough material to turn it down true with the axis of the drilled hole.
> Mark



If I was using round stock that is exactly what I would do, but if it can be helped I really don't want to tackle that chore with hex.

Regardless of what method I end up using, I will be indexing off the bore for the .875" radius to be cut along entire length of bottom as well as the 3/8" dovetail rail up top.


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## TTD (Dec 12, 2014)

Andre said:


> Could you show some pictures of your design? I would like to make a sidelever breach for my Benji Disco.



Probably won't happen til after Xmas, but when I do actually get at it I will start a new thread with all the details in the more appropriate "gunsmithing" section of forum. Here is a couple pics to tide you over til then...btw, breech is for the 22xx/Benji Disco series...


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## 12bolts (Dec 12, 2014)

Todd,
Is your lathe big enough that "if" the hex is chucked up, you can still get the carriage far enough to the right to get a boring bar in the end of your work?

Cheers Phil


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## Andre (Dec 12, 2014)

You do some good sketchup work! If you ever build full out plans with dimensions, (which I think is a great idea!) please let me know! 

Which piece of the bolt cocks the hammer? Is it that pin sticking down from the bolt? Kinda backwards, but a great idea. I like it!


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## MarkStephen (Dec 13, 2014)

Think of doing it in 2 pieces? If drilling it the full length won't work out. 3D view very quickly done to show concept only. Not to scale or to be taken literally. I think splitting at the breach face might be a viable option. Pin and/or pin and screw might work out. Like I said, it's an idea. 

I would also second Andre, you did nice work with your drawings.

Mark


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## TTD (Dec 13, 2014)

12bolts said:


> Todd,
> Is your lathe big enough that "if" the hex is chucked up, you can still get the carriage far enough to the right to get a boring bar in the end of your work?
> 
> Cheers Phil



Thanks, Phil. That's sorta how I was originally planning on doing it but with a 3/8" drill bit (pilot hole) mounted in a square boring bar holder shimmed to correct height. After center-drilling first, start with a jobber length bit, then switch to an 8" or 10" long bit to finish. Don't know if that's the correct way of going about it, but that was my plan!...lol

 With 6.5" of stock mounted (up against chuck face) and carriage all the way to the right there is only 4.75" between end of hex and carriage. Not a real big deal though as like I said, I could bore in as far as possible, then re-set the boring bar/drill bit out a bit further to finish the job.

Only part that puzzles me is how do I support the end of hex in my steady rest? Was thinking I could possibly sacrifice a 1", 6-point socket (providing it's a snug fit) and slide it on to hex bar then mount everything in steady rest....think that would work?

Ya, I know I need/want a bigger lathe, but unfortunately that will be a year or two down the road yet.


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## TTD (Dec 13, 2014)

Andre said:


> You do some good sketchup work! If you ever build full out plans with dimensions, (which I think is a great idea!) please let me know!
> 
> Which piece of the bolt cocks the hammer? Is it that pin sticking down from the bolt? Kinda backwards, but a great idea. I like it!



Thanks, Andre! I do have a complete set of drawings w/dimensions and notes but I won't post them until I build one and test it first. All the numbers add up so it *should* work fine, but we all know how the gremlin's  like to mess with you between drawing and actual finished product!

Yep, pin sticking down from bolt is what cocks the hammer. I know it looks backwards due to the angle of the link between handle and bolt, but it's actually a "retractable" bolt design. As you close the handle it first seats the pellet .010" past the transfer port, then it cams-over-centerline and "pulls" the bolt probe back so that when handle is in closed position the bolt probe sits flush with backside of transfer port allowing for full on, uninterrupted air flow....great way to make big power! 

I'm not the first (or even the second or third!) one to use a retractable bolt, this is just my version. Though AFAIK, no one has done it using hex for the breech...


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## TTD (Dec 13, 2014)

MarkStephen said:


> Think of doing it in 2 pieces? If drilling it the full length won't work out. 3D view very quickly done to show concept only. Not to scale or to be taken literally. I think splitting at the breach face might be a viable option. Pin and/or pin and screw might work out. Like I said, it's an idea.
> Mark



Thanks for the idea, Mark...never thought of doing it that way! If all else fails I may try that, but would rather have it all in one piece to stay as rigid as possible.


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## MarkStephen (Dec 13, 2014)

If you have a mill with enough travel, you could always give a try at making your own gun drill. Leave out the hole for the fluid, and just work on getting the tip correct. then fab up a couple of guides that are bored on the lathe to ensure alignment. One guide up close to the face, the other out at the end of the bed and feed it by hand. At that length the guides might work out OK using a twist drill as well. 

Mark


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## higgite (Dec 13, 2014)

TTD said:


> Only part that puzzles me is how do I support the end of hex in my steady rest? Was thinking I could possibly sacrifice a 1", 6-point socket (providing it's a snug fit) and slide it on to hex bar then mount everything in steady rest....think that would work?



Another newbie here, so take this with a grain of salt. Is it feasible to cut  your hex stock a little longer than the finished product, indicate the outboard end to align with the chucked end, then  center drill it, then mount with a tailstock center and round off a section of the hex at the  outboard end to ride in a steady rest while you drill or bore the hole? Then cut off the rounded portion when you're done?

Was also wondering, do you have an independent 3-jaw or a set-true chuck to keep things concentric without having to machine the hex surface? Or is concentricity not a concern?

Tom


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## Andre (Dec 13, 2014)

TTD said:


> Thanks, Andre! I do have a complete set of drawings w/dimensions and notes but I won't post them until I build one and test it first. All the numbers add up so it *should* work fine, but we all know how the gremlin's  like to mess with you between drawing and actual finished product!
> 
> Yep, pin sticking down from bolt is what cocks the hammer. I know it looks backwards due to the angle of the link between handle and bolt, but it's actually a "retractable" bolt design. As you close the handle it first seats the pellet .010" past the transfer port, then it cams-over-centerline and "pulls" the bolt probe back so that when handle is in closed position the bolt probe sits flush with backside of transfer port allowing for full on, uninterrupted air flow....great way to make big power!
> 
> I'm not the first (or even the second or third!) one to use a retractable bolt, this is just my version. Though AFAIK, no one has done it using hex for the breech...




Great design, I would love to build one. I detuned my Disco using a 13xx hammer spring, it reduced about 100 FPS and gained 2x amount of shots. I was making a lighter hammer but never finished it...

If the breach helps raise power I can detune it even more and shoot right where I want it (800 FPS or abouts) and get even more shots, while gaining potential accuracy by pushing the pellet in front of the transfer port. 

Also make sure the breach screw is behind the loading port, it used to be in front but got moved back about a year ago.


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## george wilson (Dec 13, 2014)

Breech,Andre.

I bored out a cannon that was too long for my 40" between centers lathe by feeding an extended length 1 3/8"(approx) drill out of the chuck. I made a special steel cup to hold the future cascabel knob(which at the time was just turned to a cylinder shape).

The drill was about 2' long. The muzzle of the cannon,which was still just a 5" straight cylinder,was rested on a special large oak block I cut to fit the ways and support the 5" cylinder. It was a bit of a pain to thus bore the cannon,as I had to loosen the chuck about every 1/8" and pull it back to clear the chips. The material was a tough aluminum bronze alloy,which was not easy to cut in the first place. Boring the cannon took a few days,but I got the job done just fine.


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