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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: David.Soliman on April 15, 2013, 02:04:47 AM

Title: Gun drilling and making a smooth twist barrel
Post by: David.Soliman on April 15, 2013, 02:04:47 AM
Hi, I had this great idea on trying to make a smooth twist barrel, but I found out that the difficult part is not rifeling but actually drilling the hole.

The idea is to twist a hexagonal bar with a .22 hole in its center. The bar being hexagonal will spin at different speeds (the thicker parts spinning faster than the thinner parts) creating a twist inside the barrel with a smaller diameter. And all of this is without the need of compressing the bar from the outside to creat the twist.

Does anyone know how to modify a normal cheap lathe for gun drilling?
And where do I get the bits and supporting equipment from?
Title: Re: Gun drilling and making a smooth twist barrel
Post by: Bent on April 15, 2013, 08:23:16 AM
No magic in that.. You can buy gundrills in custom diameters... And then oil as coolant, and lots of it at high pressure.

But I think you would be disapointed...  ::)
Title: Re: Gun drilling and making a smooth twist barrel
Post by: David.Soliman on April 15, 2013, 03:44:11 PM
Disapointed how Ben?

With the results of the rilling or the twisting? Cause I have done some small scale trials on the twisting theory and it looks promising.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: rsterne on April 15, 2013, 04:01:07 PM
Well if you've done some trials, what do you get for the profile inside the hole when you twist a hexagonal bar?.... How much does it shrink in diameter?.... How do you twist it uniformly over a given length?....

Bob
Title: Re: Gun drilling and making a smooth twist barrel
Post by: David.Soliman on April 16, 2013, 02:01:15 AM
Bob, the bar had some spirals on the inside but they were not uniform, due to the fact that the whole was not drilled perfectly centered. It would be a waste of time tring to measure the diamter since the spiral is not uniform, pellets pushed through the hole get deformed alot.

The next improvement will be trying to drill a 20 cm perfecly smooth and centered hole in a (softer iron) hexagonal bar and have it perfectly polished. I'll be twisting 10 cm piece from one end and cutting a 5 cm part and wasting it because the center of the piece seems to be affected alot more that the end pieces, this means that I end up with a spiral that has a progresivly higher twist rate and it starts to decrease again, I'll be parting the piece where the spin starts to decrease.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: Bent on April 16, 2013, 05:28:55 AM
I think everybody who in to machining, but dont have access to gundrilling and groovemakers have thought about "how to make a barrel"...  ;)I know I have..

My idea for a smooth twist barrel kaliber 10mm.

Materials
1 Stainless pipe, thin walled. Ø10/Ø12 this should be with honed surface inside.
1 pipe thin walled Ø18/Ø20

Special tool
Multigonal wrought(machined with a twist) bar, maybe 20 sides. Made of toolsteel, hardened and finishmachined.(grinded if I can find a way)

Put the tool 2" inside the pipe, press/roll it on the outside.
Pull out the tool.
There should be a shrinkage/choke and an inprint of the "twisted tool"

Line up the pipes inside each other and fill the gap with epoxy.

Could that work?
Title: Re: Gun drilling and making a smooth twist barrel
Post by: David.Soliman on April 16, 2013, 11:51:37 AM
Thought of something like that Ben, I even thought of using a modified drill bit and forging a tube from the outside on it, then extracting the bit. But it just doesn't "feel" right.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: woogie_man on April 16, 2013, 03:28:52 PM
Why not take an already made barrel and just hone off the lands infill you have your smooth portion, this way you already have your bore good and centered.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: David.Soliman on April 17, 2013, 01:39:36 AM
There are two problems with this; the hole will be larger than the caliber, and the barrel will be smooth on the outside and will be impossible to grab and twist.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: PakProtector on May 09, 2013, 11:49:51 AM
My father made a rifle with my elder half brother. Two bits of seamless tubing with a close fit, and swaged them with a powder-driven carbide rifling button he made.
cheers,
Douglas
Title: Re: Gun drilling and making a smooth twist barrel
Post by: QVTom on May 09, 2013, 02:56:37 PM
Quote
and swaged them with a powder-driven carbide rifling button he made.

Are you saying he propelled the button thru the tube with a powder charge?  ???

Tom
Title: Re: Gun drilling and making a smooth twist barrel
Post by: venxxxxx on May 14, 2013, 01:47:18 AM
I seen a video on fx smooth twist barrel factory. They got a machine clamp on and twist the round barrel at an undisclosed rate. Very cool process. Imo, its too hard for a diyer to attempt to produce a smoothtwist barrel at home from scratch...not impossible but will take a long time.
Title: Re: Gun drilling and making a smooth twist barrel
Post by: rsterne on May 15, 2013, 02:27:35 AM
Quote
They got a machine clamp on and twist the round barrel at an undisclosed rate.
I'd love to see that video.... The process I have seen photos of shows an external swaging die that puts six crimped grooves in a helix in the front portion of the barrel by squeezing it, creating a rifled choke by squeezing it from the outside.... The barrel wasn't twisted, just compressed....

Bob
Title: Re: Gun drilling and making a smooth twist barrel
Post by: Bent on May 20, 2013, 06:57:53 AM
Quote
They got a machine clamp on and twist the round barrel at an undisclosed rate.
I'd love to see that video.... The process I have seen photos of shows an external swaging die that puts six crimped grooves in a helix in the front portion of the barrel by squeezing it, creating a rifled choke by squeezing it from the outside.... The barrel wasn't twisted, just compressed....

Bob

Not twisted, just compressed over a die. Video from FX Airguns : https://www.youtube.com/watch?v=V_HTQwrTG6s (http://www.youtube.com/watch?v=V_HTQwrTG6s#)
The smooth twist is done at about 3:40

Checking, twisting and testshooting: http://www.youtube.com/watch?v=gFcaDYICq8g# (http://www.youtube.com/watch?v=gFcaDYICq8g#)
Title: Re: Gun drilling and making a smooth twist barrel
Post by: PakProtector on June 27, 2013, 07:44:19 AM
Quote
and swaged them with a powder-driven carbide rifling button he made.

Are you saying he propelled the button thru the tube with a powder charge?  ???

Tom

That is exactly how it was done. In addition, no parts sourced from fire arms industry, kit or otherwise.
cheers,
Douglas
Title: Re: Gun drilling and making a smooth twist barrel
Post by: willbird on July 12, 2013, 09:10:05 AM
First on twisting things :-)...there are a variety of high speed steel and carbide tools that have generally a pair, but sometimes other numbers too of coolant holes down the body of the tool, these coolant holes on a twist drill, endmill, reamer or other tool must be helical. They tell me they drill the holes straight then twist the blank...it works out fairly well overall.

Now to gun drilling.....I have never gun drilled, but I have drilled some 1/8" holes 64 diameters deep (8") with decent success, the key things were to use a GOOD parabolic drill (Ghuring or Titex), make a very good "spot drill" first with a rigid 120 degree carbide spotting drill (Garr 120 degree 1/4" solid carbide) then run at 80 surface feet per minute or so (2560 rpm) and feed the drill .001 per revolution with a "peck" cycle every .06" of advance (this cycle pulls the drill from the hole and returns it to within .01 of where it was before retract). This was in H13 steel which is some pretty nasty stuff really.....soft steel should be more of a picnic.

The good drills and the good spot drill I felt were the key parts of success...it would take a long time and a lot of patience to do this on a manual machine vs cnc for sure :-). I was doing it in a cnc 3 axis milling machine. The only time I ever saw it fail terribly was when another guy ran the parts, his drill had "wobble"....it was making a circular dance, and his holes walked a good 1/2" in that 8" distance.


I guess I could say I have gun drilled a little but that was an automated machine/process and I just loaded a few parts, true gun drills are a single cutting edge tool...the drills I used in the cnc mill were normal off the shelf parabolic twist drills.



Bill