Author Topic: Regulated Disco Double  (Read 14268 times)

alamih

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Re: Regulated Disco Double
« Reply #30 on: December 06, 2016, 07:22:50 AM »
Hi Bob
excellent job as usual, I'm curious what happend with Monocoque rifle project  from another
airgun forum
Best regards
Greg
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rsterne

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Re: Regulated Disco Double
« Reply #31 on: December 06, 2016, 08:46:32 AM »
I've been waiting for a chamber reamer and bullet moulds for a year now.... have the moulds now, going to have to make a reamer myself, I guess....

Bob
  • Coalmont, BC

alamih

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Re: Regulated Disco Double
« Reply #32 on: December 06, 2016, 09:17:45 AM »
thanks for answering
I'm looking forward to the progress of your work
Greg
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rsterne

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Re: Regulated Disco Double
« Reply #33 on: December 07, 2016, 04:29:53 PM »
I threaded the muzzle of my .22 cal barrel today, and it turns out it is 28", not 25" as I thought.... I will use is as is for now, until I find out what the velocity is with the 34 gr. Beasts, and maybe shorten it later (who am I kidding!).... Anyway, I assembled it for the first time to day, so that I could see it, take a photo, and weigh it....



The overall length is 46.5" and it weighs 6 lbs. 10 oz.... I still have to make the bolt and the front breech band, and alter the stock, but it is easily going to make my 7 lb. goal without the scope.... so I'm a happy camper.... I think it looks pretty slick as well, and it balances right in the middle of the forestock....  8)

Bob
  • Coalmont, BC

Monkeydad1969

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Re: Regulated Disco Double
« Reply #34 on: December 07, 2016, 08:20:12 PM »
So, how soon can we expect to see any numbers and hunting pics, Bob?

Joe
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rsterne

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Re: Regulated Disco Double
« Reply #35 on: December 07, 2016, 08:33:49 PM »
At least another week before the first test firing.... I still have to make the breech band, machine the chamber, leade, O-ring groove and port in the barrel, make the bolt and machine the recess in the breech for the cocking pin.... I am still hoping to get a chamber reamer from Sean Pero, but he isn't answering me.... If I get to the point the chamber is the only thing left, I'll make one myself.... I still need to cast some of the new 30 gr. BBTs as well.... No hunting until next spring, however....

Bob
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grumpy

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Re: Regulated Disco Double
« Reply #36 on: December 08, 2016, 06:00:26 AM »
Bob, your handiwork never ceases to amaze me !
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rsterne

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Re: Regulated Disco Double
« Reply #37 on: December 09, 2016, 02:13:43 PM »
After shovelling snow this morning, I got back into the shop and made the front breech retaining band and the bolt and handle....



I notched out the ID of the band with a small mill so that it can be slid over the tube from the rear with the valve screws in place, something I always seem to forget and have to do by hand afterwards with a file....  ::) .... The bolt nose is only roughed out oversize, it will be finished in diameter and to length after the barrel is chambered and the O-ring groove cut.... It also needs the hole for the cocking lug drilled and tapped into the bottom, but at least the main body and handle are done....

Bob
« Last Edit: December 09, 2016, 02:18:03 PM by rsterne »
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rsterne

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Re: Regulated Disco Double
« Reply #38 on: December 14, 2016, 08:42:33 AM »
Minus 27*C here this morning.... put the heat on in my shop, hopefully it will be warm enough by lunchtime to do some bullet casting.... The plan is to break in my new NOE 30 gr. mould....

Bob
  • Coalmont, BC

Christopher

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Re: Regulated Disco Double
« Reply #39 on: December 14, 2016, 02:37:45 PM »
Can't hardly wait for some test results ;D

Chris
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rsterne

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Re: Regulated Disco Double
« Reply #40 on: December 16, 2016, 06:19:11 PM »
I guess I can't put it off any longer, I have to make my own chamber reamer.... I have made a few before, but they have been a basic, single flute design.... I thought that a six-flute style was overly complex for my machining skills, so I decided to try one that uses three flutes.... The starting point is a piece of O1 (Oil Hardening) Drill Rod, I chose a piece of 3/8" diameter.... I chucked it up in my lathe, and carefully turned it down to 0.001" over the groove diameter of my TJ's barrel for the chamber portion.... Using the compound rest set at 1* off parallel with the bed, I then machined a taper from that diameter down about 0.010" smaller at a point 0.2" from the end to create the leade.... The remaining part at the end I machined down for the pilot, so that it would smoothly slide into my barrel blank, and that took about 0.0015" smaller than the measured land diameter.... I tried 0.001" but it was a whisker snug, and you can't afford to have the pilot hang up during the reaming process and damage the rifling.... I then turned the shank down about 0.020" smaller than the chamber so that it wouldn't hang up at full depth.... At this point, the reamer blank looked like this.... The front, pilot section of the reamer is on the right....



If you look closely at the section immediately aft of the pilot section, you will see a step down in diameter, and then a taper where the diameter increases at a 1* angle (per side) until the taper meets the parallel chamber portion, which is 0.006" larger than the pilot diameter.... Of that tapered portion, the first half, right behind the pilot, never touches the barrel.... As the reamer progresses into the breech end of the barrel, the pilot centers the reamer, and eventually the tapered part starts shaving away the lands until they are gone.... At that point, the parallel portion of the reamer enters the bore, and the chamber gets longer, and the leade moves forward in the bore, until you stop machining.... In my case, I will be stopping when the transition between the leade and the chamber is about 1/8" forward of the front of the barrel port.... The exact chamber depth will be determined by when the base of the bullet stops at that point.... with the nose of the bullet partially engaged on, and centered by, the tapered leade.... I want to be able to chamber the bullet easily, yet have the nose started into the rifling....

The next step was to mill the flutes.... I mounted the reamer blank in a 3/8" 5C Collet in a hexagonal holder, and then mounted the holded in the milling attachment on my lathe.... I have a stop on the vice so that I can remove and replace the holder, indexing it 120* each time to get three evenly spaced flutes.... Each flute consists of a milled slot from just behind the pilot to just behind the chamber portion, ending in the shank.... The end of the mill is stopped a few thou past the centerline, so that the angle between the cutting face and the tangent to the circle at that point is just a bit less than 90*.... If you stop right at the center, at 90* to the circle, you get a very smooth cut but extremely slow cutting.... The further you go past the center, the more acute the angle, and the more aggressive the cut.... I use about 0.010" past center on a .30 cal, so on this smaller reamer I used only 0.006" past center for the end of the mill.... The cuts are made up from the bottom of the blank, removing only 0.010" at a time with a 1/8" end mill, using conventional milling, not climb cutting (ie always cutting so that the flutes of the mill are digging into the work as you feed it into the end mill).... I made 5 cuts, so the flutes are 0.050" deep.... Here is a photo of the reamer in the Collet, after the flutes have been cut....



Notice that the flute starts aft of the pilot, at a diameter smaller than the pilot, and in the first half tapers larger in diameter until it reaches the diameter of the chamber, and then straight back to create the parallel chamber.... At the very back, it ends just behind the beginning of the reduced diameter shank.... There are three identical flutes, spaced 120* apart around the reamer.... The next step is to make sure the cutting edges are clean of burrs, and then harden the reamer by heating to Cherry red and quenching in oil.... That is followed by a final polish and tempering in an oven to give the reamer the right balance of hardness and toughness.... It is my plan to show those steps in the next post, assuming I get them done tomorrow....

Bob
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rsterne

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Re: Regulated Disco Double
« Reply #41 on: December 17, 2016, 12:04:51 PM »
Here is the hardening process.... I like using a slow running drill press (mine is ~300 rpm) so that I can heat the reamer evenly.... You don't want to clamp too much in the chuck, to minimize heat loss.... Carefully clean the reamer to remove any oil or grease, and then rub it all over with a bar of soap.... I use Ivory.... If you neglect this step, after hardening it will be coated with a black scale that is hard to remove.... The coating of soap will leave it a dull grey after you wash off the scale.... The jar of oil underneath is simply Canola cooking oil, which works fine for the quenching....



With the drill press running, you need to heat the reamer red hot, including part of the larger stub, which acts like a reservoir to hold some of the heat.... If you don't it may cool too quickly and not get hardened evenly.... I didn't have it quite hot enough when I took the photo below, so reheated before quenching.... If you are using an acetylene torch instead of propane, don't get the inner flame cone too close, it is hot enough to melt the steel (the cutting edges will melt first!) and ruin all your machine work.... You have to heat it to a nice glowing red, at which temperature, steel loses its magnetic properties.... You can test that with a magnet if you want, to make sure it is hot enough.... If it is, the magnet will not be attracted to it at all....



Hold it at this temperature for 20-60 seconds (bigger reamers need longer) to make sure that the temperature is even throughout, and then quench it quickly in the oil.... Make sure you plunge it past the shoulder, so that the entire reamer gets hardened.... In the photo below (taken after) is it not quite deep enough....



Leave it rotating in the oil for about a minute, and then raise it back up.... CAUTION, IT WILL STILL BE HOT ENOUGH TO BURN YOU !!! .... It will be a horrible looking, black, scaly mess, but once cool enough to handle most of that will come off easily.... If you missed a spot with the soap, you will know, because there will be a piece of black scale that has to be sanded off.... At this stage, the steel will be extremely hard and brittle, like glass.... You will NOT be able to scratch it with a file if it is properly hardened.... Do NOT drop in on a concrete floor, as it could shatter.... Obviously, that is no good for our purposes, so we will have to temper it.... I will cover that in the next post....

Bob
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rsterne

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Re: Regulated Disco Double
« Reply #42 on: December 17, 2016, 01:14:08 PM »
After hardening, I removed all the scale and repolished the reamer.... It looked like this....



You will note that while I spun it in the lathe to polish the pilot and shank (and the large stub), I polished the actual leade and chamber reamer lengthwise, just removing the scale.... I didn't want to make it smaller, or dull the cutting edges.... After polishing I then used my wife's oven, set at 480*F, to temper it for an hour.... This changes the molecular structure slightly, making the reamer tougher but not as hard.... After tempering and cooling, it looked like this....



The hardness of the part can be judged somewhat by the colour after tempering.... Using 480*F, which is recommended for reamers, should result in a "dark straw" colour.... but realistically, you may see anything between straw and brown.... The mottling on the reamer portion is not a result of uneven tempering, but rather of incomplete polishing, which realistically won't matter.... All that remains is to carefully hone the cutting edges on the radial surface (the part cut by the end of the mill).... In the upper photo, that is the upper flat portion, that the barrel is rotating TOWARDS....  Do NOT touch the circumference, other than to brush it lightly with 600 grit to remove any microscopic burrs from the honing, or you could make it smaller, and then it would cut the chamber undersize.... If when you go to use the reamer you find it cuts too slowly, you can lightly stone the TRAILING edge of the flute OPPOSITE to the cutting edge, putting a very slight bevel on it.... GO SLOW, as this can change the cutting rate very quickly.... That is the edge in the center of the reamer the upper photo....

Bob

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rsterne

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Re: Regulated Disco Double
« Reply #43 on: December 17, 2016, 05:13:42 PM »
Here is the process of machining the chamber.... Ready to start cutting.... I centered the tailstock using two 60* centers, and then used the pilot of the reamer as a reference to center the breech of the barrel in the 4-jaw chuck.... I had preciously faced off the breech square.... Note the cutting oil in the bore, and in the channel of the reamer.... I put one channel at the top as an oil reservoir.... I had already advanced the reamer until it just touched, you can see the shiny mark about 1/3 of the way along the flute where the taper started to touch the rifling, before I took this photo.... I cut at the slowest speed on my lathe, which is 28 RPM....



Once the leade section of the reamer starts to cut, I slowly advance the reamer in stages of about 0.008" (1/12 turn of the tailstock handwheel) and allow two full revolutions of the lathe before continuing.... Every half turn of the handwheel (0.050"), I remove the reamer and clean it and blow any chips out of the bore and add more oil.... The chips are nothing more than metal dust that turns the oil black, they are that fine.... In the photo below, the leade portion of the reamer has already entered the bore, and the parallel chamber section is about to enter....



In the next photo, the flutes are fully inside the barrel.... It is at this point the maximum load has been reached.... If you continue to be careful, you can breathe a sign of relief, the reamer didn't break off inside the bore.... At some point, usually before this point, I have already withdrawn the reamer and chambered a bullet until the nose touches the leade.... By careful measuring you can figure out how deep you need to go.... On this reamer, I am now in 1.10" from the front of the pilot, but the front of the parallel chamber is only inside by 0.40".... I need the back of the bullet even with the front of the TP hole in the receiver, which is 0.50" from the back of the barrel.... From this point on, I use up quite a few bullets in measuring my progress by chambering them, using the end of the pilot on the reamer as the nose of the bolt, and then pushing them back out from the muzzle with a cleaning rod to examine them with a magnifying lense.... This allows you to measure how far to the back of the bullet by counting turns on the tailstock handwheel....Mine is 0.100" per turn, which makes it easy.... Alternately, you can measure from the breech to the back of the bullet directly with the depth pin on calipers....



I ended up needing exactly two more turns to have the nose of the bullet nicely engaged in the leade, yet have no rifling marks on the drive band, when the back of the bullet is 0.50" inside the barrel.... The photo below shows the position of the reamer at full chamber depth....



Basically the chamber is now done.... It turned out that my reamer was slightly undersize in the chamber portion, and bullets sized to 0.217" (the groove diameter) were slightly tight, and picking up marks from the chamber.... I used a piece of 3/16" brass rod with a split in the end, and a bit of 220 grit sandpaper in it, to polish the chamber out another thou so that a bullet sized to the groove diameter loaded smoothly.... If you are going to err on the reamer, better too small than too big, you can always polish the chamber out to the perfect diameter.... Here is a photo of the reamer after use....



You will notice the major wear mark in the center of the flute, that is the portion of the leade that machines off the rifling as you advance the reamer into the barrel.... Behind that are some smaller wear marks where the reamer is rubbing inside the parallel chamber as it advances.... Here is a photo of a bullet and some pellets after chambering so that the back of it is 0.50" from the breech (ie level with the front of the barrel port)....



The top row are JSB Exact pellets.... on the left an 18gr. Heavy, in the middle a 25 gr. Monster, and on the right the new 34 gr. Beast.... You will notice the rifling marks on the head band of each pellet, but the only marks on the skirt are where it has collapsed slightly because skirts are always oversized.... The bullets in the bottom row are the new 30 gr. BBT.... On the left is a bullet sized to 0.217" but unchambered.... while the one on the right has been chambered and then pushed back out.... You can clearly see the rifling marks on the back of the nose where it has engaged about halfway along the leade.... but there are no marks on the drive band (sorry for the glare of the flash).... The parallel chamber ends (and the tapered leade starts) just forward of the front of the rear drive band.... The bullet chambers easily just pushed into the breech by hand with a 3/16" brass rod.... You can feel it engage the leade in the last 1/10" of travel.... Anyway, that is how you chamber a barrel.... As you can see, a chamber properly designed and machined for bullets can easily accept waisted pellets....

Bob
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Monkeydad1969

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Re: Regulated Disco Double
« Reply #44 on: December 18, 2016, 07:53:39 AM »
Now we are ready for some accuracy pics.  Nice work, Bob.

Joe
  • Aurora, Colorado
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