Author Topic: Regulated Disco Double  (Read 14647 times)

oldpro

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Re: Regulated Disco Double
« Reply #45 on: December 18, 2016, 09:05:34 AM »
 Serious time involved but will be very rewarding in the end.

rsterne

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Re: Regulated Disco Double
« Reply #46 on: December 18, 2016, 10:14:53 AM »
I have had a few questions about the flutes on the reamer.... Here is a sketch of the end view.... This drawing is for a conventional lathe, running forward, with the reamer in the tailstock, and viewed looking towards the headstock.... The reamer in this application is fixed, and the barrel is rotating counter-clockwise around the drawing.... The short edges of the flute cutouts are the cutting edges....



This is a generic drawing, where 1.000 is the maximum diameter of the reamer.... The flute cutouts which are milled out are shown in blue.... The short edge is where the end of the mill cut.... the long edge is where the side of the mill cut.... For three flutes, I would not go past 1/2 the radius of the reamer with the side of the mill, or you will weaken it too much.... The end of the mill stops anywhere between the centerline and about 5% of the diameter past the centerline (I have never tried more than that).... The further you go past the centerline, the faster the reamer cuts, but the rougher the finish.... If you use three flutes, they are 120* apart.... You can also make a single flute reamer, the cutout is shown as the dotted blue line.... You basically remove a 90* segment of the circle, and again, taking the end of the mill just past the centerline increases the speed of cut....

I offer no guarantees that you will find this design acceptable.... but I have used a few single flute reamers successfully (but I did break one).... and I made and used my first three point one on this build without issue.... I had my cutting edge only 2.5% below the centerline, and it cut very slowly, the chips were basically just metal dust.... On the other hand, having broken a reamer once, inside a barrel, I was being VERY careful.... I make mine from O-1 Drill Rod, which is hardened after machining by heating red hot and quenching in oil.... The reamer should then be tempered at 480*F, which should result in a dark straw to brown colour....

Bob

  • Coalmont, BC

tkerrigan

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Re: Regulated Disco Double
« Reply #47 on: December 18, 2016, 07:48:02 PM »
Thanks Bob, now I fully understand.  Regards, Tom
  • Jefferson, OR

rsterne

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Re: Regulated Disco Double
« Reply #48 on: December 19, 2016, 07:38:17 PM »
Today I finished up the breech end of the barrel.... First of all I "Indexed" the barrel.... Not by shooting it and determining the smallest groups, which is the proper way, but by chucking the breech portion in my lathe and using a dial indicator at the muzzle, I determined which way the barrel "droops", and marked which side would be the bottom so that when installed in the breech the muzzle would be at it's lowest point (6 o'clock).... This has been shown over the years to produce the tightest groups, with the second best groups occurring when the barrel bend is towards the top (12"o'clock).... Barrels tend to straighten out when fired, so if the bend is to the side, not only do the groups tend to be larger, they tend to be wider than high.... With the bend in the barrel in the vertical plane, you have more chance of using a barrel tuner (adjustable weight) to shrink the group size.... Having the bend upwards would help the bullet path intersect the scope centerline better, but I opted for the bottom as 90% of the people who bother to index their barrels prefer that.... Tensioned barrels tend to be less sensitive to barrel indexing, but I decided to do everything I could for accuracy....

Once I knew "which way was up", then I knew where to machine the barrel port, so that was the first job.... I measured the distance from the front of the magazine cutout to the center of the TP hole in the breech, added 1/16" to allow for the barrel protrusion that the MRod magazine needs to clip onto, set the barrel up in my milling attachment, and using an edge finder laid out the exact center of the bottom of the barrel, the correct distance from the breech end and drilled a center hole.... I then enlarged that with a 5/32" mill, and using a 5/16" mill made the spot face where the transfer port will seal.... I then used a 7/32" mill, which is the same diameter as the ID of the transfer port I will be using (and the valve exhaust port) and made a shallow mark in the spot face where the transfer port ID will be.... I changed back to the 5/32" mill, moved the barrel forward 1/32", and plunged the mill back in to make the back of the oblong barrel port.... I then rotated the milling attachment 30* so that I could machine the forward sloping front part of the barrel port.... I carefully positioned the 5/32" mill so that it just tickled the front of the 7/32" ID mark, and milled down until I hit the bore.... This made the barrel port 0.160" wide by 0.270" long, with the back vertical and the front sloping forward from the TP into the bore.... This gives me a barrel port that is the same area as the bore, but only 75% as wide, so that the pellets/bullets will not be damaged when loading.... I then used a 60* countersink to blend the 7/32" hole at the spot face into the 0.16 x 0.27" barrel port, removed the barrel from the lathe, and finished the job up with a small spherical diamond burr in my Dremel.... The result is a smooth transition from the 7/32" barrel port to an oblong, bore area, barrel port....

I then loosely installed the barrel in the receiver, using an MRod magazine to hold the back end in the right location in the magazine notch, and the 5/16" spot face lined up perfectly with the TP hole in the receiver.... I loosely installed the 8 setscrews that will hold the barrel in place, tightening them only enough to put small marks in the barrel.... I then pulled the barrel, mounted it back in the milling attachment, using a 5C Collet in a square holder (against an end stop), and adjusted it until the spot face for the barrel port was perfectly centered.... I then moved the barrel in 3/4", and using a center drill put a witness mark on the barrel, to make sure it lined up perfectly with the setscrew mark, and another one 3/4" further in again.... The two rows of setscrew holes in the receiver are 3/4" and 1-1/2" forward of the transfer port, and on all four sides, 90* apart.... With the barrel in the square collet holder, I could rotate it 90*, and repeat this process, and prove to myself that the shallow holes I was about to drill in the barrel would be where the setscrews were.... Everything looked OK, so I used a 3/16" stub drill and drilled eight 0.030" deep pockets in the barrel for the setscrews to tighten into.... This will prevent the cup-point screws from raising rings on the barrel surface which would damage the inside of the receiver, and can actually jam the barrel into it.... You MUST have spot holes or flats for this reason.... In addition, with my tensioned barrel, I wanted all the screws to carry equal load, and the shallow pockets will mean the side of the setscrew point will be against the pocket, instead of just relying on friction from the ring of the cup point.... This will mean that they will easily share the load of up to 1300 lbs. of tension on the barrel from the Bellevilles at the muzzle....

I reinstalled the barrel, lined up the transfer port and magazine again, and lightly tightened the 8 setscrews into the pockets.... On removing the barrel, I found that the two circular marks from the lower cup-point setscrews were perfectly centered in the pockets, but the other six were to one side or the other (although perfectly centered fore and aft).... I used that small round burr again, and ground off the marks from the setscrews in the other 6 locations.... This moved the recess over towards the point of contact with the end of the setscrew, which would allow it to tighten slightly more on the next trial.... After repeating this procedure a few times, I got completely round, centered rings from the cup-points on all 8 setscrews when they were tightened up.... This means that I don't have to crank a crazy amount of tension into them, which could distort the bore.... but that they will all share in the tension load on the barrel.... It took a bit of extra time, but produce a wonderful result that I have 100% confidence in.... You can see the pocket for the setscrews, and the nicely centered marks from the setscrews, in the photo below....



The last job was to machine the groove for the internal O-ring that seals the bolt.... Before I could do that I had to finish turning down the nose of the bolt so that it fit nicely in the chamber I reamed in the barrel.... I had left it oversize for this purpose.... I usually have problems getting a good fit between the bolt and the barrel, because I always seem to have a slight misalignment of the 1/2" holes in the front and back of the receiver.... but I knew this was the most accurate breech I have made to date, and I was not disappointed.... Once I got a nice sliding fit between the bolt nose and the barrel chamber, I put them both in the receiver, and the bolt functioned well.... I could feel a slight resistance from the bolt touching the inside of the barrel, and there is a shiny mark on one side, but it worked without having to sand one side of the bolt or turn it down smaller, so I was delighted.... I dragged out the specially ground tool I have for making O-ring grooves, it is shown in the above photo.... It allows me to machine a 0.070" wide groove inside the barrel, about 0.040" from the end, to hold the O-ring, in this case a #009.... I slowly increased the depth of the groove until it was 0.060", tried the O-ring and found it wouldn't quite go in place, so I deepened the groove until it would JUST lie flat in the groove.... I tried the bolt, and it slid smoothly through the O-ring.... There is 0.007" of compression on each side of the O-ring with the bolt in place, so I think it will seal fine.... if not, I can always use a 90D O-ring instead of the 70D I tried today....

Bob
  • Coalmont, BC

rsterne

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Re: Regulated Disco Double
« Reply #49 on: December 20, 2016, 06:22:13 PM »
I seems to take forever to get all the last little details done on a custom PCP project.... Today's job was to make and install the cocking pin in the bolt and cut the recess for it in the bottom of the receiver.... It took me all afternoon.... The hardest job was to figure out the exact spot it had to go.... The angle relative to the bolt handle was the easy part.... Too far forward the slot for the bolt handle was too short, and the handle would hit the end before the hammer cocked.... Too far aft, and the nose of the bolt wouldn't withdraw far enough to allow me to remove the magazine.... Yeah, I should have made the slot 1/16" longer, but that is a difficult thing to set up to machine once, let alone change it later.... Anyway, I finally figured out where to drill and tap the bolt for the cocking pin, and I tapped it 6-32, with a small flat for the head of the SHCS to tighten against.... Since I originally machined the cocking slot in the receiver with a 3/16" mill, I had to use a 7/32" mill to make it wider for the head of the 6-32 screw.... Once I did that, it slid back and forth fine, but the head didn't stick down far enough to properly engage the cocking pin in the hammer.... Well, it caught it, but only right at the top, which with a strong hammer spring can bend the pin, so I had to make a longer cocking pin for the bolt.... I did that by using Loctite 638 (green) to install a hex nut tight against the screw head, and then turned it down to the same diameter as the screw head.... That caused me more grief, because it was so long I barely had room to make the recess in the bottom of the receiver to clear it when it rotates sideways when you close the bolt without breaking through the side of the receiver.... Yeah, one change becomes two, then four, nothing is as simple as it seems....

Anyway, I laid out and milled the recess in the bottom of the receiver to allow the cocking pin to rotate to the side and pull back when the bolt handle is withdrawn into the J-Slot.... Again, that took multiple passes to give enough clearance without carving away more of the 1/2" diameter bolt channel than I need to.... I had to finish it up by hand, using a spherical burr in my Dremel to get the last bit of clearance for the corner of the head of the cocking pin screw.... Once finished, I tried it and it cocks the gun smoothly, so the day was a success.... Here is a photo of the receiver with the recess and the completed bolt....



You can see there isn't much metal left in the receiver beside the recess, and it's actually a bit thinner than what you see down inside at the height of the corner of the rotated cocking pin where I had to clearance it by hand.... However, the job is done, and I'm closing in on getting ready to fire the first shot....

Bob
« Last Edit: December 20, 2016, 06:25:12 PM by rsterne »
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oldpro

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Re: Regulated Disco Double
« Reply #50 on: December 21, 2016, 08:57:37 AM »
What are ypu using to cut the concave channel on the reciever?

rsterne

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Re: Regulated Disco Double
« Reply #51 on: December 21, 2016, 09:28:36 AM »
A 7/8" ball end mill.... However, carbide router bits also work fine on aluminum.... and way cheaper....

Bob
  • Coalmont, BC

rsterne

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Re: Regulated Disco Double
« Reply #52 on: December 21, 2016, 03:09:14 PM »
Well, today was the day!.... I spent the morning doing the final barrel prep work.... I crowned the muzzle, lapped the bore with JS Bore Paste, and then followed that by a polish with JB Bore Brite.... It now gleams from end to end.... I then installed it into the receiver and installed the bolt.... I slid on the front breech retaining band, and installed the PRod trigger group, then slid the hammer into place and installed my borrowed SSG assembly, which I set to minimum gap.... The last step was to measure the length required for the transfer port, and make one from a piece of 5/16" Teflon rod.... I drilled it out to 7/32", and carefully faced the end off until it was 0.010" longer than the space, so it would have a bit of "crush" to seal properly.... Bolting down the receiver was the last task before firing the first shot.... Well, except to take a photo....



As you can see, I haven't fitted the shroud, or modded the stock yet, those items will come after initial testing and tuning.... The gauge said the regulator setpoint was 1900 psi, so I loaded up a magazine, and tried the 34 gr. JSB Beasts....They fed fine, and the first shot was 867 fps (57 FPE).... Not bad for 1900 psi.... I shot a few of each weight pellet, and then shot the 25.3 gr. Monsters until the velocity started to change, and it actually went up about 20 fps at just under 1800 psi, so the setpoint is a bit lower than the gauge reads (or vice versa).... With the pressure a couple of hundred psi below the setpoint, I was able to increase the regulator adjustment, I turned the screw about 45* CCW, and refilled the lower reservoir.... The gauge now read nearly 2200 psi, so I repeated the procedure with the higher setpoint.... Here are the initial results.... The 18.1 and 25.3 gr. are JSB Heavies and Monsters.... the 27.4 and 29.6 gr. are my new BBT HP and FN cast bullets.... and the 34.1 gr. are the new JSB Beasts....



As you can see, the 18.1 gr. JSB Heavies were Supersonic, accompanied by the typical loud CRACK!!!.... The were the only pellet that shot faster at 2100 psi than at 1800, which tells me that I don't have enough hammer strike at the higher pressure.... Since I am out of adjustment with the QB spring (it is right at coil bind with no gap), I will need to come up with a different spring combination, or forego the SSG and just use the QB spring in a conventional preloaded arrangement for now.... I think I will do the latter, at least until I can establish what the maximum velocities are with the various pellets at the current setpoint.... The BBTs, both HP and FN, exceeded 60 FPE at 1800 psi, and the 25.3 gr Monsters were very close to that.... and it would seem that there is more there if I increase the hammer strike.... That certainly means that the gun is breathing well, with the bore-size porting.... Those are pretty healthy FPE numbers at such a low pressure, so I'm encouraged.... and I'm looking forward to finding out what the limit is at the ~2100 psi setpoint once I add some more hammer strike to find out where the plateau is with the different pellet weights....

Bob
« Last Edit: December 21, 2016, 03:13:01 PM by rsterne »
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Monkeydad1969

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Re: Regulated Disco Double
« Reply #53 on: December 21, 2016, 05:25:14 PM »
Cool, Bob. 
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Christopher

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Re: Regulated Disco Double
« Reply #54 on: December 22, 2016, 05:42:25 PM »
Wow, impressive at that pressure. Seems mighty nice to simply get your screwdriver and adjust the regulator then right back to shooting instead of having to degas the gun. Thanks for all the details of your build along thread. Another spectacular job. Looking forward to the results with more hammer strike.

Chris
  • dead end road KY

rsterne

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Re: Regulated Disco Double
« Reply #55 on: December 22, 2016, 05:48:39 PM »
As long as the pressure in both upper and lower tubes is LESS than the LOWEST pressure the regulator will be set at.... by, say 200 psi to give you some room fore error.... you can adjust the regulator without completely degassing the gun.... If you are increasing the pressure there is less danger of damaging the regulator than if you are decreasing the setpoint pressure.... because to decrease the setpoint you have to screw the adjustment (seat) clockwise which is towards the piston.... You don't want to be turning the seat when it is pressing against the end of the piston where the HP seal is located.... as it could damage the seal....

Bob
  • Coalmont, BC

rsterne

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Re: Regulated Disco Double
« Reply #56 on: December 23, 2016, 02:09:28 PM »
I tried four different pressures, each 1/4 turn apart on the regulator adjusting screw, and at each pressure I started at zero gap on the SSG and then increased the gap a turn at a time until the velocity dropped below 600 fps at each pressure.... I then plotted the velocity vs. gap at each pressure, with the following results....



The regulator setpoint dropped about 450 psi for 1/4 turn from 2150 down to 1700, then another 450 down to 1250, and then 350 psi from there for the last 1/4 turn, down to 900 psi.... At the highest pressure, even at zero gap, there is not enough hammer strike to reach the velocity plateau.... At 1700 psi, it is just about on the plateau at zero gap.... In both cases the maximum velocity was supersonic with the 18.1 gr. JSB Heavies.... Breaking Mach 1 on only 1700 psi is pretty impressive....  :o

At 1700 psi, the plateau appears to be at about 1150 fps,  the knee of the curve was at about 1-2 turns of gap, and the downslope started at about 3 turns out at ~1000 fps.... At 1250 psi, the plateau was 1051 fps, and the knee of the curve occurred at 3-4 turns of gap, with the downslope starting at about 5 turns out at ~900 fps.... With the pressure at 900 psi, the plateau was 956 fps (37 FPE), the knee occurred at about 5 turns of gap, and the downslope began at about 6 turns of gap, at ~800 fps....

The regulator is very easy to adjust, and 100 psi increments should be relatively easy to obtain.... From 1250 to 2150 psi was 1/2 turn of adjustment, so each "hour" on a clock face would be about 150 psi.... That works out to about 50 psi for each 10 degrees.... The regulator seemed to have good stability, returning to the same setpoint after each shot, as close as I can read the gauge, which is a 3000 psi, 180* sweep, 5% gauge, with 200 psi increments.... I am delighted with the performance of the regulator.... and equally pleased with the ability of this gun to reach 950 fps with 18.1 gr. JSB Heavies at only 900 psi....

Bob
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Monkeydad1969

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Re: Regulated Disco Double
« Reply #57 on: December 23, 2016, 05:11:13 PM »
Seems like you have it about summed up, Bob.

Joe
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rsterne

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Re: Regulated Disco Double
« Reply #58 on: December 23, 2016, 06:20:56 PM »
I reset the regulator to 1150 psi, filled to 2000 psi, and shot 10 shots with the 18.1 gr. JSB Heavies with 3 turn of gap on the SSG and recorded the pressure drop.... I then repeated that at 4, 5, and 6 turns of gap, with the following results....



At 3 turns, the average velocity was 1018 fps (42.4 FPE) at an efficiency of 1.28 FPE/CI.... At 4 turns of gap, the average velocity was 1003 fps (40.5 FPE) at 1.43 FPE/CI.... With the gap increased to 5 turns, the velocity averaged 960 fps (37.1 FPE) at 1.64 FPE/CI.... and at 6 turns the average was 844 fps (28.6 FPE) at 1.95 FPE/CI.... Remember, this is at only 1150 psi.... The ES over the 10 shots was around 14-15 fps for most strings, although for the one at 4T out it was only 7 fps (0.7%).... Typically SSGs have a narrower ES when the preload is set so that the gap is small (0.020-0.060"), but I didn't bother reducing the preload before shooting these strings, so the gap at 6T out was actually over 1/4".... (over 1/3 of the hammer travel wasted)....

I then filled the gun to 2900 psi (my Great White needs filling), and shot an entire string with the gun adjusted for 38 FPE (an average velocity of 972 fps with the 181 gr. JSBs).... I stopped when the first shot dropped below 950 fps, which occurred at shot 45.... Yep, that's a total of over 1700 FPE on a single fill.... Here is the string....



The ES wasn't great, about 2% with unsorted pellets and the large gap in the SSG.... You can see what happens to the pressure curve at the regulator setpoint of 1150 psi, the slope decreases because both tubes are dropping in pressure below that.... I got 35 shots from 2900 psi to the setpoint, another 5 below that down to 1000 psi.... and another 5 shots before the declining velocity opened the ES up to 4%.... The overall efficiency over the 45 shots was 1.44 FPE/CI, down a bit from the results above at 37 FPE.... so I appear to be right in that area where a slight change in gap and velocity makes a big difference in efficiency.... If I were really interested in tuning for these pellets, I would use less preload on the hammer spring and reduce the gap in the SSG to make the gun easier to cock.... I would expect that to narrow the ES and increase the efficiency as well....

This completes my testing of the regulator, now it's time to change out the SSG for a conventional preloaded spring (temporarily) so that I can crank the power up with heavier bullets and see just what this gun is really capable of.... 

Bob
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Christopher

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Re: Regulated Disco Double
« Reply #59 on: December 24, 2016, 01:10:45 PM »
I scanned back through this thread and looked for barrel length and didn't see it. Probably just missed it, but how long is the barrel?

Outstanding results.....

Thanks,
Chris
  • dead end road KY