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PostPosted: Thu Dec 24, 2015 7:34 pm 
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Today I had to figure out how the drill the side valve holes at exactly 90* and aligned with the top and bottom valve holes.... Normally I use a 5C collet in a 4-sided holder, but the maximum diameter collet is 1", and the tubes are 1.25".... In addition, they are 4 feet long, and difficult to handle when clamping in my short, 2.5" wide milling attachment.... The trick is to make sure that the hole drilled through top to bottom is exactly vertical, ie square with the C/L of the chuck.... I got the idea to make a fixture that I can clamp in the chuck of the lathe with two 3/8" holes at exactly 90* to the chuck, that will straddle the diameter of the tube and allow me to put a 3/8" bar through the existing 3/8" holes in the tube.... I didn't have any metal tubing large enough, so I used a piece of 1-1/4" ID plastic pipe, mounted it in the milling attachment, and drilled a 3/8" hole straight through at 90* to the wall of the pipe, and exactly on the centerline.... It's crude, but it should work....

Image

The next step is to make sure that when the tube is clamped in the milling attachment that the centerline of the tube lines up with the vertical centerline of the chuck.... I put the tube in the milling vise temporarily, and using an edge finder found the top of the tube.... It is then a simple matter to raise the vise up the radius of the edge finder (0.100") plus the radius of the tube (0.625") and the tube will then be vertically centered relative to the chuck....

Image

Next I put the alignment tool in the chuck, lined the hole up roughly vertical, and put the tube loosely in the vice and lined the hole in the tube up with the holes in the tool....

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Then I carefully slid a 3/8" diameter bar through the vertical hole, while rotating and sliding the tube around until the bar passed through all four holes.... and then I tightened up the vice, checking as I did so to make sure the rod would still slide easily....

Image

At that point, I removed the tool from the lathe chuck, and checked the bar to make sure it was vertical relative to the ways of the lathe.... As you can see, it was....

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The last set was to use the edge finder again to locate the center of the existing holes in the tube, so that when I drilled the side holes, they would line up perfectly....

Image

This gives you an idea of what can be involved just in setting up to drill a hole accurately in a piece of tubing.... I'm pleased to say that it paid off, and the side holes ended up nearly perfectly aligned with the ones on the top and bottom of the tube.... One hole need a touch with a file on one side, and the other needed to be moved over about 0.005" with a Dremel on one side so that all four valve screws could be inserted and will take equal loads when the tube is pressurized.... When I can use the 5C collet in the square holder, I usually don't have to correct the holes at all, but this worked well, considering the multi-step setup required.... Once I had the cross hole drilled, I then used that, with a 3/8" pin in the chuck, to lay out the hole for the gauge in the left side, and the slot for the cocking handle in the right side.... Here is a photo of the top and left side....

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and here is a photo of the bottom and left side of the reservoir tube.... You can see the hammer through the cocking slot and sear slot....

Image

This was a time-consuming process to go through just to drill three holes and cut one slot.... but that's the way it goes when you have equipment with severe limitations like a milling attachment on a lathe.... You can usually do it, but figuring out HOW and getting set up is the hard part.... The back end of the Reservoir Tube is now complete, the only machining left to do on it is to cut it to length and drill the four holes in the front to bolt in the fill fitting....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Dec 24, 2015 8:25 pm 
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Bob it is always that way in a machine shop. Two hours set-up and two minutes of milling. Sometimes it is worth making tooling if you know your going to have to do it again. Careful planning and measuring before you drill a single hole is so critical!!

Nice work Bob using the PVC as your fixture.

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Pardini K10
Brocock Concept .22
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Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
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PostPosted: Fri Dec 25, 2015 7:56 pm 
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Gee, guess what!?!.... I found a beautiful Millet 6-25 X 56 SF scope under the tree this morning!.... Things were quiet around here this afternoon, so I decided to cut the tubes to length and assemble the Monocoque PCP for the first time.... Here is what it looks like....

Image

I still have to add the bolt, fill fittings and barrel stretcher, and it already weighs just over 13 lbs.... without the scope!.... It is 49.25" long, although it looks longer.... It does balance nicely, in the back half of the forestock.... Then I removed the buttplate, and installed the BiPod (actually a TriPod, I guess) and the scope.... I think it looks pretty awesome....

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This is pretty much a bench gun, although it could certainly be used prone for varminting, using the BiPod and with or without the buttstock.... I really like the easy adjustability of the BiPod for height and tilt, using the handwheels.... It was a pretty cool Christmas present to put it together and look at it for the first time....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 26, 2015 8:14 am 
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Location: Tecumseh, Ontario in South Western Ontario
I'm awe struck! Not just by the gun, which I'd love to shoot, but by the skill to build it and even more the knowledge behind it.
I'll have to book up and either buy machinery or find a new hobby lol.
Can't wait to read how it performs.

--Ed.

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PostPosted: Sat Dec 26, 2015 12:13 pm 
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I think this is probably the first of my builds I can truly call a "Custom" gun.... The only major parts, other than the scope and mounts, that I purchased are the barrel and trigger group.... Everything else (except for things like fasteners, etc.) was machined from steel or aluminum.... Oh, except for the level and pulleys for handwheels on the BiPod.... It's been a long time getting to this level, and I have to admit, it feels like a right of passage.... 8)

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 26, 2015 3:35 pm 
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Today I drilled the holes in the front of the tubes for the retaining screws for the Fill Fitting and Barrel Tensioner....

Image

Here is a photo of the muzzle, showing the recess for the Belleville washers and nut that will tension the barrel....

Image

That completes the machining on the Reservoir tube.... All that remains on the Monocoque tube is the slot for the bolt handle....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Dec 27, 2015 7:09 pm 
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Yesterday and today I machined the J-slot for the bolt handle in both the Monocoque tube and the Breechblock.... I also installed a Velocity Adjuster that works by choking the barrel port by preventing the bolt handle from withdrawing fully into the lower part of the J-slot.... I consists of a 3/16" rod running in a milled slot, and a 10-32 screw to control the position of it.... In addition, there is a small set-screw which presses a plastic plug against the side of the adjusting screw to act as a brake to prevent it from moving by itself.... Here is the Breechblock, showing the J-slot, bolt handle, and adjuster.... In this photo, it is closed about 30% from wide open....

Image

I'm very pleased with the positioning of the bolt handle and cocking handle.... I was a bit concerned that your hand might hit the bolt handle when cocking the gun, but I can wrap my big mitt around it no problem and my knuckle doesn't (quite) touch the bolt handle during cocking.... Here is a photo of the gun in the cocked position....

Image

You can see that the bolt handle is fully back in the J-slot in that photo, which means that the nose of the bolt is completely clear of the barrel port.... Here is a photo of the gun unloaded, with the cocking handle forward (uncocked) and the breech open for loading.... There is lots of clearance between it and the scope....

Image

I also made a brake for the hammer spring preload position adjuster today, to prevent that from adjusting itself as well.... This completes the major part of the machining on this project.... I can assemble everything now, except I am still waiting for the bolts to secure the Valve and Fill Fitting, so I can't as yet pressure test it.... I measured the reservoir today, and it is a whisker over 400 cc, not including the volume inside the valve, so I should have about 25 CI of air available.... If I can manage to tune for a shot string from 3800 psi down to 3000 (55 bar), that works out to 1375 CI, which would work out to about 7 shots at 200 FPE, if I can get the gun to produce 1 FPE/CI at that power level (which is likely a stretch).... I am more likely to tune it for tethered use at 3800 psi, and to get 3 shots within a very narrow ES off tether.... What the FPE level ends up when tuned like that.... is now the big question....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Jan 13, 2016 2:37 pm 
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Finally got my valve screws, so I got to assemble the reservoir today and pressure test it.... Filled it 1K at a time, checking for leaks (none) and it's currently sitting at 3500 psi.... I'm topping off my Great White tank with the ShoeBox to complete the fill....

I slid the hammer down the tube, with it angled about 20*, and was rewarded with a nice loud POP and the valve sealed up again 100%, so things are looking good so far....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Jan 13, 2016 4:45 pm 
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It's now sitting at 4500 psi, no leaks I can find, so I'll leave it for a week and see what happens....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Jan 13, 2016 6:18 pm 
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Location: Victoria, BC and Clarkston, WA
rsterne wrote:
It's now sitting at 4500 psi, no leaks I can find, so I'll leave it for a week and see what happens....

Bob


Damn Good!

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-Rick
Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


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PostPosted: Mon Feb 27, 2017 11:41 pm 
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Well, I finally got back to working on this project.... The reservoir was empty, I had a very slight leak in one of the O-rings (there are only two in the reservoir), so since it was empty I took the opportunity to pull it apart and replace the 70D O-rings with 90D.... It has been sitting at 4000 psi for 24 hours, so I guess I cured the leak.... I measured the land and groove diameter, finished up my reamer drawing, and today I made the chamber reamer.... I'm very pleased with the way it came out.... Each time I do one of these, it gets just a little nicer and more accurate....

Image

I used a three flute design, like the one I did a couple of months ago for my .22 cal Regulated Disco Double.... It is machined from a piece of 3/8" O1 Drill Rod, hardened, and then polished, and tempered in my wife's oven at 465*F for an hour.... While it was baking I did a bit more reading on tempering, and discovered that it is the thickness of the transparent oxide layer on the polished surface that causes the colour.... It starts at yellow, through dark straw, brown, purple, blue, then a lighter blue, as the temperature is increased.... I was aiming for a dark straw to brown colour, which is about 490*F.... Once the oven was up to temperature, after about 10 minutes, it looked just right, but I decided to let it heat soak for an hour, and it darkened to brown with a few purple spots.... I was a bit worried that I had gone too far, but apparently even though the part isn't getting hotter, the oxide layer gets thicker with time.... One recommendation I found was to use 1 hour per inch of thickness of the part, so I really don't need to heat it for as long as I did.... If anything, it might be a little tougher, and not quite as hard, but I think it will cut just fine....

For those of you not familiar with chamber reamers, the part on the left, with no cutting flutes, is the pilot that guides the reamer by running on the lands.... The reamer is then necked down a bit, and has a 1 degree taper for about half the length of the flutes, and then a parallel section to cut the chamber.... I make my chambers about 0.001" over the groove diameter.... It then steps down again at the end of the flutes.... The only part that really does any cutting is the last half of the taper and the first part of the chamber.... You just keep running it deeper into the barrel until the chamber is the length you need for your bullets.... I will be cutting the chamber on my Monocoque to fit both the 100 gr. and 113 gr. BBTs, which means it will also fit the 98 gr. and 109 gr. HP versions.... I have sized a bunch of them (both lengths) to use for checking the chamber depth, most to 0.257", but a few to 0.256" and 0.258" just so I can judge the fit.... The aim is to have the nose of the shorter bullet starting into the leade, but not have the longer one too difficult to chamber.... 113 gr. on the top, 100 gr. on the bottom....

Image

Image

It's really nice to get back to work on this project after a year of waiting for bullet moulds and a chamber reamer (which never arrived).... It won't be long and I will be able to test fire it for the first time....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Mar 01, 2017 7:43 am 
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Location: Dowling ,ontario
Can't wait to see the results Bob. I know how hard you worked on the custom bullet /barrel combo . Hope it pays off well.

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PostPosted: Thu Mar 02, 2017 7:41 pm 
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Yesterday I reamed the chamber, and arrived at a length where the shorter bullet stopped against the leade about 1/16" before being chambered fully, and the long bullet was about 3/32" from being chambered.... This meant you could just feel slight resistance on the bolt handle to chamber the 100 gr., and a slight push to chamber the 113 gr.... That was the last bit of machining I had to do, other than machine the transfer port to final length.... This morning I gave a final lapping to the crown, and then polished the bore with JB Bore Paste, followed by Bore Brite, cleaned the gunk out of the bore, and the gun was ready to assemble and test fire for the first time.... That happened this afternoon, nearly a year later than I had hoped....

My Great White was at 4000 psi, which was about where I hope to run the gun, so I just tethered it and ran the initial tests.... I used the lightest and heaviest bullets I will be using, the 98 gr. HP version of the 3.5 caliber long BBT, and the 113 gr. FN version of the 4.0 caliber long BBT.... With the velocity adjuster bottomed out I couldn't quite cock the gun, but with it backed off 1/2 turn the gun would cock fine, and the cocking effort was still quite reasonable.... This gun has a separate cocking handle on the hammer, all the bolt does is load the bullet into the chamber.... There are so many things different about this build, although I had high hopes, I really didn't know if they would be realized.... It was with those very mixed emotions I pulled the trigger for the first time.... and was rewarded with a velocity of over 1000 fps.... I did the typical testing I always do with a new gun, find out where the maximum is (the velocity plateau) and then work back from there.... I then changed to the heavier bullet, and worked my way back up to maximum.... I only shot 1 or 2 bullets at each 1/2 turn preload adjustment, and then plotted the curves, as shown below....

Image

The maximum velocity is reached at this pressure with 1.5 turns of adjustment left with the heaviest bullet, and 2 turns left with the lightest one.... The peak performance was 1003 fps (219 FPE) with the 98 gr. bullet, and 950 fps (227 FPE) with the 113 gr.... This is basically right what I had hoped for, what I really didn't know was the pressure it would take to achieve those numbers.... Now I know it takes 4000 psi.... I shot a few more rounds, and did a bit of playing around to see what I could get for a shot string.... I'm not interested in detuning this gun for a long string, the gun will primarily be shot tethered to a regulator, and tuned for a short (3-5 shot) string off reg.... Tuning in this way keeps the efficiency reasonable, and yet enables you to disconnect for a short string if necessary.... Once the tank was down to 3800 psi, and I had a rough idea of where to adjust the preload to get a short string, I shot the following off reg....

Image

That is 4 shots, averaging 928 fps (209 FPE) within a 14 fps ES (1.5%).... The pressure started at 3790 psi and ended at 3320 psi, and the reservoir on the Monocoque is 24.7 CI (405 cc), so that works out to an efficiency of 1.04 FPE/CI.... Let me tell you, it's about twice as loud on the fourth shot as on the first, so when tethered it will be quite a bit better than that four shot untethered average.... Now that I know the gun is a success, I can work on the last piece I need.... an inline regulator that I can adjust from 3000-4000 psi by changing the shims.... That will allow me to fine tune the velocity sweet spot with the pressure, while setting the hammer spring reload to give me that 3-5 shots off tether that I desire....

During this build, I had a lot of negative comments about the 7" twist being too fast, that it would prevent me from ever achieving my goal.... and the rifling being too deep (it's 0.001" deeper than a normal .257 barrel), which would likewise ruin the performance.... I think these initial results should be enough to put the nay-sayers to rest.... I'm just grinning from ear to ear that I achieved my goal, without having to exceed 4000 psi....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Last edited by rsterne on Thu Mar 02, 2017 7:51 pm, edited 1 time in total.

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PostPosted: Thu Mar 02, 2017 7:47 pm 
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Location: P.G. B.C.
Maybe I missed it Bob - is this a 10" twist? Oh- just saw above post - 7" - kinda fast for a 100gr. BT, isn't it? - 9" maybe?

If you made your goal and it shoots accurately, doesn't matter one bit - does it - it will likely shoot a 120gr. easily in the 7".

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PostPosted: Thu Mar 02, 2017 7:54 pm 
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Boattails require a faster twist than a flat based bullet, and the 113 gr. is over an inch long (4 calibers).... The Kolbe Twist Calculator said to use a 7" twist, so that is the mandrel I ordered from TJ's.... The 100 gr., which is "only" 3.5 calibers long would do just fine in an 8".... Anyone buying a .257 barrel from Mike now has the option of 14", 10", or 7"....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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