Another QB78 Project

[rsterne]

I guessed that the average velocity is 685 fps, which works out to 18.9 FPE times 20 shots is 377 FPE.... I assume a 13 CI tank times a 70 bar drop is 910 CI or air used.... That works out to only 0.41 FPE/CI, which at that power level, frankly, is dismal.... I'm guessing the hammer and spring are stock, and as such are optimized for about 1200 psi or more.... Regardless of whether that is the case or not, you must have wayyyyyyyy too much hammer strike for the pressure you are running, hence the monsterous air use.... Since you are planning a big increase in pressure, I wouldn't worry about it, and in fact you may have to increase the hammer strike over stock to run 1800 psi.... I just thought you might like an idea of what is happening....

Bob

[remtom1200]

You hit the nail Bob. I had no intentions of operating under 1500 psi when I put the pieces together, but still a very interesting set of strings...lol.I am hoping to adjust the reg down a hair to 1600ish after it arrives. I have been checking out your adjustable hammer and thinking of a way to have one cock on close. I believe I have the design figured out, but not sure how to case harden the sear catch using a propane torch

[SeanMP]

Thats easy

1144.....my favorite material will flame harden to Rockwell 60. Propane is doable....swap the propane for a MAPP cylinder and your laughing

[SeanMP]

Here is a quick little vid on flame hardening or "direct hardening" with a propane torch

http://youtu.be/A8OlmtwnpVI

1144 or "stressproof" is the ideal material for the small shop. It is a pleasure to machine. Slightly stronger than chrome moly. Medium carbon, resulferized.Once you have used it you will never buy another piece of 1018 cold roll.

[rsterne]

Excellent video.... I thought the part looked hotter (more yellow) than what I usually do, but that could be the colour balance on the camera?.... I guess as long as it's no longer magnetic, it's hot enough?.... I've never heard of 1144.... nor any idea where to get it.... I have some 1045, and of course O1 drill rod.... any significant difference?....

Bob

[SeanMP]

Thanks Bob

Yes I noticed that the part looked brighter in the video at cherry than it really was.

1045 (shaft steel) is similar to 1144 in many ways. Both are a medium carbon but 1144 has been resulferized which increases it's machinability exponentially and decreases tool wear.

Strength Comparison "normalised"
1045 tensile 640 Mpa
1144 tensile 745 Mpa
4130 tensile 685 Mpa

1045 yeild 410 Mpa
1144 yield 620 Mpa
4130 yield 535 Mpa

Your local metal dealer should sell 1144 or "stressproof" If not shoot me a couple sizes and I'll send you out some test pieces

This is just the first blurb google picked up on a search
http://www.richmondsteelcanada.ca/steel-grade-1144.php

[rsterne]

Your local metal dealer

.... Surely you jest....

Bob

[SeanMP]

Okay so 'local" is subject to the laws of relativity.

My "local" is an hour away which makes it relatively more local than yours I'm betting.

[remtom1200]

Hmm.. I would pay dearly for anything other than 1018 around here. No one stocks nice machining metal it seems.

[SeanMP]

Hehehe.....Place your order. My guy is very reaonable