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 Post subject: Custom Trigger For QB78
PostPosted: Tue Nov 08, 2016 7:20 pm 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
I have had my QB78 for a couple of years now. I did all the usual mods, and It shot pretty respectable. The only thing that I didn't like about it was the trigger. I just couldn't get used to anticipating when it was going to fire. The trigger worked smooth enough, but being used to shooting my RWS model 48, I just had to do something about it. So I made my own custom trigger for it. The housing is made from 6061 t6 aluminum, plus the trigger itself. The internal parts are made from mild steel and the safety is made from billet 304 stainless. The safety plunger is made from brass. Every part is homemade. It works fabulous, and is all adjustable. The pull weight is very light, (even though I don't have a pull gauge) trust me it is. It has immensely improved my accuracy with this gun. It is a true, two stage trigger. I'll post some pictures.


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PostPosted: Tue Nov 08, 2016 7:39 pm 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
Some pictures didn't load so here they are.


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PostPosted: Tue Nov 08, 2016 8:19 pm 
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Joined: Sat Sep 25, 2010 7:49 pm
Posts: 1246
Location: Southern Ontario
Wow. Great work!

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Air and springs and CO, too


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PostPosted: Wed Nov 09, 2016 8:50 am 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
Thanks for the comment.Yeah, I guess I should have mentioned I didn't make the springs or screws or dowel pins. But I did make the spring for the rotary pawl.


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PostPosted: Wed Nov 09, 2016 1:17 pm 
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Joined: Wed Nov 27, 2013 12:54 pm
Posts: 518
Wow good work.

A true 2 stage trigger.
Would you be willing to show the blueprint of your work.
HOw many hours did you out in. NIce machining

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Hatsan At44 Tactical .22
Steyr hunting 5 automatic
Ruger air magnum .22
Weirhauch HW100 .22
Gamo Expomatic .177
Benjamin Marauder DougP custom stock
Theoben SlR98 .22
AlEx Custom gun .22 (JezX built masterpiece) :)
Hatsan Atp2


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PostPosted: Wed Nov 09, 2016 1:44 pm 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
I have no blueprints. I just make a lot of things as I go along. But I could make blueprints of the finished pieces when I get the time. It took me about four days between machining and designing. The real challenge is figuring how to put everything into a small space. I sometimes mock up a model of some aspects out of plastic or wood to prove my design concept, so I don't waste a lot of time machining or doing handwork for nothing.


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PostPosted: Wed Nov 16, 2016 9:31 am 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
When I started out I was going to use the original housing but I didn't want to ruin the originality. But it could be used to hold the parts arrangement. I used .125 hardened dowel pins, cut to length for all the pivot shafts. To make the holes to hold the pins, I put the housing cover on, and then with a drill smaller than .125, drilled the holes straight through both sides. I did this on my milling machine, but one could do this on a drill press too. I then took the cover off, and with a .125 drill bit, carefully opened the holes just enough that the full diameter of the bit went in about .020. This gives you a guide for the next step. At this point I changed the drill for a .125 end mill and with some measuring set the stop on my machine so that the depth of the hole would leave around .010 without going all the way through. All that's left is to figure out the length to cut your pins to, so that when the cover is put on, they are encapsulated in the holes on both sides. I cut them slightly long with a cutting wheel, and then shortened them on my bench grinder, all the while measuring with my vernier, until they were the precise length. It may be a bit tedious, but it's the type of thing that a first year machine shop teacher would be proud of you for. The wall thickness of my housing is a little thicker than the original, but I think there is enough meat on the original to use this method. I then used the lathe, to make up some thrust bushings out of brass to keep the parts centered, without too much side play. On the trigger I used delrin. Only because I didn't have any brass in that diameter. The adjusting screws are all 1/2 inch, 4:40 stainless cap style.


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PostPosted: Thu Nov 17, 2016 10:12 pm 
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Joined: Wed Nov 27, 2013 12:54 pm
Posts: 518
Thank you for all the details.
I want to try and build one
And again great work

_________________
Hatsan At44 Tactical .22
Steyr hunting 5 automatic
Ruger air magnum .22
Weirhauch HW100 .22
Gamo Expomatic .177
Benjamin Marauder DougP custom stock
Theoben SlR98 .22
AlEx Custom gun .22 (JezX built masterpiece) :)
Hatsan Atp2


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PostPosted: Thu Nov 17, 2016 10:45 pm 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
Yeah, sure give it a go. Don't be afraid to ask if there are some things you have trouble with. The only drawing that I have is just all the measurements I made of the original housing, and a basic layout of the parts. It isn't made in the typical three dimension style drafting drawings, so it is kind of cluttered with too many measurements. But like I said, when I get the time I'll draft up some proper drawings. Probably this winter when it's too cold for me to work on a car I'm building.


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PostPosted: Thu Dec 15, 2016 10:33 pm 
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Joined: Mon Nov 07, 2016 10:11 pm
Posts: 13
I thought I should mention that the springs for the trigger and sear, are just standard springs from the kits that busy bee sells, or they used to sell. I bought them 15 years ago but they probably still have them. I drilled and tapped the end of the trigger and the end of the sear with a 4-40 tap and installed a 4-40 stainless cap screw in each part. The size of the head is just perfect for the springs to mount on.


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