GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: CableStop on April 17, 2021, 03:12:16 PM
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I wanted to post some photos of a hammer I just finished up for my Dreamline, it's made of 7075 aluminum with a brass slug pinned inside for weight. I didn't have a 1/8 end mill to cut the vent grooves so I just drilled a line of shallow holes down each side using a milling machine then went back with a Dremel to connect them and square up the channels. It's not perfect but I think it should work fine for testing, that is if I can fix the massive leak preventing my Dreamline from filling. I have a hammer but no working rifle to test it in... priorities.
Anyway I also took the opportunity to incorporate a PEEK striker, it's inserted directly into the brass which allows the weight to extend almost all the way through the hammer. While this allows for more weigh, the design transfers all the force from the hammer strike straight into the brass necessitating a pin to hold it from in place. I drilled through the hammer and pressed a 1/8" pin made from O1 drill rod into the hole with some loctite 680 applied to help secure it, then I filed each end flush and used a Dremel grinding stone to sink them a little below the surface so they don't rub the aluminum tube. It weighs in at 13g compared to the stock 17g so it's noticeably lighter, and the brass slug ended up being about .1 too long so a revised version with a shorter slug will be slightly lighter.
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Nice facsimile. Interesting hammer design. I am interested in the wearability of 7075. I'm sure much better than 6061. Do you need to anodize the hammer?
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Nice facsimile. Interesting hammer design. I am interested in the wearability of 7075. I'm sure much better than 6061. Do you need to anodize the hammer?
I mostly chose 7075 due to how thin walled it needs to be, theres only a 0.05" difference between ID and OD. I was curious about anodizing but I don't have the equipment to do it at home so I'd need to send it off. I figure anodizing would just wear off after prolonged use though. My older Hill hammers have spots the anodizing has worn off and those have always been in unanodized tubes.
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Well after doing some digging I've ironically found another perk to this hammer. Apparently FX hammers will peen the valve stem hole and prevent the valve from closing if it's fired empty which is why my Dreamline won't fill. My fault for not being more careful but if the hammer striker was PEEK to begin with this wouldn't be an issue.
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Yeah. If it has peened the valve on yours you may want to take the valve out (safely - degas procedures) and address that first. It may restrict the movement of the stem (may prevent from closing eaaily). You can add a shallow recessed strike area on the stock hammer that will prevent future peening.
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Nice facsimile. Interesting hammer design. I am interested in the wearability of 7075. I'm sure much better than 6061. Do you need to anodize the hammer?
I mostly chose 7075 due to how thin walled it needs to be, theres only a 0.05" difference between ID and OD. I was curious about anodizing but I don't have the equipment to do it at home so I'd need to send it off. I figure anodizing would just wear off after prolonged use though. My older Hill hammers have spots the anodizing has worn off and those have always been in unanodized tubes.
I think it is a rather low tech acid bath and some low voltage cathode set-up. I have not set one up but Im interested in the process. I bet someone here does it regularly and maybe you can farm it out. Probably a good idea to anodize.
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Yeah. If it has peened the valve on yours you may want to take the valve out (safely - degas procedures) and address that first. It may restrict the movement of the stem (may prevent from closing eaaily). You can add a shallow recessed strike area on the stock hammer that will prevent future peening.
Yeah I lapped the stem hole and it seals now. Modding the hammer is a good idea, other people suggested countersinking the stem hole which would need a really long drill bit.
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Here is the revised hammer with some changes I decided to incorporate after messing with the first one, including making my own brass hammer weight. I have a few more ideas I'm toying with to increase the weigh since it's still about 17% lighter than the stock .30 caliber hammer.
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Well I've done some testing on the new hammer and found some issues. I didn't get the original hammer size right and it just didn't work at all, the second hammer fit and seemed to work fine until I started shooting, at which point it wouldn't cock after the first shot. I re-profiled the hammer bevel that pushes the sear down which helped but I still had issues with binding and could see marks on it where the sear dug in so I polished the sear itself since it had an almost jagged surface finish. Again that helped but I still had occasional problems, at which point I brought the hammer bevel down again, basically extending it all the way to the edge of the lip. This time the gun functioned flawlessly for 150 rounds at which point, due to finishing off the ammo tin, I had two empty spots at the end of the magazine. When I cocked it again after the final round the gun jammed worse than before, the bolt wouldn't move in either direction until I pulled the trigger and allowed it to come back, I removed the magazine and it went forward again no problem. I went and got a new tin of pellets to test another magazine and it jammed again after the first shot, but after I got that cleared by pulled the trigger again the rest of the mag fired no problem.
Given what I'd seen in my past two trials I figured there would be two marks close together on the bevel where the sear dug in and sure enough that's what I found. I believe the first was caused by the magazine putting some sort of odd pressure on the bolt and changing how the hammer hit the sear. Then once the first gouge was there it caught the sear a second time and cased it to dig in again, cocking it again may have spun the hammer enough the the gouged surface wasn't in contact with the sear.