Adjustable hamsters
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Adjustable hamsters
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Topic: Adjustable hamsters (Read 375 times))
scotton
Shooter
Posts: 37
Adjustable hamsters
«
on:
December 26, 2022, 04:04:36 PM »
Wanted to share my experience with some adjustable hamsters that are available on Thingiverse. I'm not going to link to the STL files because I'm not sure if that's cool, but if you've looked for adjustable hamsters, you've seen the two that I'm going to discuss.
Hamster 1 (in black) is a design that incorporates two geared wheels with a small middle gear that has a handle. It appears to be based/copied from a design available commercially overseas. The idea is that the hamster only moves when you turn the wheel. I printed two and spent a lot of time changing and improving the hamster and braces. The final result works, but it isn't great. The issue is that the tolerances have to be so exact that you spend a lot of time filing and sanding to get everything to fit properly. If it's too tight, it's very hard to turn. If it's too loose, the hamster changes elevation randomly from the weight of the gun. In the end, it was fun to experiment with, but if I would have paid money for this hamster I would have been disappointed. Basically, try one is a little jiggly and sometimes moves with the weight of the gun. Try two is more solid, but sometimes I need help turning the knob to adjust it. Can't find the Goldilocks zone for this design, and it's about a 24 hour print. So I moved on to ...
Hamster 2 looks a little jankier but works much better and is much easier to print. On Thingiverse I think it's referred to as a Pro Target FT Hamster. It basically looks like a Rowan, Mac1 or Submoa design except the teeth are on the sides of the wheels and everything is locked in place by friction between the two braces. With the commercial designs, there are detents around the rims of the wheels instead of teeth in the sides of the wheels. When I first looked at this one, I thought "What, you have to undo 3 screws to adjust the height every time?". But I pondered it a little and came up with some thoughts and improvements.
Improvement 1 was to make the hamster longer and a better shape. For the base, I used the file "Hamster for Air Rifles", made the hamster solid and doubled the thickness. Then I attached the wheel for the hamster (the hamster wheel, if you will) forward of center so I can more easily increase the angle for steep shots. I also cut out a curved section in the hamster so the brace doesn't bind on the hamster when adjusting. And I put a notch for a springer cocking handle (not pictured).
Improvement 2 was to change the way it attaches to the gun. My Hammerli has an Anschutz rail but I haven't been impressed with the rail inserts I've 3d printed. I have to make them so thin that I feel like they aren't very strong. Not enough material in the rail slots. So I use two 1/4" T-rail nuts from the hardware store. They stand proud of the rail, so I bore out the holes on the base and counter sink the holes on the top of the base. Two stainless 1/4" flat head machine screws go into the base and the T-nuts go in the base bottom and into the rail. Then when everything gets tightened, it's mostly metal parts doing the hard work and a long piece of the base sliding along top of the rail. For the HW97, I have a custom stock with a hamster that attaches with 4 sliding 1/4" rods, so I made another base that will allow me to use the same holes with 4 1/4" bolts in the base to use as rods, then slide the base all the way up to the gun. Neither design is intended to easily move the base along the gun. I don't tend to change the connection point on the gun once I get it where I want it, so I'm ok with this. (After I wrote this, I looked and realized I could change the flat head screws on the Hammerli to bolts with knobs, then I could slide it in the rail fairly easily if desired. I didn't do this originally because I thought that the knobs would interfere with the mechanism, but there's plenty of room.)
Improvement 3 was getting rid of the top and bottom knobs. There are three attachment points for the braces. One goes through the wheel on the base, one goes through the wheel on the hamster and one goes through the middle of both braces. I used M5 bolts and lock nuts on the top and bottom connections and tightened them down to the point where you can barely rotate each wheel. Then, when you tighten the bolt in the middle, everything locks up. I printed a knob for the middle bolt. It's not as elegant as a QR lever and I may source a QR lever that is the correct length eventually, but it works fine for now. (There is a design on Thingiverse called Hamster Field Target that's designed for a QR in the middle with a bushing between the braces, but everything rotates on round cylinders and it looks like a lot of sanding and test fitting would be involved. I'm afraid you would get into another Goldilocks situation with this one where it would be difficult to make it easy to turn and still be solid after adjustment.)
Improvement 4 was with the braces. The braces in the original design were way too long. End to end, they are 185 mm or about 7.5 inches. I don't need the hamster to reach the ground, just my knee! I re-sized the length of the braces to 144 mm, so knocked about 2 inches off.
Failed improvement 1, I tried to recess some holes in the braces between the middle connection point and the wheels so I could put some springs in there to help drive the braces apart when adjusting the angle and elevation. Because I shortened the braces, there is not enough room for the springs to not make contact with the wheels. Basically, the wheels pop the springs out when you turn them because the wheels aren't perfect circles. I considering boring out an area on each brace around the center connection point where I could put a spring that would sit between the braces and be captive on the center bolt. I may play with this later if I run out of projects. Or a QR lever may make this a moot point.
End of the day, I'm very pleased with Hamster 2 and this will be the design I use for the 2023. I hope this has been a fun read. If desired, I can do another post on my experience with scope wheels.
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scotton
Shooter
Posts: 37
Re: Adjustable hamsters
«
Reply #1 on:
January 01, 2023, 05:03:41 PM »
Update: There is an issue with hamster two. I've been shooting it at close range off the knee and its working fine, but I went to the range to shoot some 50 yard groups today and there is a lot of lateral flex in the hamster that I didn't notice before. This is because I'm leaving the top and bottom bolts loose and using the middle bolt to tighten the hamster. This works fine for keeping everything in place, but the looseness in the top and bottom are translating into flex.
The short term solution is going to be to add knobs to the top and bottom and tighten them up when shooting. I may be able to do away with the middle bolt, not sure yet. The long term solution is going to be figuring out some quick releases for the top and bottom, and maybe a spring in the middle to help separate the braces for adjustment.
I've got a couple of different designs percolating but they will need to simmer for a bit.
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scotton
Shooter
Posts: 37
Re: Adjustable hamsters
«
Reply #2 on:
January 02, 2023, 02:46:49 PM »
Final update (I hope).
I found a really good QR file on thingiverse and scaled it up to a M5 bolt. I put one on the top wheel and one on the bottom wheel and the hamster locks up like a vise (given the inherent flexiness of plastic versus metal). I tried it with and without a bolt in the middle of the braces, didn't make a difference either way. The levers on the quick releases are kind of big, but I think that's a good thing for shooting with a shooting glove.
So the final hardware for this hamster is 2 M5x50 bolts and nuts and whatever hardware needed to attach it to the gun.
Here's a pic of the final iteration. On the right of the pic you can see a hint of an extended cheek piece I printed for this gun.
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Adjustable hamsters