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Old 01-27-2016, 06:57 PM   #21
allu
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This is what happened today:

allu's projects - Slingshot Crossbows

So fitted two springs each side on it, rounded the handle and modified the arrow rest slightly. The arrow rest still kinda fails when loading as the hooks try to push underneath it, making it bend quite a bit. But it works good enough for now, maybe I'll come back to it one day if needed.

At first the performance was disappointing. Yes it was faster, punching through 9 and 7 mm plywood easily and going halfway through my new target, but I was expecting more. It wasn't until I tightened the string slightly when this thing started to show some serious improvement. All of sudden it was passing through my target and splintered a 2 cm plank with ease, although not passing through. I guess the field tips aren't really ideal for penetration, a sharper tip would be needed

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows

It's still pretty easy to span with the cocking rope but it's pretty picky on how you pull the rope. Too high up above the rail and the hooks slip off the edges and snap together or too low and it gets stuck on where the springs are attached to. But once done right it's quick and easy. The trigger pull is pretty extreme at the moment, it can be done but it could definitely be lighter. I guess I should try exploiting the let off from straight arms and make the trigger engage at that point, hopefully leading to lighter trigger pull

I'm feeling sorry for those poor commercial arrows, I wouldn't like to ruin them before I get to shoot them outdoors so I guess it's time to make new arrows. Hopefully draw weight isn't too high for those beech poles or else I have an issue, I don't really have anything else to make arrows out of at the moment. But we'll see how it works, more of that next time!

-allu


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Old 01-31-2016, 08:19 PM   #22
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Finally got a few days off from work and hence was able to do some shooting outdoors. It shoots really well, I was surprised just how accurate and (relatively) powerful it is. Although I don't have any sort of sights on it aiming down the, erm, barrel resulted in relatively good accuracy on horizontal axle. Well, accuracy on vertical axle wasn't that great due to lack of front sight or any sort of sights in the first place, so I had to kinda look through the arrow rest and guess where the arrow was pointing at. But still didn't miss once Here's some pics to put the power and accuracy in perspective:

At 10 meters against 2 cm cardboard like stuff (hard to compress) and 9 mm plywood behind it. Nearly made through it:

allu's projects - Slingshot Crossbows
allu's projects - Slingshot Crossbows

At 20 meters the results were still rather impressive! Also you can kind of see how the accuracy is okay sideways, but second arrow hit way too low. Also the damn arrow tip flew away, damn these cheap arrows don't even have glued arrow tip inserts (is that what they're called? no idea ) and then this happens, wasted money

allu's projects - Slingshot Crossbows
allu's projects - Slingshot Crossbows

Next step is to make homemade arrows that fly straight and are even relatively accurate and still quick and easy to craft. Shortening the string could also boost the performance even further as the arms don't turn enough to stretch the springs to maximum, also the let off would get greater. Hopefully that'd help with the heavy trigger pull, in theory it works but who knows We'll see how that works, more tomorrow!

-allu



Last edited by allu; 01-31-2016 at 08:42 PM.
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Old 02-01-2016, 02:20 PM   #23
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Got this done today:

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows
(Shortened the string to the point where let off kicks in, and it indeed made the trigger pull lighter).

Mounted the scope after shooting, so accuracy was still way off. The rail also didn't want to set perfectly straight, so we'll see if the scope has enough amount of adjustment to counter that slight miss alignment. Also Tried a few different ways of making arrow with more or less positive results. First it was just a simple 8 mm diameter beech pole (47 cm in length) trimmer from one end to fit tightly into 8 mm aluminium tube (5 cm in length) with 6 mm sharpened bolt at the end. Didn't work at all, not front heavy enough and the arrow landed somewhere 40 meters away in the forest, all I could see was a cloud of snow when the arrow zipped into the snow.

Next try was even simpler. 50 cm beech pole, again 8 mm in diameter, with 8 cm piece of steel tube (10 mm in diameter) as an arrow head. The tube was simply slid 5 cm over the pole and attached with a nail (after drilling a hole for it of course, obviously hammering a nail through a steel tube wouldn't work ). Then all there was to it was simply flattening the extending steel tube and sharpening it quickly. Ended up with a very front heavy arrow that flew surprisingly well considering it had no fletching. A little unstable and wobbly yes, but the further it flew more stable it was.

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows
(Sorry for the blurry photo, only one I had showing the whole arrow).

well turned out the arrow shaft couldn't quite take that +100 pounds of draw weight. It started splintering from the nock after a handful of shots and the last shot it splintered completely and flew sideways past the target somewhere in the forest again, there must be dozens of arrows by now

Obviously I have to come up with something to reinforce the nock. Maybe just a simple short piece of that 8 mm aluminium tube to go over the pole? Next arrow is definitely going to have fletching that will hopefully make it more stable in flight. But that's all for now folks

-allu

Last edited by allu; 02-01-2016 at 02:22 PM.
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Old 02-13-2016, 06:00 PM   #24
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Got a new tool, finally I'll have a chance to drill straight holes. Well it's not exactly a drill press, but rather a poor man's version

allu's projects - Slingshot Crossbows

I've wanted to build an airgun for a long time and after seeing Joerg's latest videos decided to finally buy the parts for the simplest version.

allu's projects - Slingshot Crossbows

At the moment the epoxy is still drying so no shots taken yet. I was hoping to get away without epoxy but nahh, the schrader valve lost its threads before I even had a chance to tighten it properly and the other end leaked just as badly Barrel is an old 360 mm airsoft barrel, so caliber 6.04 millimeters (measured by eyeballing it quickly lol ). The size of the bottle is ridiculous for the barrel, but couldn't figure out anything else to use as one. Besides this is just a simple test version, I've planned on ordering proper parts on amazon including air tank and QEV valve for way quicker opening times.

(Don't expect too much of this, I'm not going to run it over 4 bars/60 psi simply for the fact that I don't trust an old soda bottle to hold high pressure. Besides plastic gets brittle in cold and might just give in all of sudden, hence the duct tape to prevent shrapnel from flying around. I really need a full metal air tank ).
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Old 02-22-2016, 08:06 PM   #25
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Finally got back to my builds

Spent the evening sanding and improving my flipper. Made some significant changes to improve it overall, including a new stirrup and upgrading the tube holding the swing arms to larger in size because the smaller tube was twisting too much. Mainly due to poor attaching point, I figured out it should be attached to the stock from behind (on the trigger side) rather than underneath it since this way it couldn't twist or move backwards. Also spend more time on actually making the hole fitting instead of just rushing and failing it, it still has some slack on it but a lot less than before. Planning on finishing the sanding in a few days and painting it, we'll see what kind of a mess that will be!

Also played with the coke bottle airgun a little bit.

allu's projects - Slingshot Crossbows

The epoxy just doesn't want to set and making it airtight is too much of an effort. It's nearly airtight at the moment but not completely. But it was good enough for a few test shots. Using homemade darts tested its power against 9 mm plywood and 18 mm pine board. Well they didn't stand a chance. 9 mm plywood was pierced already with pressure of a bit over 2 bars (~30 psi).

allu's projects - Slingshot Crossbows

The pine board was tougher, but at five bars (~70 psi) it gave up.

allu's projects - Slingshot Crossbows

Rather impressive considering how low the pressure was and even with such a short barrel it was still able to penetrate. I've tried hard to find cheap parts on amazon for building an airgun (preferably with no postages) and while I'm still searching I've found some really tempting deals. We'll see if my next build will be a pellet gun of some sort

-allu

Last edited by allu; 02-22-2016 at 09:28 PM.
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Old 02-22-2016, 08:47 PM   #26
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That some great penetration.
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Old 02-22-2016, 09:18 PM   #27
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Excellent.
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Old 03-06-2016, 08:30 PM   #28
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Just giving you a quick update. Still haven't finished painting it but got pretty much finished with putty. Still a bit of sanding awaits, but soon it can be painted:

allu's projects - Slingshot Crossbows

While the putty was drying finished the swing arms and the frame. This time drilled the holes with a drill press, so tolerances are way tighter and there's so much less slack on the swing arms. Also took my time to finish the front sight and improve the trigger. Next week I'll be busy with work, but hopefully I can get it painted soon

-allu
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Old 03-28-2016, 08:09 PM   #29
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Finally after lots of sanding and painting it's finished! Skipping all the unnecessary talking and showing you some pics first:

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows

So there it is. Olive green and matte black as main colors, didn't want to go all olive green because that would have been kinda boring I'm a terrible painter and lazy, so the finishing is not the best. The stock turned out pretty good except for the edges of the plywood sucking all that paint in and leaving visible cracks, but I didn't want to add any more layers of paint on the pine board (it was getting really thick already), so had to compromise. Also I should have prepared the metal parts for painting better (proper cleaning, primer etc), but I just didn't get it done so it won't be lasting too long. But time will tell how long the paint is going to last, not too long probably

The sights work pretty well together despite the fact that they're taken from a pistol sized crossbow and G36K airsoft assault rifle. The front sight was simply epoxied in place and secured with some metal fire, because heck I'm lazy!

allu's projects - Slingshot Crossbows

It's pretty much done, I don't really know what else to add on it. Maybe a foregrip and a flashlight, and arrow holder too, but we'll see about that. It weighs a good few kilograms already and I'll try to keep that there or else shooting it without a rest will be difficult. Arrows are on the to do list next, I bought 2,2 meter piece of that 8 mm aluminium tube, so I should be able to make 6 36,33333 cm (~14 inches) long arrows out of it. The tips are cut down from a threaded rod and fletching is going to be duct tape unless someone knows a better DIY method for it? But more about that in the next update

-allu
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Old 05-02-2016, 05:31 PM   #30
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Long time has passed since my last update, being busy at work and having my girlfriend over takes its toll

But anyways, not much has happened. I managed to ruin my only proper arrow while taking a slow-motion video, so no shooting videos for now. But from that video I was able to calculate the speed of the arrow. The distance was around 10 meters ("around" because I couldn't/didn't realize to measure it more accurately) and a music editing software showed it took 0,211 seconds for the arrow to hit the target. So we get an initial velocity of ~47 m/s or ~ 155 fps with 20 inch aluminium arrow with a field tip. I'm pretty impressed with the results, definitely not bad for a weapon powered by trampoline springs!

Lighter arms and a proper string would definitely improve the performance and accuracy which is rather poor right now. You can hit something with it, but there's a lot of random variation going on. From the video I was also able to see that the arrows leave with their tip pointing slightly upwards before stabilizing mid flight? No wonder this thing is so picky on the arrows. The string also seemed to be doing its own thing instead of just reaching the resting position smoothly as right after the arms reached their final position the string jumped upwards and waved a little bit. Maybe this caused the poor stability of the arrow? I guess it's time to learn how to make proper bow strings I guess!

-allu


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