Reverse enginerding, does it work?



Author Topic: Reverse enginerding, does it work?  (Read 3875 times - 1 votes) 
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #20 on: March 05, 2018, 02:00:50 PM »
You are correct, piston 66 is free riding on the valve stem and it is forced forward before shot by spring 78.

I know these are signs of too large valve, but I also think it should be possible to get better result with the one I have. Valve is clearly shown here http://steyr-sport.com/en/downloads/steyr-air-pistols/parts-lists-with-exploded-views/131-service-info-2017/file

I only need 5,5 joules or 4 fpe from this gun and it more than serves the purpose.

Throat diameter is 5 mm and valve body has two 1,5 mm vent holes to feed the piston. Radial air exit holes are 2,5 mm and there is five of those, I suspect that if the throat and radial holes were smaller and vent holes removed altogether, there would be a better chance of success. Piston would still get air from valve stem hole clearance, but it would be bled out in the barrel slower.
« Last Edit: March 05, 2018, 02:21:52 PM by Finn »
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #21 on: March 05, 2018, 08:19:20 PM »
Made some modifications, now it autoloads with plugged magazine from 85 to 50 bar even when I backed out the mainspring adjusting screw whole five turns, it has a 0.8 mm pitch. Previously it didn't work at all with magazine, only worked if the transfer was sealed shut. I made special test pellets to make testing easier, basically slightly tapered steel pins that will not fit trough completely. Actual pellets do go out of the barrel in a hurry but the mechanism will not cock itself, I hate the idea that maybe I need yet another tighter fit mag. Something is still not quite right but much better than it was.  Any ideas, what should I try/test?
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Offline MJP

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Re: Reverse enginerding, does it work?
« Reply #22 on: March 05, 2018, 11:50:56 PM »
Good improvement, but I would keep the 3.5mm port, and make a valve with 4mm sealing lip out of peek.
Conical valve seal needs much more force to open and you dont need the extra flow from the conical valve seat.
Then you could open up the bleed to the piston a bit to get more air to cycle the gun.

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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #23 on: March 06, 2018, 05:34:01 AM »
It does now cycle the action even with v1.0 o ring valve, so I think it is not good idea to open the bleed to piston too much. Actually that excess bleed may have been the main problem. As soon as valve is opened and piston is pressurised, it starts braking the hammer and reduces valve lift. If the piston gets air too early in the cycle, the valve lift is too small no matter what the hammer force is. I will turn couple more valve housing blanks to test ideas. I do not have any peek, but it probably works if i use POM for test purposes.
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #24 on: March 06, 2018, 07:28:38 PM »
Made another valve housing today, or maybe yesterday. It has same specs as 2.0 but I increased the piston size from 7 mm to 8 mm and made new flat valve, had to make the seal diameter 4.5 mm though as 4 mm:s would leave too narrow margin.
Anyway I tested the conical 5 mm valve earlier and max speed was 130 m/s with 0,54 g pellet and the barrel is not that long (183 mm). Still it did not cycle the action with normal pellets.

I only had few minutes of time to test the newest valve and 8 mm piston, and surprisingly it now only lets out only a slight puff sound with blocked magazine and nothing moves but with pellets it was able to shoot and index the magazine. Did not quite reach the sear to stay cocked after each shot but it has never before done the magazine indexing with normal pellets and it is only 1.6 mm more rearward movement from that point to where the sear would catch the hammer again.
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Offline Rob M

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Re: Reverse enginerding, does it work?
« Reply #25 on: March 06, 2018, 07:47:59 PM »
this is great news!!!!!!!!!!!!!!!!
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #26 on: March 07, 2018, 02:26:41 PM »
I will have to tweak some things a little bit, newest valve system does not perform well as something is binding slightly and it requires a lot more force to open the valve than what was expected.
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #27 on: March 07, 2018, 07:22:02 PM »
This is truly the most confusing thing ever, nothing works as expected.

Case 1. If valve stem is practically air tight to valve body and thus doesn't let much air to the piston, the gun fires pellets with good velocity even with minimal mainspring tension but does not cycle. However autoloading works every time if magazine holes are blocked with tight steel pellets.

Case 2. If valve stem is loose fit to valve body (radial clearance 0.1mm) I need to tighten the mainspring tension a lot to get the same velocity and if magazine is now blocked the gun will go full auto for a second or less but does not stay cocked. If the gun is fired with no magazine or empty magazine, the slide cycles almost all the way back but does not stay cocked after shot.

Should I make that stem hole little bit bigger and just hope it will work, because if it doesn't I'll have to turn another valve body.

There must be some small detail that I am missing here, if only there was someone willing to give me their Steyr LP50 to study, this would be solved in a minute.  I refuse to believe there is a part in that gun that I couldn't make.
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Offline cobalt327

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Re: Reverse enginerding, does it work?
« Reply #28 on: March 07, 2018, 07:46:10 PM »
Looking good.
I modeled my .308 after the AA S510 TC and then made it in my design.

https://www.pyramydair.com/s/m/Air_Arms_S510_TC_PCP_Air_Rifle/2386

Don't know if the pics will show up due to Photobucket's ransom fee's.

https://www.gatewaytoairguns.org/GTA/index.php?topic=82820.0
Hope the photos will show up as attachments...
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Offline MJP

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Re: Reverse enginerding, does it work?
« Reply #29 on: March 07, 2018, 11:54:38 PM »
This is truly the most confusing thing ever, nothing works as expected.

Case 1. If valve stem is practically air tight to valve body and thus doesn't let much air to the piston, the gun fires pellets with good velocity even with minimal mainspring tension but does not cycle. However autoloading works every time if magazine holes are blocked with tight steel pellets.

Case 2. If valve stem is loose fit to valve body (radial clearance 0.1mm) I need to tighten the mainspring tension a lot to get the same velocity and if magazine is now blocked the gun will go full auto for a second or less but does not stay cocked. If the gun is fired with no magazine or empty magazine, the slide cycles almost all the way back but does not stay cocked after shot.

Should I make that stem hole little bit bigger and just hope it will work, because if it doesn't I'll have to turn another valve body.

What I would make is machine a small flat on the valve stem, you can test with that and dont need to make another frame part.

Marko
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #30 on: March 08, 2018, 05:16:23 AM »
I will do the flat first and if the theory is proven I will maybe then drill the valve body. Stem could also have tapered section to change the airflow in relation to valve lift but first test would be with flat.

I could also just change the stem itself because it is separate part from valve head. Stem is threaded in and it expands and crimps the o ring in. I might have even saved the nc program for stem but it is better to write new parametric program if different sizes are needed.
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #31 on: March 08, 2018, 05:45:29 AM »
I just noticed something important while watching a video around 0:30 seconds mark you can see where the sear catches the bolt. I definitely messed up somewhere because my sear catches very late in the cycle and it might just be that the hammer rebounds hard from the rubber buffer before the sear has time to flip up. Evidence supports this because if the transfer is blocked, the piston has more pressure at the end of the cycle to counter the rebound and sear has time to flip up to locked position.  See attachment, could this be it, new sear and we are done.

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Offline MJP

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Re: Reverse enginerding, does it work?
« Reply #32 on: March 08, 2018, 09:19:56 AM »
That could be the reason for full auto. That is pretty formidable difference in cocking distance.
Changing the valve stem to conical would be interesting to see how it effects the cycle.

Marko
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #33 on: March 08, 2018, 11:28:52 AM »
Surely I will be testing every combination once the sear is remade or modified. There is one added benefit with moving the sear lip forward, it increases the leverage and hammer will start accelerating much easier because it has to push against sear spring and disconnector when gun is fired.
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #34 on: March 09, 2018, 05:49:30 AM »
Much time could have been saved if I had been more observant while designing the gun, I watched everything available on youtube many times and still didn't care to check the sear position.

It now works as it should, I was able to rapid fire at least 6 full magazines of crosman destroyers before I took the gun apart for inspection.
Test pressure was 65 bar, if higher pressure is required a new tighter valve stem must be made to reduce hammer brake effect.
Only thing I changed to make it work was the sear, hook was moved 2mm forwards.

There are still things to do make it absolutely reliable but at least now I know every aspect of the clockwork and what needs to be adjusted.

I will leave the valve assembly for now and start making the following parts

-RH cocking lever and safety lever
-regulator and air reservoir
. barrel shroud
- Target sights
- anatomic form grip
-trigger shoe
-regulator tester
-spare magazine
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Offline Rob M

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Re: Reverse enginerding, does it work?
« Reply #35 on: March 09, 2018, 09:04:29 AM »
THIS IS AWESOME NEWS!  congrats/.... I cannot imagine how many hours  it took to get this far ..
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #36 on: March 09, 2018, 10:13:21 AM »
It is around 200 hours give or take plus the cad design and web research. I had to make many tools that are not shown here and probably need to make more. 8 hour day job limits the speed but I do all the machining at night anyways so there is no one bothering me with anything else.
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Offline MJP

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Re: Reverse enginerding, does it work?
« Reply #37 on: March 09, 2018, 06:35:47 PM »
Nice going man, really nice!
It is truly interesting to see your work, its always so different.
Makes me feel like a hack, I'm just tinkering with stuff.

Marko
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Offline Hobbyman2007

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Re: Reverse enginerding, does it work?
« Reply #38 on: March 09, 2018, 09:34:38 PM »
Congrats on getting this fine pistol figured out and working . Your attention to detail is astonishing great to see it all worked out.
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Offline Finn

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Re: Reverse enginerding, does it work?
« Reply #39 on: March 13, 2018, 09:30:11 PM »
Nice going man, really nice!
It is truly interesting to see your work, its always so different.
Makes me feel like a hack, I'm just tinkering with stuff.

Marko

Don't feel bad, your projects have manly man qualities and at least you will be an actual engineer and that is something  ;)


Grip work has started, it is the most difficult part to get right. I started with machining the shape of my hand in some random block of wood, cutter is 12 mm ball shaped made of tool steel. I didn't machine the external shape, it will be done with hacksaws and files and whatnot when the gun is fitted in the grip. I'm trying to get that grip as high as possible and in a large angle where my wrist is locked downwards it will help to get a proper sight picture quickly. Took down largest of sticks and ridges with sandpaper, it fits in my hand and doesn't hurt like h***.
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