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Discussion Starter · #1 · (Edited)
Hello Snipers!

As I am using the AA HopUp Unit with different BB wights, the adjustment from below really ennoyed me. So I have 3D printed a mechanism that allows to adjust the hop from the top of the barrel - like a "normal" TDC mod.
It has a low profile so that it fits under a scope a 45mm (outer diameter) scope on a low mount on my FN SPR.

There are 30 fixed positions around one revolution ogf the adjustment screw - so this is even more fine then I could do it with a hex wrench from below! The postions are fixed by a springloaded ball which glides in pits.

Easy installment, perfect in function :tup:

Partslist:
1) TDC turrent + TDC base: Shapeways
2) 2 pcs of M3 nuts
3) DIN 7984 M3-flathead screw: Length ~16-20mm , then lathe the head down to a diameter of 3.4mm
Germany:ebay
UK: eBay
4) M3x7 Spring plunger like this one:
Germany: Maedler
UK: eBay



Install guide:

(1) Buy the right screw

Make sure you get a "Flathead Screw", because this it is evident to use a small hex-wrench!


(2) Modify the M3 Flathead Screw





(3) Prepare the TDC Turrent



(4) Drill a hole in the outer barrel

For this mod , it is evident to have the turrent perfectly centered with the hole for the M3x16 screw (the screw in the HU).
Take a 2.5mm drill and drill trough the HU. But becareful not to destroy the HU!!!
When the leadhole is done, use a bigger drill (up to 10mm). So you can insert the tiny plate from above.



(5)Glue the TDC Base onto the outer barrel

Make sure it is perfectly centered/aligned with the HU. If the drilled hole is not in-line, that's no problem aslong the TDC Base is aligned with the hole for the M3x16 screw.
I'd suggest Loctite 435 for a perfect fit (or any other good glue).

(6)Choose your nub according to your HU rubber used

I have 3D printed the types of nubs which fit without any wobble into the AA HU:
A conacve nub for Marpel Leaf rubbers
A H-block nub for regular rubbers
A flat nub… for you guess a flathop

https://www.shapeways.com/shops/skeee



(7) Put the nub in the HU



(8) Put the spring into the hole of the lever




(9) Insert the HU

If If your drilled hole in the outer barrel is about 10mm in diameter, you must not insert the tiny plate yet (as shown here).


(10)Push the HU in the correct position



(11) Insert the M3x16 screw and add the tiny plate



(12) …until the tiny plate hits the HU arm



(13) Mount the TDC Turrent

Hold the M3 screw in place and turn on the TDC Turrent until you feel it fits snug and the spring plunger does ist nice little „clicks". The Turrent may not move up/down anymore!

Do not overtighten the screw, as the very little shoulde of the head might damage the HU.


(14) Tighten the TDC Turrent

Put the upper M3 nut onto the M3screw. Tighten it until the M3 screw + TDC turrent is one solid part. But be careful: Hold the M3 screw with a key. Only turn the nut with pliers! Do not turn the screw. Otherwise the lower nut might break out off the turrent!



(15) Fix HU-Block

Finally mount the HU-fixing-block and you are good to go!



Have many hits with it! And feel free to contact me via mail or PM in german, english or french.
 

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I like it.
When I did it I just used the old TDC hole I had but if someone drills a new one like you have then they are onto a winner.
 

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Any way you can make some for us? ;)
 

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Those who are interested in top down adjustment can try retrofiting a W/E turret from an old scope. The screw pitch is usually 0.5mm and has typically 60 clicks per revolution, which translates to about 8 microns of linear translation per click. Somehow install a very stiff spring under the turret to take out the backlash as inherent in any screw mechanism and your golden.

Sent from my D5833 using Tapatalk
 

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Discussion Starter · #9 · (Edited)
@Newcomer: That's where I copied the principle! But as I have no old scope, 3D printing was my way.

@TacticalBeard /BearGames: Of course I can... As I add all my material costs it is 45€ including registered mail to USA (I live in Germany).
What is your outer diameter of the outer barrel? Mine is 30mm. To fix the 3D printetd parts on your outer barrel just use some superglue (Loctite, JB...).
 

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I noticed in your cutaway view you have 2 nuts to hold the screw. Good thinking there to take out the backlash.
If you want to go finer you can try purchasing fine adjustment screws from Thorlabs. They go all the way down to 0.25mm pitch.

Sent from my D5833 using Tapatalk
 

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Discussion Starter · #11 ·
Thats a good idea, but the main play is in the springloaded ball which can move in the grooves. But this has no influence on the contstancy of the hop.

Ah and of couse the little plate pushing onto the hopuup arm has a regular thread, so I can not just change to a srew with finer threads without making a new plate.
 

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Son of a B! I was just thinking about making something like this because pulling out the Allen wrench to make adjustments on the fly sucks.

So glad y'all think this way. Nice Job.

Edited:
So I just read up and it all sounds good. Sent you a PM Skeee.

So thinking out loud... If you lathed a new plate that supported a selected fine adjustment screw
https://www.thorlabs.com/navigation.cfm?guide_id=131 would you still be able to install it into the turret? I guess it depends on the turrets inter screw size. Also you would need to have a way of it attaching to your outer barrel and I am not sure JB welding would hold that (not enough contact points)... Just thinking out loud.
 

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Discussion Starter · #14 ·
Mh perhaps I do not understand what you mean, but the fine adjustment screw in the link won't work in my concept, because it always requires that the head of the screw is hold in postion by the hopup chamber...
 

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Hell I might be confusing my self while I write this.

but here it goes...
I am using the images
http://www.opticstalk.com/photoserver/images/photos/2743.jpg
and your images attached showing how the mod works. (its your last one)

So base on a normal turret you have a screw inside the turret that pushes down on the internals of a scope to give elevation and deviation. What if you lathed a screw that acted in the same function as the turret screw and connected to the plate inside the hopup unit?
So in theory every time you turned the turret you are essentially moving the hopup plate to give you less or more hop up.
 

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Discussion Starter · #20 ·
Thanks, shorty! But keep in mind, that this concept needs the AA chamber to work! This mod ist just to adjust the AA hopup arm from the outside of the rifle (without removing the mag and twiddle with the little hex wrench).
 
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