adapter silencer (moderator) for Benjamin Akela

[Phil_7833]

Hi all
I  am search  a 3d file  for akela
male/male adapter : 1/2 - 20 UNF  <=>  13/16×24 TPI
Akela doesn't use it  Standard 13/16×28 TPI silencer adapter as for Armada, Marauder and Fortitude rifles.

Thanks for your help

[naptemp]

Hi all
I  am search  a 3d file  for akela
male/male adapter : 1/2 - 20 UNF  <=>  13/16×24 TPI
Akela doesn't use it  Standard 13/16×28 TPI silencer adapter as for Armada, Marauder and Fortitude rifles.

Thanks for your help

I have seen some adapters on Aliexpress.
I do not have the link

[Phil_7833]

Hello thank you for this feedback,

On Ali*** I also looked and found 1/2-20 UNF <=> 13/16 x28 adapters
not  13/16x 24 TPI

Unless someone can confirm that 13/16 x28 tpi is ok for the akela.
my information on 13/16x24 may be wrong

[Robert 5mm]

I use the DonnyFL adapter on my Akela
https://donnyfl.com/collections/adapters/products/benjamin-akela-1-2-x-20-unf-adapter-a8

[Rick67]

Hello thank you for this feedback,

On Ali*** I also looked and found 1/2-20 UNF <=> 13/16 x28 adapters
not  13/16x 24 TPI

Unless someone can confirm that 13/16 x28 tpi is ok for the akela.
my information on 13/16x24 may be wrong

This one’s in your neighborhood:


https://www.suppressor-thread-adapter.com/product/silencer-adapter-crosman-benjamin-akela/


European silencers use 20 TPI.

28 TPI is a US thing for rimfire, .223/5.56, and 9mm.

[Rick67]

What brand is your silencer, Phil?

[Phil_7833]

Hi Rick67,

My moderator  is a still 4 (SAPL)
I bought this adapter but there is too much instability with my moderator.
I made a 3D moderator. which works well.  so I'm looking for a 3D file with the correct threads.

[Rick67]

Hi Rick67,

My moderator  is a still 4 (SAPL)
I bought this adapter but there is too much instability with my moderator.
I made a 3D moderator. which works well.  so I'm looking for a 3D file with the correct threads.

Have never ever tried a 3D moderator.

There are stores, rather store, as I only know of a particular one, in the UK that ship airgun silencers, even to the US for less than $10 tracked—-$10 is the shipping cost, just to be clear.

[subscriber]

Philippe,

I can generate an STL for the adaptor you are looking for; if you specify the length of both male threads, and the diameter of the flange in between.  I assume the flange OD would be the same as your Akela shroud OD?

That said, I think that unless you print this part from a glass or metal powder filled plastic, it will droop at the 1/2" thread end due to material creep.  This suggests that you are likely to damage you moderator when shooting it, eventually.  This is because PLA, PETG, ABS and all the common plain 3D printing plastics creep, even when small loads are applied for long periods.  So, rather than just telling you to buy a metal adaptor (a good idea), I have come up with 3D prints that might be a workable solution:

I have attached two printable moderator designs for your Akela, that integrate the 13/16 - 24 thread.  The larger moderator has a 35 mm OD, with the cylindrical length at 150 mm.  The smaller moderator is 25.4 mm in diameter and 105 mm long. 

Actually, there are two versions of the smaller moderator.  One has a tapering rear end, while the other is cylindrical.  If I knew your shroud OD, I could be more sensible about which would look better; so you get both.

The inspiration for the sizes is that you might want a very compact moderator, and only need a bit more sound attenuation.  Or you might not mind a larger moderator, and desire a lot of sound attenuation.  So, I offer both options.

You need to print these parts standing on their front end, with the threads pointing up, otherwise the internal baffle cones will no print correctly.  So, rotate the parts in your slicer before printing.  The walls are thin, so print at 100% infill. 

You probably should print the threaded section by itself first to see if it mates properly with your shroud.  If the test print screws into the shroud OK, then go ahead and spend the time and material printing the full moderator/s.  On the other hand, if the test print has the threads too tight, then adjust the X and Y axis in the slicer down to perhaps 99%.  Keep the Z-axis at 100% or you will distort the thread pitch.

If the sample thread is too loose, increase the X and Y axis to 101 or 102% in the slicer.  Each 1 percent change from 100, changes the thread OD by about 0.1 mm.

The integral 13/16" male thread is not as droop resistant as a printed 1/2-20 female thread when a metal male thread is used; but, the 13/16 thread is over 4 times stiffer in bending than a 1/2" printed thread.   Also, the central bore hole affects the larger OD thread less than the 1/2" OD thread.

If the moderator dimensions seem like an odd choice, I recycled designs I did recently for other people.  If you have very specific dimensions in mind, I can do a version of that too.  Else, buy a metal adaptor...

[subscriber]

Philippe,

I generated an Akela to 1/2-20 adaptor design, as you described.  The STL is attached below.

My concern is still the lack of strength at the root of the 1/2-20 male thread.  Specifically to resist bending, resulting in moderator droop from material creep.  Now, it is possible that I am being overcautious; as long as you are not taken by surprise, if the part droops or breaks off.

Note that the flange has horizontal overhangs that will need printing supports.  See images below. 

[subscriber]

If you want to see what a "no print supports required" adapter version would look like, here it is.  It has a 40 degree overhang, rather than 45, so a finer than 0.2 mm vertical resolution would be good.  Also will produce better threads.

[subscriber]

You could cut that tapering flange section above flat, by gripping the 1/2-20 threads in a lathe collet, so as to restore the original intent....

[Phil_7833]

Hi Subcriber

Many thanks for your help and above all your very wise advice.

I bought a metal adapter, to use a .22 LR moderator metallic.
But the assembly is not stable. and the silencer is not in the axis?
(tolerance problem).
This moderator (still 4 ASAP)  is quite heavy 250 gr (0.551 lbs)

Last night I made a 3D moderator in ASA by tightening the threading,

I think that the solution of the small moderator with the filtering is for the PCP the strongest solution

I'm going to print an adapter, to check that my moderator has no faults.

[subscriber]

Thanks for the update, Philippe

Let us know how your adaptor works out.

[Phil_7833]

Hi  Subscriber,

Thank you again for your help and advice.

Currently I no longer have a filament 3D printer available at home; only a resin printer. It's not great for making this type of piece. I print at a friend's house.
I will also have to add an addon to blender to manage the threads, probably bolt factory.

What software do you use to model the parts?

My problem comes from the adapter/moderator (SAPL) pair, both of which were purchased in metal. There is a
free adjustment too large, moreover the height of the 1/2 thread is not long enough
and when it comes to a stop, . the moderator axis is not aligned with the barrel 

So I made a short ASA moderator, which I tried on the metal adapter, tight thread that I had to rework.
With a quick adjustment I group in 5cm (1.9 inch) at 25m (27.34 yards).

The second step is to test the metal moderator with one of the adapters that you kindly sent me.
I just need to find a slot to print it with my friends. With the Olympics + the holidays, around Paris many have gone on vacation.

[subscriber]

Hi Philippe,

Your groups with the moderator attached seem a bit large (assuming good pellets).  How does this compare to no moderator installed?  If it is not shooting groups smaller than 25 mm at 25 m, then perhaps the airgun need some improvement?  This assumes shooting off a stable rest.

It may be that the moderator can move angularly during the shot, and that its position is different from one shot to the next.  This can affect the barrel harmonics (vibration), or the air flow around the pellet in the moderator.  So, taking excess slack out of the threads is a good idea.

If air flow inside the moderator is involved, using a mod intended for .22 should help.  Unless it is too long and heavy, so making the movement in the thread worse.

I use the most basic level of Solidworks from 2015 for my designs.  It does not have the ability to add threads automatically.  I use a spiral of the right diameter and pitch, and drawing the thread form to generate the threads.  Laborious, but it lets me make any adjustment I need easily.

Your CAD system makes very realistic images.  To get that with SW would cost a lot of money I don't want to spend.

If you are using a resin printer then my concern about printing supports would be different that for filament printing. 

If you would like me to alter my adaptor design to meet the thread length and flnage specs, I can do that for you.  I notice that your design has a lot of material "machined" away at the start and end of the thread.  This my be required for actual machining, but is not required on a printed part.  Not unless a long thread would interfere with the mating part somewhere.

Usually, parts would align squarely by means of a shoulder, and in this case, a flange making solid contact.  How coaxial the barrel (or shroud) and adaptor are does depend on the clearance between threads, but for metal threads, they tend to center themselves due to the V shape of the threads.  Plastic threads may not center as strongly, so printing them with minimal clearance is a good idea.  An even better idea is to print the plastic threads with extra material, then to use a tap or a die to clean the threads up afterwards. 

A 1/2-20 tap is not expensive, but a die to clean up a male thread can cost a lot of money.  The larger the thread diameter, the more expensive.  So, if you can iterate the thread design, you should be able to get both male threads to be just snug.  So you can screw them on easily, but not have obvious "slop" (wiggle).

I wonder if you could coat your metal threads in resin, then screw the adaptor into the metal moderator, with the moderator standing on a level table, on its front end?  That way there are no forces trying to shift the moderator relative to the adaptor, until the resin sets.  You might be able to use low temperature Locite for this, but need to consider that separating the parts in the future could be difficult.

Then there is the movement in the larger thread, that screws into the shroud....

There is no substitute for printing and measuring parts; or using a trial fit of the threads to refine the thread specification.  The simplest way to change the thread diameter is X/Y calibration, but it will affect both threads equally, and you may need on thread adjusted more than the other.  That will need to be done in CAD.

I like the wrap around primary blast chamber of the short moderator design.  I have several such designs.  For instance:




Cheers

Peter

[Phil_7833]

The still silencer is made for the 22lr, with the possibility of being disassembled and cleaned.
It is very long and heavy for PCP.
the threaded part is in fact a threaded part which is inserted into the tube. (Perhaps a cause of offset between the axis of the thread and that of the moderator?)
For PCP, a printed moderator is more than sufficient.

I don't plan to leave the silencer permanently, so no thread lock

The akela is a new acquisition and I have not yet tested the different pellets at different distances. It’s due in 2 weeks.
With the metal selector the grouping was worse and not really stable.

My moderator is admittedly a little big, but it was to test. I had arrived for the PCP that this type of moderator was very effective
 short, compact moderator with 4 conical baffles, the first and last of which are vented to strip and entertain air.

I only hear the air in the valve and the impact on the target

.I wholeheartedly accept your adapter proposal.
13/16x24 length 9mm
Flange 10 min
1/2 20 15mm
.
lead passage diameter 7 mm (minimum)

I think the moderator with the thread is the most solid solution.

The resin (at least the one I have is really too brittle  for this type of part

[subscriber]

Philippe,

I have designed two adaptors based on your specs, with an exception that I will explain further down. 

As you are printing with a resin printer and those tend to be more precise than filament printers, and have a Version 2 with 0.05 mm less "lash" or clearance in the thread than Version 3.  Version 3 would be the one I would choose for filament printing; but you may want to print both and then choose the fit you prefer once you have the parts.

I am assuming that your Akela shroud OD is 22.2 mm?  If so, the chamfer on the helical knurling would eat into the mounting shoulder on the larger of the two threads.  As it is hard contact at the shoulder that forces parallelism of the three bore part axis, I did not want to compromise that shoulder.  So, the shoulder diameter is preserved at 22.2 mm, with the knurling OD at 23 mm.

If I have misunderstood your shroud OD, then I can reduce the OD of the knurling to 22.2 mm - if you deem that important.


The STL files for both Version 2 and 3 are attached in the same ZIP file, directly below.

[Phil_7833]

Good morning,
I'm sorry for this late return, I was traveling and I was only able to do a test recently.
Conclusion with the metal moderator and the 3D printed adapter. the tests were quick because the thread quickly split.

The tests confirm your advice.
with a printed moderator, you might as well make a one-piece moderator which incorporates threading. More resistant and we can adapt the silencer to the weapon.

otherwise you might as well use a metal adapter. It's easier to adjust the thread in 3D

on the akela .117 a silencer as big as my first 3D print is not necessary, to reduce excess noise.
The impact in the target and the release of the air in the weapon is more noisy at 3.4 meters.


On the other hand, I find a large first enveloping bedroom interesting. like my model or like your short version.
I need to find the best length, width and noise reduction ratio.

Do you have the opportunity to test your short moderators on PCPs?

[subscriber]

Philippe,

I am not really setup to test my moderator designs, but plenty of people on this forum have.  So, we have a pretty good idea of what would work, providing a given PCP is not tuned poorly.  A PCP that wastes air due to hammer bounce, for example will be louder and require a larger/longer moderator.

How large/long a moderator you can tolerate, and how quiet you need it to be are part of the equation for a custom design.  Often an existing design can be adapted to work for a new application, such as the ones show here: https://www.gatewaytoairguns.org/GTA/index.php?topic=215268.msg156548064#msg156548064