3D Printed Aperture

3D Printed Apertures the You Can Build

Before you begin, scroll all the way to the bottom and read through the disclaimer.

History

A year ago, my daughter's JOAD team was taking steps toward getting each shooter using a clicker.  The problem is, they all use arrows that are too long to use a normal clicker hitting a clicker plate on the riser.  There are the well-regarded clicker solutions that mount to the sight extension bar, but they are a little on the expensive side for many of the team's families.

I decided that I'd design a simple bracket to mount to the sight extension that would allow attaching a less expensive conventional magnetic rod clicker.  I designed it in 3D modeling software and got them 3D printed.  These adapter brackets are still in use a year later.

I've been looking around at various sight aperture solutions that are available, but the ones I liked best were very, very expensive.  Sure, they're nice, but I thought I figured I could probably get pretty close to what I was after by designing it myself.

The Concept

My concept is to make a less-expensive but good performing recurve aperture that would allow archers to configure the aperture how they prefer.  There are two unique aspects to this project though:
  1. The aperture housings are 3D printed
  2. I am not selling these apertures
You may be thinking, "what's the point of designing a product that you don't sell?" Although I will not be selling them, anyone who wants to try one out can.  This brings me to the third unique aspect - the archer buys the parts and assembles it themselves.

The Design

The design of the first iteration of these apertures followed these ideas:
  • The housing is 3D printed out of nylon
  • The housing accepts a standard-headed, standard-threaded (8-32) machine screw
  • The screw is held onto the housing with a nut
  • The housing can, if desired, hold a zero-power piece of glass, to which an aiming dot can be affixed if desired
  • The glass is held in by an o-ring, or if no glass is used, o-rings may be used to alter the inner diameter to taste
  • The aperture housing would be inexpensive and use parts available at hardware stores

1st iteration seen in 3D design software














1st Iteration, printed and assembled







Three Versions

After the first iteration was printed and tested, some improvements were made.  The first iteration was designed around a 15mm diameter glass, which some people might find too large.  So, another version was drafted around a 12.5mm diameter glass.  Furthermore, many people might never want to use a glass, so a third version was drafted, which can only accept o-rings to alter the inside diameter.  Lastly, the location of the machine screw head slot was moved to not only improve appearance, but to make it so the housing could be used left or right-handed without modification.

Cost

One of the design goals was to keep the cost down as much as possible.  Here's a rough guide to what the average person's cost would be:
  • Aperture housing ~$5 (shipping is extra - see tips below)
  • 8-32 x 2-1/2" stainless steel pan head machine screw ~$0.40
  • 8-32 stainless steel nut ~$0.10
  • Rubber o-rings ~$0.80 (optional unless you're using a glass)
  • Anti-reflective zero-power glass ~$11 (optional, shipping is extra)
So, as you can see, assembling one of these isn't expensive.  

Putting it All Together

Now to the nitty gritty.  If you want to put one of these apertures together for yourself, you'll need to do the following:
  • Order an aperture housing
  • Acquire the machine screw and nut
  • Acquire o-ring(s)
  • Order the glass, if desired

Order the Aperture Housing

The aperture housing is ordered directly from the 3D printer.  The current company handling this is Shapeways.  (www.shapeways.com)
To find these housings, simply use the links above or search for "recurve aperture".  There are three aperture models to choose from, as seen in the photos above.  Choose the one(s) that you like.  You can get them in white, black, blue, purple, pink, and red colors.

Acquire the machine screw and nut

You will need the following:
1 - 8-32 thread, 2-1/2" long, pan-head machine screw and 1 - 8-32 thread nut

You may choose to use less-expensive zinc-coated screws, but stainless steel isn't a lot more money and is not only stronger but will not corrode or rust like the cheap screws will.  IMPORTANT: You must use PAN HEAD screws - others (round head, tapered head, hex head) will probably not work.

Acquire O-Ring(s)

The opening you look through on these housings can be modified by the use of different sized rubber o-rings.  Also, an o-ring is required to hold the glass in if you choose to use glass.  The o-rings seat in a groove inside the housing.  

Rubber o-rings are commonly found in the plumbing section of hardware stores.  You can buy them in a variety of sizes, and they're sold with specifications for outer diameter (O.D.) and inner diameter (I.D.)
  • For the 15mm housing, you will need 5/8" O.D. o-rings.  If you are using glass, you will want a 5/8" O.D., 1/2" I.D o-ring.If you are using glass, this is the only size that will work.
  • For the 12.5mm housing, you will need 1/2" O.D. o-ring.  If you are using glass, you will need a 1/2" O.D., 3/8" I.D. o-ring.  If you are using glass, this is the only size that will work.
  • For the 1/2" O-Ring housing, you will need 1/2" O.D. o-rings.  Choose your I.D. as desired.

Order Glass (if desired)

The housings designed to accept glass (15mm and 12.5mm) are designed to accept high-precision optical glass windows.  These windows are zero-magnification/zero-power glass that you would use purely if you want to have an aiming dot.  The glass is sourced from a well-known supplier in the United States, Edmund Optics (www.edmundoptics.com)

The item you are looking for are called "Commercial Grade Float Glass Windows".  Here's a link: http://www.edmundoptics.com/optics/windows-diffusers/visible-windows/commercial-grade-float-glass-windows/3525
  • For the 15mm housing, you will need a 15mm x 1mm window
  • For the 12.5mm housing, you will need a 12.5mm x 1mm window
You can order either regular glass or anti-reflection coated glass (MgF2 coated).  I highly recommend that you get the anti-reflection coating, because it makes a big difference and doesn't cost a lot more.

Assembly

  1. If you used glass, carefully insert the glass into the housing
  2. Carefully insert the rubber o-ring into the housing, making sure it seats in the groove
  3. Slide the machine screw head into the slot on the housing
  4. Tighten the nut on the machine screw so that the nut is snug and the housing is secure
  5. Mount in sight and shoot away!

Tips Regarding Shipping

For small quantities (under 100), the shipping cost for housings is a flat rate.  In fact, if you only order one housing, you will pay more in shipping costs than you will for the housing.  If you want to reduce your shipping cost, try organizing a group of buyers so you can order many housings at once.  If you divide up the shipping costs, it will save a lot of money.

The glass windows are a similar story - the shipping charge for one glass will be the same as for 50 of them, so your best way to reduce shipping costs is to organize a group buy.

Drilling the Glass for a Fiber

One thing I hadn't mentioned thus far is that you can, if desired, get the glass drilled to accept a fiber.  I do not currently have a source for someone to provide this service.  I got a quote from Edmund Optics but the cost was far, far, far beyond astronomical.  I would recommend inquiring with someone like Brian's Custom Lenses to see about whether he can drill the glass for you.  Note that you could use one of his lenses, but they're thicker than the float glass the housing is designed for, so the o-ring won't seat in the groove if you try it.  you will be better off using the glass from Edmund optics.

Disclaimer

Should you decide to build and use one of these housings yourself, all the risk and liability is on you.  I will not be held responsible for any damages, injuries, or lost tournaments, or missed Olympic team opportunities due to your use/misuse of one of these housings.  I am making these available as a gesture of good will to the archery community with no promise of durability or strength.  The nylon material of the housing has proven to be durable, but all materials have their weaknesses.  If you treat it with the care you would use with any other precision part of your kit, you should have no problems.  If you have problems ordering the parts from Shapeways or Edmund, I cannot assist you, as the deal is between you and them.  Sorry I have to include such language, but in today's litigious environment, it's necessary.

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