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Fall adjustment sight

A place to ask general spud cannon related questions.
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Fall adjustment sight

Unread postAuthor: boilingleadbath » Sun Feb 26, 2006 3:46 am

Although this doesn't pertain to the acctual launch of the projectile, it is usefull in that endevor, and thus I'm posting it.

Essentialy, this is a peep sight wherin the hole at the rear through which you look is mounted on a rail, so it can be moved up & down. This is usefull for shooting stuff at varying distances, or with varying payloads.
<a href="http://img.photobucket.com/albums/v611/car2/IMG_2065.jpg">An overveiw of the system.</a> (that's 4" pipe)
<a href="http://img.photobucket.com/albums/v611/car2/IMG_2066.jpg">A detailed picture of the componets.</a>
<a href="http://img.photobucket.com/albums/v611/car2/IMG_2068.png">A veiw through the sight</a>
Now that I'm done with that, on to the construction details:

The front pin is built on a 1/4-20 bolt.
First, a hole was drilled down through the top, into which part of a nail was hammered. This was made perfectly inline with the threads first by spinning the bolt with a drill, and hammering the nail strait, and secondly by spinning the bolt with the drill while applying a dremmle abrasive wheel.
A couple nuts where then epoxied in place so that it would be at a reasonable height when screwed into place.
Finaly, a 1/4-20 threaded hole was tapped into the end of the launcher. This is important, because my previous sighting pin was knocked off, and having a sharp object out there is unsafe.
One lesson learned: drilling holes into stainless steel bolts is really hard, and dangerous to your drill bits... save yourself money and just use a normal steel one.

The back sight is more complicated:
The part that slides up and down was macheined from some 2" sch 40 PVC that was heated up in hot oil and shaped flat in a vice.
Then, it was put in a mill, and 2 notches where removed on both sides to make it look a bit like a really short "T".
A hole was drilled on the breach side to look through, and a bigger one on the muzzle side. The small one was subsequently countersunk.
To make the "lock" that prevents the slide from sliding when you don't want it to, a hole was drilled and tapped on the muzzle side, and a bigger hole that the thumb-screw could fit through was drilled on the breach side. A washer was used to prevent "erosion" of the PVC.
To make sure the sight is vertical, a .74$ bubble level from mcmaster was epoxied below the hole, in a groove made with a dremmel to prevent it from sticking out too far. It's acctualy fairly easy to use.

The post was also machiened from some 2" sch 40 PVC. The 90* bend was done while the material was hot.
The bent shape was milled to a uniform .75" width.
A 1/4" (6mm) groove was machiened down the length of the post.

The "well" that the post plugs into was macheined from a peice of a 4" fitting.
A rectangular area was milled out, .75" by a bit more than the thickness of 2" PVC pipe by roughly 1.5".
A second peice of that fitting was epoxied onto the top, and a hole was drilled and tapped through both of them to accept the locking thumbscrew.

The markings on the post and slide where made by scratching grooves in the plastic with a very sharp nail (sharpened with the old "spin with drill and use dremmel" technique), rubbing with a crayon, then rubbing the excess wax away with a peice of paper.
No, that's not a vernier scale. There are markings on both mearly so that I wouldn't have to make a mark every 1/8" (3mm) on the 3" (7.5cm) length of the marked region of the post, as that would require more marks. (and be more confusing)

And there you go, one fall adjustment sight. (distance from front pin to peep-hole is 20" [49 cm])
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