When I initially embarked on my speargun building journey all the information I read on forums and videos I watched on You Tube about building spearguns all went something like this; Step one, cut the track. Step two, mortise a cavity for the trigger mechanism. Step three, pin the mechanism etc, etc. For me (in the beginning) step three was always the step that (A) took a long time, and (B) I worried about messing up. Even with an installation jig getting those two holes drilled in the right spot was time consuming and nerve-racking. If the holes were off by just a tiny bit a couple of bad things could happen. One; the pins fail to go through the mech housing at the same time. Second; the mechanism sits too low and now the shaft hits the top of the housing and won't engage. Those are the two most common problems you can run into when installing a pinned mechanism. Eventually after several builds I had a reliable system down that wasn't as nerve-wracking or time consuming but the method still seemed kind of clunky.
One thing that always bothered me about the cavity for mechs that are pinned in place was the tear-out of wood fibers created by the drill bit plunging through the outside of the gun into the cavity for the trigger mech. I would sometimes cut little pieces of wood to put inside the mortise to back up the wood fibers and prevent tear-out but that was another step that I would sometimes forget to to do.
The other day I was working on two new builds. I had the track done and the Neptonics Reef Mech pinned. I was getting ready to cut the slot for the line release but I had another gun with finishing epoxy hanging and curing and I didn't want to create any dust in the shop that could land on the wet epoxy. I was about to call it a night so the gun with the epoxy on it could cure but then I thought "Might as well drill the hole for the line release pin." I drilled the hole and then thought about how there would be no tear-out inside the slot for the line release because the pin hole was drilled prior to the slot being routed out. That's went the lightbulb went off; "If I can drill that pin hole prior to the line release slot being routed out I should do the same thing for the trigger mechanism!"
So here is my new tear-out free, super easy method for installing any trigger mechanism that is held in a speargun with round pins. In this example I will be installing a Neptonics Reef Mech with auto-resetting tab. This is one of the most popular mechs being used by DIY speargun builders today.
1 - Placement
Figure out where you want your mech to sit along the length of your stock. The gun in my example is a small 30" hole gun being set up as a midhandle. When I install the Neptonics reef mech in a midhandle build I usually position it within one inch of the back of the stock
I use a straight edge to draw some lines on the stock to the dimension of the mechanism. The second part of placing your mech housing is determining how far into the blank you want it to sit. To make this idiot proof I recommend making the top of the mech housing flush with the top of the speargun blank. If you have the Neptonics Systems Reef Mech Installation jig all you have to do is lay it on top of your blank lining up the front of the jig with the front line you drew on your blank that shows where the front of your mechanism will be after installing it.
You want to line up the front edge because the jig is slightly longer than the actual mech housing. If you line up on the back edge your holes will not be where you want them to be. If you don't have the installation jig then you have three options; Buy one from Neptonics, make one from a piece of angle aluminum, or, use the reef mech you will be installing as a jig. If using the reef mech lay the blank and the reef mech upside down on a perfectly flat surface. Slide the mech up against the blank in your predetermined location and mark the position of the forward hole with a punch or a drafting pencil.
2 - Drill
Using a drill press is always going to be the best option when drilling these holes but if you don't have access to one a hand drill can be used, you just have to concentrate on keeping your bit perfectly straight as you drill through the blank.
Once the front hole is drilled all the way through your blank drive a pin about 3/4 of the way through the hole and put the jig or the reef mech on the pin. If using the mech make sure the top of the housing is perfectly straight along the side of the blank. Once everything is in position drill the second hole.
Drive another pin into the second hole and then take your mech to check your work. If you did everything correctly you should be seeing something very similar to the below image. It's handy to have some extra lengths of stainless rod on hand for this part of the process. I like to round off the end which makes driving them through the mech a little easier. You can also chuck them up in your hand held drill and insert them that way rather than hitting with a hammer.
If you put a piece of masking tape on the opposite side of your blank you can limit or eliminate any tear-out as the drill bit exits your blank. This leaves nice clean holes.
That's it, done. Your mech is pinned in 5 minutes.
3 - The Track
To determine the depth of the track to be milled you will need a shaft, preferably of the same thickness you will be installing into your final product. Take the mech and your shaft and lay them on the side of the gun. You can use pins to hold the mech in place. Make sure the shaft is sitting perfectly straight and measure how deep your track will need to be.
Once you have this measurement head over to your router table and take several passes gradually going deeper until you have reached your measured depth. If you want to be super careful you can stop short of the depth you measured. You can check how close you are coming to your mark at the muzzle end of the gun.
4 - The Pocket
Once your track is done you can mortise the pocket for the reef mech housing. The most common methods use a router table or a milling machine but if you are good with hand tools you can have at it with a chisel. Use whatever method you are comfortable with to make the pocket. Start by pinning the mech to the side of the blank and double checking your layout. Once you are confident those lines are correct get busy removing wood!
5 - Test fit
Once you've finished your mech pocket it's time to test fit everything. Insert the mechanism into the pocket and drive some pins all the way through the blank.
Once the mech is pinned in place check to make sure the shaft slides in ok. On my initial test the shaft was bumping into the top edge of the housing so I had to make my track just slightly deeper. With the mech housing flush to the top of the blank you might run into another small problem; depending on the height of the shark fins (or you may be using a notched shaft). If your shaft is too deep and the shark fins or notches are a little bit below the top of the stock then you can use a planer, block plane or your tablesaw to remove some material from the top of the blank. That is what I ended up doing. As you can see in the photo below the top of the mechanism is no longer flush with the top of the blank. The shark fins are well above the top of the stock making it easy to power up with dyneema wishbones.
6 - Line Release
First just a reminder that these instructions are for the Neptonics Reef Mech with the auto-resetting feature. I carry these mechs here in my store. You can also purchase directly from Neptonics but you must specify you want the auto reset version.
There are two parts to installing the line release. A hole needs to be drilled for a pin to hold the release lever in place and a 1" to 1.5" long by 3/16" to 1/4" wide horizontal "pocket" needs to be routed on the side of the blank all the way through to the inside of the mech pocket. I always used to route the pocket first and then drill the hole for the pin but I will be doing it in the reverse sequence now because I always hated the ugly tear out of wood fibers from the drill bit plunging through the cavity for the line release lever. Below is a page from my notebook with the measurements I use for drilling the line release pin. I've used this measurement on every Neptonics auto resetting reef mechanism I've installed to date and it works every time. I really recommend using a drill press for this hole because if you don't drill straight you could very easily go off course and wind up inside the mech pocket.
To clarify the above measurement. The hole to be drilled should be 1/8" away from the edge of the mech pocket and 7/16" back from the front of the trigger mechanism. Once you've marked where the hole is to be drilled very carefully drill the hole!
Here is what it looks like when drilled using the above layout.
For part two; routing out the cavity for the line release lever you use another set of fool-proof measurements. First pin the mechanism to the side of your blank to use it as reference when drawing your layout lines.
Below are the precise measurements I use to make this cavity
After pinning the mechanism to the side of the blank measure from the bottom of the mechanism 3/16 of an inch (below) and draw a line parallel with the bottom of the mech housing. This is the top of the cavity, not the center. Whatever router bit you use (I use a 3/16 or 1/4" straight bit) make sure the cutter does not extend upward beyond this line.
The cavity you route out in the side of the blank should extend 1/4" beyond the front of the mech housing and have a total length of an inch to an inch and a half. If you are using a wide blank that will eventually be tapered to a more narrow width you may find that before the tapering the line release jams on the back of the recess when trying to load the shaft. Once tapered this problem should go away. If you are not tapering and you have this problem then you may need to extend the cavity a little further back than what you have. I suggest testing and then adjusting if you need to
I use a milling machine to make this hole so below is all I need as far as marking are concerned. If you are using a router table you will need some lines on the opposite side and the end of the blank to position the blank correctly while cutting.
After milling test fit the parts
With a shaft loaded pulling the trigger should allow the line release to move in a forward direction.
If you are a first time gun builder I always recommend practicing on some cheap wood before cutting into your "for real" wood. Take your time, get comfortable drilling and routing then go for it. Have fun and remember any mistake you make can be repaired. Epoxy is a wonderful thing!