Steps to Making A Machined Teak Speargun
Get parts: handle, trigger mechanism (with pins), line release (with allen screw), trigger pushrod, Lexan for trigger slide, line wrap post, break-away. You need stainless steel screws for handle (3 #8 X 1" oval head), break-away (1 #8 X 1" flat head), and (6 #8 X 1" flat head) for pushrod cover.
Get or make plans which has all specifications and measurements. Steve Alexander sells blue prints for $5. For our guns the typical starting width is 1 7/8 in by 2 7/8 to 3 inches tall by whatever lenght of gun you intend to create.
Ideal tools are a table saw, a mill, a router, a drill, and random orbital sander. Click here for more introductory information on machining and here for a more advanced tutorial.
Always check your setup visually before making any cuts. You can easily damage tools, yourself, or your gun if you are not careful.
If making a cut for the first time or if you're unsure of your measurements, make an outline cut .005 deep and check first.
Use long fluted aluminum milling cutters.
Select a hardwood (e.g., Teak ) with low internal stress (i.e., grain should go straight up the block of wood - no swirls)
You may laminate the gun. When facing the gun butt, the lamination seams should split the gun from top to bottom (not side to side). Use West System Epoxy 105 with 205 hardener if you do laminate - other glues probably will not hold. Note lamination does not mean you can skip the aging step below. However the more verticle laminates you use the less prone the gun will be to warping and the sooner you can end the aging process and begin building the gun. If you use 8 verticle laminates you can usually get by with one week of aging.
Cut block to approximate size (about 1/8" over in width and height)
Age block at least 6 weeks to let it adjust to the change in structure from cutting. 2 to 12 months is better. Let the block stand straight up with little or no sideways stress perhaps by leaning against a wall with the butt near the wall.
Straighten gun block by shimming high spots then bracing against a straight edge (held in place with masking tape), then push through the table saw. This straightens the fresh-cut edge, flip and straighten other sides.
Final straighten may be done by passing through mill sander until top edge is clean, do all four sides and block should be extremely straight and square. Tool is a 1/2" thick round disk pressed onto a 1/2" shaft which goes into the mill. Sand paper is glued onto the disk.
Hint: cut mechanism pocket and track in same set-up to ensure alignment. Be careful not to chip top of track when cutting pocket.
Technique: use mill vice to take 6" cuts, reset and cut next 6 inches, and so on, always making cuts in the region held by vice.
For Delrin insert, cut track for Delrin (use 1/2" bit 1/2" deep, then .752 ball cutter for second pass), pin Delrin with 1/8" pins at each end then evenly spaced about every 6". With a 1/2" end mill, flatten the top of Delrin so it is flush with the top of the gun.
Cut track for bit shank:
for 9/32" shaft use 3/16" bit 3/16" deep
for 5/16" shaft use 1/4" bit 1/4" deep
for 3/8" shaft use 1/4" bit 1/4" deep
Cut enclosed track so ball cutter is flush with top of gun
for 9/32" shaft use 0.300" bit
for 5/16" shaft use 0.330" bit
for 3/8" shaft use 0.395" bit
(Note we sell ball cutters for these standard shafts.)
Alternatives: open track, enclosed track in wood or in Delrin insert
Trigger Mechanism Pocket (be sure to measure mechanism first)
Kitto Mechanism Installation
Hint: if you must make multiple passes at a given depth to cut the pocket, make first cut at a given depth up the center then cut each side to minimize flexing of the wood. Otherwise, pocket will be slightly over-sized.
For an Alexander Mechanism Cut mechanism pocket using long 3/8" bit
Mark 0,0 at front center of desired mechanism location
Cut +- 0.046 in Y direction, Cut -2.355 in X direction
Cut down 1.1" in .3 increments
Spring Relief (in Alexander Mechanism pocket)
Change to 1/4" cutter
Move to center Y, 1.6675 from rear of mechanism pocket
Cut back to 0.2 at depth of 0.2
Set zero, then raise bit and adjust stop so bit won't touch vice when bottomed
Return to zero and cut forward .75 until through bottom of gun
Square round corners of mechanism pocket with corner chisel
Pinning of Alexander Mechanism
Align with shaft so shaft releases easily when trigger is pulled
Align second mechanism on side of gun to locate pin holes
Use 3/16" bit with aircraft adaptor
(leave pins sticking out a bit for alignment of line release slot)
Drill front pin hole and insert pin
Drill rear hole and insert pin
Trim trigger flush with bottom of gun
Line Release Allen screw on Alexander Mech
place gun in mill vice with top up
Set 0,0 at right front corner of trigger mechanism
Come back to 1.2845 in X and out 0.250 in Y
Drill line-release pin hole using #43 drill bit (.079)
Be sure hole is deep enough so it is below surface after edging
Alternatives: Under-gun release (Alexander) Wrap around rear fin tab (Heinrich)
Line Release Slot (Alexander Mechanism)
Place mechanism on side of gun with alignment pins in place
Locate placement of line-release slot then cut with 5/32 cutter
Total handle dimmensions are typically 5.340 by 1.185, however there is typically enough variation from handle to handle to warrant measuring each one prior to install.
Dimmension from start of handle pocket to start of trigger pocket is 1.752
Example: if you're using a 1/4" bit, and 0,0 is at center front of handle pocket, then you compute 1.185-.25 = 0.935, divide by 2 to get .468, so cut Y +- .468 For X, 5.340 - .25 = 5.090, so you cut from 0 to 5.090 on X. Come back from 0,0 to 1.752 from front, then cut 2.25 inches to get a 2.5 inch slot.
Cut handle pocket using 1/4" cutter
Mark 0,0 at front center of handle pocket
At depth of 0.12
Cut +- .468 in Y direction, Cut 0 to 5.090 in X direction
Cut Trigger Slide slot
Return to 0,0 at front center of handle pocket
Move back 1.627 and zero X
Cut back 2.5 at depth of .25
Cut pushrod slot from trigger hole to center of handle using 5/32" bit 0.3 deep from top of underneath side of gun
Make trigger slide to fit handle, drill 1/8" hole for pushrod (xxx from edge)
Attach handle with trigger slide and pushrod
Alternatives: detachable handle, stainless straps or lexan for cover
Measure dimmensions (THICKNESS, LENGTH, WIDTH) - (this piece is not precision machined)
Use 1/4" cutter
Set 0,0 at front bottom of desired location
Cut square THICKNESS depth LENGTH-.25 in X direction WIDTH-.25 in Y direction
Drill screw hole (1/8" drill)
Alternatives: reel mount, gun-attached shooting line
Use long 1/2" cutter
Place bit so top of band slot will be 0.25 to 0.3 below track
Start front of band slot .8 to 1.2 in from tip of gun
Make multiple cuts at depth of 0.3 - alway deepen the cut with the bit in the center of the bandslot cut to guard againt break-out damage when the bit protudes through the other side of the stock.
Cut back #bands X 9/16" minus .5 for 9/16in bands" or # bands time 5/8 minus .5 for the thicker 5/8 in bands.
3 bands: 1.1875"
4 bands: 1.750"
5 bands: 2.3125"
6 bands: 2.875"
Cut angle from tip to front of handle (extended 1" at tip)
Leave 1/3 to 1/2 inch below band slot
Mark pushrod cover top and put speargun ID on cover
Band Access Slot
Raise saw blade all the way up
Cut band access slot into center of band slot
Cut 25 degree angle up to bottom of access slot
Alternatives: for a stronger muzzle, don't cut a band access slot - just tie bands into band slot.
Trim from thinnest portion to appropriate size to cover pushrod
Machine recess for trigger
Grind taper near handle
Drill and attach with 6 #8 X 1 screws
Trim off any excess at gun butt
Line Wrap Post
Drill post holes on bottom of muzzle with jig (just behind band slot)
Use 1/8" drill bit
Shaft Retaining post (for open track guns)
Drill post hole on top left side of muzzle with jig (behind band slot)
Use 1/8" drill bit
Position router guide to prevent gouging
Keep top of track downward on router table if possible
Make multiple passes removing small amounts to remove lots of wood
Keep wood moving to avoid router burns
Pull wood away from bit if you must stop moving to reposition your hands
Rout top of gun with 45 degree bit
Rout bottom of gun with round bit
Alternative: use a wood rasp and shape by hand
File line guide at tip of gun (right handed on right side, visa versa)
note gun must be rigged as it will be used (e.g., reel must be attached)
remove shaft from gun
add small increments of weight until gun starts to sink
remove sufficient weight for gun to float
insert shaft (with lightest spear-tip you plan to use) into gun
distribute weight across gun until it balances just in front of handle
machine recesses into gun in appropriate places
insert weight into recesses
Remove all hardware
Sand with 100 to shape and eliminate machine marks and surface burns
Final sand with 220 to remove sanding marks
Remove all hardware
Fill with epoxy sealant - 2 to 3 coats
Sand lightly with 220 between coats
Apply 2 to 3 top coats of Tung Oil Finish with UV protectant
Sand lightly with 330 between coats
Alternatives: epoxy, polyurathane, marine urethane
Attach with generous coat of 5 minute Epoxy then trim off excess
Tack down any loose spots with super glue
Medium density EPDM foam pad makes excellent butt padding
Tap and attach Line Release Pin
Tap line-release pin hole using 4-40 tap
Insert Line release and pin, be sure it moves freely
Attach Remaining Hardware
Make and Attach Shooting Line
Crimp line to shaft fin
Thread line around gun two wraps using figure eights (to reduce tangles)
Crimp loop for end attachment
Can use line protectors in one or both loops
Mono hollow tube
Make and Attach Power Bands
Make wishbones with double overhand knots at each end
Insert 1/8" rod into band end and grind taper at each end of band
Insert knot into each end of power band using custom tool
Tie tight double Constrictor Knot over each end using Waxed Wipping Line
Knot should be aligned with edge of taper, then pull ends very tight with two slotted dowels rods or delrin rod scraps (with tag end slid into slots)
Trim and sear ends of waxed line
Spear shaft must be straight - any slight bends will hurt long-range accuracy
Do not use metal wishbones with wood enclosed track, ok with Delrin