Making an Adjustable Cheek Piece
First question, is why?
My preference is for a high mounted scope. Yes, I know many pursue getting the axis of the scope as close to the barrel as possible, but through a happy accident I choose another way. For a while I fitted my long scope to my 97K, this covered the loading port and made placing pellets in the barrel downright awkward. The scope is a 56mm objective lens, and Nikko Sterling ĎExtra Highí mounts were not enough, so a pair of 12mm raisers were fitted. Having zeroed in the sights I noticed that the amount of adjustment I needed to dial in for longer range shots was much less, it also removed any amount of hold under needed if I was just using that way of compensating for distance, only hold over is needed. It seems the high point of the trajectory is effectively pushed further away from the gun, meaning the pellet doesnít rise through the sight line then back down to the zeroed distance (35 yards) anything like as much, negating the need for hold under. Check this out for a full explanation: http://viriato.net/airgunning/bfta_setup_manual.pdf . So Iím hooked on this now, and the same mount arrangement has been used following the exchange of the sight on to my HW100, the only problem being that Iím resting on my jaw rather than the cheek, which needs sorting, so here we are.
Iím a believer in ĎThe KISS Principleí, Keep It Simple Stupid! So when it came to deciding on how to arrange the means of adjustment I wanted something which could be made from Ďfoundí parts, which was going to look ok. Iíve settled on using stainless steel dowels fixed into the cheek piece, which slide in and out of holes in the stock, locking is via a single slot headed grub screw on the front dowel, though I may have to add another on the rear one if itís not stable enough.
Material for the dowels is going to be M8 S/S bolts, Iíll drill and thread tap the cheek piece and simply screw the dowels in. The existing bolt head will be cut off and a hole drilled for a Tommy bar to tighten them, alternatively a slot may be used.
The threaded section into which the locking screw will fit is a stainless steel rivet nut, which Iíll expand/glue into the RHS of the stock. The locking screw itself is a M6 bolt, head removed, and slotted for a screwdriver.
So hereís the target:
The first stage is to mark the cut line on the stock. This is simply masking tape, and a pen line drawn around a cut template derived from my drawings. More tape is on the other side to protect the stock as it moves through the saw. A piece of plastic has been fixed to the butt end of the stock to provide a datum face which will sit on the saw table to keep the stock upright whilst cutting.
In this image you can also see the bolts to be used for the dowels etc, and the threaded sleeves which are the rivet nuts.
First job in the workshop is to cut the cheek piece out. I donít have a band saw which is probably the best tool to use, but with care a cheap scroll saw does the job fine. Letting the saw blade do the job by not forcing it through can give good straight cuts. Note the guide plate fixed to the butt end keeping the stock true. You can see the straightness achieved when checked against a straight edge.
On this kind of parallel dowel arrangement, true parallelism is a must, other wise itíll simply bind up or not work at all, so here the cheekpiece is being set up using a simple spirit level on two axis. The piece is clamped in some soft plastic jaws to protect it.
Also to aid trueness a centre drill is used to start the holes. If you try and plunge a drill bit straight into the workpiece itíll just wander off, guaranteed! A pillar/pedestal/stand type drill is a must to ensure a vertical hole.
Tape is used on the drill as a depth marker. This is a 7mm drill for a 8mm thread. The true tapping drill size is smaller, but previous experience tells me that itís best to err on the side of caution as the tap can force wood apart splitting it.
Still in the pillar drill the thread tap is wound in by hand. All these things ensure straight holes.
Trial fitting the dowels (bolts) reveals if they are parallel or not. In this case they closed in at the ends by 0.018Ē, which moved as the bolts were turned. Good enough
Drilling the stock needs the same setting up, here a parallel block of hardwood is used to allow the spirit level to sit.
The stock is drilled out to 8mm, again using the centre drill first. Some fiddling may be needed to get the right drill size, but following some tests an 8mm bolt was a nice fit in an 8mm hole. This could vary.
Using the plastic guide the stock is set up for the grub screw hole to be drilled. This ensures a true hole and permits the insert to sit nice and flat. The hole is a slight interference fit on the insert.
Masking tape is placed over this hole and cut out. This stops the epoxy from getting into the surrounding wood pores, which will then resist finishes and remain visible. The insert has been roughed up for good adhesion.
By screwing the insert on to a bolt the insert can be tapped into place neatly.
The insert is then swaged out using a tool not unlike a pop riveter, as itís tensioned the insert swells out, binding into the hole.
The insert in place.
The bolts for the two dowels and the grub screw were then cut to length, slotted for a screwdriver, and polished using 2000 grit abrasive.
With the cut faces sanded down the grain is filled and rubbed back in the normal way.
The pic above where the cut surfaces
are an even brown shows the grain filler before sanding off. Almost all of this
is sanded away, it's only the pores that we want filled.
This gun has an oiled finish, not my preference, but it is easier to make good after work like this than a lacquered finish.
After initial sanding the wood fibres are raised by damping with water, a damp cloth gives best control for this for me. Use a hair dryer to dry it and sand off the fibres that have stuck up, repeat this till it either stops, or just seems to not be getting any better. Avoid doing anything other than trimming the raised fibres off, over zealous rubbing will just expose new fibres and you'll just carry on till the wood disapears.
Once it's levelled out apply grain filler, or in this case simple Ronseal 'dark' multipurpose filler watered down. Use the hairdryer again to set this off, warming the wood before filling helps with speed too. This time when you rub it down again you'll get a smoother finish.
It's easy for me to say that when you apply the oil follow the makers instructions, but that is the best thing to do. This photo taken after just two applications shows how the filler in the pic above has been removed, and the figure allowed to show through.
Putting it all together is was good to note that the sliding action was reasonably smooth, and that only the one grub screw was needed, as the accuracy of the system means the cheek piece canít move around with only one fixing point.
And so to the finished article. Well almost, still some oiling up to do, but that will take a few applications to sort. Good enough to shoot with though.
Having set the height of the cheek piece I was quite surprised where it ended up, quite high really, but there we are!
Here's some pics of other stocks modified in a similar way: