Friday, December 20, 2013

Hammerli 850 Cheek Rest

elevated cheek rest

Lately I've been busy improving my Hammerli 850 air rifle.  With the new trigger job, this rifle is quickly becoming one of my favorites.  The next problem to tackle is the height of the cheekpiece on the stock.  It is too low for my scope.  For best accuracy your cheek should be pressed firmly against the stock with your eye perfectly centered in the eyepiece.  To see through my scope, I must lift my cheek off of the stock.  Not comfortable and bad for accuracy.  Good target stocks will have an adjustable cheek piece.  If this were a wooden stock, I could just cut it and install a mechanism to raise it.  Not so easy with a hollow plastic stock; so I decided to make a new cheek rest.

kydex formed to stock

I purchased a sheet of kydex  from Amazon.  I went with a thick piece (0.118") for the extra strength.  Next I cut the kydex sheet in half (6" x 12") with a pair of sheet metal shears.  Then I preheated the oven to 350 degrees and placed the kydex in a Pyrex dish for three minutes.  I checked the sheet with a spatula to make sure it was very pliable.  Then I scooped it up and placed it on the stock folding it over the cheek piece with gloved hands.  I quickly got the alignment just right and held the kydex tight against the stock as it cooled.  In about 5 minutes the kydex had cooled and was rigid.  It formed perfectly to the shape of the stock and the pattern and color even matched the stock.

tracing the pattern

To make a pattern, I wrapped a piece of paper over the stock.  Then I traced the edges of the cheek swell with a scrap of aluminum sheet.  The aluminum worked really well, cleanly marking only the edge.  I carefully cut the pattern out with an x-acto knife.  I placed it back on the stock and drew some witness marks on the paper and stock so I could lines things up later.  Finally, I cut the pattern in half.

spacer taped to stock

The next step was finding the correct height for the new cheek rest.  I experimented by placing pieces of rod under the cheek rest until my eye was perfectly aligned with the scope.  Turns out a 1" rod and a Bic pen tube provided the perfect height (1.319").  I taped the spacer to the stock and put the kydex over it to test.  Perfect.  Now to make the bottom of the new cheek rest match the contour of the stock.  I coated the back of the pattern pieces with spray glue.  Then using the witness marks, I lined each pattern up on the stock and stuck them to the kydex.

hlaf of pattern glued to kydex

The bulk the excess kydex was trimmed away with the metal shears.  Then the kydex was formed exactly to the pattern on the belt sander.  Now to attach the new cheek rest to the stock.  I was going to make the cheek rest adjustable by cutting slots in the kydex but why bother?  I only needed to set it correctly one time.  And most adjustable cheek rests have large ugly knobs on one side to tighten the bolts.  I wanted a cleaner look.  So I carefully laid out the position of the screws and drilled two 3/32" pilot holes through the kydex and into the stock on each side.  I then opened up the holes on the kydex to 13/64" and countersunk them so the screws would sit flush.  I enlarged the holes in the stock to #25 and tapped them for 10-24 screws.  Although the stock is hollow, it is thick enough where the cheek rest is providing plenty of threads.

screw holes in kydex

The pattern peeled off the kydex rather easily and I cleaned up any residual glue with Goo Gone.  I cleaned up any uneven spots on the belt sander and dressed the edges with 220 grit sandpaper.  Finally I screwed the new cheek rest to the stock with stainless flat head socket cap screws.  I was going to back up the screws with nuts but the plastic held the screws tight.  I added a drop of thread lock to each screw just to be sure.

finished and installed

height relative to scope

The new cheek rest is great.  It looks like a factory accessory and is rock solid.  Now that I don't have to move my head around looking for the eyepiece, I can get on target much faster.

PS - If you are cutting kydex on a scroll saw, I found that a 15 tpi blade at 500 rpm gave a very clean cut.  No melting and minimal saw marks.

No comments:

Post a Comment