What's a bloke to do on a rainy weekend but to tinker in the shed?
If you like to build your own stuff or can't afford to buy masks for all your scopes and lenses or you aren't happy with the amount of light your existing
Bahtinov mask lets through (or maybe you're just looking for an excuse to spent some quiet time in the shed
) then maybe a
Bahtinov Racquet is the go for you.
I used a jig saw to cut the frames from some scrap 3mm MDF, but there's a couple of tricks to making these.
Firstly I drew them full scale in CAD, including the lines for the strings and the centrelines and PCD for the holes. I printed the patterns full size, and used "Clag" school/paper glue (from the newsagents) to stick them to the MDF.
Then use the jigsaw to cut out the frames.
I drew the holes in the pattern at 3mm diameter, but only used a 2mm drill. This meant I had a circle left drawn around the hole after drilling so I could check the holes was accurately in the right place. To help achieve this I used a centre punch and pushed a "centre pop" where each hole was to go. If the centre pop wasn't quite right, it's easy to fix by just just working the centre punch in the direction the hole has to move until the pop mark is central to the hole circle on the pattern
.
Once it is cut out and drilled, just peel the pattern off. The wax in the MDF doesn't allow the clag glue to permanently stick to the board
. I'm not sure if it will work the same with other materials like Ply, or plastic, but it's worth a try.
Sand it up and scrape the holes a little with a reamer of some sort (I used an old hacksaw blade I ground to a wicked little concave point
) and spray with clear lacquer if you want. In my usual impatience I didn't let my lacquered frames dry long enough
... they were dry to touch but after the handling required to string the things, they were tacky and covered in finger prints (they are definitely mine!
).
The ED80 racquet I cut and glued a piece of thicker MDF to the frame to support it on the scope, but for the C11 and my camera lenses racquets I used some recycled shelf supports
.
I'm yet to string the camera lens racquet, that'll probably be today's job.
The centre bar to support the strings I made 8mm wide in all cases, though I could've possibly gone as narrow as 6 for the camera lens racquet
.
I used the last of my supply of fishing line when I built the racquet for my C8 ages ago, so I had to buy more line. I bought the lightest stuff I could find, but with my eyes that's not necessarily the best thing to do
. I don't think the weight of line matters much to how it works, but thicker line would've been easier for me to work with.
Oh yeah, the fishermen among you may have better ideas, but I tied my strings off with surgeon's knots and applied a dab of "Multigrip" general purpose glue to the knots just to be sure...
Al.
Wow 
