Ad Astra Observatory

I spent some time today figuring out what would be necessary to create the pole seats.

I landed on the “dual seat, split lengthwise, horizontal through-bolt to clamp” style (as opposed to the “separate blocks + wedge” style), because it seemed easier to get everything correct.

I calculated out the layout on the spreadsheet, taking into account the distance I wanted between the pole tips once the block was cut, angle through the block, etc.

When I got home, I pulled out the chop saw, as I’ll be needing it for 2 cuts per pole seat (one to cut out the primal for the part, the other to chop it lengthwise once it’s drilled). I added a jig to the saw so that cutting the correct (and same!) length will be a snap. I ended up cutting the primal out on the (manual) miter box, because it’s quieter, but the chop saw will be doing the lion’s share of the work when I go “into production” with this.

I had a problem with drill bits; I was unhappy with the quality of the hole that the 1-1/4″ hole saw was giving me yesterday, but I only have 1-1/8″ and 1-3/8″ Forstner bits. I hemmed and hawed a little over which one to use, and opted for the smaller diameter, on a whim.

I spent a little time setting up a jig for the drill press, too. Once I got that clamped down, getting the cut set up was dead simple.

I checked the angle with my iPhone. I’m not 100% convinced that the iPhone does a great job at being a level (especially around ferric parts), but it had worked OK last night, so I went with it. I will be pedantic about the angle when I am cutting “for real”; this time, I got it to about 14.3° (I wanted 14.5°), and did the cut.

Against my better judgement, I then leveled the drill press table, to lay in the through-bolt hole.

Over to the chop saw for a quick lengthwise cut, finish off the through-hole with the drill press (bit’s not long enough to traverse a 2×4 laterally in one shot), and I was ready to test.

Next problem was finding a 1/4-20 bolt long enough to test with. Turns out I had a 2′ section of threaded rod in 1/4-20 lying around (gotta love standardizing on one size of hardware!), and so I hacked off a chunk of that to use. I came inside, grabbed the thumbscrew knob I’d bought for this purpose, and popped in the two tester poles…

I need a 1-1/4″ Forstner bit.

The poles didn’t fit very well, but I got them in there enough to test the clamping action — that worked great. The tips of the poles are a little too far apart, I need to look at my calculations and work in the fact that I’m not cutting all the way through.

I was pretty happy with how secure the tester poles felt in the clamp, so I went out to the observatory and test-placed the clamp on Trixie’s lower ring. I’ll need to shave off the corners a little to make it look nicer, but it really does fit like a glove in the spot I’ve designated.

I tested with the 36″ poles, and noticed that the center-to-center distance was only 17-1/4″ instead of 18″. Between the inaccurate beveling measurement, the mis-sized holes, and the tube spacing being a little off, I’m letting 3/4″ go for now.

The clamps again held like crazy, and the 36″ poles can even stand up on their own inside the clamp, so that’s a nice feature.

I need to figure out how to capture a nut (Tee nut, drill a hole for it, …), because at the moment, I need to use pliers to hold the nut in place as I tighten the thumbscrew. I am still considering using cam levers, like the quick releases on bicycles.

In all, the prototype clamp did really well, and taught me a lot of good information about what needs to be done for the next test, which is all I was really aiming for tonight. Sure, it would have been great if the thing came out perfect, but at this point, I can bang out prototypes pretty quickly, with the jigs in place and the spreadsheet all set up to tell me where to put the holes.

Off to the hardware store for a new Forstner bit, and maybe some 2×3, because I think 2×3 will work just as well, and will be have a little less overhang than the 2×4. And before I make too many of these, I will have to figure out what hardware I’m going to use for the through-bolt (cam, long 1/4-20 bolts+thumbscrews, …)