Focuser Modifications

I was able to brute force the screws through the too-small holes in the drive plate, so the focuser came together for testing. Looks like we’ll call this one v0.1 as 0.5 was a little optimistic:

So far, it only works with a gravity assist, which I believe means the drive plate in standard Onyx bends too much. The next one(s) coming in the mail will be continuous carbon fiber reinforced, and as such should give aluminum a run for its money in terms of stiffness.

The whole assembly seems a little too wobbly. The drawtube sags when held at a 90 degree angle with an eyepiece in it. Part of this is probably the drive plate, some is probably the bearing spacing: a little under 0.4″. I knew this was ultra-close, but I wanted to see what would happen.  Turns out, wiggliness happens.

So I moved them apart until they are about an inch:

As a result, the focuser is now considerably taller. Also, the maximum movement of the drawtube diminishes by the same distance. As Jerry Oltion pointed out to me, it’s easier on a binoscope to parfocalize all your eyepieces than to manually focus each pair of eyepieces every time. Enter 3d printed parfocalizing rings. I don’t know if I’ll do full-length rings the right length for each eyepiece, or if it would be better to do a standard-height 6mm ring with a locking grub screw. Gotta get my money’s worth out of that German 0.9mm hex key.

So the focuser becomes a tool for adjusting vision discrepancies between observers rather than between eyepieces.

I’m fine with that, although now the dual-speed focuser is going to have to be even that much more compelling to make the cut. It feels lopsided weighing half a pound on a focuser that weighs a couple ounces, and it’s not cheap. Either way, I’ve made up my mind to design custom knobs to replace the stock ones. There’s nothing wrong with the stock ones (they’re actually very nice), but they are the same knob found on every GSO focuser. I’m going to experiment with TPU to create something that is soft and inviting to the touch and color-coded to shout, “This is where you adjust the focus!” A binoscope looks different and works differently, so visual design cues teach bystanders how to use it without having to ask someone.

As you can see, the drive plate has also been widened, with the mounts on the receiving end of the drawtube beefed up to compensate. My thought is this will also help reduce play in the system and give the drive shaft more surface to push.

The extra hardware arrived from McMaster-Carr today. I’m going to have to start labeling heat-set inserts. The nylon thumbscrews for the drawtube look nice. Twisting them back and forth in an insert a few times seems to smooth out any manufacturing imperfections in the threads. Black would look cooler, but white screws actually have a non-zero chance of being found on the ground at night. The PTFE discs for the shaft retention knob sure are slippery!

Can’t wait for the next prints to arrive!

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