Posts Made By: P. Lee Stock

Appleply is both lighter and stiffer than Baltic birch. The difference in weight is noticeable just hefting two comparable sized pieces in your two hands. You can make up for stiffness, if necessitated by your telescope design, by using more Baltic birch (laminating pieces together), but then the resulting scope is even heavier.

Still, I've decided it's not worth 2x the price unless you want the natural maple finish of Appleply for its beauty or the resulting scope will be too heavy if you go with Baltic birch.

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12) Cell assembly modifications…

The original Starhopper cell was designed for a conical mirror. I sold the mirror and the heavy upper half of the cell it was glued to. I quickly found that I really needed all that weight on the back end to keep the center of gravity low so the tube didn't bottom out in the rocker box. To remedy this, I bought two cast iron plumbing caps--ground one down to fit inside the other and welded them together, then painted the outer one and screwed it onto a rubber stopper I used to replace the original weak and insufficient collimation spring. Convenient: two birds with one stone/stopper.

Well, my tube had the focuser hole drilled already and was a little too short for my eyepieces to come to focus conveniently with this mirror, so I opted to move the rear assembly almost an inch out of the tube rather than drill an ugly new focuser hole. This meant making extension mounting blocks and a rear fan solution that is also completely outside the tube. Three fans should cool the mirror very quickly.

Finally, I took that compressed rubber stopper idea from my “tent snap telescope” and used it to wedge the battery in the rocker box. Battery slides out without much effort, but I made an RCA plug for my charger so I don’t have to—I just unplug the RCA cable that goes from the on-switch on the rocker box to a jack on the tube (for the fans) and plug charger into the rocker jack—makes life easy.

Woodwork is usually most of my telescope-making time, so this actually went faster than building something from scratch, even though I changed almost everything.

Hi Chris,

Given that you don't mind moving the primary mirror, here is a (pretty) simple suggestion that will tackle all your problems at once--

Buy your favorite 2" focuser and see if your eyepieces come to focus. If they do, then smile and be happy.

P.S. But if they don't, then follow these instructions:

Determine if you need to move the primary mirror toward the focuser or away from the focuser. It should be easy to tell because you'll see stars starting to come to focus and then you'll run out of focuser travel. If focus is inside the tube, then advance the primary toward the secondary mirror until your eyepiece reaches focus (31mm and 22mm Naglers are eyepieces that need lots of in-travel, so if you have one of those, you can use it to benchmark). Once you get a 31mm Nagler to come to focus, you can pretty much count on not needing any more in-travel for another eyepiece in the future.

If memory serves, all TeleVue eyepieces come to focus within about 1-3/8" of focus travel, so you should be fine with a 1.5" drawtube, but you can get a 2" if you want to be super safe, though the drawtube may protrude into the light path just a teeny bit (no big deal, IMHO).

I wouldn't choose a 2.5" travel drawtube unless I had a refractor or folded folded refractor where intrusion into the light path isn't likely/possible. In any case, should you go with a 1.5" drawtube and find you don't have enough out-travel after setting up for the big FL Nagler, the eyepieces that generally need more out-travel on TeleVue's list have 1.25" barrels, so you can use a 2" to 1.25" adapter and plug those eyepieces into that to achieve the same result as a longer drawtube.

You should visit TeleVue's website and look at their eyepiece specifications. The spec called "flange level" in column F, I believe, are relative distances for each TV eyepiece where they come to focus relative to each other. So, for example, where a 31mm Nagler has a flange level of -.31 and a 7mm Nagler has a flange level of +.25, this tells you that the 31mm comes to focus .56", more than 1/2", farther in (in-travel) than the 7mm. So, if your 31mm reaches focus when your drawtube is almost all the way racked in, then a 7mm will reach focus with about 1/2+" of room left to spare.

So, to summarize, I'd buy a 2" focuser and any TeleVue eyepiece on that chart and mount the focuser centered on your current secondary mirror and go from there with the primary mirror and cell. You can buy a cheaper TV eyepiece and, using the spec chart, ensure you set the focal plane relative to your focus in/out-travel so future eyepieces will come to focus, i.e. if you buy an eyepiece with a +.50" flange level, then move the primary mirror until the eyepiece reaches focus when the drawtube is about 7/8" racked out to ensure your future 31mm or 22mm will have enough in-travel when you finally buy it.

Anyway, that's my story, and I'm sticking to it ;^).

A study in sliding counterweights, continued...

I found some .035" wall 3/8" OD "rigid" (Alloy 3003-H14, extra manganese) aluminum tubing priced at $4.77 for 6-feet at McMaster-Carr and ordered it. Specifications say it can't be flared or bent.

The other option was "general purpose" 6061 tubing in various wall thicknesses-- .035", .049", .065". These could be bent and flared, would be heavier, and cost $9 to $12 for a 6-foot piece.

So the stuff I got sounds more brittle, and I wonder how it would compare to the other options? Specifically, I wonder how it will do suspending approximately approximately 3 lbs. of counterweight compared to typical 6061...

Any thoughts?

My opinion is it is a collimation headache to rotate the upper ring/cage on a fast F/ratio scope you assemble each time. When Sky Valley Scopes was making complete telescopes, they did a neat rotating OTA design that really should have been more popular than it probably was, IMO.

I used to make them like this before I figured out what I was doing on the lathe. The hole through the top of the holder is oversized and there's a rubber washer inside the holder to put the assembly under tension so you don't need to take up slack when adjusting one collimation screw (and to assist with the pivot action). The vanes are steel banding strap material--which I still use.

That's really nice!

Saturn is great right now, if you can stay/get up for it, especially since it's not too cold yet.

There ya' go... a first refractor you can actually use. And it looks like you could mount something even larger on it for yourself.

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I hadn't considered that the threaded rod would need to join to the motor absolutely centered on the motor's drive shaft and turn perfectly in line with the motor--and the closer, the better. Hence my search for a way to drill a perfectly sized hole in the barrel connecting the motor shaft to the leadscrew (***Please see my plea for help below ;^).

If the threaded rod does *not* turn perfectly in line with the motor's shaft, due to oversized or off-center linkage, the rod will wobble the motor up and down as it turns just enough to pivot the tangent joint and cause the table to move forward a bit, pause, and maybe even go backward a few thousandths before moving forward again. Dab'nabit ;^).

Still, you *can* reset it in 1.5 seconds and it might work great anyway as is, or after I make the perfect connector (got fingers crossed). I'm always looking for ways to make things more convenient while observing, so cranking a nut back to start position, or doing a 4-minute electronic rewind just didn't make sense to me.

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***Plea for help!! :

I could actually use some machining advice here--I assume that if my motor shaft is .315", going up just .001" to a .316" reamer is sufficient? Too much? Not enough? I really want to squeeze this motor shaft into a connector that barely fits it, so please send your recommendations on sizing a *really* tight hole. Thanks!

A 550" wide binocular? Like a military range-finder? Wow, that's original.