Rusted

Whoah! Reverse Engineered Alien Technology alert! 👃🏻 I am unworthy! 🐵🦴

The weakest factor of any tripod is the radius out to the tilt line [hinge] between any two feet. Which is why tripods are so unstable relative to any increased number of points of contact. A four legged [quadruped] is far more stable and the reason there are no tripodal animals. A tripodal mountain goat is basically a non-starter in Darwinian terms. The Martians wouldn't stand a chance in a real War of The Worlds. It would only have taken a car and a brave chap with a rope to pull one over. For the same reason a tricycle is hideously unstable compared to a quadricycle of the same track and wheelbase. And a three legged stool, only has value on a rudimentary, brick or paving slab floor. Every additional leg provides greater stability because it better equates to the full radius of a circle. Which is why executive, swivel chairs [and my own computer chair] have five feet or castors.

Hi Sophie, I have some images on my blog from back when I dismantled my secondhand PST for the internal parts. https://fullerscopes.blogspot.com/2018/02/pst-dismantling-images-of-parts.html Try clicking on Newer and Older Posts at the bottom of my blog page for more blog posts with more pictures. For focusing, the PST relies on a prism which slides diagonally on rails inside the black box. Unfortunately the prism can become rotated on its mounting blocks which doesn't help. Removing the black box cover is essential to examining the situation inside. With luck you won't have stripped screw heads like my secondhand PST had on arrival. If your views are very dim then you might have a rusted ITF filter. This is a filter inside the black box. I had exactly the same problem of dim images and had to buy a new ITF filter. I bought a new one from Maier in the US. From memory it cost about £90 equivalent with postage. Possible customs charges too? Beloptik of Europe also offers replacement ITF filters but they are rather more expensive. Fitting the new filter is probably for those with some DIY and/or optical experience. An experienced member of a local astro society might be able to help if the job is beyond your practical skills. You don't want to damage anything.

Hi Adrian, The one [blindingly obvious] thing missing from the video was a second, safe support placed near the chair. Had there been another support, which completely avoided a bent back, then the heavy OTA need never be lowered to the ground. With all the attendant risks of injury from lifting and lowering. Instead of which the OTA could be carried out from a support of similar height in storage and returned to it after use.

Thanks Dave I tried all the usual ploys to undo it no effect. Nothing I did made any difference to the strike through.

Simply, that one cannot make false assumptions to obtain true accuracy. For example: You cannot add a flexible extension to a micrometer to measure a longer distance. Though you can use a rigid extension and make relative measurements using a micrometer. You have absolutely no idea of the true length of the rigid extension to the same accuracy as the micrometer. Your jig offers almost zero hope of true accuracy but might offer repeatable relative measurements. Emphasis on repeatable. You are making relative measurements. Which require close repeatability to have any value to you in this context. The question remains: Is your pivot tube perfectly upright and absolutely inflexible? If not, then you aren't measuring your track at all. You are only measuring errors in the pivot tube relative to the track. If you falsely assume that the pivot tube is accurately set and rigidly so, then you might remove half a meter of track depth for no good reason. I hope this makes it clear.

Hi Ryuno, I know it sounds too simple: Find something quite large that weighs 20kg and see how easy it is for you to manage it? A clean dustbin? Or a garbage can? Not sure what you would call these in Japan. They are only suggestions for something about the correct size. It just needs to be about the same diameter as the telescope and weigh about 20kg. You might find something suitable to "wrestle with" in a DIY or furniture store. A large diameter, smooth tube is very hard to handle unless you fit lifting handles. It is too big for your arms to go around to get a proper grip. I use very grippy rubber gloves but it is still a struggle. You can use one of the RASA11 dovetails to fit handles or a long, lifting bar.

Marcus, I agree and it's not silly. If it were my project I'd just be using long sanding blocks. With various paper grades getting finer over time as needed. Or even a diametrical, cross board pivoted on the pipe/bearing with an abrasive paper covered block running around the track. As you say, use the jig only for measuring. Double check that every single radial measurement is fully repeatable before even trusting the jig at all. Using maths to analyze "a length of string" is a common fallacy. EDIT: Can't understand the strike through text! Can't get rid of it either!

Episode 13: Saddle and Declination attachment: There is a lot of strain on the saddle to Dec shaft connection. So I used another Tollok bush embedded in a hefty brass sleeve turned in my lathe from a piece of scrap. Only the short, flange section has quite a thin tube encasing it. The rest of the Tollok bush is encased in the full thickness of the massive bush. Ensuring great resistance to expansion and flexure. The top, inner section of the Declination flange bearing fits tightly into the brass sleeve. Providing extra stiffness and a tidy appearance. The saddle consists of two heavy 4" wide, channel sections of aluminium bonded and then bolted together at the flange and tube rings. I shaped the two channel sections for maximum strength at the center while allowing the tube 8" rings to clear the channel at the tips. The ring of washers under the 10 x M10 screws helps to spread the loads from the saddle into the end of the Declination shaft. I deliberately drilled and countersunk an inspection hole in in the center of the saddle. So I could easily confirm the shaft was pushed right up to the underside of the saddle. The entire length of the Tollok bush carries the loads from its flange, through the heavy brass sleeve into the Declination shaft. The Tollok bushes are easily removed from their respective shafts by removing the ten clamping screws. Then the same sized screws are inserted into separate holes to push the two tapers apart. I used stainless steel fasteners but was careful to lubricate all the threads to avoid galling during removal.

You can use your micrometer head to confirm the uprightness of your central tube relative to the ring in its present form. It should read close enough to an average figure over one complete revolution of your jig before you even consider a run. Any bias in one particular direction will thin, or thicken, your track in that direction, depending on the slope of the tube. I still think the angle grinder is a fierce tool for this task. It has no finesse. Nor any pretensions to accuracy. If it digs in, then it will pull the tube over in that direction as a form of positive, mechanical feedback. Bad! I just wish I could think of a tool which better suits the task. Your jig just isn't up to using milling tools or even end face, router bits. There is bound to be far too much flexibility for the accuracy you desire. Or any accuracy at all! I wouldn't be surprised if it resonates like hell just with the motor free running. There just isn't enough mass or stiffness. What about an ablation laser? Shouldn't be any vibration. Don't you have a tech college nearby which could treat your project as a class exercise? The machine tool tutors might like oddball projects. Makes a nice change from the usual humdrum. They might have some useful ideas before you break something important. A vertical, turntable lathe would do nicely if anyone had one. Try a crane manufacturer?

I agree and questioned my motives [afterwards] for using the ring as its own reference. So what is your reference and what exactly you are trying to achieve? Is it your pipe? Is it perpendicular to a fraction of a second of arc? Is it infinitely rigid? Is it equally rigid in all angles of rotation? Is the base absolutely rigid when fully loaded? If not, the ring will change form. It will sag between the feet or be "shaved" over them. Giving you a gentle, roller coaster track.

I ordered a lot of different O-rings for my PST etalon motor drive system. 42-50mm x 1.5mm all from UK suppliers found online from a search for O-rings. Every single one was too thin at 1.5mm diameter!

Episode 12. Drives: Wormwheels & worms: I waited months for the wormwheels and worms from Beacon Hill. I had ordered an 11" and an 8" with 50mm bores and matching stainless steel worms. After endless excuses they admitted they could not supply them. So out of desperation I accepted a pair of wormwheels with the wrong bores. 60mm instead of 50mm. That meant turning bushes [in my lathe] to match the difference in diameter. Which is a serious "No-No" in mechanical terms. Concentricity of the insides and outsides of the bushes must be maintained or the wormwheels will be eccentric. So I turned and bored [brass] bushes without removing them from the 3-jaw chuck. It seems to have worked. On arrival, the 11" wormwheel proved to have some serious "issues" apart from the "bad teeth." The single nylon pad "clutch" soon proved to be totally inadequate to the task. So I radial drilled the wheel hubs and the new bushes to make three clutch pads each. Then the worms would immediately wind themselves out of their bearing housings during slews. So I added screws and oversized washers to restrain them inside and out. The drive belt timing pulleys couldn't possibly grip the worm shafts well enough with only one grub screw. So I had to drill the hubs of those for extra grub screws. [Much shorter than shown here.] Then I had to drill the edges of the worm supports so I could use a long series, hex key down the hole to reach the invisible grub screws. The worm bearing housings are just a short slice of channel profile. It really isn't up to the task without further reinforcement. More on this later. All this extra work was vital to making these commercial products into useful drives for a large mounting carrying long and heavy telescopes. Without a lathe and bench drill it would have been impossible. Note that I used stainless steel hardware throughout. I hate rust! I have no idea if Beacon Hill is still offering wormwheels. At the time they blamed an elderly machinist giving up his role in their production. In the next episode I shall show the worm bearing supports in more detail.

Thank you for your very thorough post Simon. It all sounds fascinating. We really do need to see some pictures of the results of all your great ideas and all that effort! I was able to access 50mm stainless steel bar at cost, locally. So maximized all the consequences of that choice. It is a difficult to pin down what will work with particular telescopes. A lengthy, f/12 refractor is not remotely a compact f/12 SCT. So I used the D&G optical website for shaft size suggestions against refractor size. They have been at it for decades so know what works. An AP Titan was just outside my "scrap metal builder's "budget. Rather than respond directly to all your points I will post another episode on the drives today. That will share the information more widely in case it aids other's build projects. I have been rather busy building a new 6" H-a telescope. This will be a foot [30cm] longer and a bit heavier than the last one. I shall be mounting the 180/12 and 150/10 side by side again but no 90mm/11 this time. Plans to make the scopes easily removed and replaced individually did not work out. Not even with my 3x4 overhead, pulley system. The scopes were actually quite manageable. Adding and removing 5kg weights from a stepladder was just too difficult and too dangerous for me!

That tube is not going to offer much support without some help even if you triangulate. Think of it as merely a center guide pin. What about adding some counterweights on a horizontal extension to balance the angle grinder and jig materials? You don't need any pressure for "cutting" and fighting the weight will require too much adjustment to take up unknown levels of backlash. The triangles can be scrap ply. That board isn't going to offer much resistance to twisting on the axis of the angle grinder. You could add a roller on the tail end. Your track is the only accurate surface you can trust as a register so you might as well use it. You could add further rollers at the widest part of the jig. Inline skateboard wheels? The jig will have to be widened to suit.

Chaos always expands to fill the space available. I have decades of absolute proof. My wife insists that an aircraft hanger would never be enough to test my limits. Perhaps two, if I showed unusual levels of discipline? I visit a farmer now and then to buy gravel and sand. His vast sheds and barns are so cluttered that I might finally have found a match.

With respect, I have some recent experience in trying to "machine" the inside of a 3m diameter plywood ring using a central pivot and a portable router. The result was extremely violent chatter! I then duplicated the radius arms into a horizontal triangle and this helped to smooth the chatter but not by much. I used 20x100mm timber arms to form the horizontal triangle. What was missing from my radius bar system was 3D limitation on the radial cutter. The router could hop up and down despite the sheer weight of the triangle. I believe you need a pyramidal radial limit system to avoid tool rotation in all planes. If you use a simple, vertical triangle, as shown, you cannot restrain the cutter [angle grinder] motor from bodily rotation. Your cutter is of large radius and has absolutely no reason to obey your reasoning. The radius bars shown cannot be stiff enough unless you make them seriously large in cross section. I think you will need to triangulate both your supports in the plane of the drawing to avoid torque effects causing severe digging in! Admittedly your radius is much smaller. But your demands are for very high precision and the tool radius is uncontrollably large. Perhaps you can produce a very solid, double triangle, plywood arrangement like a double wishbone, car suspension? Two solid triangles. One horizontal. The other sloping down to the angle grinder support bar. The bases of both triangles firmly supported by your bearings, as shown, with serious vertical restraint between the bearings. I still wouldn't practice on anything precious to you! EDIT: Image added for my initial cutting triangle using alloy, tubular radius arms. Pivoted at the center 1.5m away. This was replaced by a broader triangle of 20x100 planks for better damping. Neither system had any chance of real accuracy. The crossed timbers formed my central pivot. Again providing too little stiffness.

What is says on the tin: Sun's surface seen in remarkable new detail - BBC News

Congratulations Tim! It is a relatively tiny spot, compared to many, so well spotted!

Some proms between heavy cloud. Lens has finally cleared.

I don't remember seeing interstitial dew before. Regularly lose imaging time to back of rear element dew but not in between. That's why I have invested in the heat bands and controller. The hair drier didn't seem to help despite 20 minutes of blasting the objective cell.

Thanks Dave. I am seeing much the same detail on my monitor as I am capturing. First time ever to see magnetic lines [?] radiating from "bundles" and the spot. I've left the new dew heaters on over lunch to see if I can clear the dew between the lens elements. Haven't had that problem before. Can heat bands cause internal dewing?

Here's a reworked copy to bring out more contrast and detail: There is a strong gradient across the image unfortunately.

Very steady seeing but constantly teased by thick and thin cloud. Element spacing fogged up in my 6" f/8 objective despite or because of [?] new dew heater straps. Quite pleased considering the difficult conditions.

I was basing my statement about pillow block bearings on half a century of examining mostly amateur, equatorial, mounting designs. The wide spread of the "ears" on the pillow block, bearing housing usually suggests a flat plate approach to fixing the axes bearings. Having handled strips of many different materials over a very long period, I have become aware of their natural characteristics. Pillow block bearings on the tops of fork tines make more sense. Though flange bearings will better spread the loads into the sides of the tines. Handling a wide variety of beam shapes, I, U and T, and the typical, double-U "girder," it is obvious where real stiffness lies. They all lack stiffness in rotation. Torsion loads will twist each of them far more easily than round tubes or tubular box sections of similar proportions and materials. One only has to handle the same cross sections in plastic to become acutely aware of how much larger sections in steel will behave. Depth of a section is vital to beam stiffness but the width of the section must also match the likely torsion loads. Deep floor joists are typically braced against rotation. Using any "steel girder" section as a telescope pier will be an exercise in frustration! Too heavy to lift unaided, but still twists like a plastic roof gutter! Gutters are one of the weakest sections in torsion you could possibly imagine.