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Michele Scotti

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Everything posted by Michele Scotti

  1. That's Planewave direct drive specification - 10 ticks/arcsec. Maybe it works with less but they kind of set the standard in case the DD is coupled directly to the axis.
  2. Hi John, you're right the stroke is dead center and the tool I think sub-radius - like 45% of the diameter. We tried a full tool but the friction was way too high. The main grinding was done with a CNC diamond tool. I'm definitely not an expert in making mirrors - I've only done few , long time ago. For sure I'll ask about your consideration and come back to you. Btw I've cobble up another video - not advisable if you're seasick ;D https://www.youtube.com/watch?v=w4HIsp1-zXw
  3. Work continues with #800grit: Aiming at #1000 then #1500 to prepare a pitch lap and check if we have something that resambles a sphere.
  4. I saw this several times and it is saved in my favorite yt folder. Did you try to use any water or was it messy? This is another good example: https://www.youtube.com/watch?v=eRdr86gXBLI Although it started like this....: https://www.youtube.com/watch?v=lonAulU-kWA
  5. An update on the mirror side of the project as a part of the club has been working on the mirror for a few months now. The bulk of the material has been ground off at a machine shop that works on granite. Subsequently, the hogging was done with a half tool to smooth everything out with #80 grit. You "may" notice that the route we took is the ....most impervious...but cheaper and readily available. Also not very recommendable which is a flat 25mm float glass. All in all, I'd consider this a practice run for the part of the team who works on the mirror - we'll gain some experie
  6. Well done - much of satisfaction when things turn for the best. Would you be able to make another video just like those before to check what it's fixed and what are the residual contributions. Btw is now the motor/worm assembly fixed solidly and not sprung anymore, right?
  7. The SiTech controller accepts 5v pulses as 'telescope encoder' so that gives an easy way to directly wire industrial encoders to it. In the last few months I managed to salvage parts of a Renishaw encoding system - now 'obsolete'. I suppose they are coming from some CNC machinery. Here I'm testing one of the 3 read-heads which has a 1micron resolution although the final system needs 0.1micron resolution. This equals ca. 30 pulses each arcsecond - hopefully it should be plenty for tracking accuracy. This is a very crude test just to see if the salvaged hardware i
  8. Hi Rusted, sorry I missed some of the last messages. Did you identify the source of the substantial wheel movement as per your vid here: https://youtu.be/bWKQBCOkrNw?t=14 ? Also, I recall you ordered angular bearings - were you able to instal them? Did you notice any improvement?
  9. Hi Huw, can you explain this sketch? Apologies if it's explained somehre else but couldn't find anything.
  10. If the camera is on a tripod on the floor what I see is that the wheel is moving away from the wormgear assembly. I almost have the fealing that the entire RA shaft is pushed around by the reaction on the teeth. On the video from the right side you clearly see that the housing and the mounitng plate experience small deflection. From the 'front view' video instead the deflection of the wormgear assy is more pronounced. I'm a bit baffled - would you agree with the observation? For peace of mind I'd take a vid from the left side too and another one where you can check whether the m
  11. Preparation work for grinding the Altitude rails and achieving correct precision. Stacking up the 2 pacmen and fastening them together. I'm using two steel beams to overhang the pacmen so that the swiveling 'apparatus' can go around the circumference with ease. To start with the run-out (departure from ideal circumference) is checked using a digital gauge that can sense microns. The dial starts from 0.000 at one end of the pacmen and climbs up to almost 2mm. However that seems to be attributed to the hinge point being off-center by interpreting the plotted
  12. Very useful vids - I see 3 things: 1) the wormgear sliding into the bearings - is that what is fixed by the missing washer? 2) the hosing movement - you describe it as flexure but it's not clear from the vid. Another video from the side would clear that. Again I'm a bit skeptical that a 5mm square tube will move much. It's maybe more likely that it's sliding/tilting due to the screw that allows the springed housing? 3) the big plate the housing is mounted on is seen deflecting small movenet but it's there. It'd be surprise that such plate is flexing - if it's the RA shaft housi
  13. Can you explain what do you mean with that? Can you see where the flexure is stemming from? A close-up video would be a great aid although by looking at your set-up it could be the fixings clearance for adjusting the wormgear housing. I wouldn't rule out the bearings though The big plate looks like 10mm, the square tubing 5mm, the worm housing is possibly 8mm thick. That is enough material to make a robust system. Should be somewhere else
  14. I agree although the clutch plays a role - I suggest to detach the wormgear assy and attach a camera and mark the wheel. You can then focus on freed axis and make it safely rotate around the pier - then you can take notes of the measurements conviniently fom the video. Something like this set-up: https://youtu.be/OGJyjb-h-G8 Btw I recall you started a topic to explain the build - can you attach the link pls?
  15. Brief and rough trigo. --> arctg(um/R)= ca. 1.5arcsec i.e. for every micron (um) of 'detachment' of the worm from the wheel's teeth means 1.5arcsec of backlash and that is the same you'd see at the telescope. A more 0.1mm of 'sloppiness' would give you back 2.5arcmin. Quick and tad cryptic - let me know if it makes sense though. Wrt to RA flange bearing I would not be concerned - gravity loads them always in the same position and take away any bearing clearance (but not roundness isssue although not likely to be an issue in this application. Can you test with th
  16. I think your system has high potential - baby steps: if your shaft is 12mm there could be fairly inexpensive angualar bearings (not as good as taper ones but for these loads they would do). Youd need to pre-load them but it's easily done with your current set-up - if interested I can sketch-up something for you. Don't use adapters - you'll add errors. Here you need to remove them oen by one. https://www.ebay.co.uk/itm/7001-Single-Row-Angular-Contact-Open-Ball-Bearing-12x28x8mm/143541090346?hash=item216bb7382a:g:4NMAAOSwuvpcR2-C
  17. Hi Rusted, I previously said I was giving it a go. Game changer! Time went down from 20min to 5min - without the piece to get hot thus the benefit of spraying water to cool it down...and producing a nasty swarf.
  18. I took the liberty to sketch up how I would do approach this - courtesy my daughters' crayons. Taking the brave pill I'd split the wheel in an inner flange and a crown - the latter being adjustable. The 2 are connected by a plate (I envisage a 5mm steel plate which needs to be machined at least on one face). Wrt the investigation with camera check out this post: https://stargazerslounge.com/topic/340154-800mm-telescope-project/?do=findComment&comment=3787165 On a video the resolution could be lower but if you use a mild tele and a camera I'm sure you can crack the 0.01m
  19. Out of curiosity: straight or helical tap?
  20. Forgive me if I got it wrong by missing some info already stated in this thread. You have a run-out issue – can you measure that? From an engineering standpoint it would be crucial to quantify the gap to your ideal situation and see what improvement(s) are closing it up. A 0.01mm dial gauge is pretty cheap nowadays. You could place in the not-hobbed rim or fabricate a probe tip that gets into the grooves (going to take longer to measure but more accurate). Do you have nay mean to fine tune the cantering of the worm wheel? It’s one of the most usual issue and I guess it might have bee
  21. Hi Rusted, it may seems slightly off topic but is the wormgear supported by ball bearings or conical/taperes ones?
  22. Brief update: had a chat with the sales manager at Renishaw - he confirmed the feasibility to use their magnetic encoding system - 0.24um resolution. Pro: it should be cheaper than the optical one Cons: magnetic has some hysteresis when changing direction. The amount is less than 2um which is less than an arcsec in the 800mm project set-up. On top of that - possibly to simply convince myself!- i'd say that hysteresis would affect mainly the pointing accuracy rather than tracking provided an exposure that doesn’t change the direction of the axis.
  23. Jonk thanks a lot for looking into that - I understand that it's pretty complicated and time consuming given the volume. My concern about turning stems from the fact that when I had the Aluminium parts turned in a CNC shop they initially rejected the job due to a 3mm wall thickness - similar OD, similar lenght. TBH I need to have the Alu parts pretty accuracy - say +/-0.01, nowhere near this plastic bit. I might just giving it a try as I have the plastic pipe around. My second choice would be making it out of carbon fiber. I used this method to make the central hub of the spider.
  24. I bought a 6mm wall thickness pipe some time ago but when planning the process on the lathe it just looks like a nightmare. You'd need to make flanges to support the turning of the OD alone and then you are left with a big ovehang on a thin wall to turn it down to 2.5mm. Not impossible but slim chances to do it rigth tbh. The item is suppose to be sort of sleeve bearing for one hundred 3mm ceramic ball bearings I already got.
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