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Michele Scotti

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    138
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About Michele Scotti

  • Rank
    Star Forming

Profile Information

  • Interests
    Telescope making - Instagram #800mm_telescope
  • Location
    Woking, Surrey
  1. I've checked online in a few website, thanks to the STL from Jonk. The cheapest quote is £140 - way more than I expected - I guess it goes with the overall volume.... I guess I need to make friends with somebody tha owns a printer! Any suggestion for on the material? FDM or PA are those more basic. The only characteristic that I need it's probably that I can drill it easily, all the rest doenst count
  2. Is height the main parameter that makes it not achievable for 'satandard' printers? Would it be easier i.e. easier to find a more common printer, to split the item in 2 and glue it later? it would be Having to do smal drilling is there a recommended material? There's virtually no room for any ribs unfortunately. Here's the overall design if anyody is curious: Fantastic! Thnx a lot!
  3. I agree about the grating - i guess they are glues inside the Alu casing -although I'd be ok to try and debonnd a scale. The only source of an optical grating in a reel is from China and it's £400 a meter....that won't do for me. I have the impression that magnetic scales are cheaper. Sag is inevitable but I have a couple of considerations: 1) the design is somehow taking that into consideration - see post: 2) sag in a properly designed and executed mount -not saying it's my case!- is predictable and proporsional i.e. it could be mapped out 3) the sag for given an amount of tracking time seems -at first glance- manageable. IT should be less than 1arcsec each Altitude degree. Aiming at 10min integration time I'm not that worried about - we'll see iwhen in operation if all of this ijust theory....
  4. I actaully have bought such a pipe but the turning is just a nightmare - and I'd need to make flanges to support the whole thing. While pondering on all those aspects I got my Eureka moment.... 3D printing.! Glad to see you all cleared my doubt about thinkness. Are there online businesses that can print out on;y one piece? Do they need a specific CAD file (like STEP) or do I need to create the model witha special software? Any idea of the cost? Cheers
  5. From what I got so far the resolution resides mainly in the readhead - i.e the digitalization of the sinusoidal information -. whereas the accuracy/repeatibility is in the grating of the scale -regardless if it's magnetic or optical. Apparently magnetic scales are """"fairly""" affordable - the optical ones (with 20/40um grating- are nowwhere to be seen...that's weird because the matching readheads are plentiful on Ebay...just like the one I bought.
  6. Thanks Michael and David, smoothness and robusnes are not important for this application - it's just a sleeve carrier for ceramic ball bearing of the focuser. Thanks for the prompt feedback!
  7. Hi there - question for the much- envied 3D printer experts. The focuser/derotator for the 800mm project needs a part -a simple cylinder - that can be made of plastic material. The rest of the focuser is made of Aluminium. As said earlier, a cylinder with OD 120mm, height 135mm, wall thickness 2.5mm Is it feasible or the wall is way too thin? I don;'t have very stringent need for roundness as long that it doens't look oval! Cheers, Michele
  8. Just for info, I've started a thread on a CNC forum - great chaps there too- and getting a lot of suggestions. All in all it looks like a tape scale + encoder readheadwith a 0.1um is the way to go. The challenge is to find the hardware in the used market to contain the expense and stay true to the spirit of the project. Read-heads seems fairly attainable on ebay ( like less than 100$/£ for a RGH22/RGH24Series if you're lucky and patient). If I could only find linear scales that are inexpensive then bingo! but I seem not to find any of them – the optical ones with 20/40microns gratings, at least. Still puzzled about how to salvage them from a CNC machine. Also, what is not entirely clear is if and optical encoder is better than a magneic one. The both are available to 0.1um resolution
  9. That's the same as Planewave i.e. 50 ticks per arcsec anyway I just talked to the chap that developed the tracking system and he says that I should aim at 10 ticks/arcsec
  10. HIgot this one - according to the data sheet it's a 1um resolution with digital output. for phase A and B in quadrature. But I don't think there's a "quadrature" signal. However the SiTech II has separate inputs for A and B so I suppose it performs the quadrature?
  11. Hi, it’s about time to spec the encoders for the telescope. The current set-up is as follows - I have a SiTech II and I deem the axis encoders essential for tracking capability and long exposure. There will be an off-axis guide however I’d like to get the most out of unguided operation - and I have a couple of doubts to clear.... Right from the design phase, I wanted some easy way to attach a linear scale to an accurate surface rotating with the axis. The pac-man is an example of that – once it’s ground it can accommodate a linear strip. Currently my first (*) route is to use linear incremental encoders and sourcing them as used parts from scrapped CNC machinery. Linear scales can be purchased as strips and glued, taped or somehow fixed to the trunnion. To start with: Resolution. The trunnions provide a ground SS strip with an approx. diameter of 1200mm. This provides a ratio of (360deg x 3600arcsec) / (1200mm x Pi) è 343.8 arcsec/mm or 0.34arcsec/um. Linear scales with 1um resolution are pretty “standard”. QUESTION #1: is 0.34arcsec/um or better ca. 3 ‘ticks’ per arcsec enough to track? Accuracy: Just like Sun Divisional Error, I’m not that concerned if adopting CNC equipment – they are usually pretty decent and unlike a CNC machine, when it comes to tracking for several minutes the portion of the scale is relatively small. QUESTION #2: or should I be concerned?? If anyone here has some advice that’s much appreciated – I have a background on encoders but I lack insight and practicality. QUESTION #3: also, can I directly connect the TTL (0-5V) A and B phases directly into the SiTech? Btw, I’ve ordered a Renishaw readhead – it was just too cheap not to buy it. Looks like scales that go with that are not that inexpensive. I’ll post the image as soon as I received – so we can see if I just wasted some (more) money… (*) I have a couple of concepts to develop a similar or better system suitable for DIY but in our club we are currently lacking somebody with Electronics experience to develop a functioning prototype. Cheers, Michele
  12. Before going into the next phase i.e.grinding the pac-men rails I ran a quick&dirty vibration analysis check using readily available and easily accessible techniques. With the Lower Telescope Assembly pulled together we were curious to check the ability to record and analyze the frequency spectrum of the physical modal response. We downloaded AnaHertz free app on Apple store and double-sided tape the phone directly to the assembly in the area that feels more flimsy. The excitation is provided by a suitable....hammer. By no means this wants to be an exact analysis but rather and attempt to see if some info can be extracted with a tuned-down methodology that usually costs few grands. That part of the structure - the upper part in the back- is at 5Hz which by itself doesn't meet the project target. however, this is just a warmer while the test that counts will be conducted on the whole telescope. The front upper area returned a slightly higher 9Hz wheres the bottom is much more constrained and felt more rigid. Also, this is possible as the mass of the phone is more than a magnitude less than the probed structure Amazing to see what you can do today with te MEMS in your phone and a free app!. Here's the full video: https://www.youtube....h?v=Uy-H-QXyRwc
  13. I might actually ahve a suitable cutting disc with inserts. I'm a little bit unsure about the jig holding the piece. As of know I'm using ALuminum specific thin abrasive disks for angle grinders. The pieces are getting sooooooo hot I ned to keep spraying water on it. it's a solid 30/45 min work per piece
  14. Small update - small parts. With bigger elements starting to come together it's coming the time for smaller parts needed for the final telescope assembly. The truss heads are found at the trusses/beams ends. There are 6 beams hence we need 12 heads that will slide into the beams end and eventually secured with glue. These end bits are made of aluminium and they have been turned into shape and hollowed on a lathe. The hollow end is tapered to make the parts as light as possible. The following step is to cut and mill the element of the head that is mating with the flanges on the upper and lower sub-assemblies - that's an 8mm flat. The cutting operation, which is meant to alliviate the milling effort -given that we have a mini-mill- is fairly painstaking....3 out of 12 are completed so far.
  15. LTA assembly dry-run. After trimming some beams we pulled together the entire sub-assembly. That was mainly to check the robustness of all joints but also for the sake of seeing how it looks like. The structure feels sound and light enough to be carried by a single individual if you stay inside the structure - otherwise it's very bulky. Overall it's should be around 28kg/60lbs. Next up is grinding the Altitude bearing surfaces. Despite the SS strips are bonded to a CNC machined surface and there are no screws or discontinuities, they do not provide at all the accuracy required by this project. During grinding I'll take some before/after run-outs measurements. What's following from that is a specific assembly procedure This is critical to ensure that the two rolling surfaces sit on an ideal cylinder. At this point we have all the 4 main assemblies that took shape: UTA, "tripod", Azimith table and now the Lower "Tube" Assembly. Still a lot to do though. Cheers
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