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About tonyowens_uk

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    Hillwalking, cycling, engineering, travel, wine, politics, telescope-making, model-making, invention, history
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    Wicklow, Ireland
  1. tonyowens_uk

    First try on Orion Nebulae

    With respect Waruna the first thing to address for me anyway is the size of your uploaded files. It isnt convenient for some folk to download TIF files of this size. Could you either transcode these to for example PNG's or post links to a neutral hosting location? Thanks! Tony
  2. tonyowens_uk

    Another self build 3D Printer

    My apologies Chriske - I think I misunderstood which type of bearing you were referring to! Almost no machine tool builders use round shaft linear bearings carrying cylindrical recirculating ball bushes anymore. Those MGN rails are from HiWin ( https://www.hiwin.de/de/Produkte/Profilschienenfuehrungen/Baureihe_MG/Laufwagen_MGN/21089 ) and for most practical purposes are as good as those from the populariser of this style of bearing, i.e. THK Tokyo. Static load capacity of each truck (in the 12mm MGN profile rail used in that printer) is 580 KgF and stiffness is far better than anything else used in 3D printing including ball bushes. There should be no problem with contamination and abrasive wear as they all have effective wipers. Life is measured in thousands of Km gernerally - there is an approximate calculator here: http://www.efunda.com/DesignStandards/bearings/bearings_linear_ld_life.cfm The main issues with using this style of linear bearing are: 1. the need to fix them onto a flat stiff support surface and the problems of getting them and keeping them parallel especially in the flimsy structures typical of most RepRap. That is what chappie in the Thingiverse video discusses. 2. the effect of the wipers on breakaway friction especially where multiple bearing trucks are used. The second point could be an issue in high precision (but low stiffness) belt-drive machines like 3D printers which operate open-loop position control but aspire to carriage positioning repeatability to within a few tens of microns. It manifests as higher positional repeatability than one would like. Ballscrew drives ideally with servomotors will solve this. The poor man's solution is to just remove the wipers and substitute a block of wool/acrylic felt soaked in NLGI 2 grease! Hope that helps! Tony
  3. Thinking hard about a rich man’s AZGTi . The concept is exactly right but the execution is too cost-focused. How about x2 times the imaging capacity, same size, but with much more refined mechanics, transmission, servomotors and encoders. For x2 times current retail price

    1. Alan White

      Alan White

      I bet something well executed and well made would be more than x2 the price.
      But it would be tempting to many I should think.

  4. tonyowens_uk

    Mak wrap - should really break the CoC

    I think the issue you are experiencing is due to sub-cooling of the OTA metalwork below ambient temperature under clear night sky. This is a recognised problem that has been investigated and solved elegantly some years ago by noted planetary observers with engineering inclinations such as Anthony Wesley of Canberra, AU: http://www.acquerra.com.au/astro/cooling/ballarat/ The effect is identical to the one that results in frost on the roofs of cars but not on vegetation. Radiation exchange between the metal tube of a scope with enclosed optics and the sky, whose black body temperature is far lower than that of the earths surface results in subcooling not just of the tube exterior but also of the internal air adjacent the skyward surfaces, causing slow convection currents. The cure involves some or all of: 1. avoid use of enclosing tubes (truss scopes better than Newts better than SCT's better than Maks better than refractors) 2. minimise large thermal masses in the OTA (e.g. primary mirror) 3. protect the OTA exterior against subcooling below ambient temp (usually done by making the exterior surfaces reflective to longwave IR radiation using aluminised plastic film or by polishing a metallic tube exterior) 4. avoid the temperature of the OTA components deviating significantly from ambient air temperature (keep scopes in unheated buildings) 5. active temperature control of the primary (various methods) 6. stripping of boundary layers of warmer or colder air relaitve to ambient air (i.e. causing refraction) that might fall within the light path 7. making the scope tube from insulating material (or lagging it with cellular material supporting minimum convection and conduction through its thickness) For general use 4. is often good enough. For high resolution use in so-so seeing (where Maks and large refractors justify their existence) the other factors come in. Remember the filtered vents and 'porous' internal tube baffles used by Intes-Micro on their instruments to try and minimise wall currents. They work to some extent. For larger apertures this isnt enough and the full suite of treatments need to be considered if max resolution is an objective. Anthony Wesley took one direction with his 13" and 16" conical mirror planetary imaging Newts. Martin Lewis took a somewhat different direction with his 20" planetary imaging Newt: http://www.skyinspector.com/fossil-light--450mm-dobsonian Both have delivered images of amazing quality. I looked at the issue for my Intes-Micro MN86 around 18 months ago. I used a research-grade thermographic camera to assess the effect of removing the back of the mirror cell on cooldown of the 210mm dia x 30mm thick Sitall primary in my own use. I usually install one of various scopes kept in an unheated building with an insulated roof onto a permanent-sited outdoors mount. The thermographic video (taken on an evening in June) tells its own story. EDIT: I should have added that the 50-frame timelapse TG videorecord below was shot at 2 minute intervals. Starting temperature of the primary was 14C . After an hour it was 10.5C. After 80 minutes it was 10.2 degrees while the upward-facing vegetation was just under 8C and the upper end of the tube appeared to have cooled to 0.4 deg below the 8.8C of the bottom end. The last 8 frames of the video are corrupted by my having altered the temperature-to-colour mapping of the camera (very silly). I concluded that: 1. the motors and counterweights of my mount were hot-running and thermally massive respectively 2. Not all vgetation is at the same temperature as cooldown proceeds, while cloud cover drastically affects sky temperature. 3. Even an exposed primary that is allowed to exchange radiation with surrounding objects still takes hours to equilibrate to within a degree of ambient air temperature 4. The sky-facing parts and upper ends of metal telescope tubes tend to cool faster than ground-facing parts. 5. Reading thermograms like these is mistake-prone due to the effects of reflection, and really accurate work takes a lot more prep and planning than I had time for! 2019-02-11_MN86_cooldown.mp4
  5. tonyowens_uk

    Computer Suggestions

    Bear in mind we specced a 4K display and pretty powerful graphics card in that configuration which was targeted at large assembly solid modelling and mid-sized CFD models. Not everybody is h/w constrained as we sometimes are. We originally specced a 500 Gb SATA HDD for all local storage and used a mixture of Business Dropbox and a decent Synology NAS with RAID 5 to look after data. When we ran out of local storage we added a 2Tb SSD for a mixture of OS files and temp files generated during larger CFD and FEA sims. This made a noticeable difference to the performance of the machine. When we replace this system we will look at refurbished systems too, as Moore's Law has crashed and we will be looking for a faster memory bus and even more premium processors. This is also fair comment. This was my point about 'certified hardware'. For work onsite with clients we use Dell Precision M3800 machines with 15" 4k displays and a low end Nvidia graphics card. They cost around 2k new 4 years ago and have been very reliable for us and with i7 processor and 16Gb RAM and 1Gb SSD's surprisingly capable when asked to run medium sized models in our usual CFD code. The only thing I would change is the 4K display which proved to be too small to support a 4K display for many technical/scientiific programs. The M3800's replaced an indestructable Dell Precision M6400 'laptop' dating from 2008 which ran CAD applications offsite for us for many years without complaint. But the 5 kg weight became unacceptable eventually.
  6. tonyowens_uk

    Computer Suggestions

    I run a Dell Precision T7810 mini-tower workstation in our business for compute and graphics intensive work e.g. CFD/FEA structural engineering sims which we manage remotely via Teamviewer. We bought this new 3 years ago and its been very reliable and as a desktop easy to alter the configuration as needs change. We have mixed feelings about Dell Support (apart from the premium business support service the only other support is a call centre in India operating off defensively-engineered conversational scripts and of little practical help). The products themselves are fine. Pricing is less of an issue by buying Dell Refurbished kit which is often actually unused while UK/Ireland zone deliveries are fast. We configured this 8-core workstation with a reasonable 48Gb RAM and a mix of SSD and spinning storage and a fast CAD vendor-certified Nvidia graphics card. I believe at the time we paid 5-6k euros for that. Tony
  7. tonyowens_uk

    Whats your thoughts on this?

    I'm not surprised at the price. The main use for Accoya seems to be posh decking and outdoor furniture. It would be a Rolls Royce solution I suspect. I wonder what wood species and treatments are used for shingles and exterior wood products in residential construction in New England in the US and the East coast of Canada?
  8. tonyowens_uk

    Whats your thoughts on this?

    On the East coat of Ireland the weather is cold wet and windy for much of the year. Here in Wicklow no softwood timber structure tends to keep its strength much beyond 20 - 25 years in outdoors conditions. On the other hand the design integrity of most residential garden wooden structures in UK/Ireland zone is minimal, as is apparent from what passes for garden sheds. Now I'm a consulting engineer not an architect, but an architect friend of mine with environmental interests talks enthusiastically about the virtues of Accoya which is an acetylised softwood of great longevity and strength especially in outdoor applications. See here: http://www.timberireland.ie/accoya.html But its expensive and not available in convenient panel format. There is a gradual shift away from conventional EU building materials - steel and concrete - towards wood laminates due to environmental damage. Compressed laminated timber made from bonded pieces of Sitka spruce is starting to displace steel and ferro-concrete for trusses in large buildings and homes with complicated rooflines. Another low cost lightweight weatherproof approach is 'kingspan', i.e. phenolic foam sandwiches faced with thin sheets of steel or aluminium generally with plastic coating. An observatory might look like a factory built for Hobbits done this way, but from my layman's perspective I would have thought cost could be low and insulation and durability beyond reproach if an Accoya frame building were clad with aluminium-faced Kingspan panels. Hopefully some of the construction professional's reading this will correct me on this! Tony
  9. tonyowens_uk

    Carbon tube for 10" OO mirror

    That figure sounds fine to me Rob. Its easy to add a front baffle later to kill off-axis lighting during critical lunar imaging or similar. Tony
  10. tonyowens_uk

    Carbon tube for 10" OO mirror

    OK I see. Well there is no real rule for tube extension length beyond the focuser that I'm aware of apart from the matter of adequately baffling the background visible at the eyepiece around the secondary mirror. There are two extremes. 1. Dematerialised to just a potato chip-shaped flocked disk opposite the focuser like in many ultralight truss Dobs 2. At the other extreme (Intes Micro Mak-Newt's) it can be a set of close-pitched knife-edged baffle rings stationed along the tube directly opposite the focuser hole, and the provision of an external internally-baffled tube extension (dewcap/baffle tube) of around a 1.5 times the scope aperture. Your choice will reflect convenience, weight, hassle and the quality of baffling you need which depends on what you want to do with the scope! MN86 from Intes Micro. Note huge dewcap/baffle ...with internal knife edge baffles ...and yet more baffles behind the secondary. The scope is pointed a few degrees away from the Sun (light entering from the LHS) but the off-axis light is fairly well suppressed even thought this is a Newt This is the tube and optical layout for an unmodified MN86 Mak-Newt (no dewcap/baffle in the model). It is almost identical to an 8" F5.9 regular Newt in baffling and layout. Food for thought perhaps? Tony Owens
  11. tonyowens_uk

    Carbon tube for 10" OO mirror

    Robert re tube design and baffling see here: http://www.download82.com/download/windows/newt/ It gives internal baffles and their effects too. It does assume you have an accurate figure for the FL of the primary... Tony
  12. tonyowens_uk

    What was your first scope?

    After a year of nagging, my father travelled to Farringdon Road London and returned with one of these. Its a Fullerscopes 4" F10 Newt on a Mk II equatorial, mounted in a crude concrete pier in a 8' x 8' lathe and hardboard observatory with folding roof I built for it at age 15 or so. I was obsessed. I cast my own concrete counterweights to balance my crude SLR holder for afocal photography and was inspired by Sam Browne's 'All About Telesopes' to build a dodgy clock drive for the Mk II using a wooden lever-arm with a piece of hose clamp (worm wheel sector) and threaded rod. Needless to say in time I graduated as a mechanical engineer, became a research engineer then built my career in engineering R&D consulting. I know those cold Irish nights learning the sky with Norton's Star Atlas and dreaming up mechanical contrivances I could build with very limited resources and meeting other astro-nerds at Armagh Planetarium and at conferences in Dublin had a profound effect on my confidence as a designer and later on my career development. The 4" Newt is long gone alas as is a superb pair of 7 x 50 Pentax binoculars of that era whose aromatic grease and razor sharp images blew me away at the time. I dont clearly remember what 'lit the spark' re astronomy and telescope engineering for me. I know before I was 10 y/o I was hooked. I have no clear recollection how that came about. It is important to me to reconstruct what happened to me. One reason for this is that one of my children, now 15, super smart, has zero interest in the physical and the 'real' and none in astronomy. Another, 17, is emotionally moved by what I have shown her of the universe in much better scopes today than I had available back in my bucolic Irish childhood. But no obsession. What combination of nature and nurture, what refuge from commercial and social pressures allowed me and people like me to read about and get hooked on a 'hobby', that even 40-50 years later allows me to decompress almost entirely, yet is apparently not available to my own kids or to most teens and young adults? Where did the magic go? I can follow them into modern music and poetry, into internet-based business models and opportunities yet they cannot access the spiritual crutch that the sky and what lies beyond has been for me. I am searching for credible answers to this. So is the chairman of one of the better known astro equipment manufacturers who is appalled by the generational shift in interests as Alice, our offspring, has passed though the Looking Glass into a virtual internet world that is mutable and immaterial and insubstantial and utterly different to the world that sustained me as a teen!
  13. tonyowens_uk

    baader on ebay

    Perhaps Baader has discovered the darker arts in B to C marketing?
  14. tonyowens_uk

    "GinaRep Concorde" 3D Printer

    I note you have managed to move the motors out of the enclosure (box) Gina. Are you provisioning for a heated & ventilated build chamber as a later development? If so, while a wooden structure is not particularly good at insulating it is supremely good for rapid modification e.g. holes for lights viewing windows fans and cameras! I'll be interested to see how 'square' the XYZ linear axes turn out to be relative to the bed. What are you planning for the bed anyhow? Tony
  15. tonyowens_uk

    Mirror Cell question

    My suggestion would be to forget about making anything until you have a design. To have that, you need to start with some ideas about your goals. Is this primarily for looking through or for imaging? If its an imager, is it for hi-resolution lunar/planetary or widefield and optically-fast deepsky? Does it even need an eyepiece or can it be prime focus? Once that is clearer, you will need info about the mounting interfaces to bought-in parts like the hub of whatever mirror you want to use., before you can detail a design On occasion it is easiest just to buy the part and measure it. Some people like to use paper and pencil, some use 2D CAD, some use 3D CAD. Whatever works. But when you have a concept you a re happy with, prepare working drawings of the various bits to be made. Before laying out money for a set of waterjet-cut aluminium plates (or anything!) consider making a partial or complete mockup using furniture grade plywood which is easy to cut and modify and can be pinned screwed and glued easily. It is also a very decent natural composite that in many cases is as good as aluminium or CFRP depending on what you are trying to do. Stay away from heavy plates in your design. The goal should be to create a structure in which every piece of material is loaded in tension or compression, but not in bending. You also need to make sure that the various 'hardpoints' - places into which heavy loads are punched - are strong enough. I dont know how much research you have done already but lightweight telescope structures are an internet meme. There is a huge amount to be learned from the work of other people. Check out Martin Lewis at www.skyinspector.co.uk, Mel Bartels at www.bbastrodesigns.com/NewtDesigner.html Take your time and enjoy the journey! Tony

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