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Ajohn

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Everything posted by Ajohn

  1. I'm trying to figure out why you have the table and the head tilted Richard. My Raglan was the square headed one, not seen the round headed one before. As yours the width of the bed was a lot bigger than on myford 7's. The variable speed lever on them is nice - I tend to be Mr 600 RPM, even fitting carbide if things might get a bit hot. I'm aware of the inverter low speed problems. I do have a larger milling machine about but of the rising table type. No space available to use it and quill is fixed but it may be possible to fix that. My boxford came with gearbox and a lot of change wheels so I did a spread sheet and with some intuition found out what they can do especially metric but so far DP and modules has defeated me. One day I might find a screw cutting plate for one that could do them and would then have a good start. To be honest though I am toying with the idea of buying a small metric lathe for bits that need metric threads. OTT really as I can just fit change wheels but ........................ Ideally it would also be super precision and capable of very high speeds. Tough thing to find with screw cutting. Fairly easy without. Argggggggg I may finish up trying to make a high speed headstock that aligns to um to the bed for a small low speed lathe. Sounds fun but I have several things to do. Being fair to Myford I have come across several people who enjoy using ML10's and Speed 10's. Once again they aren't as they should be really. There should be a slot down the middle of the bed to align the tailstock and head. That way it can have a long saddle as all decent lathes have - the ends can pass the tail stock and headstock. This model has a dovetail bed so wear can cause more problems. Headstock bearing problems are fairly easy to fix as it uses taper rollers so there will also be adjustment. I have 2 dividing heads - very part made one from a kit that can divide analogue fashion to 1/100 of a degree or be used in the normal fashion with index plates. As the miller came with one also made from a kit it hasn't been finished. Really the only parts that need to be bought are the worms and wheels. A small old lathe tailstock or block of what ever can be used for the body. It's even possible to make them on a lathe. That is why most of the kits aim to have the spindle centre height the same as the lathe. People just pack up designs intended for Myford 7's. Some have used stepper motors to drive them but this really needs a precision stepper. It's possible to make all sorts of expensive tooling relatively cheaply and there is plenty of information around to help people along. One trick that isn't mentioned very often is that on some lathes it's fairly easy to convert the compound slide to a vertical slide - a part people often lust over as it allows them to mill on the lathe. Ease depends on how it is held in place. John -
  2. Personally I would use low side switching for this anyway. 2 reasons really. Lower on resistance is readily available and easier to switch rapidly from one state to another and also the fact that all of us have 3 core cable all over the place carrying earth, neutral and live 240v AC which seldom causes problems, if cable frays we see it and replace or throw it away. If I was concerned I would just fit a fuse. If I was using a battery source there would most definitely be a fuse associated with that anyway, right at the battery. The gear on a telescope is usually run at something like 12v dc which has no where near as many problems as the mains does and actual earth doesn't have to have anything to do with it. 0 volt is not earth. I would be more concerned about the cable to the dew heater being up to the job current wise. For short runs like that a mains cable rating should be more than adequate and have a lot more insulation than it really needs. If that type of cable can't be found with a suitable rating cheaper heavy duty speaker cable could be a suitable alternative, no need for gold plating. Automotive applications are a bit different because the chassis of the car forms one of the conductors and there is plenty of opportunity for cable running through bulk heads etc to chaff and cause a short. They fit fuses anyway and also use high side drivers because the part being driven is often some way from the switch itself which is likely to be in some ECU somewhere on the vehicle. John -
  3. Just in case some one wants to do this sort of thing thoroughly. The maximum current level is needed in order to answer the question. Taking the IR3315 for instance that will be sort of ok with 2.8 amps continuous without a heat sink. You need to consider when the unit is first turned on. Mount it on a 60C / watt heatsink and even at automotive ratings it will be happy with 3.9 amps. Automotive ratings are at 85C ambient. Yours will probably be lower and there should be enough info in the data sheer to work this area out if needed. It's a simple calculation , say the 60C / watt was changed to 120C. The temperature rise would double and the device would go pop some where around when it reached 125C. If changed to 30C/watt the temperature increase would halve. Sums are done by adding the numbers up starting from the junction to tab figure and adding a bit for an insulator, then the value for the heat sink. 2 other aspects complicate this area. As the device gets hotter the resistance increases which makes the dissipation higher. This can result in thermal run away. The answer to this is to look at the curves and make some assumptions before doing the above sums. The other aspect is switching on and off. This often dissipates more power than when the are on continuously if the rate is high enough. This is why IR mention a 1msec min pulse at a rate of 200hz under automotive conditions. They show a graph of the transient thermal resistance for sorting that aspect out if needed but it doesn't seem to account for repetition rates. I've been away from this sort of thing for some time now. There is probably application data around and also I would suspect a Spice model for sorting this sort of thing out under simulation. There is an interesting simulation package here called electronic work bench. http://sine.ni.com/nips/cds/view/p/lang/en/nid/202311 It has oscilloscopes, power supplies and meters etc so is pretty intuitive to use. No idea of prices or if it has a thermometer but sometimes copies of it and similar packages crop up on ebay, even official ones. It really should have some form of temperature measurement as it's a rather thorny area when power circuits are designed. There may also be an open source etc simulation package around. John -
  4. I suspect it would be worse if you lived in Germany. I just couldn't believe my eyes when I eventually found the translation for a left hand tap - tap, in English can mean a number of things, in this case a thing to produce threads in holes to accept screws etc. Threads itself can mean different things. Worse still it had to be a left hand one. No translation tool helped me. I'd guess one might with terms as simple as metal and maybe ferrous, how none is added to that is likely to vary from one place to another and there might be a specific word. John -
  5. When I suggested B&Q I didn't notice Netherlands but maybe they or similar outlets are there too. Most "metal" suppliers will cut it to what is required and sell to anybody without any problem. There are some large scale suppliers who will also cut to suite. I just go there and ask for what I want. Probably the easiest way to find ones that are local is to google things like what area you are in plus the word metal, none ferrous or what ever. Stainless steel will usually come up with pots and pans etc but none ferrous supplier and the others will also often stock it. Best ask for free cutting - the other type can be a pain to do anything with. The free cutting ones will generally be slightly magnetic. Free cutting mild steel is easier to cut with a decent finish as well but the bright drawn variety that is about now isn't so nice as good old fashion black bar. It tends to have a tough skin. Suppliers quality varies in this respect too or did. Since things went "standard" that's probably not so common now. John -
  6. Some use steel tape or pieces of a steel rule, strips of the same or aluminium. You will probably find some suitable metal strip in B&Q warehouse outlets if all else fails. John -
  7. A pointless comment really RAC from Nick. No doubt Mr Dob doesn't both collimating the scope before he does it so then it is simpler but still not a reliable way of checking a mirrors figure. Any form of testing needs some form of collimation. I use Mr Dob's method to check any scope I buy - high magnification so that I can see diffraction rings. John -
  8. If you do use Faucault Damian not squaring up the tester to the mirror can cause some confusion. Vertical comes first. If the source was dead on axis the mirror would throw an image exactly back onto it. Pity a knife can't be used then. You seem to using a vertical knife 1/2 over source and below it set up so the source needed to be slightly above centre and the reflection down below it onto the knife. The return beam can be caught on a piece of card and this sorted out. You should try and keep the separation from the source as small as you can. I'd get them vertically aligned as well. Then comes axial alignment. You may be able to do that at least roughly with the same set up. Perhaps a more usual method is to watch to see that shadows in a mask or between pins change equally side to side across the mirror as the stage goes back and forth. Some people use an x-y stage so that at least initially until things get really close they can align it every time a separate reading is taken. That alignment is easier with a stationary source. Actually I wonder just how much this area can give odd effects with a ronchi screen. Uncle Mel reckons that radial measurements can be taken by looking for a constant line width. So say you get one size at the centre and then move the tester it's now on the radius of the area of the mirror that has the same line width. I don't think anyone really reckons that this is a good way of measuring a mirror but when I look at the shots posted I wonder about some of the changes. Pass really as I just knocked one up and played with it but only on a sphere and I found other methods were a lot better but in some ways tied up to a fixed source tester. Not the knife exactly on centre though but I feel that may be hard to call unless it's pretty close to a sphere and it takes an incredibly fine adjustment even then with a slit anyway, 40um slit means the image is that size too so the knife has to be put 1/2 way through it or there abouts. As mentioned earlier - there doesn't seem to be much about on lining up a moving source tester. I maybe initially people could locate the tester on a pin at the back and swing it slightly if needed as readings are taken. Accuracy. People have made mirrors of all shapes and sizes using Faucault and other checks have found them to be equally as good. Even some famous ones later finally checked with a Hartmann test. One of the major catches as I see it is R. That needs measuring well enough to make the error insignificant. Easy to check with say fringexp. Bigger mirrors in some respects help and faster F ratio's make things worse. Another which might be significant on some mirrors is the formulae used - it's part of a series. Another term may be needed on some. There are some ideas about on maximum separation between knife and source as well. Pass, just seen and forgotten. John -
  9. The big difference to a dob really is that they are all equ mounted and no flip problems like a german mount. I'd agree about the dob and alt az other than smaller scopes which can finish up too low so need a stand - for me anyway. There are some photo's taken using that style of mount about on the site. Seems it's sized to give 2 hrs of guiding and easy to reset. It looks like the steel tape and smooth sector to me. There are separate detail on that elsewhere on the sites. Mirror 1st. That way you can design the sizes to suite. I'm not a fan of mig. I've hammered away at it and found that it wasn't really welded, thin sheet - some one else's to. Never had that happen with stick and have for instance welded the floor back in a 911 proving you can weld rust after a fashion. I'd guess stitching aluminium with a tig welder wouldn't be too bad with some practice, seam welding it via fusing it is tricky. I've never tried mig on aluminium and didn't even know it was possible. I have done a bit of stainless. Maybe I shouldn't sell my mig. I am intending to and probably wont change my mind. I found the site I posted via this one some how http://www.astrosurf.com/astroptics/index.html John -
  10. Oddly that's what I have decided to go for. F5 should give good wide field results with a coma corrector and also hopefully wont push eye pieces needs too far and 10in makes a fairly compact scope for equ mounting. John -
  11. I'm pretty sure they are made of timber. There are plans of some of them about on the site or off one of the links. One is timber with aluminium bearings. This one for instance. CTBX 15 seems to be 15mm marine ply http://serge.bertorello.free.fr/details/sirius/sirius-fourche.html I fabricated a dob tube in the same way they seem to in 1/4" exterior ply. Hexagonal though and I suspect octagonal would be a better option. I just carefully set up a jig saw at the right angle and used a length of wood as a straight edge - checked by eye. It worked better than I expected. I just glued the edges together and expected to have to add some fillets but it worked fine without. Very well damped and no problems with tube currents. I tried tig welding 1/4 plate once just fusing the edges using industrial gear - it's not easy. I used to hide behind the welding curtains for the odd 1/4 hr when no one was looking at work. As I have had an interest in this area asking around some one told me that Machine Mart do a range of welders but the smaller one doesn't come with TIG gear but will work with it. Meant to mention there is an excellent design for sector drive on there. It pulls steel tape round the sector, no problems with friction drives slipping etc. John -
  12. Googling "canon camera hacks error "code 30" " comes up with a suggestion that it's a jammed shutter - they might detect that via movement or the current drawn when a shot is taken - pass. The shutter parts are often called curtains, 1st and 2nd. Fast exposures are taken by one following the other with the gap setting the exposure. Some time ago one of these curtains went electronic. When a camera is in live view mode both are effectively electronic. On mirrorless cameras they are always electronic. Just a note on screwdrivers. If you find that a Philips screw driver doesn't fit the screws perfectly and it can rotate or even rock a little when it's in the screw they are probably JIS. This is a modified Philips head with reduced cam out. Not sure on cameras but with the tightness of some screws in things like microscopes they are essential. Mine came in a set of 3 from a place like this link and are branded Hozon. The rather large middle sized one with a 5mm dia shaft tends to fit all screws what ever size they are. I've yet to find a use for the smaller 4mm dia shaft or the larger 5.5mm one. They were cheap but I had to spend some time looking around for them - most showed out of stock. They are used on motorbikes, model aircraft and model helicopters. http://www.probuild-uk.co.uk/aircraft-division/tools/screwdriver-sets/jis-screwdriver-set.html John -
  13. This link should give you some posts to look at and more information on them http://stargazerslounge.com/index.php?app=core&module=search&section=search&do=search&fromsearch=1 On the other hand it doesn't seem to have the search terms so - go to search, top right of the page, click the gear symbol, enter barn door in the search term and diy astronomy in the forum section. John -
  14. If some one doesn't want to spend much it should be worth trying this company - same applies to all of the things they sell. They try hard at the cheaper end. http://www.arceurotrade.co.uk/Catalogue/Measurement As usual I have nothing to do with them but they are pretty well known amongst home and small business machinists in the UK. John -
  15. Posting in part because people might not be aware of this site and there is a lot of information about on it. This is but one example - fork mounted equatorial newtonian, fork made of timber - hollow. I understand the same idea has been used up to 400mm and it would be easy to lighten it these days but sizes indicate Texereau style rigidity and even full thickness mirrors. http://amas.free.fr/?page=instruments/pegase/pegase Found by following links from this page http://serge.bertorello.free.fr/index.html There are some technical pages on various things that have been translated to English but there is far more in French. If feel that they are often a lot better than similar ideas and information from elsewhere. John -
  16. The best option is 2 identical achromat for a plossl. Choose any that according to the calculator give a focal length that interests you. It can take a while to find lenses that are stocked in the UK but it can be done with google and I am not sure what is available. You will probably find that the real optical component suppliers work out too expensive. As an example astromedia show an 18mm dia lens with a focal length of 26.5mm, according to the calculator that will give a focal length of 15mm. They also show an 18mm dia with focal length of 39.5mm which will give 21mm. There is also a 26mm dia 99.6mm focal length which should give about 51mm. IRPoiser on the web sells other sizes but frankly I feel he is too expensive at £15 each really. SurplusShed have all sorts of things kicking around including lens kits for eyepieces. Personally I would stay away from 3 or more element designs unless the lenses come from people like that. It's hard to be sure that they will work just picking lenses at random. There is a much bigger variety of lenses available in the USA cheaply including on their ebay. SurplusShed even sell precision achromats cheaply but providing that they are normal types the ordinary ones should give satisfactory results. When I was interested in this sort of thing I didn't have a lathe at home so as I had an 8in SCT and wanted a very long focal length eyepiece for it I asked Poiser to make it for me. Focal length something over 3in and a massive exit pupil. I've since found on a much smaller scope that as the mag gets lower and lower a hole may appear in the centre of the view. Not sure why but think it's down to it being a very short scope. In terms of making though I happened on a lens suitable for a rather large finder so at some point will be making an eyepiece to go with it. It will also use a normal diagonal so that it can be used as a guide scope. John -
  17. Better to clean the anvils of either with a bit of paper - that way the zero on digital callipers will remain correct. The easiest way is to close them fairly firmly on a bit of printer or writing paper and pull it out / move it about. Not so important when measuring diameters as the contact area is small so pressures are high but it can still make a difference - it will make a difference when the anvils are bought together because of the area and same when measuring across flat surfaces. John -
  18. If some one wants to measure bores with some accuracy the cheapest option is telescopic guages. There is a technique to using them. Let them spring open in the bore at a slight angle, clamp them lightly and then swing past the actual diameter point, clamp fully, then check that they really are on the diameter. There should be definite resistance as they are tilted through the actual diameter. Then measure the gauge itself . Might not make much sense until some one has a set in their hands. Unfortunately bore micrometers can be expensive, especially the type that centre on the bore automatically. Digital callipers can be useful for metric imperial conversions - they do get the right. Personally as far as machines go I have stuck to imperial. Reasons relate to Henry's thumb again as surprising as that might sound - accuracy. John -
  19. You could make some eyepieces. Plossl's a pretty easy and can be rather high quality. Only problem with them really is that eye relief is low at very short focal lengths. There is one way of doing that shown here along with a focal length calculator http://www.astronomyboy.com/eyepieces/index.html Some suitable lenses are available here http://www.astromediashop.co.uk/Components.html Plossl's are just two decent quality achromatic lenses arranged together as shown. You might find other sources of suitable lenses, ebay, google cardboard suppliers etc. Items can be bought from SurplusShed in the USA. No tax providing total value is less than £15. I sometimes ask them to split orders into 2 to get round that. The tax we have to pay is one thing but the charge for collecting it is rather excessive on low value items, it can be over £10. The longer focal length 50mm lens astromedia sell should make a decent finder. Also the 40mm. Magnification, just in case you don't know is focal length of objective / focal length of the eyepiece. The exit pupil, the size of the beam out of an eyepiece that needs to go into the eye is diameter of objective / magnification. A limit is usually set at about 6mm for that in dark sites maybe 4 if there is low level light about. In practice there isn't much harm having one that is too big to pass through the eye's pupil because the head can be moved around to take in all of the view. Actually I use one like that on a telescope at times - lots of contrast but I can't take in all of the view in one go. A small newtonian finder maybe - pass, not sure how well it would work out but they do have suitable mirrors even though the 2ndry would be oblong. There are other sources of eyepieces. Some loupes use a 3 element lens and are well corrected. That type usually folds out of a metal cover. Their focal length is 250mm / magnification. Some eyepiece designs you come up with might have problems near the edge of the field because they need a field stop - a disk with a hole in located on their focal plain. Astromedia do a number of kits often making things out of cardboard. Could be converted to reprap or even metal. Any parts in them will still be useful in some cases. Some people have made their own equatorial head. One method is in a recent post on here. Another is to use heavy large pipe and fittings using the sort of pipe that they run around factories and probably some schools too. There are designs about on the web. If you want to make something the best idea is to try and find some way of making items you want or need. John -
  20. There is always this sort of option - with a smile on my face of course but they can be made. Many of the designs out there are too complicated. They can be made completely adjustable. John -
  21. Fag packet - encouraging a bad habit. I smoke a few roll ups as I can't inhale them. When I read that I thought why not use shim - various thinknesses of either brass,steel,stainless or even plastic these days. Then looked on ebay - ouch price wise much to my amazement but I suspect real suppliers would be cheaper. On the other hand I found ebay 201230882069. I needed shim some time ago so have plenty and it was cheap. Brass shim can be cut with scissors up to maybe 1mm but will bend. Steel can be too but much thinner, B&Q do some fairly cheap metal shears. Never used plastic shim so no warrantee claims but given where it's sold from that pack will very probably be ok. John -
  22. I'd hope that an eq4 would cope with a scope like that but best let some one else comment. Frankly I feel some of the mounts shouldn't be available but scopes tend to be sold at various budget levels rather than on the base of usability - that applies to bigger ones too really. If you build a dob I suspect you will want to put it on some sort of stand to raise it up some what as it may be rather low to use. Personally I am not too thrilled with dobs for higher magnification use. To me an equ mount with a star drive is not all that far off essential and the equ aspect a lot more so. The latitude can be set by eye on the scale, levelled, pointed north and the whole thing swung round or the adjustment used until it tracks to an acceptable level for visual use. People with dobs often get interested in equatorial platforms for them at some point. There main gain really is in the bigger and bigger mirror area but there are complications such as the one I just mentioned. It's worth having a look what is around on here, this one for instance http://www.astrobuysell.com/uk/propview.php?view=96856 Earlier versions of the GP-DX's crop up as well. People used to put F6 10in newtonians and bigger on those along with a short tripod or pier - well past what they were intended for really. There is also a goto version about. It's a bit noisy - stepper motor ticks and all bronze gears - but easy to use. A lot of the shake you have is probably down to the tripod. It usually is. There is a thread on here on making timber ones. I think Beconhill sell some tripods but you would probably need an adapter. I recollect seeing the Tal wooden tripod offered there but don't know how good it is. Actually there are several good rigid older mounts such as the meade LXD 650 and 750, both usually goto but I have never seen one for sale. Also the one that they used on the cardboard tubed newtonians - it was even used on 16in scopes. I've looked at several of the 1/2 fork mounts that are about. Mixed feelings personally and in any case probably not up to your length of scope. There are a lot of alternatives but the need for a decent mount eventually crops up with most people. John -
  23. I have tried several but eventually bought Mitutiyo 200mm ones. The extra length is useful and the battery life is a lot better than some I have had. In real terms though they don't compete with a mic if very accurate reliable measurement is needed. I find digital mics a bit heavy and cumbersome compared with the normal ones. It's probably down to making them try to read accurately to 1 um but in practice that level of accuracy is a bit of a joke. I've always found it fascinating that 1/10,000 of the supposedly width of king henry's thumb turned out to be a practical unit that can be measured with relatively simple gear. The mm doesn't fair so well. Some one with eye problems with normal mic's etc might find a simple credit card size fresnel magnifier useful. John -
  24. Might be a bit late but Beacon Hill provide what I feel is a better range of abrasives than Galvoptics. They are perhaps a bit over the top on the finer grades. As a company they have been around for a very long time too. http://beaconhilltelescopes.org.uk/ Strange site - it's looked like that since they went on the web. Maybe it's "if it isn't broke don't fix it". I tried to link to the correct page, just hit continue and then prices to see what they have. If anyone wants to follow the old worm wheel should match the diameter of the scope this is probably the only place to go - up to 14in. The matching tool with the blanks may be thinner. If concerned ask. This comes from early suppliers. For 8in the actual blank would be around 30 -35mm thick and the tool 25, sometimes with raw edges rather than ground. John -
  25. Good some one did answer - I ate dinner mid way through. One thing I meant to mention see what Beacon Hill have. I think they still do mirror blanks and grinding materials etc. There is also that German supplier I linked to. His prices aren't too bad for what he offers. John -
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