Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.



  • Content Count

  • Joined

  • Last visited

Everything posted by Ajohn

  1. This question relates to an EQ3 Pro Synscan but probably relates to all Synscan mounts. I had the impression that they all started by putting the peg on the tripod north and levelling it, aligning one way or the other and pointing the scope roughly at polaris then going through the goto alignment routine. I'm not sure if I have the correct manual. The mount I have bought suggests otherwise some one has put alignment marks on that suggest that the scope is pointing east or west, rather roughly as the scope wouldn't be horizontal. This leaves me wondering if there is some way of persuading it to work that way? It is has some advantages, Suppose some might wonder what advantages. So When I mount a telescope on this type of mount I always turn the mounting plate so that it is more or less horizontal with the clamp screws pointing upwards. That way it's easy to get the scope in and it's relatively safe even with the clamp a little loose to allow it to be balanced. It seems a little silly to then have to swing it up to point at Polaris. Worse still it's dead easy to set the scope level in this position with a spirit level. As the scope is a lot easier to sight along than the mount it's also easy to align it east west with a compass which in turn will align the mount to the north. It's even possible to roughly estimate true north. Eg where I am at the moment true north is 1 1/2 degrees off magnetic. At another site I observe from it's 2 1/2 degrees. The spirit level is likely to set the scope horizontal to better than that. I have used mounts that align like this and it can be surprisingly accurate so wonder why on earth any one produces scopes that have to be set up differently. John -
  2. You could try phoning Celestron UK. They do carry some spares or maybe be able to get the smaller parts. Personally if replacing myself I would replace any plastic gears with brass ones if I could. There are details on the web concerning gear design. These can allow people to measure the gear, count the teeth and determine what the pitch is. There are some pretty simple rules for that. John -
  3. Skywatcher seems to have the dropped the EQ3 Pro Synscan from their web site, mentioning 7 goto mounts but showing less. There are plenty of adds about though eg http://www.firstlightoptics.com/skywatcher-mounts/skywatcher-eq3-pro-synscan-goto.html Odd just found the page on their web site http://www.opticalvision.co.uk/astronomical_accessories-telescope_mountings/eq3_pro_synscan.html Interesting to note that the motor control seems to be for a tubular tripod. As the firmware was not up to date the seller swapped the handset from the one for an EQ6. I wonder if both of these parts are common. What would be really interesting is if people measured the size of the steppers used on the pro range. The EQ3 pro uses one which is 35mm square by just over 30mm long - the actual motor neglecting what is on the end. I don't know how old this head is but it clearly needs the gears cleaning and the grease replacing. John -
  4. Some people have made them out of inkjet cartridges - hasn't worked out on the ones I have looked at - no signs of a hole. Maybe they or it were blocked. If people want to get light down a fibre optic more will come out if they drill down into the LED as close as they dare to the chip, add some oil and then put the fibre in. Bit like oiled objectives not needing to be polished as the oil nulls the surfaces out. Personally I think a ball bearing is best. It's even possible to view diffraction rings off them if they are small. Only problem on say a SCT is it's best to have the scope pointing up rather than horizontal as there may be a tiny bit of mirror tip. John -
  5. Interesting that this thread popped up recently - or maybe I didn't notice it before. When reading this do bear in mind that I do have a far more robust mounts. I just bought an EQ3 Pro Syncan on an EQ5 stand. Used. I mostly want to use it with an Orion 150mm F5 newtonian so took that with me. I would say it's a pretty comfortable stand with that on it. The speed it damped out at actually surprised me. Unfortunately there wasn't enough light to try it with a 3mm eyepiece and 2x Barlow but if I had much doubt about that I wouldn't have bought it. There was scarcely enough light to use 3mm other than getting a feel for the amount of shake when focusing manually and tapped firmly. Skywatcher claim that this mount offers the same sort of tracking abilities as the synscan on the other pro mounts. I'd say with this particular scope that it does stand a chance of taking decent photo's but auto guiding would be a good idea - as it is with just about any mount. Motors pass but I have noticed from a quick look that the upgrade kits seem to cost very similar amounts which ever one they are for. Fix - Auto guiding again. Personally I wouldn't buy an synscan upgrade kit for an EQ3 as it should be possible to buy a used mount for less / a similar amount of money. In fact the whole mount doesn't cost much more. Mount £379, kit £300 I think, maybe less according to the supplier. I don'r rate the style of tripod supplied with these mounts at all. Junk springs to mind unless it's very light loaded. People would be better off making a wooden one. I wont be selling my Vixen GPDX though or the heavy one. Astro photography - all sorts of things are possible - this one for instance 3 sec subs on a fork mounted lx90 on it's alt az stand and no guiding. http://www.astrobin.com/229615/B/ Astrobin seems to be very very slow today. I had to hit reload 3 times before it came up to check the link and even longer for the comments to pop up. Camera lenses can be very interesting too. Pretty pictures can be obtained without supa dupa optics. Modern cameras are way more sensitive than out eyes so very short exposures can be feasible. My AP experience - zero except on film but I do take notice of what others achieve as long as I know that the results aren't faked. They might be on that astrobin shot but the numbers and results do make sense. Plus the size of the image of course. John -
  6. Gunson have made an automatic batter charger with a float setting for permanent connection for a long long time. It works rather well. John -
  7. I don't find the zeq25gt too bad really other than it being different especially in terms of no clutches of the usual type and their style of alignment. I'm not convinced about the weight limits they quote but it does need very careful scope balancing and setting of the worm to wheel engagement. There is plenty of info about on the web concerning adjusting them - as there is on other mounts. The crazy aspect as I see it is not selling it with the 2" tripod as standard but it does seem to be fairly rigid. My only beef with it really is alignment. The options aren't as flexible as others and ideally I need that flexibility which is why I wonder about resurrecting a vixen gpdx. As to capacity I quickly mounted around 5kg+ of 150mm Newtonian on it to test terrestrially and didn't have any problem manually focusing cleanly at 500x. The scope wouldn't have been well balanced. I've tried various methods of obtaining a light weight mount and would say for it's weight that is pretty good. Better than pretty good really. It would be a lot better with a shorter scope. I was using it at F10 via a heavy 2" barlow. I've seen comments that an EQ6 is a mount for life. Mine is an elderly Meade goto that Astrophysics used to rebadge and rework a little. People need to realise what they are buying when choosing mounts and lightness does have it's penalties. I didn't buy mine until I had seen AP results from it from an owner. There is another source of info in that area https://www.astrobin.com/gear/15441/ioptron-zeq25gt/ 12kg though. I suspect that may be possible with a rather short scope - compound in other words. John -
  8. This might well interest me in the future. Thanks for the work. There is a source of large diameter worms and wheels in the uk and in some ways making the rest of a mount isn't that hard. I'm getting a little sick of what can be bought. John -
  9. I keep looking for a lighter mount than an old meade I use for heavier things but have a Vixen GPDX with Skysensor 2k on it, It hasn't seen much use because of the noise when it's tracking. Very loud on quiet nights easily heard yards and yards away - or should I say metres. That wouldn't make much difference. I might even say 10's of either. I'm not so concerned about slewing. I've noticed that these can be fitted with Skywatcher upgrade kits but which one? They offer the pro and none pro and just to confuse things sell a pro eq3 which I would assume uses the EQ5 pro upgrade parts. There is only around £30 difference in price between all of the upgrades from a quick look. I have wondered if the Vixen drive is so noisy because of the way that they drive the steppers but then have to ask if any of the Skywatchers are quiet. Same sort of gearing so no real reason other than drive why they should be. The other aspect is that the mount already has two perfectly adequate stepper motors. I can use a soldering iron so wonder if there are any other alternative that would involve using them - especially if it keeps the price down. Any ideas would be appreciated plus answers to the query concerning the upgrades. These mounts have traditionally carried a lot more weight than they were intended for so retaining motors is some what attractive but EQ5's ones may be similar or maybe the same motors are fitted on both EQ5's and EQ3's. I think the EQ6 upgrade is the same price as well. John -
  10. I'd avoid de ionised water but it probably depends on the degree. I used to work in a place with lots of industrial chemists around and also a large laboratory with an analytic chemist in it, Every time I went in there the distiller was running producing double distilled water. They also had a real de ioniser so I asked why they didn't just use that so they showed me. He ran some off and stuck some litmus paper in it. It went rather acidic very quickly. CO2 being taken out of the air. He then poured some distilled water out and tested that and it was more or less neutral. Basically he said that de ionised water was too reactive with all sorts of things to use for his tests. He even included taking mercury out of peoples fillings if they were stupid enough to make their coffee with it - pass but apparently some had done that and suffered as a result. Talking to another chemist later he explained in a different way. Water is rather corrosive in and odd sort of way and will dissolve small quantities of all sorts of things and just doesn't like being fully de ionised so is even more "corrosive" and there is no saying what it might take up. He also pointed out that this characteristic - the ability to dissolve tiny amounts of all sorts of things is what basically makes life possible. It also capable of dissolving small quantities of things that may do us harm - lead water pipes for instance. This was with a resin deioniser though. The membrane types may not be as bad. depending on what is actually in it. Osmosis is sometimes used for large scale. I did keep discus some years ago and used a small none resin deioniser to fill the tanks. It took ages. The water generally went acidic but more neutral after things were put in to harden it a little. Some breeders will admit that the water they keep the fish in doesn't do them much good. Me well I will just buy distilled. It isn't that expensive. Labs use a detergent to clean glass ware and wouldn't be very happy if it left traces behind but they do rinse with distilled usually before use if critical. Tepol is popular. They seem to have branched out into several areas so it looks like Tepol L is the correct one. It can be bought mail order. I used to be able to get small quantities for free but it's all gone now. It can also be used as a wetting agent. John -
  11. That is a big catch with alcohol solvents and those in general - they evaporate and leave some of what was removed behind. In fact I get the impression that IPA may sometimes have something a bit oily in it. Hydrofluoric acid - well I can read what is written on the side of bottles and have cleaned lots and lots of optics of varying sorts but not reflecting telescopes so I just used my loaf - an expression we sometimes use over here. Actually I don't think ammonia in it would cause me much concern but if any one does anything like this there is obviously a need to try a small area. I once tried to clean a mirror in a variable magnifying head for a microscope and found it was uncoated - impossible job. Some people on a forum who lived in the USA laughed when I moaned about the lack of coating and pointed out that the part had been made there and not in Japan as the rest of the scope was. They over coat all mirrors so that they can be cleaned. The best way I have heard of cleaning really dirty mirror say caked in dust is to put it under the shower set at a tepid temperature. I sold one once like that very cheaply and the buyer took great glee in telling me how he cleaned it. I though he would have to have it recoated. Extreme but worth trying if needed. I believe most if not all telescope mirrors are over coated with something - silicone dioxide at least if I remember correctly. Very high end might even use quartz. I have a flat mirror coated with that out of an industrial shadow graph. Even sulphuric wont shift it - I wanted to use it as a mirror blank I have wondered about Alan's soap and water but am always concerned about the additives in soaps but a mirror needs to be shiny. Pure soft soap seems to be thin on the ground. Smoking - no. Afraid I do that and it has never had that effect but I don't leave scopes just lying around. All in boxes or cases as are any bits and pieces. The mirror was literally a bit greasy anyway. It could be easily smeared with a finger. That's why I wondered about anti fogging compounds, Maybe it was steam etc from cooking but there is a cap for each end. The LX90 had been stored in a steel cabinet in a garage. Way more of what ever it was than I would expect from paint drying but an interesting idea. Anyway it's good that they can be cleaned but the torch test shows that they don't do an incredible job of polishing the corrector - Texereau would have a fit but given the errors the ripple could introduce it doesn't really matter anyway. It's just noticeable due to the coating and the torch being held at various angles. Meade do warn about using this test so don't confuse this with grease etc. John -
  12. Yes I suppose it does sound gung ho. Window cleaner in spray bottles is the mix you mention probably with slightly more detergent. I used clear. Some are blue which might mean they use meths rather than ipa as that type of alcohol has to be dyed. Pure ethanol might be better but can't easily be obtained in the uk I carefully tested the coatings on the mirror as I have come across uncoated ones. In some cases the reflective coating on these is actually silver which has to be over coated again so that it doesn't tarnish. So called enhanced high reflectance mirrors. I am not sure what Orion used so was even more careful. I have also cleaned a Meade diagonal in a similar but some what drier way without problem. What must be avoided is rubbing dust around on either as that may well scratch. It's also a good idea to clean very wet and lightly to be sure when that is possible - it probably isn't on an APO or refractor etc as it may get into the cell or even between the elements. Very wet is why I used window cleaner first. I have used it many times on microscope optics and know of one famous pro that never uses anything else for those. I do have a small bottle of specialised cleaner that should be used on these - triple distilled water and a wetting agent and nothing else. Meade suggest making your own and using biodegradable dish washer liquid as a wetting agent. I couldn't find any so have recently bought some photographic wetting agent. Very very little of either is needed. Maybe a few DROPS per ltr. However having said all of this it wouldn't be a good idea to clean optics often. Only if it is really needed. I am at a loss in that respect and have no idea how they accumulated so much muck. None of my own scopes ever have. Perhaps it's from where they were stored - regularly dewing up internally is the only thing I can think of. Just in case some one tried this and thinks de ionised water - don't. It's strange stuff and doesn't like being that pure. Distilled is more stable. John -
  13. I recently bought a used Meade 8" LX90. I tried it terrestrially at silly magnifications and wasn't that impressed. Good but hoped for better then I looked at the glass with a torch and thought oh dear. After cleaning using window cleaner for volume and then what Meade recommend which is basically the same thing I tried it again and found I could now get a good clean focus with a 3mm eyepiece. The corrector and mirror were coated in something almost greasy leaving me wondering if a new fashion had started - using anti fogging agents on telescopes. Not sure how old the scope is. Could be US, China or Mexico made. I think they did make early ones on the goto alt ax fork mount in the US. Feeling Xmassy I noticed a used 6" 1/10 wave Orion Newtonian for sale so bought that and probably paid too much for it as the finder was removed. 2 years old and following a check the mirror was much the same as the SCT so cleaned this too. No test certificate so I wanted to get the mirror out anyway to check the engravings. That focuses cleanly with a 2x barlow and the 3mm eyepiece, little iffy but the collimation is out - just set with a laser gizmo. An eyepiece less optics showed how much it was out easily. I have a collimating eyepiece on order as mine went years ago. Neither scope showed spotting from dew so I wonder where the muck comes from and thought the subject might be of general interest. Bought because of interest in using cameras rather than aperture for a better view and ease of moving about. A lot to sort out. Sort of thing that should be started at the start of summer really. John -
  14. This one is a bit "big" but the site may have some useful ideas. In French so needs a browser that can translate http://www.astrosurf.com/durey/telescope.html There may be others about via links from this site http://serge.bertorello.free.fr/telescopes.html Some of the mounts shown there make me wonder about thin mirrors and maybe putting a counterweight on the end of the scope so it can be fork mounted instead of having the usual wobbly thing on the end of a projecting shaft and the scope hanging on the opposite side. Just the right thing to help it all shake about. There is also a construction articles on a REALLY big dob. John -
  15. Maybe it would be worth stressing that style of testing a bit more and using it right from the start and forgetting Ronchi all together. From my own experience knife edge testing didn't come that easily but as that is all I used on my first mirror I soon got the hang of it. My results got more consistent as time went on so in the end I did have confidence in the results. Even so I finally checked it several other ways. I even knocked up a Ronchi screen as at the time I couldn't get my hands on one. It can be done with fine wire. Can't say I was impressed and can well understand why RAC uses it for initial work making sure he doesn't over correct. I would be inclined to ask people just how skilled they think they are to make effective use of it to that level. I'd be inclined to think it will take a lot of practice - far more than people are likely to have on their 1st mirror. The thing I found interesting on my first is just how long I spent chasing those last few fractions of a wave. Useful really because it gave me some idea of what strokes do and how quickly. A personal view is that I'm pretty sure people would find testing with a knife edge easier if they build in a simple method of changing the size of the source on their tester. That could just be something in front of the LED or what ever with a drilled hole in it. These old 'farts that used pin holes or slits to gain more light might not be as mad as some might think, just from thinking about what is going on when a knife edge is used especially with a mask. Tiny holes will generate strong bright diffraction rings around the holes in the mask or even around pins across the mirror but they also give sharper cut off points at the knife so what is the balance ? I'm probably wasting my time mentioning this but it is worth thinking about. One of the problems with the mask shown earlier is that it will show up mirror sag so it's not so popular as it has been with a few due to the use of thinner and thinner mirrors. John -
  16. I've not tried to do this but have a feeling that the lens needs to be focused onto the mirror not infinity. The reason for changing the lens on a web cam is to get a bigger image as the standard ones are fairly wide angle. The feeling comes from eyeball testing and also messing about with taking photo's from what comes out of an eyepiece where the camera does have to be focused on infinity. I'd be interested to know if I am correct as the idea of a nice big image on a PC screen appeals. So basically place the camera with the lens a little outside the centre of curvature, focus the camera onto the mirror. Having the knife edge close to the camera is mentioned here for instance. I'm sure I have seen the same thing mentioned elsewhere. http://foucault.sourceforge.net/#docs That test might be worth a go but I would cross check with a mask the usual way. A mask on the mirror would help to see if the web cam can be focused. John -
  17. I found the attached file on the web for download so no problems attaching it. It covers just about everything I have ever seen mentioned on dental stone but avoids using epoxy for sticking tiles. I suspect that is what people will have to look for in the UK not plaster. Some have used hydra stone over here, or a name very like it. It's a much stronger type of the usual modelling plaster. Some one on the youtube uses a mixer to mix dental stone up quickly (Gordon ??). It sets pretty quickly so probably best to mix a little to see what happens rather than just diving in. I've attached the file in pdf format. I saved it in odt which is a Linux word format so used something else to convert to pdf. If Adobe wont accept I can post in some other format if needed. Tex casts squares, heats them over a low flame and plonks them down on a warm mirror. From other sources I have seen this seems to be the pro way even on very large mirrors. He mentions that Ritchey ( as in Chretien telescope) painted hot bees wax on poor quality pitch. I've used Howard's method. Let it cool somewhat, pour in a spiral on the warm mirror, cover everything with rouge and rub around to achieve full contact, then cut slots with a wet saw when it's fully set. Messy so next time I'm going to cast strips, cut squares and stick them down tex style. Bet it sticks to what ever I cast it on. Whoops One thing to add. For sub diameter Gordon ??? again seems to have decent method. He uses an annular ring of wood of some sort to act a former with what ever is used to form the sides running down onto the mirror. Looks like he uses the thin plastic film (fablon) that can be stuck to shelves etc in the kitchen to stop the plaster from sticking to the mirror. John - tiletool.pdf
  18. I wish I had one Damian but I wont spend what they usually cost plus some only have 1/2" travel. Some people who test thin mirrors test vertically to avoid mirror flex problems. That makes an easy build x-y jig difficult but it's possible to manage without the 2nd axis testing in the normal fashion. Many do. It's also ideal for that caustic test I mentioned but if your having the mirror checked some other way that's over the top. That mic spindle on mine has a 1/10000" vernier on it and that has real meaning on that test. The only woolly part is the actual mirror rad. I tried push pull and a rule as a scale for rough figuring but found I prefer the mic spindle. That could even be a chopped up mic. Also pin pricks on paper measured afterwards. Stub mentioned the bolt. Knobs can be found with the graduations on them. There are cheaper digital machine scales about. ArcEuro maybe. There are all sorts of options really. Once some sort of stage is made it's pretty easy to try a number of things out including stationary source, slits, different ways of moving and measuring etc all part of the "fun" - ? if that's the right thing to call it. My feeling is that it is worth spending some time on the stage what ever type it is. Sometimes it's just a straight piece of wood with the moving part pressed against it. I simply thought that a piece of rod and a couple of brass V's was just as easy and it would definitely slide well. The tilt bolt could also run on brass or glass even. The main problem with mine was the knife tilt bolt - the thread is too coarse so I should have added a big knob or use something finer and probably a knob as well. Texereau gets round that by making the platform a lot wider and uses a finer bolt than I did. I'm might just soak the rusty bits in a mix of 25% molasses and water for a few days to get rid of the rust and more or less use the stage as it is. It's time for an upgrade on it anyway to try a big moving source but I'll probably still make another slit. John -
  19. I think Howard's book is on the archive. I did try drilling holes in callipers but found I needed a carbide drill and went of the idea. Lots of people like the idea of using a dti. Some move by hand some move mechanically. A lot depends on what is around. A spare focuser can be used as has been shown. Used micrometer spindles can be cheap. DTI's too. The metal parts I used don't cost much either and where metal is best used really easy to make. John -
  20. Thanks for mentioning off setting the knife. I've been webbed. That tester crops up all over the place and is what I intend to make but it can't work on axis, the mirror will return the image of the source right back above it and the knife wont cut it at all so it needs offsetting to cause the return beam to hit the knife. Leaves me wondering if it would be better to leave the led unobstructed and just have the knife central too it and above it. Minimising the offset does improve the accuracy. This is what I have used. It was in a loft room when we had the roof done. Covered in dust and got damp. It a fixed source version but the idea for the sliding table can be used with any type. It's easy to make. MDF etc would do but the sliding table needs some weight added even in aluminium. The tilt screws just run on a bit of metal plate under them. I added my own thoughts. As I used a slit I tilted the source rather than having a separate piece that can be tilted mounted on the knife. I also added a zero facility for the mic spindle - set mic to zero, slide table about to pick up the centre and then slide the bar up against the mic spindle and lock it in position. I didn't add a spring to pull back the table onto the mic, just used finger pressure on the table. Most people don't mount the bar the table runs on in blocks and just screw it down onto a board of some sort. In that case the mic spindle can be arranged to press on something on top of the table. It is best to make the V's that rest on the bar out of brass. It slides very smoothly. The slide going across has the V's made of aluminium and seemed ok. The other gubins that moves the knife across is for a version of the caustic test. For that a wire is mounted on the knife and I just held a 10x eye cup type loupe in my eye focused on the wire by moving my head. This test does need a slit. I've lost that but it was made as per Texereau. His way does work. No shadow reading at all with this test as it uses diffraction. I used it as a final check. The all thread - for playing with a Dall null test. I might play with that again and get a better lens for doing it. Abuse of the Ross tests looks easier though. Just move the lens and tester around until the mirror nulls flat and look for ripple and small zonal errors etc. John -
  21. That's odd really. The camera should work just the same way as the telescope does in the photo of the test rig I pinched of the web. It doesn't care that the frame of the tester and the knife edge is blocking the view. The knife edge has to for the test to work. I'd guess that getting the camera on axis and square to it would be a bit tricky though and some zoom lenses can do odd things used on systems like this. There was a mention of the Ross test. This can tempt people but on faster and larger mirrors the measurement accuracy needed form tester to lens and lens to mirror to make it worth while is very extreme. John -
  22. Trying to help again. The problems with Foucault testing are likely to be down to the tester used. There are lots of nvg info about however there is a sensible one shown on this page especially for some one with an x-y stage but that can be made up in all sorts of ways. http://www.stathis-firstlight.de/atm/foucault_tester.htm?sa=X&ved=0CDwQ9QEwEzgoahUKEwiw0eCp_frGAhUOKtsKHa0IBFg This one The telescope is optional. Note the comment on the web page about sanding the led or using a diffuser. I would add a flat ended led, If it's round ended just sand it flat. Some sort of plastic diffuser as mentioned isn't a bad idea anyway. What he doesn't mention is alignment. He's done many mirrors so will have some sort of bench set up so that the mirror can be placed on a stand and align well with the mirror. What I would do is fix the knife edge more securely and have a piece of cardboard with 2 holes in it. One to let the light through and the other smaller one to indicate where the knife edge is. If the centre of the led was say 10mm down from the top of the mounting this small hole should be 10mm above it. Best make that distance as small as possible but the return image or the led must clear the woodwork so the distance depends on the size of the led in some respects. If the cardboard is place in front of the tester it will catch the return image of the led from the mirror. At the ROC the image of the led and knife edge will be sharp and the set up can be manoeuvred around to place the image on the knife edge hole. Fiddle with the knobs and it should be fairly easy to null a near sphere now but the adjustments will be very sensitive. That can be helped by mounting say 50mm dia disks some how on the end of micrometer spindles. When a mask is used for measurements the shadows have to move equi spaced around the centre of the mirror as the knife is moved back and forth. For initial rough measurement the shadows can be evened up side to side with the other axis but that needs to remain fixed for final figuring. Old time testing using a fixed source will already have taken care of that and people without an x-y stand can use this sort of tester in the same way to set it up - alter it's angle until the shadows move evenly. This can also be done roughly with the cardboard in front of the tester as the return image will move from side to side. To use Ronchi just remove the knife edge and clip the screen on but set up in the same way. Setting up is a pain. A simple solution for most people if they haven't got a bench that is long enough and things can't be left in place, lack packing to raise the tester up etc might be a shelf on a wall. Maybe 2 one for the mirror and another for the tester so that mirror sizes and tester height can be at least part adjusted. I have seen a professional who made lots of mirrors daily work on a shelf. It seems to work well but he was mostly making 10in F6.2 mirrors so his tester was built for that size. Me I had a bench and a bookcase which made up the lengths The bookcase was taller than the bench so height adjustment wasn't a problem, just adjusted the height of the mirror. Once set up the mirror could then be just dropped in place, the tester checked for axial alignment and measurements taken. I haven't got that any more so am looking for a wall for shelves that wont upset the wife. One warning about bright sources. After a long session I found the pupil in my right eye was a tiny pin [removed word] and the other a lot larger. It took a while to settle down. The telescope on the tester in the link - just used to make the mirror look bigger. A converse view is to use one backwards to improve the view of the shadows. Pass never tried either. Whoops - People need to be able to get their eye behind the tester. Might not be easy as shown. Remove one side / turn it around etc but turning it around would need some slots in the cardboard to clear the frame or what ever is used for that. The knife will probably need moving forwards by 1/2 the thickness of the cardboard if the return image has been sharply focused. John -
  23. Not to be out done by Stub here is a bit of brass work done with the tip shown and hss in places such as screw cutting the inside of the larger tube and the parts that screw into it.. No polishing of any sort just straight turning. It is as good as it looks but brass goes dull over time. It's a centring telescope for setting up a microscope and had to be made up from several parts. This is a macro shot of poor quality silver steel thats been turned using the tip shown. Marks are at the micron level and it feels as smooth as glass. Patterns are down to bearing noise and vibrations even as hefty as a boxford is. I did this to try the tips out on a quick and dirty tap I had knocked up and finished with. 0.5mm pitch. The thread that can be seen was cut with HSS. Cut dry. Cutting oil would improve both but I don't think it's a good idea to use that and run so fast that things smoke. It wont work so well and lots would be needed rather than a thin smear on the work. It's better to use black bar really for this sort of thing. Silver steel equivalents are available in it. Any lathe with decent bearings and reasonably tight slides should produce work like this. Loose slides spoil the finish on many lathes. Actually from the rings I can see that the bearings were a tiny bit loose in some way. Probably just slight miss alignment front to rear. Believe it or not I have used better but no chance what so ever of having that sort of machine at home or being able to afford a really good example. John -
  24. Shame here too but on larger lathes a 1in deep exchangeable tip parting off blade makes good sense. I bought one with holder from RDG. It wouldn't surprise me if I later bought a 1in blade of APT given the source but the holder is ok. Might have posted this before but these style of tips are pretty good and can be fitted in small holders. They are intended mostly for finishing on big machining centres. They are 11mm a side and will fit the cheap sets sold on ebay but best get the ones that come with a set of torx screws as the socket screw soon wear out a hex key. They are raked tips which helps and also have small nose rads which is a better option really than broad ones for several reasons. The ones for stainless work well on all materials but the dedicated aluminium ones are better on that. I buy my tips from APT Carbide, google will bring them up from that. I've bought ebay bargains in the past but from the time they last I'm sure that some have been used. The tips that come on the holders are so so but ok so wont be waisted. These are better though. The holders I use are the 10mm really 3/8in ones but I think others are available for the same style of tip. Some use square tips for the extra point but these will work cleanly into shoulders allowing them to be faced and even recessed to get rid of the rad they leave in corners. I use the V pointed holder most as it will turn both ways and face - actually that's what I usually grind on HSS. I have some stellite to play with now. The rake goes the wrong way cutting to the left with them so the capability is limited but ....... I do at times, The tips will cut both ways. APT also sell their own brand of holders. They are excellent value but as far as these tips go the smallest they do is 1/2in shank and they usually sell out quickly. John -
  25. Accuracy in my terms comes down to taper and out of roundness not what people can machine to and measure correctly. Taper and out of roundness go together when machines wear and also if the lathe comes with it spindle poorly aligned to the bed. I have a more or less given me lathe similar to the one stub posted except it will also screw cut. There is wear in the bearings. Take light cuts say 1/2mm and the finish is very poor. Worse still if thinner. If I used carbide on the tips would probably break regularly. Up the cut to 1 1/2 to 2 mms and the finish is excellent providing the feed is dead even. The reason is simple that size of cut exerts sufficient pressure on the spindle to lift it along with the chuck and work and push it firmly into the worn part of the bearings. The even feed keeps it there so the finish is fine. The wear is generally upwards and to the rear which is why things don't turn out round as well as having a taper. If I tightened up the single pinch bolt on the bearing caps the casting would probably break. It's not that unusual for lathes to give worse finishes as the feed rate and or cut size is reduced even in mildly worn situations. Lathes with say 12in chucks, huge things might take half decent rather fine cuts due to the weight of the chuck and parts. The toolroom answer to this when accurate high finish work is required from a lathe is to have sufficient stock to start off with to be able to take 3 cuts of the order of 0.050 or so either way. Ideally all of the same size so that the actual cut taken can be measured and corrected - accurate lathe work in a toolroom though is seldom if ever needed. They have grinders. That's where accurate work is done. I'd guess Seig's worry about taper rollers is down to the fact that they have to be preloaded to work effectively. This mean the head stock has to be able to take the force from that as well as cutting forces. As the Chinese often cut bits of bed away etc where it can't be seen this could cause problems especially if some one over tightened them. Actually there is nothing at all wrong with using roller bearings at the front, they are ideal for taking radial loads and rather poor at taking axial ones so another bearing would be needed to take that. Even a deep groove ball race at the other end of the spindle would be ok for that after a fashion. As it would wear loose an adjustment would be needed to move the outer race and close the bearing up if needed, bit difficult with just one bearing as the front bearing wont locate the spindle axially. Plain roller bearings would have to be replaced when worn. Tapers can be adjusted. Lathes like the unimat use 2 deep groove ball races and use disc springs to take out wear for some time. Not sure what Wabeco and Hobbymat do. I suspect some cars now use a single plain roller bearing in the wheels. Not sure, just something I think I read some where. This suggests that they can take all sorts of loads in practice. Pass really I'm not sure and it would be something I read a long time ago and of little interest. Backplates and face plates can be made on the lathes that use studs to hold the chucks etc to the spindle but locating the stud holes accurately in the new part isn't easy. If a small face plate is available fit it. Then get a slice of what ever material the new part is going to be made of. Drill and tap a 1/4 bsw or say M8 thread in the centre of it. Then use a draw bar (all thread) to pull it back on either the spindle face or the face plate. It would be best for people not used to doing this sort of thing to turn up 2 bushes for either end of the spindle that are a close fit in that and the draw bar to make sure that it's pulling on the work axially in line with the spindle, or one long one at the back - if it's at and angle it may appear to be tight but is likely to work loose while turning. Just do it up firmly, not so tight that the threads start stripping. Slowly face the side that's out, reverse and face that and then what ever. Stub would probably eventually mount it on his Peatol vertical slide and either drill it for tapped holes or figure out some way of cutting T slots in it etc. Morse taper blanks end arbours in the head stock can also be turned down to have threaded spigots on them to take face plates of another lathe. To make things secure pull the mores taper in with a draw bar. Chucks too for rather light work. A big morse drill chuck will usually grip a wide range of sizes fairly accurately for light work. Adding draw bar may be taxing or it might already have a hole for one. I'm not going to get drawn on eventually learning the skills to get round problems. It's a mine field and really depends on what is being made and what the problem is. John -
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.