philjay Posted April 21, 2014 Share Posted April 21, 2014 (edited) As part of the restoration of the 1870 Cooke mount for the 4" F15 project Ive taken on restoration of the RA circles. Some time in its history a previous owner had either replaced the original circle plate or filed off the original engravings and for some reason had divided it into 22 hours instead of 24. Ideally a dividing head would be the weapon of choice for doing this but Im going to have a bash doing it manumatically. It wont be as accurate but I have the original dec circle with full engraving so the RA needn't be too accurate, just enough to put me in the ball park of an object with the scope. So I had a chillout day today in the garage and started on restoring the correct 24 hour scales. I started by cleaning off the existing marks on the lathe Then I made a template for hours and half hours to work from I used this to transpose the Hours and 30 minute marks onto the rim of the brass circle, suitably inked with engineers marking ink. Then I set a pointed dremmel engraving tip in my milling machine and spent a happy hour engraving the graduations So now I have the hours and 30 minutes marked, just got to build up courage for doing the 10 minute sub divisions now I have some 3mm number stamps coming in the post which will finish the job off unfortunately not in the Victorian style that the dec circle is in but they will do. Edited April 21, 2014 by philjay Link to comment Share on other sites More sharing options...
Doc Posted April 21, 2014 Share Posted April 21, 2014 Nice work Phil but watch for teeth marks from that vice. Link to comment Share on other sites More sharing options...
oldfruit Posted April 21, 2014 Share Posted April 21, 2014 We are all to aware that you like your old refractors Phil. It is nice to see such dedication to restoring these sort of instruments to their former "glory" and functionality. Is it just the RA circle that needs doing or does the whole mount need an overhaul? Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 21, 2014 Share Posted April 21, 2014 Bolting a Wixey level onto the lathe chuck (anywhere on it), together with the RA circle would give you full 360 degree coverage. Convert to RA time is easy as 10 minutes RA = 2.5 degree etc etc. Link to comment Share on other sites More sharing options...
philjay Posted April 21, 2014 Author Share Posted April 21, 2014 The vice is smooth jawed Mick, its toothless :-) Its just the Ra Mark, Ive done the rest of the mount I thought abought a wixey Richard but previous owners had butchered the centre hole as I found when skimming the old marks off. If this doesnt work well enough I shall make a new circle and get someone to scale it on a dividing head Link to comment Share on other sites More sharing options...
+Graham Posted April 22, 2014 Share Posted April 22, 2014 (edited) If your lathe has a gear driven lead screw Phil you can use the gear train as a dividing head and the tool as a scriber. If you have a 60 tooth gear put it on to chuck spindle. Place a pointer or draw a line on the back of the head stock. Each tooth will be 1 min. Scribe a line onto the brass circle using a tool in the tool post. Move the gear round counting the teeth as they pass the line and repeat. Simples. Edited April 22, 2014 by Graham Link to comment Share on other sites More sharing options...
philjay Posted April 22, 2014 Author Share Posted April 22, 2014 Fantastic Graham, never thought of that, think i have a 60 tooth, you watch all my existing marks eill be off now :-) Link to comment Share on other sites More sharing options...
+Graham Posted April 22, 2014 Share Posted April 22, 2014 Fantastic Graham, never thought of that, think i have a 60 tooth, you watch all my existing marks eill be off now :-) Phil If you put a thread cutting tool on its side in the tool post you can cut the grooves at the same time, no need to use the mill. Link to comment Share on other sites More sharing options...
philjay Posted April 22, 2014 Author Share Posted April 22, 2014 Yeah ta. Just thought, needs to be more than 60t, the ra circle is 24 hour divisions, 48 half hours, for me to do 10 minute sub divisions I need 144t, need to do a bit of digging Link to comment Share on other sites More sharing options...
+Graham Posted April 22, 2014 Share Posted April 22, 2014 (edited) yes thats true you do. Been thinking a 72 tooth will work if you use the top and bottom of the pitch. Edited April 23, 2014 by Graham Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 23, 2014 Share Posted April 23, 2014 A Wixey just placed on the same chuck jaw each time is so easy....and more accurate too. Link to comment Share on other sites More sharing options...
philjay Posted April 23, 2014 Author Share Posted April 23, 2014 Im sure Richard but I have lathe but dont have Wicksey Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 23, 2014 Share Posted April 23, 2014 (edited) Sorry, double posting Edited April 23, 2014 by peepshow Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 23, 2014 Share Posted April 23, 2014 (edited) I would be happy to loan you one, Phil. If so, send me a PM with your address, or meet you near Ashby de la Zouch if you are ever over that way. Edited April 23, 2014 by peepshow Link to comment Share on other sites More sharing options...
philjay Posted April 23, 2014 Author Share Posted April 23, 2014 Thanks Richard but Im about 50 miles away. The project is on hold at the mo, I rushed it today wanting to get it sorted and made a cods of it, numbers out of line etc. Serves me right for doing it on a bad day. The index marks were too big anyway, nowhere near as elegant as the originals on the dec, sooo... I intend to make an ali index ring which will fit over the original disc, suitably turned down, this will then save me having to silver it, I can just black the index marks. Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 23, 2014 Share Posted April 23, 2014 Thanks Richard but Im about 50 miles away. Well Phil, Royal Mail can easily travel that distance. :D Anyway the offer to you to borrow the Wixey it is there if you ever go ahead with the project. Link to comment Share on other sites More sharing options...
+Ibbo Posted April 23, 2014 Share Posted April 23, 2014 same offer here Phil but you will have to put a battery in it Link to comment Share on other sites More sharing options...
Guest peepshow Posted April 24, 2014 Share Posted April 24, 2014 same offer here Phil but you will have to put a battery in it Mine comes with a spare battery........... I can hire batteries out...................... Link to comment Share on other sites More sharing options...
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