This is a complete set of prints for a 70mm aperture wide-field astronomical telescope.
It is an advanced build as you will need to do some basic engineering - notably tapping!
You will need to add some additional parts.
A 70mm (nominal) diameter lens. The 'high quality achromatic doublet' one from Astro Media is ideal http://www.astromediashop.co.uk/Components.html
This has a focal length of 280.1mm but you can use any ~72mm diameter lens and adapt the tube length to suit.
A length of 76mm o/d by 3mm wall thickness aluminium tube, about 100 mm shorter than the focal length of your lens. Expect to experiment to find the ideal length for your lens. (I have edited this to recommend a shorter tube in case you want to use thw scope with a star diagonal - I recommend starting with an over-length tube and shortening it until you get the focuser range you need.).
Four 3mm bore by 8mm diameter ball races https://www.arceurotrade.co.uk/Catalogue/Bearings/Ball-Bearings-Metric/3mm-Bore
Two 4mm by 8mm diameter ball races
Lengths of 10 x 2mm and 15 x 2mm aluminium extrusion (try B&Q).
A length of 4mm stainless steel rod.
Matt black stove paint.
Adhesion primer and suitable paint to finish the tube.
M3 screws in various lengths (5mm countersunk, 10mm cap head, 25mm cap head).
M6 x 25mm nylon screw.
Two M4 x 15mm nylon screws of knurled thumbscrews.
An 18mm square of teflon or similar slippy plastic.
Use 0.4mm nozzle, triple wall thickness and plenty of fill for the focuser body. If it is not rigid enough it will distort and the focuser tube will bind. the thick walls are essential to give successful tapped holes. do not drill out holes before tapping, just use plenty of f(gentle) pressure to make sure the taps cut and don't spin and strip the thread. Be careful not to overtighten fixings.
Building Your Scope
Print the scope baffle small end down! This ensures sharp edges. Fit it 10mm inside the lens end of the scope tube. it should be a tight friction fit. Spray the inside of the tube matt black. The baffle has been modified as the scope was a bit 'over baffled'.
The lens cell and dewshield is best printed large end down. Spray the inside matt black. The lens just drops in, use the lens ring so that the aluminium tube doesn't bear directly on the lens. It slips over the end of the tube and should be held in place by 2 or 3 5mmcap screws. Drill holes for these through the collar into the tube, countersink the holes in the collar and tap the holes in the tube M3.
The Crayford focuser body fits to the other end of the tube in the same way. Print it small end down, and tap all 8 holes M3. Use 10mm screws to fit the four ball races in the pockets.
Print the focuser tube large end down. Spray the inside matt black. Fit three lengths of aluminium extrusion in the three channels. You may need to clean up the channels and file the ends of the strips to get a good fit. Tap the three holes M4 and fit thumbscrews to two of these.
Spray the Focuser Tube Ring matt black, after putting the focuser tube through the Crayford body, it fits over the end and holds the three metal strips in place. On final assembly superglue it to the end of the focuser tube.
Print the Crayford spindle block. Tap the large hole M6. Fit a 4mm x 8mm ball race in each end of the block. Pop the PTFE square into the square recess inside the block, and thread a length of 4mm stainless steel rod through the bearings. Check the length and fit a knob (you have to print 2) at each end so they don't rub on the block. Fit the M6 nylon screw so it gently presses the PTFE square against the rod.
Use four 25mm M3 screws to fit the focuser spindle block to the focuser body. The spindle should bear on the 15mm wide metal strip on the focuser tube, the 10mm wide strips bear on the two sets of bearings. Do not over tighten, it's OK to have a small gap between block and focuser body. Use the nylon screw to adjust pressure on the spindle if required.
You should get nice smooth in and out movement of the focuser tube. Glue the focuser end ring permanently in place inside the focuser and attach the assembly to the tube.
The tube is suitable for 2" diameter eyepieces and accessories - if required either print of fit a 2" to 1.25" for smaller eyepieces. As I don't know what accessories (e.g. a star diagonal) you want to use, you will have to adjust the main tube length to suit your equipment. Once this is sorted you can remove lens and focuser to paint the tube (sand it to a dull finish, spray with adhesion promoter then finish with several light coats of your desired colour).
I leave it up to you to decide how to mount the scope, as this will depend on your tripod. You can fit 75mm tube rings or a clamshell around the tube or screw a wedge to the tube. Such fittings can be bought or printed.
The simple RDF bracket clips into the bearing pockets on the focuser and can be used to mount an inexpensive Baader style red dot finder.
Make sure the focuser is well aligned with the lens (it helps greatly if the ends of the tube are cut nice and square). The excellent baffle arrangement and large diameter focuser should ensure your new scope will be as good as the lens you have fitted to it.
If you tackle this advanced project, please post a make.
Check out my book "3D Printing for Model Engineers" on Amazon or search ISBN 9781785004254 :-)
Visit www.stubmandrel.co.uk for more 3D ideas and my astrophotography!