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3D Printed Newtonian Telescope

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Neil Wyatt02/05/2020 23:36:14
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Tonight I had 'first light' with a 3D printed Newtonian scope, built around a 6" f6 mirror set I was given. I had to get the mirror recoated but it appears to be a really good one.

The adjustable mirror cell/rear cover and secondary mount and spider are both two-part assemblies based around big (nearly 8" diameter) prints combined with end rings.to reinforce the tube.

I also 3D printed the tube rings, focuser mounting plate and finderscope shoe. The tube itself is 8" PVC venting duct reduced to 7" with the cut out section as a reinforcing strap.

It needs a little more work - black flock inside the tube, better fitting secondary adjustment bolts (it needs M5 but I only had M4 long enough!)

I trid it out tonight and it gave exceptional views of the moon, performed really well splitting the double star Mizar and just picked the globular cluster M3 out of the moonlight murk.

Neil

Steviegtr02/05/2020 23:47:37
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Good god. Awesome work. I take it you have regular sightings of Martians. I have never followed this hobby, my father did. I think the reason is that when in a foreign country with bright night skies I end up asking myself too many questions.

The best night sky I have ever seen was in Mauritius, The moon was crescented the other way round due to I guess the southern hemisphere. It was so beautiful. A coral island where I got married on the beach to my beautiful young wife.

….. Rollback. Where I married a flaming leach. The sky was great the wedding did not last long.

Steve.

Jeff Dayman03/05/2020 00:15:39
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Nice job Neil, telescope looks great!

I see you are using the old steel nut in hex pocket trick to get heavy duty fastening of 3D printed parts. If you ever need to make the nuts snug in a part so they don't fall out during assembly, a tiny tapered spike printed up 3 of the hex pocket walls, interfering with the nut by a few thou, works OK. A better way to secure nuts is make separate hollow drum shaped printed parts with a clearance hole for the fastener, and secure them in a counterbore shaped pocket above the nut entry opening. The drum pieces are glued in over the nuts so they stay put. I've also heard of people stopping a print after the hex pockets are done, dropping in the nuts, then continuing the print to lay down wall over the nuts to secure them. Just food for thought for future use.

Ed Duffner03/05/2020 00:17:14
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Looks very professional Neil, well done indeed. Will you need to darken the inside of the OTA?

Ed.

Rod Ashton03/05/2020 06:40:02
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Neil - What printer do you use please. Also some details of layer and nozzle size would be interesting.

Martin Kyte03/05/2020 07:01:19
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Posted by Steviegtr on 02/05/2020 23:47:37:

The moon was crescented the other way round due to I guess the southern hemisphere. It was so beautiful.

Steve.

I think the moon does that in both hemispheres Steve.

Interesting scope Neil. Do you do any testing on your mirrors excepting that on stars?

regards Martin

Joseph Noci 103/05/2020 07:18:44
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That is superb work Neil! 3D printed has certainly enabled many developments that would have been impossible for the Amateur before. Very nice indeed!

How does the spider at the mouth of the tube affect the collected light? Presumably negligible else you would have done it differently, but still intrigued.

The drive mechanism controls in azimuth and elevation I presume - how do you set that up to track a star/planet - does it have GPS and a data base of Kep elements that you update, or is it purely manual track that you set up?

The Telescope, and that counterweight, and the whole drive mechanism has quite some inertia I would guess and tracking must be very precise and vibration free - could you tell us a little about that - If tracking Jupiter for example, what is the effect of the mechanical movement on the image - does the image stay in-place in the viewfinder or move about a little..

Every time you post images I am all enthused and go digging on building such a device, just a small one, maybe like 3inch.. and then give up with the lack of stuff available to me in that field! From our UAV stuff I have some very nice Antenna trackers that can drive a 40kg antenna - that might work well for the positioner, but there it stops! We have maybe a third of a years nights that are beautifully clear, without mist, but I I fear I would need to recoat the mirror at least every year with the corrosion here. The coating on the mirrors in the bathroom survive at best 3 to 4 years!

Very impressive Neil!

Joe

Peter Spink03/05/2020 08:07:26
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Wow that's a super job!

+1 for details of your printer and set up please smiley

mgnbuk03/05/2020 12:19:43
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+ 1 for very impressive. 3D printing seems to open up so many possibilities - far more than I expected before I finally bought one.

If you ever need to make the nuts snug in a part so they don't fall out during assembly, a tiny tapered spike printed up 3 of the hex pocket walls, interfering with the nut by a few thou, works OK

Very early days for me with 3D part design (FreeCad), but the first part I came up with had an M8 hexagonal recess for a nut.

030520201240.jpg

The recess was specified as 8mm AF and the nut is a firm press fit without any "fudging" requirements - was I just lucky ? If this post is an an inappropriate place, please remove / relocate.

Nigel B

Neil Wyatt03/05/2020 13:49:48
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Hi folks, some interesting thoughts there.

@Jeff the little spikes idea is a good one. I've devised a few different clips and joiners, and I use a lot of thread direct in the print, just tapping a thick walled print for small threads and M6 up printing them direct. The spider is secure as a clip on fit, the base with the mirror is heavier so had four tapped holes for M4 screws through the tube, just in case. I once printed a cubical maze, with a captive 10mm ball bearing inside.

@Joe the curved spider is designed so the angles add up to 180 degrees, as each spike is double sided this spreads the pattern over a full circle making the diffraction spikes you get with straight vanes disappear for a tiny cost in contrast. the mount is a German equatorial mount which you align to the pole star so it moves in RA and EC. That one is capable of being guided (with an ancillary scope) to an accuracy of 0.6 arc-seconds for astrophotography.

@Ed I will use self-adhesive flock on the top end of the tube and paint the lower end with matt black stove paint (ordinary matt black reflects IR so is poor for photographic use).

@Peter I have a Prusa i3 clone built from a kit which is no longer available. I have extended the Y-axis to allow me to print up to ~205mm diameter. For these prints I uses a 0.4mm nozzle and 0.2mm layers, the material is Monoprice PLA Plus which is excellent for this sorts of thing as it gives very clean prints. It does have two flaws - it's layer adhesion isn't as high as ordinary PLA unless printed very hot (which tends to make it stringy) so poor for parts subject to bending like spring clips, although strong enough for parts like this where loads are spread out a bit. It's other flaw is it isn't good for big overhangs (e.g. the bow of a '3D Benchy test model).

@Martin life may be too short as I have so many hobbies but I would like to make a big mirror one day, which would mean things like Ronchi tests. As my scopes have all been built around existing optical elements my measurements have been restricted to determining focal length (or radius of curvature for a mirror, which is twice focal length). hat was a nice experiment - just creating an illuminated crosshair in the middle of a screen and setting the mirror to project an in-focus image of the cross hair back on the screen. The tape measure distance was 72", so the focal length is 36". It's a 6" mirror so that's f6, a nice balance between light gathering and susceptibility to coma, which affects faster mirrors.

@Steve the first quarter evening moon is reversed in Southern Hemisphere with the light part on the left, and vice versa for the last quarter early morning moon.

I still want to make some changes, I'm waiting for M5 30mm grub screws for adjusting the secondary mirror. The temporary M4 bolts are not only loose in the holes which makes adjustment hit and miss, they protrude out the end and are vulnerable to knocks. I've also found the main mirror collimation adjusters (25mm diameter knurled nuts) are easy to knock when pointing the scope. Most scopes have lock screws so I'm going to reprint the base so it takes three of the M5 grubs with captive nuts for this purpose - then only one Allen key for everything.

And as I'm reprinting, I will put a circular shrouds around each adjuster which will also act as feet.

It will be a 13-14 hour print with those changes! Picture below is printing the first version of the end cap which includes a light-baffled vent.

The nice thing about this is that once 'perfected' the parts will suit any 6" mirror set, you will just need to reduce an 8" ventilation duct down to 7" (you can use the printed parts as a jig, I worked the other way round) and cut it to the correct length for the mirror/focuser combination.

Phew, there's so much going on with this I might stretch it into an article for MEW!

Neil

dscn9655.jpg

Enough!03/05/2020 18:34:40
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Posted by Neil Wyatt on 03/05/2020 13:49:48:

the first quarter evening moon is reversed in Southern Hemisphere with the light part on the left, and vice versa for the last quarter early morning moon.

 

Isn't that due to the reversal of the observer - facing North instead of South?

Edited By Bandersnatch on 03/05/2020 18:35:20

choochoo_baloo03/05/2020 19:05:17
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That's bloody good Neil. Do you get a 'trinity' type diffraction pattern around bright stars at the eyepiece?

It used to get on my nerves when using my Skywatcher Newtonian when starting out in astrophotography. Speaking of which below is the promised photo of my astro rig. You'll see the mould is all gone now

scopes.jpg

Neil Wyatt04/05/2020 12:45:02
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Posted by choochoo_baloo on 03/05/2020 19:05:17:

That's bloody good Neil. Do you get a 'trinity' type diffraction pattern around bright stars at the eyepiece?

It used to get on my nerves when using my Skywatcher Newtonian when starting out in astrophotography. Speaking of which below is the promised photo of my astro rig. You'll see the mould is all gone now

Nice mount!

The curved supports mean no spikes, but I did a star test and the stars were a bit triangular. Can't be pinched optics as the mirror is glued in with clips merely locate it/catch it if the glue were to fail.

I use Mizar and that means the pattern was very small. I'll try again on a very bright star like Arcturus which might be a bit easier to work with.

Neil

Neil Wyatt04/05/2020 12:56:36
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Posted by Bandersnatch on 03/05/2020 18:34:40:
Posted by Neil Wyatt on 03/05/2020 13:49:48:

the first quarter evening moon is reversed in Southern Hemisphere with the light part on the left, and vice versa for the last quarter early morning moon.

Isn't that due to the reversal of the observer - facing North instead of South?

Six of one, half dozen of the other

I can get the same effect by standing on my head!

Neil

choochoo_baloo04/05/2020 19:22:36
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Posted by Neil Wyatt on 04/05/2020 12:45:02:

I use Mizar and that means the pattern was very small. I'll try again on a very bright star like Arcturus which might be a bit easier to work with.

Neil

Yeah sounds a good idea - much higher S/N ratio. If poss can you share a picture of the diffraction pattern? Would like to see the pattern you're getting.

Neil Wyatt04/05/2020 19:41:49
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I'll probably take some pics as an experiment, I suspect the plastic OTA might flex a bit too much.

Neil

Enough!06/05/2020 16:03:05
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Posted by Neil Wyatt on 04/05/2020 12:56:36:
Posted by Bandersnatch on 03/05/2020 18:34:40:
Posted by Neil Wyatt on 03/05/2020 13:49:48:

the first quarter evening moon is reversed in Southern Hemisphere with the light part on the left, and vice versa for the last quarter early morning moon.

Isn't that due to the reversal of the observer - facing North instead of South?

Six of one, half dozen of the other

I can get the same effect by standing on my head!

Hmm .... so are you also one of those people who think, since the year is actually 365.25 (rounded) days long and to correct that we add a day every 4 years, that after 2 years we'll be 1/2-day out and midnight ought to occur at midday?

devil

Nick Clarke 306/05/2020 16:28:03
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Posted by Bandersnatch on 06/05/2020 16:03:05:

Hmm .... so are you also one of those people who think, since the year is actually 365.25 (rounded) days long and to correct that we add a day every 4 years, that after 2 years we'll be 1/2-day out and midnight ought to occur at midday?

devil

Locked down at present with my 21 year old daughter who I suspect is of the same opinion as she appears to have gone nocturnal.

Neil - Thinking of my own faltering and hesitant steps into 3D CAD and 3D printing. I am lost for words. Well done - the jobs a good 'un!

Nick

Neil Wyatt06/05/2020 16:46:32
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Posted by Bandersnatch on 06/05/2020 16:03:05:
Posted by Neil Wyatt on 04/05/2020 12:56:36:
Posted by Bandersnatch on 03/05/2020 18:34:40:
Posted by Neil Wyatt on 03/05/2020 13:49:48:

the first quarter evening moon is reversed in Southern Hemisphere with the light part on the left, and vice versa for the last quarter early morning moon.

Isn't that due to the reversal of the observer - facing North instead of South?

Six of one, half dozen of the other

I can get the same effect by standing on my head!

Hmm .... so are you also one of those people who think, since the year is actually 365.25 (rounded) days long and to correct that we add a day every 4 years, that after 2 years we'll be 1/2-day out and midnight ought to occur at midday?

devil

No, but I do think we should work from a Sidereal clock...

Neil Wyatt06/05/2020 16:49:30
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At completely the other end of the scale I'm trying to get rid of all my little 'reel ends' - so I'm printing little two-part asteroid models downloaded from the NASA website at about 50mm long. The one I'm doing now (Kleopatra) is only 5g of filament and I had to increase its size to 500% to make it that big.

Neil

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