Author Topic: Astro Photography Mount  (Read 549 times)

Offline Joules

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Astro Photography Mount
« on: January 11, 2020, 03:42:48 PM »
Building a tripod extension for mounting a light weight equatorial mount on.

Just before Christmas I got myself a Sky Watcher Star Adventurer, they are meant for lightweight astro photography.   As I have an old tripod for a telescope, I decided to use that.   One issue these days is doing a polar alignment with the north star, the tripod is too low and my days of bending double are long gone.   Look around the workshop to see what we have.....  Ahhh, what looks like a length of aluminium scaffold pole, that'll do for starters, saw a length off and face the ends.   I ended up using my fixed steady for this not knowing how much damage might be done to the tube wall by the steady fingers.  As it turned out, very little.

A Delrin blanking plug was made for the tailstock end of the tube so it could be skimmed to final dimension.  Unfortunately the tail stock had to be fully extended and when I locked it the centre move over 0.0015" so the tube ended up with a 0.003" taper.  Not a big issue over 400mm long tube.  The Delrin plug worked very well having being machined precisely in the 3 jaw chuck.

I made some end caps and a fitting for mounting the tube and picking up the draw bolt used on the tripod, I forgot to get any pictures during the making of these.   Then I had a moment whilst checking the top mounting plate, and dropped it on the kitchen floor.  It put quite a ding in my new part and raised a lump on the machined surface, fortunately it was the rear and I could afford to skim a few thou off but it still left the ding on the side.  That will get sorted later.
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Offline Joules

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Re: Astro Photography Mount
« Reply #1 on: January 11, 2020, 05:30:40 PM »
Once this lot was done, a test assembly of the parts and think about the stud on top for screwing the mount on.

A rather nice trip to visit Rob (slowcoach) resulted in some brass bar coming into my possession, cheers Rob.   I had been thinking about making this part in steel, but worried about it rusting, so the brass was ideal.  Unusually I didn't do any CAD for this part it was all on the fly and done this afternoon.  I opted to use a taper than the flange I had originally thought about.  Makes life easy as you can set the top slide and do both components at this setting for a guaranteed match.  The stud was profiled and parted off.  I then remounted the stud in the 3 jaw chuck using my play in the scroll to get it accurately mounted.  Yes that is 0.00025" runout, Rob might confirm this technique works just like setting up a 4 jaw, but quicker as you are down a jaw, but only on round stock.

Next get the stud ready for threading 3/8 UNC, since I had a die I thought I might as well use it.   I made a bit of a balls up doing the threading, I had either left too much material on the stud, or my die isn't very sharp.  It was hard work and despite the jaws being tight, they slipped and marked the part.  No big issue as this part is out of sight, but annoying just the same.

Time to machine the taper in the top plate of the extension and get the stud to fit just below the surface.  I had to swap to outside jaws and re zero the part, all went well with no issues.
« Last Edit: January 11, 2020, 07:37:51 PM by Joules »
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Offline Joules

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Re: Astro Photography Mount
« Reply #2 on: January 11, 2020, 07:24:29 PM »
I should have added in that last post, the stud is threaded 6mm at the rear.  The tube has an M6 stud running through it that pulls the whole assembly together making for a very rigid mount.  For this to work the stud needs a couple of holes for a pin wrench to tighten the stud. I had used a centre drill on the stud before finishing it, this enabled me to quickly set up the stud on the mill.

The final image for now is the head on the extension tube.   Once the weather improves I can run some tests on how rigid the setup is, if I find any vibration I have the option to fill the tube with dry sand to add a little more mass and damping.


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Offline slowcoach

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Re: Astro Photography Mount
« Reply #3 on: January 13, 2020, 10:16:10 AM »
Looks good Joules!

Rob  :thumbup: