Alt-azimuth base

Changelog

V4, 01-06-25:  Reinforced the Top part where the Altitude adjustment screw lives, to reduce bending during loading. Adjusted dimensions on the barrel nut housing in the hope of reducing movements (housing is now closed on one end to potentially add a spring to pre-load the barrel nut, to be tested). Adjusted tolerances.

V2, 11-06-24: Changed the altitude axis adjustment system to a push-pull instead of just pushing on the altitude rocker. This adds an M5 barrel nut to the hardware list but ensure that the altitude axis cannot flip the other direction when you load the base. Old files are in V1 folder.

Alt-Azimuth base mount intended for equatorial mounts and trackers. 

This design is part of my project to create a 3d printed functional motorised equatorial mount for astronomic observation/photography. It will link with my other on-going designs.

Uses a 3/8"-16 standard photo screw for mounting the base to a tripod (the base is 100mm in diameter), and a 1/4"-20 screw for mounting whatever you want on it. Four M5 insert are possible as well, with a spacing of 35mmx25mm. Azimuth can be adjusted by using the two opposed adjustment screws, and altitude is adjusted by the central screw. Locks into place by screwing the two handles on both sides.

My unit printed in PLA withstand quite a large amount of weight, I was able to step on it without any damage. It start moving slightly after 8-10 kg of force applied ~100mm away from the rotation axis in my setup.

Hardware

This build requires one specific piece of hardware, which you will probably have to make yourself: the 5mm diameter, 80mm long axis with M5 threads on both sides for the locking handles. I made mine in brass and threaded the ends with a M5 die (brass is easier to thread than steel). 

Hardware list:

• 1x 5mm, 80 mm long axis (see above).
• 4x 625(-2RS) ball bearing, 5x16x5mm.
• 1x 1/4"-20 grub screw 1" long.
• 1x 3/8"-16 T-nut, apparently used in furniture (not sure of the official name, see here).
• 3x small screws for the T-nut installation (hole are 1.8mm in diameter and 15mm long).
• 5x M5 nuts
• 1x M5 barrel nut, 8mm diameter, 20mm long (see here)
• 4x M5x25mm bolt with hexagonal head
• 1x M5x35mm bolt with hexagonal head
• 2x M5 washer.
• (Optional) 4x M5x5x7 brass insert for the head.

Print parameters

Be sure that your printer is correctly tuned before starting, especially the skew (you want circles to be circles). This is not a challenging print but you want dimensions to be as accurate as possible.

Use a rigid material, I used Polylite PLA from Polymaker (look for the elastic properties of the materials, pick the one with the highest resistance to deformation). 

I used 25% infill, 4 perimeters, 4 top/bottom layers, 0.3mm layer height, 0.4mm extrusion width. The resulting mount weighs 350g and I can step on it with my full weight without anything moving (roughly 70kg).

Instructions

Print the top, base, one rocker (choose the angle closest to your latitude), one adjust thumbscrew_alt_adjust, 2 screw_bars and 5 screw_nuts. 

Sand the mating cylinders of the top (inside) and bottom (outside) parts until the bottom smoothly fit inside the top. There is no tolerance between them to account for that sanding.

Install the 3/8" T-nut inside the inner part of the base with 3 screws.

Using a M5 bolt, a washer, a nut and a wrench insert 2 bolts (2x25mm) inside the screw_nuts parts (while tightening the assembly, the head of the bolt should insert itself inside the part). Do the same for the 2 bolts of the base (2x25mm), and the bolt of the thumbscrew (1x35mm)

Similarly, insert 2 M5 nuts inside the screw_bars. Insert the 2 remaining M5 nuts in their pockets in the top part.

Screw the 1/4" grub screw inside the rocker and/or place the inserts in the rocker.

Press-fit the ball bearings inside the rocker and top pieces. 

Install the altitude adjustment thumbscrew in its opening in the top piece.

And finally, assemble everything by inserting the 5mm axis through the top and rocker piece (might be a tight fit, I sanded my brass axis lightly until it went through with reasonable force) and push the base inside the top part. Screw in the nuts securing the base as well.