Buttery smooth adjustment bolts

[Fraunhoffer]

I started to get a bit stressy with my EQ mount altitude adjustment bolts when doing my polar alignment in the gloom.
The long bolt would frequently seize up and the pressure have to released before continuing.

I have a Bresser EXOS-2 mount and it looks very similar to the Vixen GP mount / LXD75, EQ5 pro and others of this style.

The altitude is adjusted by 2 long bolts that push against a spur on the mount head altitude axis. The spur is at an angle depending on the latitude setting and this angled surface twists the end of the bolt down when pressure is applied. The bolt then jams in the screw threads making adjustment difficult.

Ive added a sketch.

My solution was to make a shaped block of a hard waxy plastic that would support the end of the bolt to prevent it twisting, and would also slide within the channel where the spur is located.
I had hoped to use some PTFE but used a small block of HDPE plastic instead. This is a hard waxy and durable plastic that is actually used for plastic milk cartons. A hard waxy wood might also be used.
I cut a card template for the shape of the channel and then transferred this to the plastic and cut and filed by hand, removing a little at a time until it fitted nicely in the channel. I checked the height in relation to the altitude bolts so that the top was the same height as the centre of the bolt (bolt removed for this). Be careful not to jam the block in the channel (if this happens a small hand drill or an awl might help dig it out).

The final task was to use a round file and remove material to make a groove in the top at the same height and depth as the adjustment bolt to support the end; removing a little at a time and checking frequently.

The result? A buttery smooth altitude adjustment bolt. I can finely adjust my polar alignment altitude without any bolt sticking or jerking or getting too stiff to turn easily. The first time I tried it I effortlessly managed to achieve 1’30” polar alignment error.

My mount might not be the exactly the same as yours but I hope this may be useful to some. The usual waivers – you modify your own mount at your own risk.

In retrospect this was such a simple fix to an irritation in an otherwise lovely mount.

(PS. I have also made a thin large circular washer from a cut up HDPE milk carton that goes between the tripod and mount head - buttery azimuth bolts too).

 

Happy Adjustment Bolts everyone 🙂

 

(PPS. I didn't use a metal block since I thought it would wear the threads at the end of the bolt, whereas a firm plastic would not damage the threads. I expected the bolt to bite into the plastic, but using a hard waxy substance would enable it to slide a sthe bolt was adjusted. It doesn't usually have to move very much anyway)

 

Edited June 23, 2020 by Fraunhoffer