Alt/azth clamps for dobs?

mental4astro (Alexander) · #1 07-09-2009, 08:56 PM

Hi all,

A recent star party at a school brought the notion of some type of clamping system for the altitude & azimuth axis. Well balanced dobs are a pleasure to use, however they are very easily pushed out of direction by less experienced people,

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Does anyone know of some clamping system, DIY prefered, to offer some resistance to accidental push & pull?

This may be the last design element needed before I start on remodelling my big dob. What ever clamp systems are mentioned can be easily incorporated into the final design. This is in no way to 'take up slack' in an unbalanced system, though may come in handy if some over sized EP were to be used,

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Thanks in advance,

Mental.

rmcpb (Rob) · #2 08-09-2009, 12:21 PM

How about a strap that goes over the top of one of the alt bearings. If it is normally loose it will have not effect but if tightened by a bolt it would bind the alt bearing and effectively work as a brake.

hikerbob (Bob) · #3 08-09-2009, 03:20 PM

I've been thinking about the same issue for the same reason. I've got a Skywatcher so the Alt is not much of an issue but it's amazing how many people seem to give the scope a little shove away from themselves as they step away as well as those who push their eye against the eyepiece hard enough to push the scope off target. I've been trying to think of a drag system for the az which does not become something to catch on in the dark (or when transporting the mount).

mental4astro (Alexander) · #4 08-09-2009, 08:22 PM

Hikerbob,

You've given me an idea for an az. stop using one of those spring loaded plungger door stops. Would have to use some grippy tape on the ground board tracing the pattern travelled by the plungger.

To transport my 10" dob I've attached push bolts to secure both axis. The photo shows the bolt used to fix the alt bearing. It's seen towards the bottom centre of the scope.

The strap idea sounds good. Trying to figure out a bolt configuration that would provide variable pressure too.

hikerbob (Bob) · #5 09-09-2009, 07:30 AM

Mental I've thought of a press down through the upper board onto the ground board. I've not got myself to the point yet of being comfortable enough to start drilling. I've been thinking of something like nylon rod fixed to the end of a bolt (drill the end of the bolt to attach it) and control tension by turning the bolt.

Bob

mental4astro (Alexander) · #6 11-09-2009, 01:00 PM

I've been thinking on an alt bearing solution and one particular thing comes up, that the clamp would need to be as passive in its function so as to not create undue residual stresses in the scope and rocker box, and be completely disengaged on release.

One solution I've thought of would be to have a bolt threaded into the alt bearing so that it would trace an arc as the scope is moved in alt. Running parallel to the bolt would be an arc of ply attached to the rocker box. The head of the bolt would extend beyond the top edge of this ply arc so when it is wound into the bearing it would inturn push the ply into contact with the bearing providing a braking effect, with the more the bolt is wound the greater the braking effect.

This plywood arc would need to be fixed to the rocker box, maybe at two points, and on a flexible mount (spring loaded?) so when the 'brake' is engaged, it does not create excessive lateral stress on the rocker. Any forces experienced through the braking mechanism are all in the vertical axis which the rocker box is designed to handle.

I had thought of having the bolt connected to the rocker box and push onto the bearing, but this would cause the effect of pushing the scope & rocker box against eachother - not good.

What do you think?