longer counterweight bar?? why not an extension bar??

[Andrew*]

The common problem: not enough counterweight

I'm considering a longer counterweight bar so that I don't need to haul around so much weights, but I thought to myself what a wonderful woooorld why don't they sell a bar which screws onto the safety knob thread and ends in one, saving you replacing the entire bar, and a few quid??

Surely this is a better solution?

Andrew

[blinky]

I know what you mean Andrew, I had also wondered that. I came to the conclusion that the weights hanging off the extension rod may me too much for one small screw to take.

[saturn5]

That one small screw will take a lot more weight than the counterweights needed to balance your scope,a stainless 6mm eyebolt(BS 4278) has a vertical safe working load of 100kg,there is also a factor of safety built in so it would probably take double that to shear/strip the thread so the screw will take the 3/4 5kg counterweights with ease.

[Macavity]

Yup. I see e.g. the Tele-Optic Giro uses the M10 standard, for their "extension bars". But I found (in practice!) that extending the size of "the system" (mount) makes it much more prone to vibration. Moral of the story: "heavy weights close to the axis". I see some (brave) astronomers even cast their own LEAD weights into tin cans etc!

[Andrew*]

Hmmm!! Every answer changes the story dramatically!

From what I've read on the forum, most people prefer to get an extension bar rather than load the mount up with many heavy weights. If vibration's an issue with longer bars, I'll just use more weight.

Thanks a lot Chris - good to see you active again

Andrew

[saturn5]

Another point worth mentioning is that if the counterweight shaft is in horizontal position or near it the shaft takes the weight ,not the screw,only when the shaft is vertical does the screw take the full weight,if the shaft is at 45deg then the weight is roughly split between the counterweight shaft and the screw.

[Macmarch]

Be very carefull. I used to supply extension shafts for the EQ6. Then switched to replacement extended shafts, several companies now do them. The 1/4" thread is only 4mm dia at the root. Even using hi tensile bolts I found that two 5kg weights down on the 'extended bit' caused a 5deg bend at the joint. I have not calculated the shear force but I immediately stopped producing the extension shafts that screwed in.

[saturn5]

Just put more weights on the standard shaft,it WILL take it easily,i think this is a case of looking for a problem that isn't there in the first place.