Dovetails - What is 'belt and brace'?

[Jonny_H]

Hi all,

As above - whilst researching different types of losmandy dovetails etc.... I have stumbled across a few people commenting on 'belt and brace'. 

From what I can gather it seems to relate to an extra bit of security in case of saddle failure/slippage.

Curiosity has got the better of me and I am intrigued to see what this method is but I cannot seem to find any photos or more info on it.

Can anyone shed some light on this mythical method? 🤔

 

Thanks,

Jonny

 

[PeterCPC]

Could be a safety bolt and the front of the dovetail to stop it if it slips backwards - I use them on my set ups.

[Stu]

12 minutes ago, PeterCPC said:

Could be a safety bolt and the front of the dovetail to stop it if it slips backwards - I use them on my set ups.

It’s an interesting look, isn’t it? 😉

It actually means adding redundancy to the setup, so if one method fails, the other keeps things safe.

I can’t actually think of a method that prevents the most common failure, which is the dovetail not being seated properly and falling out of the clamp, or a clamp failure, though the latter are fairly rare.

A bolt at either end of the dovetail certainly stops the scope slipping out when pointing up towards the zenith, and this has saved me more than once in the past.

[chiltonstar]

In my case, it is a length of nylon cord with a 1/4 Whit bolt on one end screwed into the scope rail, with a loop at the other end around a knob on the mount. Saved my scope on one occasion....

.

Chris

[Stu]

50 minutes ago, chiltonstar said:

In my case, it is a length of nylon cord with a 1/4 Whit bolt on one end screwed into the scope rail, with a loop at the other end around a knob on the mount. Saved my scope on one occasion....

.

Chris

Sounds like a plan Chris, I guess that would save the scope hitting the floor even if it fell out of the clamp?

[Jonny_H]

1 hour ago, chiltonstar said:

In my case, it is a length of nylon cord with a 1/4 Whit bolt on one end screwed into the scope rail, with a loop at the other end around a knob on the mount. Saved my scope on one occasion....

.

Chris

This sounds similar to what I have done albeit mine seems more 'bodged' in the sense that I have just used heavy duty cable ties. See pic 😉

I was just curious what the belt and brace method was as i wasn't sure if it was a 'system' that could be purchased.

Re: the stop bolt method - that works well for my newtonian but with my Esprit 100, I assume given the additional weight, the bolt doesn't really do anything. In test when the bolt catches the edge of the saddle the entire lot then tips up and backwards and would otherwise just fall out.  I have tried using different length bolts but to no avail - hence the use of cable ties.

Regards,

Jonny

[Mr Spock]

iOptron dovetails have a nice arrangement. Two hex head bolts to stop any slippage.

[Zermelo]

I haven't heard that expression, but I did have exactly that concern when I started using my current scope:

I didn't want to replace the dovetail on the OTA, so I ended up drilling a small hole through the upper end and installing a nut and bolt. 

[scotty38]

4 hours ago, Jonny_H said:

This sounds similar to what I have done albeit mine seems more 'bodged' in the sense that I have just used heavy duty cable ties. See pic 😉

I was just curious what the belt and brace method was as i wasn't sure if it was a 'system' that could be purchased.

Re: the stop bolt method - that works well for my newtonian but with my Esprit 100, I assume given the additional weight, the bolt doesn't really do anything. In test when the bolt catches the edge of the saddle the entire lot then tips up and backwards and would otherwise just fall out.  I have tried using different length bolts but to no avail - hence the use of cable ties.

Regards,

Jonny

The bolt in the dovetail is to stop it sliding out rather than tipping out, the idea being the clamp is not quite tight enough (left loose after balancing etc) rather than being completely undone as it were.

[Jonny_H]

4 minutes ago, scotty38 said:

The bolt in the dovetail is to stop it sliding out rather than tipping out, the idea being the clamp is not quite tight enough (left loose after balancing etc) rather than being completely undone as it were.

Hi Scotty.

Yes I admit my 'test' was simulating a clamp failure so probably a tad OTT ☺️ I suppose in those scenarios you would likely be in trouble anyway!

I have switched back to the stock skywatcher losmandy temporarily as I am experimenting something with my ADM losmandy.  That was really the reason for the cable ties as there is nowhere to add a stop bolt on the standard SW plate as it is so tiny in length.

[scotty38]

Yep if the clamp fails in that manner the belt and braces plan b needs to swing into action.....