Single arm barn door mount tips and maths?

[martiandictator]

Hello, I'm attempting to build a simple one armed barn door mount however I'm unsure of some of the calculations.

I have an M8 rod that's 18 threads per inch, though I'm unsure how to calculate how far away it should be from the hinge?

Also, does anybody know where I can get a couple of 3/8 tee nuts to attach the mount to my tripod and the ball head to mount - preferably from a non-web source?

Thanks very much

[gkec]

You can put the rod anywhere you like, it is then the rotation speed that governs how much it moves.  

Screwfix maybe, if there is an outlet near you?

[martiandictator]

You can put the rod anywhere you like, it is then the rotation speed that governs how much it moves.  

Screwfix maybe, if there is an outlet near you?

For simplicity I want to turn the rod at 1rpm.

[JCJC]

There is some math in these 2 pages, you may be able to adjust the numbers or the thread size.

http://massapoag.org/astro_2/Equipment/Barndoor_Tracker/Barndoor_Tracker.html

http://astunit.com/atm.php?topic=handscotch

jcjc' dad

[Lonestar70]

Hi,

If your rod has 18tpi I suspect it is 5/16" Whitworth... 8mm is normally 1.25mm (approx 20.32 tpi)

18tpi = 0.05555" pitch = distance traveled in 1 rotation per minute. = length (

Earths rotation is once every 23hrs 56 minutes and 4 sec. = 86164 sec per rotation.

(360 / 86164) x 60 = 0.25068474deg/min = angle (

Length of offset = length b x cot B.... cot B = 228.5556502

:- Length of offset = 0.05555 x 228.5556502 = 12.696".... or 322.485mm

I hope this helps.

Best regards.

Sandy.

[Lonestar70]

Not sure why the smillies have replaced bracketed characters.

That should read as length b.

And angle B.

All the best.

Sandy.

[Peter Drew]

The advantage of configuring the turning rate to 1rpm is that you can follow the second hand on a clock face to pace yourself if driving the mount manually. 

[martiandictator]

Thanks for the advice guys.

This little barn door mount is quickly getting expensive mainly because all the odd fixtures and fittings are difficult to source. 

Does anybody have a 1/4 20 tee nut they'd be willing to send me for a reasonable price?

[martiandictator]

Or rather than using a 1/4-20 tee nut to secure the base of my mount to the tripod ball head, do you reckon a 1/4-20 hex nut sunk into the wood and glued into place would provide adequate support for the mount and camera? Bear in mind that the total weight of my camera and 300mm lens is less than 600g.

[Lonestar70]

Hi,

It rather depends on the thickness of the wood... if you can sink the nut fully and use epoxy glue then it might be adequate... although I would not want to risk the camera and lens to such a small area of glued surface.

Alternatively... solder the nut to a small piece of brass plate (say 1/16" thick) big enough to extend beyond the outer edges of your Ball Head top plate. (I am assuming that this has a quick release plate of some sort)

This could then be screwed onto the underside of your mount using small wood screws with the nut sunk into the wood.

Hope this makes sense.

Best Regards.

Sandy.

[martiandictator]

Right I have all my materials, just need to assemble.

Does anybody know where I can purchase a cheap but sturdy ball head for the mount? It only needs to hold a very lightweight camera and lens so I don't want to pay any more than £20 really. 

Can't wait until it's ready and we have some clear weather  

[Digz]

Have a look on WEX Photographic, although you might be hard pushed to find a sturdy ball head for that price. What camera and lens combo are you thinkin of using?

[martiandictator]

Have a look on WEX Photographic, although you might be hard pushed to find a sturdy ball head for that price. What camera and lens combo are you thinkin of using?

Panasonic and 100-300mm equivalent lens. Total weight of body and lens is 500-600g. It's ridiculously light.

[martiandictator]

Hi,

It rather depends on the thickness of the wood... if you can sink the nut fully and use epoxy glue then it might be adequate... although I would not want to risk the camera and lens to such a small area of glued surface.

Alternatively... solder the nut to a small piece of brass plate (say 1/16" thick) big enough to extend beyond the outer edges of your Ball Head top plate. (I am assuming that this has a quick release plate of some sort)

This could then be screwed onto the underside of your mount using small wood screws with the nut sunk into the wood.

Hope this makes sense.

Best Regards.

Sandy.

Now I have the materials I see exactly what you mean. I don't think I can trust the entire weight of the mount, cam, and lens on such a tiny glued nut. What I'd be happier doing is embedding and gluing the nut in the bottom side of the wood and then securing the top portion with another nut. However, the screws on bullheads are ridiculously short. 

[Lonestar70]

Hi,

I don't think you will find a ball head much cheaper than this one: -

http://www.scopesnskies.com/prod/tripod/ball%20socket%20head/simaballsokhead.html

I can easily make you a suitable mount adaptor like this: -

Tracker mount addaptor.pdf

If this would help, PM me your address and I will send it to you... let me also know the thickness of your tracker baseplate wood.

Best regards.

Sandy.