1/4" x 20TPI x 4" bolt for BarnDoor tracker?

[mikehab]

Hi,

I've been looking at various different instructions for building my own BarnDoor tracker mount and they all seem to suggest using a 1/4" Whitworth 20 TPI x 4-inch long round-head bolt ... .but I'm really struggling to find anywhere that sells them. Does anyone know where I can find one please?

Many thanks,

Mike

[simonmc]

You could try some of the suppliers in the sticky, but have you concidered just swapping it for a M6? The thread is a bit finer so if its powered and used to control the tracker arm then the gearing would have to changed a bit (about 27% faster i think) but i guess that depends on the design.

Simon

[simonmc]

Sorry, it sould be 1.27 times faster. Or shorten the lenght of the lever so that the movement is the same.

Simon

[Chris Rowland]

The magic number is 229 . Multiply the pitch of the screw by 229 to get the distance it needs to be from the hinge, i.e. 229mm for a 6mm dia 1mm pitch screw.

See http://www.astronomyedinburgh.org/publications/journals/39/haigmount.html

Otherwise look for a traditional ironmongers. That's the sort of place that will have 1/4" Whitworth parts.

Chris

[Astrobits]

The standard camera and tripod head thread is 1/4" 20tpi, or standard 1/4" BSW. If it is to attach to any camera item then 6mm will not do.

Nigel

[Lonestar70]

Hi Mike,

You can obtain 1/4" x 20 BSW studding, dome nuts and standard hex nuts all in stainless steel from: -

http://www.stainlessautomotivefastenings.co.uk

Cut the studding to length required and fit a DOME nut on one end (use a touch of araldite or loctite if you want it to remain fixed) this will replace the round head... then you can use a standard nut for adjustment/driving purposes if required.

Stainless steel will be better suited to outdoor work in the cold and damp.

Finding off the shelf round head bolts at 1/4" x 20 whitworth is no longer that easy... especially 4" ones... thanks to metrication.

Hope this helps.

best regards.

Sandy.

[Peter Drew]

Any reasonable thread size will do, you just have to alter the motor speed or component dimensions as advised in the previous posts.

[simonmc]

Mike,

This all looks interesting. Is the tracker your building a single or double barn door tracker?? I have really been trying to keep up my daughters interest in astro photograpghy and building one of these may be ideal from a cost point of view. What are you going to drive the threaded bar/bolt with?

Simon

[mikehab]

Thanks to everyone for all the replies and suggestions so far.

This all looks interesting. Is the tracker your building a single or double barn door tracker?? I have really been trying to keep up my daughters interest in astro photograpghy and building one of these may be ideal from a cost point of view. What are you going to drive the threaded bar/bolt with?

I'm going for the most simple / basic single-arm version as per instructions here ... http://www.philharri....net/scotch.htm

I know there are better, more complicated but more accurate versions, but I'm interested in seeing just how much more tracking accuracy you can get from this basic single-arm version compared to using nothing at all. I'll start with the manual drive and see how it works out but then may add a motorized drive later - I have a few micro-servo motors which I have already modified for full-rotation and may be able to use one of those to drive later on if needed.

Thanks,

Mike

[mikehab]

Built my BarnDoor tracker today (huge thanks to "Gweedo" for the nuts & bolts!) ...

Hideous light polution tonight, but managed to grab a single 30sec shot @ 55mm to test the tracking (manual rotation of the wheel). Quite pleased for a first attempt...

Mike