6 replies to this topic

[photographingfedorp]

Hi everyone! How large should the hex-head bolts, used for making collimation adjustments on the mirror cell, be for a 6" f/5 Dobsonian reflector? The hex-head bolts are attached to the rear blockhead. In addition, what is the typical size for the push and pull bolts attaching the mirror cell to the rear block head? My friend and I are making a DIY Dobsonian for our senior project, and we're trying to figure out the size of our bolts because our guide only gives us the size of the tee nuts and not the bolts themselves. 

 

If it helps, the mirror cell and blockheads are 7X7 3/4" plywood pieces, thank you for any and all advice!

Edited by photographingfedorp, 10 May 2024 - 10:45 AM.

[MeridianStarGazer]

As for diameter, it depends whether you want kids being able to adjust it.

[slepage]

As far as size goes, I'll let other chime in on that, but what I can offer is to make sure that you get extra fine threads.  If you go to McMaster-Carr's website, you can fine "extra fine" 1/4-32 (for example), they also have ultra fine.  This will have you much more control when dialing in collimation.

 

Steve

[photographingfedorp]

As for diameter, it depends whether you want kids being able to adjust it.

thanks for responding! If so, what should the diameter be? Most people using the telescope would be in highschool and you normally dont have to make collimation adjustments right?

Edited by photographingfedorp, 10 May 2024 - 11:02 AM.

[MeridianStarGazer]

thanks for responding! If so, what should the diameter be? Most people using the telescope would be in highschool and you normally dont have to make collimation adjustments right?

Dob knobs appear to be 1/4" knob, or even 3/8". I advise against Allen heads since you have to have the right size; Philips is much better. As for the shaft, I think 1/8". As for what is back there, I've seen 3/4" and 1" knobs. Good for collimation, bad if a 5 year old gets curious.

I bet ultra fine is 40 per inch. Less likely to change as much or come out.

Edited by MeridianStarGazer, 10 May 2024 - 11:19 AM.

[photographingfedorp]

Dob knobs appear to be 1/4" knob, or even 3/8". I advise against Allen heads since you have to have the right size; Philips is much better. As for the shaft, I think 1/8". As for what is back there, I've seen 3/4" and 1" knobs. Good for collimation, bad if a 5 year old gets curious.

I bet ultra fine is 40 per inch. Less likely to change as much or come out.

Thank you! and what does 40 per inch indicate?is that how fine the thread is?

[MeridianStarGazer]

Thank you! and what does 40 per inch indicate?is that how fine the thread is?

Yes. 40 per inch is usually black in the hardware store, and sold in drawers. 32 can be silver and sold in bags.