Feathertouch focuser threads

[PadrePeace]

I have a Feathertouch 3” focuser that I am trying to fit a Pegasus Focus Cube 2 onto. The Cube comes with M4 bolts which Pegasus say fit the focus locking thumb screw and associated grub screw so that you can mount the cube. I have found that these ‘M4’ bolts don’t screw all the way in only about 2 turns before binding. I have physically compared the two threads side by side and the Feathertouch thread is not M4. Pegasus say they are M4 on their 3.5” but I don’t have one of those so that’s not really helpful. 

So What?

Has anyone fitted a Auto focuser to a FTF3035b 3” focuser and can tell me what thread size bolt I need? I’m guessing it’s imperial.

Edited September 21, 2020 by PadrePeace
Text change

[Adam J]

8 minutes ago, PadrePeace said:

I have a Feathertouch 3” focuser that I am trying to fit a Pegasus Focus Cube 2 onto. The Cube comes with M4 bolts which Pegasus say fit the focus locking thumb screw and associated grub screw so that you can mount the cube. I have found that these ‘M4’ bolts don’t screen all the way in only about 2 turns before binding. I have physically compare the two threads side by side and the Feathertouch thread is not M4. 

Has anyone fitted a Auto focuser to a FTF3035b 3” focuser and can tell me what thread bolt I need? I’m guessing it’s imperial. 

Have you got a set of imperial taps? If so you can lay the locking screw against them to see which thread it lines up with. Not sure but I might have some imperial taps. 

Adam

Edited September 21, 2020 by Adam J

[PadrePeace]

Thanks Adam. If I don’t get a definitive answer I’ll have to take you up on that. I asked Starlite but they haven’t replied. 

[The Admiral]

25 minutes ago, PadrePeace said:

what thread size bolt I need? I’m guessing it’s imperial.

¼" UNC is a very close match for M4, but the threads are slightly different, enough for binding to take place after a few turns. You can get them on eBay in small quantities for little money, so it'd be worth a punt just to see. Try here.

Ian

[johninderby]

FeatherTouch focusers don’t use metric.
https://starlightinstruments.com/store/index.php?route=product/product&product_id=263

[PadrePeace]

John

Thanks for that link. I’m guessing the thread is 6/32 then?

[johninderby]

Probably but hope Starlight can confirm it. 🤔

Perhaps pick up some 632 bolts cheap on eBay and try one for fit. 

[MarkAR]

You need to find 6-32 UNC thread machine screws.

https://www.margnor.co.uk/machine-screws/mild-steel-machine-screws/recessed-pan-head/unc?imp_dia=344

[Adam J]

18 minutes ago, PadrePeace said:

John

Thanks for that link. I’m guessing the thread is 6/32 then?

Odd that is 3/16 in my money, might have suggested that before not sure?

Adam

[MarkAR]

The designation for the threads is:

Number 6, UNC

32 threads per inch.

Closest metric sizing  is 3.5 mm diameter x 0.8mm pitch.

[The Admiral]

Ermm, sorry, my mistake, 1/4" UNC is nearest to M6 not M4. Ignore that post then. Ah, I see you already have ☺

Ian

Edited September 21, 2020 by The Admiral

[johninderby]

Ah the quaint old fashioned Americans and there old fashioned screw threads. 😁

[Adam J]

1 hour ago, johninderby said:

Ah the quaint old fashioned Americans and there old fashioned screw threads. 😁

The joke being that they use the "imperial" system having gotten independence from the UK and we use metric having invented imperial.

[PadrePeace]

Thanks everyone for chipping in and for the humour. 6/32 it is and hot of the press Pegasus are mailing me what they think are the correct bolts having accepted that M4 on an FT focuser won’t work. Good on them.