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coxy322

Skywatcher Dovetail / DSLR Tripod bolt

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Hello.

I would like to mount my DSlR to the EQ5, using the supplied white, fatter and shorter dovetail plate.

I have tried B&Q but the closest bolt doesnt fit :-(

There is a story in Aug S@N magazine, page 77. Refers to two websites but have no idea how to search or find the bolts they refer to!

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If they are tripot bolts then I believe that they are 1/4" x 20 pitch but whether they are whitworth or whatever I am trying to find out as well. I have tried everywhere that I can find 1/4"x20 bolts and order half a dozen, but so far the pitch has always been wrong and it won't screw into the hole that I want it to fit. A fellow SGL persons kindly let me have a couple of spares that he had, but I now need longer ones, but am at my wits end as to where to get them. It isn't like the old days when you could taken your fitting with you and try one out in the shop as they all come neatly pre packed so you have no choice but to buy and them chuck them in the drawer with the other no-goers. Please PM me if you find anywhere that supplies them - I need them with a c/s head and and at least an 1" long.

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I wrote the article in question and spoke to both Namrick and Orbital before completing the piece. Both companies can obtain these but they are not listed on Orbital's site and only a small range are listed on Namrick's site here and here and here so it would be better to speak directly to the companies as I did.

Namrick:- 01273 779864

Orbital:- 01923 777777

Failing that, 1/4" Whitworth bolts are as close to compatible as you can get and in my experience are interchangeable as the thread is so relatively coarse. I have used both types in numerous situations successfully.

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The actual tripod thread is, I believe 1/4"-20 UNC. When I wanted one, I used the screw from one of my Skywatcher scope rings.

James

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I've used A Series myself when I wanted some special bolts for my Feathertouch focuser - another good and reliable company, thanks for posting, Steve

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1/4-20 unc is the true camera mounting thread but 1/4 whitworth are so close in thread form and pitch they are interchangeable

Sent from my iPhone using Tapatalk. Blame Apple for the typos and me for the content

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Given the antiquety of tripod threads (back to victorian days) I always assumed 1/4 BSW was the standard in the uk and 3/8 on the continent. UNC is predominantly a Candian/USA standard.

There is a minimal differance in pitch angle of the thread between 1/4 BSW and 1/4 UNC. If the receiving female thread is not to precise either will fit.

Just be aware that sometimes the manufacturere will actually tap the hole precisely.

Edited by astrofox

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My solution to this type of DSLR/Dovetail, i remove the head from a Slik Tripod, drilled out one of the holes on the Dovetail bar to enable a bolt to go through the hole and clamp the tripod head to the Dovetail, the head of the bolt acting as a stop when the Dovetail was clamped in the Mount....

2012-03-13180805.jpg

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It's certainly worth mounting a tripod head on to the dovetail so you can adjust the orientation of the camera

Sent from my iPhone using Tapatalk. Blame Apple for the typos and me for the content

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To allow for orientation with the minimum risk of flexure, I use a Manfrotto #234 tilt head mounted on a Vixen dovetail bar using a 1/4" x 20 UNC bolt.

wide_swivel.jpg

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On ‎16‎/‎07‎/‎2012 at 23:34, steppenwolf said:

To allow for orientation with the minimum risk of flexure, I use a Manfrotto #234 tilt head mounted on a Vixen dovetail bar using a 1/4" x 20 UNC bolt.

wide_swivel.jpg

Hi Steve

Old thread resurrection! Lol
I’ve been looking for a way to mount my D5300 (480g) + Tamron 135mm lens (370g) onto my HEQ5-Pro, along with a finder-guider. I’ve been eyeing up the Manfrotto 234 tilt head and Dovetail bar setup, which is how I came across your post above (from back in 2012!).
As far as I can tell, the Monfrotto 234 has a standard 3/8”-16 thread in the bottom, but most dovetail bars only have 1/4”-20 sized holes. I see you used a 1/4”-20 UNC screw on yours. Do you mind if I ask a few questions?

1. Did you just use a bushing adapter to connect the Manfrotto to your dovetail?
2. How long do you recommend the screws should be? I don’t want to order ones that are too short/long. Where did you source yours from?
3. Did your setup give you any problems, e.g movement or differential flexure?

Thanks in advance!

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Hi Ciarán, an old thread indeed!

1. Did you just use a bushing adapter to connect the Manfrotto to your dovetail?  Yes

2. How long do you recommend the screws should be? I don’t want to order ones that are too short/long. Where did you source yours from? The Thread is 17mm and the total length of the countersunk bolt is 20mm. I countersunk the hole in the bottom of the dovetail bar so that with the bolt inserted, it was flush with the bottom of the dovetail bar. I had the bolt in my 'spares' box as it was one supplied with a Sky-Watcher tube ring fitment for a camera attachment but any 1/4" -  20 UNC countersunk bolt will be fine but you will have to do as I did and cut it down to size unless you can find one that is exactly to my spec. but to be honest, one of these would be perfect!

3. Did your setup give you any problems, e.g movement or differential flexure? No it was pretty solid but there is the propensity for differential flexure in a system like this but the camera and lens were light so this helped a lot!

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Just to clarify: Whitworth threads are expressed as "threads per inch" (TPI) and diameter, whereas UNC threads are expressed as pitch and diameter, although the majority of tables will indicate the TPI of the UNC thread. The included angle on a Whitworth thread is 55 degrees as opposed to 60 degrees for a UNC thread. For a 1/4 inch bolt both UNC and Whitworth have 20 TPI. However, the thread depth is somewhat different, predominantly as a function of thread angle.

Nevertheless the most important consideration is the  thread angle mismatch by using a Whitworth "bolt" in a UNC "nut" or vice versa, as it generates effectively a single point, or in the above scenario a single ring contact area. As a consequence there would be a tendency to over tighten such combinations in order to achieve the required tightness due to the significant reduction in surface area and subsequent reduction in elastic stretch within the mismatched thread combination; this in turn does eventually lead to palling of the thread and in extreme cases failure of the thread(s) themselves.

It would be a real shame for a very expensive lens or camera to hit the concrete for the sake of  a 25 pence bolt.

K

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On 08/01/2019 at 23:34, steppenwolf said:

Hi Ciarán, an old thread indeed!

1. Did you just use a bushing adapter to connect the Manfrotto to your dovetail?  Yes

2. How long do you recommend the screws should be? I don’t want to order ones that are too short/long. Where did you source yours from? The Thread is 17mm and the total length of the countersunk bolt is 20mm. I countersunk the hole in the bottom of the dovetail bar so that with the bolt inserted, it was flush with the bottom of the dovetail bar. I had the bolt in my 'spares' box as it was one supplied with a Sky-Watcher tube ring fitment for a camera attachment but any 1/4" -  20 UNC countersunk bolt will be fine but you will have to do as I did and cut it down to size unless you can find one that is exactly to my spec. but to be honest, one of these would be perfect!

3. Did your setup give you any problems, e.g movement or differential flexure? No it was pretty solid but there is the propensity for differential flexure in a system like this but the camera and lens were light so this helped a lot!

Thanks Steve!

ps - out of curiosity, what camera and lens were you using? (i can't really tell from the picture, was it a QHY of some sort?) Just wondering what sort of weight you were holding, compared to the weight i will be supporting (a little over 1Kg) 

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On 09/01/2019 at 13:53, KevS said:

Just to clarify: Whitworth threads are expressed as "threads per inch" (TPI) and diameter, whereas UNC threads are expressed as pitch and diameter, although the majority of tables will indicate the TPI of the UNC thread. The included angle on a Whitworth thread is 55 degrees as opposed to 60 degrees for a UNC thread. For a 1/4 inch bolt both UNC and Whitworth have 20 TPI. However, the thread depth is somewhat different, predominantly as a function of thread angle.

Nevertheless the most important consideration is the  thread angle mismatch by using a Whitworth "bolt" in a UNC "nut" or vice versa, as it generates effectively a single point, or in the above scenario a single ring contact area. As a consequence there would be a tendency to over tighten such combinations in order to achieve the required tightness due to the significant reduction in surface area and subsequent reduction in elastic stretch within the mismatched thread combination; this in turn does eventually lead to palling of the thread and in extreme cases failure of the thread(s) themselves.

It would be a real shame for a very expensive lens or camera to hit the concrete for the sake of  a 25 pence bolt.

K

Thanks Kev. Although i'm still not sure which is the right one, a UNC or a Whitworth?

In any case, before i saw yours and Steve's post, i ordered the parts today. Hopefully they will be ok! Here's what i went with in the end:

I got this adapter to connect to the bottom of the Manfrotto (it's sold specifically as a Manfrotto adapter, so has the right sized 3/8 Male screw on the top, and a standard 1/4" Female end on the bottom). 

811434671_ManfrottoAdapter.jpg.c1f7df0666ba4114235346a88a380028.jpg

The whole thing will then reside on a Celestron Universal Mounting Plate (CG5), specifically on one of the 1/4" threads near the right hand edge. Note, the dovetail itself is 15mm thick:

94213-hole-distances.jpg.3b41551fc02d954d27c722a10cb8a834.jpg

The Celestron dovetail has a flat bottom, and i didn't want the screw to foul it, so i needed a 1/4" grub screw to connect the dovetail to the Manfrotto adapter. I went for this, at a length of 3/4" 

https://www.ebay.co.uk/itm/UNC-A2-Grade-Stainless-Steel-Socket-Grub-Screws-Allen-4-6-8-10-1-4-5-16-3-8/292725587589?ssPageName=STRK%3AMEBIDX%3AIT&var=591518004116&_trksid=p2057872.m2749.l2649

s-l1600.thumb.jpg.2926a1c5e1fe94dfa1e4321d380048b8.jpg

 

Any thoughts on this guys? My only slight concern is the grub screw. Just want to make sure it's going to be strong enough to do the job.

Cheers!

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9 hours ago, Xiga said:

ps - out of curiosity, what camera and lens were you using? (i can't really tell from the picture, was it a QHY of some sort?)

This supports a Starlight Xpress SXVF-M25C CCD camera and a Canon 200mm L camera lens.

8 hours ago, Xiga said:

i'm still not sure which is the right one, a UNC or a Whitworth?

1/4" - 20 UNC is what the original designers used but it just so happens that Whitworth is very close to this. I always use UNC for this application where possible but have never had an issue with a 1/4" Whitworth when I haven't been able to find a suitable UNC.

 

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1 hour ago, steppenwolf said:

This supports a Starlight Xpress SXVF-M25C CCD camera and a Canon 200mm L camera lens.

1/4" - 20 UNC is what the original designers used but it just so happens that Whitworth is very close to this. I always use UNC for this application where possible but have never had an issue with a 1/4" Whitworth when I haven't been able to find a suitable UNC.

 

Good stuff. Thanks Steve! 👍

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The only way, on a realistic basis to establish what threads are what is to utilise a "thread form gauge"  held against the thread and then up to the light to establish the included angle of the thread (external). Internal thread forms are determined by using a precision ground thread "plug gauge". Both of which are beyond the scope of  the average person namely due their cost and the fact that in a "domestic" situation they would be used once in a blue moon.  I am sure (no liability accepted) that for our particular lightweight requirements a 1/4 UNC and 1/4 Whitworth thread are effectively interchangeable; however, in an engineering perspective it is always best practice to establish what is what before use. Or it might be me just being pedantic.

 

Edited by KevS
yet another senior moment

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