Esprit 100 tube ring screws

[Andyb90]

Hi Everyone,

I'm looking to replace the tube ring screws that I got with the Esprit 100 for countersunk ones.

I have some M5 screws but they don't fit the threads in the tube rings. However my 5mm hex key does fit into the Skywatcher screws.

So I think maybe the thread pitch/count on the Skywatcher screws is different. If anyone knows the proper spec for the screws it would be great to know.

Andy.

[DRT]

Andy,

Can you please post pictures of the rings?

Standard SW rings have camera attachment threads on one side and M6 on the other for attaching the dovetail. Perhaps you are trying to attach your dovetail to the camera threads?

Edited February 18, 2017 by DRT

[Davey-T]

It should have proper CNC rings thread is probably 3/8" UNC if 6mm don't fit.

Dave

[Andyb90]

Below is a picture which shows the bottom of the rings. They are CNC ones. They're attached to my losmandy plate with the Skywatcher screws.

You can see the screws protrude. They are cap headed. I want to replace them with countersunk or button versions that (hopefully) won't protrude.

I had a reply on CN saying the screws are 1/4 20. From what I can gather that is imperial UNC. So I've ordered a few to try.

Andy

Edited February 19, 2017 by Andyb90

[darren west]

can you please take a pic of the bolt over a tape measure for me the width of the thread should be close to 6mm if they are indeed 1/4 unc 

also is the plate aluminium and if so don't be tempted to order stainless steel bolts as you will cause issues 

Edited February 19, 2017 by darren west

[Andyb90]

2 hours ago, darren west said:

can you please take a pic of the bolt over a tape measure for me the width of the thread should be close to 6mm if they are indeed 1/4 unc 

also is the plate aluminium and if so don't be tempted to order stainless steel bolts as you will cause issues 

Below is a pic. It does seem to be about 6mm

The losmandy plate is an Altair TMS one. It has this description. "Made from the highest grade British aerospace 6068 T6 tempered and artificially aged aluminium, which has the highest strength in the 6000 series alloy range and is extremely corrosion resistant". So I guess it's an Aluminium alloy?

The bolts I've ordered are stainless steel. I've just looked for aluminium versions and found a website that does them, but they are custom made and the minimum order quantity is 100. How much of a problem would the stainless steel ones be?

Andy

[Davey-T]

Looks too coarse for 6mm, metric has about 23 threads per inch, UNC has 16 TPI

I use stainless steel screws and haven't had any problems

Dave

            UNC on the left            metric on the right

Edited February 19, 2017 by Davey-T

[101nut]

Not sure what problems are suggested with stainless screws as they're widely used. If in doubt a dab of thread sealant or even furniture wax will solve possible corrosion issues in very damp 'telescope' environments but problems are unlikely ...

Stop considering aluminium screws unless you really know what they are and the mechanical properties you expect of them ... IMHO simple plated mild steel would be a better option than aluminium.

If your new screws don't work for any reason:-

My Altair vixen clamp was supplied with low-profile cap head screws for flush mounting in shallow counter-bores. I could not find longer replacement screws with the low profile heads so simply ground the heads down of some new but 'standard' stainless cap-head ones enough to be flush with the plate. The hex socket is obviously much shallower but, in my case at least, was still more than deep enough and the metal tough enough to take a well-sized allen key. A Dremel or such like would probably work.

AndyG

[Andyb90]

This is proving to be a bit of a pain. I got the 1/4 20 screws I ordered and the thread is a match to the tube rings but the screw heads are too wide to fit into the slots of my losmandy plate without protruding. Here is a picture:

And this shows the slots:

I've just been trying to file down the edge of one of the button cap screws to see if I can make it fit but no luck so far. Have given up for now as I need sleep! I thought this issue would be simple to sort out!

Andy

[RayD]

Have you tried Astroboot, they have all sorts and may well have the exact replacement?

Astroboot

I'm lucky that I have a fastener supplier close by who I can take the 2 parts I need to fix and they have a huge stock of items from which they have always found a perfect solution, so may be worth investigating whether there is something similar in your area if no joy with Astroboot.

[Davey-T]

Had the same problem with Losmandy plate holes and just reduced the head diameter with a bench grinder, I think a file will take ages.

Strangely some button head screws I had already had smaller heads so guess it's just pot luck.

Dave

[Andyb90]

I've had another look on the web and found some low head cap screws with the right spec.

https://www.accu.co.uk/en/64-low-head-cap-screws

The heads have a smaller diameter, so I think they'll fit into the holes. I've ordered a few to try.

Also another website suggested putting the button head screw in a drill and pressing a file against it rather than hand filing. I could give that a go if the new screws don't work.

Or even get a grinder as they seem reasonably priced.

Andy.

[Andyb90]

Fortunately the new low head cap screws are a good fit, they don't protrude at all :-). In case anyone else comes across a similar problem here is a full link to the ones I ordered.

https://www.accu.co.uk/en/64-low-head-cap-screws#elasticsearch_id_feature_352218=352218_697&elasticsearch_id_feature_352248=352248_1&elasticsearch_id_feature_352230=352230_16&elasticsearch_id_feature_352249=352249_729&elasticsearch_id_feature_352138=352138_161&id_elasticsearch_category=64&orderby=ranking&orderway=asc

Andy

[Andyb90]

I have another issue now. I'm trying to bolt a dovetail bar to the top of the tube rings for my st80 guide scope. But the 1/4 20 unc screws don't fit the center thread on the top of the rings. Oddly enough they fit the 2 threads either side of the center one. Here's a picture. After 2 turns the 1/4 20 screw sticks in the center thread.

Does anyone know the spec of the screw needed for the top center thread? I assume it will be a unc screw.

Andy.

[DRT]

I suspect it is a metric thread (M6?) which is intended for exactly the purpose you are trying to use it.

[Andyb90]

I got a 1/4 20 tap and wrench this morning and was able to open the threads up. Looks like It was the anodizing causing the issue. My 1/4 20 screws now fit, which is a bit of a relief :-)

Andy