Options for custom connecting piece for Baader Steeltrack - advice wanted!

[Giles_B]

I'd like to connect a Baader Steeltrack to my ScopeTech STL80A-L - I've come across this thread on astrosurf - a french astonomy website - which suggests it is feasible http://www.astrosurf.com/topic/137491-changement-porte-oculaire-critères/ although I can't quite work out what is going on with the Baader side of the connection from the design sketch.

I've also found an engineering shop nearby who are willing to take on the production of a one-off part.

As the Baader side of the connection is not clear in the thread I can think of two possible design options, sketched in section below, but I'm very new to doing DIY on the telescope and I'd be interested which you thought would be the better design (or if an alternative would be better).

The options are

A - Connect to the Baader steeltrack using the steeltrack's integral 88mm dovetail. The custom part slides over the outside of the steeltrack and is screwed into the dovetail with 6x M5 screws

B- Connect to the Baader steeltrack using the M68 connector it comes with. The custom part is machined with a M68 thread and screws on.

In both cases the connecting piece slides inside the Scopetech tube, and is connected with 3x M4 screws.

Apologies for my sketch, but hopefully the options are clear:

[markse68]

Hi Giles, not familiar with the steeltrack but from the pictures in the linked French forum post they have put a male circular dovetail that fits inside (not outside) the base of the focuser, and grub screws tighten the steeltrack onto that dovetail, ensuring a secure, centred, and square junction with the adapter, with a parallel tubular part that fits inside the ota sufficiently long to also assure squareness.

Mark

Edited January 28, 2023 by markse68

[Giles_B]

Thanks Mark  - the dovetail part of the sketch is confusing, because the steeltrack has an integral dovetail:

Moreover the photo on astrosurf doesn't seem to show a dovetail - or am I missing it?

I really can't see how the dovetail in the sketch would connect to the steeltrack (unless the steeltrack is of an earlier design than the one above)

[markse68]

Oh that's strange- the focuser they show seems to not have that male dovetail- must be a different version. 

In that case yes I'd go with your first option- what diameter is your OTA tube? Maybe not M5 grub screws- my Feather touch is held on with M3 or M4 I think- you want something that will push on the sloping side of the dovetail to snug it up. That will also allow you to rotate the focuser to desired orientation. Will mar the surface though unless you use nylon tipped screws but they wouldn't be so secure. If you did the second option it would avoid marring the dovetail but maybe not so easy to orient it? How does the M68 connector attach to the steeltrack? Would that allow orientation? If so either option should work well

Mark

Edited January 28, 2023 by markse68

[Giles_B]

Thanks Mark. The baader comes with m5 grub screws to fix to the dovetail. It also has a locking screw - so long as this is loose the part mounted on the dovetail can rotate, so the m68 adaptor can be reoriented.

One of my worries was that the dovetail would be secured by a 2mm thick piece of aluminium in design A, and this wouldn't be strong enough - but this doesn't seem to be a concern you have, so I'm reassured on that front.

[markse68]

Hi Giles, I hadn't noticed that actually. It is a bit thin but maybe OK- you're only going to get a couple of threads for the grub screws though.

Is this the M68 adapter it came with? If so then if you made the wall thickness the same as they have and use the same 6 nylon screws and lock screw in the first design.

Then you'd effectively have a custom version of this that they sell for refractors with a 97mm inner diameter. If it's good enough for Baader it'll probably be fine

Mark

[Giles_B]

Thanks Mark, that's good advice. I appreciate having talked it through. I  think I'll increase the wall thickness by another millimetre at that end of the connector.

The lead time from the engineers is about 5 weeks on the part, but I'll post back with a full report once I've received it.

[Giles_B]

Apologies for this very belated follow up to the original post.

It took a long time to get the part, the original shop going incommunicado to my emails, more shopping around and finally finding a second well reputed local engineers who specialise in making custom parts, but at a much higher quote than the original one, which meant further saving and delaying.

After some discussion they recommended keeping thing simple with a connector that would attach to the M68 adaptor. This meant that the adaptor could stay short and achieve maximum robustness at minimum length. I was happy with part when it turned up, and it mated the two parts well - the little movement on the telescope side disappeared after painting the part:

I've now had the part about eight weeks. Initially had to return it for a skim of the inside diameter so there was better side to side movement of the focuser to allow collimation. As you see on the photo the collimation is not quite there when checked with a laser, but there is no splitting of the laser as it passes through the objective, nor is any miscollimation visible to me on a star test. In any event my experiments with realigning using the adjustment screws on the focuser have shown it is tricky to achieve a better result than the one shown.

 

The scope is well balanced despite the extra weight of the Steeltrack focuser, and the most important result - to achieve more in-focus with this excellent scope, has been achieved very nicely - I have a massive 35-40mm more in focus and am able to achieve focus even with my Naglers (although they aren't well suited to the usual seeing conditions of solar observation). After painting the part with blackboard paint inside and out, I am also very pleased with the visual appearance as well as the performance

 

 

Edited April 9, 2023 by Giles_B
added information