6 inch f15 Open Tube Refractor Build

[spearbearer]

Hello to anyone looking in.

Seven whole years ago I began a thread about a proposed build of a 6 inch f15 refractor. Several members of this forum were kind enough to express interest in the project and some of you offered very useful advice. Just as I was about to start the build, I somehow allowed myself to be diverted by  a sudden interest in small stationary steam engines. I decided to make a 'quick' detour, but this led to my building two engines, and needless to say it was not quick at all...

After that I moved (two and a half years ago) from Guernsey in the Channel Islands to the Isle of Skye, and the dust is just beginning to settle with a house in the process of being refurbished and a brand new workshop which is almost finished but already useable. Unfortunately at no point did I come back to the forum to explain my absence. I apologise for my rudeness in this, given that people had been so interested and helpful. I was a little shocked to realise that seven whole years had passed. The previous thread has been archived due to inactivity and I know no way of resurrecting it, so I am now starting a new one.

I am now just about to finally make a start on the build. I have the iStar 150 mm f15 objective, a set of black anodized aluminium tubes and some marine plywood and aluminium plate for the rings. My plan is to try something a bit different and make the scope more portable and storeable by building it in three sections which can be taken apart when not in use. I have a reasonably clear idea of where I'm going with it, though I can foresee that there will be some challenges - not least of which could be with regard to maintaining collimation. But nothing ventured, nothing gained! If it doesn't work out I'll try something different, using as many of the same materials as possible. However, I am hopeful. 

I intend to post regularly on this thread with a bit of a build log. I'm still busy with our house here in Skye, but the evenings will be reserved for this project so although progress will be slow there should be some development over time.

Meanwhile, I will try to message each person who commented on my earlier thread given my rather abrupt disappearance seven years ago.

All the best,

Gary

[bosun21]

Good luck with your endeavour. How many lenses do you intend to use?

[spearbearer]

Thanks!

The iStar is an achromatic doublet. My thought is just to use my existing eyepieces with it - a Baader Planetarium Hyperion Universal Zoom 8-24mm and a William Optics Swan 33 mm 72 degrees. I'll likely use a star diagonal with these.

Optically it will be based on Richard Berry's design, though it will be very different in terms of appearance.

Is that what you meant?

[John]

Great to hear that this project will get up and running again - thanks for the "heads up". I will keep dropping in to see how things progress 🙂

 

[NGC 1502]

Welcome back😊.    I’m familiar with the “Richard Berry” style refractor style alt-az mount.  I think that’s a practical solution to mount a long and large refractor for visual use.  An EQ mount for such a beast would be a massive affair to be successful.

Good luck and keep us posted👍

Ed.

[spearbearer]

10 hours ago, John said:

Great to hear that this project will get up and running again - thanks for the "heads up". I will keep dropping in to see how things progress 🙂

 

Many thanks John - great to hear from you again. I look forward to checking out what you have been doing too. 👍

[spearbearer]

10 hours ago, NGC 1502 said:

Welcome back😊.    I’m familiar with the “Richard Berry” style refractor style alt-az mount.  I think that’s a practical solution to mount a long and large refractor for visual use.  An EQ mount for such a beast would be a massive affair to be successful.

Good luck and keep us posted👍

Ed.

Hi Ed, and thanks for your comment. Yes, a Berry-style alt-az is the plan . I may tweak the appearance of it a bit, but the mechanics will be based on his. Cheers, Gary.

[Peter Drew]

I'm still interested after 7 years!  I have built several 6" refractors including my Ha solar refractor which has an Istar 6" F10 objective.

[Rusted]

I can't remember if I responded to your last thread.

I have two iStar objectives. Both excellent. 6" f/10 H-alpha. 7" f/12 R35.
I built a offset/counterbalanced Berry style mount for my home made 5" f/15 back in the 1980s.
Whereupon I discovered that the push required was almost perfectly matched in all directions.
Until I reached the black hole near the zenith. Then things became distinctly sticky.

I also discovered that unwanted twisting of the tripod legs caused backlash.
I used 2" scaffolding tubes for the legs.
The weakness lay in their connection to the head via simple angle brackets.
I suggest a substantial pier if it is at all possible. At least 6"/15cm diameter.

 

[spearbearer]

5 hours ago, Peter Drew said:

I'm still interested after 7 years!  I have built several 6" refractors including my Ha solar refractor which has an Istar 6" F10 objective.

That's great to know, Peter. I appreciate it!

I look forward to catching up with your  own topics as soon as I can.

[spearbearer]

5 hours ago, Rusted said:

I can't remember if I responded to your last thread.

I have two iStar objectives. Both excellent. 6" f/10 H-alpha. 7" f/12 R35.
I built a offset/counterbalanced Berry style mount for my home made 5" f/15 back in the 1980s.
Whereupon I discovered that the push required was almost perfectly matched in all directions.
Until I reached the black hole near the zenith. Then things became distinctly sticky.

I also discovered that unwanted twisting of the tripod legs caused backlash.
I used 2" scaffolding tubes for the legs.
The weakness lay in their connection to the head via simple angle brackets.
I suggest a substantial pier if it is at all possible. At least 6"/15cm diameter.

 

Thank you, Rusted! I don't recall you responding to my original thread, but great that you have responded to this one.

I have a lovely 8 inch ductile iron pipe with a flange at each end (and in mint condition) that I plan to use as a pier. That's a serious tripod that you built, though.

Nice looking scope, too. What is the tube made of?

I'll check out your stream as soon as I get a chance. 

 

[Rusted]

The tube was a common [or garden] PVC drainpipe.
I replaced it with a laminated 1mm marine ply tube of two layers.
Ultralight and stiff. I now use dust extractor tube in thin, galvanized steel.
A single straight seam rather than spiral. Stiff and lasts forever.
Available in many diameters and two meters long.

 

[PaulC-I]

Hi Gary,

Good to hear you are nearly back on track with original plans.

 

[PaulC-I]

Hi Gary,

Good to hear you are nearly back on track with original plans.

 

[PaulC-I]

The berry style mount definitely works well but requires a good balance with weights to ensure it keeps even pressure across the horizontal plain of the 12" az bearing. BTW 8" f12 Istar

[spearbearer]

50 minutes ago, Rusted said:

The tube was a common [or garden] PVC drainpipe.
I replaced it with a laminated 1mm marine ply tube of two layers.
Ultralight and stiff. I now use dust extractor tube in thin, galvanized steel.
A single straight seam rather than spiral. Stiff and lasts forever.
Available in many diameters and two meters long.

 

Wow! You have been very creative with materials, and with an ongoing sense of experimentation. What a fabulous looking setup. Thank you!

[spearbearer]

40 minutes ago, PaulC-I said:

Hi Gary,

Good to hear you are nearly back on track with original plans.

 

Hi Paul - great to hear from you again. Thanks for your ongoing encouragement. Now that I have gathered my main materials together I hope to start making some first cuts sometime over the next week. Pictures to follow!

All the best,

gary

[spearbearer]

38 minutes ago, PaulC-I said:

The berry style mount definitely works well but requires a good balance with weights to ensure it keeps even pressure across the horizontal plain of the 12" az bearing. BTW 8" f12 Istar

Thanks Paul - I'll keep that in mind when I get to that stage.

I see from the photos that you are  putting yours to good use with these fabulous scopes!

[John]

You have probably seen this Gary but just in case not, here are some pics and info on the Istar TCR 150 F/12 tubeless refractor. It weighed 8.4kg which is remarkably light for an F/12 6 inch refractor. The solid tube Istar Perseus 150 F/12 that I had weighed around twice that ! (as @PaulC-I knows 😉)

 

Link: Perseus TCR 150-12

 

 

Edited Saturday at 22:58 by John

[spearbearer]

Hi John - I have seen this scope before, but not this photo of it. It's worth another look regardless as it is a thing of beauty.

Will check out the link also.

Thanks for posting it.

gary

[spearbearer]

Greetings from a damp, dark, windy evening on the Isle of Skye.

I'll be updating this thread regularly with progress on the build.

I have a reasonable idea of where I'm going with it, though there are aspects that I haven't yet fully thought through. This will be particularly true once the main tube is built and I get into details such as the focuser, the mount and the finder scope. I regard making things up as I go along as part of the fun.

Accordingly, please feel free to offer alternative ideas and constructive critique, especially if you see me about to do something that you believe could be done better another way! I don't promise to follow every piece of advice I am offered, but I will certainly give all suggestions due consideration and make changes when it feels like the right thing to do.

The scope will be built in three longitudinal sections which will be connected to each other by bolts which will pass through the rings at the end of each section. All of the rings will be cut from marine plywood, but the rings at the end of each section (I'll refer to them as 'section end rings') will be faced with an additional ring cut from 6 mm aluminium plate. I am hoping that this arrangement will create joints which will be stable enough to minimise any loss of rigidity arising from the scope being made in sections, and to avoid jeopardizing collimation too much. It may even be a little over-engineered, but better that than under-engineered, I reckon... 🙂

My starting point will be these aluminium rings for the middle section of the scope. I don't have CNC, so as I bought this tool to try:

 

It's a circle cutter designed for mounting in a drill press. It's adjustable for diameter up to 300 mm, so I have set it at its maximum as that's exactly the diameter I have decided on for the rings. How it will perform against 6 mm aluminium I have no idea  - I can only try it and find out. Much will depend on the quality (i.e. hardness) of the cutting tips. If it doesn't work I'll just have to do it another way or modify the tool. In my favour is the fact that my drill press has been retrofitted with a 3-phase motor with variable speed, and when this is dialled down to minimum in combination with the slowest belt setting it gives me a speed which is very low indeed. I reckon that this - with plenty of cutting oil - will probably give me my best chance of success with this tool.

The aluminium plate is on order and should arrive by the end of the coming week...

Cheers,

gary

[Rusted]

You could do a hell of a lot of damage with that tool! 😱 I can't imagine anybody surviving within the blast radius!
That means firmly fixing down your work-piece and standing well clear. Like several hundred meters away! 
Preferably switching it on and off from across the field behind a sandbag barricade!
I doubt the chuck will remain in place for a microsecond with the loads being applied!

Where a ring is too large for my vintage lathe I just use a small power router with a circle cutting jig and high quality router bits.

 

[spearbearer]

Well, right enough I did originally buy it to see if I could open up a wormhole in my workshop so that I could travel instantaneously between it and the house to avoid the wind and the rain ...

At the drill's lowest speed the thing will crawl round very slowly with serious torque. I'll see how it goes with a slow downfeed. It didn't cost a lot, and if it doesn't work, there are as you say other options, a router compass being one of them. But not my lathe - it's not big enough for these rings either.

👍

 

Edited Monday at 09:05 by spearbearer

[Mr H in Yorkshire]

Interesting project. I too enjoy fairly complex projects and am very slowly working on a f/5 6" binoscope mounted on an alt az motorised chair mount, itself mounted on a trailer. The pace of project work with other life commitments is slow enough but changing direction and moving from one end of the country to the other is understandably going to slow you down!

I have a question about design and a small suggestion about cutting aluminium. 

Question: If you are making the telescope in sections in order to compact it for portability, are you also going to make the berry-style tripod in sections, because it is an enormous beast, quite the opposite of easily portable? 

Suggestions: Re the telescope, had you considered hinging the sections, you would end up with a zig zag folded unit but might help with maintaining alignment?

Re cutting aluminium, I have had some success with a jigsaw followed by a router for this task. First jigsaw the approx dimensions then gradually plunge cut the desired circumference. It does create the devil of a mess with very fine aluminium micro sized 'needles'. My workshop is in our cellars, I was not popular with the domestic powers.

[John]

Interesting to hear your thinking on approaches to this.

I feel the biggest challenge will be to create a structure that will maintain rigidity so that the focuser optical axis remains aligned with the optical axis of the objective and thus good collimation can be held. Even at F/15 the collimation (focuser tilt and objective tilt) needs to be accurate to secure a good star test and optimal performance. I found this with my much more modest brass tubed F/16 75mm refractor. The objective cell was colimatable but was locked down for transport when I took delivery of the scope and some adjustment was needed to get a satisfactory cheshire test and a nice star test.

So collimation adjustment facility for the objective and, ideally, the focuser should be an objective alongside a tube design that has a fighting chance of not "drooping" (technical term 😁) at either end. I'm sure these are just the sort of issues that are on your mind as you think the design though 🙂

 

Edited Monday at 11:41 by John