Modifying TAL-1

[AndyH]

The big lump of alluminium is starting to take shape. Shall follow it's progress with interest.

[bambuko]

Focuser base roughed out before final machining:

[bambuko]

More updates:

Focuser base ready and being fitted to the tube.

I have made a cut-out in it, to allow space for spider fixing.

It will mean that if I ever want to take spider out I will have to remove focuser first, but since it is not exactly everyday job I am quite happy to put up with it.

Of course it doesn't have to be made from shiny aluminium   - anything including wood could have been used and it could have been made simpler if I didn't have machinery to do it.

At this point I could have used off the shelf focuser (the base provides convenient fitting for anything you have), but I don't have spare focuser (and don't think much about cheap Skywatcher thingy I have on my other scope anyway, not to mention the fact that I cannot afford decent focuser that would cost about x15 what I have paid for the TAL-1   ) so I am making my own one:

It will be 1.25" Crayford.

Body is big enough to accommodate 2" but it is not necessary for TAL, so for now it will be 1.25 and if I ever move it to another OTA I might modify it later.

More to follow...

[bambuko]

Next step was to add bearings.

Bigger dia (11mm OD) than usual ones, for smooth operation.

On reflection, next time I will probably use even bigger diameter.

Next I need to sort out the front roller shaft and adjusting knobs.

[nightfisher]

You are making a very tidy job of this, look forward to the finished scope

[AndyH]

To paraphrase Jerry Lee Lewis, "There's A Whole Lotta Millin' Goin' On"

Lovely stuff,

Andy.

[bambuko]

At long last bit more progress!

Just received bit of stainless I needed for the focuser tube:

It is 38mm OD and 32mm ID - should be just right with a brass compression ring inside.

BTW it was expensive and very difficult to find (in quantity I needed )

In future any focuser projects will start with finding the focuser tube and everything else will be designed/built around it...

not the way I did it this time - having designed and build the body only to discover that sourcing of the focuser tube is right PITA

[bambuko]

Picking up where I left sometime ago   (well... actually long time ago, but that's another story).

Assembled focuser, with two adjusting wheels (one large dia for precise and one small dia for quick adjustment) still to be fitted:

Eyepiece tube (stainless steel) is lined up with brass to protect eyepieces.

Eyepiece securing bolts are nylon, again - to protect eyepieces.

Openning dia is 1,25" precisely, so that (for example) collimating tools fit snugly in, remaining parallel when secured with retaining bolts.

Testing with some cheap eyepiece:

Hopefully, all will be fitted and ready for Monday eclipse session (touch wood, weather promises to be kind )

[bambuko]

And a bit more progress today:

Main bearing block. You can see the design - on the right ball the thing pivots on and on the left spring that tensions it.

And below the business side - silver steel, hardened pin to roll eyepiece drawtube up/down:

Getting closer to the first test:

More to follow...

[bambuko]

First light with new focuser tonight (just enough breaks in the cloud to try full range of eyepieces on the moon).

Everything works perfect.

Drawtube does not enter inside the scope tube when eyepiece is focused - I was worried about getting this wrong.

With moving the mirror by 33mm and new focuser there plenty of room for muck ups but it seems I got away with it...

Adjustment/focusing is light and precise.

OK... I could have made it smaller and less tank like , but I am happy with my first focuser.

I am ready for eclipse on Monday and then next stage of this project - I am planning to fit it on TAL-2M mount.

TAL-1 mount is more robust and steady than comparable far eastern contraptions, but as far as I am concerned GEM can never be too beefy,

so TAL-2 mount and TAL-1 tube will be just made for each other (plus of course TAL-2 mount is motorised on RA, so a lot better than TAL-1 mount).

[bambuko]

None of you esteemed readers of this thread have noticed it (or at least nobody commented...), but I've got an admission to make - I made a "deliberate mistake"

The drawtube (and specifically the way that eyepiece is secured) is rubbish

Not that you would notice it if you used the scope for just visual (and TAL is very tolerant anyway!), but it becomes noticable when one is collimating it.

Every time you insert cheshire it is in slightly different position.

Two screws securing it against one fixed point opposite make the alignment quite random depending on which screw is tightened frirst etc

Schoolboy design error and quite embarrasing, but the solution is very simple, well know and used in the workshops since time immemorial

Vee block, secures any round bar repeatably, precisely and easily:

So my new/replacement drawtube will follow this principle.

More to follow...

ps I hear that some chap in US has patented this idea, gave it fancy name and sells it as a telescope adapter...

[Roy Challen]

I really like the different size focuser knobs. Great idea!

[bambuko]

Not my idea

I've found it both here and on Cloudy Nights (and I guess somewhere else), where people were adding large knob out of various scrap bits to enhance precision focusing.

So it seemed like a good thing to try, and yes! it works very well indeed.

[nameunknown]

OK - I can see where this going (I have an old TAL as well) - steam-punk TAL upgraded to Hubble quality, shot into space with warp drive based on TAL behaviour uncertainty....Russian technology conquers the galaxy (with percussive maintenace)....

[bambuko]

Modified focuser:

From this angle you can see two brass pads forming vee that locates eyepiece, cheshire etc:

Everything (in this case my own diy cheshire) locates precisely, positively and repeatedly:

I am ready for Gravimetric Field Displacement Manifold launch

[AndyH]

Am enjoying this ongoing build thread. Keep up the good work !

Andy.

ps: especially love the knurled knobs.

[bambuko]

There is one minor (un-intended) benefit of this design for the drawtube:

It will happily accept any eyepiece from 30mm dia to 32mm dia - small eccentricity being of little concern as long as eyepiece is pointing the right way... and it always is because of vee block design