Zhumell Z100 100mm f/4 Newtonian

[Alan64]

One more to go...

The last strip applied, and very last one that I'm about to install, each strip is in two pieces, as I'm using scraps to avoid having to cut into my main roll.

[Robert72]

That is looking pretty good.  Sounds like you have a terrible cough there though Alan64.  Take care.

[Alan64]

The flocking of the optical-tube is completed, although I do need to matte-blacken just in front of the edges of the flocking at both ends of the tube all round...

With the cowling and primary-cell attached, along with their mirrors...

...lovely, lovely, lovely.

Note the light peeking through at the back.

[Alan64]

5 minutes ago, Robert72 said:

That is looking pretty good.  Sounds like you have a terrible cough there though Alan64.  Take care.

Thank you Robert72.  Oh, that's just a bit of comedy there.

[Alan64]

The inner surfaces of the ends of the tube were matte-blackened up to the edges of the strips of flocking...

Now to prime and gloss-blacken all the rest where needed, including the primary-cell mounting-extensions, then the tube itself will be completed.

[Alan64]

Never again will I buy another less-than-$1 rattle-can of Wal-Mart's house-brand.  I shook the very devil out of that can, and still the paint lacked enough pigment to brush on even five times to cover.

So, I got a rattle-can of Rust-Oleum 2x "Ultra Cover" gloss-black, and to touch up the tube all over; filled holes, and scratches made by the tips of the bolts used to mount the tube-rings to the dovetail-bar.  I need to grind those down a bit more.  I had stupidly rotated the tube within the rings, whilst having forgotten about those bolt-tips needing more work. 

The first touch-ups have been applied.  In about 30 minutes I'll need to apply a second and final coat, then the tube will be completed.  You can see where one of the filled holes is...

It looks as though there's a screw-head rising up off of the surface.

I just want them sealed, along with those scratches.  It shall be pretty enough in the end.  Pretty is as pretty does.

[Alan64]

The optical-tube has been, at long-last, completed...

It will be a day from now however before the tube can be handled, and for the gloss-black paint to cure, but I do not have a pressing need to handle it.  I may now tend to the focusser, finder-base, and dust-cap here on out.

[Alan64]

And now for the ugly side; the touch-ups for the optical-tube...

Scratches...

Filled finder-holes...

Where the dovetail-bar was attached...

Where the primary-cell mounts...

The rattle-can paint isn't as black as the original...

But under normal lighting, and certainly in the dark, they shan't be noticed.  After all, this isn't an Aston-Martin.

[Alan64]

This is one of the worst plastic focussers, and with which I've ever had to tussle...

 

Hours I spent today, installing the drawtube's bearing materials, ripping them out, then re-installing them.  I had to use several layers of aluminum-foil tape, to build up the substrate.  However, I had to step the layers, a partial length here and a full-length there...

...trial-and-error, over and over.  Now, the drawtube racks in and out along its entire, albeit short, length straight and true, smooth as butter, and with no slop or binding whatsoever.  I had almost given up hope, but now, I don't how to act.

Now to re-blacken the interior of the drawtube, and satin-blacken that part of the drawtube which descends into the light-path.

[Alan64]

I neglected to mention, within my last post, that at f/4 the condition of the focusser is most critical; more so than an f/5, f/6, f/8, et al.  It is of particular importance when collimating, and of course, whilst observing.

The drawtube was prepped, first by racking the tube all the way inward, then taking a hobby-knife and describing a line all round the tube where it meets the underside of the housing.  That lowermost portion of the tube is then sanded, and with 220-grit in this instance...

...including the sides and tip of the rack.  Then, the interior of the tube was sanded, and the tube washed, dried, and masked off...

The interior of the tube was then matte-blackened...

Isn't that lovely?

Edited November 5, 2019 by Alan64

[wormix]

10 hours ago, Alan64 said:

This is one of the worst plastic focussers, and with which I've ever had to tussle...

 

Hours I spent today, installing the drawtube's bearing materials, ripping them out, then re-installing them.  I had to use several layers of aluminum-foil tape, to build up the substrate.  However, I had to step the layers, a partial length here and a full-length there...

...trial-and-error, over and over.  Now, the drawtube racks in and out along its entire, albeit short, length straight and true, smooth as butter, and with no slop or binding whatsoever.  I had almost given up hope, but now, I don't how to act.

Now to re-blacken the interior of the drawtube, and satin-blacken that part of the drawtube which descends into the light-path.

I have a horrendous focuser on an Orion XT10 that flaps about all over the place  so need to give this a try.

Is it just a case of lining the draw tube with aluminium tape and overlaying that with Teflon?

[Alan64]

3 hours ago, wormix said:

I have a horrendous focuser on an Orion XT10 that flaps about all over the place  so need to give this a try.

Is it just a case of lining the draw tube with aluminium tape and overlaying that with Teflon?

The procedure works particularly well with metal focussers...

...but that is a rack-and-pinion, and as the plastic unit that I'm working on currently.  The adjustable bearing, there at the top within the image at far left, allowed for precise centring, with a tolerance of +/- 0.5mm all round.

However, I believe that your focusser is a Crayford-type, and has set-screws to adjust its alignment.  Although, there just might be a way to improve it nonetheless via this method.

This is a distributor of PTFE sheet there in the UK...  https://www.directplastics.co.uk/ptfe-sheet

The 0.25mm, the thinnest they carry, is nigh the equivalent of a sheet of .010" that I have, and at 0.00985".  I've used that  slightly thicker within these projects; 0.015" and 0.020".

These are the materials I use when working with the PTFE...

The roll of clear tape is double-sided.  The aluminum-foil tape is that used for HVAC systems, air-conditioning and heating.  You may not need the aluminum however.  It is only to build up the substrate of the focusser's housing.  It all depends upon the spacing round the drawtube when inserted.  The aluminum tape does allow for fine adjustments, as it's even thinner than my thinnest sheet of PTFE(0.005"), and at 0.0035" to 0.004".  If the spacing is rather tight, then all you'd need is a single layer of double-sided clear-tape applied to the housing's surface, and then the appropriate thickness of PTFE.  In addition, all bare surfaces to be joined must be wiped down with either 91% rubbing-alcohol or !00% acetone, and for proper adhesion.  If you apply a second layer of aluminum on top of the first, then the first will need to be wiped, and so and so on; also, the surface of the PTFE before pressing it onto the double-sided tape.

The PTFE will lift straight up from the double-sided tape easily enough, perpendicularly, but when pulling the PTFE parallel to the tape, it will not budge in the slightest; good thing that the drawtube slides in and out, bearing against and parallel to the PTFE.

Edited November 5, 2019 by Alan64

[Alan64]

The drawtube was carefully masked off, and the bare area satin-blackened...

Only one moderate coat was applied, as you don't want it too thick.  Once the paint cures, in about a day, the sides and the stop-block of the rack, and the rim of the tube's opening, will be matte-blackened.  The tip of the stop-block will be flocked however.

[wormix]

6 hours ago, Alan64 said:

The procedure works particularly well with metal focussers...

...but that is a rack-and-pinion, and as the plastic unit that I'm working on currently.  The adjustable bearing, there at the top within the image at far left, allowed for precise centring, with a tolerance of +/- 0.5mm all round.

However, I believe that your focusser is a Crayford-type, and has set-screws to adjust its alignment.  Although, there just might be a way to improve it nonetheless via this method.

This is a distributor of PTFE sheet there in the UK...  https://www.directplastics.co.uk/ptfe-sheet

The 0.25mm, the thinnest they carry, is nigh the equivalent of a sheet of .010" that I have, and at 0.00985".  I've used that  slightly thicker within these projects; 0.015" and 0.020".

These are the materials I use when working with the PTFE...

The roll of clear tape is double-sided.  The aluminum-foil tape is that used for HVAC systems, air-conditioning and heating.  You may not need the aluminum however.  It is only to build up the substrate of the focusser's housing.  It all depends upon the spacing round the drawtube when inserted.  The aluminum tape does allow for fine adjustments, as it's even thinner than my thinnest sheet of PTFE(0.005"), and at 0.0035" to 0.004".  If the spacing is rather tight, then all you'd need is a single layer of double-sided clear-tape applied to the housing's surface, and then the appropriate thickness of PTFE.  In addition, all bare surfaces to be joined must be wiped down with either 91% rubbing-alcohol or !00% acetone, and for proper adhesion.  If you apply a second layer of aluminum on top of the first, then the first will need to be wiped, and so and so on; also, the surface of the PTFE before pressing it onto the double-sided tape.

The PTFE will lift straight up from the double-sided tape easily enough, perpendicularly, but when pulling the PTFE parallel to the tape, it will not budge in the slightest; good thing that the drawtube slides in and out, bearing against and parallel to the PTFE.

Great summary - thanks Alan I will give it a try. 

Alas my Focuser is a rack and pinion type not a super advanced Crayford 

cheers

[Alan64]

18 hours ago, wormix said:

Great summary - thanks Alan I will give it a try. 

Alas my Focuser is a rack and pinion type not a super advanced Crayford 

cheers

In that case, all the better.  I prefer rack-and-pinion myself.  I do have a Crayford, just one...

[Alan64]

The drawtube is completed.  I elected not to bother with flocking the tip of the rack...

In any event, there will no longer be a reflective tip aimed at both mirrors.

On the underside of the focusser's housing, round the opening and the edges of the PTFE strips were matte-blackened...

The focusser completed...

Quite frankly, I don't think that much of what I had painted will jut into the optical-tube during actual use, if any at all...

...but better safe than sorry.

[Alan64]

The gaps when test-fitting the focusser onto the optical-tube...

How would you go about rectifying that?  Where there's a will, there's a way.

[Alan64]

I've had these black-plastic sheets for a while.  Shims they will serve as, and to compensate for the gaps.  I'll be going inward with them almost halfway from the edge, but not quite as the flange is curved....

Any fine-tuning required, and in getting the focusser, the drawtube specifically, true and square to the optical-tube, can be accomplished with other materials that I have at my disposal.

[Alan64]

5-minute epoxy was used to attach the shims.  The epoxy set up quite fast, and a credit to its type.  The surfaces to be joined were scored, but for some reason I didn't sand them beforehand.  I don't think they'll pop off however...

After a bit, I'll trim them flush.  I only wanted to build up the surface, one step at a time.  This is just the first layer of material.

[wormix]

On 09/11/2019 at 17:03, Alan64 said:

The gaps when test-fitting the focusser onto the optical-tube...

How would you go about rectifying that?  Where there's a will, there's a way.

Is it my imagination or is the tube slightly angular right under the focuser?

Squeezing that back will close up those gaps some?

 

[Alan64]

2 minutes ago, wormix said:

Is it my imagination or is the tube slightly angular right under the focuser?

Squeezing that back will close up those gaps some?

 

The tube simply has a steeper curve compared to the shallower curve of the focusser's flange.  It was not matched well, at all, at the factory overseas.  It would better fit a 130mm or even a 150mm tube.

[Robert72]

Sorry bungled post.

Edited November 10, 2019 by Robert72

[Robert72]

17 minutes ago, wormix said:

Is it my imagination or is the tube slightly angular right under the focuser?

Squeezing that back will close up those gaps some?

 

Looks like it may be the seam?

[Alan64]

The focusser teeter-tottered side to side, like a see-saw, but no more since I installed those shims.  An aerial view, and after they were trimmed...

To those I need to add something...cushiony, like craft-foam, felt, or flocking, or all three.

[Alan64]

Here, I've bolted the focusser onto the tube...

...but only as a test-fitting.  Much improved it is, very little if any teeter-tottering, and over the condition in which it had arrived.  I could just leave it at that.  The focusser appears true and square, and with very little deformation of its flange.  This type of plastic is rather stiff; not flexible at all.

It needs a bit of dust-proofing, and some lock-washers.  Now, the angle at which I had taken that photo is by no means true and square.