Chriske

This OCAL tool can  not be used on stars as I thought it would.
Initial collimation is done by pointing the scope at the sky during daytime. So I did.
Later on, during night, I found out that collimation was not perfect at all, although OCAL told me it was.
Some more collimation needs to be done.

I also found out I put to much tension on the mirror. Remember I needed to fasten  the mirror in it's holder, but doing so I pushed(screwed) to hard resulting in slight astigmatism.

Later on today I will perform final collimation not using this OCAL tool...🙄

Forgot to mention : still 1.1m to add to this tower = another 5 floors.

Peter busy adding a few floors

Only now I see that someone has already tuned this scope in the past.
The (red)seals of two collimation bolts are broken. The one on the upper left is intact the other two bolts have been rotated.
Normal factory procedure is that seals are applied after collimation is completely done.

Made a quick drawing showing 4 different ways to work with nuts and bolts in printed parts.
The one on the right is a hole big enough to add a insert Alan showed higher up.There are some special insert for printed parts. But they're not as good imo.

I hope this topic will help others repairing or collimate their Mak if needed.

Busy repairing a 125mm Maksutov
It is one of the 'travel instruments' from our local observatory.
From what I've been told someone has dropped it on the ground...🙄...

First thing I've noticed was a major image tilt during focusing. I know this is common issue with these scope, even SC have a very small image tilt. But with this little scope it was severe. Stars moved more then halve the field of view during focusing. On top of it there was gigantic coma.
Work to be done.

This Mak ETX125 has no collimation bolts at the outside of the tube. So I completely took it  apart to see what had happened during it"s 'free-fall'.
First thing I've noticed that the primary mirror could be tilted in it's holder. With the aid of its central threaded ring I pushed it back toward it's holder.
After re-assembling there still was coma in the centre of the FOV. Took it apart again and bought a electronic collimator from OCAL.
Also printed a few rings to hold this ETX on a mount any mount. I had to go this way because there's no way to support the scope after removing the lower part of this ETX.
I also printed a eyepiece holder because the focuser also is part of that lower part.
This ETX (22 years) old is not designed for easy collimation if something happens...😡
If I'm not mistaken the latest ETX version do have easy access collimation bolts at the back of the scopes.

Waiting for clear skies to do final collimation....

Digging in an old box filled with spare parts I found a little polaraxis-scope from an old Vixen mount.
The eyepiece  has a reticle on board marking the distance between the exact North and polaris.
I also found on the net the correct value distance Polaris-TN : 40'37"

The only thing I  need to do is add a red LED to illuminate that reticle.

Prusa slicer can do the same thing if I'm  not mistaken.

These inserts Alan posted higher up, I use them all the time.
They're intended to be used in wooden constructions but they work just perfect for printed projects too.
Ours here look a bit different.
Anyway, I heat them a bit for easier insertion in printed projects.

One more important issue about tapping in printed parts... GO S*L*O*W... very slow...!
It is a soft material indeed and you might think tapping fast just because it is very soft.
Well, the problem is that the material will not release by itself from the tap, while your tapping in printed parts. The trick, like tapping in metal, turning the tap once in a while counterclock a little bit does not work in printed parts at all.
Blind holes (depending on how deep you need to go) are done in 4 'sessions'. Tap a few mm and remove the tap completely, clean the tap and continue tapping. Removing is also done very slow...!
Tapping a hole were you can see the tap at the other side sticking out(thinner parts)tap in one session, first remove the material sticking to the tap and then remove the tap, again very slowly.

Needles to say tapping in printed parts takes time...

If you tap in one go without cleaning the tap, the rubble will destroy the thread completely.

1 minute ago, CraigT82 said:

Thanks, are these dimensions specific to PLA?

For any filament type...
The figures in that list are for any material as a matter of fact, even (any)metal.

So for a thread M5 you need to draw a 4.2mm hole. After a part is printed I always clean these holes with the correct drill..

3 minutes ago, CraigT82 said:

Thanks for that very useful info.

So if I design the holes into the drawing of the part, would the slicer software add the infill wall around the hole?  Or would I need to design that hole wall into the initial model?

If I planned the holes for tapping, how much smaller does the designed hole need to be?  Say for a M5 tap would the initial hole want to be 3mm? 4mm?

Cheers 

1 hour ago, qisback said:

If 3d printed it’s always better to plan the holes rather than drilling.

During the print it will layer a 100% infill wall around the area which is almost always solid rather than infilled. You can then put brass threaded inserts secured with a small dab of glue/plastic weld, this means the force from tightening the screw will be spread through the brass threaded insert through the 3d printed part.
If you secured directly by drilling and tapping the 3d part, the hole is would almost certainly be drilled through an infilled area (normally 15-25% infill unless changed) which is almost impossible to tap, you would need to design the holes into the print to be smaller than you needed so a wall is printed and thus is able to be tapped, however the force would be applied directly to the PLA which is soft (also changes with temperature) and is easier to strip.

 

+1

I'll add : if the parts does not come apart I'll always tap in the PLA itself. Drawing a hole in advance, so the position of the holes are perfectly in line. The upper part is always drilled a bit bigger, so no tapping in that part at all, Only the lower part needs tapping.
If the parts do come apart very often for some reason you absolutely need to apply inserts...!!

It should run much smoother. That's the purpose of these precision rods...👍

Finishing this scope I have to deal with a few minor issues.
There are a few reflections from white (printed) parts. Needs to be blackened. It's known problem with folded scopes
A few baffles here and there.
A proper fork, I'm thinking of a 'Berry style' fork. The one in the picture is a 'two minute' fork so I could test right after installing the optics.
Adding some weight to shift the balance point a bit more to the centre of the optical tube. I like to keep the difference in height of the eyepiece (between high and low observing point) as small as possible. But I'm afraid I'll need lots of weight to compensate for this issue.
Finishing the mount that goes with it.

Again... first light was  👍

Just had a quick peek and this lens is surprisingly  good.
Need to test some more because the Moon was not to high in the sky and a few tree branches were in the line of site.

Maybe later on this evening ; first light. Made a dummy fork to support that scope.

You should see them now, correct...?

Also printing five F1 thrusters

Assembling LUT

Last night first test for the laser position. And with success.
The laser was collimated in it's aluminium tube, was done in a lathe.
The two holes, for polar axis and laser unit were printed parallel.
Mounting the laser in its unit and aiming it toward the exact north. I had no aid to do that, so eyeballing. But with the knowledge that North was about 0.5° from Polaris and in the direction of beta Umi, I was very close. Aiming the laser was done by adjusting the mount of course.

I was so close in fact that I could track a star at the equator for about 25minutes without the need for correction in declination at all(at 125x). I was a bit surprised as a matter of fact.
Yesterday's tracking was done manually, now the only thing to do is connecting the stepper to the RAMPS.