WO FLT98 Resurrection

[Stefan Buda]

I was approached by an IIS member who hasn't been able to get his FLT98 working anywhere near expectation and had such a bad experience with WO customer service that he gave up on them.
The scope was producing severely elongated stars on one side of the field and non symmetrical vignetting.
The owner of the scope had done a lot of tests showing that the problem was somewhere at the front of the OTA.

After receiving the the OTA, I turned a fixture on the lathe and screwed on the lens assembly for a spin to check the alignment of the lenses. Reflections from a laser showed only slight wobbles - not enough to explain the aberrations seen.

Next a visual examination of the front end of the CF tube showed a gap where the front aluminium ring was glued on, suggesting that the ring was not properly pushed home when it was bonded to the CF tube.

Next I will make a fixture so that I can screw on the tube and give it a spin.

[croweater]

Hi Stefan, very disappointing that WO aren't interested in helping out with such a problem. I'm sure a lot of people will take note of this to WO detriment. Hope you can help our member out. Cheers Richard :)

[GrahamL]

Poor customer support and even poorer QC says a lot.

[Stefan Buda]

It may have something to do with the fact that he bought the scope second hand.

Anyway, I made the fixture for the tube and I was amazed when I gave it a spin. I wish I could upload a video here. The focuser end of the tube had a runout of over 10mm. That explains not only the elongated stars but also the non symmetrical vignetting.
Next I manipulated the fixture until the tube was running true and used my diamond wheel attachment to cut it off, nice and square, with minimal length loss.
Then I re-clocked the ring with the fixture and turned out the remains of the CF tube. That is when I discovered where they went wrong: The 10mm deep cut that was machined in the ring, for accommodating the CF tube, for some reason it was a bit tapered and the tube would have got jammed before bottoming out, during the bonding procedure.

Next I will make a black anodised adapter that will join the ring with the tube and make up for the lost 4mm of length.

[Stefan Buda]

All ready for bonding.

[multiweb]

Fascinating.

[CeratodusDuck]

Sure goes to show all glitzy and glamourous finishes means NOTHING if it isn't assembled right. I have never been thrilled with W.O - just glossed up Chinese items.

[Atmos]

Love your work and attention to detail Stefan :thumbsup:

[Stefan Buda]

Thanks for the comments. I actually like this scope. They botched the assembly but the thing is well designed. The CF tube is really well made and also the lens assembly. One thing I learned is that they definitely do the collimation of the lenses before they assemble the OTA and they don't test afterwards.

The bonding is done now and I also painted the inside of the anodised adapter to further cut down reflections.
Should have a happy customer by Christmas if Australia Post can deliver.

[croweater]

Nice job Stefan. Great to see there is someone around capable of such excellent work. Cheers, Richard. :)

[AstroApprentice]

Hi Stefan,
Your problem solving posts are enthralling - seeing how you diagnose an issue and then set about rectifying it with skillful precision is really enjoyable. I'm sure you have better things to do, but I can't wait for the next poorly manufactured or QC-lacking equipment to come your way...

[Stefan Buda]

Thanks guys, but I actually don't like doing repair jobs. I much prefer making things from scratch, but when someone approaches me with a unfixable problem then I can't resist the challenge. And then there is also the bonus of learning how other makers do things.

[bojan]

Yep, we are lucky (http://www.iceinspace.com.au/forum/showthread.php?t=138076&highlight=canon+400mm) to have you on this forum :-)