TAK FSQ-85 Reducer modification

[kirkster501]

The FSQ sure is a wonderful scope.  I am sure that optically the reducer is too.  However, the same cannot be said for the reducer's frankly pathetic grub screws that hold the locking mechanism together.  These were slightly loose such that I was getting slightly elongated stars, not good for a £500 reducer.  Also the whole imaging train hangs off of this. To make matters more worrying the grub screws were starting to round off as well due to my previous (and careful) attempts to tighten them to correct this issue

I removed the grub screws and found some small bolts in my bolt drawer in the garage. I am not sure what "M" type these screws are but they are exactly 2.76 mm in diameter across the shaft of the bolt. The foreshortening effect in this picture makes the bolt look thicker than the grub screws but they are exactly the same in diameter, I measured them with my precision callipers.

Using a junior hacksaw I shortened the bolts so they are about 6mm or so long and roughly filed the ends.

I then pressed down hard and tightened the bolts up which will give, I hope, a perfectly flat field!

And here you go:

Since the bolts are flat headed I hopefully won't have a problem of them rounding off.  if they ever did foul a bit I can easily hacksaw a slot - much easier than drilling out an embedded Allen bolt that rounds off on such an expensive and delicate piece of gear!

Will report back if this works!!!  If it doesn't it must be the thickness of the metal work that is not the same on the mechanism in my example leading the chip to be none-orthoganal and it will be going back.  All my gear works perfectly other than the reducer.  

[kirkster501]

Scopes out at the moment gathering 300s M31 in Lum.  Fingers crossed but a quick look at the FITS looks promising

[steppenwolf]

I hope it works for you - poor though that such a high priced piece of kit should require an engineering mod like this! Fingers crossed for you.

[kirkster501]

I hope it works for you - poor though that such a high priced piece of kit should require an engineering mod like this! Fingers crossed for you.

Agreed. It's nicely engineered but just very poor grub screws holding it together. I don't think I'm the only one with this issue either. My TAK focuser slips a bit too but that's a new thread I think....

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[ollypenrice]

I agree that those little screws are a bit potty. My only thought would be about the other end of the new screws. It the point of contact at the gripping end is assymetrical (by which I mean 'off axis' if you like) they might have a tendency to push the adapter in and out a little during tightening rotation. However, I think you may well have cracked it.

Olly

[kirkster501]

I think I cracked it.  If I am very critical a tiny bit of "eggyness" at the bottom left.  Tiny and I reused my polar alignment from the previous week so it could be  a slight bit of field rotation.  What do you think?  This is ten subs of 300s luminance.  The moon was rising and i was plagued with satellite trails.  No processing at all on this other than imaging calibration and stacking with PI.

[kirkster501]

I agree that those little screws are a bit potty. My only thought would be about the other end of the new screws. It the point of contact at the gripping end is assymetrical (by which I mean 'off axis' if you like) they might have a tendency to push the adapter in and out a little during tightening rotation. However, I think you may well have cracked it.

Olly

I don't think that will be an issue Olly.  The amount that I tightened those screws up I doubt they'll ever come off again. Indeed my worry now is that I may have tightened up too much and caused distortion to the barrel and hence the optics....! TBH I don't think so since the metalwork of the reducer is pretty chunky!

I need to get more more data to prove one way or another if I have cracked it for100% certain.  However, I think the stacked luminance subs above look pretty OK do you think?  Still a little inconclusive.  Very slight eggyness, very, very slight....

[Martin-Devon]

The image looks largely OK to me, if there are still some tiny eggy stars in the left corner it's not possible either to say categorically that these are caused by the reducer since the spacing to the CCD is also critical at this F ratio. I've also had issues with these exact same grub screws though on my Tak reducer, with tilt being introduced into my imaging train. In an earlier version of my set-up I had limited ability to rotate my imaging train via the capstan on the focuser due to the guide scope being in the way and I resorted to undoing these grub screws and thus rotating my CCD - what a mistake that turned out to be - tilt everywhere. I now have an OAG, so have removed the guide scope and can rotate 360 degrees now with the focuser. Still took me ages to get rid of the tilt though, but I think it's now gone and I swear I'll never touch those grub screws ever again. I used CCD Inspector a lot as well to guide me on the tilt, and where it was - this helped a lot. 

[strutsinaction]

My TAK focuser slips a bit too but that's a new thread I think....

Ian King visited Takahashi Europe recently and I think this was on the agenda i.e. how to adjust the focusser. Maybe give him a call for advice?

Regards

John

[kirkster501]

Yes John, I'm going to call Ian and ask him if he knows how this is done.  My focuser creeps at about 1mm every few seconds unless the lock is applied.  It's rather annoying and makes the scope fiddly to focus.

Steve

[kirkster501]

The image looks largely OK to me, if there are still some tiny eggy stars in the left corner it's not possible either to say categorically that these are caused by the reducer since the spacing to the CCD is also critical at this F ratio. I've also had issues with these exact same grub screws though on my Tak reducer, with tilt being introduced into my imaging train. In an earlier version of my set-up I had limited ability to rotate my imaging train via the capstan on the focuser due to the guide scope being in the way and I resorted to undoing these grub screws and thus rotating my CCD - what a mistake that turned out to be - tilt everywhere. I now have an OAG, so have removed the guide scope and can rotate 360 degrees now with the focuser. Still took me ages to get rid of the tilt though, but I think it's now gone and I swear I'll never touch those grub screws ever again. I used CCD Inspector a lot as well to guide me on the tilt, and where it was - this helped a lot. 

Thanks Martin, I am largely satisfied the reducer is now a good 'un.  Take a look at the mess on the left in the image here with the reducer as it was before this modification!

[ollypenrice]

Looks good, but some word from the ever Sphinx-like Takahashi would be helpful...

Olly

[Peter Drew]

I've not seen a Tak reducer but I would have expected the three grub screws to tighten down on to an inclined face, nipping the screws up should pull the two parallel faces firmly together eliminating any tilt. (?)    

[kirkster501]

I've not seen a Tak reducer but I would have expected the three grub screws to tighten down on to an inclined face, nipping the screws up should pull the two parallel faces firmly together eliminating any tilt. (?)  

It isn't mate.  The inside of the ring and the outside of the body are flat at 90 degrees with respect to each other.  However, I think I've got this working OK now.  I'd like to get some more subs to be certain though.  Either way, not a great deal more I can do if it doesn't work.  The reducer is a year old and out of warranty.  I have had precious little time to test it in that year with rubbish weather and personal difficulties.

[Barry-Wilson]

Steve

I read the same solution on the Tak Users Yahoo Group and it was reported as very effective.  I have spare 3 x 3mm caphead screws and am contemplating replacing as you have done, so I'm interested to hear your views on success as you gather more subs.

Barry

[ollypenrice]

I've not seen a Tak reducer but I would have expected the three grub screws to tighten down on to an inclined face, nipping the screws up should pull the two parallel faces firmly together eliminating any tilt. (?)  

I think, Peter - but Takahashi are very zen on this matter - that the whole point of the nasty little grub screws is to allow you to tune out tilt, so they deliberately do not bring the grub screws to bear on a self centering cone. Quite honestly, Lord help anyone trying to tune out tilt by this means. Other than that I can't see any need for the reducer assembly to be in two parts at all. I'm sure most of us would be more than happy to see it machined as one with no grub screws to faff about with.

If I am missing something, which is perfectlyu possible, it only needs Takahashi to talk to us. Don't hold your breath...

Olly

[Peter Drew]

Bit of a design blunder then IMO, I would prefer a component to be inherently accurate, tilt outside this component is either another issue or someone elses problem.    

[ollypenrice]

Bit of a design blunder then IMO, I would prefer a component to be inherently accurate, tilt outside this component is either another issue or someone elses problem.  

Agreed.

Olly

[dave_galera]

Quite honestly, Lord help anyone trying to tune out tilt by this means. Other than that I can't see any need for the reducer assembly to be in two parts at all. I'm sure most of us would be more than happy to see it machined as one with no grub screws to faff about with.

Olly

I totally agree Olly, and as you know we have both had this same problem. As someone commented above some guy did a similar mod on the Tak Group but he used 6 larger grub screws (or maybe they where cap head, can't remember) and it solved the problem........must get around to doing mine as in some positions the stars are a little big eggy.

Dave

[kirkster501]

I totally agree Olly, and as you know we have both had this same problem. As someone commented above some guy did a similar mod on the Tak Group but he used 6 larger grub screws (or maybe they where cap head, can't remember) and it solved the problem........must get around to doing mine as in some positions the stars are a little big eggy.

Dave

It is relatively simple to drill and tap an additional three screws.  Of course, that would require the tools and know-how to do so.  The question of course is that, at this price point, should you have to?