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weird yet potentially lovely little Tak mount

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#1 doole

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Posted 01 December 2010 - 05:44 PM

Anyone in here have experience with a Takahashi "Sky Patrol III"? I'm rightly confused about this little mount because I find myself forced to make a modification (no, not the Lapides deal, I believe that's already been done) before I can even use it and I haven't seen mention of the trouble I've had anywhere else. I simply can't believe it has worked out of the box for anybody else, either.

It's an absolutely gorgeous little mount. (Or will be when I'm finished with it.) The trouble I'm referring to stems from the way that it assembles. Two conical screw heads project from the dec / counterweight bar assembly which you insert into two corresponding holes in the clock drive / R.A. assembly and then tighten it using nearly microscopic (and I'm not exaggerating that at *all*) set screws through the side of the clock drive using an allen key that I actually believe I could swallow without ill effect. (Although obviously I don't recommend that.) The declination bearing is attached to the counterweight bar in the same ridiculous manner.

There's no problem assembling it that way, except that those tiny set screws can't possibly keep the thing together under any load. When I put my old Brandon 80mm on it (about 6 pounds with rings and a plate) it works quite well until I actually move the scope, at which point one or both of the referred to attachment points will simply pop loose, pretty much immediately.

No particular problem, I plan to simply replace the conical head screws with ordinary round head ones with big enough heads (with washers, if necessary) to cover the entirety of the holes that they insert into and thus make the whole assembly permanent. Should be a simple fix that works extremely well, but what I can't understand is how anybody ever expected this arrangement to work in the first place. (Or how there haven't been any complaints about it.) Anyone?

#2 giorgio_ne

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Posted 01 December 2010 - 07:10 PM

Hello Doole, I'm having exactly the same issue on my little used Sky Patrol III. I've ended up tightening the little screws so much that they have literally eaten into the two conical support screws. My mount is nowpermanently assembled over the tripod but I don't think it would do any good to it if I had to frequently assemble/disassemble it. No need to say that I'm also curious to know how other people have dealt with this problem.

#3 doole

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Posted 01 December 2010 - 07:21 PM

Giorgio, does my explanation of how I'm dealing with it make sense to you? I will say that removing the existing screws was a real job. There's paint inside the threads and the screws get pretty beat up since you'll almost certainly be resorting to large pliers and so forth to get them out. I still wonder if they were cross-threaded. Now I have to go down to the bolt shop and match them up...

#4 Larry Geary

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Posted 01 December 2010 - 10:24 PM

I can't help with your problem, but I am curious what amount of periodic error this little mount has, if anyone can tell me. And is there any vibration when you focus a scope?

#5 doole

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Posted 01 December 2010 - 10:31 PM

Once I get it working, I'll post it here. It don't think it'll set any records, there's no worm gear or anything.

#6 Larry Geary

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Posted 01 December 2010 - 10:36 PM

Thanks. I wonder why Tak couldn't shrink down the NJP or EM series mounts to make something this size. The P2Z is basically a small and more spartan NJP.

#7 doole

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Posted 02 December 2010 - 11:12 AM

Wonder if the people at Tak realize they're building a mount that doesn't really work without mods. It doesn't seem like something that they would do. It's puzzling and troubling to me.

#8 doole

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Posted 02 December 2010 - 11:16 AM

Nice little questar btw Larry. What's with the brass dec knob, is that what the motorized dec looks like these days? (Mine's an '86...)

#9 doole

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Posted 02 December 2010 - 11:21 AM

...of course, they've done it before, haven't they? :foreheadslap:

#10 Larry Geary

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Posted 02 December 2010 - 01:09 PM

That's a picture of the 25th Anniversary Questar. It isn't mine. Only a few were sold before Mrs. Braymer (the late owner's wife) stepped in and vetoed the project.

You might want to contact Art at TNR and ask him about the mount. Maybe you're doing something wrong, and if not, he'll let Tak know the product has problems.

#11 doole

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Posted 03 December 2010 - 06:13 PM

Hi Giorgio, I'm happy to report that the mod that I had visualized works quite well. The gotcha is that the original arrangement with the conical screws is self-centering, so it's possible in the new arrangement for things to slide around a bit unless you make it very tight. I imagine that it will go askew occasionally at which point it should probably all be readjusted anyway. And it's better than no mount, which is what we've got otherwise.

The threads were quite easy to match up in a local bolt shop, mine turned out to be M5 x 20's. I used socket heads with M6 flat zinc washers. If you put the washers on upside down and really tighten, they'll taper themselves a little and you get a bit of the self-centering back. Again, not ideal but a distinct improvement. Hope it works for you, too.

#12 doole

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Posted 03 December 2010 - 06:15 PM

...by the way the original screws were VERY difficult to remove.

#13 giorgio_ne

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Posted 04 December 2010 - 02:20 PM

Hi Doole, thank you for letting me know it worked. I'll leave mine as is right now since it is quite stable and I don't need to disassemble it for the time being.

Cheers,
Giorgio

#14 doole

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Posted 04 December 2010 - 02:58 PM

Cheers youself! :smirk:

#15 doole

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Posted 05 December 2010 - 05:28 PM

BTW, here's a shot of this arrangement where it holds the dec axis to the ra arm. It's the same where RA axis attaches to the RA bearing, but it's covered by the RA motor. (You have to dissemble the ENTIRE mount to do this. Be careful to mesh the drive gears properly when you put it back together. It's a little tricky and you will most likely have to readjust the motor angle.)

Note the tiny set screw near the slow motion. THAT's what's supposed to have supported everything...

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#16 doole

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Posted 05 December 2010 - 06:02 PM

I might also add that this isn't about how I assembled the mount. As I mentioned before, in the stock version the set screw exerts pressure on the side of a conical self-centering screw, resulting in a tiny pressure point against an outside curved very smooth surface - obviously an unstable equilibrium. This could never have worked.

#17 jmiele

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Posted 06 December 2010 - 02:09 PM

I think I remember having the same issue using one of these couple years ago. Maybe the II. Tighening the grub screw actually cocked the assemble a bit. It was a bear to tinker with but as I recall worked rather well for "very light weight" wide field work. Good Luck .. Joe

#18 doole

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Posted 06 December 2010 - 02:43 PM

The little bugger holds a fair weight, when it's working. I've got about 7 pounds on it, ok for visual. I might not bother at all with photography, it's just what appears to be an alarm clock motor with a couple of extra gears to reverse the rotation. This mod was very simple though, and it makes a nice little martini-on-the-deck-after-dinner kind of setup.






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