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CEM26/GEM28 Minipier Mini-review

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#1 larryjh

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Posted 23 October 2021 - 09:55 AM

It's a minipier, so it gets a mini-review.  This minipier is all but impossible to find, but I managed to score one from OPT.  I have been needing this for my setup so that I can comfortably do meridian flips without worrying about a tripod leg collision.  Normally I would expect a piece of equipment like this to simply fit and not be a problem, but since this minipier has some important design flaws, I thought I'd post what I've found.

 

The first problem is that the raised rim on the outer edge of the top of the pier is thinner by 1-2 mm as compared to the raised rim on the tripod base.  Therefore, the azimuth pin sticks up further into the mount cavity where the pin goes, enough that it hits the top of it and the mount cannot be put down flush onto the pier.  My solution was to grind about 2mm off the top of the azimuth pin, but I was not pleased to have to do that.  Another problem is that the 12mm center pin hole is too tight and I had to ream it out very slightly to get the pier to easily fit onto the tripod base.  Finally, a minor annoyance is that the bolts that attach the pier to the tripod do not have the same hex wrench size as the az locking bolts (which use the wrench that comes with the mount).

 

After dealing with these issues, the pier does its one and only job of raising the mount 5.5 inches and now my meridian flips easily clear the tripod legs.  However, iOptron really could have done a better job with this minipier.


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#2 Tom M

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Posted 23 October 2021 - 12:15 PM

Thanks for the review. It's clear they machined the surface to provide a decent mating surface so that the mount head will slide easier when rotating it during the PA alignment procedure. However they obviously didn't take into consideration the impact to the overall height needed. The clearance/interference issue should have been obvious in any CAD system.

 

An alternate, albeit not totally elegant, solution to the too long alignment pin is to replace it with a 20mm or longer M6 socket cap head bolt. There is a bit of play in it as it won't lock down in  place but since it's really only used for the push/pull capability it solves having to grind down the pin supplied in the kit. The play could be removed if some sort of a spacer (tubing?) is used but I didn't bother to mess with that though may in the future.


Edited by Tom M, 23 October 2021 - 03:40 PM.


#3 Tom M

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Posted 24 October 2021 - 02:23 PM

Did some experimenting and used a stainless M6x30mm bolt (the store didn't have any stainless hex cap screws), washer and nut and it's solid now. Using 30mm is just long enough so 35mm or longer may be better.

 

The bolt or cap screw will thread through and extend out the bottom allowing a washer and nut to be used to tighten everything down. Since I used a hex bolt  the adjustment screws were used to ensure it was rotated to so the faces were square with the adjustment screws and then tightened the nut underneath.



#4 eknock

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Posted 13 November 2021 - 08:04 PM

I decided to go with one of these for my GEM28 much for the same reason the OP stated. Got lucky and sourced an 8" minipier but was surprised to learn upon unboxing that iOptron, presumably to save a few pennies, had left it up to the user to dismantle a 5.5" minipier and reassemble it into an 8" one with the supplied hardware (longer hex screws and aluminum spacers).

 

I didn't run into any other issues but sitting the unit flush with the tripod took some rubber-mallet-convincing since the mating for the center pin was just too snug. Happy with the results overall ... a worthy upgrade.




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