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Connecting a large refractor to a GM 3000 mount?

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#1 Trackerthedog

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Posted 13 November 2019 - 04:28 PM

Hi. In December, I will be taking delivery of a TEC 250mm Apo and a 10 Micron GM 3000 mount. Yuri, at TEC has asked what I would prefer to connect the scope to the mount with. I'm hoping to get some advice on the choice for that here. ... There are AP 15" and 24" plates that do not use a dovetail (apparently). There is also 10 Micron's own system that uses a Maxi dovetail clamping plate and flange connector to the mount. 10 Micron's system seems to be smaller than the large AP plates, but it is recommended for large scopes. Here are the links for their product(s):

 

https://www.10micron...mping-plate-4/ 

 

http://www.10micron....-plates-gm3000/

 

I will be doing astro-imaging with the setup, so I'm wondering if anyone has any advice on which connecting setup would be the most stable and useful? Does a setup with only a connector plate work better or should I go for the 10 Micron dovetail plate and flange connection system? ... I thought that 10 Micron would know the best system to connect their own mounts to a large telescope, but their system seems to be considerably smaller than the AP plates. ... Any comments, wisdom, advice would be very much appreciated! Thank you in advance.



#2 petert913

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Posted 13 November 2019 - 05:42 PM

Boy, I would pay admission to visit that scope !   Please post photos when it is all set up.



#3 Trackerthedog

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Posted 13 November 2019 - 05:53 PM

Thank you, Petert913. I am only able to buy this setup because my mother left me an inheritance. Otherwise I would not have had any chance of buying the equipment. ... Well, an incredibly understanding spouse is also indispensable.


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#4 macdonjh

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Posted 13 November 2019 - 06:11 PM

If you are going to be set up in an observatory, perhaps get something that doesn't use a saddle with clamps: bolting your tube rings to a plate, then the plate to your mount.  Perhaps something like this:

 

 https://astro-physics.com/1200rp15

 

I'll bet Astro Physics knows how to drill the plate to mount directly to your 10 Micron mount, too.


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#5 Stelios

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Posted 14 November 2019 - 01:45 AM

I don't have personal experience with non-dovetail mounting. Normally it seems it would make balancing the scope harder as you change things in the imaging train. However, with a 10" TEC, you probably will just loosen the rings and slide the scope forward, so it seems that just bolting the rings onto a plate permanently may be best.

 

The little dovetail saddle offered by 10 Micron looks very inadequate to me. I like at least 3 screws (and a long dovetail bar) to make me feel secure in mounting my scope, and my scope is far smaller than a 10" TEC.



#6 Trackerthedog

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Posted 14 November 2019 - 12:17 PM

Thank you for your replies! Clear Skies.



#7 macdonjh

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Posted 14 November 2019 - 12:33 PM

Normally it seems it would make balancing the scope harder as you change things in the imaging train. 

That was my thought when I said, "if permanently mounted in an observatory".  It seems like equipment would be more "static" in a permanent installation.  All bets are off if Trackerthedog is taking his new scope and mount on the road.  Then a traditional dove tail saddle might be required.  Although, the plate and rings could be left bolted to his mount and the scope settled into the rings during set-up.  Then simply close the rings and tighten a bit.  Slide the scope within the rings for balance, then finish tightening.

 

While reading Traackerthedog's initial post I was thinking about a friend's observatory.  He is also mounting a big, heavy, costly scope.  His mounting plate is something like 3/4" thick and has four or six bolts to secure the scope to the plate and a like number of bolts to secure the plate to his mount.  No tube rings in his case.



#8 Trackerthedog

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Posted 14 November 2019 - 02:28 PM

The telescope is being permanently mounted in an observatory. I have decided to go with the 24" AP ribbed mounting plate. Thank you again to all who posted.


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#9 EFT

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Posted 19 November 2019 - 05:17 PM

While 10Micron has saddles up to 5-inches wide, I would probably favor going with the direct-mount attachment in this case.  With no need to be repositioning the scope, then the plate may as well be permanently attached to the mount leaving the rings as the only source of adjustment.  The key in any case is to make sure that the plate used is sufficiently rigid to not sag/bend when in use.  The AP plate might be an issue if the holes do not match up to those on the mount due to the ribbing on the underside.  If the plate does not sit fully supported on the mount face, then it will not be as stable as a solid plate.


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#10 Trackerthedog

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Posted 21 November 2019 - 12:43 AM

TEC is going to mill the plate so that it fits the 10 Micron mount.


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#11 macdonjh

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Posted 21 November 2019 - 09:18 AM

TEC is going to mill the plate so that it fits the 10 Micron mount.

Man, superior customer service and good optics.  Can't beat that.



#12 ltha

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Posted 21 November 2019 - 09:52 AM

Years ago I had a D&G 8” f/12 and planned to mount it on a Parallax HD150. Initially the Parallax had a Losmandy saddle and I tried a 17” plate. The image shook more than I found acceptable. My friend Al George, who owned a D&G 15” f/12, told me to have a longer, thicker custom plate machined to bolt directly to the declination axis. I went with a 3/4” thick, 30” aluminum plate. By eliminating the saddle the scope sat closer to the mount, and the rings had a longer base to hold the tube. The shakes disappeared. I think the 24” option bolted directly to the mount is the better choice, assuming tube balance and accessories do not collide. You will have to move the OTA to balance the scope, but with such a large OTA I found that easier than loosening the saddle and shifting tHE D plate, then retightening. 
 

I have a HGM-200 with a 24” Losmandy plate under my TEC200ED. The mount is very solid, holding the scope shakes to 1-2 seconds after a hard rap on the tube. 


Edited by ltha, 21 November 2019 - 09:54 AM.


#13 Kent10

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Posted 21 November 2019 - 11:09 AM

Years ago I had a D&G 8” f/12 and planned to mount it on a Parallax HD150. Initially the Parallax had a Losmandy saddle and I tried a 17” plate. The image shook more than I found acceptable. My friend Al George, who owned a D&G 15” f/12, told me to have a longer, thicker custom plate machined to bolt directly to the declination axis. I went with a 3/4” thick, 30” aluminum plate. By eliminating the saddle the scope sat closer to the mount, and the rings had a longer base to hold the tube. The shakes disappeared. I think the 24” option bolted directly to the mount is the better choice, assuming tube balance and accessories do not collide. You will have to move the OTA to balance the scope, but with such a large OTA I found that easier than loosening the saddle and shifting tHE D plate, then retightening. 
 

I have a HGM-200 with a 24” Losmandy plate under my TEC200ED. The mount is very solid, holding the scope shakes to 1-2 seconds after a hard rap on the tube. 

This is very interesting for me.  I have a Tec 200FL on an AP 1100 mount that shakes more than I would like.  I am using a Rayox saddle and a 12" plate from Tec.  I am considering getting an 18" AP plate that I can attach directly to the mount.  Do you think it is the length of the plate (to separate the rings more) or the fact that the plate is closer to the mount that helps with stability.  Is one more important than the other or do you think they are equally important in mitigating the shakes?  Would the 18" plate be enough or would you go even longer?

 

Thanks.


Edited by Kent10, 21 November 2019 - 11:13 AM.


#14 555aaa

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Posted 21 November 2019 - 01:31 PM

The wide AP dovetail plate P style is based on the planewave dovetail. It's almost 8 inches wide.

#15 macdonjh

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Posted 21 November 2019 - 01:58 PM

This is very interesting for me.  I have a Tec 200FL on an AP 1100 mount that shakes more than I would like.  I am using a Rayox saddle and a 12" plate from Tec.  I am considering getting an 18" AP plate that I can attach directly to the mount.  Do you think it is the length of the plate (to separate the rings more) or the fact that the plate is closer to the mount that helps with stability.  Is one more important than the other or do you think they are equally important in mitigating the shakes?  Would the 18" plate be enough or would you go even longer?

 

Thanks.

Kent, I've not done any math on this, but it's likely a combination of:

  • Scope closer to the mount (less moment arm, reducing the moment of inertia of the system)
  • A more rigid plate (since it's thicker)
  • More separation between the rings, lowering the flex in the OTA (If you could put the rings at 1/4 of the OTA length and 3/4 of the OTA length, the flex and vibration of the OTA would be minimized)

Trackerthedog, another thing I've heard being done for long refractors in using three tube rings.  That makes for a stiffer connection.



#16 ltha

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Posted 21 November 2019 - 02:11 PM

This is very interesting for me.  I have a Tec 200FL on an AP 1100 mount that shakes more than I would like.  I am using a Rayox saddle and a 12" plate from Tec.  I am considering getting an 18" AP plate that I can attach directly to the mount.  Do you think it is the length of the plate (to separate the rings more) or the fact that the plate is closer to the mount that helps with stability.  Is one more important than the other or do you think they are equally important in mitigating the shakes?  Would the 18" plate be enough or would you go even longer?

 

Thanks.

Bootstrapping off of all of the reasons Macdonjh mentioned, I think both helped. However, if I could only change one it would be mounting the plate directly to the DEC. housing. Al was adamant that the plate be thick and long arguing that wider spaced rings helped stabilize the long tube, but I was dealing with an 8” f/12 rather than an f/8. I just looked at the 18” AP plate and would think it is heavy enough, especially solidly attached to the AP1100. My admitted bias: when it comes to mounting scopes, I fall into the  “takes no skill with overkill” camp.


Edited by ltha, 21 November 2019 - 02:21 PM.


#17 Kent10

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Posted 21 November 2019 - 02:21 PM

Thanks macdonjh and Itha.  I will give it a try at some point.  It was disappointing for me to find out how unstable my new Tec 200FL was after mounting it.  I am also going to try different materials under the ATS portable pier legs.  Wood panels are next.  Thanks again.



#18 macdonjh

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Posted 21 November 2019 - 07:37 PM

My friend Al George, who owned a D&G 15” f/12 

A 15" f/12?  Jinkies.  I must have purchased his cast off finder scope years ago:

 

DandG 3.JPG


Edited by macdonjh, 21 November 2019 - 07:39 PM.

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#19 macdonjh

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Posted 21 November 2019 - 07:47 PM

Kent, I've not done any math on this, but it's likely a combination of:

  • Scope closer to the mount (less moment arm, reducing the moment of inertia of the system)
  • A more rigid plate (since it's thicker)
  • More separation between the rings, lowering the flex in the OTA (If you could put the rings at 1/4 of the OTA length and 3/4 of the OTA length, the flex and vibration of the OTA would be minimized)

Trackerthedog, another thing I've heard being done for long refractors in using three tube rings.  That makes for a stiffer connection.

I should also note that if you are mounting a scope using a dovetail plate and a saddle, the saddle also contributes quite a bit to the stiffness of the mounting.  So you don't need as thick a dovetail if you're using a saddle as you will without a saddle.  As with mounting plates longer is better.  In that photo above, that Robin Cassady saddle is 12", the Losmandy dovetail is 17".

 

If you're having a custom mounting plate made there are things you can do, but each of them costs money:

  • Least expensive is simply a thick piece of metal with appropriate holes drilled (as ltha says, "there's no skill needed with overkill"
  • If you need to reduce weight, have the plate milled so it looks like it has ribs, like the Software Bisque and Astro Physics plates.  That's similar to the I-beam: material where it does the most good only.
  • If your mounting plate is wide enough you could add side rails.  It's not as efficient as an I-beam, but a C-channel (even oriented the "wrong way") is stiffer than a flat plate.


#20 ltha

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Posted 21 November 2019 - 08:23 PM

Al in his observatory with the D&G 15”. Great guy who we lost several years ago.....

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#21 Kent10

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Posted 21 November 2019 - 08:39 PM

 

I should also note that if you are mounting a scope using a dovetail plate and a saddle, the saddle also contributes quite a bit to the stiffness of the mounting.  So you don't need as thick a dovetail if you're using a saddle as you will without a saddle.  As with mounting plates longer is better.  In that photo above, that Robin Cassady saddle is 12", the Losmandy dovetail is 17".

 

If you're having a custom mounting plate made there are things you can do, but each of them costs money:

  • Least expensive is simply a thick piece of metal with appropriate holes drilled (as ltha says, "there's no skill needed with overkill"
  • If you need to reduce weight, have the plate milled so it looks like it has ribs, like the Software Bisque and Astro Physics plates.  That's similar to the I-beam: material where it does the most good only.
  • If your mounting plate is wide enough you could add side rails.  It's not as efficient as an I-beam, but a C-channel (even oriented the "wrong way") is stiffer than a flat plate.

 

Thanks again, macdonjh.  Unfortunately, I am not much into making things unless I have a lot of time.  I was considering this plate from AP but it is only 18"   https://astro-physics.com/fp1800   It would only give me about 6 more inches of separation for the rings but then I wouldn't be using a dovetail and the scope would be closer to the mount.  Here are some pictures of my setup.

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  • PA060006 (Large).jpg
  • PA100008 (Large).jpg


#22 macdonjh

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Posted 22 November 2019 - 07:46 AM

Thanks macdonjh and Itha.  I will give it a try at some point.  It was disappointing for me to find out how unstable my new Tec 200FL was after mounting it.  I am also going to try different materials under the ATS portable pier legs.  Wood panels are next.  Thanks again.

I think some wood mats under your pier's feet will help some.  I can't help but think the stock feet are digging into the dirt.  Spreading that load out some will help make your pier stable.

 

Since the Takahashi FS152 is now unobtanium, I'll be taking my lottery winnings to Yuri's shop.  There's something magical about fluorite...



#23 Whichwayisnorth

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Posted 22 November 2019 - 11:28 AM

This setup was at 2017 winter star party I believe.  Here is a video someone did that shows the TEC + 10u combo you have.

 

https://youtu.be/yRc86gnuCjA?t=173



#24 Trackerthedog

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Posted 22 November 2019 - 10:04 PM

Man, superior customer service and good optics.  Can't beat that.

I cannot speak highly enough of Yuri Petrunin (and TEC). They have been extremely helpful to me

and have answered all of my questions. I owned a TEC 140 for many years, which was a very fine

instrument as well. Yuri has even made suggestions that would save me money rather than

make him money - an honest man who knows his business and makes incredible telescopes.


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#25 Jeff B

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Posted 23 November 2019 - 12:25 PM

I too highly recommend bolting a big thick plate directly to the top of the mount, then bolt the rings directly to that.  I have found it to be a more stable solution.

 

For example, with the two AP 1200 mounts, one carries a big Parallax 11" F7 newt weighing about 85 pounds in total and is ~ 80" long.  It is mounted to the 1200 with a long Casady saddle and a long D dovetail.  There is a bit of flexure in the system.  The second 1200 sports an 8.75" f12 achromat that tips the scales at 80 pounds and is ~100 inches long (a much longer moment arm than the 11").  It's Parallax rings are bolted to a 24" AP plate which is bolted directly to the top of the mount.  There is no flexure at that joint.  I also did a similar thing with the D&G 11" F12 and the Parallax 250HD Observatory mount.  It has two thick plates.  No flexure.

 

So based upon my own experiences, for a scope that size, weight and moment arm, I'm with the camp that advocates a long thick plate bolted direct to the top of the moiunt with the rings bolted directly to the plate.

 

Jeff  

Attached Thumbnails

  • Parallax Zambuto F7 Aa.jpg
  • 8.5 Inch Achromat B.jpg
  • 250 G.jpg
  • Installed C.jpg

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