Jump to content


Photo

Dovetail modification for the Vixen Super Polaris!

This topic has been archived. This means that you cannot reply to this topic.
14 replies to this topic

#1 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:16 PM

I've been a big fan of the Vixen Super Polaris mount for a long time. I have owned several small German Equatorials, and the VSP is the best of the bunch - in fact, the VSP completely outperformed the Orion AstroView I had been using previously. The VSP is smooth (no Chinese sticky grease), robust, and has nice touches like fully-functional setting circles and vernier scales on both axes. Simply put, it's well made and a pleasure to use - mostly.

To me, the one big critical flaw in the VSP design was the lack of a dovetail/saddle provision. This mount was designed so that the scope OTA rings are bolted directly to the mount head. There are two holes in a flange on the mount head to attach the rings - this results in a fixed spacing of the rings with no options for changing the distance between the rings. This was an annoyance for some time, but not a deal-breaker. I mounted several scopes on the VSP and the lack of dovetail/saddle facilities did not become a major issue until I bought my Synta 6" Mak-Cass.

The Synta 6" Mak-Cass has a Vixen/Orion dovetail attached to the OTA which cannot be removed easily - not without removing the meniscus to access the captive bolts inside the tube which hold the dovetail to the tube. This is more surgery than I was comfortable with on my new scope. Worse, the stock dovetail runs the entire length of the OTA - leaving no gaps or space to use hinged mounting rings. Apparently you either mount this OTA with a dovetail-compatible mount, or you use the OTA as a paperweight. Using rings was not an option. So now I had a nice mount and a nice scope, but I couldn't put the two together. I had a problem.

Due to the shape of the VSP mount head, you can't simply bolt a flat plate with holes tapped in it to the mount head - it won't sit flush because of raised ridges which are cast into the mount head. Any piece of metal that is going to be bolted to the top of the head must be shaped to mate with the ridges on the mount head - a minor PITA and a deal breaker to a guy like me without access to a metal-working shop. I looked around the garage and through my junk piles, looking for some low-tech solution to this problem - something I am usually quite good at. "Jerry rigging" is an artform I have mastered, but in this case, I couldn't find any cheap solution that I would trust to hold my $500+ OTA.

So I started thinking about the people I know. Who do I know that can fashion some kind of adapter for me? Right away a name popped into my head - Steve Forbes, or "Telescopeman54" here on CN.

I've done a bunch of gear deals with Steve over the last few years on AstroMart and I know that Steve is a talented tinkerer and fabricator. He has fully-stocked shop and the skills I lacked. So I contacted him and asked him if he could make an adapter for me that would allow a modern dovetail equipped OTA to be mounted on my old-school Vixen Super Polaris GEM.

He said "No Problem, piece of cake, send it to me." :)

So I boxed up the mount, minus the tripod and counterweights, and shipped it to Steve via USPS Priority mail with Insurance and a tracking number. It cost me about $30 each way to ship it, so about $60 total cost for shipping. I could have saved a few bucks by shipping Parcel Post or UPS, but I didn't want to wait over a week each way in transit. $30 and Steve had my mount sitting on his front porch in about 3 days.

Within a couple of days, I got an email back from Steve - complete with photos. It showed my VSP with a block of some kind bolted to the head - this "block" is a piece of steel that Steve machined to fit perfectly flush against the VSP mount head - the raised ridges on the head mated with grooves Steve had provided in the adapter block. The adapter block is then bolted to the mount head with two large rosette knobs which Steve provided from his personal junk pile. Any standard bolt/nut combination would work, the rosettes just look better and make swapping out the adapter a breeze.

The adapter block simply sits on top the VSP head, bolted securely in place. The block has a slot in the top of it to accept the OTA dovetail bar - two rosette knob tightening screws lock the dovetail into the adapter/saddle.

Steve painted the entire adapter block black and supplied me with the necessary rosette knobs. When I got my mount back in the mail, I was amazed at how this simple modification had greatly improved the utility of my old near-obsolete mount. I could now mount any scope to my VSP using a widely-available Vixen/Orion style dovetail bar. The Synta 6" Mak-Cass now rides perfectly balanced on my VSP and the entire rig sits ready to go at a moment's notice in my computer room.

I share all of this because I know there are a lot of Vixen Super Polaris mounts out there in use. And I know many of the owners may be like me - frustrated by the lack of a dovetail provision on an otherwise superb mount. I asked Steve if he would make these adapters for other VSP owners, and he said "SURE". So, consider this post a "heads up" for VSP owners - if you want your mount modified to take modern dovetails, contact Steve. He'll hook you up.

What did this adapter cost me? Well, first off, it cost me about $50-$60 for shipping expenses to and from Steve's shop. Steve and I had done many deals before, including several gear trades, so we worked out a "unique" swap deal - Steve gave me the adapter and I hooked up Steve with some astro goodies he was needing. So I didn't pay a set cash fee for his services. Anyone wishing to have Steve fabricate an adapter will have to chat with him and hammer out a deal. I can just say that I am very happy with the final modification. :)

Here are some photos of the modification...

First, here is the final product - my 6" Mak riding on the VSP using the dovetail and modified "saddle" adapter.

Attached Files



#2 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:17 PM

Here we see the mount head with the new adapter in place. The red line shows the point where the old mount head meets the new adapter plate.

Attached Files



#3 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:20 PM

Another shot of the mount head, showing where the adapter bolts to the original mount head.

Attached Files



#4 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:22 PM

This photo shows the top end of the saddle adapter plate. Notice Steve has placed two rows of felt on the top edge to protect the OTA from being scratched. You can also see the two holes tapped into the plate which allow it to be bolted to the VSP head.

Attached Files



#5 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:23 PM

The adapter plate can be easily removed and the mount restored to 100% original condition. Just un-bolt it. :)

Attached Files



#6 Glassthrower

Glassthrower

    Vendor - Galactic Stone & Ironworks

  • *****
  • Vendors
  • Posts: 18373
  • Joined: 07 Apr 2005

Posted 09 March 2008 - 12:33 PM

It should be noted that Vixen offers a modification plate and saddle for the VSP mount. But this part is never stocked by stateside Vixen dealers - it must be ordered from Vixen Japan overseas. The adapter plate and saddle cost over $100 US (and getting more expensive each day with the plunging dollar and exchange rate) and that doesn't include international shipping to get the part here. I had explored this option and ruled it out because I didn't want to spend $150 or more just for an adapter that I could get stateside for less money and with less wait time.

Steve's mod looks professional and once installed, I don't even notice it's there. It's very solid, and I don't regret not getting the Vixen OEM adapter.

I readily recommend Steve - he does darn good work and he's a straight shooter. Here is a link to his CN profile :

http://www.cloudynig...at=0&User=30256

#7 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1715
  • Joined: 16 Aug 2007

Posted 09 March 2008 - 12:53 PM

Mike:

Thank you for the glowing recommendation.

There are a few details that may not be obvious to anyone reading this message.

1) The adapter was made from aluminum, not steel.

2) Stainless Steel hardware was used to hold everything together.

3) There are two slots milled into the bottom (they show in the pictures) to prevent excessive stress on the cast metal head. If this was not done then over tighnening could cause the casting to break!

4) I supplied three different sets of fasteners (not shown in the pictures) to clamp the saddle plate into the adapter because I wasn't certain just what clearance was available under your OTA.

The rig was then field tested with a 4" f/15 refractor to make certain that it worked properly.

I'm glad that I was able to make your life easier and that you are now able to use your equipment to its fullest.

Again, thank you very much for sharing this with the rest of the CN group.

CS

Steve


sbf

#8 Jim7728

Jim7728

    Cosmos

  • *****
  • Posts: 7928
  • Joined: 10 Apr 2005

Posted 09 March 2008 - 01:24 PM

Nice work, Stephen! :cool:

I think Mike likes it, too! ;)

#9 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1715
  • Joined: 16 Aug 2007

Posted 09 March 2008 - 04:33 PM

"Hey! Let's give it to Mikey!"

"He LIKES IT! Hey Mikey!"


OK! How many are old enough to remember THAT one?!! :shakecane: :rofl2:

CS

sbf

#10 Jim7728

Jim7728

    Cosmos

  • *****
  • Posts: 7928
  • Joined: 10 Apr 2005

Posted 09 March 2008 - 05:26 PM

I remember. :gramps:

Mikey likes it! :lol:

#11 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1715
  • Joined: 16 Aug 2007

Posted 09 March 2008 - 09:09 PM

Welcom to the "Old Geezers Club"!!

I'm so old I remember when God said "Let there be light!" I asked him where He wanted me to put the switch!

sbf

#12 Jerry Hyman

Jerry Hyman

    Messenger

  • -----
  • Posts: 491
  • Joined: 29 Mar 2007

Posted 09 March 2008 - 09:19 PM

Here is another possible option for those of us who have a Super Polaris. Ken's rings makes this one:

http://www.kendauzat...er/1126071b.jpg

~jerry

#13 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1715
  • Joined: 16 Aug 2007

Posted 09 March 2008 - 09:26 PM

Ken makes very nice stuff, however, there are no relief slots and if one were to mount this onto the original saddle and over tighten the bolts, the casting would break right off. This is even more probably in colder climits.

sbf

#14 BarrySimon615

BarrySimon615

    Pa Bear

  • *****
  • Posts: 2825
  • Joined: 01 Mar 2004

Posted 16 July 2009 - 10:00 AM

Mike:

Thank you for the glowing recommendation.

There are a few details that may not be obvious to anyone reading this message.

3) There are two slots milled into the bottom (they show in the pictures) to prevent excessive stress on the cast metal head. If this was not done then over tighnening could cause the casting to break!

CS

Steve

sbf


The fastening tabs at each end of the mounting plate at the top of the Super Polaris and Super Polaris DX mount can and will crack or snap under the stress of overtightening. I have both of these mounts and with some configurations I have mounting plates with the proper hole spacing for the SP mounting holes. The mounting plate serves as an interface and allows me to mount rings where I want thru additional threaded holes. Due to the problem with the ridges I use a somewhat less elegant but still functional solution to relieve stress due to the "gap" between the mounting tabs on the mount and the mounting plate - basically I use an appropriate sized nylon washer or stainless steel washer to fill the gap. So far this has worked very well for years on both mounts and has not interfered in any way with photographic results, etc. I do agree that the solution described in detail above is more elegant.

I obtained a top dovetail assembly for a Losmandy G8 mount at the last Deep South Regional StarGaze which in turn can be mounted to an interface which itself is hard mounted to the top of the mount, either using my simple solution or a more elegant fix.

One issue not discussed with all of this is that any additional interface weight, dovetail weight, etc., must be added to the weight of the payload. Another consideration is that it moves the telescope tube assembly and mounting rings further from the polar axis of rotation which has an additional net effect on the payload, meaning counterweights have to be moved further down the declination shaft and/or the counterweight "weight" has to be increased. With a system which may already be pushing the weight limit, this could be a concern. The Robin Casady website has a page devoted to figuring counterweight needs based upon payload weight and distance from the polar axis.

Barry Simon

#15 BarrySimon615

BarrySimon615

    Pa Bear

  • *****
  • Posts: 2825
  • Joined: 01 Mar 2004

Posted 16 July 2009 - 11:13 AM

Further comments regarding the potential susceptability of the Super Polaris mounting tabs to crack under overtightening stress -

The Super Polaris mount and many other cast mounts for that matter including most clones, the Atlas mount under this name or any other name, the CG5, the Great Polaris, etc., etc. have the major housing made from an aluminum alloy, they are not milled from aircraft grade aluminum. Aluminum alloy covers the spectrum, for more information on grades of aluminum and aluminum alloy see:

http://en.wikipedia....Aluminium_alloy

The advantage, of course, for the manufacturer is using an alloy, particularly one that approaches the consistency and properties of what we might call "diecast" is that it is cheaper to fabricate. The disadvantage for us is that it is relatively brittle compared to pure aluminum or some other aluminum alloys. (Witness a recent thread which detailed a cracked housing on an Atlas mount in and around the polar axis elevation screw.) With better engineering and a better grade of aluminum, I doubt this would have happened. Mounts such as the the Losmandy G11 and G8 have major components milled, not cast, a much better (stronger, more expensive and better looking solution). If the Super Polaris top declination plate been made from aircraft grade milled aluminum, I bet it would take a heck of a lot more pressure to snap the mounting tabs than what has happened on several occasions with this mount as configured.

Note, I am not saying it is a bad mount; I have two of them and they are great. It is just that to meet a certain price point, a diecast type aluminum alloy is the only viable option.

On another point, I believe most mount manufacturers could do a better job by making every attempt to try to shorten the distance between the polar axis of rotation and the mounting plate area for the tube assembly. The further the tube assembly moves away from the polar axis, the smaller the payload can be without issue (payload capacity). I just got a used Takahashi EM10 and it is a great mount, but, it has a relatively long declination column above the polar axis, meaning it needs more weight to balance the payload. I am not an engineer but I do believe this distance could have been reduced by at least a third with an improved design. That may have very well meant that payload could have been increased by 2 or 3 additional pounds, maybe a bit more, without any other change. (The Super Polaris does a bit better job here as it has a shorter declination column on the telescope side of the polar axis.

Barry Simon







Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics