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Another Berry-style Refractor Mount

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#1 Jeff Morgan

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Posted 24 April 2011 - 07:34 PM

I just finished my second Richard Berry refractor mount and thought I would share a few photos and lessons learned along the way. Two of the hardest parts of fabrication are building the central hub, and drilling the holes for the tripod leg bolts.

The hub is built up by cutting individual pieces from plywood and laminating them together. The issue is consistency in measuring the 120 spacing, and getting accurate cuts. It seems inevitable to have considerable overlap as the layers are glued together, leading to lots of sanding. To solve this problem, I glued the central hub together first, then cut a polygon on the table saw. Very slick. Unfortunately, I either made a measurement error or my original table saw mitre guide failed to cut the proper angle (I have since bought a new mitre guide). So, the legs are not precisely spaced at 120 degree intervals, but at least little sanding was required.

The second issue in fabricating the Berry design it drilling straight and accurate deep holes in the hub for the tripod leg bolts. To solve this issue I used two matched blocks of wood to make each lobe. These were drilled with a forstner bit then glued to the polygonal hub body. I used a biscuit joint for strength, and after the top of the hub was attached I added an additional dowel pin. I found this variation to be extremely successful.

For added rigidity, I upsized all of the hardware from 5/16” to 1/2” bolts, all in bronze sleeve bearings to eliminate wear on the wood. I hardly every use 1/4” in my projects anymore.

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#2 Jeff Morgan

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Posted 24 April 2011 - 07:38 PM

The sleeve bearing for azimuth pin. Another advantage of 1/2” hardware is I can attach my Losmandy GM-8 equatorial head to the tripod with a MA adapter. The Walnut plugs cover dowel pins used to reinforce the leg mount blocks.

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#3 Jeff Morgan

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Posted 24 April 2011 - 07:44 PM

On a tip from a CN member who wished to remain anonymous, I used Black Walnut for the legs. This person claimed in quantitive tests this species bested 30 other common hardwood species in damping. I just liked the looks.

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#4 Jeff Morgan

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Posted 24 April 2011 - 07:45 PM

This is a spare set of altitude bearings that can attach directly to the Astro-Physics rings that came with my scope. The fit is very tight, and they angle somewhat depending upon how tightly the rings are closed. Seemed like a good idea at the time, but these will sit in the closet in the event I every lose the primary ring set.

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#5 Jeff Morgan

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Posted 24 April 2011 - 07:45 PM

And this would be the primary ring set.

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#6 Jeff Morgan

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Posted 24 April 2011 - 07:46 PM

And the finished product. I want to build a backgammon table, so I decided to practice some simple wood insets using PurpleHeart, Mahogany, and Black Walnut. Kind of busy looking, but I was having fun.

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#7 Jeff Morgan

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Posted 24 April 2011 - 07:50 PM

End view. I’ll probably use the remaining PurpleHeart to make a Telrad platform that attaches using Neodymium magnets. Those little suckers are strong!

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#8 Jeff Morgan

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Posted 24 April 2011 - 07:56 PM

Front view of the mount. Last Thursday was the shakedown, and I am pleased with the overall rigidity and performance. Tracking was rather easy at 339x. However, the mount is balance sensitive. I can balance to use my heavy widefields, or my lighter Brandons. Using both in the same session is a bit problematic now. I’ll have to work on that a bit.

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#9 Jeff Morgan

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Posted 24 April 2011 - 08:00 PM

And lastly, a Minimalist Glass Lover's dream. APO doublet, dialectric diagonal, and 48 Brandon. I actually bought the scope because it had about the optimum focal ratio to maximum this eyepiece for my eye.

Dark nebula can run, but they can't hide.

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#10 Don W

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Posted 24 April 2011 - 08:09 PM

Beautiful job and one of my favorite scopes that I wish I'd never sold.

#11 avarakin

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Posted 24 April 2011 - 08:28 PM

This scope is really lucky to be mounted on such a beautiful mount!

Alex

#12 StarStuff1

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Posted 24 April 2011 - 08:28 PM

Nice work! Beautiful form and great function. :waytogo: :waytogo:

#13 plyscope

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Posted 24 April 2011 - 08:56 PM

That is a really nice mount Jeff. Thanks for the great pictures. I am planning another Berry mount for a 5" achromat. This thread is great inspiration.

Andy

#14 Mr Magoo

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Posted 24 April 2011 - 09:05 PM

Very nice work Jeff. A question, how do you determine the length of the counterweight tray?

#15 Tom Andrews

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Posted 24 April 2011 - 09:51 PM

Truly awesome build! Gorgeous.

Makes me want to buy a refractor just to have an excuse to build one of those!

#16 Brian Reed

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Posted 24 April 2011 - 10:04 PM

The inlay is stunning. Awesome Job!!! :waytogo:

#17 Jeff Morgan

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Posted 25 April 2011 - 04:23 AM

Very nice work Jeff. A question, how do you determine the length of the counterweight tray?


Thanks guys!

As to the length of the cradle, there really is no set dimension. It's function is to hold the tube on one end, and counterweight on the other. So if you make it long you can get by with a smaller weight, but it is more cumbersome to transport. Make it short, and you need a heavier weight. There are a couple of other options:

1) Eliminate it completely and do the "Weightless Woodshop Refractor" style that Chuck Hard had published in S&T. Basically, the overhang is replaced by a teflon tipped hook that catches under the hub. I built my first one like this, it works well (photo attached). Come to think of it, I can't recall why I did not do this one that way.

2) Truncate the extension and mount a horizontal counterweight shaft. My Star12 only weighs 11 pounds (call it 13 operational weight) so a steel shaft by itself would almost be enough.

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#18 Mr Magoo

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Posted 25 April 2011 - 04:33 AM

Thanks Jeff. I really like the hook idea. I had not seen that article.

#19 Bob Myler

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Posted 25 April 2011 - 07:45 PM

Simply stunning work. I understand that accurately drilling 5-1/2" straight through each leg hub is an iffy proposition at best - especially since you can't vertically square Berry's trefoil hub on a drill press. Somewhat akin to drilling thru a mountain and hoping you arrive at the right place on the other side.

Jeff, your solution is elegant and makes much more sense.

#20 plyscope

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Posted 25 April 2011 - 09:07 PM

Some more apo's on Berry mounts but I like yours better Jeff!
AP and TMB on Berry

Andy

#21 rboe

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Posted 25 April 2011 - 09:52 PM

You are getting some woodworking skills. :bow:

#22 Jeff Morgan

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Posted 25 April 2011 - 11:10 PM

Beautiful job and one of my favorite scopes that I wish I'd never sold.


Oh, I think we all have a scope we wish we never sold. :p

That was first light for the Star12 (for this owner). First impression was stunning. Only looked at a three targets in a short session of 2/5 seeing, but the Star12 still handled Gamma Virginis with contemptuous ease. Wow.

I can see why people wait years for AP scopes.

#23 Jeff Morgan

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Posted 25 April 2011 - 11:16 PM

Simply stunning work. I understand that accurately drilling 5-1/2" straight through each leg hub is an iffy proposition at best - especially since you can't vertically square Berry's trefoil hub on a drill press.



Exactly the problem. And even if you could square it on the drill press the length on a forstner bit is inadequate for a solid block. I was afraid a spade bit would not cut a precise hole, leading to a source of wobble in the mount.

#24 Jeff Morgan

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Posted 25 April 2011 - 11:18 PM

Thanks Jeff. I really like the hook idea. I had not seen that article.


I don't have a reference immediately available for you, but the author is on CloudyNights from time to time. You could probably pm him for more details. It's a clever idea.

#25 Wes James

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Posted 26 April 2011 - 04:13 AM

Not much I can add to other's comments.... other than to agree- beautiful, exquisite craftsmanship and execution, Jeff-
What kind of plywood did you use in the hub of the tripod? Looks like Maple piano pinblock material!
:bow:






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