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Anyone with a good knock-down Dob base?

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#51 jtsenghas

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Posted 06 January 2015 - 07:20 PM

Kfiscus, since you are making your base such a stand-alone showpiece are you considering attaching your side panels with something that detracts less from the aesthetics than the rails with floating tenons or biscuits such as the bar knobs I showed on post 17 of this thread? It wouldn't be quite so quick to assemble and disassemble but you're turning that base into a picture frame that you might not want to mar with such a utilitarian frame. Holes for T-nuts wouldn't show up much on a black base, nor would a couple of blind dowel pin holes if you want to add a couple of locating pins to the bottoms of your uprights to make it easier to find your threaded fasteners. Securing your sides that way also eliminates the need for the short locking rear panel I drew above which would tend to obscure your planisphere. For a piece of art like that I suspect you wouldn't mind an extra minute and a bit more care to assemble it if it allows you to better display it. 

 You DID say your primary design criterion is "JSO", right?


Edited by jtsenghas, 06 January 2015 - 07:22 PM.


#52 kfiscus

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Posted 06 January 2015 - 08:50 PM

No decision on attachment method. Am open to suggestions and still considering the cool ideas already gathered here.

#53 jtsenghas

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Posted 06 January 2015 - 09:10 PM

No decision on attachment method. Am open to suggestions and still considering the cool ideas already gathered here.

 

OKAY EVERYONE, THERE'S YOUR CUE!

 

Let's continue to fill this thread with suggested construction methods for knock-down rocker boxes to replace the tall heavy ones out there holding up dobs with altitude bearings far from their mirrors. This is indeed a different kind of project than rocker boxes that sit low and support large bearings near heavy mirrors. I'm always looking for new ideas!



#54 kfiscus

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Posted 07 January 2015 - 12:03 AM

I was leaning toward using 3 low-profile cleats like those drawn up by J T. I envisioned using solid birch mouldings (cove?) and hardwood biscuits. To anchor the uprights I was thinking of using 2 captive bolts threading downward into the base. I won't be using a 4th side.

Edited by kfiscus, 07 January 2015 - 12:05 AM.


#55 Chriske

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Posted 07 January 2015 - 02:46 AM

OKAY EVERYONE, THERE'S YOUR CUE!

 

Let's continue to fill this thread with suggested construction methods for knock-down rocker boxes to replace the tall heavy ones out there holding up dobs with altitude bearings far from their mirrors. This is indeed a different kind of project than rocker boxes that sit low and support large bearings near heavy mirrors. I'm always looking for new ideas!

 

 

 

Not a rocker box, but maybe someone like to copy this idea..?

 

Jules01.jpg

 

Jules02.jpg

 

Jules03.jpg

 

Jules04.jpg

 

Jules05.jpg

 

Jules06.jpg

 

Jules07.jpg


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#56 jtsenghas

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Posted 07 January 2015 - 07:01 AM

Chris, well done! I like it!

I see that you worked out a very similar method to those above for offsetting one hinge rearward by a panel thickness so that everything folds flat. As such, the triangle is not exactly equilateral, but there is absolutely no reason it has to be. I like the way you cleared the lower edges so that the feet will sit firmly even on slightly uneven surfaces and how you bent the fender washers on the attachment bolts.

Because that base sees very small side loads the threaded inserts see very little stress and are, I expect, more than adequate. If this concept is used on a larger set-up where greater stresses are encountered (such as anything anyone stands on, or anything that may see significantly sideways loading) I would strongly recommend using those cross nuts mentioned in my post #29 on this thread instead of inserts into the edge of a panel. If cross-nuts are used the bolt holes would have to be drilled carefully parallel to the face of the panel containing that cross-nut, however. It might also help to counterbore that bolt head surface with a Forstner bit, or even a spade bit if it is used carefully,

This project shows that knock-down assemblies are useful also for raising smaller dobsonians to a convenient height and that making such assemblies modular has further advantages. By making the rocker box in essentially two pieces including a riser pedestal like this it becomes easier to store, transport and set up.


Edited by jtsenghas, 07 January 2015 - 12:55 PM.


#57 jtsenghas

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Posted 07 January 2015 - 09:30 AM

I was leaning toward using 3 low-profile cleats like those drawn up by J T. I envisioned using solid birch mouldings (cove?) and hardwood biscuits. To anchor the uprights I was thinking of using 2 captive bolts threading downward into the base. I won't be using a 4th side.

Since the primary purpose of the biscuits or tenons in the above designs are to hold the panels DOWN against the base, and you are considering doing that with at least two captive bolts, I think that idea of using both hold-down bolts and biscuits is a bit redundant--along the lines of the idea to wear both a belt and suspenders.   If you want to put your base on display for the planisphere to be seen without the uprights, you may object to half of each biscuit being visible then also. In your particular case hold-down bolts only might make the most sense.

 

If biscuits or floating tenons are used I'd recommend that their centers be at least 1/2" from the lower edge to reduce the risk of splitting the side panels. That is why in my above designs I had the side rails that you call cleats a full inch tall. It sounds like you would want them lower anyway for appearances. Making them low profile would compromise things quite a bit structurally on the lower edges of the side panels if those panels were slotted too close to their edges.  If you only want to make a low molding to register your sides against to facilitate finding your T-nut holes for assembly, you could put it on the outsides of all three uprights with the corners mitered and dressed up with a nice quarter-round, or cove, or even ogee curve on the outer edges for aesthetics. 

 

Note that on my proposed design the gap between the side and front "cleats" was to allow the panels to be hinged while standing on the base and slid fore/aft for engaging on the inside of the front panel and to allow clearance at the corners for them to be opened.  If you consider using four captive vertical bolts you could open your panels to 90 degrees, slide all three of them within your moldings from above, and then secure them.  Four bolts total, as close to the corners of your side panels as possible, would be sufficient and strong.  The front panel would be attached to the sides continuously with the piano hinges and, since the nearest bolts on the sides would be only a few inches away, the front board would not have to be secured to your base--unless you want to further stiffen that base with a fifth bolt at the center of that front panel.  I suspect that wouldn't match your concept of a nice wide ellipse in the front panel in keeping with the design appearance of your planisphere horizon.  For that matter, if you use bar knobs as described in post 17 above, you could make their access holes elliptical in keeping with the design.  You commented earlier that making ellipses was "a pain", but if you use a router pattern bit you could make a pattern for the front ellipse and possibly the access hole ellipses for the bar knobs in a scrap piece (finessing them with a drum sander), then rough cut the ellipses in your panels with a hand-held jigsaw, and then clean them up as virtually perfect identical ellipses with your patterns clamped to the undersides of your panels. (Just make sure your patterns are big enough that your router base doesn't interfere with your clamps). Ellipses would also be a little more hand-friendly for clearance during assembly and disassembly. Would that be in keeping with your "JSO" intent?


Edited by jtsenghas, 07 January 2015 - 01:04 PM.


#58 kfiscus

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Posted 08 January 2015 - 05:51 PM

The plan du jour is a piano-hinged 3-pc. mount with an outline like that shared by JT. I would keep my signature elliptical cutouts. My local ACE Hardware stocks the fasteners for pre-manufactured furniture. I will probably imbed 6 cross screw nuts near the bottoms of all 3 upright panels (2 per panel). Countersunk flat-headed bolts will penetrate the rockerboard base from below- tightened by an Allen wrench. Unlike the 20-second setup of JT's design, I would imagine this mount will take about 5 minutes. Access to the 6 bolt heads will be gotten by removing the central bolt that joins the groundboard and rockerboard.

Edited by kfiscus, 08 January 2015 - 05:56 PM.


#59 jtsenghas

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Posted 08 January 2015 - 08:30 PM

Kfiscus, I'm glad you are using cross nuts if your screws will be from below and that should keep appearances elegant, in my opinion.

I have a few construction tips, however. It is absolutely critical that hole spacing be almost perfectly matched among your side panels and the base. It would be difficult to accomplish that by transferring holes from the bottom board to the edges of the side panels, or by relying on layout lines alone. A drill jig from a board drilled with the clearance diameters you use could be used for both the holes in the bottom edges of the sides and the holes in the base. If you have a drill press, but not a good horizontal boring setup, such a jig could help you to drill those holes centered and perpendicular to the edges of those side panels--not unlike using a doweling jig. That will also help you to carefully center your cross screw nuts to those holes. You could drill those last by transferring the axes of those clearance holes to the sides of your panels with a sharp pencil and square, and then drilling the 1/2" (or whatever diameter the cross screw nuts are) to match the actual locations of the bolt holes. That sequence should minimize accumulated error in lining up the bolt and nut holes. Alternatively, you could make both bolt holes and nut holes in your jig using a drill press to carefully have them intersect through their centers (as if you were to assemble that hardware into the jig) and then you could use the jig to transfer the nut holes to the sides of your panels.

Are your "signature ellipses" going to be angled 10ยบ to match the side profiles I showed in the views that had Saturn instead? Would you like me to finesse the designs of the side panels in CAD to help you with laying out the patterns of the sides?


Edited by jtsenghas, 08 January 2015 - 08:39 PM.


#60 kfiscus

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Posted 08 January 2015 - 09:17 PM

Thank you for the offer, JT. I'll contact you when I'm ready- it may be many weeks. I have to get my hybrid scope's OTA done and the alt bearings attached.

Yes, on the 10-degree tilt. I'd like the main ellipses to be a little fatter, basically the minor axis being the diameter of the Saturn circle.

Edited by kfiscus, 08 January 2015 - 09:26 PM.


#61 jtsenghas

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Posted 08 January 2015 - 09:39 PM

Thank you for the offer, JT. I'll contact you when I'm ready- it may be many weeks. I have to get my hybrid scope's OTA done and the alt bearings attached.

Yes, on the 10-degree tilt. I'd like the main ellipses to be a little fatter, basically the minor axis being the diameter of the Saturn circle.

No problem, and I'm not trying to commandeer your design work. It's simply that it would take me only a few minutes to stretch and modify what I have to give you layout dimensions including pin locations for the ellipses. It may be that you want slightly different dimensions than I presented anyway. I simply tweaked things for a four foot square piece of plywood. It looks like your altititude bearings on your base shown in post #2 might be offset a little rearward of your azimuth bearings and, if so, you may have good reasons for that. If you send me a scan of a dimensioned sketch when you get to that point I could finesse it carefully centering ellipses, determining their foci for pin locations, and blending tangents within minutes.



#62 kfiscus

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Posted 08 January 2015 - 10:30 PM

No worries on any commandeering. ;)

There is no offset- the az bearings are dead center. That is an illusion. I took a rakish angle off the great big slabs of the stock rockerboard sides, rearward of the bearings. That angle probably saved over a square foot of plywood.

Edited by kfiscus, 09 January 2015 - 01:14 AM.


#63 Jim Romanski

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Posted 09 January 2015 - 05:21 PM

These folks make collapsible mounts and gave me ideas for mine:

http://www.astrogoods.com/

 

I will have to take some pictures of mine which isn't quite finished yet.



#64 jtsenghas

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Posted 10 January 2015 - 11:30 AM

Kfiscus, does this represent the sides you want?  The perimeter isn't changed, unless you want to add the radius shown near the top of the hinge.  The interior ellipse you suggested is rounded to the nearest 1/16" after setting it 3 1/2" inside the rear edge. Both ellipses have the foci shown with 1/2" circles. If you use these dimensions and lay it out with a loop using the string method it might be easiest on the larger ellipse to set the loop length to just reach the top edge of the panel just forward of the altitude bearing and blend the radius slightly on the rear edge if you have any mismatch there.  The 7 1/4" x 17" ellipse could have the string length set to just reach that minor radius at 3 5/8".

 

side w kfiscus oval.PNG

 

 


Edited by jtsenghas, 10 January 2015 - 09:59 PM.

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#65 kfiscus

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Posted 10 January 2015 - 12:16 PM

Perfect- the radius added by the hinges was the solution I lacked.  I wasn't liking the sharp corner.  Thank you very much, JT!



#66 jtsenghas

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Posted 25 January 2015 - 09:45 AM

Yesterday I improved my own knock down base with my suggestion proposed in post 30 of this thread.

 

I am really pleased with the increased rigidity it provides, as evidenced by the elimination of the slight slop I previously felt when reversing the azimuth direction while tracking. In this case I angled the bolts only 10 degrees to match the edge of the panel that the hexagonal tube just cleared.

 

First I turned a couple of plastic knobs 3/4" diameter x 1 1/8" long by screwing them onto a 1/4-20 bolt whose head I had removed so that it fit into a router collet on my wood lathe.  A couple of wide files produced the shape in short order, and a chainsaw file was used to make flutes by hand every 45 degrees that were easy to grip with fingertips. (These flutes were inspired by one of my favorite screwdrivers).   I then made a new rear panel for my rocker box that was slightly larger than the original (which the tube had cleared by 3/8"), bored 9/32" holes from the ends, and made my access holes using a scrollsaw.

 

rocker knob 1.jpg

 

Note that in the above photo I also sharpened the bolt that had been used to chuck the knob in the lathe to make a transfer punch for the side panels.  The access hole is 3/4" longer than the assembly of the knob, star lock washer, nut, and flat washer (that were used in the final assembly) combined.

 

Making the mating holes for the T-nuts required a bit of care, but I managed to hide the T-nut under the original reinforcement plate the original latch had been screwed to on the outside of the rocker box.  The only reason I didn't angle the bolts higher to take advantage of a higher attach point and improved angle for the forces was that I was targeting the original latch location for aesthetics. I didn't want the rocker box to look reworked or to have visible T-nuts (gasp!). I adjusted the jam nuts on the bolts so that I had good pressure of the flat washer against side of the access hole without quite bottoming out against that reinforcement plate.

 

Assembly is very rigid, and also makes the stiffness of the fold-out diagonal reinforcements on the sides of the rocker box more apparent. It does take about thirty more seconds to put together than the latches had, but I don't mind.  In the end I verified that I indeed had the 1/8" clearance to the tube I had expected.  I'm getting close to painting and varnishing this project!

 

rocker knob 3.jpg


Edited by jtsenghas, 25 January 2015 - 06:46 PM.

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#67 kfiscus

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Posted 25 January 2015 - 11:08 AM

Beautiful work, J.T.!



#68 synfinatic

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Posted 28 January 2015 - 10:38 PM

Wow, amazing work everyone!  Wish I had the skills & tools to be able to do something like this!



#69 kfiscus

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Posted 01 May 2015 - 10:21 PM

Bumping this thread back into the daylight.

 

I'll be cutting the steel tube for the replacement lower body tube of the 12" Lightbridge tomorrow.  Its length is critical to drawing out the side panel pattern for the knockdown base we worked on this winter.  This is my first Saturday with time available to restart the base with the planisphere in the base.  The OTA will be like a Lightbridge but will have the adjustable alt bearings of a Zhumell.

 

OTA will be fully flocked and I have a new Astrostuff shroud ready.  Will have Astrocrumb filter slide rails to hold my four 2" filters.  I'll have to use some counterweights at the lower end because there will be a Telrad and straight finder up front.

 

BTW, can someone tell me if there is a lower tube dust cap for Lightbridges?  I've never seen one or heard one mentioned.



#70 kfiscus

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Posted 03 May 2015 - 07:25 AM

The steel tube cutting was a success.  The hybrid Z12 / Lightbridge is ready for me to start making sawdust.  For anyone interested in the steel and aluminum work involved with the hybrid, see page 23 of the Mega-Mods to Zhumell thread in the Reflectors Forum.

 

One photo of the completed hybrid tube.  I haven't decided what color to paint everything.

Attached Thumbnails

  • Hybrid Scope 001 25%.jpg

Edited by kfiscus, 03 May 2015 - 07:27 AM.


#71 kfiscus

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Posted 09 May 2015 - 01:05 PM

Rocker board sides after roughing out.  All of the work is being done to the two stacked sides to keep everything symmetrical.  The two screws hold temporary registration tabs.  Next step is spindle sanding the curved edges.

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  • 249 25%.jpg

Edited by kfiscus, 09 May 2015 - 01:08 PM.


#72 kfiscus

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Posted 09 May 2015 - 01:19 PM

The rocker board sides just sitting in place after all of the spindle sanding.

 

The right side will have its front edge cut back 1.5".  This piece will be reattached to the right side with a 12" piano hinge to facilitate the knockdownability.

 

The next step will be using my largest diameter spindle on the sander to get the perfect fit in the altitude bearing sockets.  The sockets are intentionally cut too small so that the sander does the final sizing.  I allow enough "slop" for the TINY thickness of 3 coats of lacquer finish.

Attached Thumbnails

  • 250 25%.jpg

Edited by kfiscus, 09 May 2015 - 01:27 PM.

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#73 kfiscus

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Posted 09 May 2015 - 08:31 PM

All of the upright pieces have been joined by the the 12" piano hinges.
 
I then flipped the rockerboard base downside-up to locate the spots for the eight assembly holes.  The holes are all about 5 inches apart. There will be three bolts holding each side piece and two bolts holding the front panel.

Attached Thumbnails

  • 251 25%.jpg

Edited by kfiscus, 10 May 2015 - 02:20 AM.

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#74 kfiscus

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Posted 09 May 2015 - 08:41 PM

Next step is making a hole drilling jig to get the eight holes perfectly spaced in both the base and the 3 upright sections.  The jig is especially important to get the holes perfectly plumb/centered in the 3/4" Baltic Birch plywood.  I'll be using the jig on both the base and uprights.  (Thank you, J. T.!)  The bolts will be threading into cross nuts imbedded in the three upright sections.  I will be inserting them from the insides of each piece to make them less noticeable.


Edited by kfiscus, 09 May 2015 - 08:43 PM.


#75 kfiscus

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Posted 09 May 2015 - 10:04 PM

Almost a valentine-shape when the uprights are all folded up.

 

(The EbonyStar ring for the azimuth bearing can be seen to the right.)

Attached Thumbnails

  • 252 25%.jpg

Edited by kfiscus, 09 May 2015 - 10:08 PM.



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