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Rocker box joints

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#1 Piero DP

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Posted 25 February 2021 - 06:29 PM

I've been thinking to connect all the boards of my rocker box with groove and tongue joints. Then, Titebond 3 and nails or screws.

Has anyone used these joints for the rocker box? Would they be good enough?
Box joints are better and look attractive too, but they are beyond my current skills.

#2 astrokeith

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Posted 25 February 2021 - 06:44 PM

I would say it could be OK.

 

Key will be:

 

Reasonably tight fit joints

Good quality baltic birch ply.

some internal corner brace pieces

Clamped well for a few hours.

Completely sealed with your paint/varnish

 

Or an excuse to get yourself a dovetail jig smile.gif


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#3 Beeham

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Posted 25 February 2021 - 06:48 PM

If you have a table saw you could do splined joints at the corners, I've used them often and they're quite strong - and they don't require a dado stack or a box-joint jig.

 

Failing that, tongue-and-groove with titebond-III and maybe a triangular brace in the corner would probably be fine.  Like astrokeith said, tight fits and good clamping are key.

 

Good luck!


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#4 stargazer193857

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Posted 25 February 2021 - 07:08 PM

I've not yet figured out how to easily get good alignment. Splines and such likely are the easiest.

NMT uses a mortise and tenon, but I suspect that takes more time to cut. Much faster to glue though.

Edited by stargazer193857, 25 February 2021 - 07:08 PM.


#5 Piero DP

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Posted 26 February 2021 - 08:12 AM

Thanks guys. Very much appreciated! :)
I'll go for groove and tongue then.

By the way, are there recommendations about the groove depth? For my mirror box I cut 7mm deep using 15mm thick Baltic birch plywood.

For this rocker box the panels will have these thicknesses: 15mm (front/back panels), 30mm (side panels), and 24mm bottom panel.

It is expected to be a rather shallow rocker box (mirror box is 11" deep).

#6 MitchAlsup

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Posted 26 February 2021 - 11:38 AM

The era of the rocker box is so 2010...........

 

The era of the flex rocker is now !!

 

13newbase02.JPG

 

Rocker box weights less than 1 pound, takes almost no space, delivers the gravitational loads directly to the "ground board"......


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#7 astrokeith

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Posted 26 February 2021 - 12:23 PM

Thanks guys. Very much appreciated! smile.gif
I'll go for groove and tongue then.

By the way, are there recommendations about the groove depth? For my mirror box I cut 7mm deep using 15mm thick Baltic birch plywood.

For this rocker box the panels will have these thicknesses: 15mm (front/back panels), 30mm (side panels), and 24mm bottom panel.

It is expected to be a rather shallow rocker box (mirror box is 11" deep).

i was taught that half the thickness is a good starting point. 


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#8 Ed Jones

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Posted 26 February 2021 - 06:33 PM

With plywood a simple butt joint will have half the wood grain in a favorable orientation for gluing so I prefer butt joints.  When set I go back and drill and glue in dowel pieces every few inches then sand them down flush with a belt sander.  It looks good and will take a lot of punishment.  I like simplicity.


Edited by Ed Jones, 26 February 2021 - 06:33 PM.

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#9 starcanoe

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Posted 27 February 2021 - 10:03 AM

Even more low tech and a bit stronger...and a bit easier to align...simple butt joint with a short strip of lumber (or even a stip of the same plywood) already glued to one of the pieces...such that in cross section you don't have an L shaped made by your two panels....you have an L shape and in the corner of the L is a square/rectangle formed by your lumber/plywood strip. At least double the gluing area...more self aligning...a stiffer corner (not to be confused with the strength of the corner) AND it allows any screw or dowels used to not be working right a the edge of the panel (particularly helpful when trying to countersink holes for screws).


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#10 stargazer193857

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Posted 27 February 2021 - 01:14 PM

Even more low tech and a bit stronger...and a bit easier to align...simple butt joint with a short strip of lumber (or even a stip of the same plywood) already glued to one of the pieces...such that in cross section you don't have an L shaped made by your two panels....you have an L shape and in the corner of the L is a square/rectangle formed by your lumber/plywood strip. At least double the gluing area...more self aligning...a stiffer corner (not to be confused with the strength of the corner) AND it allows any screw or dowels used to not be working right a the edge of the panel (particularly helpful when trying to countersink holes for screws).


True. But when glued boast being stronger than wood, they mean perpendicular to the grain. Furniture makers still only use joints that take advantage of the grain for extra strength. But for a telescope, your only notice the difference if you drop it on the ground a height. Also, panels on all 6 sides give the strength needed.

#11 HunterofPhotons

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Posted 27 February 2021 - 01:57 PM

To the OP:

You haven't said what type of wood, or plywood, you will be using nor have you told us what tools you have that you are comfortable using.  That's kind of important.

I will assume that you have basic woodworking skills and some basic power tools.

From what you have said I don't think that a tongue-and-groove joint is appropriate for you.  It's more appropriate for thicker materials and requires a tight fit for a good joint.

An easier and stronger joint would be a splined miter joint.  This will work for thin sides and it works with solid wood or plywood.

Take a look at this:

 https://www.woodcraf...e-sawn-splines#

Scroll down to 'keyed miters'.

If you use the technique shown here you'll have a strong joint.  If you have a router table outfitted with a simple straight bit you can produce a joint that looks like a box joint.  If you put in a dovetail bit you'll have what looks like a dovetail joint.

I've done all of these joints hundreds of times.  Most of the time it was for drawer sides when you need a joint that is quick and simple, but is still strong enough for constant use.  And it looks fancier than it really is.

Whenever I would make one of these joints I would make an inverted V with the test piece and stand on it with all my weight.  They all passed muster.

A plain miter joint is not very strong but the keyed elements strengthen it immensely.

 

dan k.



#12 Bob4BVM

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Posted 27 February 2021 - 02:33 PM

The era of the rocker box is so 2010...........

 

The era of the flex rocker is now !!

 

attachicon.gif13newbase02.JPG

 

Rocker box weights less than 1 pound, takes almost no space, delivers the gravitational loads directly to the "ground board"......

Sigh,,,  this one makes me wish i was building another Dob ! :)



#13 Bob4BVM

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Posted 27 February 2021 - 02:42 PM

With plywood a simple butt joint will have half the wood grain in a favorable orientation for gluing so I prefer butt joints.  When set I go back and drill and glue in dowel pieces every few inches then sand them down flush with a belt sander.  It looks good and will take a lot of punishment.  I like simplicity.

I built my big Dob exactly as Ed says here, also adding a glued in inside gusset strip in each corner of the box.

The scope has travelled countless rough unpaved mountain roads in the back of my Jeeps since 1991. Compared to that treatment, the stress during actual use is trivial. No sign of joint failure yet smile.gif

KISS

 

Cheers

Bob


Edited by Bob4BVM, 27 February 2021 - 02:44 PM.


#14 Piero DP

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Posted 27 February 2021 - 04:31 PM

To the OP:
You haven't said what type of wood, or plywood, you will be using nor have you told us what tools you have that you are comfortable using. That's kind of important.
I will assume that you have basic woodworking skills and some basic power tools.
From what you have said I don't think that a tongue-and-groove joint is appropriate for you. It's more appropriate for thicker materials and requires a tight fit for a good joint.
An easier and stronger joint would be a splined miter joint. This will work for thin sides and it works with solid wood or plywood.
Take a look at this:
https://www.woodcraf...e-sawn-splines#
Scroll down to 'keyed miters'.
If you use the technique shown here you'll have a strong joint. If you have a router table outfitted with a simple straight bit you can produce a joint that looks like a box joint. If you put in a dovetail bit you'll have what looks like a dovetail joint.
I've done all of these joints hundreds of times. Most of the time it was for drawer sides when you need a joint that is quick and simple, but is still strong enough for constant use. And it looks fancier than it really is.
Whenever I would make one of these joints I would make an inverted V with the test piece and stand on it with all my weight. They all passed muster.
A plain miter joint is not very strong but the keyed elements strengthen it immensely.

dan k.

Thanks for your comment.

I use Baltic birch plywood with thicknesses specified in a previous comment.
Basic skills, really. I have a router (DeWalt, both fix and plunge bases), drill, jigsaw, and a sander, as power tools.

I used tongue and groove joints for my mirror box, but not fully sure whether it's a good idea to use the same type of joint for the rocker box.

Possibly, starcanoe' suggestion is what I should do.

Edited by Piero DP, 27 February 2021 - 04:31 PM.


#15 bobruben

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Posted 02 March 2021 - 05:43 PM

I made mortise and tenon joints in shop in 8th grade. Once was enough.

 

My grandfather was a cabinetmaker from Germany, but I'll adapt.

 

When left to my own choice, back in 2002, I used dowels with a dowel jig to fasten the sides of my mirror box and rocker box.

 

Sure, there are more complex ways of jointing wood, but I'm with the Bill Ockham dude who said that "entities should not be multiplied without necessity"

 

lol.gif


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#16 Piero DP

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Posted 03 March 2021 - 12:33 AM

Food for thought!

#17 nighty

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Posted 03 March 2021 - 08:53 AM

Butt joints with pocket hole fasteners have worked very well for me. Good clamping is needed to ensure the pieces stay where you want them when using Baltic birch plywood. With square cuts and good glue this method makes a very strong joint.

 

I may try to drill pilot holes in the next one I build.



#18 starcanoe

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Posted 03 March 2021 - 09:05 AM

Random point here...while I've never had a properly done wood glue joint fail...the fact that you can do it wrong by having the glue too thick...or squeezing out to much of the glue has always bothered me a tiny bit.

 

West Systems make a 2 part epoxy that comes in a caulking gun cartridge that mixes itself. Not only is it a very strong epoxy and suitable for a variety of materials it has a few other useful properties.

 

It has the consistency of vasaline...so unless you have large blobs projecting out unsupported horizontally it doesn't run and stays put. It is a gap filling epoxy so you don't have to worry about good fits like you do with wood glue. And since you aren't worried about good fits or small gaps....you just get the parts reasonable....which also means you are less likely to squeeze out too much epoxy either.

 

Has a reasonable working time...given that and the fact it doesn't run allows you get the parts in just the right place even if you have to adjust and fiddle with them a bit. 

 

And for an epoxy it has a pretty mild odor.

 

Also has a small bit of flex...so unlike more brittle glues or epoxies it is less likely to fail due to a shock load.



#19 rfiol

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Posted 03 March 2021 - 12:29 PM

The era of the rocker box is so 2010...........

 

The era of the flex rocker is now !!

 

Rocker box weights less than 1 pound, takes almost no space, delivers the gravitational loads directly to the "ground board"......

This is awesome!  Really nice.  I have a couple of questions:

 

1- How does the azimuth rotation work?

2- Any concerns about tripping over the legs?

 

Beautiful telescope.



#20 MitchAlsup

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Posted 03 March 2021 - 01:43 PM

This is awesome!  Really nice.  I have a couple of questions:

 

1- How does the azimuth rotation work?

2- Any concerns about tripping over the legs?

 

Beautiful telescope.

1. Here is a look at the bottom of a corner of the flex rocker

 

assembly17.JPG

 

There is a Teflon pad onto the ring, and a finger reaches out to the inside of the ring. At the end of the finger there is a 1/4-20 bolt and onto that bolt there is a rotating wheel. The 4 wheels were machined such that there was only 10-thou of slop around the "center". The ring itself was machined to a handful of thou of perfectly round.

 

2. The plane of each pair of legs points at the CoG of the scope. So, no, there are no issues with being kicked over.



#21 Garyth64

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Posted 03 March 2021 - 07:20 PM

Wood glue or epoxy, use clamps or screws to keep the joint tight. Don't use nails.  Old German carpenter told me, "the nails only hold the wood together until the glue dries." The nails do not any strength.  For more strength, put in corner bracing.  If you're going to use corner bracing, you don't need fancy joints.  Sure the fancy joints make it a bit stronger, but it would also be just to make it look pretty.



#22 Pinbout

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Posted 03 March 2021 - 07:57 PM

rocker boxes Are typically 5 sided boxes.

 

The 5th side (bottom) adds all the support strength you need for a corner.

 

you could glue and staple butt joints all around and be fine.

 

68118636-F495-415C-BC27-443A10425A83.jpeg


Edited by Pinbout, 04 March 2021 - 08:21 AM.

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#23 rfiol

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Posted 04 March 2021 - 08:45 AM

1. Here is a look at the bottom of a corner of the flex rocker

 

There is a Teflon pad onto the ring, and a finger reaches out to the inside of the ring. At the end of the finger there is a 1/4-20 bolt and onto that bolt there is a rotating wheel. The 4 wheels were machined such that there was only 10-thou of slop around the "center". The ring itself was machined to a handful of thou of perfectly round.

 

2. The plane of each pair of legs points at the CoG of the scope. So, no, there are no issues with being kicked over.

This is great.  Well done, sir.



#24 Garyth64

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Posted 04 March 2021 - 08:51 AM

rocker boxes Are typically 5 sided boxes.

 

The 5th side (bottom) adds all the support strength you need for a corner.

 

you could glue and staple butt joints all around and be fine.

 

attachicon.gif68118636-F495-415C-BC27-443A10425A83.jpeg

Did you use those biscuits in it's construction?



#25 Pinbout

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Posted 04 March 2021 - 11:08 AM

Did you use those biscuits in it's construction?

in that box, yes..... but I have boxes I've stapled with a air compressed staple gun... like nails or screws only hold the parts together till the glue dries.




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