# Puzzle block



## straze (Mar 20, 2012)

On and off for a few months I've been trying to make one of these puzzle block but kept failing to obtain matching radius on the dovetail.
Last week I finally cracked it with various jigs and managed to make 2 of these interesting blocks. I should be able to set up and cut the joint right each time now.

It's 2.25" x 4.5" x 4.5" and made of English Oak and Sepele. The finish is an interior spray varnish from a rattle can (I quite like the grain being seen as apposed to a glass smooth surface)

The two halves are held together with magnets that hold ball bearings in place. A good sharp blow to the top will cause the bearings to drop and allow the dovetail to slide. (A much harder blow than people would think) 

Many have tried to 'win' the pound coin inside and failed.:laugh:


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## lenh (Feb 27, 2009)

straze said:


> On and off for a few months I've been trying to make one of these puzzle block but kept failing to obtain matching radius on the dovetail.
> Last week I finally cracked it with various jigs and managed to make 2 of these interesting blocks. I should be able to set up and cut the joint right each time now.
> 
> It's 2.25" x 4.5" x 4.5" and made of English Oak and Sepele. The finish is an interior spray varnish from a rattle can (I quite like the grain being seen as apposed to a glass smooth surface)
> ...


Really cool box, Kevin. I love making little "trick" boxes. Any chance of sharing the jigs you used? I have never tried a dovetail on a radius.

Len


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## straze (Mar 20, 2012)

Hi Len

I will do a 'how I did it' set of photos this week.

Regards
Kevin


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## Semipro (Mar 22, 2013)

Nice job Kevin will be looking forward to your ( how to)


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## Marco (Feb 21, 2009)

straze said:


> Hi Len
> 
> I will do a 'how I did it' set of photos this week.
> 
> ...


Great job.. I love it!. Looking forward to the play by play.


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## JOAT (Apr 9, 2010)

Never saw one like that before. Very nice job.


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## Gaffboat (Mar 11, 2012)

A clever, sneaky puzzle box. I like it!


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## harrysin (Jan 15, 2007)

That is a job to be proud of, I too look forward to the photo-shoot.


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## OPG3 (Jan 9, 2011)

Kevin - That is SUPER COOL and very well executed. The color contrast and differences in woodgrain are beautiful as well. My guess is that our friend Oliver [Gaffboat] will make one with a live rabbit that jumps-out, instead of the coin!

Otis Guillebeau from Auburn, Georgia


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## Daikusan (Apr 12, 2013)

Kevin
Very nice thanks for sharing.


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## Barry747 (Jun 16, 2011)

Great puzzle box. I'd like to try something like for my grandkids. Looking forward to the pictures. Nice choice of wood and finish. I always struggle with the finish.


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## PaulH (May 30, 2012)

Brilliant Kevin


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## RainMan 2.0 (May 6, 2014)

That is really cool . I to had no idea you can make a radius in a dovetail . When I looked at it briefly I wondered what all the fuss was but I get it now


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## straze (Mar 20, 2012)

Here are a few photos showing the set-up I used to make the puzzle block.

A sheet of ply with slots etc to fit on router table (this is my old circle cutting jig and I intend to make another with a formica finish and a much narrower centre bit slot) Clamped straight edges each side to keep things running parallel and a spike to rotate the work piece on.
The scribbling marks were made by a candle to make things slide easier.


Two stops and spacers.


A simple guide to ensure accuracy of pin position.


Mark the centre of the dove tail cut, place the block over the centre pin and adjust the jig to line up with the mark (I used a pointy cutter for this)
Once lined up clamp jig to table then clamp the stops and one spacer up to jig.


Fit the dovetail cutter and set up to required height.


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## straze (Mar 20, 2012)

Clamp on a backing board and make the first cut. This is quite a severe cut to do in one hit and would be easier if the bulk was cut out first with a straight cutter. 


Once this cut is made remove one spacer from the stops, slide the jig up to the stops and make another cut. Then place two spacers between the stops and jig to make another pass. You will have to ensure the work piece is rotated the right way so as not to climb cut.

You now have one half of the puzzle cut.
Matching this the other half of the puzzle is what I struggled to do but this way seems to work well............
Place the first cut block back onto the pivot pin and with a sharp pencil mark onto the jig the insides of the dovetail. Remove block.


Next place the pre-drilled second block over the pin and transfer the marks to this block like so.


You are now ready to cut the dovetail top tip up to either side of these marks. This is where my fence fine adjuster came in handy.




This is what you will end up with. Although they wont yet fit together you can at this stage see if it is going to fit or not. If the joint is too tight another fine cut can be made BUT if it too slack there is nothing you can do about it.


Cut and trim off by hand the corners on the second block and the two halves should fit together.


That's as far as I got today and I will complete this puzzle next week.

Regards
Kevin


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## lenh (Feb 27, 2009)

Thanks for instructions, Kevin. Excellent. Looking forward to the remaining. One question. Since you have made the original box have you noticed any problems with humidity affecting the fit? The last box I made with sliding dove tails (straight) drove me crazy with wood movement. One day the fit would be perfect, the next too loose, the next too tight. I was able to finesse the joint to where I was happy. Somehow I can't imagine trying to find a happy medium with the curved dovetails.


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## jw2170 (Jan 24, 2008)

Excellent photo tutorial, Kevin.


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## Gaffboat (Mar 11, 2012)

jw2170 said:


> Excellent photo tutorial, Kevin.


+1. A nice "how to".


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## tuffy1234 (Jun 4, 2014)

Thank you Kevin, for the puzzle and the tutorial.

CW


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## straze (Mar 20, 2012)

Todays progress

Screw the two parts together and give them a good old sanding.


Stick on four bits of plywood with double sided tape, to hold things together) and cut out the corner


With the ply and tape still in place clean up on the bobbin sander


This next stage is as far as I got today but it is important.

A ply template was made to enable accurate lining up of the ball bearing locking points and a nail used to mark the drilling position.


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## bosox (Jun 12, 2012)

Can someone enlighten me how this puzzle block works? I've seen some other type of puzzle boxes but this is one is interesting!


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## straze (Mar 20, 2012)

bosox said:


> Can someone enlighten me how this puzzle block works? I've seen some other type of puzzle boxes but this is one is interesting!


The two halves are prevented from sliding open by steel ball bearings held in place by magnets.

One side has shallow exact size holes with the magnets fixed into the bottom of the holes.


The other half has clearance holes that are deeper than the ball bearing. This enables the bearings to be knocked off the magnets and fall into these holes allowing the two halves of the puzzle to slide open. 
To 're-arm' the puzzle just slide closed and tip upside down, the bearings will now be held into the locked position by the magnets.


Hope this helps.


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