Tag Archives: dovetail

Impossible Dovetail Joint

For this week Impossible object, we will revisit the dovetail joints and have a look at some interesting variation on the theme. This time we will use the “master sketch” technique in Inventor to build our different pieces.

 

This technique is using a single part with all the sketches required to model the whole assembly. Each piece is then derived from the master. To update the model, you just have to update the master sketch, and if everything is properly built, your whole assembly should follow.

Result_picture1

The inventor result files links are at the end, with the STL and the thingiverse link.

  • To start, create a part with a bunch of user parameters to control the design. Then on the horizontal plan XY create a sketch with the outline of the 2 main blocks (length*width).
    impossibleDovetail_01_userParam
  • The dovetails are extruded on a non-vertical plan, so the easiest way to control the result is to create a sketch in XZ plan and draw a segment with ‘Tilt’ angle from the horizontal. Then use this segment and the origin point to create the work plane using “Normal to axis through Point” tool.
    impossibleDovetail_02_TiltPlan
  • The next sketch will be on this newly created plan. The left triangle and the left side of the center one are drawn and the rest is a mirror copy. The base of the left triangle is at length/5=10mm. To allow some clearance in the pieces, all triangle have been “offset” inside by “clearance” parameter (0.25mm here).
    impossibleDovetail_03_DovetailSketch
  • The final master sketch part should now look like the view under.
    impossibleDovetail_04_Mastersketch
  • Now we create a new part to model the first piece. From the manage tab, select the “Derive” tool and choose the master sketch part. Then make sure that the User parameters and the Sketches are shared (yellow plus) and validate. The master sketches will appear in you new part. Now any change in the master sketch will update the part (you will have to press the update button / thunder bolt)
    impossibleDovetail_05_Derive
  • Each sketch will be used multiple time to build the piece, so don;t forget to make them “visible” again once they have been used by an operation. The first thing will be to create the “male” dovetail in the center, so the first step is to extrude the small version of the center triangle by a very large amount on both side.
    impossibleDovetail_06_Centerdovetail
    Then extrude the left rectangle by height and keep only the intersection. to create the dove tail.
    impossibleDovetail_07_CenterdovetailFinished
    impossibleDovetail_08_CenterdovetailFinished2
  • Now the main body can be created by Extruding the right rectangle by “height”.
    impossibleDovetail_09_body
    To create the 2 side female dovetails, just select both the external rim and the internal triangle on both side and cut into the main piece.
    impossibleDovetail_10_body
  • To finish the piece you can add a fillet on the internal side of the dovetail.
    impossibleDovetail_11_finish
  • The second piece is created the same way, from a derived part except you have to do the “negative” geometry.
    impossibleDovetail_12_PieceB

And here is the result assembled with a “wood” finish 🙂

impossibleDovetail_Result01

impossibleDovetail_Result02

I’ve printed the result to check that the piece would indeed fit and yes it works!

The STL files are available in Thingiverse here and the Inventor files are here.

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Brain Teaser: the Padawan Dovetail Box

And here is this week puzzle: the Padawan Dovetail Box. Once more you have to wonder how is it even possible to have dovetails on only 2 sides and the “L” shape prevent to use the same trip as previous puzzle… The goal is to open the puzzle to access the compartment inside the assembly but this time gravity force will not help you… Time to work on your Jedi powers young padawan!

padawan_assembly

The Puzzle is build around 2 main pieces and two 1/2″ diameter (12.7mm) steel ball bearings. I’ve settled for 1/2″ because it’s the standard size for small marbles called peewees. In this case we need steel balls for the puzzle.

padawan_PartA

First piece of the Padawan Dovetail puzzle (and steel ball bearings)

padawan_PartB

Second piece of the Padawan Dovetail puzzle (and steel ball bearings)

A transparent side view of the puzzle reveals that the holes are tapered so whatever the direction you hold the puzzle, at least one ball is in the way to prevent sliding of the puzzle…

padawan_section

I will let you figure out how to solve it, but I’ve included clues in my post that should help you. I can’t wait for my printer to come and try it.

To assemble the puzzle, push the steel balls in each holes and hold them between 2 fingers. Slide the pieces starting with the arrow side, then try to open it again!

As always I’ve uploaded the STL on Thingiverse here.

Happy brain teasing!

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