photopdf iconCaptured Nut Puzzle

           ... a YouTube Shop Student Project

This project was developed to help a beginning machinist or hobbyist develop machining skills using the metal lathe. Please keep in mind that I am a beginner myself and not all procedures in this document may be correct, but I have done all that I can to minimize error. Also keep in mind that like skinning cats, there are other ways this project can be completed. Meaning the steps that I outline here are not set in stone.  You can download the complete project by clicking the PDF icon in the upper right of the screen.

Why a captured nut puzzle?

While the end result is only a toy of little practical use, I think the operation involved in making it are a great benefit to the beginner machinist. Operations that need to be performed to complete the project include facing, center drilling, drilling, turning to diameter, grooving, chamfering and single point threading. These operations must be mastered along with others while learning to use a metal lathe. And that, my friend, is why I decided on this project.

A note about accuracy

When making the puzzle, it is important that we work as accurately as we can. Not because the puzzle requires it, but rather because we need to hone our budding skills. If you mess up a little trying to get to a certain dimension, don’t sweat it too much, the puzzle will turn out just fine. However, do try your best to machine your parts as accurately as you can.

A note on safety

Revolving machinery can be deadly if steps to work safely are not observed. I assume that you know things like wearing safety glasses, no long sleeve shirts, no neck ties or jewelry, etc, etc. Safety when operating you lathe is YOUR responsibility, not mine or anyone else's. Please observe all safety practices while using the metal lathe.

What is included?

I have included a drawing and assembly diagram for the puzzle. In addition I have listed out the sequence of operations that I have taken to complete the project. Keep in mind as I repeat from above, there are probably as many ways to do this project as there are machinists. If you have a better way of doing it, then please feel free to change things up.

An invitation to watch

I have completed a series of videos on my YouTube channel demonstrating how to make this puzzle. I invite you to watch them and if you are very new to machining, I encourage you to do so.  I have inserted the videos below if you care to watch them.  They are also on the YouTube Shop Student Page.


Questions and Comments

Any questions and comments are welcome, or if you would like to send me a picture of your finished puzzle. You can email me at xavier at gtec dot com or through the contact menu link above. I will do my best to answer questions that you may have. Additionally, constructive criticism is welcome. Anything that you may add to make this a better project is welcome.

De intentione cordis gratias ago

I would be remiss if I didn’t thank the following people for the friendship, help and technical guidance.

Art Eckstein
Richard (MSFN) -

Thank you gentlemen!

The Drawing

The drawing below shows the project to be made.  You can download the complete project with a much larger drawing by clicking the PDF icon at the top of the page.  Alternatively, you can click the image of the drawing below to download just the drawing in PDF format.

Captive Nut Drawing

Assembly Diagram

I have also provided a 3D rendering of the assembly diagram.  Again, you can download the complete project from the PDF icon at the top of the page, or click on the image below to download the PDF of the assembly drawing.

Assembly Drawing

Sequence of Operations

Again let me reiterate that there are many ways that this project can be completed.  The following sequence of operations are those that I took to complete it.  Feel free to change them up any way you see fit.  Additionally, the images I have included here are quite small.  To see a larger version of the image simply click on it and it will open in a modal window.

The material I used to make this was a length of 3/4" 12L14 material purchased from Hobby Metal Kits.

OP   01 100v(1) Extend stock 1-3/4” from chuck Jaws

OP   02 100v(2) Face end of bar square

OP   03 100v(3) Center drill with #3

OP   04 100v(4) Cut off to a length of 1-9/16” (1.563”)

OP   05 and 06 100v(5) Reverse part in chuck, (6) Face to length of 1.500"

OP   07a 100vOP   07b 100v(7) Center drill, then drill to depth of 1/2” with #7 drill. [Tap drill for ¼-20 UNC]

OP   08 100v(8) Tap hole ¼-20, follow with bottom tap

OP   09 100v(9) Lightly chamfer opening of thread to remove raised burr from the tapping operation and remove part.

OP   10 and 11 100v(10) Extend stock from chuck about 1” (11) Face end of bar square

OP   12a 100vOP   12b 100v(12) Center drill and then drill to depth of 1/2” with #7 drill.

OP   13 100v(13) Tap hole ¼-20, follow with bottom tap, gently chamfer thread to remove burr from tapping.

OP   14a 100vOP   14b 100v(14) Assemble first part [step 8] to this using ¼-20 stud and extend enough from chuck to allow the first 4” to be knurled. Support the end of the work with a center.

OP   15 100v(15) Knurl for a length of 4”

OP   16 100v(16) Very gently face end of bar to remove the burr the knurling tool pushed over. The material is hanging out quite a distance so only take a very light cut.

OP   17 100v(17) Cut thread grooves 0.188” wide to a diameter of 0.392” Note that the puzzle is in its assembled state and the width of the heads are 0.500” and the length of thread including the thread relief groove is 2.000”

OP   18 100v(18) Turn thread Major Diameter to 0.493”

OP   19 100v(19) Single point thread, ½-13 UNC 2A

OP   20 100v(20) Verify threads by measuring with thread wires.

OP   21 100v(21) Chamfer exposed edges of puzzle ends 0.063”

OP   22 100v(22) Part off to a length of 3-1/16” [This is the main puzzle]

OP   23 100v(23) Face off remaining stock in chuck until just cleaned up

OP   24 100v(24) Part off 5/8” of the knurled section remaining on stock

OP   25 26 and 27 100v(25) Mount main puzzle body in chuck using some soft packing to prevent damage to knurl. Face puzzle end to length, (26) Center drill end with #3 center drilling, (27) Chamfer end 0.063. Removed finished puzzle body

OP   28 100v(28) Using soft packing, clamp nut in chuck leaving at least 3/16” exposed.

OP   29 100v(29) Face nut just enough to clean up

OP   30 100v(30) Chamfer 0.063

OP   31 100v(31) Turn nut in chuck and face to length

OP   32a 100vOP   32b 100vOP   32c 100v(32) Center drill #3. Pilot drill ¼” through and finally drill through with 27/64” drill [tap drill for ½-13 UNC]

OP   33 100v(33) Tap through ½-13 UNC

OP   34 100v(34) Chamfer 0.063”

OP   35 100v(35) Chamfer ½-13 threads on both sides of nut

OP   36a 100vOP   36b 100v(36) Assemble puzzle proper and amaze your friends.

END OF PROJECT (last update 2018 MAY 25)