Quick tip to align a part with a thin tab in a lathe

     The problem: Align the holes in a part with plastic flat plate that should go underneath. The workshop I have access is very modest. No fancy CNCs, no DROs, the machines are small. Luckily the plastic plate fitted in the drill press, otherwise I would need to use the hand-held drill to poke the holes.  

     My plan:  Use a joint alignment pin (commonly used in woodworking), to indent the holes position in the plastic board, drill the holes with the drill press, hammer the pins in, go to town and have some beers. 

     The flaw in my plan: The holes in the part has a unusual dimension (5.35mm) and the shank in the commercially available  joint alignment pin has always full numbers dimensions (4, 6, 8 mm). 

     My workaround: machine the shank in the lathe to my number.

    The problem with the workaround: I would need to hold the part by a very thin tab. 

I don't now exactly how to call this, but I found in the internet as joint alignment pins

      I found out that the collet holds this well enough to machine it. The problem is that even in the collect this is not easy to align. If super precision was required I could use the dial indicator, but the part doesn't needed to be super precise.  So, here comes my quick and dirt solution to this case. I used the tailstock chuck to hold the shank, pulled the tailstock close to the headstock, and this way inserted the part in the collet. 

Using the tailstock to insert the part aligned in the collet

Voilà, we're ready to make some chips

     Well that's a trick useful only for very specific operations, but anyway, something to keep in mind.

An anti-kink device for a novel high tech cable

     Well, its been a long since the last post. I apologize about that. I had a little life twist and ended up married in Switzerland. I've spent the lasts months adapting myself to the new life. So far, a great time. I'm currently working at nanoleq,  a Zürich based startup trying to make a novel high tech cable. Up to now we are a 3 man company, but the energy around is great, such a cool team. 

     Going to the point of the post, It's about a anti-kink device for our novel cable. The idea was to make an cable prototype, that would be something to show other people our tech, something that you could hold in your hands, put to use, etc. In my opinion much cooler than just talking about our idea in the business meeting with the companies we visit to try to raise interest in the our technology.

      My approach was to make a 3d print mold of an anti-kink device and then fill it with silicone, so we should end with a cool transparent part. Been a big fan of open-source software, I used Freecad+Cadquery to achieve my goals. Cadquery is a great software. It's very convenient when you don't know exactly the parameters of your design, so you can do a second iteration very quickly. The next image shows my design. 

The cadquery code to obtain this model is the following.

     I know that there's a lot of room for code improvement to make the design really parametric. In the middle of the development of this prototype the other folks at nanoleq decided to put this project aside, as other priorities appeared. So I stopped working on this, but at this point I already had some results, the ones I'm showing in this post. Still, to have a refined results, other iteration would be necessary. After making the first cable I saw that I should made the riser channel bigger, so you have a silicone reservoir in case of leaking or shrinkage. Other thing I would make different is this sphere cavities. This was my idea to have some indexing between the two sides of the mold, but only two spheres is not enough, you still have some play when you try to put the mold together. Not a big deal, as you sense the misalignment with your finger and correct it. Anyway, if I would do it again  I would try to put another sphere on the upper side of the mold to see if I get better results. 

     Here is the 3d printed part with the ball bearing balls epoxy glued in place.

     The three cables twisted (ground, left and right) and with the headphone jack soldered.

     Here is the final result. A little rough, but I'm sure that with more time to finish the mold, a smooth finish could be achieved.


Well, thats it! Thanks for reading.

Edi

Stress along a cut line in Calculix

     This videos is about how to plot a entity value against a cut line (node sequence) generating plots like this:

Energy comparison plot revisited

     Looking back in my post about energy comparison graph,

http://jungletools.blogspot.com.br/2016/07/car-motorcycle-and-bicycle-energy.html

is easy to see room for improvement. So in this one I'm sharing a code to make the same plot, but in much more pythonic way. Take a look in the code:

     In the first time I refused using "def" to define the function, thinking this would be overkill for a simple script, and would affect the readability. I was wrong, now the code bloat is reduced, and the readability is even better. The way python works, permitting that you define the parameter value inside an array (look at lines 31, 32, 33), keeps the readability, and also makes the order of the parameters in the array unimportant. Sweeeeeet.

Hexahedral Mesh Refinement in Salome

     In this video I show some ways to refine the hexahedral mesh of the beam we did before. This procedure is meant to be more clever than simple making the "number of segments" parameter bigger and bigger.

Thanks again!

Cantilever beam finite element analysis using open source software

     In this video I'm modeling, meshing and computing a cantilever beam using open source software. For the model and mesh, I've used Salome7, and the finite element computations were carried out with Calculix. This is meant to be an practical introductory video to free fea software. Theres an insane amount of theoretical books about this subject out there, take a look on them before designing your own cranes (LoL). 

The code for the calculix input deck:

Cheers!

Plotting Beam Diagrams with Python

     Today I'm sharing how to plot Beam Diagrams using python. More specifically the code is about a cantilever beam subjected to gravity load, a special case of uniformly distributed load. There's a bunch of cool python features in this post, like the very convenient use of "x>" to evaluate a function, or part of it, only after a specified value in the array.

For example, the code: (my blog font shows this symbol =, as equals, this is a minus -)

import numpy as np
x=np.linspace(1,10,10)
y=2*x*(x>5)
print x
print y

returns these two arrays.

[  1.   2.   3.   4.   5.   6.   7.     8.   9.    10.]
[  0.   0.   0.   0.   0.  12.  14.  16.  18.    20.]

     Values with "false" boolean condition returned 0, and the values with "true" condition were evaluated. This is very useful when computing singularities functions, also known as Macaulay method, due to the British mathematician William Herrick Macaulay.  Oddly this method was first proposed by the German mathematician Alfred Clebsch. 

    Other features that worth take a look is how to make very neat plots using matplotlib subplots method.

The code:



The plot:

See ya!