Pillow block / stepper housing designed with Cadquery

     Just to share one cool pillow block / stepper housing design. This was designed to take a pair of 6801 bearings and a NEMA 17 stepper, hence the parameters in the script. In my application it will receive a shaft loaded in cantilever. 

The assembly for my application (without bearings), to hold the bearings in place, we have in one side a flange (purple),  on the other a flanged nut (not shown) screwed to the shaft. In red is the shaft designed for my application, with a groove to receive a belt. In black is a representation of a stepper motor. 

Here is the pillow block / stepper housing alone. The feature on the top is an access slot for easy access to the curved jaw coupling. Inside the cylinder theres a ring, meant to be an spacer for the bearing pair. 

    The cadquery code for this part:

	import cadquery as cq
	from Helpers import show
	# pillow block
	height = 42 #cube parameters
	width = 42
	length = 35
	cyl_dia = 32 #cylinder parameters
	cyl_lenght = 17
	between_holes = 31 #holes parameters
	bore = 3
	cbore = 6
	cbore_depth = 18
	fbore = 2 #threaded hole for flange
	fbore_depth = 10
	ring_dia = 18 #inner ring diameter (bearing spacer)
	bearing_OD = 21
	acess_slot = cq.Workplane("front").box(14, 20, height/2).edges("|Z") \
	.fillet(4).translate((0, -5, height/3))
	pb = cq.Workplane("front").box(width, length, height).edges("|Y").chamfer(2) \
	.faces("<Y").workplane() \
	.rect(between_holes, between_holes, forConstruction=True) \
	.vertices().cboreHole(bore, cbore, cbore_depth, depth=None) \
	.faces("<Y").workplane().circle(cyl_dia/2).extrude(cyl_lenght) \
	.faces(">Y").workplane().hole(ring_dia) \
	.faces(">Y").workplane().hole(bearing_OD, 45) \
	.faces("<Y").workplane().hole(bearing_OD, 5) \
	.faces("<Y").workplane() \
	.polygon(6, cyl_dia-6, forConstruction=True) \
	.vertices().hole(fbore, fbore_depth)
	pb = pb.cut(acess_slot)
	show(pb, (204, 204, 204, 0.5))

view raw pb.py hosted with ❤ by GitHub

Some pictures of the part after the machining:

All the parts ready for the assembly

The shaft with the groove for the belt

A custom hand ground HSS tool bit made to cut the groove in the shaft. Worked like a charm. 

Once again, 

Cheers,

Edi

Line boring on the Schaublin 102

     Today I'd like to share some pictures and insights about a technique called line boring. The part we're going to make along this post looks simple, and in fact, it is! But some care is made necessary in a few aspects. To cite the two I find to be the most important: Bore accuracy and bore misalignment. The first is important because if end up with a hole too small, the shaft will be locked, and that's if you're able to put it in place. If the hole is too big, the shaft will be lose around the hole, and you probably can't call anymore your bored surface as a journal bearing. The second important factor, the bore alignment is the topic we're going to talk about here. As you can imagine, if you have a casing, and the holes in walls which the shaft is going to seat are not aligned, ....problems again. 

      

 The part I need to get done, 40x40x40mm U profile with 4mm wall thickness. The holes should be in the center of  the part and are specified to 12mm diameter h7 tolerance. The holes will act as a journal bearing to a shaft passing trough.

     By the way, this part is good example of a designer's dilemma. You can choose between a part simple to manufacture but using off the shelf products, or go with simple design but high precision demanding. On the First case you need to look for the products in catalogs, make the order, pay, wait for the post to deliver the parts.  The second you need the craftsmanship needed for precision work, patience to set up the parts. Overall: both are time consuming, but in different ways. (If you read until the end you'll know which path I took.)

      Back to the topic: The easiest way to achieve a good precision in this case is to ream the hole, with a reamer long enough to go through one side and reach the other side in the same setup. This is the spirit of the Line bore. In addition to that, if all goes well, the reamer should leave a h7 hole in place, solving at the same time the hole accuracy problem. 

       Luckily, by the geometry of the part, and knowing that we have at hand the necessary tools, we can proceed with the line bore idea. Enough talk, let's do some work.

Started cutting the aluminum U profile with a hacksaw. Most surfaces will stay untouched as they are already to spec. So the only care here is about the length.

Wow, when you are just rolling the mouse wheel to down the web page it seems so easy. Here due to the magic of photo time shift, we already have the part cutted, perfectly squared and deburred. Effortless .. uhhm ehrr not really.  

 Marking the part. Not really needed, but that helps in keeping Mr. Bozo away.

Using my favorite Dial Indicator to make the surface perpendicular and parallel to the ways of the lathe. Surprisingly this is an imperial one. The angularity error here was one thou (of an inch) over 40mm. I need to write more about this indicators someday.

The tools separated for the job. Is always a good idea to open the hole progressively, so here you see the drill bits  (2x6 spot,  6 , 8 ,10, 11.8 and 12h7 reamer) and their respective collects. In the end I think I could used 8 and then 11.8 direcly, but I didn't want to take the risk as my setup was not so rigid.

Spot drilling. Here you can see my setup as well. The workholding is not ideal, but did the job. Looking at the picture now, maybe I'd try different things, but in the workshop the clock is ticking, and you or you spend your time improving things, or you make your move and get the job done.

Bigger drill bit

The 12h7 reamer in action

The reamer trough both bores. 

Top view

Here is the final part

     Ok, not super precision stuff, yet there's some precision involved. Definitely was much much faster than buying something on-line and wait for the arrival. Took me less than 1 hour, and it was fun to make.

Edi

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.

	import cadquery as cq
	from Helpers import show
	# parameters
	sr_OD = 12
	sr_lenght = 13
	nSides = 6
	fillet_size = 2
	cutcone_BD = 12
	cutcone_SD = 2
	cutcone_length = 10
	jackplug = cq.Workplane("front").box(5, 8, 5) \
	.faces("<Y").workplane().circle(1.8).extrude(2) \
	.faces("<Y").workplane().circle(2.25).extrude(3) \
	.faces("<Y").workplane().circle(1.75).workplane(offset=13).circle(1.65).loft(combine=True) \
	.faces("<Y").workplane().circle(1.5).workplane(offset=2).circle(0.5).loft(combine=True)
	jackplug = jackplug.translate((0, 6, 1.5))
	cutcone = cq.Workplane("ZX") \
	.circle(cutcone_BD/2).workplane(offset=cutcone_length) \
	.circle(cutcone_SD/2).loft(combine=True)
	cutblock = cq.Workplane("ZX").box(sr_OD, sr_OD, sr_OD).translate((0, 6, 0))
	cutblock = cutblock.cut(cutcone).translate((0, sr_lenght-4, 0))
	cutcable = cq.Workplane("YX").circle(1.4).extrude(15).translate((0, 6, -12))
	luer_taper = cq.Workplane("ZX") \
	.circle(3.9/2).workplane(offset=8.6) \
	.circle(4.9/2).loft(combine=True) \
	.faces("<Y").circle(3).extrude(-3) \
	.faces("<Y").circle(1).extrude(-2).translate((0, 18, 0))
	strainrelief = cq.Workplane("ZX").polygon(nSides, sr_OD, forConstruction=False) \
	.extrude(sr_lenght).edges("<Y").fillet(1)
	strainrelief = strainrelief.cut(cutblock).edges(">Y").fillet(fillet_size)
	cone = cq.Workplane("YX") \
	.rect(8, 8).workplane(offset=20) \
	.circle(1.4).loft(combine=True).translate((0, 6, -1))
	strainrelief = strainrelief.add(cone).combine()
	sphere1 = cq.Workplane("ZY").box(5.201,5.201,5.201) \
	.edges("|Z").fillet(2.6).edges("|X").fillet(2.6).translate((0, 0, -20))
	sphere2 = cq.Workplane("ZY").box(5.201,5.201,5.201) \
	.edges("|Z").fillet(2.6).edges("|X").fillet(2.6).translate((0, 15, -12))
	box_R = cq.Workplane("ZY").rect(36, 24).extrude(8).translate((0, 8, -8))
	box_R = box_R.cut(strainrelief).cut(jackplug).cut(cutcable).cut(luer_taper) \
	.cut(sphere1).cut(sphere2)
	box_L = cq.Workplane("YZ").rect(24, 36).extrude(8).translate((0, 8, -8))
	box_L = box_L.cut(strainrelief).cut(jackplug).cut(cutcable).cut(luer_taper) \
	.cut(sphere1).cut(sphere2)
	box_L = box_L.rotate((0, 0, 0), (0, 0, 1), 180)
	box_L = box_L.translate((0, -9, 0))
	# Show
	show(box_R, (204, 204, 204, 0.0))
	show(box_L, (204, 204, 204, 0.0))

view raw antikink.py hosted with ❤ by GitHub

     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:

	#Program to plot graph of car, moto and bike power
	#Written by Eddie Liberato in 25/10/16
	import numpy as np
	import matplotlib.pyplot as plt
	import matplotlib.font_manager as font_manager
	import matplotlib.patches as mpatches
	font_path = '/usr/share/fonts/truetype/strasua/strasua.ttf'
	font_prop = font_manager.FontProperties(fname=font_path, size=14)
	plt.figure(figsize=(10, 5), dpi=1200)
	ax = plt.subplot()
	#General parameters
	VKmh=60
	Vms=VKmh/3.6
	V=np.linspace(0,Vms,512)
	a=0
	g=9.81
	#Defining the main function in SI (Watts)
	#m=mass, C_d=drag coef, C_r=rolling resistance coef, I=hill steepness(rise/run)
	def potxvel(m, C_d, C_r, I):
	f_ine=m*a
	f_aer=C_d*V**2
	f_rol=C_r*m*g
	f_grav=I*m*g
	return V*(f_ine+f_aer+f_rol+f_grav)
	#Evaluating funcion with the parameters and coverting to imperial(hp) at same time
	Pcarhp=potxvel(m=1000+75, C_d=0.5, C_r=0.03, I=0.02)/735
	Pmotohp=potxvel(m=150+75, C_d=0.4, C_r=0.03, I=0.02)/735
	Pbikehp=potxvel(m=20+75, C_d=0.45, C_r=0.02, I=0.02)/735
	V_label=V*3.6
	#Plotting the results
	plt.plot(V_label,Pcarhp, linewidth=3, color='#7E1137', label="Car")
	plt.plot(V_label,Pmotohp, linewidth=3, color='#55BA87', label="Moto")
	plt.plot(V_label,Pbikehp, linewidth=3, color='#377EB8', label="Bike")
	plt.fill_between(V_label,0,Pbikehp,facecolor='#377EB8', alpha=0.8)
	plt.fill_between(V_label,Pbikehp,Pmotohp,facecolor='#55BA87', alpha=0.8)
	plt.fill_between(V_label,Pmotohp,Pcarhp,facecolor='#7E1137', alpha=0.8)
	ax.grid (True)
	plt.xlim(V_label.min(),V_label.max())
	for label in (ax.get_xticklabels() + ax.get_yticklabels()):
	label.set_fontproperties(font_prop)
	label.set_fontsize(13)
	plt.title("Car VS Moto VS Bike", fontproperties=font_prop,size=16, verticalalignment='bottom')
	plt.xlabel("Speed (Km/h)", fontproperties=font_prop)
	plt.ylabel("Power (Hp) ", fontproperties=font_prop)
	plt.legend(loc='upper left', prop=font_prop)
	plt.savefig('PotXvel.svg', format='svg', dpi=1200)

view raw pxs.py hosted with ❤ by GitHub

     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!