Question for Atlas - cost of wheels

[peteski]

Yes, both a CNC lathe with sub-spindle and a Swiss Screw Machine look to be very versatile and capable of making very complex parts.  It is really amazing to see them in action (thanks to YouTube).    When I remembered mention of the Swiss Screw Machine I followed your lead and looked it up on Google (and found the info and videos I posted).

[narrowminded]

Yes, both a CNC lathe with sub-spindle and a Swiss Screw Machine look to be very versatile and capable of making very complex parts.  It is really amazing to see them in action (thanks to YouTube).    When I remembered mention of the Swiss Screw Machine I followed your lead and looked it up on Google (and found the info and videos I posted).

They are pretty amazing machines, aren't they!   And it becomes less of a mystery how some parts appear seemingly by magic.  No magic, mood, or opinion involved in machinery.

At some level all of those machines shown could be considered "Swiss" style machines.  I try to stay clear of many industry buzz words when explaining basic functions to an audience that may not be familiar with them because they often don't tell a story sufficient to actually understand the point.  Sometimes I think they are used to give the "expert" a little boost of "expertiness" instead of explaining something in a way to be understood clearly by any audience.    Choose the method based on the goal.

In this case the sub spindle isn't a mandatory component in a generic "Swiss" style machine (although it is a fairly common feature these days) yet it is a key element to the efficient running of these parts.  I also didn't use the industry standard reference to X, Y, and Z travel directions, each with a + or - direction, as those mean nothing to a layman and they aren't necessary to fully grasp the working concept.  In and out, left and right, up and down, can totally explain the functions to a layman of average intelligence without introducing terms that need to be understood so that simple concepts, explainable in plain english, can be understood.  It's just the way I roll.

[nkalanaga]

X,Y,Z are great for programming the motion, but the problem for even educated laymen is "which axis is which?".  Sure, there's probably an industry standard, but how many outside the industry know what it is?  And, are all industries using coordinate systems using the same one?

[Lemosteam]

WRT shorts and guage;

Tolerance accumulation, repeatability and capability are the enemy of assemblies, regardless of the machine(s) used.  I.e. the more parts you make, capability becomes critical as each part cannot be fully measured so statistically, there are a number of parts that my fall slightly outside of the bell curve yet still are used.

On some of my FVM wheelsets, while designing my tender trucks for my kit, I found the point to point measurement was all over the place, like +/- 0.10 in one 12 axle bag.  This is not a criticism of FVM axles, I just understand how tolerance affects manufacturing and design (end tapers are very difficult to maintain tolerances of length).

Assembly process variation is also an issue.

Cleanliness and temperature, yes temps, also contribute as they both affect the assembly process. 

Say you are pressing a wheel onto a shaft with a shoulder as a stop.  Most press operations do not use the shoulder as a functional stop because they typically monitor pressure (plus they might bend the shaft if they they contact before pressure is achieved)  I.e. when the pressure reaches a certain level, they can assume that the parts are assembled properly... unless, temperature has affected the two diameters (shaft and hole) being pressed, the machine will stop earlier because the pressure is reached earlier, or say a metal shaving is on the shaft and gets sandwiched between the back of the wheel and the shoulder, the press will stop early again with a gap behind the wheel.

We have a saying in design- the simplest parts cause the most issues and although you might think the assembly of a shaft, isolator and two wheels is a simple assembly there are many tolerances and process variations (and controls) involved that can cause these issues.

Smaller parts tend to be affected more as tolerances affect them in a more profound manner when they are being used in environments such as track made from molded plastic with high levels of variation, even expansion and contraction, which is cause post-manufacturing.

This is where I agree with the plastic wheel argument.  From a variation perspective, they are manufactured in one shot and only suffer minor expansion and contraction issues.

[nkalanaga]

We have a line at work that puts brass inserts into holes in an injection molded part.  It's supposed to go by depth, but the air pressure sets limits on force, and it frequently faults out.  The solution is to put another insert on top of the one that didn't go all they way in, and run it again, then remove the extra insert.  Of course, that run faults, because again, the ram didn't go far enough.  They could solve the problem by raising the air pressure, but it's easier to let us rework the part.  Raising the pressure would require adjusting the regulator, and that would require a work order, which would require an engineering study, which would require corporate approval, from above the plant manager's level. 

Another of our lines makes a fuel filter assembly:  Three large injection molded pieces, and an injection molded filter with the filter paper cast into it.  Two of the pieces are welded together on the molding lines, while that subassembly and the other molded piece are screwed together on our line, with the filter inside.

The two welded pieces have to be welded while they are still hot, literally right out of the mold.  Thus, they go into the "totes", for storage and intra-plant transfer, hot.  However, if we try to run them hot, they invariably fail the leak test.  There is nothing wrong with the part.  Let it cool to room temperature, which in our clean room is (supposed to be) 68F, and it passes fine.  Why?  Even the maintainers and engineers don't know, but the leak testers refuse to pass a hot part, even though all they do is pump the part full of air, then measure the pressure decline.

That gets to be fun in the summer, because ONLY the clean room is air conditioned.  When the rest of the plant is near, or over, 100F, the parts can't cool off enough to run, unless they sit in the clean room for several hours. 

[Lemosteam]

Yes, most inspection requirements are only permitted in a controlled environment.  This is why the inspectors refuse to pass a part because typically the process control plan agreed by the customer don't permit them to.

Repeatability in a consistent environment is the key there.

Even high strength steel truck frames expand at those temps and push hole locations out of the positional tolerance if the part is inspected above 68F.