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My boss ordered a screw pump driving spindle from an alternative maker. That spindle, as expected, cannot turn with the two idle spindles inside the housing.

Now he is asking for the spindle dimensions so that he can fabricate a correct spindle at some workshop.

Ok, the height. But how to measure the epicycloid curve? How somebody measures a screw pump spindle?

i am inside a ship i only have a vernier and a micrometer.

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  • $\begingroup$ one option is to use a turn table 3d scanner, to scan the object, and then do the measurement into a cad package. $\endgroup$
    – NMech
    Commented Aug 12, 2021 at 13:08
  • $\begingroup$ Thank you very much you are always helpful but i am inside a ship i only have a vernier and a micrometer $\endgroup$ Commented Aug 12, 2021 at 13:18
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    $\begingroup$ @Larsaseeidaklaxtarsa why is this information missing from your question? ... please edit your post $\endgroup$
    – jsotola
    Commented Aug 12, 2021 at 16:30
  • $\begingroup$ Slice up the part (or a mirror image casting of it, eg from wax) and scan with flatbed scanner .... $\endgroup$
    – Pete W
    Commented Aug 14, 2021 at 18:12
  • $\begingroup$ Do you have the working driving spindle or only the idle spindles to measure? $\endgroup$
    – mart
    Commented Aug 19, 2021 at 20:18

2 Answers 2

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I suppose you could just measure everything. I would frankly expect that no matter how accurately you measure, however, you may or may not get back what you want.

But,

  • OD of threads
  • "Thread" width at root and tip and several points between
  • Distance between threads at root, tip, and several points between Thread
  • OD of the shaft without any thread protrusion (minimum diameter of the thread section
  • Full dimensions of shaft extending past the screw including key location and size.

I'm guessing you're at sea so you don't have access to a machinist, but generally this would be done by either ordering the part from the manufacturer (preferred) or taking the entire assembly to a machine shop. I would probably have the machinist make it a bit over-sized so you can then machine to fit once you're in port.

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Just a general method to considering form, fit, and function when measuring any part:

Start with the overall outer dimensions and areas where it would interfere or interface with other pieces (fit). Since this is where the previous attempt failed, be sure to give it extra attention.

Then focus on the areas that allow the part to do its job (function). This could also include additional requirements for be where it interfaces with other moving parts or bears structural loads - such as special treatments or different materials.

Finally (form), if you were to sketch the main views of the part, knowing what the part is, what other dimensions/annotations would you need? For strange curves, assume some reasonable shape approximations (ellipse, circle in an alternate view, parabolas) and take at least two additional measurements to verify each approximation (if 3 points make a circle, take 5 and see how far the other two fall out of the circle determined by the 3). Use any existing specifications of similar parts for reference.

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