Inspecting and comparing parts

[PixMan]

So the part I made using a print sent by the machine manufacturer appears to be either:

1) Out of specification
2) Not the same part as the old one

I pick No.2! I know I made the features all within the dimensions and tolerances given on the print, so let's find out why it doesn't fit.

First, Darren told me that the new part doesn't seem to sit flat into the mating part, the milling head for his Kondia. OK, start by measuring the height of the Ø43mm boss that centers the part.

A depth micrometer is the right tool for the job. Turns out the original part is 0.066" (1.676mm) lower than the new one. Easy fix, mill the thing off! Let's check a few more things first.


Next, I notice that visually the depth of the Ø38mm counterbore appears deeper than the new one. Set both parts up on the back datum surface and place a short ceramic "parallel" I have into the counterbores. The new one was made to 14.30mm per print, the old one is 14.45mm. I can't make that thicker, so a .006" shim is easy if needed.


Darren reported that the two M6x1 socket head cap screws didn't quite line up. First check is the easy one; use a digital electronic caliper. No pics of this, but just check to make sure both holes are the same size (they are), "zero" the caliper within one hole, measure across both, 45mm center distance. The part print I worked from said 44mm, that's what the new part is.

Now to check the distance of those two holes as measured from the datum. The center of the Ø14mm bore is that datum, so set it up with two pins (drill shanks work fine here) to locate the part along the top of my "deadnuts" good angle iron, a pin I'd made into the Ø14mm bore.

Using a good old-fashioned Vernier height gauge, touch the top of the Ø6.5mm drill shanks, take the reading and subtract 1/2 their diameter. Now touch the top of the Ø14mm pin, take the reading and subtract 7mm. The difference between the two readings/centers is that distance I need. New part made to print it's 19.25mm. Measurement of old one, 17.25mm. This agrees with Darren's assessment of "the holes on the old one seem closer to the bore."


Some concern was expressed about the location of the long Ø16mm bore in relation to the other features. That was a challenge to measure mainly because the bore in the old part is extremely worn, and the mating part (which I'm glad Darren sent along) is also worn though only by 0.001" or so, and not the whole length.

By checking the height over the sliding part at both extremes of the play, I determined that if averaged out the new part was exactly the same as the old one in that respect.


Sorry for the fuzzy pictures, all were taken with my cell phone and I apparently didn't clean the lens very well.

In the end, they're close but not quite and it looks as though I should just try making Verson 2.1, as soon as I get more material. The deal breaker on just altering the new one is that hole location. Because the two holes are 1mm further apart and 2mm closer to the datum in the other plane, there's just not enough "meat" there to move the holes. I thought to make plugs and weld them in, but the old part is also 1mm wider overall and I'd need to build up the sides in a few places.

Perhaps you can see what I mean in this view.


I'll be metal shopping over the course of the next week and hope to make the new one next weekend.