Continuing through my practice examples I came across the following diagram and I have a question on how to interpret the depth of the part.

Exmaple 103

I have the part drawn up in inventor, but when I went to do my extrusion I started interpreting the spacing between the plates in different ways. What is throwing me for a loop is the note "BAR DIA.70 x 76 LONG" and the 28 dimension.

I have interpreted it these ways:

  • 9.5 sticking out the front.
  • 19 thick front plate.
  • 12 thick rear plate.

Option A)

From the face of the 9.5 protruding 66 dia. cylinder (assumed machined down to) to the back of the cylinder is 76 mm and there is a 28 mm space between the plates.

Option B)

There is a 76 mm cylinder between the plates and it protrudes 28 mm beyond the back of the back plate.

Option C)

There is a 76 mm cylinder starting at the back of the front plate that is 76 mm long and a 28 mm space between the plates.

What is your interpretation for the setting the various depth?

Option D) being something I have not considered and please provide details.

  • $\begingroup$ You need a section cut through the link to see how is the transition from the 70 mm dia. bar down to 66 mm dia. bar, how deep is each bar sitting on the respective bore. I read the thickness of the back bar is 12 mm. $\endgroup$
    – r13
    Commented Oct 15, 2021 at 22:12
  • $\begingroup$ All I have is the sketch to follow. Thank you for pointing out my typo. that 20 will be corrected to a 12 $\endgroup$
    – Forward Ed
    Commented Oct 15, 2021 at 22:13
  • 1
    $\begingroup$ If I zoom in, it looks like 28 (units?) between plates, but hard to tell. I'd hate to rely on a drawing like this for anything. $\endgroup$
    – Pete W
    Commented Oct 15, 2021 at 22:34
  • 1
    $\begingroup$ if it were not for the fact its from an example exercise book, I would be requesting clarification from the designer. $\endgroup$
    – Forward Ed
    Commented Oct 15, 2021 at 22:35
  • $\begingroup$ My guess is the 76" bar extends 36" from the back of the 12 mm bar (76-12-28=36). It at least has to provide the length of the 66" bar to be correct. $\endgroup$
    – r13
    Commented Oct 15, 2021 at 22:57

1 Answer 1


There is not enough information in the drawing to give a definitive answer

The question effectively is, which of the three highlighted surfaces should serve as the "start point" for the "76 long" dimension, given that we can't see the back side of the part.


In my opinion, it should be the very front face of the part. My reasoning for this, is that the note here is intended for the fabricator, to allow them to select the correct stock material for the job. The inner surface is smooth without any join, so the bore is made of a single piece of stock material. The 66mm diameter is simply a segment of the 70mm diameter stock material, which has been machined down to fit.

Smooth inner face

My interpretation


  • 1
    $\begingroup$ That was my initial thought as well, since I saw all the other parts called out for depth based on a component they were being fabricated from. However, being far from an expert in this field I was wondering if I was missing something. $\endgroup$
    – Forward Ed
    Commented Oct 16, 2021 at 1:05

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