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.0625 Rounding up to .063 in generic model, but down to .062 in Family Table

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Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

Sorry, but you're cherry-picking your example.

How about .375 + .875?

Or .125 + .625?

Personally, I prefer a consistent upward rounding to one that could go either way...

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

This is why I dislike rounding on engineering drawings at all. If the feature is modeled at .625, the dimension should be displayed as .625. If you want 2 places, change the dimension to the one you want; don't leave .005 discrepancy between what the model is and what the drawing says.

That way the model adds up exactly the same way as the drawing says it will.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

Both of your examples add .01 to the design intent dimensions.

I agree with Dave, dimension it the way it is modeled! If you want 2 places on the drawing, model it at 2 places.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

If this is implemented then it should definitely be an option.

Do similar rounding rules exist in other (non-US) standards?  I wasn't aware of it in ISO.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

    "Sorry, but you're cherry-picking your example.

      How about .375 + .875?

      Or .125 + .625?

      Personally, I prefer a consistent upward rounding to one that could go either way..."

Excellent point to show that "even" rounding is still not consistent.

I simply believe that numbers ending in 5 should always, and forever round up.

I would be OK with it if it were a option.

That way either side of the argument could win.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

The even rounding rule is stupid for a number of reason.

  • If you're averaging numbers, you shouldn't be rounding them before they are average, you only round after they are averaged.
  • With computers doing all of our calculations, measurements, etc. the phantom "0.01" isn't an issue.
  • A large part of the design/manufacturing industry works in fractions, and a large number of those people are going to automatically enter something stated as 0.63" to 0.625" w/o giving it a second thought. You have to know your customer (whether that is a sales guy, fabricator, or end customer).

There are 2 huge issues here that no one has touched on.

  1. PTC doesn't release ANY information that I am aware of on what standards they do/don't follow, or on how their system works. If they would simply say what they are doing, then we could accurately work with it regardless of how it is designed.
  2. You cannot have a system that works with numbers in multiple ways.

A great example of #2 is that we built relations into some of our start parts to automatically right descriptions. One of those is for pipes. Based on the OD and schedule we assign to the part, the relations set the wall thickness and then write the description. After writing these relations we spent hours trying to work through what it is rounding, what it is truncating, and how to accurately get the results we wanted. It was the same issue point out above... in some cases numbers were rounded, in some places they weren't at all, and in others they might have been truncated but we never could tell for sure. We finally got what we needed, but that was because we had a limited amount of data that we had to troubleshoot. If you're using family tables and/or relations there could be a unlimited number of results and we should be able to know what the system is doing to take full advantage of this. That isn't currently possible without knowing how PTC is handling every number it deals with, and it is extremely difficult since numbers are handled differently depending on where they are being used.

And I work for a company where generally 1/32" of an inch is extremely tight tolerancing. I cannot imagine what it would be like where thousandths matter.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

    "This is why I dislike rounding on engineering drawings at all. If the feature is modeled at .625, the dimension should be displayed as .625. If you want 2      places, change the dimension to the one you want; don't leave .005 discrepancy between what the model is and what the drawing says.

    That way the model adds up exactly the same way as the drawing says it will."


I understand you point, but it is just not that cut and dry.

You may not have thoroughly comprehended the example that I gave in my earlier post?

Just to be clear, here it is again with some added information to help see the point of it.

Example:

Lets say I nave a part that begins its life as a casting:

    I would make the casting drawing and machining drawing from the same model via a Family Table.

          The casting, requiring less accuracy, would have a 2 decimal .63 dimension, and would be noted to the caster to add chip for machining.

          The machining drawing would have a 3 decimal .625 dimension.

BTW,  I incorrectly typed .62 rather than .63 in my earlier post.

The main reason for ding it this way is to allow the tolerance standards in the title block of the drawing to do their job (Tighter for 3 decimals, looser for 2 decimals) however a company sets it up.

Setting all casting dimensions to 3 decimals would force the designer or drafter to tolerance each and every dimension that did not require the tighter tolerance. That can get into a lot of wasted man hours, in extra work up front, and down the road in extra dimension management.


I used to work for a company that manufactured high performance pumps for the oil and gas industries. All of the pump bodies, heads, impellers, and many other parts were made as castings, then machined.

Setting every dimension on a casting drawing as 3 decimals, and then having to tolerance them, would have eaten them alive in detailing time.

I guess that there is a case to be made both ways.

Again PTC should simply let us choose.

1) Round Even

2) Round Up

3) If they insist - Round Down

We all know that we are paying enough for their software for them to fix this.

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

Another side note... I just saw another thread that posted ASTM E29.6.4.3 as a standard for rounding.

6.4.3 When the digit next beyond the last place to be

retained is 5, and there are no digits beyond this 5, or only

zeros, increase by 1 the digit in the last place retained if it is

odd, leave the digit unchanged if it is even. Increase by 1 the

digit in the last place retained, if there are non-zero digits

beyond this 5.


I found this here: http://www.galvanizeit.com/uploads/ASTM-E-29-yr-13.pdf

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

Haha, You'll never get agreement on rounding/tolerancing/etc...too many variables, too many company standards, too many individual opinions.

You probably should try to re-direct back to the original problem, the dimension shows /rounds differently when shown as a dimension than when shown in a table.

I think this is a real problem. There should be no discrepancy between these too.

Have you submitted support ticket to PTC. I think they really need to explain this particular aspect.

Stephen Williams
Pro/E Version 15/16 (Circa 1995/1996)

Re: .0625 Rounding up to .063 in generic model, but down to .062 in Family Table

The ASME standard currently references ASTM SI10 for conversion and rounding.