TechDraw: going to be useful

Discussions about the development of the TechDraw workbench
tinman
Posts: 13
Joined: Thu Jul 31, 2014 9:36 pm

Re: TechDraw: going to be useful

Postby tinman » Mon Nov 25, 2019 12:00 pm

Hello,

Sorry to jump into this but this seems to be the topic where the change to TechDraw since 0.18 under/over tolerance originated.

I would have expected an under tolerance of 0 to have a negative sign? I am not a professional drafter so do not know the rules and maybe I am wrong. I got this when trying to allow some over tolerance and no under tolerance:
Capture.PNG
Capture.PNG (3.89 KiB) Viewed 258 times
I would have expected the under tolerance to show as "-0" not "+0". Of course, there is no way to enter a negative zero in the properties.

Thanks.
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wandererfan
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Re: TechDraw: going to be useful

Postby wandererfan » Mon Nov 25, 2019 3:11 pm

tinman wrote:
Mon Nov 25, 2019 12:00 pm
I would have expected an under tolerance of 0 to have a negative sign? I am not a professional drafter so do not know the rules and maybe I am wrong. I got this when trying to allow some over tolerance and no under tolerance:
I would have expected the under tolerance to show as "-0" not "+0". Of course, there is no way to enter a negative zero in the properties.
I am not a professional drafter either and under tolerance did have a "-" sign once upon a time. Knowledgeable users have since informed me that it is perfectly acceptable to have an under tolerance that is a positive number:
PositiveUnder.png
PositiveUnder.png (16.81 KiB) Viewed 234 times
Don't quite understand the real world implications of this, but I listen to the experts.

I could be convinced that a value of zero should never have a sign in front of it.
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DeepSOIC
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Location: Saint-Petersburg, Russia

Re: TechDraw: going to be useful

Postby DeepSOIC » Mon Nov 25, 2019 3:27 pm

wandererfan wrote:
Mon Nov 25, 2019 3:11 pm
am not a professional drafter either
Neither am I. But given I've seen drawings that say 1.00 +0.02 -0.01 being interpreted as "target value is 1.00, real manufactured dimension must be in 0.99 to 1.02 range". So if I see "1.00 +0.02 +0.01", i'd be confused if it should be interpreted as "0.99 to 1.02" or "1.01 to 1.02". The programmer in me leans to the second interpretation, but common sense leans to first, because the base value isn't in the range, making it nonsense. "+0" definitely looks weird on the lower tolerance. "-0" and "0" look ok IMO. Neither is wrong, i.e. at least it can't be misinterpreted.
ickby
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Re: TechDraw: going to be useful

Postby ickby » Mon Nov 25, 2019 3:53 pm

to my (little) knowledge this makes sense for certain types of "passung", I think press fit in english. E.g. in german norms the 10p6 press fit: You have a rod and a hole with 10mm diameter each. To assure a press fit the rod must always have a bigger diameter >10mm, the hole always a smaller one <10mm. To ensure this the tolerances are set both positive for the rod, both negative for the hole, so that they are guaranteed to overlap.

so deepsoics programmer interpretation is correct.
Syres
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Re: TechDraw: going to be useful

Postby Syres » Mon Nov 25, 2019 7:16 pm

Interference Fit is terminology I was brought up on in the UK.
aapo
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Re: TechDraw: going to be useful

Postby aapo » Mon Nov 25, 2019 7:46 pm

DeepSOIC wrote:
Mon Nov 25, 2019 3:27 pm
wandererfan wrote:
Mon Nov 25, 2019 3:11 pm
am not a professional drafter either
Neither am I. But given I've seen drawings that say 1.00 +0.02 -0.01 being interpreted as "target value is 1.00, real manufactured dimension must be in 0.99 to 1.02 range". So if I see "1.00 +0.02 +0.01", i'd be confused if it should be interpreted as "0.99 to 1.02" or "1.01 to 1.02". The programmer in me leans to the second interpretation, but common sense leans to first, because the base value isn't in the range, making it nonsense. "+0" definitely looks weird on the lower tolerance. "-0" and "0" look ok IMO. Neither is wrong, i.e. at least it can't be misinterpreted.
Tolerances that don't include the nominal size are indeed used in interference fitting, i.e., when making shafts and bores to fit when both are nominally the same size. Depending on the tightness of fit, the tolerances in different parts may be both positive, both negative, or normal (negative and positive).

https://www.engineersedge.com/manufactu ... _13166.htm
tinman
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Re: TechDraw: going to be useful

Postby tinman » Tue Nov 26, 2019 10:22 am

wandererfan wrote:
Mon Nov 25, 2019 3:11 pm
under tolerance did have a "-" sign once upon a time.
Just in case you didn't realise, it still can have a negative sign. You just need to enter a negative value in the under tolerance value if you want it.