Do you scale up tolerances when scaling dimensions?

[swirnoff]

Hi. I'm scaling up some old shop drawings. The thickness of a given piece is 0.5mm with a tolerance of +5 microns to -15 microns.

I'm scaling the drawing up to 2:1, so I need a 1mm thick piece. But is my tolerance tge same as the original? Or does it also double to +10 / -30?

Or something different? If it matters, the item is going to be hand operated, without much stress placed upon it.

 

[ChazzC]

Are you just scaling up the drawing, or also the finished part?

Tolerances are determined by the use of the part and how it interacts with what it is being used in.

 

[Pylonracer]

Hi. I'm scaling up some old shop drawings. The thickness of a given piece is 0.5mm with a tolerance of +5 microns to -15 microns.

I'm scaling the drawing up to 2:1, so I need a 1mm thick piece. But is my tolerance tge same as the original? Or does it also double to +10 / -30?

Or something different? If it matters, the item is going to be hand operated, without much stress placed upon it.

There are some tolerance standards that take care of increasing dimensions and their associated tolerances. See link below although as ChazzC says tolerances in many cases are determined by the function of the part but not in all cases.

https://www.dau-components.co.uk/doc/General_Tolerances_-DIN_-ISO_-2768.pdf

 

[ChazzC]

With an “unbalanced” (+5/-15 microns) it appears that these are not general tolerances but tolerances that were specified by the design/designer. Also, general tolerances are normally one order of magnitude different than the base dimension: 0.5mm +/- 0.01mm, not +0.005/-0.015mm.

 

[Asm109]

Generally no you don't get to increase tolerances just because dimension is bigger.

Its all about fit and function. Sometimes larger material is not available with same tolerances so you have to live with that.

 

[swirnoff]

Are you just scaling up the drawing, or also the finished part?

Tolerances are determined by the use of the part and how it interacts with what it

Generally no you don't get to increase tolerances just because dimension is bigger.

Its all about fit and function. Sometimes larger material is not available with same tolerances so you have to live with that.

Thanks. This is helpful.

 

[projectnut]

I would agree with the fact that in almost every case the tolerances remain the same even though the dimensions do increase. A few years ago, I found the plans for a 12" sheet metal brake online. I liked the design, but the overall size was too small for what I wanted to use it for. I upsized it to 36" but left all the dimension tolerances the same.

Here's the finished product.

 

[verbotenwhisky]

Hi. I'm scaling up some old shop drawings. The thickness of a given piece is 0.5mm with a tolerance of +5 microns to -15 microns.

I'm scaling the drawing up to 2:1, so I need a 1mm thick piece. But is my tolerance tge same as the original? Or does it also double to +10 / -30?

Or something different? If it matters, the item is going to be hand operated, without much stress placed upon it.

My answer would be no. The answer is a bit more complex, the tolerance will need to be adjusted but it doesn't scale. My suggestion is to consult "Machinery' Handbook"'s limits and fits section which has a set of charts which will define the required tolerance for the parts based upon the scaled sizes, you will need an understanding on the type fit you require.

 

[ChazzC]

I would agree with the fact that in almost every case the tolerances remain the same even though the dimensions do increase. A few years ago, I found the plans for a 12" sheet metal brake online. I liked the design, but the overall size was too small for what I wanted to use it for. I upsized it to 36" but left all the dimension tolerances the same.

Here's the finished product.

This an excellent example: even though blade/anvil positions are adjustable, increasing the tolerances could result in interference.

I think for piston/cylinder engines the tolerances would actually be tighter the larger the diameter since expansion due to heat would be greater (same coefficient, but larger starting point).

 

[markba633csi]

That's correct the tolerance really has no direct relationship to the size of the piece, it's all about fit and function