+/- ,13mm (.005") on length tolerance not possible

[duk748]

hello - I have a small question - an outside company has designed a shaft for us which is approximately 3 meters in length - it is approx. 100mm in dia. - the length tolerance specified on the drawing is +/-.13 mm (.005") - someone in our group said that this tolerance is impossible to hold on that length that .4mm (.015") was the best that was possible - I was wondering if that statement is true - I would think that w/ laser measurement devices & cnc machining it would be possible in this day in age - the shaft length does need to be held & I would assume that w/ some redesign it could be changed to fit this tolerance - any info would be greatly appreciated just for a better understanding for myself - thank you

 

[TheTick]

You can measure with your smart phone. There's an app for that. However, you will need to convert the units from angstroms to nanofurlongs, and then to inches or millimeters.

 

[KENAT]

The person saying it's impossible is wrong.

If you are willing to pay the $$, accept yield issues, measure & machine only in carefully temperature controlled environments.... then almost any tolerance is possible.

ISO 2768 (as much as I hate it in its entirety) does provide a potentially useful guide of typical machining process capability. Of course the data on which that spec is based was collected several decades ago so may no longer be a really good guide but still useful. However, the 2768 extract I found on the web doesn't give a value for 'fine' class for lengths over 2 meters and medium is +- 2 mm.

http://www2.mae.ufl.edu/designlab/Lab Assignments/EML2322L-Tolerances.pdf

figure 15.6 appears to imply what you are asking is within realms of reality but I'm skeptical.

This may actually be a better question for forum281 or elsewhere so see what responses you get and then consider either deleting this thread and posting else where, or possibly put a thread elsewhere with a link to this one and ask them to respond here.

Whether or not you re-post I suggest giving a bit more info on the material type, any finishing requirements, and any other information that will help folks give a good answer.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[duk748]

hello again & thank you for the help & the document - i have re-posted this at the machining forum - once again i thank you

 

[KENAT]

duk - really should have put a link to this thread, to try and keep the discussion in one place. If you cut and paste the thread number with the word thread from the top of the screen (below the title) then you get a link to that specific thread e.g. <thread 1103-406749> but without the space gives you thread1103-406749 which is the shortcut to this thread.

The other thread is here thread281-406766 in machining forum.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ctopher]

It may not be possible with the tools at your company, but it's possible somewhere.

Chris, CSWP
SolidWorks '16
ctophers home
SolidWorks Legion

 

[monkeydog]

Another issue you will encounter, is once you find a shop that can build and inspect to your requirements; you will need to transport it and install it into your "gadget" without losing your tolerance.

 

[djs]

I would think thermal expansion in normal working temperature range would be greater that that. So you have to specify a temperature at which to measure the length.

 

[KENAT]

djs, most drawing standards (e.g. ASME Y14.5M-1994) state at what temperature the tolerance applies.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[1gibson]

Is it possible would be the second question I'd ask. Is it necessary would be the first.