Problem Solving

[deepikanegi]

If there is an issue with assembling two components but when gauged separately look good, how would you approach the problem?

 

[Enghabashy]

* some of manufacturing of components & assembly processes could need also Jigs or fixtures at designated stages
** If there's more information about this case , we can provide more study ; as below " for example only :
***When I specify hole diameter & the bar /shaft diameter ; the fitting should be classified also " clearance ; transient or interference fit"
****The grade of gauges could differ accordingly " Grade H of Hole & h or g for the bar/shaft ; anyhow the allowance between both maybe need more study.

 

[Bev D]

If there is an issue with assembling two components but when gauged separately look good, how would you approach the problem?

welcome Can you elaborate on the actual “issue”? Getting the Problem statement right is the first best step.

Without more information my first instinct is to look for two other parts that will “assemble correctly”. Actually you should have 3 ‘pairs of correctly assembled and 3 pair of assemblies with ‘issues’. Then swap one of the parts between the 3 pairs of good and bad assemblies. Let’s call that part A (Agood and Abad) If the Problem follows the swapped part (A) you need to look at what is different between the 3 Agood and Abad Parts. If the Assemblies stay in their original condition then you need to look for differences between the 3 part Bgood and part Bbad…

The real key here is to not think about in spec or out of spec - look for differences. Remember that the specifications can be wrong.

 

[Miner]

It could be a potential tolerance stack up problem. Try running a Monte Carlo simulation to see if that is an issue. It only takes a few minutes and could save a lot of time.

 

[Steve Prevette]

Happens all the time. If the nut is at the low end of the spec, and the bolt is at the high end, then they might not work. Simplest answer is to review and revise the specs such that the nut at the low end of the spec (plus some wiggle room) will engage a bolt at the high end (plus some wiggle room). Proper "wiggle room" could be determined through a good Gage R&R.

Honda automobile got rid of a lot of those problems by using standard bolts and nuts and minimizing the various differing sizes.

 

[mattador78]

Happens all the time. If the nut is at the low end of the spec, and the bolt is at the high end, then they might not work. Simplest answer is to review and revise the specs such that the nut at the low end of the spec (plus some wiggle room) will engage a bolt at the high end (plus some wiggle room). Proper "wiggle room" could be determined through a good Gage R&R.

Honda automobile got rid of a lot of those problems by using standard bolts and nuts and minimizing the various differing sizes.

I agree it happens loads the amount of time we have had to advise people that they have left no plating/painting tolerances on machined parts is ridiculous. This isnt just one man band outfits either even had this issue with F1 car companies

 

[MOester]

"In spec" does not equal "parts work." At best "in spec" means "we THINK they will work."

 

[John Predmore]

"In spec" does not equal "parts work." At best "in spec" means "we THINK they will work."

I had one coworker who referred to engineering drawings as “cartoons”. He also said engineering tolerances were one man’s opinion of what dimensions ought to work. Parts in an individual assembly either work or they don’t, which is determined by their shape and the way they are made and the circumstances they are in, and not the drawing. Dorian Shainin famously said about problem-solving, “talk to the parts” instead of the engineers. The parts do not lie.

 

[MOester]

I had one coworker who referred to engineering drawings as “cartoons”. He also said engineering tolerances were one man’s opinion of what dimensions ought to work. Parts in an individual assembly either work or they don’t, which is determined by their shape and the way they are made and the circumstances they are in, and not the drawing. Dorian Shainin famously said about problem-solving, “talk to the parts” instead of the engineers. The parts do not lie.

Yep. I've yet to see a DV where we make a handful of parts at MMC to every tolerance and a handful at LMC and test the extremes. They're just copy pasted from print to print. We have a good handle on critical dimension because we have a lot of data on prior models.
And Lord help you if you find out you can increase a tolerance for manufacturability AFTER launch. It's super easy to tighten them. But loosening them - I haven't found that magic spell yet. It's often less work to just live with it. You consumers are going to pay anyway, eventually.