Effective Design Checking Techniques for Mechanical Engineers

[scar3850]

Hello,

I Have been working as a mechanical engineer for 3 years at an OEM shop and I graduated in 2013.
I am the sole engineer responsible for both coming up with designs as well as coming up with assemblies and drawings for the machines and fixtures we create. A pitfall I come across is making dumb mistakes when designing whole assemblies (collisions, poor fit of parts). This is especially true when we have a lot of hot jobs and I have to juggle a bunch of assemblies. My question is whether anyone as a good methodology or rubric for reviewing designs and making sure everything fits and works as intended.

TLDR: Anyone have a good methodology or rubric for reviewing designs and making sure everything fits and works as intended.

 

[Mech_Engineer]

One method I use often is to be extra detailed in your CAD model design work, especially the assembly design work and mating conditions. I find that accurate CAD models (especially vendor parts) can help you avoid potential issues; more importantly, inaccurate CAD models (especially vendor parts) will bite you in the end.

Do you create assembly models right now, and if so, do you create motion profiles and make the parts move as intended in the CAD design?

 

[JBA]

You are in a really difficult situation because there is no substitute for a second set of eyes reviewing your drawings before release. My normal answer with regard to the assembly fits would be to make a spreadsheet worst fit analysis; but, that can be very time consuming as well.

Assuming you are using CAD, because everyone does these days, I recommend not try to check your drawings on your computer screen. It is essentially impossible to do a good job of checking while looking a such a compressed view of a drawing; and, gives you no opportunity for mating drawing comparisons.

Before your final checking and sign off, make a hard copy print of all of the assembly parts drawings so that you can place the drawings of adjoining parts next to the one another and compare their mating dimensions for fit. That way you are basically checking two drawings at a time while comparing your mating dimensions; and, you have the option of red lining your full assembly set of parts drawings before going back and correcting your CAD versions.

 

[donpacino]

If you find you consistently forget to do certain things, consider making a release checklist. Some of those items on the checklist might be...

1. check intersecting gear tolerances
2. double check screw lengths

etc. going through the checklist will remind you to double check certain critical points.

 

[Mech_Engineer]

2. double check screw lengths.

Always double check screw lengths! I've been bitten by this more than a couple times...

 

[xxChrisxx]

Well first of all. How do you work? What is your current procedure?

If you are the sole engineer and you realize that you are running into challenges, it would highlight that training is needed. Design for assembly, interface analysis etc.

 

[scar3850]

One method I use often is to be extra detailed in your CAD model design work, especially the assembly design work and mating conditions. I find that accurate CAD models (especially vendor parts) can help you avoid potential issues; more importantly, inaccurate CAD models (especially vendor parts) will bite you in the end.

Do you create assembly models right now, and if so, do you create motion profiles and make the parts move as intended in the CAD design?

Thanks for your reply. Yes this is definitely something I've noticed. I do try to add in all the vendor components i can get models for. I do implement accurate mates but I have not created motion profiles. What I would really like to do is develop a criteria or rubric which I can use to make sure I am paying attention to the right things.

 

[scar3850]

You are in a really difficult situation because there is no substitute for a second set of eyes reviewing your drawings before release. My normal answer with regard to the assembly fits would be to make a spreadsheet worst fit analysis; but, that can be very time consuming as well.

Assuming you are using CAD, because everyone does these days, I recommend not try to check your drawings on your computer screen. It is essentially impossible to do a good job of checking while looking a such a compressed view of a drawing; and, gives you no opportunity for mating drawing comparisons.

Before your final checking and sign off, make a hard copy print of all of the assembly parts drawings so that you can place the drawings of adjoining parts next to the one another and compare their mating dimensions for fit. That way you are basically checking two drawings at a time while comparing your mating dimensions; and, you have the option of red lining your full assembly set of parts drawings before going back and correcting your CAD versions.

Thanks for the advice this is definitely something that helps as

 

[scar3850]

If you find you consistently forget to do certain things, consider making a release checklist. Some of those items on the checklist might be...

1. check intersecting gear tolerances
2. double check screw lengths

etc. going through the checklist will remind you to double check certain critical points.

Yes that is exactly what I'm trying to do. You bring up a good point as far as looking at the types of mistakes I make in order to develop my criteria.