Sending out RFQ 2D Drawings v 3D Models 7

[Finglas]

Is there anyone here that doesn’t actually send out 2D drawings, just 3D models when getting RFQs? I’m quite ignorant of the the differences but I suppose logic tells me that people are more used to 2D, they are probably a bit more personal with more info than a 3D model plus the receiver has more checking to do on a 3D model hence more time for them.

Are there any advantages for the receiver/manufacturer to receiving 3D models and some ways to make the model more receiver friendly? As far as I remember dimensions can be made visible in a 3D CAD model and when it's just for quotation purposes manufacturers would just need the critical dimensions/tolerances to decide what price to charge?

I’m asking as I’m doing some research as part of an Agile thesis I’m working on and am mapping out the design process, drawings take up a lot of time and things can get messy when revisions are made and hard copies are floating around etc etc.

 

[drawoh]

Finglas,

When you send out a purchase order to Billy Bob and Cousin Elmo's machine shop, you need to provide clear instructions. Think of the PO as a contract. Think of your part info, 2D[ ]drawings, 3D[ ]models, scribblings on napkins, etc., as clauses in your contract.

This is less critical at the RFQ stage, but, however much Billy Bob and Cousin Elmo love fabricating stuff, they need to make money. They will learn whatever it takes to not under-quote. When they mess up stuff you did not specify clearly and accurately, they will do the re-work for free, and they will build this effort, along with the time they spent on the phone asking questions, into their next quote. The quality of your information will affect quality and cost.

2D[ ]drawings can be prepared to a well-documented standard like ASME[ ]Y14.5. I claim that the clear definition of what everything means actually is more important than the GD&T. If your 3D[ ]model is sufficient to define your part and provide clear accept/reject criteria, send them the 3D[ ]model. This is not the same thing as sending a complete 2D[ ]drawing, then sending them a DXF or 3D[ ]model when they ask for it. In this case, the drawing is the legal reference.

--
JHG

 

[KENAT]

finglas, there have been quite a few posts about Model Based Dimensioning (MBD) on this forum and elsewhere on this site - suggest doing a search (not necessarily using the google bar at the very top but using the search button in the silver/gray ribbon just below thread title).

There are services that will machine/mold/3D print just to the model but essentially only say they'll keep to their typical process capability regarding tolerance. By implication these places also quote to just the model. We use these services for prototypes and the occasional 'one off' or very low volume production part that don't have any finish requirements etc.

For MBD to work the information on things like tolerances, and what would normally be in notes or title block (e.g. material, surface finish...) need to be included in the model and accessible to the user.

So, much of the time saved on 'drawing creation' will now be spent in annotating the model more thoroughly - and revision of the model still needs to be controlled etc.

Things may have improved but not long ago when I last looked this was only really possible in fairly integrated supply chains where the people creating the MBD were if not on the same CAD system as the users at least in a position to coerce them into getting viewers etc.

Y14.41 is the relevant ASME standard.

We routinely send 'dumb' models of parts (as reference) along with the drawings to help shops program CAM etc. They may use this to help them estimate, not sure.

Another point is a lot of machine shops don't seem to do a very good job reviewing the drawings etc. when quoting - and this is when it's all laid out in front of them in an easy to read format. Once they are working in a model having to retrieve saved views and various things my guess is they're even more likely to hit snags when they actually take the order.

However, maybe I'm a luddite trying to protect his job.

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[MadMango]

For RFQ, we send PDF 2D drawings and neutral format 3D STEP models. It really depends on the vendor you are working with regarding how well either help.

"Art without engineering is dreaming; Engineering without art is calculating."

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[HGMorgan]

We work RFQs all the time, and have seen about every variation you can think of.
MBD (as it's done today) is not the answer.
If it's a simple project: a good PDF drawing with all the views and requirements will work.
A complicated project: a good PDF drawing and the models. The customer should inquire about your CAD, otherwise IGES or STEP.

Harold G. Morgan
CATIA, QA, CNC & CMM Programmer

 

[Finglas]

thanks for your answers guys, as I said I'm ignorant so this is really useful advice.

I had done a search and looked at the first 3-4 results but din't know the MBD acronym was relevant.

 

[btrueblood]

Yes, we always prepare a 2D print to, at minimum, document the file name for the solid model (matches drawing number and revision, typically), call out materials and finish, tolerances, and any other useful information (weight of castings, e.g.). The 2D print controls in our world, the 3D model is provided as a convenience.

"When its just for quotation purposes" - if I were a machine shop, I would routinely no-quote RFQs based on nothing more than a model, as such jobs are likely not going to gel soon, and will not reach economical quantities for awhile - thus are time wasters for people who want to make money.

"...drawings take up a lot of time and things can get messy when revisions are made and hard copies are floating around etc etc."

Maybe taking a little more time to finish a drawing will help the design get a bit more refined and a bit closer to reality. Revisions are a problem with model files as well, and without a system to track/control changes, things can get equally messy.

 

[cowski]

I had done a search and looked at the first 3-4 results but din't know the MBD acronym was relevant.

PMI (Product and Manufacturing Information) is another acronym that may turn up some relevant information.

 

[Finglas]

I agree that it might appear to be a time wasting thing from the machine shop side, but if you have a good working relationship with them and they know you're not messing them around just sending you parts that they will never get to manufacture, then I think this shouldn't be a problem. I guess i should drop the "just" for quotation purposes. It's interesting the way things can get miscommunicated in writing.

"Maybe taking a little more time to finish a drawing will help the design get a bit more refined and a bit closer to reality". This wasn't likely to happen in the setup I was in last. The designer just hands parts over for detailed drawing when he/she is done with the design. i goes trust and collaboration has a big part to play. I guess not all manufacturers have the software however to be able to view files.

 

[MadMango]

"Collaborative" works with vendors too. It's always good to contact a vendor separately from your Purchaser/Buyer and let them know you may be open to design changes to your parts that align with their capabilities.

"Art without engineering is dreaming; Engineering without art is calculating."

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[Finglas]

We didn't really have purchasers/buyers. It was a guy who worked closely with the designers and basically managed all documentation in the design office included detailed drawings/RFQs/small batch production orders/project management etc. Man he was good at his job but put in serious hours. It was a thankless job, rather like a lot of engineering roles I would hazard to guess, and the cross referencing was a killer but he was always coming up with ways to reduce it.

 

[drawoh]

"Maybe taking a little more time to finish a drawing will help the design get a bit more refined and a bit closer to reality". This wasn't likely to happen in the setup I was in last. The designer just hands parts over for detailed drawing when he/she is done with the design. ...

I do my own fabrication drawings, and it does not take very long. Since I am the designer, I know how the part must work, so I know what tolerances must be applied. In 3D, I slap on dimensions and I slap on tolerances. The only time things get difficult is when my tolerance stack-ups do not work, but this is a design issue, not a drafting issue. It is best not managed by a CAD[ ]monkey.

--
JHG

 

[Finglas]

ya, there are definitely times when some parts which the designer knows are NB, then the designer should draft them.

 

[ctopher]

We send out both STEP files and PDF 2D drawings. The 2D drawings indicate material, notes, tolerances, etc that the model does not indicate.

Chris, CSWP
SolidWorks '16
ctophers home
SolidWorks Legion

 

[KENAT]

I would say for a drawing to be worthwhile it's almost essential for the 'drafter' to either know the design intent or have it clearly communicated to them before they do the drafting.

A good way to communicated design intent is via a properly prepared drawing...

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[TheTick]

You don't get what you want. You get what you ask for. Ask carefully.

 

[dgallup]

Only time we do 3D models only is for rapid prototyping. Anything else has a 2D drawing and might include a STEP file if it's a casting or molding.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[WKTaylor]

Following-up with what TheTick said [I'm adding his words to my 'wise-quotes' file, credit TheTick]... another way to look at this.

An old/wise fastener engineer in the company I work for stated this elegantly as follows: "You deserve to get what you ask for: but if You don’t ask for very much, don’t-expect to get very much.” Every part has details not shown on the drawing. Raw material, heat treatment, fab processes, machined surface finishes, general tolerances and machined-miss-match allowances, DI, NDI, corrosion protective finishes, etc/etc. ALL of these details must be carefully thought-out and evaluated in-sequence of manufacturing; and clearly/concisely [non-ambiguously] added to the drawing and/or contracting data.

EXAMPLE
I am currently evaluating a machined-magnesium casting design for local manufacture [machined 'hogout'] from aluminum plate. The M&P side is relatively easy: Yes 7050-T7451 plate 5--8-inches thick is a suitable substitute material [with corrosion protective finishes for aluminum]. HOWEVER, it is NOT rocket science to understand why this part was a casting: very complex/acute/internal geometry that might be impossible [or not-cost effective] to machine. We will need to consult with the guys who will be 'tasked' to machine it... then decide how to proceed. A 3D model for complex NC machining will probably be required. However, This part might be better/best suited for low volume [steriolithography 3D-printing] of the wax model for a lost-wax aluminum sand-casting.

NOTE. Venting...
What really bothers me is when a simple machined part on a clear 2D drawing cannot be machined by a competent machinist... since most machinists are no-longer capable of 'hand machining' operations: it's a programmed NC machine-job, or nothing.

Regards, Wil Taylor

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