Need help developing title block verbiage for undimensioned drawings 2

[blades741]

Hello all, and thank you in advance for the help I know I'll receive here. You've collectively been so helpful in the past, and I thank you for that!
I work for a company who's core manufacturing process is laser cutting & bending sheet metal parts. For the sake of this question, we can disregard the sheet metal bending aspect. Most of our parts start out as a flat pattern of a bent part. These flat patterns can be complex in shape, and also contain complex shapes cut out of them. Fully dimensioning them is neither practical nor necessary, as we deal with the DXF files for use in laser or water-jet processing. I know I can add a SURFACE PROFILE note or title-block tolerance that can control the outer profile of the part, but can this same profile tolerance control the interior profile shapes (slots, holes, complex contours, etc.)as well as the location of these various cutouts within the part? Would a "CAD IS MASTER" note along with the general surface profile tolerance note be sufficient to convey the intent of both the profiles and location of the profiles?

 

[greenimi]

Do NOT use "Unless OTHERWISE SPECIFIED" unless you know what you are doing

See the last couple of debates about this issue.............

 

[MintJulep]

What is the goal? That is to say, what are the drawings to be used for?

 

[blades741]

Trying to develop the note mostly to give our expectations to outside vendors who supply us with the laser or water-jet processed flat parts. There's never been an issue, but it's still a good idea to have dimensional controls in place, so we're not buying bad parts. Right now, the only useful info on the drawings specify the material to be used. Part processing has always been via. DXF files.

 

[drawoh]

blades741,

Are you a jobbing shop that fabricates parts to the customer's drawings?

The really important thing standards like ASME Y14.5 do is define everything I put on my drawings. You offer to fabricate my parts as per my drawings. The drawing is an unambiguous specification of what I want. My purchase order calls up my drawing.

If you are creating drawings in-house for your fabrication department, there are no contractual issues. You and your fabricators should be working as a team.

The note "CAD IS MASTER" has no meaning to me. On our drawings, after "UNLESS OTHERWISE SPECIFIED", the note states that "ALL UNDIMENSIONED FEATURES ARE TO BE FABRICATED TO THE SIZE OF THE 3D CAD MODEL.", accompanied by some notes on default profile tolerances.

I was under the impression that punching and laser/waterjet cutting were accurate processes, and that the big tolerance issues involved bending and welding. Are you solving a real problem?

--
JHG

 

[blades741]

We are a manufacturer, and the note I am looking to formulate is for our outside suppliers who do primarily water-jet cutting. We do our own laser cutting in-house, so the note is more for the benefit of outside suppliers. Yes, the typical tolerance expectation for laser or water-jet is quite close (+/- .002, typically, on our 30 year-old laser). I'm wanting to put a 'Profile of Surface' tolerance of .010 for our UOS callout. To reiterate, my real concern is if (or how) I can control the overall part tolerance.

Let me ask drawoh, your note that states "ALL UNDIMENSIONED FEATURES ARE TO BE FABRICATED TO THE SIZE OF THE 3D CAD MODEL"... does this fall under the jurisdiction of a 'general' profile tolerance on your drawings? Something needs to govern the undimensioned sizes of features & feature locations.

 

[MintJulep]

Something like

CAD model defines BASIC dimensions. All cut edges subject to a profile tolerance of xx.

Of course you need to establish appropriate datum features too.

 

[KENAT]

blades, profile tolerance will control internal features. Whether it controls them to the required functional tolerances is another matter.

Our default notes for hybrid MBD are:

NOTES: UNLESS OTHERWISE SPECIFIED
....
X. DIGITAL PRODUCT DEFINITION PREPARED IN ACCORDANCE WITH ASME Y 14.41-2003.
Y. THIS DRAWING SHALL BE USED WITH MODEL (INSERT PART NUMBER) (REVISION PER THIS DRAWING) FOR COMPLETE PRODUCT DEFINITION. MODEL GEOMETRY IS BASIC.

At the end of note Y if applicable I'll add a default surface profile tolerance.

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[drawoh]

blades741,

If you are sub-contracting waterjet cutting, then you need proper drawings.

Yes, we have a titleblock that assumes that the fabricator will work to our as-modelled dimensions. The note also states that the undimensioned features are basic, and yes, you need to specify datusm. The "UNLESS OTHERWISE SPECIFIED" part is important too. If we have critical features, we explicitly apply tolerances, which over-ride the titleblock.

--
JHG

 

[3DDave]

This is a contractual obligation and should be spelled out in the contract as to which model file will be sent. It's never made sense to me to have a 'see cad model' note because with a drawing in hand there is no cad model. It needs to be spelled out somewhere and building the drawing and the model file as attachments to a contract via PDF keeps them all together. The contract tells where to look for the right data, not the drawing.

 

[KENAT]

Given that drawings form part of the contract why not on the drawing Dave?

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[3DDave]

Because the drawing does not embed the data. It also doesn't have the terms for forwarding any updates where the drawing would not change but the CAD data does change, for example layers or accuracy.

Basically a drawing does not set the terms for data transfer, unless someone puts a four or five paragraphs that would be in the contract on the face of the drawing.

Payment terms, inspection documentation requirements, and delivery schedules are also not on drawings. The contract specifies what data and in what form the data will be transmitted and should include checks to make certain that the intended data is the data that is sent and used.

It's lazy on the part of the contracts department to push off items that should be under contractual control to an ad hoc process. And it is lazy on the part of the contracts department to feign stupidity and an inability to understand data transfer. "Send them a CAD file so they can make the part" is not a responsible attitude.

 

[KENAT]

"It also doesn't have the terms for forwarding any updates where the drawing would not change but the CAD data does change, for example layers or accuracy. "

If the document control rule is that the revision of the model match the revision of the drawing - as my note implies - then the rev of the drawing ticks up if the model changes.

I'm sorry, but I'm just not getting your point on this one Dave.

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[drawoh]

3DDave,

Sending the model is a purchasing procedure. The drawing, in its own, obviously, is not sufficient to do fabrication.

--
JHG

 

[dgallup]

I don't think the model, in the form of 2D DXF is sufficient for fabrication either as it does not communicate anything about tolerance, material, etc.

----------------------------------------

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.

 

[drawoh]

dgallup,

In our case, the assumption is that the fabricator has a PDF of our drawing and the 3D[ ]model in the form of a step file. It actually is a process I dislike intensely. I am perfectly capable of producing complete drawings to the ASME Y14.5 standard complete with GD&T, quickly. We know that at least one of our shops takes the models and the drawings, and they complete the drawings. Another assumption is that our shops have CMMs. One of our shops doesn't, and as far as I can tell, they just don't do inspection, and neither does our in-house inspector.

We do not have a clear understanding of how MBD saves money and/or improves quality.

--
JHG

 

[3DDave]

Kenat,

As in all things local circumstances make a great difference. For those with captive manufacturing, either in house or just never going to a different outside supplier, and especially for 'typical' manufacture, such as making molds for plastic parts, then almost nothing needs to be put in writing.

For the more turbulent procurement where who knows what will get the package, then it doesn't mean much to see that note on a drawing. One supplier will want one of the dozen versions of STEP, or some tweaked IGES file, or just a pile of DXFs or won't be satisfied without some other format. To say there is CAD data elsewhere is possibly true and entirely uninformative. It's 2016. Of course there is CAD data elsewhere. But the contract is going to cover who gets to decide what the format is, how it is delivered, and how disputes over the suitability of the CAD data will be handled.

Until they read the contract a note that there's some other source of data is not enough to decide on whether or not to even accept the contract. After reading the contract the note will be redundant.

It still tickles me that people put "CAD Generated" in the margins of drawings. It's like putting a "Horseless" sticker on their car so people aren't confused.

 

[KENAT]

The note on the drawing can serve as a flag to doc control/purchasing that a copy of the model needs to go out with the drawing. It's a flag to the vendor to ask for the model (and specifically what model) if they don't receive it with the drawing.

Again I say the drawing is part of the contract.

I haven't seen anywhere near the amount of confusion you allude to on 'generic' CAD format. Rarely have I had use of step questioned on piece parts. (collaboration with vendors on larger assemblies is another matter).

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(probably not aimed specifically at you)
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[blades741]

Most of our 3 or 4 outside machine shop vendors request either STEP or DXF files of the parts they produce for us, even though the part is fully defined on the drawing. They are reminded when we supply the CAD files that they are still responsible for delivering parts TO PRINT. We even have some vendors that actually re-draw the entire part from our print, on their sheet/title block format. I haven't quite figured out the economics of that just yet...

 

[berkshire]

As a contract drafter who sends files to laser and water-jet cutters , I send a dimensioned print of the flat pattern with tolerances and revisions also with a revision number in the title box, together with an un-dimensioned " Cutting Pattern" together with a one inch " test square" included in the step or DFX file also with a revision number. This way the cutter can check their finished part to the dimensioned drawing after the fact and make any tool offsets if needed.
B.E.

You are judged not by what you know, but by what you can do.