Why dimension sheet metal flat patterns? 1

[STeliczan]

I'm looking at an opportunity to save time on drafting parts for my company. Currently we dimension all features in the flat as well as the formed part. To me this can be excruciating when trying to layout a part that has a lot of features in it. I just want thoughts on why dimensioning for flat pattern parts is not necessary maybe other than for secondary operations like tapping, c'sinks, etc. We make all of our own parts and are in charge of the software and laser. To me, we are wasting too much time on something that can be validated in a few simple steps.

 

[ajack1]

I would have thought that some CAD packages don’t allow you to design parts that cannot be made, although I do doubt that, whilst others do or can be overridden to allow them to, backs up what I was saying?
To do extra work that has no benefit costs time and money and should be avoided, however if it adds benefit in any way that needs to be viewed against the cost.
Pretty much everything has pros and cons and it is a question of getting the balance right for each individual case, so it is unlikely that always or never is the right answer. At least in my mind.

 

[drawoh]

MikeHalloran,

When I say "determined and stupid", I am not talking about doing sheet metal from scratch in SolidWorks. That process is valid, and SolidWorks maintains its flat pattern. It just generally does not suit what I am doing.

I talking about loading your functional sheet metal model, and, perhaps, thickening one wall by 2mm. This is completely doable. I can even add a chamfer to the thickened edges to make it look good. The fun starts when somebody tries to fabricate it.

--
JHG

 

[3DDave]

On a PTC post one user was pining over creating an upset pierced dimple that was threaded and the Sheet metal software was balking at flattening it. The feature was made as a sheet metal cut followed by a solid revolve.

It's pesky because you know it can be done to a real piece of metal, but it's one of those CAD features that doesn't have a good transformation analog from formed to flat. Smashed integral dimple rivets are another one. Also what happens around PEM nuts.

 

[btrueblood]

"Also what happens around PEM nuts"

Oy. Over modelling is a curse. I think Mike H talked about vendor CAD files where needless detail is included, and the result is assembly files that bloat to ridiculous numbers of bytes and stop working.

To the OP, I do admit I have created dimensioned flat patterns. Did one just last week. Caveat: I only dimensioned one length on the folded model, as it was the only critical dimension, and this is a one-off part/assembly. I knew the locations of holes and whatnot would be "close enough" from the flat pattern, based on the vendor's previous work - where he used the flat pattern from a CAD file. Giving him the flat pattern saved us both about a day in emailing back and forth. We'll see how this works, but I'm pretty confident.