Cad model or Print

[Frank]

Hi all : I’ve got a problem, and I was hoping for some advise on how most of you process your programs. First of all 90% of my programs are machined 2d, for instance I have a transmission case that I spin on a horizontal using 115 tools. What use to be the norm was a paper print only, and from there creating the file in Mastercam all sides and machining the part. When there are print dimensions missing you call the engineer and get them straightened out. Then the part gets a thorough inspection, and changes are made (hopefully not) and the part is ran.

Now with Cad models of the part, and a paper print, I pull up the cad model and double check some critical locations to the print, translate the whole part to our machining 0’s and start cutting. I just use the print for tolerances and as a reference. The boss has been very weary of asking the customer for the model because he feels I should only use the cad model as a reference and the print as the bible. What is really upsetting him is that if there are missing locations or dimensions on the print, the inspection room comes to a stand still until the engineer is contacted to clear it up. What I feel, is that my job is a lot more productive, is a thorn in the boss’s side. So my question is should I forget about the cad file and just use paper, or is using the cad model, the way to go ? I know it makes my job a lot easier to just use the cad file. Also is anyone familiar with using a cad file on the CMM’s ?

 

 

Thanks,

Frank

PS If the responses are how I think they will be I will print it out for the man !

[Quickmike]

I think cad should be do all and end all. We have issues once in a while when a cad model is not the same as the print. Usually we will call the customer and make them sign off which ever way they would like it made. However this is only when we "by chance" see a discrepancy. I believe what the job is quoted (print or cad) is when issues like this should be resolved. Sometimes things move in such a short timeframe we may have parts done and the customer has issued a new rev level but it didn't move through our system fast enough At one point we were doing confirmations with each order. It would state what cad file,rev level, material etc. and the buywould have sign it and fax it back. I'm not sure why we stopped doing it.

[Frank]

Quickmike.....How are your parts inspected without paper

[MACHINEMASTERG]

we use the model also ..and the print for tolerences and for shop reference plus you could make a mistake recreating the geo from the print !!!model is the bible here

[Dan Schnars]

Solidworks model here... Import it into MC and start programming... We use the print for QC and operator reference...

[robk]

quote:

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model is the bible here

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+1000

 

Usualy the print gets made from the solid model anyways (at least from the jobs that have been coming through here lately).

[Guest CNC Apps Guy 1]

The Model is the bible unless there is a discrepancy and then the engineer is contacted for what he /she would like.

 

Boeing is Model

Lockheed is Model

 

Tell him to get off the "Old School" bus and join the 21st Century, this is the electronic age and I'd say in the next 10 years, paper will be a thing of the past except in cases where a model does not exist.

 

JM2C

[IntegrexMan]

We use all Pro/E models here. It takes way to long to redraw from paper. The only issue we ever have is the models are sometimes unitoleranced, meaning they are not drawn to the mean, but to on side of the tolerance. We have the Engineers fix the model before we ever program it. We also check critical dimensions on the model before we program it. Generally if a customer is giving you a good print, he should have derived this print from a model. The model should be right. Stick with the model.

[Tim Johnson]

Parasolids here, but print is the gospel. The problem here ( and most likely other places) the engineers dimension +???/-.000 then draw the model to .000. When asked to draw the part to the middle of tolerance the answer is "I want it at 0". So we have to add geometry to a dumb solid to machine to the middle of tolerance.

[Guest]

Cad is the bible and like Robk said they usually make the print off the model anyway and if you see discrepancies it is usually a rev change.

[Wally]

Here the print rules - the quote is made from the print. The cad file is requested after the quote is accepted. If there is a discrepancy we call to sort out. I send our inspection lab an IGES file for the CMM. Example - last week, the print and cad file had 2 different wall thicknesses. The print was correct. So inspection had to compinsate for the variance.

[Harryman]

Model to nominal.

[HevyMetl]

Model is the only way we fly. I had the engineers start dimensionine everything to nominal and we are of and cooking. Print is only a reference for critical dimension call out.

[cadist]

We mostly rely on models. Prints only for changes.

[TREV]

imo how can you have a good print and a bad model?prints are made from models.we have some old schoolers here that work from prints but only doing 2-d work. for the guys doing every thing else models only.it is to the point where for me if i have to look at a print it just gives me a headache.i work in a mold shop and have been building molds long enough to know the diffrence between molding and shut off.tolerancing goes hand in hand with that.

trevor

[Frank]

Thanks for all the replies....but like I said I am doing only 2d work, but very large 2d work. For instance Chevy Blocks that I turn on a rotory, or like I said, Transmission Cases, or Heads. Does anybody here do the same line of work ? And if you use just the model do you also inspect the finish product with it ? Thanks again !

[Guest CNC Apps Guy 1]

For engine blocks I'd go with a full 3D model because of the rotary issues and overall complexity. You machining castings or billet forgings?

[Frank]

All castings....mostly aluminuim, Nascar blocks are compacted graphite.

[Jack Mitchell]

Frank,

 

I hear what you're saying - believe me!

Your supervisor is correct in the archaic methodology that he is following.

A print has exact details – if these details are machined then any variation is the customer’s responsibility to clarify.

Bottom line is that if there is a problem then it is clearly the customer/drawing issue which also means the customer has to pay the bill.

 

I have done lots of prototype and machined lots of parts – only to do the job a second time; basically what happens is the shop gets paid twice for doing twice as much work.

It all comes down to liability and in this case I agree with your supervisor.

 

Regards, Jack

[Quickmike]

Sometimes we only recieve a 3d model in which case we will create a print from the 3d model. As far as tolerancing we use our "house tolerance" (.5mm). Unless of course a specific feature has been discussed in which case we will accomadate the customer. We make prototype stampings, thats why sometimes there is no print. Sometimes the customer just wants to know if the part formability feasable or they might do testing for strength or NVH (noise, vibration, harshness).

[steve f]

I know this doesn't help to know now, but everything is heading the way of electronic files. The whole concept behind the STEP file system is that all information to manufacture a part will be incorporated into the file, including tolerances, machining method, surface finish quality, etc.

 

If using just a model is faster and eaier for you, maybe sell the boss on the whole productivity end of things.

 

steve

[Guest CNC Apps Guy 1]

quote:

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...Your supervisor is correct in the archaic methodology that he is following...

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Bahhhhhhhh. Horse feathers!!!!

 

I disagree. There are things you just can't see unless you're working on a full 3D model. IMHO when engineers can't/won't create a 3D SOlid model that is correct it's 1 of 2 things, they are inept or they are lazy.

 

JM2C

[Frank]

Where my problem is ...is that if I only use the model, and reference the print, I miss the places that the engineer forgot to put a hole location, or it's missing a sectional view (which happens a lot). And even though I still can program, the boss hits the ceiling, when the inspection room checks the part and finds the missing print details, and I never asked the engineers, for a fax, before it got to inspection. So the boss asks how can he call the engineer and ask for the missing dimension, when we allready have the part machined ?

[Jack Mitchell]

These things can and will cause some friction between you, your supervisor, inspection, and even the customer. Really, you should follow the chain of command “even though it is somewhat ridiculous”. It’s almost déjà vu and rarely works out without an appreciation of effort/results.

 

If your not sure then ask often appears on drawings for this very reason.

 

 

Regards, Jack

[Harryman]

quote:

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So the boss asks how can he call the engineer and ask for the missing dimension, when we allready have the part machined ?

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You have the dimention, right there in the model. Tolerance is all that you don't have, and if the model was done properly you do have the tolerance.

 

You need geometry to program with CAM. If the model is correct, the part is correct. With a good model drawn to nominal you will be good for all but very tight tolerances. Recreating geometry from a drawing is stupid. Import the file and go for it.

 

Machining an engine block on a horizontal is exactly a 3D part. Yes it can be done as a bunch of 2D geometry, but was it designed that way? Use the model and a good post processor and don't look back.