All the rage today is “my customer supplies the CAD drawing” or “my customer supplies the model”. Great … just use your CAD/CAM software to make a G code program from that. RIGHT ????
CAD/CAM USERS BEWARE !!
The “TRUTH” that no one ever talks about is that more and more … due to either CAD operator inexperience or … whatever … drawings, solid models, and similar … suppose to be able to be used directly to create G code programs are not to scale … oftentimes require re-drawing … or at least a thorough double-check. Very time consuming … and very costly … and could even be catastrophic if no one checks and parts are produced.
But Don’t Take My WORD For It …
The “TRUTH” that no one ever talks about was recently stated most eloquently by “SIM” on the Practical Machinist forum at www.practicalmachinist.com. Here is a quote of what he had to say about his NEW PET PEEVE … along with some replies.
“New Pet Peeve- CAD drawing not in Proportion.
Its like going back to the old hand drawn sketches on a napkin. The width may be a little longer then the length, a large circle could be a small hole, a 1″ boss 1/2″ high could just barely fit in a 4″ square and look as tall as the 2″ plate is sits on…but it was a hand drawn sketch and it usually came with a person who went over each detail with you. I understood, made my own drawing to a semi proportionate scale and we made part.
CAD came into play and life became easier in that no longer could you draw a 1″ circle inside a 3/4″dia boss, a 1/4″ keyway just looked wrong inside a 4″ shaft, tapers machined matched tapers drawn…you could look at a CAD drawing and knew what the part was going to look like. You knew you could pre-drill a feature and had room to clean up later as the hole just looked bigger…so it was. I saw all through features where far from the edge, so didn’t worry about parallel placement.
So the peeve is this…I am now getting drawings in CAD that are not proportionally correct. I didn’t even know this was possible. Simple rectangular part dimensioned 2″ wide x 3″ tall has proportions were it is drawn wider then tall. Do you know how many times you need to verify the part is correct when that happens. Each time you go to another op…the part just looks wrong. Yes, I can and did redraw…but is was supposed to be a simple do at the machine job. Plus redrawing opens a new place to make errors.
Simple plug in a bunch of drilled hole locations from datum, parts a 1/2″ thick…all holes situated way more then that thickness from edge…1/4″ parallels will be fine…nope holes hit the parallels. Yes, we need to watch a bit more carefully…but again simple job that can, should have been done at machine.
Part with tapered feature turns out making part wider then drawn…My fault…I didn’t layout the dimensions to verify stock size..just went off the dimensioned width,everything fell within. But now plug in the angles and material needs to be a quarter inch wider to fit that feature.
I have encountered this before from college students making prints in Power Point??? But those drawings just looked wrong in every conceivable way…so the Red flags had already gone up. But lately I am getting drawings from customers “engineering departments” Drawings look good, no flags go up till its a bit on the late side.
Rant over…lesson learned, assume nothing and verify everything. So much for the added edge of getting a CAD file…the big drawback used to be the happy zeros…the more the merrier. 1.0000 Clearance hole for 7/8 bolt…ahh those were the days.”
Response from “adamm” :
“It’s funny you say that. Many of the CAD drawing templates that I see have a note that says something to the effect of “Not to scale”, and “Do not scale drawing”. It has been a while since I’ve seen some truly out of proportion drawing, but I have had some lately where there are two close elements, and the dimension extension lines don’t point at either of them. … ”
Response from “Joe Miranda” :
“We have begun to add to our quotes that if we have to re-draw the 2D or 3D drawings that we add $100 per hour and our typical charge is 2-4 hours. Re-drawing is not free and besides that we become liable for the outcome which is a situation that we prefer to avoid. ”
So if you are a 100% CAD/CAM programming model shop … you have been warned.
If you are thinking that CAD/CAM and customer supplied CAD files and models will help you get a leg-up … you have been warned.
Our Kipware® conversational can help you put a STOP to the CAD/CAM OVERKILL … gives you an alternative to having to always use a CAD drawing to create G code … and allows you to use “print dimensions” to create G code. Which … after what you’ve read above … ain’t such a bad idea !!
Kenney Skonieczny – President