3D cad design sequence

Jasonb said:

i was going to note about cars too as my son has an auto repair shop . They hav it dow pretty well now they unplug all electrical near the fire wall then lift the car up ans using a second hoist remove the body or the whole front k member with the enginge Some time just to change spark plugs they just did a transmission r&dr and took the whole k member down they changed the trans sitting on roll around stills I don’t know what the charge was but in the neighborhood of a good used car . Cad has allowed using every cubic inch of space but they don’t allow for the human factor A v 6 or v8 plug change is almost always a remove the body or k member with the engine attached best to replace plug wires coils and about anything els the needs servicing . Diesel trucks are almost always a remove the cab thing . I’m just glad I went to engineering when I did . At least assembly lines have built in access Some areas you had a doorway so you could go right inside the machine often we had spots for service people to put a tool box on might have to have a fork lift put it up there but wrenching was pretty easy .
I did not go and look at Atom 3D when I wrote that reply but actually I don't think it has a hole option at all. So you just need to sketch a circle and cut extrude that.

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ajoeiam said:

good point I always iuse fully defined sketches . It’s the old saying “ garbage in garbage out”
Hmmmmmmm - - - - someone (its not clear who) wrote that "parametric design has 'improved things".

I would posit exactly the opposite.
Having this supposed error proof method is what has cars that need an engine removed to change spark plugs, has 'features' on other engines which mean that I need to have hands that are about the size of a 4 year old's to get at things and a lot more other things I could mention. What we have lost is the hands on knowledge gained by physically doing the stuff. The software says things are great - - - - well its a classic GIGO routine - - - the assumptions written into the software say its ok but - - - in the real world - - - - those assumptions are pure deluxe 'garbage'.
Even better is when the errors are pointed out the amount of time used on justification far exceeds the original work - - - - sometimes by a factor of 10 or more.
I am of the opinion that a lot of our tools today are not near as useful as the are purported to be.

(Reminded of when I looked at a turret lathe that was for sale fairly reasonably. The sales guy told me that the company had replaced the machine with a cnc after the old timer that ran it for a very long time retired - - - - he told me that the company hadn't been able to get the cnc to even equal the productivity of the very very old iron - - - - but that was likely because they had a hugely skilled and quick old timer and they bought a mid road cnc and maybe a top end cnc would have improved things but its the HAND skills (includes knowing how to use equipment) their people have that makes a difference - - - - not their 'paper' skills.)

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Gordon said:

I am sure that my biggest problem is that I am used to 2D and I am having a problem trying to adapt to a different way of doing things. Even the mouse buttons do not work the way I am used to.

I am trying to work on a V twin which I obtained PDF drawings for from another forum. I drew them in my 2D cad because that gives me a better understanding of function and fit etc so I know what I am aiming for. I am having a problem with having my sketch fully defined and that means that I cannot go to the model to extrude , copy etc. I do some operation and the next time it does not work. I have watched some YouTube videos but it is hard to follow them because something happens and I am left wondering how did that happen?

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Richard Hed said:

What V-twin are you working one? ICE or Steam? Is the engine dwgs in public domain?

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ajoeiam said:

Hmmmmmmm - - - - someone (its not clear who) wrote that "parametric design has 'improved things".

I would posit exactly the opposite.
Having this supposed error proof method is what has cars that need an engine removed to change spark plugs, has 'features' on other engines which mean that I need to have hands that are about the size of a 4 year old's to get at things and a lot more other things I could mention. What we have lost is the hands on knowledge gained by physically doing the stuff. The software says things are great - - - - well its a classic GIGO routine - - - the assumptions written into the software say its ok but - - - in the real world - - - - those assumptions are pure deluxe 'garbage'.
Even better is when the errors are pointed out the amount of time used on justification far exceeds the original work - - - - sometimes by a factor of 10 or more.
I am of the opinion that a lot of our tools today are not near as useful as the are purported to be.

(Reminded of when I looked at a turret lathe that was for sale fairly reasonably. The sales guy told me that the company had replaced the machine with a cnc after the old timer that ran it for a very long time retired - - - - he told me that the company hadn't been able to get the cnc to even equal the productivity of the very very old iron - - - - but that was likely because they had a hugely skilled and quick old timer and they bought a mid road cnc and maybe a top end cnc would have improved things but its the HAND skills (includes knowing how to use equipment) their people have that makes a difference - - - - not their 'paper' skills.)

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Gordon said:

OK A question for Alibre users. I have worked on two part sketches. I have extruded them and one is complete and the other is partial. I cannot figure out how to get back to my original basic sketch. The original sketch was fully defined and turned black so I extruded it and added features and extruded them etc. Now I cannot find a way to get back to the original sketch. There is nothing shown in the tree view which brings me back to the original basic sketch. I can get the individual later extrusions witch are things like a single circle which I extruded but what happens if I want to change something on the original basic sketch? Suppose that I wanted to make it bigger or just modify a chamfer or a fillet.

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L98fiero said:

3D CAD and and parametric design as little or nothing to do with where your hands will fit(or not), the design is based on fitting all the modern technology into the smallest space possible and making it easy to build, service considerations though, seem to be a ways down the line from there. As anyone who's been in the field for some time will agree, especially when the drawings were done manually or in 2D CAD, things were drawn the literally could not be made.

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ajoeiam said:

Don't know about the 'easy to build' part either.
Granted my experience is with FreeCAD only (don't have the $$$$ to fart with any of the pricey ones!!) but, imo anyway, you just can't build with tolerances.
Yet tolerances seem to only become 'normal' in the 2D drawings that are pulled from the 'model'.
That makes for stupid things - - - you know where the shaft is specd to +0.000 and - something or other and the mating hole (feature whatever) is to -0.000 and + whatever. Have you ever tried to put those kind of parts together - - - - absolutely garbage - - - one needs a stock of 4 of each to pick and choose to get ONE pair that will fit - - - - and that's call design - - - - better - - - trash!!!!

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L98fiero said:

True, as far as I know, no CAD allows you to build with tolerances, maybe higher end software but I've not used them so I can't comment on them but frankly, neither does drawing by hand, in all cases, someone has to put tolerances on the 2D drawings that are sent to the shop for manufacture. You can build in clearance or interference fits but tolerances are why there are still engineers.
In Alibre, and I suspect other 3D CAD, you can in an assembly, insert a new part and to do that use existing surfaces, project to sketch which means pull 2D drawings from existing parts, draw your new part, change hole sizes and make offsets of existing components and dimension everything relative to existing components and then create the 3D part. Then, if at a later date, you change the parts the new one is relative to, your new part will change so it fits the new design. Yes, on paper you could do an overlay and trace your existing parts, this is just easier, more accurate and the design is updated when a change is made earlier in the design tree.
I still often use 2D CAD for simple parts, but more complex parts and assemblies are where 3D CAD shines.

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Jasonb said:

The drawings are on MEM forum , search for 2-Bits. You will need to join (simple and easy) as they are attachments ands not available to guest users

Gordon watch the piston, I just drew it out and if sectioned there is an issue between the oval cutout and the ring groove eg no thickness.

View attachment 141532

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Richard Hed said:

How do you "project to sketch"?

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Jasonb said:

The drawings are on MEM forum , search for 2-Bits. You will need to join (simple and easy) as they are attachments ands not available to guest users

Gordon watch the piston, I just drew it out and if sectioned there is an issue between the oval cutout and the ring groove eg no thickness.

View attachment 141532

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