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Posted by Jim Wilkins on June 22, 2008, 7:22 am
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> I agree with these others: solid modeling. =A0It is the natural approach.=
=A0
> Fitting assemblies is incredibly valuable. =A0Projections, sections,
> isometric views, exploded diagrams, all come for free.
Maybe it's just my limited experience, but I've seen more mistakes in
3D Solidworks designs than in conventional 2D drawings. I learned
drafting back in the pencil and blueprint days when there was
considerable emphasis on developing a mental image of the part and
knowing how to transform it from plan and elevation (cabinet?) view to
isometric. Because of that training I don't usually need to make more
than a quick sketch except to document a customer's job. It seems that
3D CAD lets people draw things they don't really understand.
Jim Wilkins
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Posted by Ned Simmons on June 23, 2008, 12:20 am
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On Sun, 22 Jun 2008 04:22:30 -0700 (PDT), Jim Wilkins
>> I agree with these others: solid modeling. It is the natural approach.
>> Fitting assemblies is incredibly valuable. Projections, sections,
>> isometric views, exploded diagrams, all come for free.
>
>Maybe it's just my limited experience, but I've seen more mistakes in
>3D Solidworks designs than in conventional 2D drawings. I learned
>drafting back in the pencil and blueprint days when there was
>considerable emphasis on developing a mental image of the part and
>knowing how to transform it from plan and elevation (cabinet?) view to
>isometric. Because of that training I don't usually need to make more
>than a quick sketch except to document a customer's job. It seems that
>3D CAD lets people draw things they don't really understand.
>
>Jim Wilkins
If you're seeing more errors in 3D parametric designs than in 2D CAD
or board generated designs, that's a failing of either the designers
or the environment they're working in. It's true that an inexperienced
designer can produce impressive looking 3D models and detail drawings
of a poor design with a 3D modeler and toss it over the transom and
let manufacturing deal with the errors. If the business environment
allows, or encourages, inexeperienced, or just plain bad, designers to
pump out crap with no feedback, that's not the fault of the software.
The current crop of modelers really can improve the both the quality
and accuracy of designs. On the other hand, I'm sure they can also
generate good looking garbage with great efficiency and little skill,
if that's what's called for.
I got my ME degree and started my machine design career on a drafting
board, and experienced the infancy of both PC based 2D CAD and
parametric modeling. I used to enjoy working on a board and would not
have been awfully disappointed to give up Autocad and return to manual
drafting. I feel very differently about Inventor, the modeler I'm
using currently.
--
Ned Simmons
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Posted by Jim Wilkins on June 23, 2008, 6:49 am
Please log in for more thread options > On Sun, 22 Jun 2008 04:22:30 -0700 (PDT), Jim Wilkins
>
> >Maybe it's just my limited experience, but I've seen more mistakes in
> >3D Solidworks designs than in conventional 2D drawings....
> >Jim Wilkins
>
> If you're seeing more errors in 3D parametric designs than in 2D CAD
> or board generated designs, that's a failing of either the designers
> or the environment they're working in. It's true that an inexperienced
> designer can produce impressive looking 3D models and detail drawings
> of a poor design with a 3D modeler and toss it over the transom and
> let manufacturing deal with the errors. ...>
> Ned Simmons
Or an overworked mechanical engineer asked to squeeze in a little temp
help for another department. Since I don't have a Solidworks license
and don't know the program anyway, I had to redraw the dimensions on
paper from measurements before I could make changes.
The full-time CAD operator produces beautiful drawings for complex
sheetmetal that fit together perfectly.
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Posted by F. George McDuffee on June 22, 2008, 5:05 pm
Please log in for more thread options On Sat, 21 Jun 2008 00:31:56 -0700 (PDT), kuikahi
>I am new to cad/cam/cnc software.
>What is the the most affordable or cheapest software I should
>get or buy to learn?
>I want to get into small metal parts manufacturing.
>thanks for any help you can give.
===========
Some good observations from most posters, including our resident
grenches.
Two cautions if you are thinking about going "art to part" from
customer supplied cartoons.
#1 -- While things are improving, many of the customer supplied
cartoons are still drawn using the LAR [looks about right]
drafting standards, and the actual specifications are in the
notes & dimension text, which the cam programs ignore, as they
generate the program from the cartoon. In many cases this is a
result of quick and cheap engineering changes where only the
dimension text was updated. You will however still generate
scrap using a program generated from the [old, not updated]
cartoon.
#2 -- The tolerances specified are not equal/bilaterial from
nominal, for example 1.7500 +0, -0.010, while the customer
cartoon is drawn with the feature at 1.7500, not 1.7450 +/-
0.005, so when the program is generated you are machining to max
which will also tend to generate scrap with any tool wear
(assuming outside machining).
Another factor is the rampant excessive cost cutting which has
eliminated many essential engineering steps such as product
design review and drawing checking, so the customer cartoon with
notes and dimensions may not be producible, such as specifying a
1/2X20 [instead of a 1/4X20] tapped hole in the end of [or
through] a 1/2 ř shaft. Effectively, the contract machine shop
is now not only expected to produce the part, but to also check
the drawing and conduct the design review. It is therefore
essential that your standard order acceptance form include a
disclaimer that the part will be produced to the customer's
cartoon, if that is what you intend to do.
Good luck with your career in CNC machining. and always remember
that the technical stuff is the easy part.
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
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Posted by James Waldby on June 22, 2008, 5:51 pm
Please log in for more thread options On Sun, 22 Jun 2008 16:05:54 -0500, F. George McDuffee wrote:
[...]
> Another factor is the rampant excessive cost cutting which has
> eliminated many essential engineering steps such as product design
> review and drawing checking, so the customer cartoon with notes and
> dimensions may not be producible, such as specifying a 1/2X20 [instead
> of a 1/4X20] tapped hole in the end of [or through] a 1/2 ø shaft.
[...]
Yes, the practicality of that depends a lot on specified thread
fit, material tolerances, and equipment accuracy. Here's a
picture of a 3/8"-16 bolt threaded through a tapped hole in 3/8"
bar: http://pat7.com/js/m/bolt-28.jpg which was one of half-a-
dozen such attempts before I decided it was a bad idea because I
couldn't center the hole consistently enough. :)
-jiw
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