CAD /Autocad Help

[Mike Ginn]

Guys
Having started this thread I am really enjoying the comments and banter. The thread has moved in several directions but generally kept to the theme which is good. My original question question was answered in several ways and I now am aware of many more CAD programs. The 2D/3D debate continues and I see both sides. I would like to be able to model a complete engine and "extract" the 2D drawings but its a steep learning curve. I frequently need to "sketch" aspects of a structure and 2D works well for that.
My conclusion is that there is a place for both 2D and 3D and we model folks probably need to become conversant with both. As with the normal distribution there will be those who believe in only one or the other and that's fine in a tolerant society!
Have a great weekend
Mike

 

[Henry K]

Zeb,
I am 74 years old and first learned 2D drafting in 1961. That was followed by a BSIE and 52 years of engineering experience in various industries.
I love the Spitfire drawing and all its' dimensions. In retirement, I teach a few machine shop labs at a local university. The drawings the students show up with are usually either terrible 2D or unmentioned 3D. To make it even worse, the "drawing" is saved on their phone so you only have a minute or two to view the drawing before the pone screen goes dark.
The Spitfire drawing is a great example of a real world complex 2D drawing that would be ridiculous to put on a phone for your "working" drawing. Can you post a readable drawing or send one to me somehow?
Thanks

 

[SmithDoor]

Guys
Having started this thread I am really enjoying the comments and banter. The thread has moved in several directions but generally kept to the theme which is good. My original question question was answered in several ways and I now am aware of many more CAD programs. The 2D/3D debate continues and I see both sides. I would like to be able to model a complete engine and "extract" the 2D drawings but its a steep learning curve. I frequently need to "sketch" aspects of a structure and 2D works well for that.
My conclusion is that there is a place for both 2D and 3D and we model folks probably need to become conversant with both. As with the normal distribution there will be those who believe in only one or the other and that's fine in a tolerant society!
Have a great weekend
Mike

I hope post later how it work out or how fix the problem.

Dave

 

[SmithDoor]

Zeb,
I am 74 years old and first learned 2D drafting in 1961. That was followed by a BSIE and 52 years of engineering experience in various industries.
I love the Spitfire drawing and all its' dimensions. In retirement, I teach a few machine shop labs at a local university. The drawings the students show up with are usually either terrible 2D or unmentioned 3D. To make it even worse, the "drawing" is saved on their phone so you only have a minute or two to view the drawing before the pone screen goes dark.
The Spitfire drawing is a great example of a real world complex 2D drawing that would be ridiculous to put on a phone for your "working" drawing. Can you post a readable drawing or send one to me somehow?
Thanks

The biggest problem today is most new draftsman have hard time reading the old 2D drawings and do to mush in 3D.

Dave

 

[nealeb]

It's great to hear comments from a wide range of people here, but one thing to bear in mind is for whom you are producing the drawings. If I were in a professional drawing office, producing drawings to be used by someone in the factory that I shall never meet - or perhaps on the other side of the country or even in a different country - then I had better be pretty sure that my drawings contain everything relevant, dimensions, tolerances, surface finish, etc, and ideally to recognised international standards to avoid confusion.

But I'm using 3D CAD at home and purely for my own use. In the same way that I do not fit idiot-proof door interlocks and so on on my machines (as I'm the only idiot operating them) I do not need tables of tolerances when I generate 2D drawings from my 3D model. I don't care about numbers of decimal places, within reason, as I understand why they are there and when to ignore them. But to produce the 3D model on screen, then quickly generate the 2D drawings I need and probably an isometric view in the corner to remind me what the part looks like, is a great feature. To be honest, these days, I probably make more parts without drawings as I go straight from 3D model to CNC toolpath. I'll maybe make a quick sketch on a scrap of paper with a few dimensions noted, just so I can position the clamps clear of the toolpath. That's one reason I'm creating a 3D model of the loco I'm building at the moment - to be able to use CNC where I can - but I'm also doing it to be able to visualise how the bits go together, which is not always easy from a set of 2D engineering drawings, as well as to cross-check the original designer's dimensions. I bet if he had been using 3D CAD back in the 60s, he wouldn't have drawn the tender so that one set of wheels clashed with part of the frames...

While I find the comments about lack of understanding by draughtsmen of the engineering side and partly blaming it on the use of CAD - "it was never that way when they used drawing boards!" - I can't take it very seriously as when I talk to retired friends from the engineering profession, it sounds as if it was always like that. "They would never have drawn it like that if it was them that had to make it!" A friend was telling me a couple of weeks back of his experience as an apprentice draughtsman. If he was sent to deliver a drawing to the shop floor, he would not even dare to pick up a screwdriver. If he did, everyone immediately downed tools and watched him until he left. Great way to encourage communication and understanding between departments!

 

[Henry K]

If the machinists were "union" and the draughtsman was "management" I had a similar experience. About 1971 I worked in a factory (Western Electric) with about 18,000 employees at that location. I was walking through the shop and bumped into a lady holding a tray of about 600-800 electronic parts of about 80 types. The try fell to the floor and, being a nice young man about 23, I felt a strong need to help the 40-50 year old lady help her clean up the big mess. I had only just knelt on the floor when the local union rep taped me on the shoulder and politely told me to stop helping explaining that cleaning up the mess was a union's person job. I got up, apologized to the rep and the lady and went on my way.

 

[Bentwings]

Yes, my favorite is the concentric GD&T callout that makes the part 100X more expensive. My favorite callouts to bewilder inspectors are "use Ø3/8 drill bit".

It is true that engineers have gotten worse in terms of real world experience, but I think it's a symptom of a different problem. The same tolerancing data is transferred, but in a different way. A lot of 2d drawings I worked with from very talented drafters had all sorts of ordinate stacking errors along with missing constraints required for manufacture.

Here's an example of PMI. Tolerances are transferred down to the measurement inspection tools, so the job only needs to be done once. Just a different way to define tolerance (in 3D).
View attachment 136239

This spitfire drawing has several ordinate errors. A CAD workflow caught all of them, because it forced fully defined sketches. Production aircraft have even more deviations from the drawing. But yes, the drawing is glorious to look at, and who am I to judge when they were at war when they drew it? Still admirable, and still they won in the end.

View attachment 136240

*edit grammurly

I have to agree with y’all here. I came up through the machine shop as apprentice then got a so called tool maker certificate, for what it was worth then I got smart and went back the mechanical engineering school fo that sheep skin.

Drafting and it’s unbelievable spellings was a big part of initial schooling . I already hated drafting with a passion . Doing endless shading and various other art work was obvious worthless in the real world. I saw early on that cnc machine was the coming thing so I got into that too. What really toasted me was when the computer programmer changed all the drawing standards to something the cad was not able to handle without itself being redesigned. Old school drafting guys didn’t like the auto generated dimensions and attempted to force the cad program to change to some unusual standard. This resulted in numerous errors and some real heated arguments in weekly meetings. No amount of convincing could change the old schoolers times and situations change . The cad was done according to many really logical standards that might not match the company standards. Thee lots of papers swished to the floor and doors slammed. In some cases arguments came close to real fist fights. . When things went paperless it really got heated over tolerances often beyond 4 or 5 digits. The cnc machines had limits that they could produce. Getting closer required precise tool settings and micro program adjustments making some parts manual operation on an automatic machine. It took a while for it to sink in that many early cnc machines could not be tweaked in there were tolerances called out that were not possible even though parts fit correctly. So paperless became the norm so a 1/2” hole became the best the machine could make not 1/2” +_ some number . You designed around what was economical to produce. Machines improved so today you can get micro fits that you simply don’t even have to make a drawing for . Hence paperless. The shop just gets a file with some specs, material, heat treating and others. They French don’t even get to see your solid model. It takes too much time to call it up and look at it . The last place I worked at we did not do any shading or coloring beyond the default except if we were doing some kind of show and tell meeting with a customer. I always thought they were a waste of time to put aluminum shading , plastic coloring steel coloring etc. I often just used an exploded view as it was easy . Then just used my laser pointer as I talked . There were still an occasional few drawing but the generated bill of materials gave auto generated sizes then as noted there was a standard specification as noted. You had to know what machines were in the shop and what they cold and could not do. It was and still is a good engineers job to create good relations with the shop guys. Every team member is important. When the shop calls and says” hey mister engineer, you need to come out here we can’t figure out what you got modeled. It ain’t gonna fit “. That usual means you missed something and they just saved your rear end by stopping and asking a question before making a 10 grand scrap part.

So if you are making one off stuff and polish to fit , so be it . The part is in your mind . Tolerance to fit your own specs .

It’s if you have to have another made that you will have to live with limits unless you have unlimited funding.

Byron

 

[SmithDoor]

I have to agree with y’all here. I came up through the machine shop as apprentice then got a so called tool maker certificate, for what it was worth then I got smart and went back the mechanical engineering school fo that sheep skin.

Drafting and it’s unbelievable spellings was a big part of initial schooling . I already hated drafting with a passion . Doing endless shading and various other art work was obvious worthless in the real world. I saw early on that cnc machine was the coming thing so I got into that too. What really toasted me was when the computer programmer changed all the drawing standards to something the cad was not able to handle without itself being redesigned. Old school drafting guys didn’t like the auto generated dimensions and attempted to force the cad program to change to some unusual standard. This resulted in numerous errors and some real heated arguments in weekly meetings. No amount of convincing could change the old schoolers times and situations change . The cad was done according to many really logical standards that might not match the company standards. Thee lots of papers swished to the floor and doors slammed. In some cases arguments came close to real fist fights. . When things went paperless it really got heated over tolerances often beyond 4 or 5 digits. The cnc machines had limits that they could produce. Getting closer required precise tool settings and micro program adjustments making some parts manual operation on an automatic machine. It took a while for it to sink in that many early cnc machines could not be tweaked in there were tolerances called out that were not possible even though parts fit correctly. So paperless became the norm so a 1/2” hole became the best the machine could make not 1/2” +_ some number . You designed around what was economical to produce. Machines improved so today you can get micro fits that you simply don’t even have to make a drawing for . Hence paperless. The shop just gets a file with some specs, material, heat treating and others. They French don’t even get to see your solid model. It takes too much time to call it up and look at it . The last place I worked at we did not do any shading or coloring beyond the default except if we were doing some kind of show and tell meeting with a customer. I always thought they were a waste of time to put aluminum shading , plastic coloring steel coloring etc. I often just used an exploded view as it was easy . Then just used my laser pointer as I talked . There were still an occasional few drawing but the generated bill of materials gave auto generated sizes then as noted there was a standard specification as noted. You had to know what machines were in the shop and what they cold and could not do. It was and still is a good engineers job to create good relations with the shop guys. Every team member is important. When the shop calls and says” hey mister engineer, you need to come out here we can’t figure out what you got modeled. It ain’t gonna fit “. That usual means you missed something and they just saved your rear end by stopping and asking a question before making a 10 grand scrap part.

So if you are making one off stuff and polish to fit , so be it . The part is in your mind . Tolerance to fit your own specs .

It’s if you have to have another made that you will have to live with limits unless you have unlimited funding.

Byron

When took drafting spelling was not a big deal as we used 3 letters for all details.
I just used sheet with all the 3 letter abbreviations.
Made class simple

Dave

 

[Zeb]

Zeb,
I am 74 years old and first learned 2D drafting in 1961. That was followed by a BSIE and 52 years of engineering experience in various industries.
I love the Spitfire drawing and all its' dimensions. In retirement, I teach a few machine shop labs at a local university. The drawings the students show up with are usually either terrible 2D or unmentioned 3D. To make it even worse, the "drawing" is saved on their phone so you only have a minute or two to view the drawing before the pone screen goes dark.
The Spitfire drawing is a great example of a real world complex 2D drawing that would be ridiculous to put on a phone for your "working" drawing. Can you post a readable drawing or send one to me somehow?
Thanks

I have nearly the full set of available Spitty drawings. Will send some to you.

On another rabbit traile...
Paul Monforton's Spitfire Mk IX & XVI Engineered is a beautiful e-book that discusses using Autocad to document two Spit models. It is not complete, but it is very well done. Highly recommend! I bought his CAD files as well and finding the correct autocad conversion was a total nightmare but worth it.

 

[Bentwings]

What you said makes sense. However, I thimkpfs that 3D was easier to learn than 2D

that an interesting thin about forget about drafting and think in 3D terms. I really agree. I got m start archery very beginning ofv3d with wire frame modeling. A big thing was the hidden line removal or conversion. When you could just take your 3D model and a drawing page then select 3 views either projection view and it would drop the view needed in the right position on a page . Then came auto dimension. Here you just deleted the excess dimensions you could select the dim style as needed you could edit dimensions as needed. Then if you wanted changes to the part you just edited as needed. Dimensions automatically updated. Worst case was if you had added or subtracted something . But you just deleted an unused dimension. Or deleted all then did auto dim again maybe adding a note or so. The worst would be to delete a needed dim accidentally . Since it was paperless there was no need for sending new drawings out hut a message to the cnc that something was changed. You might have a revision note if required but no drawing unless customer wanted paper often not just a revision identifier. Individual products had rev identifiers so an exact reproduction of an original part was possible. Sometimes automated assembly or machining required a part made to exactly the revision number so it was easy to do. Data management systems keep this organized if done right. This can be the hardest part of engineering now but you simply save a modified part with the rev number built in . So if you need part 0001 rev A it’s easy to find the original file and cnc makes it just like original even though the as used part has 25 more holes in it . Too bad , you didn’t say you had added 25 new holes that might be revB but it’s the owner fault for not advising changes so proper part could be made . Communication is the key here .
When you down load on line parts you have to check rev identifiers otherwise you may design around the wrong part. Communicate

Byron

 

[SmithDoor]

I have nearly the full set of available Spitty drawings. Will send some to you.

On another rabbit traile...
Paul Monforton's Spitfire Mk IX & XVI Engineered is a beautiful e-book that discusses using Autocad to document two Spit models. It is not complete, but it is very well done. Highly recommend! I bought his CAD files as well and finding the correct autocad conversion was a total nightmare but worth it.

Just want you the list of abbreviations.

Dave

 

[Bentwings]

Hmmmmmmmm - - - what I'm seeing is that using models rather than drawings has resulted in an increase of pieces that just don't work.

To explain - - - - when I look at 2D drawings its easy to see that the shaft MUST be +0.0000 and better -0.0005 to -0.0015 (even) and the mating part needs to be +0.0005 or better +0.0015 to +0.0010. You just can't assemble AND disassemble a tang and receiver without having at least 0.0010 if not better 0.0020 of dimensional difference between the two parts.
When you see it as part of a model - - - - its not as clear that there must be clearance- - - (why) - - because on paper any clearance works.
Using a model makes it far too easy to not understand that GD&T is crucial - - - but then real world experience (re: hands on creation) is becoming ever rarer and of course the model is 'always correct' (NOT!!).

when you use 3D cad you use exact numbers. The programs often work out to many decimal numbers the last number I remember was something like was 14 decimal places you just plug in
The exact number you need for a hole and make the shaft the exact size you need . It up to you to determine clearance allowed then design it in . This is why ou design around what your shop can produce . If they do grinding you can get about anything you want or need depending on budget if th cnc lathe cant give the +_ .0005 you need well the Bart may have to be finish ground maybe both I’d and od . You have to understand geometric tolerance just a part of engineering . I think most cad systems have an interference check procedure where you can specify clearance needed and it will show interference so you can correct it bolt hole patterns are another area. Most new machine can locate holes better than size them as some poor quality drills won’t drill a round hole . Many cnc machines todaycan mill a better hole than poor drills can drill
My little steamer has 3 mm blind tapped holes that would be almost impossible to do manually . They were cnc threaded I’m sure . They just allow an exact length screw to bottom out leaving a very small clearance under the screw head the screws are not machined this close so realy an unnecessary thing the holes could have been through holes with conventional tapping .

 

[Bentwings]

Specified to 4 decimal is problem with CAD drawings. Like 9/16" or .5625. You round off to .56 . I just edit the dimension to 9/16" diameter.
Clearly is 9/16" diameter hole not 0.56"

Dave

Hi I have been out of really doing a lot of cad work due to just plain getting old. You could say quitting . However I did play sports most of my life even while I worked in some high tech fields . In sports quitting was never an option I played until the game over bell sounded win or lose . There were some bad nights going 0 for 5 and getting called out on 3rd strike for the last bat of the game many nights limping off the football field. Continue playing hockey with eye lid hanging and head in bandage. I never screwed around in school so I was under detention and missing practice. Kicking a helmet or busting a bat I’ve my knee just was not part of my game. So end of life s coming but I’ll be around until it arrives .

So I have a cad question. One of my younger sons s interested in cad 3D printing and machine shop. He is an accomplished artist and makes some nice art work and build beautiful Rc aircraft . He is interested in fusion 360 as Ian. However he really does not have a handle on how 3 d solid modeling works. He said he would like me to help him . So I’ve given some thought those of you who are today’s experts may step in and help me too.
So in I’m no artist no critic . Where to begin my thoughts art usually begins with a shape then the artist gives it depth by various shading and shodowingahadowing. A process I hated back when I had to do manual drawing in drafting as cad started I could see this was the coming process so I jumped in and just forced learning the process then adapted as it changed and evolved. So my son says how do I model something I can draw on a sheet of paper so far I’ve taken him from creating a sketch and using correct terms that I feel are necessary . But without an engineering background I’m trying to get him to “see” and think of things as solid objects that we cut shapes out of . Cut the corner out of a rectangular shape I’m trying to help him learn that the sketch is the basic shape and you have to define it in terms of 3 d environment rather than just draw dotted lines or do some fancy shading he is having a hard time transitioning to this I’ve got him to to learn there are axis planes and that you can make your own planes and axis of rotation he is having a hard time learning about relations and constraints I’ve begun showing him how to change unit systems and that there are thousands of pre defined things on the internet . I’ve showed gem some results of an incompletely defined model and how you can release constraints and change dimensions to achieve a shape or condition needed. Then fully constrained it For the final product .

So I’m asking for maybe some guidance on doing more complex things if I can get to first base with him we may take up fusion 360 and apply it to his Rc models . There are many model parts being 3 d printed now so we could start doing some ourselves . Anyway I’ll talk to him a little further I YHINK fusion offers a free trial so I’ll look into that as well.

Byron

 

[TonySteamHobby]

So I’m asking for maybe some guidance on doing more complex things if I can get to first base with him we may take up fusion 360 and apply it to his Rc models . There are many model parts being 3 d printed now so we could start doing some ourselves . Anyway I’ll talk to him a little further I YHINK fusion offers a free trial so I’ll look into that as well.

Byron

I learned 2d drafting in high school. Learning to recognize how an item looks from different views helped me in my 3D drafting. Probably, the most important thing to realize in 3D is that a x,y,z point in space from one view may be completely different in another view. Learning that early in the process will save a lot of aggravation later….
For example; Build (or load) a cube then turn off snaps, set a single view from the front, move a point on the cube or draw a line to the cube then switch to the right, left or top to see what happened to the position of the point or the line. Usually, it’s not what you expected. To avoid these issues, I always work with four views at a time, top, left, front and orthographic to make sure what I planned to draft actually occurs.
Also, I find that following along with a tutorial points out weak spots in one’s learning curve. I’ve been 3D drafting for years but I still hit the internet tutorials when I’m trying something new.
One last thought, today‘s cad work involves subtractive modeling as you pointed out, but additive modeling works too. Building a shape can be achieved in either method, sometimes one is easier than the other, like adding clay or chiseling stone. Good luck.

 

[Bentwings]

Thanks for the comments I forgot about the additive idea I’ll have to present this I too learned drafting in HS it continued through early college before a local large con donated 3 work stations of wire frame 3 d. This you had to creat your own holes snd toolbox items. It didn’t offer hidden line removal at first so when it came to actual paper drawing you had to manually make them. Ink pen plotters What a mess. Then ammonia base blue print machines It was quite a time and several different cad systems before hidden lines were automatic then sutondimentioning I got involved in the middle of tolerance snd proper way of stating text and dimensions. The company had an led standard they wanted incorporated into the cad system . Mean time standards in cad had Ben made that were slightly different than co standards. It was a very heated deal. Old school vs new school . It took goingvto the first ofvthe solid modelers to settle it turns out it didn’t matter information was transmitted and the argument went away . Paperless was still a dream. Eventually I got involved with paperless. All that was nessary was a list of files that needed machine work. The cam group created their files for each machine in the shop. They often didn’t see the model until it came up for machine programming tolerances went away too it was based on what the cnc machines could produce . As engineer I only had to list specific things that the cnc guys had to look at to see what they were capable of. In some cases a special tol could be purchased or engineering might be tasked with creating a special tool model that cnc made and took care ofheat treating or others services we did work closely with then but a couple weekly meetings took care of most questions . Most of us knew we were pretty advanced but there were other mfg places that were further along than we were .
One memorial experience comes to mind. I got an urgent hone call “ hey mr. engineer, you need to get out here right away. I though I had made some reall dumb mistake , maybe designed a paradox. I dash out to the shop and met the shop guys at a new machine I had designed . The chief said “ press the green button” I thought. Oh boy they are really goingvto take me to the cleaners. So I pushed the button. There was a bunch of clattering and movements but the machine started making parts at an incredible rate the shop guy said it was running at design speed out ofvthe box and shook my hand. He said Rc will be qualified by end of day, and it was. It was the first of many new automation devices made that ran out of the box this is pretty standard now I hear . Bring good information in get good results first time very little debug a far cry from my first machine that information was supplied with a big box of black perforated tapes from a shop that barely had equipment to read the ASCI tapes I sat for months with a pencile counting and translating these tapes just to model what was supposed to have been designed. Basically a concept made in someone’s garage that was incomplete

Anyway thanks again for a new direction to take showing my son about the world of 3D modeling . It will be a good review for me as well . I’m home bound and not supposed to drive so ultimately we will have to work online together. Even that will be a challenge for me. My son knows lots of tricks on the internet so it will be a trade. I’m actually excited to get back into this again . It’s good mind exercise .

Thanks

Byron

 

[Bentwings]

Thanks for the comments I forgot about the additive idea I’ll have to present this I too learned drafting in HS it continued through early college before a local large con donated 3 work stations of wire frame 3 d. This you had to creat your own holes snd toolbox items. It didn’t offer hidden line removal at first so when it came to actual paper drawing you had to manually make them. Ink pen plotters What a mess. Then ammonia base blue print machines It was quite a time and several different cad systems before hidden lines were automatic then sutondimentioning I got involved in the middle of tolerance snd proper way of stating text and dimensions. The company had an led standard they wanted incorporated into the cad system . Mean time standards in cad had Ben made that were slightly different than co standards. It was a very heated deal. Old school vs new school . It took goingvto the first ofvthe solid modelers to settle it turns out it didn’t matter information was transmitted and the argument went away . Paperless was still a dream. Eventually I got involved with paperless. All that was nessary was a list of files that needed machine work. The cam group created their files for each machine in the shop. They often didn’t see the model until it came up for machine programming tolerances went away too it was based on what the cnc machines could produce . As engineer I only had to list specific things that the cnc guys had to look at to see what they were capable of. In some cases a special tol could be purchased or engineering might be tasked with creating a special tool model that cnc made and took care ofheat treating or others services we did work closely with then but a couple weekly meetings took care of most questions . Most of us knew we were pretty advanced but there were other mfg places that were further along than we were .
One memorial experience comes to mind. I got an urgent hone call “ hey mr. engineer, you need to get out here right away. I though I had made some reall dumb mistake , maybe designed a paradox. I dash out to the shop and met the shop guys at a new machine I had designed . The chief said “ press the green button” I thought. Oh boy they are really goingvto take me to the cleaners. So I pushed the button. There was a bunch of clattering and movements but the machine started making parts at an incredible rate the shop guy said it was running at design speed out ofvthe box and shook my hand. He said Rc will be qualified by end of day, and it was. It was the first of many new automation devices made that ran out of the box this is pretty standard now I hear . Bring good information in get good results first time very little debug a far cry from my first machine that information was supplied with a big box of black perforated tapes from a shop that barely had equipment to read the ASCI tapes I sat for months with a pencile counting and translating these tapes just to model what was supposed to have been designed. Basically a concept made in someone’s garage that was incomplete

Anyway thanks again for a new direction to take showing my son about the world of 3D modeling . It will be a good review for me as well . I’m home bound and not supposed to drive so ultimately we will have to work online together. Even that will be a challenge for me. My son knows lots of tricks on the internet so it will be a trade. I’m actually excited to get back into this again . It’s good mind exercise .

Thanks

Byron

I do have a tutorial so I’ll give it a try . I waded through some of it already but it skips around a lot going from simple sketches to creating a paper drawing then back again .

 

[Bentwings]

I do have a tutorial so I’ll give it a try . I waded through some of it already but it skips around a lot going from simple sketches to creating a paper drawing then back again .

i like your test . I used 3 plane plus iso view for most individual models assemblies I mounted most items as they were to be used . Some places required fasteners and hardware . In order to build BOM . Used to just edit as needed. BOMs got tangled when others got involved especially newbies or trainees. I tended to update BOM as I built assemblies some places were fanatical about showing fasteners but then choked when more memory was needed. When multiple people were on a single project someone was elected to check the BOM it was a tedious process if you came into the project after the fact . I edited my own assemblies and BOM as I went . Ordering parts and materials was always an issue. Getting quotes and following up realy messed up development ofvthe project . The few companies that had good purchasing depts you could “ just throw it over the wall and it got purchased as you wanted or needed. Some times the penny pinchers would cut corners an you ended getting the wrong items or wrong material because “ someone “ knew a better way “ it was a mess when meeting time came and you said where is my XYZ. Part ? “ oh we got something similar for $50 cheaper “ I would ask is that so ? When will it be here? “ oh 10 weeks or so. It was last laugh to say you know this project is to go out the door in 3 weeks and it will take several weeks to qualify your untested parts my spec would have had it here yet this week tested and ready to go . I’d add “ well you contact the customer and explain “ this is why it’s called jut in time. Not your time . Engineering was a challenge I loved it .