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Old October 28th, 2010, 06:43 PM   #1
OkiePC
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AutoCad 3-D modeling for mechanical drafting.

This is long winded, so just read the bold if you're in a hurry!

At work, I am now the default mechanical draftsman.

I have to create about 5 or six mechanical drawings a week, usually from a blurry pdf scanned from a hand drawing or an actual part.

Most of them are shafts or flanged bushings. Some are simple, some are complicated, like UHMW bushings with special slots and flanges with hole patters.

Some are more like sheetmetal drawings, for covers and plates and brackets.

I have had the full license for Mechanical 2010 for a few months, and never took a 3D Autocad class. In '96 I took a very good 40 hour vo-tech class using rev 14, and taught myself since then. When I started here, I jumped from Autocad 2000 standard edition at my old job, and LT98 (Autocad Lite) to Autcad 2004 Standard here, then two years ago I got 2008 Electrical, but none of our existing drawings use the components from electrical, so I still use my old library of objects I have been using since I used AutoCad LT98 for five years successfully at my old job.

So, I have drawn a few 3D shafts and modeled a few bushing by trial and error, and sometime I give up and just make two and three view drawings with rectangles and dimensions.

I know I am close to becoming a productive 3-D modeler, but I still need a class, or a good tutorial.

There are some fundamentals missing from my Autocad skillset, I am sure of it but don't know what they are. Here are some questions for Autocad 2010 Mechanical Users:

1)I know how to use the viewports, and 3-D view, and orbit, but how do I switch the default plane that my drawn objects will be inserted without having to change views? Basically, I want to rotate the User Coordinate System with respect to the model, so X and Z or Y and Z are swapped. So when I draw a cylinder to create a pipe or a shaft, I can draw the objects that are parallel from one view, rotate the coordinate system into the Z plane without changing my view of the object, and then insert all the cylinders that are 90 degrees to the first one, and so on and so forth.

I never needed that for electrical drawings. Now that I have typed out this question, I seem to recall seeing "Rotate UCS" on one of the main menus ... doh!

2)Don't they have 3-D key slots and tapped holes? I modeled a plate and had dropped in the Component list ANSI-UNC 1-4” 20 TPI into the model, arrayed it to my 16 bolt pattern, and then viewed it from an isometric (ISO) angle and found out the threads were 2-d objects, and some were on a plane 3 feet above the plate! So somehow, I moved the origin of where I was drawing and it followed me from top view to one of the isometric views, and then back to top view, my z was at a different height, unbeknownst to me until I switch views again. For the keys lots, I just exploded them and used push/pull and subtract but those are all wasted steps.

I got around this "top view design, wrong z plane" problem by putting in a PIP (picture in picture) of an ISO viewport and glancing at it all the time, but I appear to be missing a fundamental grasp of controlling the 3d position and 3-d rotation of the UCS.

3)I needed to draw a guide rail 60 inches long, 1/2” round stainless steel with a bend at the last 20 inches. I drew the straight section as a cylinder, and then drew a spline for my curve from its end center point (since the built in library of round stock is a script that generates 2D). Then I rotated views and drew a circle on the end of the spline and used the sweep command to draw the curved shaft by sweeping the circle along the spline. It is now a 3-d object according to the properties, but in the MODEL tab it renders as a wireframe and strangely, only has one “wire” running between the two circles at the end of the spline (curved line). When I switch to a front view, I get two “wires”, top and bottom of the bend and it looks normal. All other views, it looks like a piece of wire with two 1/2” diameter hoops on each end. I can, however, see the actual 3-d solid that was generated if I type RENDER on the command line. I can't find a render dialog box and don't know the commands.Can't I change the wire frame settings of individual objects or for the whole model tab drawing environment?

4)Should I put the template I am using on the model tab, or only on a layout, with viewports? The latter seems to work better, but still has some drawbacks, but my whole life I have been drawing electrical ladder drawings by starting out with a sheet template on the Model tab and drawing inside it.

5)The Power-Dimension. How in the world can I control the STYLE especially SCALE of the "power dimensions" I have already created? I figured out a crude way to make the text bigger, one dimension at a time, but I haven't found where I can scale the whole power-dimension STYLE if there is such a thing.

My only official Autocad class was in '96 on rev.14. It was a very good class, and I came out of it very comfortable with the keyboard commands and the menu driven organization, but it ended with a mere intro to 3d modeling. I am too advanced to take a level 2 type of AutoCad class because I have learned on the job intermittently for 15 years. So, I am thinking of ordering some DVD tutorials so I can learn at my own pace and jump to subjects on an as needed basis. Any recommendations for training materials and especially online resources is appreciated.

I have used some Autocad forums for very specific issues with good results. I have looked but not found any local in-person classes that fit the bill. I need a curriculum from which to learn modeling at a fast pace that covers the bases from the ground up.

Surely I am just a few basic commands and 3-D libraries away from being proficient with modeling. It should be faster than drawing in 2D to represent shafts, bushings with slots and flanges with bolt patterns. Things like that are very time consuming in 2D for me, and 3D isn't much faster for me yet, but it's getting there.

TIA
Paul
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Old October 28th, 2010, 10:56 PM   #2
CharlesM
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You may want to take a look over at the cnczone.

http://www.cnczone.com/forums/autode..._inventor_etc/
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Old October 29th, 2010, 03:42 AM   #3
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I can't answer any of your questions although my old college buddy left college and went the mechanical route as i went electrical

He reckons autocad and mech desktop sucks for any 3d work, can't remember his terms of phrase but it is very funny

He's been a mechanical engineer for 26 years now and has his own business

All his 3d design and modelling is done with solid works


http://www.solidworks.com/
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Old October 29th, 2010, 03:51 AM   #4
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Don't use that mechanical 2010 ****. Inventor 2011. Plenty of sites have it. And prehaps adopt a top down design flow.
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Old October 29th, 2010, 06:35 AM   #5
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I have a few answers for you.

1) With "UCS" you can rotate around one of the axis by 90 degrees and then use "PLAN" to view that plane.

2) Don't know.

3) Don't know.

4) IMO, you should always use Paper space for your titleblock and model space for your drawings. It makes it so much easier to make drawing changes if done through a view port.

I have to agree with HJTRBO. If you are going to be doing a lot of 3-d drawing, Inventor is the better product to be using. It is much more intuitive to use. You are going to find yourself struggling with the 3-d aspect of ACM. Also, Autocad Electrical and Inventor can pass info back and forth.

Bob
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Old October 29th, 2010, 06:51 AM   #6
OkiePC
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Excellent feedback so far. I demo'd one of the predecessors to solid works many years ago, but have only gotten proficient using Autocad Standard with my own block libraries.

testsubject: thanks for #1) I rarely ask easy questions anymore, but I can always get good answers here, this place is a great sounding board and a wealth of technical information. And thanks for confirming #4.

I jes wanna app for that. I wanna hold Tom Sawyer's iPhone (that's my IT guy...really) up next to a machine snap a few pictures, and have a 3-d model appear in my inBox.

6) Should I only put dimensions on my paper space when doing mechanical drawings, esp. 3D? And, what is the command to keep the paper space dimensions scaled to the model, but their components (like text heights, and arrow size) scaled 1:1, so 1/8" text stays 1/8" tall, no matter how you alter the printed paper size and viewport you're plotting? Yes, I am asking too much of AutoCad? Not the right ma$$ive CPU anchor for my desktop dell I should be using?

At least it buys me time to check in here during work.
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Old October 29th, 2010, 07:25 AM   #7
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I would recommend putting your dimensions in model space on their own layer (Say "DIMS") and then create a Text Style that uses Annotative Text. Use this style for all your dims.. This will scale the text in a paper space viewport to the size you want to print out at. Do a search for "Annotative Text" in ACAD help for info on how to set this up. I am not sure how this will affect the "spacing" between dimensions that are side-by-side so you may have to experiment with that.

I have been using AutoCAD Electrical since '97 and swear by it for panel/schematic designing.

Bob
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Old October 29th, 2010, 10:03 AM   #8
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Thanks again.
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Old October 29th, 2010, 10:28 AM   #9
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I will be blunt--you're using the wrong software. I was in a similar spot about 8 years ago; I wanted to start using 3D modeling but we only had AutoCAD and the company wasn't interested in purchasing anything else (at that time). I was already proficient in AutoCAD 2D, so I dove into the 3D side for some machine design work.

Talk about an exercise in frustration. It is only possible to create the most basic of shapes in the modeler, and setting up viewports for detail views and dimensioning is a pain as you have discovered. Assembly management is nonexistent. I eventually got the project done, but now I'm the only one in the department who can work with the drawings because nobody else wanted to waste their time learning 3D in AutoCAD.

I was finally able to convince management to spring for real 3D software (UGS Solid Edge - similar to SolidWorks). The difference is night and day. From concept to detail drawings, the workflow is at least 50% faster, even for simple parts. To me, the biggest advantage is the intelligence built in to the parts, assemblies, and drawings. Creating orthographic drawings from a 3D part or assembly takes about 10 seconds. Forget viewports and all this SOLPROF nonsense in AutoCAD. If you change a part (very easy--not so in AutoCAD), drawings and dimensions automatically update. If you're creating assemblies of parts, you create relationships between the parts so that the parts will adjust accordingly when changed. You can create holes with threads, counterbores, or countersinks, and this information carries over to the detail views.

The biggest issue with 3D in AutoCAD, besides that it sucks, is that it is not an industry standard by any means. Look at it this way: Lots of companies use AutoCAD 2D. Lots of companies use "real" 3D software. But hardly anyone uses 3D in AutoCAD. You would be putting yourself in a situation where (1) your drawings would be Greek to most people in the business, and (2) you're obtaining a skill that has minimal value outside your current situation.

If you're locked into AutoCAD, then I guess you'll have to make the best of it. But if there's any chance that your employer would upgrade, I would highly recommend that you pursue it. Programs like Solid Edge/SolidWorks/Inventor typically run $4k per seat. Getting training on AutoCAD 3D is like getting Allen-Bradley PLC-5 training in 2010. Sure, people still use them, but is it really worth your time?
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Old October 29th, 2010, 11:48 AM   #10
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If you are open to using new software, check out Alibre. It is a very nice low cost 3d parametric mech design software.

Agree with the guy above on point 4. Use model space for the drawing and paper space for your print management using viewports. you can also use templates for your title blocks. I usually create 1 8 1/2 X 11 and 1 11 X 17 template.
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Old October 29th, 2010, 03:33 PM   #11
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Very good info, guys. I think I should stick with drawing parts in 2D, and not try to "save time" by learning to use the modelling.

I don't know what the company will want to do as far as 3-D drafting. There is no real necessity for it. I just thought, "Well, since we're paying for this high dollar Mechanical version of AutoCad, I should try to make use of some of the features", and I expected that it would end up saving me time...apparently this is not the case.

If the need for mechanical drawings grows and gets more complex, I will talk to them about getting better software, but for now, I think I will forget modelling in Autocad, and go back to drawing three views the old-fashioned way with construction lines, circles and rectangles...

Good to know that it's not just me that thinks 3D in autocad is a PITA.

Thanks,
Paul
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Old November 1st, 2010, 09:53 AM   #12
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I think that this is the best Forum for PLC, and AutoCad Forums is the best for Drafting.
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Old November 1st, 2010, 12:25 PM   #13
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Plain vanilla AutoCAD is not the best 3D modeling package by any means, but what it does include is more than enough for the type of drawings you are making. I have drawn many fully detailed mechanical assemblies with hundreds of parts and generated 2D 3 view drawings from them all with plain AutoCAD.

For no. 1, turn off the UCSFOLLOW variable. This will allow you to change your coordinate system without changing the display. Use the VIEW toolbar to switch to Top, Front, Side, and SW,SE,NW,NE isometric views as needed then zoom in and set your UCS. The Rotate UCS commands are on the same toolbar.

2. You'll need an expensive add-on to get key slots and tapped holes that are as convenient as a pushbutton in electrical. For key slots you'll have to model a rectangular box and subtract it from your shaft and pulley. For tapped holes you'll need an AutoLISP routine that generates 3D bolts with threads, place the bolt inside of your solid to be tapped, and subtract it to leave a tapped hole. There are hundreds of free and shareware customization routines available in the forums at Autodesk.com

To get better 3D representation of curved surfaces, increase the ISOLINES variable to at least 6 or 8.

The only thing on the Model tab should be the model itself, drawn full scale. Use viewports in Layouts to generate your 2D views, including title blocks and dimensions. Later versions of AutoCAD have many features for multiple scale factor dimensions on Layouts. You will want to develop dimension styles.

Go to Autodesk.com and spend some time in the forums there. You will find links to many free online tutorials on how to draw in 3D. Persistence will pay off. The time investment for mechanical 3D is much larger than electrical drawings.
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Old November 1st, 2010, 12:43 PM   #14
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I think that this is the best Forum for PLC, and AutoCad Forums is the best for Drafting.

I strongly disagree. There are folks on this forum that wear many hats and they will have a different perspective of mechanical drafting than the strictly mechanical folks.

I have been using AutoCAD since the dark ages of DOS. It is a great tool for 2D work and pretty much an industry standard here in the US.

Because of the way it works internally, the kernel as it's called, it will always fall short for solid modeling as many above have found.
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Old November 1st, 2010, 01:12 PM   #15
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Thankfully right now I do not do mech drawings. THe guys here do use AutoCAD Inventor. They just made the switch in the last 18 months. From what they tell me there are several pluses and minuses.

The reason they have switched to Inventor is not for individual parts but for the assembly process. They say for parts they still prefer 2D.

The reason Inventor won out over Solid was that when we surveyed our vendors and customers it was the one used the most.

From what I have seen unless you want to put the machine together on paper, 3D really doesn't have an advantge over 2D.
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