By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Is CAD for Me?

All Topics | Latest Posts

Search for:  in Thread Title in  
Neil Wyatt05/06/2019 16:28:01
avatar
Moderator
18409 forum posts
718 photos
78 articles
Posted by Nigel Graham 2 on 05/06/2019 11:43:11:

Neil - ...

The difficulty is that I've none of the prior CAD knowledge the software publishers and their manual-writers assume you have.

That's why we had a start-from-scratch-no-prior-knowledge series in MEW. If you download the trial from Mintronics and activate it I suspect they will be willing to send you a link to access a free pdf of the tutorials.

Neil

SillyOldDuffer05/06/2019 17:10:46
Moderator
6681 forum posts
1501 photos
Posted by Kiwi Bloke 1 on 04/06/2019 22:58:48:

Anyone here got any experience of Linux CAD packages - FreeCAD for example? I've installed it, and some of the supporting literature, but it looks completely baffling (where are the nursery slopes?). FreeCAD is also available for Windoze and Muck operating systems.

Getting into FreeCAD is a little difficult because it supports multiple Workbenches for Architectural Drawing, Ship, FEM etc etc.

The one mechanical engineers want is 'Part Design'.

Starting FreeCAD gives this rather intimidating screen:

freecad_cold.jpg

Clicking on '+ Create New' gets a little further, but still no coconut:

freecad_start.jpg

So, Click on the start button, and choose 'Part Design'

freecadcreatebody.jpg

The tasks panel lists 'Start Part Create Body', click which produces 'Create Sketch':

freecadcreatesketch.jpg

Clicking 'Create Sketch' asks another question, which plane should we draw on:

freecad_setplane.jpg

Choosing one of the planes opens the sketch editor, and lots of new buttons. Those with red dots and white lines are drawing tools ( the white circle with two red dots draws radius circles ). The Red buttons set constraints, forcing lines to be Vertical, Horizontal, or of a particular dimensioned length or angle etc. Hovering over buttons with the mouse for a second or two pops up a a description

freecademptysketch.jpg

I used the editor to draw two circles

freecad_twocircles.jpg

Closing the editor gives a new list of Tasks:

freecad_padtask.jpg

Clicking 'Pad' allows the area between the two circles to be extruded as a 3D cylinder. Length, your choice:

freecad_pad.jpg

The new object can be viewed from any angle:

freecadpadrotated.jpg

More in next post:

Dave

SillyOldDuffer05/06/2019 17:36:35
Moderator
6681 forum posts
1501 photos

Clicking on the top face of the cylinder selects it:

freecadselectface.jpg

One of the Tasks available is another 'Create Sketch'. Clicking it opens the editor, this time working on the top of the cylinder where I've drawn a square, half on half off:

freecaddrawsquare.jpg

As an aside, note FreeCAD is complaining 'Under constrained sketch with 4 degrees of freedom'. This is because the object I've created has no constraints. I didn't set a specific radius on either circle, or put any dimensions on the square. Although it looks OK, FreeCAD knows it's dodgy. For rough work, this may not matter much, but it's not a good idea to leave objects imperfectly defined. In a complex model it can cause peculiar behaviours that baffle the user!

Closing the editor, opens up another list of tasks:

freecad_pocket.jpg

Choosing 'pocket' lets me cut a keyway inside the cylinder, I've left it halfway (dimensioned 5mm deep), but changing type to 'Through All', would create an end-to-end slot:

freecadpaddview.jpg

Most 3D CAD packages work like this. A sketch produces a solid object, which is modified by more sketches that add or remove material. Sketches can be extruded along a path to create objects like coil springs.. Common operations like holes, threaded holes and chamfers etc can be done without sketching. The package can probably draw common common objects like gears by specifying the number of teeth and diameter required.

The learning problem is getting started, how to produce objects that don't break the laws of geometry, how to apply draw and sketches, and how to use a few hundred buttons that make life easy once you know how they work! In the case of FreeCAD, 'getting started' is a tad convoluted because you have to do some non-obvious setting up. Once mastered though, it's the same every time, and takes much longer to describe than do.

Hope that helps!

Dave

An Other05/06/2019 18:54:26
178 forum posts
1 photos

Maybe not relevant to the thread, but I found the following info on available CAD systems for linux users which may be useful, since the question of which CAD app to use frequently comes up in this forum.

**LINK**

Michael Gilligan05/06/2019 20:18:09
avatar
17037 forum posts
756 photos
Posted by SillyOldDuffer on 05/06/2019 17:36:35:

...

Choosing 'pocket' lets me cut a keyway inside the cylinder, I've left it halfway (dimensioned 5mm deep), but changing type to 'Through All', would create an end-to-end slot:

freecadpaddview.jpg

...

The learning problem is getting started, how to produce objects that don't break the laws of geometry ...

.

Nice demonstration, Dave ... and it highlights one 'feature' of CAD that can catch-out the unwary: That half length keyway is very easy to draw, but would be tricky to machine.

MichaelG.

JasonB05/06/2019 20:25:09
avatar
Moderator
19568 forum posts
2142 photos
1 articles
Posted by Michael Gilligan on 05/06/2019 20:18:09:

 

Nice demonstration, Dave ... and it highlights one 'feature' of CAD that can catch-out the unwary: That half length keyway is very easy to draw, but would be tricky to machine.

MichaelG.

Would the same not apply if you drew the part with pencil and paper?

On the other hand if you also have CAM you can run a simulation and that will help to show up what you can't machine. I was creating some tool paths about 1/2hr ago and the cad left some metal shaded in another colour where my cutter could not reach. Still at least with CAD it was a simple couple of clicks to adjust the two features so the tool could pass between or I could just have easily selected a smaller dia tool.

tool wont fit.jpg

Edited By JasonB on 05/06/2019 20:30:08

Edited By JasonB on 05/06/2019 20:35:05

Michael Gilligan05/06/2019 20:40:18
avatar
17037 forum posts
756 photos
Posted by JasonB on 05/06/2019 20:25:09:

Would the same not apply if you drew the part with pencil and paper?

.

Well yes, of course you could draw something by hand that was unsuitable for manufacture ... but I think the pace and convenience of CAD makes such errors 'easier'.

I was careful to use the word 'and' not the word 'but' ... i.e. I was making a positive comment about Dave's tutorial.

MichaelG.

Nigel Graham 205/06/2019 20:50:16
913 forum posts
16 photos

Dave-

I am intrigued - why does FreeCAD show that programme code at the bottom of the screen? Is it something to do with creating NC control files?

I once saw something like your example, at work, but its equivalent pocket had 1mm corner radii and was on a ledge deep inside an object resembling inside, the interior of a die-cast stepped pulley. Not sure how the draughtsman thought it would be milled - I don't think you can obtain 2mm slot-drills 100mm long!

Andrew Johnston05/06/2019 21:02:48
avatar
5828 forum posts
662 photos
Posted by Nigel Graham 2 on 05/06/2019 20:50:16:

I am intrigued - why does FreeCAD show that programme code at the bottom of the screen? Is it something to do with creating NC control files?

I've never used FreeCAD but the "code" is nothing to do with CNC. It's simply a representation of the Python function calls the CAD program is using.

Andrew

Edited By Andrew Johnston on 05/06/2019 21:03:14

Michael Gilligan05/06/2019 21:09:48
avatar
17037 forum posts
756 photos
Posted by Michael Gilligan on 05/06/2019 20:40:18:

Well yes, of course you could draw something by hand that was unsuitable for manufacture ...

.

Just as an aside ... A true story:

My dad got a new job, as 'technician' for a University department.

One of the clever academics asked him to make an item 'to drawing' and his drawing was a Penrose triangle.

Dad took it all with a straight face and, next day, duly presented the prankster with a beautifully constructed item, made [flat, of course] from wire.

MichaelG.

.

https://en.m.wikipedia.org/wiki/Penrose_triangle

 

Edited By Michael Gilligan on 05/06/2019 21:11:31

SillyOldDuffer05/06/2019 21:44:25
Moderator
6681 forum posts
1501 photos
Posted by Michael Gilligan on 05/06/2019 20:40:18:
Posted by JasonB on 05/06/2019 20:25:09:

Would the same not apply if you drew the part with pencil and paper?

.

Well yes, of course you could draw something by hand that was unsuitable for manufacture ... but I think the pace and convenience of CAD makes such errors 'easier'.

I was careful to use the word 'and' not the word 'but' ... i.e. I was making a positive comment about Dave's tutorial.

MichaelG.

Michael makes a good point, CAD packages won't save a bad designer from doing silly things. Good design, however it's done, is skilled work. On the other hand the 3D representation did make it easier to spot that hard to make flat bottomed slot.

Now I'm going to tell a whopper and claim I always planned to have the item 3D printed from GCode:

blush

gcode.jpg

I produced the G-code from FreeCAD's 'Path' Workbench. Pretty sure it's rubbish because I didn't set anything up first! You're supposed to define tools and stuff before pressing buttons at random and there are lots of options hinting at milling, engraving, contouring etc. As I don't understand any of it, only a lucky guess would have produced meaningful GCode. But, in theory, I could have FreeCAD outputting the instructions needed to make the object by subtraction (machining), or addition (3D printing).

2D drawings are generated from the Drawing Workbench.

freecaddrawing.jpg

Not trying a hard-sell. Although I think FreeCAD (version 0.18) is the best Linux 3D CAD, and it does most of the basics, it's a good few years behind the commercial products. I often use it for checking out and thinking about simple parts, switching to Fusion360 for anything complicated.

Dave

SillyOldDuffer05/06/2019 21:50:29
Moderator
6681 forum posts
1501 photos
Posted by Andrew Johnston on 05/06/2019 21:02:48:
Posted by Nigel Graham 2 on 05/06/2019 20:50:16:

I am intrigued - why does FreeCAD show that programme code at the bottom of the screen? Is it something to do with creating NC control files?

I've never used FreeCAD but the "code" is nothing to do with CNC. It's simply a representation of the Python function calls the CAD program is using.

Andrew

Edited By Andrew Johnston on 05/06/2019 21:03:14

That's right. The Python console can be turned off. Mostly it just shows what the program is doing behind the scenes. It's possible for the user to type modelling commands into the console as well, but I've never experimented with it.

Dave

Kiwi Bloke06/06/2019 07:15:50
500 forum posts
1 photos

SOD - Brilliant! Thank you! Now you've shown where the front door is, I'd better be brave and venture in to FreeCAD. Ever thought of writing a bit more on the subject for MEW?

FreeCAD appeals to me because this is a Linux-only household, but the fact that it's free (and runs on any platform) should surely appeal to many of our colleagues, some of whom appear to be as tight as myself...

You say FreeCAD is a few years behind some commercial products; is this a bad thing, is it significantly handicapped? Most of us use manual machines, conceptually designed, or even dating from, the turn of the last century. We are used to old-fashioned stuff - ourselves, partners and friends included...

SillyOldDuffer06/06/2019 09:52:52
Moderator
6681 forum posts
1501 photos
Posted by Kiwi Bloke 1 on 06/06/2019 07:15:50:

...

Ever thought of writing a bit more on the subject for MEW?

FreeCAD appeals to me because this is a Linux-only household, but the fact that it's free (and runs on any platform) should surely appeal to many of our colleagues, some of whom appear to be as tight as myself...

You say FreeCAD is a few years behind some commercial products; is this a bad thing, is it significantly handicapped? Most of us use manual machines, conceptually designed, or even dating from, the turn of the last century. We are used to old-fashioned stuff - ourselves, partners and friends included...

I've thought of doing a FreeCAD article but they're hard work. I'm struggling at the moment to write one on producing photo-resist artwork for Inkscape. ( See Terrance Holland's Barclay Well Tanks of the Great War Part 49 in ME4614 20/6/2019 for a good description of etching from artwork. Also Neil Wyatt in ME4477. ) In Part 48 Terrance describe ways of making masters involving a mix of manual, photographic and computer methods. My article aims to show how most of Part 47 can be done more simply and with greater range with an appropriate software tool. For this purpose Inkscape is better than a Word Processor, MS-Paint, 2D-CAD, and 3D-CAD. All the others could have a crack at signage, but are clumsy &/or limited. Wrong tools for the job.

barclaywell.jpg

cityoftruro.jpg

90% Linux myself. It is the true faith! Not always the best software though, and I don't feel guilty about using MicroSnot.

FreeCAD suffers a little in comparison with commercial packages because Mechanical Engineering is only one of several Workbenches they have in development. FreeCAD can do things like model a ship's hull that Alibre and Fusion can't, but that's not much use to me, I'd rather all the development effort was put into Part Design. And that plethora of CAD functions to choose from on the start screen is liable to confuse newcomers.

FreeCAD's still being developed, which means that some of the web advice is out-of-date, another source of learning confusion. One or two updates have been buggy, which is off-putting if you don't upgrade regularly to get the fixed version!

FreeCAD's Part Design is good for drawing single objects. Most individual items can be modelled. What's missing at the moment is any facility to combine parts together in a realistic way. So you can draw a bush and a spindle separately, but not assemble them together. It's possible to combine them as a single new part, but that's not what's wanted. Assembly has to align the spindle part inside the bush and allow it to rotate, or slide, or both. FreeCAD doesn't do that yet.

I don't think learning FreeCAD is a dead end; I found Fusion 360 follows much the same get you started basic principles, albeit with many extra features, differences in the detail, and conveniences. From what I've read about Alibre, its basic way of working is similar too.

Dave

Nigel Graham 206/06/2019 10:26:29
913 forum posts
16 photos

Kiwi Bloke 1 -

Manual machines and software "behind" commercial rivals: "A bad thing"? No, not necessarily at all.

If the machine or software does what you need it to do in a manner satisfactory to you, the age of its concept or reality are not important. And many of us have no real choice anyway, when pecuniousness alloweth not even a small NC machining-centre.

Really, much of the development in modern engineering tools and methods is concerned with increasing commercial production efficiency as much as improving the products physically. As was thus 100 years ago, too.

Of course we can adopt modernity in our home workshops. Many model engineers now use CAD to form machine-controlling files, either to purchase cut profiles, or indeed for their own CNC machine-tools.

There have been letter-exchanges on the philosophy in ME (I don't if they've also appeared in MEW), but I see reductions to artificial "purity" by personal taste miss the essential point of a creative hobby. I regard us as making things for the joy of making and usually too, using, them; and that includes acquiring the skills to achieve the aim. Whether you choose or need to use manual drawing and old machines, somewhere in between, or all-CAD/CAM, each route requires considerable skills of its own.

You impress by, say, cutting your own gears for a miniature traction-engine, but unless you are after the big-name trophies, few would seriously object if you copy modern manufacturers by buying appropriate stock gears and machining the bores and keyways to suit. For a "non-model", e.g, workshop equipment, or miniature-railway passenger-truck, it is entirely appropriate to use modern methods, fittings etc. you would not use or could not disguise on that traction-engine.

My own machine-tools are all conventional and Imperial, though I am fitting a DRO set to the mill, readily enabling both mm and inch work. By completing one axis at a time it's already helping make the brackets for the next axis!

[Imperial machines... Fine, but SIX tpi on two of the leadscrews, 8tpi on the third, on my Denbigh H-series horizontal mill? Anyone any ideas why?]

On drawing methods, manual drawing may be very satisfying intrinsically, but CAD's potential is the time invested in learning it, ultimately releasing more precious leisure-hours to turn the design idea into reality - whether on antique machine-tools, or modern CNC versions.

Michael Gilligan06/06/2019 11:10:11
avatar
17037 forum posts
756 photos
Posted by Michael Gilligan on 05/06/2019 13:14:59:
Posted by Nigel Graham 2 on 05/06/2019 11:43:11:

... I tried that Mintronics site again with the same result, and since most web-site links do work from here (except embedded e-mail addresses) it could be tripped by a security software quirk. Or, possibly, some mis-match if Mintronics use MS-WIN10 and my PC is on WIN 7 Pro?

.

Did you try the link that I provided ?

MichaelG.

.

I'm bumping this, just once, because I have seen no response from you, Nigel

There has been a lot of discussion since I posted, so perhaps you missed it

... or maybe I'm on your 'ignore member' list crying 2

MichaelG.

Nigel Graham 206/06/2019 12:11:07
913 forum posts
16 photos

Michael Giiiigan;

Re Mintronics link etc.

Sorry, I wasn't trying to ignore you.

The whole discussion has become a tangle of different conversations, with notifications appearing in my e-post list randomly, and so I missed your post.

I did indeed find Mintronic's Alibre Atom page, possibly not by quite how you suggested, and I posted a direct quote from it as it might help others. It announces a new version and prices to come, plus possibly one-day courses. Prices with VAT and rounded, £240 alone; £360 with support.

At least I thought I'd posted it but I can't see it. I might have become logged out of the whole site without my realising it.

I'd also commented that whilst I understood others' suggestion I change from TurboCAD to Alibre, I don't know if the [.tcw] drawings I'd want would be transferable to Alibre; and the combined cost of Alibre + the abandoned TurboCAD, makes the change an expensive gamble. A gamble because I can produce rather rough but workable 2D drawings in TurboCAD and leave its optional 3D side as useful if I could learn it, but Alibre jumps right in at the 3D deep end with no guarantee I can learn that either.

Nigel Graham 206/06/2019 12:14:03
913 forum posts
16 photos

" Giiiigan " ??

Sorry - Gilligan. With ells not ayes. Now you know why I won't use lap-tops and so-called " smart "- 'phones " !

Michael Gilligan06/06/2019 12:17:40
avatar
17037 forum posts
756 photos

Thanks, Nigel

smiley

MichaelG.

Nigel Graham 207/06/2019 10:17:54
913 forum posts
16 photos

Having thought about what others here have said, I tried Alibre's "Free Trial Version" again...

It failed on a "trial period ended" notice. It took me a few minutes to twig this was because I had previously installed it in line with the MEW series.

Mind you, it didn't tell me this until I'd sat patiently waiting for it to set itself up.

Oddly, the programme itself is all there, just switched off; but not the accompanying pdf exercise book. Or if it is, it's in a very obscure folder I have yet to find.

(This exercise models a Hookes' Joint arrangement that if made physically would be a mere "executive toy", though would show why universal joints have to be used in pairs!)

+++

I had another go at a 3D TurboCAD exercise, a 2-throw crankshaft similar to that for my wagon engine. I tried a subtractive method as potentially feasible.

It looked promising but failed when I tried to change something part-way through. TurboCAD lets you produce simple " Primitive " solids like cylinders directly, but doing anything to them automatically dissolves them into " TC Surfaces " - polygonal prisms of adjacent but independent facets, so the former " solid " cannot be edited. An extruded cylinder from a circle is a TC Surface by default.

Now a crankshaft with disc webs is a chain of symmetrical, simple cylinders of known sizes, so can be assembled by calculating their centre co-ordinates. If the assembly is of more complicated, varied, unsymmetrical elements and sub-assemblies, such calculations become just too difficult.

So just don't expect me to model the rest of the engine around the shaft!

This leads to a particularly disheartening aspect created unwittingly by the CAD manufacturers' web-sites. Understandably they illustrate what their software can be used to produce; but obviously by staff draughts-people using its most advanced techniques to the limit, far beyond anything I could be fairly expected to achieve.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
ChesterUK
Warco
EngineDIY
cowells
emcomachinetools
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest