Learning CAD

Jason, my area is design so I am not fully conversant with current CNC driver technology but I was under the impression that they utilise servo technology these days which would tend to point towards the ability to describe true curved paths rather than the tiny step movements of early stepper drives but I would be happy to learn otherwise. I know that the drives for the "old" Agie wire erroders were capable of holding +/- 3 microns on form from a machine at least 15 years old now but what the form looked like below that level was beyond our ability to measure! Certainly some of the projects I have worked with have nano positioning axis that can repeat to better than a few nanometers but I could not tell you how they interpolate moves from point to point along a curve, how small a line are you thinking?

Mark

Jason, Not quite, watch a CNC going thru a curve, both motors move simultaneously, no move one then move the rest.

Another unrelated point to get back onto 3D CAD is to choose a program where it's well supported by all sorts of users.

No good trying to learn one that is only for advanced geeks.

Alibre, now Geomagic has been mentioned before but I'd like to point out they have a very good and active user base and forum with users from absolute beginners to advanced and recently they have swapped over the paid for training videos to completely free.

This means you can see if the programs works the way you want without even bothering with the download first.

Edited By John Stevenson on 25/10/2013 22:13:45

If i was going to buy a program it would be alibre design or the equivalent geomagic personal edition, its very similar to early versions of solidworks that i used to use years ago. Don't forget too that siemens do their 2d cad software , solidedge, for free. Its very good and the equal of autocad imho.

Although I can't help much with Alibre (as a professional Solidworks user) that is very good, sage advice and I suspect it would fulfil most of the model engineering requirements. I also doubt it is going anywhere anytime soon so would be worth the time investment to learn how to use it - as far as I have seen, it is "quite" similar to all the main stream packages so the experience gained is going to be fairly transferable.

Mark

Is nit picking finite or infinite ?

Ha ha, John.

Jason, The encoder feedback they use is capable of "reading between the lines" as far as I understand it, there is some sort of software (analogue?) method of determining the precise position of the servo and this gives "infinite" resolution and positional accuracy - in theory.....

Mark

reading between the lines....

working with encoders talking about 39k pulses per rev,,,and 20mm pitch ball screw..looks like 2k pulses per mm or about 0,5 micron.. and have certainly worked with lathes with 0.1 micron programming [typically internal resoluion is 1 or 2 orders higher].. yes lots of lines.. but the machine is still computer NUMERICAL control..and draws curves [even G02 or G03] as a series of lines..even G01,G00 ... more so when CAM generates the G code..

the steps even if in nano meters will be there..

but this doesn't answer to the OP..

Hi All

When choosing your cad program make sure that there is a lot of YouTube support.

The following search may help

Youtube basic 3d cad -autocad -solidworks -inventor

**LINK**

Note the (Minus) -autocad -solidworks -inventor used in the search to stop the search being overwhelmed by the three market leaders while giving all the found video that contains the words 3d and cad in the title for finding other cad programs.

There is quite a few......

In My case I use AutoCAD, having done so for many years, Every now and again when I am stuck chances are someone has answered the question on Youtube.

Here is one for an AutoCAD command: "Union" One you will use a lot if you do 3d

Search used: AutoCAD union command
**LINK**

Regards
John

Edited By John McNamara on 26/10/2013 07:57:08

> Jason, The encoder feedback they use is capable of "reading between the lines" as far as I understand it, there is some sort of software (analogue?) method of determining the precise position of the servo and this gives "infinite" resolution and positional accuracy - in theory.....

Any digitally controlled system will be 'stepped' at some degree, even if that degree is less than the surface roughness left by the tool (when it, of course, ceases to matter).

In absolute terms materials are made of atoms and ultimately the 'analogue' and 'digital' approaches both share a final limit at +/- 1 atom!

(Actually SEMs can sense to less than this and they are digitally controlled, and the smallest things ever 'made' were done by manipulating single atoms).

Neil

Edited By Stub Mandrel on 26/10/2013 09:08:45

If you can't measure it in a home shop using normal instruments why even bother getting excited about it ?

Jason, I understood the CNC thing to have gone from analogue systems (hydraulic copy attachments and the like through to fully digital with stepper drives and on to high end stuff running servo drives in hybrid digital/analogue systems - the only digital limit being the length of the number itself.

Neil, aren't atoms sort of round fuzzy balls of "stuff" anyway - no straight lines anywhere? One of the accessories to the thing I mentioned is an atomic force measuring probe which measures the topography of atoms but I do not know how the electricary part works or what resolution it uses (but I imagine it is going to be quite high).

Of more interest to the choosing and learning CAD, tiny gaps cause more headaches than most anything else in 3D drawing. When you start drawing and the thing refuses to extrude or cut it will either be due to a gap (sometimes so small you run out of zoom before you can see it and other times they simply will not go away) double lines (lines drawn in the same place twice - they don't like that one little bit) or the infamous "zero thickness geometry" where you have tried to draw something that has a feature with zero thickness at some point (think of a block with a hole in it and the whole edge is tangent to the block edge - hence the tangency point would have "zero thickness" but at what scale [lets try and avoid the digital precision thing in this example]).

Anyway, I am off to dress the off hand grinder before I sharpen the old gramophone needle I will use in my latest workshop AFM project.....

Mark

rebekah

3d cad- learn a direct modeller like fusion 360 from autodesk you have an advantage and its paid for subscription £25 quid a month only as you use it or month by month on subs rather than 5-6k up front or an illegal download

Another otion sign up for a course at college get a  student card an purchase a student edition of one of the big vendors for much much less (hundreds) as opposed to thousands 

i have used solidworks from 95 onward ,Unigraphics Catia Inventor pro e you will find they are dying the technology (though the sales pitch is magnificent when you hear the sales guys full parametrics( a load of crap i doubt you will use it for your uses) are of little use

nearly 20 years on im now classed in the cad world too set in my ways to change ,you can learn something and not be constrained by all these packages did it this way mentality which all of us now have because all 3d cad works the same and does the same just with different icons for the buttons

Secondly find one with free support or a large user base , it seems everyone has a seat of Catia with all the bells and whistles these days though i doubt its paid for in any way, and really as i demo for solidworks occasionally everytime i see a guy saying how do you do this on a seat of solidworks its obvious who is licensed and who isn't, i should be reporting it

Edited By mike mcdermid on 26/10/2013 11:22:45

Edited By mike mcdermid on 26/10/2013 11:25:04

Edited By mike mcdermid on 26/10/2013 11:26:35

.

John,

As I suspect you are fully aware ... the excitement is Philosophy, not Engineering.

The Greeks knew that there is no accurate conversion between Rectangular and Polar co-ordiates: Hence the classical geometry, where construction is done with only compasses and a straight-edge.

Squaring the Circle, etc.

MichaelG.

Hi Rebekah

A few thoughts.......

Parametric design Meaning you draw an object say a box of no particular size then dimension and "constrain" it. You can then change its size by changing its dimensions, it will automatically resize. You can also set relationships between lines for example parallel to another line or perpendicular to another line, there are many other constraints for lines and constraints for circles etc.

Solidworks, Catia and Autodesk inventor among other all work parametrically. These programs are focussed at mechanical engineering. They are not good for civil and construction engineering work.

If you are planning a career in engineering design working for a large corporation, This would be a good direction to head in. In industry a knowledge of AutoCAD is also a necessary. As you will receive many files in DWG format to work on. Some other programs can read them but sometimes not very well.

For architecture Many Architects designers and the building industry use AutoCAD. Have a look around for .dwg files on the net **LINK**

AutoCAD also has limited (and optional) constraints capability

A fairly recent program Autodesk Revit Is also parametric If you are engaged in civil and construction engineering it is gaining market share. I find the families "Feature" restrictive, far to slow for drawing use once objects, Great if you are drawing a high rise building with repeated features.

The CAD work I do is one off never to be repeated apart from small fittings files that I keep in a folder to include in a finished design.

There are quite a number of competing architectural cad programs.

You will also find thousands of 3D solid model files of parts for engineering in AutoCAD DWG format. Not drawn parametrically But drawn in 3D as solids. You can include these in your drawings or draw your own.

To clear the Air I have no connection with Autodesk apart from owning a Building design suite that contains among other programs AutoCAD and Revit.

The above will probably start a war in here so put your hard hat on!

If in the other hand you just want 3D models for home based CNC Don't be fooled by the slick sales people,

In my case I need to be able to do architectural 3D modelling for my day job, I have also generated STL files for 3D printing and DXF files For CAD cam. No problem and without a parametric program. If you take a disciplined approach to your work you should not get any bugs in your files.

As mentioned before if you are a teacher or student you may be entitled to a student version in some cases free, check on the web.

Regards
John

Wow I was gonna reply earlier but was too busy reading the replies.

some interesting choices.

just to illustrate what I'm trying to do, I borrowed this picture from another forum.

this is the sort of thing I'm going to try and produce. About 110 of them.

the following is also in my table

for those that can't make it out, it's a piston hydraulic rotary motor. On paper it's built, but just need to get it physically made.

Edited By rebekah anderson on 27/10/2013 08:32:35

Edited By rebekah anderson on 27/10/2013 08:32:52

The trackplates should not be too hard to draw, you should be able to do those withing the free trial period though not sure if you will be able to export the file from the Alibre trial. Quick sketch of one here, someone else can draw the motor

Edited By JasonB on 27/10/2013 09:04:57

Becky,

That trackplate whist looking complex is actually a series of 2D modules. It could be drawn in a far simpler program than a 3D modelling program.

But and it's a big but, if you are starting off with a clean sheet [ pun intended ] then it would pay for future work to start off with 3D sooner than learn 2D , pick up bad habits and then have to learn 3D in the future which will make the move harder.

I know because I'm at this point and it's a hard move for me.

As John points out, the trackplate is a series of quite simple 2d jobs that would probably need to be exported as a DXF file to your CAM program.

DXF files usually contain curves (lines, circles and arcs etc.) rather than 'solids' and are what you will be using for something like 90% of the time in your CAM program, that is unless you spend much of your time cutting curvy shapes like propellers, boat hulls or computer mice, in which case a 3d solid model is more appropriate.

The CAD program you choose should therefore have good DXF import/export capabilities in addition to its other modelling abilities. Even some of the more expensive CAD software is not necessarily well equipped in this area, so do make sure before you commit to buying.

Martin.

Edited By blowlamp on 27/10/2013 10:35:13