Learning CAD

[jason udallParticipant @jasonudall57142]

” to a limit”…
Yes servo drive but stil with encoder feedback..thus finite resolution
Yes both ( and up to 12 ) axis synchronised but again finite resolution… 12

[John Stevenson 1Participant @johnstevenson1]

Is nit picking finite or infinite ?

[jason udallParticipant @jasonudall57142]

Finite

[Mark CParticipant @markc]

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

[jason udallParticipant @jasonudall57142]

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..

[John McNamaraParticipant @johnmcnamara74883]

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

[Sub MandrelParticipant @submandrel]

> 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

[John Stevenson 1Participant @johnstevenson1]

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

[Mark CParticipant @markc]

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

[mike mcdermidParticipant @mikemcdermid41977]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 26/10/2013 09:12:56:

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

.

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.

[John McNamaraParticipant @johnmcnamara74883]

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

[rebekah andersonParticipant @rebekahanderson95322]

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

[JasonBModerator @jasonb]

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

[John Stevenson 1Participant @johnstevenson1]

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.

[blowlampParticipant @blowlamp]

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

[jason udallParticipant @jasonudall57142]

Like John S says learn 2d cad and then face un learning it for 3d packages…

…. So if new to it m go straight to 3d.. ( my shared experience John)..

getting plan elevation front view from a 3d model is simple and once modeled a host of export features exist…

[John Stevenson 1Participant @johnstevenson1]

One other point is I, personally hate to recommend programs as we all learn differently and what suits one will not suit another.

You need to download the demo's and have a play, or watch the you tube videos but if using a demo put aside at least 3 or 4 full nights. You cannot do justice to one in a night flying about.

plenty of different programs have been bandied about but before you start look at the pricing structure and what you get in the module.

No good spending time on demo's if the package you need is out of your price range.

Inventor, Autocad, Solid Edge 3D [ not the 2D ] and solid works are all around the £5,000 mark.

Fine for a business, claim most back and productivity will pay the rest but for a hobby ? Unless CAD is your hobby then you need to look somewhere else.

One program not mentioned is Bobcad, this is a combined 3D CAD / CAM package and can be bought for as low as under £500 complete as a hobby package which isn't cut down in any way.

Again try You tube.

[John McNamaraParticipant @johnmcnamara74883]

Hi Rebekah

Swash plate pumps are available from many sources. You mention you want to get one made, do you mean outsource the work? If so you may find looking for second hand or new if need be automotive air conditioning pumps… they come in various sizes including quite large ones for trucks. Anyway there are a lot of images and links to suppliers below. Getting one made on a one off basis would be quite a project, requiring hardened and ground pistons in lapped bores, The swash plate and the piston pivoting caps would need to be similarly treated.

**LINK**

For fun I drew up a rough draft of a 3D AutoCAD solid of your track link. With the right cam software and an end mill with 2mm radius corners (Not standard but not that hard to make from a standard cutter) you should be able to produce it in two settings With most of the cutting on the back side then turn it over to do the base

Of you have a fourth axis driving a rotary table (You would need to make a fixture) you could do it in one setting.

The image below is a solid model. Effectively a void surrounded by a tight skin.

It took me about half an hour.

It was made by drawing a closed polyline of the end section. Polylines are just lines but they are joined end to end. Well not really! but the program treats them as a single entity. The is an option to close them into a loop or leave them open. when making a solid they must be closed.

Next the section was extruded to length with the extrude command. so easy.

Next the hole was made. I simple drew a circle 20mm in diameter, then extruded it to a random length I made it 500mm so it is easy to see it poked through the track and placed it in the centre of the track.

Next the Subtract command was used remove the cylinder from the track piece The cylinder disappeared leaving the hole, Voilà

Finally the cut outs for the hinge on the edge. You guessed it they have to be cut away too.

I drew a rectangle in this case 50mm square, then chamfered two corners to 4mm radius then extruded that to 500mm length. creating a bar with two sides chamfered.

The bar was moved to the correct position cutting through the track and duplicated for the second cut out.

Then the subtract command used again to chop away the recess. Again as with the cylinder the bars disappeared leaving the track.

3D is easy when you think of the work as shown when making the track you only need to memorise a dozen or so commands to start with:

POLYLINE (AND LEARN ABOUT POLYLINE CLOSING, ALL ENDS MUST TOUCH)

SUBTRACT (REMOVES ONE SOLID FROM ANOTHER)
UNION (JOINS TWO SOLIDS TOGETHER)

FILLET (CREATE FILLETS ON SOLIDS AND POLYLINES)

EXTRUDE (EXTRUDE A POLYLINE INTO A 3D SOLID)

CIRCLE (DRAW A CIRCLE)

And set the program to draw autographically unless you want draw an angle,

Before you start watch a couple of getting started videos on you tube to get you familiar with the interface.

The above is for Plain vanilla AutoCAD, other programs should have similar functionality.

 

Re DXF Files. Unfortunately Autodesk who invented the DXF format change it periodically to keep up with changes to the DWG format. this can create problems if another CAD company does not update their DXF interpreter. A DXF file is simply a plain text file representation of DWG files. This allows other programs to read the text file, CAD CAM programs for instance. When exchanging files with another party find out what version they can read. You can hopefully do a "Save as" to their version.

Regards
John

Edited By John McNamara on 27/10/2013 13:36:45

[John Stevenson 1Participant @johnstevenson1]

John,

Seeing as it's a scale model Becky is building I think finding an off the shelf swash plate motor about 30mm diameter will be a bit hard to find

[JasonBModerator @jasonb]

Interesting that it took 1/2hr to draw, the one I did took less than 5mins but went about it it a similar way though I drew the hole and notches as one and cut them out as one step.

 

J

Edited By JasonB on 27/10/2013 13:43:46

Edited By JasonB on 27/10/2013 13:58:35

[John McNamaraParticipant @johnmcnamara74883]

Hi John

I guess this is a working model? will the motor scale down and still work? Tracked vehicles are heavy and there is a lot of friction.

Here is one that used a simpler setup using a ball bearing as the swash plate.

**LINK**

Regards
John

[John McNamaraParticipant @johnmcnamara74883]

Hi Jason

Yeah It takes time to do a write up taking a reader through the steps in detail. not just wack up a sketch.

Regards
John

Edited By John McNamara on 27/10/2013 13:56:53

[JasonBModerator @jasonb]

Ah, they way it read I thought the drawing took that long.

[blowlampParticipant @blowlamp]

A video of a slightly rough version in MoI here.

Martin.

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