noob question

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
buick455
Posts: 14
Joined: Sun Mar 10, 2013 8:55 pm

Re: noob question

Postby buick455 » Thu Mar 14, 2013 6:06 pm

I was looking through the forum trying to figure out why I can't seem to understand/replicate Norms tut (the part about the External geometry tool and the circle, in his tut he selects 1/2 the circle, when I do it it selects 3/4) and found some topics about FreeCad and STL's. Is FreeCad broken to the point where even if I do learn it, I still wont be able to make STL's with it??
User avatar
NormandC
Posts: 18534
Joined: Sat Feb 06, 2010 9:52 pm
Location: Québec, Canada

Re: noob question

Postby NormandC » Thu Mar 14, 2013 7:05 pm

buick455 wrote:in his tut he selects 1/2 the circle, when I do it it selects 3/4)
This is inconsequential. That it selects 1/2 or 3/4 of it has absolutely no effect on its use. As I said already in my mini-tutorial
normand wrote: (It does not copy the whole circle, but rather an arc. This is one of FreeCAD's quirks.)
buick455 wrote:and found some topics about FreeCad and STL's. Is FreeCad broken to the point where even if I do learn it, I still wont be able to make STL's with it??
Please do not jump to wild conclusions and infer that "FreeCad is broken". FreeCAD remains a highly useful CAD program, even if it's not complete, even if it has its lot of quirks and bugs.

STL generation is only a small use for a CAD program. And actually what I consider a "garbage out" feature, because STL in CAD is really a garbage format. In CAD you cannot do anything with mesh, as the mathematically precise surfaces of your solid model are degraded into polygonal facets. BTW most commercial CAD software can do absolutely nothing with imported STLs (not even take measurements!), while FreeCAD can somehow work with them and even convert them to solid (although the faceted faces cannot be smoothed).

STL is a 25-year old format, I still can't understand why with the computer power at our disposal now it hasn't been deprecated in favor of a more modern, real CAD format for such purposes as rapid prototyping.

In any case, the problem with STL seems to be caused by Open Cascade, which is the third-party library used as a geometric kernel by FreeCAD, and over which the FreeCAD devs have no control of. If you look more closely at those topics, you'll see that the problem is with highly complex meshes. With prismatic shapes such as your model there are no problems, even though the polygon count will be rather high.
buick455
Posts: 14
Joined: Sun Mar 10, 2013 8:55 pm

Re: noob question

Postby buick455 » Thu Mar 14, 2013 8:20 pm

Yeah for the life of me I just don't understand how exactly you did the slots :oops: I must be over thinking it. I thought when you said it grabs the arc instead of the whole thing that your using the 2 points on either side to get your slot (3mm wide).. IDK, I'm screwing it all up. I'll keep tinkering with it. :)

Maybe I should have worded that differently, "broken" is pretty vague. Maybe I should have worded it:
" Is FreeCad unable to export files that I can use with my 3d printer at this time? If the answer is no, is it planned and do you know when? "

Sorry for the misunderstanding, I know it isn't broken in the sense that it can do lots of things (just maybe not what I need it for). I expect bugs, every piece of software has bugs, but If I can't create something then print it, FreeCad isn't going to do me any good right now, ya know what I mean. If it is going to be able to do what I need (in the very near future) then I can justify spending time to learn it and share my experience with other people in the reprap world. I cant be the only person that doesn't enjoy using OpenScad. I have been hording parts to build a CNC router and I would like to learn one program to rule them all, This seemed to fit the bill.

I should have added this: (My msg above looks like I'm still asking)
I did export my model in STL then loaded it up to netfabb cloud. It looks fine to me (I haven't printed it though).
keithsloan52
Posts: 1450
Joined: Mon Feb 27, 2012 5:31 pm

Re: noob question

Postby keithsloan52 » Thu Mar 14, 2013 9:59 pm

Norm trouble is people need STL for 3D printing, especially RepRap
User avatar
NormandC
Posts: 18534
Joined: Sat Feb 06, 2010 9:52 pm
Location: Québec, Canada

Re: noob question

Postby NormandC » Fri Mar 15, 2013 2:59 am

I've been having a lot of trouble with the forum lately. Time outs that make my replies disappear. :evil:
buick455 wrote:Yeah for the life of me I just don't understand how exactly you did the slots
My mini-tutorial shouldn't be seen as all-inclusive, I left a lot of details out. This is where a video tutorial would be better. I may try to make a few in the future, problem is the sound card's microphone jack in my new PC sucks big time. I'll need to buy either a new card or an USB powered microphone.

You should watch John Durston's videos on Youtube. They're more than 10-12 month old now, which in FreeCAD time makes them almost obsolete. But the one that introduces sketching and the other about degrees of freedom should still be relevant. https://www.youtube.com/user/5needinput

The problem you're having with the slot is probably caused by the tangent auto constraint that kicks in too soon. The dev responsible for the sketcher is aware of it. (Here's the bug report)

A workaround would be to disable auto constraining (there's a tick box in the Task panel when in sketch edit mode) but you'd have to add a lot more constraints manually.

What I prefer to do is, when I have similar problems, to draw my geometry a good way out of where I actually want it, so the sketcher solver does not attempt to add constraints that I don't want. So click on the polyline tool, and draw your rectangle a good distance from the red and green axes. Also, create the reference geometry (the magenta arc) after you've drawn the rectangle. That makes one less object the solver will attempt to constrain to.

When you've drawn the first slanted line, toggle the M key. This is the "modifier" key. The polyline has multiple modes. One of them locks the next segment perpendicular to the previous one. Then there are arc modes (perpendicular or tangent). Play with it, it's very cool, this is new in v0.13.

When you move your mouse pointer while drawing, watch the pointer icon. To the lower right of the cross an icon of the active tool is shown. When hovering over an element, a constraint icon will show up besides it to indicate that the solver detects a possible constraint. It is a smaller version of the constraint icons in the toolbar. When you click while a constraint icon is showing besides the pointer, the corresponding constraint will be applied.

Once you close your rectangle, you add the external edge constraint to the hole. Then, drag your rectangle to its approximate place. You select either a line or a point, then when it's green you drag it. When dragging a point you can rotate the rectangle. When you've dragged the sides near the circle, add the tangent constraints. BTW, you wondered about the fact you got a 3/4 arc. One of the lines may not be in apparent contact with the arc. This does not matter: if you apply a tangent constraint, the line will be positioned where it would touch if the arc was longer.

After that you set the length of the rectangle, then you draw the small line as I explained in my tutorial post.
User avatar
NormandC
Posts: 18534
Joined: Sat Feb 06, 2010 9:52 pm
Location: Québec, Canada

Re: noob question

Postby NormandC » Fri Mar 15, 2013 3:19 am

buick455 wrote: I cant be the only person that doesn't enjoy using OpenScad.
LOL I understand the feeling. I'm baffled by its popularity in the RepRap community. I've been using CAD in my field of work for more than 15 years. To me design is not typing lines of code. They say OpenSCAD syntax is easy, well it is Japanese to me. I'm used to build models in a GUI in real time, not have to "recompile" to see the result.

Of course Thingiverse's customizer based on OpenSCAD is very cool. It's nice for end-users, but I'm not the one who will create the script in the first place.

One thing that annoys me on Thingiverse is people posting files made in proprietary software such as SolidWorks or Inventor. I wish they would at least post a STEP translation.
keithsloan52 wrote:Norm trouble is people need STL for 3D printing, especially RepRap
I know. There was some talk a couple years ago of replacing it with CSG. I sure hope they don't!!! But as I said, for simple objects STL export is fine. The problem I had was with my balloon-powered jet car which has very complex surfaces. I didn't have trouble with the wheels, Slic3r accepted the STL without complaint.

I modeled in FreeCAD the printed parts for the upcoming Lulzbot TK-0. The Lulzbot people generated STL files from the FreeCAD models without trouble. I've been in occasional contact with jebba (Jeff Moe) and they are making about 25 machines as a test run.

My original files are on Github but the guys at Lulzbot have made quite a few changes since.

So yes, there's a problem with STL generation in FreeCAD, but I think it affects a minority of what people would model for 3D printing.
buick455
Posts: 14
Joined: Sun Mar 10, 2013 8:55 pm

Re: noob question

Postby buick455 » Fri Mar 15, 2013 4:08 am

normandc wrote: The problem you're having with the slot is probably caused by the tangent auto constraint that kicks in too soon. The dev responsible for the sketcher is aware of it. (Here's the bug report)

A workaround would be to disable auto constraining (there's a tick box in the Task panel when in sketch edit mode) but you'd have to add a lot more constraints manually.
Grrrrr... I just did it and it worked, I don't know if I did exactly as your tut said to but turning that off fixed the runaway verts/lines. It was all my fault, I remember in one of the videos I watched it said to turn that off :oops: maybe just add that to your tut "turn off auto constraints" in big letters for forgetful folks. Is there a way to have it off all the time?
normandc wrote: LOL I understand the feeling. I'm baffled by its popularity in the RepRap community. To me design is not typing lines of code. They say OpenSCAD syntax is easy, well it is Japanese to me. I'm used to build models in a GUI in real time, not have to "recompile" to see the result.

Of course Thingiverse's customizer based on OpenSCAD is very cool. It's nice for end-users, but I'm not the one who will create the script in the first place.
I just don't like typing and the re-compile just to see that I screwed up a translation or size of something. To use it I have to sketch the parts out on paper just to "code" them correctly in OpenScad. I have done some coding like this before, but that still doesn't make it any easier. The creation of modules (like my wonderful slotted holes), variable data (M3_Hex = 3;) stored in another scad file are the only things I like about it.

Like I said a few posts back... Sketch quick like Sketch-Up (using Push/Pull on X, Y & Z), Have the ability to create config files for variables and drop in modules like OpenScad and the flexibility to add filets, chamfers ect like FreeCad. I would be in heaven :lol: once I understand FreeCad like I do the other 2.
normandc wrote: So yes, there's a problem with STL generation in FreeCAD, but I think it affects a minority of what people would model for 3D printing.
Is there anything I should avoid trying to do in order to not get a bad STL? I did export what I have been working on and it looked fine (in netfabb). I didn't load it into Slic3r at all though.
User avatar
NormandC
Posts: 18534
Joined: Sat Feb 06, 2010 9:52 pm
Location: Québec, Canada

Re: noob question

Postby NormandC » Fri Mar 15, 2013 4:18 am

Actually I've read that the problem is with v6.5.x of OCC. Since the Windows version uses the old v6.3.0 it's possible you are not affected.

Other than that as I said, parts made with pads and pockets should give no trouble. Have you looked at my toy car? It is *not* made that way. ;)
buick455
Posts: 14
Joined: Sun Mar 10, 2013 8:55 pm

Re: noob question

Postby buick455 » Fri Mar 15, 2013 4:07 pm

Well I successfully went back in the model and corrected the slots. When I couldn't get it to work Norms way (b/c I was stupid and forgot the Auto Constraints needed to be off) I did it the long way and just kept adding features to the model. This caused me a little grief b/c I couldn't figure out how to add back the external geometry to the sketch. I did finally figure out that I can't re-select a face, but I can hide everything and only show the Sketch I'm working on and a Pocket before it. Then I was able to add the external geometry that I needed. This is a good day in my book (so far anyway) :D
buick455
Posts: 14
Joined: Sun Mar 10, 2013 8:55 pm

Re: noob question

Postby buick455 » Fri Mar 15, 2013 7:12 pm

Another quick question... :lol:
I need to add hexagon pockets to the model for the captured nuts. Is there an easy way or am I going to have to draw them out (which doesn't sound like a lot of fun)?

This is what I got so far if anyone is interested..
Image