FreeCAD Quick Tips - A simple method to avoid topology issues when using datum planes.
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- Опубликовано: 19 окт 2020
- As most people that use FreeCAD know there can be some topology issues if you create sketches on faces of an existing model. If the model is modified and more faces are added the existing faces can change name, this causes a referential issue with the sketch drawn on that face. This video shows a very simple method for avoiding these topology issues and results in a very robust solution.
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Datum planes help a lot.
Yes they do, and they are good practice .
I've been running into this a ton, and you have just saved me so much pain. Thank you!
Thanks for the feedback. I am glad it helped. Don't forget if there's anything else you want to see in a video, just let me know.
@@Adventuresincreation I'm about to get into scripting and macros. The wiki is great, but it misses on some of the "why" behind their scripting wiki's.
Videos on when to use scripting/macros vs just designing a part and saving it to include in an assembly...
Would be terrific.
@@Adventuresincreation To expand on my earlier comment... I'm designing a rack and enclosure system for my 3D printers and smaller PCB mills.
There are many common parts like DIN Rails and Aluminum extrusions of various size that I'm thinking of using scripts/macros so I can more easily include these in assemblies of the entire completed project.
The alternative is of course saving a file with each part that has set property values for dimensions.
As a career programmer, that feels like a DRY smell to me, and wondering if the return on scripting/macros would actually be better than just firing out the dozone or so different files of the various sizes i need of each sketch.
If you are making lots of similar parts with minor variations a macro/script might be the way to go.
excellent!! I just learnt 3 or 4 new functions just by watching this video
Excellent!
Thanks for the video. Very useful.
You are very welcome. The next one will have some more tips on using revolves and deeper into spreadsheets
Now I know what a Datum plane is, thanks. I solved my issue when I changed dimensions in the spreadsheet. I have to select the last element in the build tree and say OK,. That seems to update everything. I still use .18 'cause I am on a 15 year old iMac, which I plan on continuing to use until the squirrel retires.
They have released 0.19.1 as the current release now. I don't know if it's any harder on the processor. I have one of those old macs too, bless it.
This topological naming defect is a major hindrance, and it's still there today. I was thinking about learning FreeCAD and using it for personal projects. But on closer look, I don't want to invest learning time into FreeCAD.
The solution is coming, stick with it and find out
Slick.
Thanks
The issue that I'm running into is that on a more complex part with 50 different dimensions of all shapes and sizes, how does one actually offset the sketch accurately to a face without having to use the measure tool every 5 seconds to find the actual amount it needs to be offset?
First, try to keep the sketches and steps simple. Second, you can always calculate the offset and use a spreadsheet to keep it constant even when you change something.
Would you consider a video to explain datum point, line and plane. Where, when and how to use them?
Absolutely, I will put something together for you
@@Adventuresincreation Thanks for your prompt reply.Looking forward to it
Thanks for this video, i'm subscribed now. It would have been really helpful if you had taken this one step further and shown how to constrain the pocket to the middle of the sketch if its width had changed rather than just its depth. How do you constrain things in terms of the underlying sketch geometry without building in a topological-naming trap?
Take a look at some of the other videos, you will see how to do that. You just have to consider the way in which you constrain. If you use geometry you are going to run into issues but if you keep it as offset from the LCS you should be fine.
@@Adventuresincreation Hey, thanks for the reply. I'll definitely keep watching and hope to grow more proficient. Would be nice if the external-geometry tool would set up a spreadsheet entry for both the source and target sketches instead of just a name reference. That way you'd have the convenience of just clicking on the reference point you need, without setting a topological-naming trap for yourself.
Do you have a tip for avoiding the topology naming problem with LCS markers moving around when another feature is added?
I typically create a part and use separate plane to add holes then attach LCSes to the edges of the holes. But if I later add another hole the names of the hole edges change and with that the LCS references. Consequently the assembly becomes a mess until I edit LCSes that “moved”.
Until the topo issue is resolved, use the major planes to position things, you can offset from them with angles and distances. It may involve a little more mathematics but it's doable for now.
@@Adventuresincreation I already do that. My parts are simple models of steel plates, angles or rectangular tubing. I put holes in them with sketches on major planes. Nothing fancy. But as soon as I add or remove a hole the names change and with that the LCS reference move. I am sufficiently frustrated fixing the models that I started learning Alibre. I invested a lot of time into FC but now I am wasting a lot of time fixing messed up models, drawings and assemblies.
I hope Alibre handles assemblies better than FC.
Thanks for the helpful videos.
Any reason you don't copy and past variable names and sketches? I've noticed you don't do that in most of
your videos
Hi Joseph, I am not sure what you mean. Are you talking about copy and pasting variable names within a sketch?
Thanks!
But what if my datum plane is angled and stays on the surface created by a chamfer operation? It would be a damn PITA to calculate the right distance (from origin?) from the chamfer data...
Thanks for the feedback. It can be a pain to calculate but relatively easy. However if it's something where you have to sketch on a face, I recommend doing that last, that way if you need to redo it the pain is minimized.
@@Adventuresincreation in other words: draw "dangerous" stuff at the end. Thanks for the hint!
Hi, I am a total newcomer to FreeCAD but was a past AutoCAD and SolidWorks user. I followed your instruction to pocket a pad but now cannot close the datum plane? My model has this active datum plane all the time. I have reviewed the part where you dismiss your datum plane (4:52) loads of times but can't follow how you do it?
No worries John, it takes a little getting used to. Simply go to the datum plane in the model tree on the left, click on it then hit spacebar. This toggles it on and off.
@@Adventuresincreation many thanks. I started with a tutorial book but got fed up with it and seeing as though I had a project to do I decided the best way was to chuck myself in at the deep end. Initially I struggled and was on the point of giving up but it obviously did work, the problem was me! I persisted and with the help of you tube I have made great strides but there is a lot to learn (especially if you are ancient like me!). Thanks for taking the time to reply, you are a star!
@@johnbailey9651 Keep at it John, you will be surprised how quickly you get the hang of it. - I think FreeCAD is an excellent tool and you can't beat Free :-)
Why don't you just enter into the z-offset of the plane? This would automatically update the plane whenever the pad dimension changes and avoids thr need to create spreadsheet.
Because I didn't know that, thanks Harald :-) I will give that go.
It's actually .Length but it does work and you can use math on that. Thanks for the tip, I will mention it in the next video. I generally use the spreadsheet because I am likely to have more than just the one variable at work. It makes organizing them easier.
no chevrons are only required when you want to use a label that you chose instead of the native object name Pad
Spreadsheets are an excellent tool which I use very effectively on some parametric projects.
freecad how to manipulate datum planes would be a nice video.
Take a look at my channel, there is a video on offset sketches and datum planes
It's sad that FreeCAD doesn't have the ability to reference the newly extruded face in case of a pad, symbolically.
Like, pad.FrontFace.
Because what you're doing here, is basically reimplementing a pad with a datum plane, by referencing the pad length.
But it will break if for example, you rotate the attachment plane of the sketch used for the Pad. It kinda works because a simple setup like this one is using only the three basis planes, but this will be messy in general, because you will have to find a way to compute the orientation of same face without referencing it by Face number, and you just moved the topological naming issue somewhere else.
Yeah, it means you have to consider carefully what references you use. However, I believe the solution to the topological naming issue is in sight, fingers crossed.
What is the benefit of datum plane? Why not sketch the pocket on the face directly?
You will have trouble with the topological naming issue. Sketching on faces can have undesirable results if you later modify the model.
@@Adventuresincreation I see, but what those issues would be like? could explain more, please.
@@alisaied4958 The faces will change their ID and the reference will be lost. The model will be broken.
@@Adventuresincreation thanks
Is that a hint of an Australian accent?
No, I am English but live in the USA, when you mix the two you get a British accent with a hint of American that sounds to some like an aussie accent 😉
@@Adventuresincreation Great accent nonetheless and great tutorial too. Thanks!
no need for the datum plane. offset the attachment of the second sketch. the datum plane is superfluous, just added steps for no benefit.
You can use either an offset or datum plane. I find it easier to use a datum plane if I am going to have multiple sketches that reference that plane. There is always more than one way to skin a cat ;-)
This is fundamentally why I stopped using FreeCAD, basic functionality like this shouldn't need convoluted work arounds it should just work. Why they keep wasting time adding new 'features' rather than fixing basic problems like this one baffles me, especially as this problem has already been resolved in a FreeCAD fork.
They are working on it now as a high priority.
@@Adventuresincreation Still not fixed in 0.21.0 I tried recently though. Maybe I will look at it again in another year when 22 comes out.
@@schrodingerscat1863 probably not a bad idea