OnShape - hints and tips.

[adrian]

For various reasons I've delved into the world of 3-D modelling, I tried Fusion360 but I struggled a bit with it as it wasn't always clear to me what it was doing. In learning any software I tend to try something and see what happens, if it doesn't work as I expected then I undo the edit and try something different. With Fusion360 I struggled with the undo/redo to get back to the point to start again.

Following suggestions from @Bill Bedford and @RyanOPlasty I tried Onshape. Working in a browser makes it platform independent - I can easily open up a model (and edit!) on my phone to show what I'm working on.

Anyway after that preamble as I delved into Onshape I have figured out what I think are a few useful tips so I have decided to start this thread to collect hints and tips of working with Onshape. I can also recommend the tutorials they publish as a very good introduction to the software.

So first off is dimensioning sketches. When I have done 2D drawing I prefer draw things out full size so I don't have to mess around with any scale conversions. Then once the drawing is complete I can scale the complete drawing to the required scale. Now in QCAD I could mix units so I could dimension something as 20' 6" and it would work fine. However Onshape didn't accept it in this form.

It asks for a valid expression, i.e. an equation. Now it's only a small change but using a plus sign creates that expression to 20ft+6in is acceptable.



Of course this does mean that you can mix units from different measurement scales if you really need to.

If you have set the drawing units to mm it will then convert this expression into mm for the display.


You can also use variables in your expression so if you define this before your sketch.



Then when you dimension your sketch you can add in a gnats tadger to any dimension required. Note it appears that the variable has to be in brackets and a unit defined.



Please feel free to ask any queries about Onshape or add any useful tips.

 

[geoff_nicholls]

I prefer draw things out full size so I don't have to mess around with any scale conversions. Then once the drawing is complete I can scale the complete drawing to the required scale.

There could be a problem when using this method, as there are always compromises which need to be made with smaller parts such as locating pins, piping etc. On the real object there may be a 1/2" thick pipe, or hexagonal bolt. the CAD will be happy scaling it down to 1:43.5 or whatever, but the 3D printer, laser cutter or etching service machinery will have their own tolerances, or limits on physical sizes. Those limits relate to the resultant object, not the real thing.
So, rather than have a two-stage process, where you scale it down, then make adjustments, I prefer to do all the CAD in the desired scale, you can see on the screen how any compromises fit with the rest of the object, right from the start.
I usually print a scale rule to match the drawing, using what Turbocad calls "Linear Fit Copy". Thus I can measure off the actual size in millimetres, without needing a calculator to do the conversions

 

[adrian]

I can see the pro's and con's of both routes and have tried both. It's just for the drawings I ended up doing working to full scale seemed easier, the drawings I was working from weren't the best reproduction, when scanned they were not perfectly flat so straight lines weren't etc. So I tended to use the printed dimensions rather than a scale rule and being lazy I didn't want to convert lots of feet and inches to scale and just typing them in directly appeals to me. I don't see the real world tolerances as a problem as I use a scale variable to make them up to full size. So for example on the etches I did in 7mm where a 2mm border was required the dimension was multiplied by either 12/7 to convert to inches or by 43.5 to convert to mm.

 

[geoff_nicholls]

sorry to hijack the thread.
A free CAD application accessed via the browser, with no installations or upgrades to deal with, does sound a good idea.

 

[Big Train James]

My preferred platform is Autocad, mostly because I've been using it for so long. I really should get proficient at Solidworks for professional reasons, but I need access to the software.

For various reasons, I prefer drawing at full scale, and then making adjustments as necessary for scale applications. But it's really just a product of how I learned cad combined with my personal proclivities. Anybody that has ever used cad, or really probably any other program, knows that there are many ways to do things to achieve the same result. My rule of thumb with Autocad is that every single person you encounter will teach you something you didn't know about the program, often a better way of doing something, even if you have been using it for a long time.

In the end, if any of us wanted to utilize the drawing at different scales (say make parts for 7mm and G1), then some scaling and adjustment will have to take place to re-balance between prototype accuracy and scale practicality.

What I would like is a set of digital calipers with model railroad scales as an option, to make measuring and converting model dimensions simpler.

 

[RyanOPlasty]

I have been experimenting with 3D printing using models from Onshape. Following on from the Mark model, which I have had printed and managed to finish to a reasonable standard I am now working on MK3. A nice thing about onshape is the ability to share models, so with just a link, anyone can view and examine. Here is a link to Mk2 before I decided on a different approach. Onshape

I have now imported some scanned photographs into onshape to assist with the modelling along with some of the original drawings.

 

[Bill Bedford]

If you draw at a scale of 12mm:1ft full size measurements can be read off drawings as inches and entered as millimetres. Any scaling from 12mm to you preferred modelling scale is also less likely to run into tolerance problems than starting from full size. It also seems easier, at least to me, to keep in mind model specific dimension, such as minimum material thicknesses etc.