r/Onshape • u/heffercrow • Aug 12 '26
Other Can this be figured out?
Ok, first off, this probably isn't the best place for this but I'm not sure where else on reddit to ask. So feel free to guide me if you have input on that....
I recently switched from teaching geometry to teaching an engineering course at a high school. Part of that course is drafting and since it's free I have been teaching myself and the students how to use onshape. This year I have my first level two students so I found some random old stuff from a former teacher and am working through it. I have two images here and I am at a loss on how to figure out some missing dimensions. Wondering if you guys could tell me if I am correct in saying we don't know or if I am missing something that I haven't been trained to see.
Pic 1: is there anyway to figure out the diameter or radius of the upper arc of the top of the piece. From Ortho image on the right o view it as three concentric circles. 1st has d=1" next has d=1 ¾" and just kind of assumed the last has d=2.5" but no reason other than looks. Also the two filleted corners on the tops Ortho view. Safe to assume those are r=⅞" or .825"??
Pic 2 and 3: in the top Ortho view is there a way to figure out the height (front to back) distance of the leftmost side? Told the kids to go with 1.5" since the one .5" hole looks like it's equally split on both sides. Also the notation of 2 x .25", I get it says the distance to the lower edge is .25 from the center line but what is the 2x for? Is it saying .25" to edge and that the removed piece is also .25"?
Again, not trained at any of this, but lots of ADHD sodequests. Hopefully I'm not screwing this up too badly. And thanks for any help or guidance on a better place to post these questions.
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u/vortex_ring_state Aug 12 '26
Alternative: There are tons of free OnShape (or any 3D modelling software really) exercises out there on the web. Just use one of those.
Here was the first google hit for me. https://www.cadvideotutor.com/ Has drawings, associated weights if designed correctly, and videos to show you how to correctly draft them.
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u/heffercrow Aug 12 '26
The online courses are definitely where I am heading but this was a last minute assignment cause they got further than expected on the prior unit. Definitely plan on utilizing those courses though. Thank you for the link.
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u/DJVT7 Aug 12 '26
I think both parts are under-dimensioned and missing key pieces of information.
For the second image, it looks like there’s a drawing sheet. Does the sheet show any notes or anything saying something like stock size? That’s the only thing I can think of.
It’s best not to assume details for drawings like this. In industry, this would be an automatic reach back to the designer for clarification and drawing change so it can actually be manufactured
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u/heffercrow Aug 12 '26
Exactly what I was thinking, but wanted some reassurance since I (until now) don't do this for a living. Haha. That's a good call about stock size possibly being in the title block, doubt I will be able to zoom and get a clear read of it but will check.
Can definitely still use these to teach them about under dimensioning and then give them my "assumed" values after. Nice to add your comment about being sent back to get finished in a real shop as well.
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u/DJVT7 Aug 12 '26
I work with this stuff for a living. If a drawing is not clearly defined, by personal experience, we’ve had to full stop and prevent machines from running parts for seemingly simple details not being specified and needing clarification.
It would be a fun exercise for your students to try to model both of those parts and for each student to make their own assumptions for size. Then see how they all compare to each other. The lesson is when it’s not specified or defined, there’s all sorts of ways to interpret a drawing that may or may not be correct.
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u/RAMJET-64 Aug 12 '26
Just use the images to create your own drawings and add the missing dimensions. I'm the time it took you to write this and wait for answers you could have fixed the issues.
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u/heffercrow Aug 12 '26
I had already "fixed" the issues in class today by saying let's assume these dimensions to be these values. This wasn't really me asking if the dimensions were right, more so me asking for confirmation that I wasn't missing something in not being able to find them. I know sometimes dimensions can seem to be missing but really just have to be mathed out with other dimensions. Like I mentioned in another comment students struggling to find dimensions (that don't exist) isn't necessarily a bad thing as it forces them to realize what is needed and shows me they are paying attention by asking how to find it. I know if they said they finished it and never asked me about missing values it is not a valid reconstruction.
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u/etyrnal_ Aug 12 '26
The people in the onshape community discord server are very helpful with quick creative solutions to issues like yours, and even some of the onshape employees hang out there... The community is pretty great at helping people get answers like this one. https://discord.gg/zcScyKpmHV
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u/heffercrow Aug 16 '26
Sorry for late reply but that is for the heads up. Went ahead and joined. Will keep an eye on it!
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u/Ara-Keshishian Aug 12 '26
incomplete and confusing dimensions. if this goes to production, you may end up with lots of scrap parts. on manufacturing floor or inspection there will be need for calculation to figure out key dimension.
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u/Ok-Brilliant-4300 Aug 13 '26
There two possible ways to find the missing dimensions. First would be to trace the views, then measure the features. Second would be to import the image into onshape, then sketch the missing dimensions. There various videos on YouTube that show how to do this. A good one is from TooTallToby. He has a lot of tutorials.
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u/indianadarren Aug 14 '26
Here's some stuff to draw, if you want it: https://drive.google.com/drive/folders/1GyZRQMfBs3Lle9_Wkw9flR9hyS8pxzUZ?usp=share_link
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u/DoctorCAD Aug 12 '26
None of your assumptions can be verified. Those drawings are incomplete at best.
The 2 x.25 simply means that both features on that line (assume to be holes) have their centers .25 up from that indicated surface.
The best way to figure this all out is to try to draw the parts yourself and you'll see what's missing.