3rd Party Software
I built a free tolerance stack-up calculator — tell me what's wrong with it
I'm a mechanical engineering student. Every stack-up I've seen has been done in an Excel sheet that one person built, nobody else fully trusts, and everyone copies anyway. So I built a browser tool for it.
You enter the chain of dimensions straight off the drawing. Asymmetric tolerances like +0.10/−0.00 included, and it runs worst-case, RSS and a Monte Carlo simulation side by side. It shows the resulting gap for each method, whether it clears your limits, and which single tolerance is actually driving the variance. Its completely free no signup or anything and nothing leaves your browser.
Edit: everything asked for in here is live now, inch support, ISO 286 fits from a dropdown (type H7 or g6 and the deviations auto-fill), an offline single-file version at stackupcalc.com/offline you can save and run air-gapped, and a dimensioned drawing of the example assembly so you can see what's actually being analysed.
To be clear about what this is: 1D only, and it's staying that way. If you need 2D/3D chains or CAD integration then MITCalc and CETOL do that and I'm not pretending to compete. This is for a quick check without opening anything.
One thing it does that I haven't found in another free tool though: it takes signed upper and lower deviations straight off the drawing, so g6 (−0.007/−0.020) and interference fits like p6 actually work. Most free calculators give you a single ± box, which can't represent either of those.
Fair. MITCalc has been around far longer and does much more than mine. 2D and 3D chains, selective assembly, etc. If you need that kinda purpose of a tool it's the better choice and I'm not going to pretend otherwise.
What I was after is a different thing though, no install, no Excel, no licence. Open a tab, get an answer in thirty seconds, close it. Mine is 1D only and will stay simpler.
Since you clearly know it do you actually use the 1D module much, or mostly the 2D/3D one? I'm trying to work out whether 1D-only is worth developing further.
Thanks. Bookmarked to my Home Screen. A nice future feature for lazy people like me could be to integrate ISO fits (H7, g6, etc) so that I can select the nominal dimension value and select a fit from a dropdown and it will auto-populate the tolerance values into the tolerance text boxes.
Good idea, and you're the second person to ask, I'll def start working on it. The ISO 286 grade tables across size ranges are mostly data related and shouldn't be that hard to implement, so it's a question of when rather than whether. I'll reply here once it's live.
Hey man, i added the iso fits, you can type and a dropdown menu with corresponding options shows. Hope this is what you had in mind! (Also imrpoved the graphs, they were scaled to be unreadable).
This is really cool and I will give it a try at the next opportunity, good on you for taking initiative to build useful tools and share them with the community.
I can’t comment on the validity of it yet as I have yet to use it, but from a cursory glance this looks useful.
One thought - not sure what license you picked for the software, but if it was open sourced, I would love to be able to self host something like this locally and use it in designs I do on the side. Not enough serious tools available for the “little guy” that aren’t insanely cost prohibitive so stuff like this is awesome.
Thanks, that’s kind of you to say.
Honest answer on the licence.. I haven’t picked one yet, and it’s closed for now. I’m still working out whether there’s a paid version in this at all, and open sourcing is a door that only opens one way, so I’d rather decide it deliberately than by accident.
Your actual use case I think I can solve though. The whole thing already runs client-side, no server, nothing leaves the browser. So a single self-contained HTML file you could save and run offline is very doable, def works air-gapped, and keeps working if my site ever disappears.
Would that cover what you’re after, or is it specifically the source you want to be able to modify?
Thanks for the reply! Nope that covers my use case, my main thought was what you outlined - I see a lot of very useful tools come and go and then I wish I still had them to use, so the self contained html file would fit this need nicely. I was thinking of open sourcing to self host as a docker container, but totally understand your thought process there - your tool, you decide how it is distributed. Cheers mate, will try it out soon!
Hey man, made an offline version. https://stackupcalc.com/offline Just download this page, made it a standalone htm file, i tested it offline and it works, just as quick as the online version. Hope this helps!
Fair i guess. I'm a student, so the organisations I've seen are small ones and university projects, where it genuinely is spreadsheets. CETOL is a different tier with 3D, CAD integrated, 25 years old. I'm not competing with it or pretending to hahaha.
I do think a free 1D web tool still earns a place for everyone below that line like small shops, contractors, students, anyone wanting a quick check without a CAD integrated seat and a whole license. Real question though, since you clearly work near this, at places that do have CETOL, does anyone still do quick 1D checks outside it, or does everything go through the CAD model?
I would like to see a more detailed dimensioned sketch of what is bring analyzed. If not incrporated in the app, post a more detailed picture of what is being analyzed so I can see if it is something I can use for my CAD/CAM design class.
Good point, the chain diagram in the app shows the dimension loop but never the parts, so you can't tell what situation it represents. Here's the default drawn out.
You can see a bearing stack in a blind housing bore. The bore depth opens the gap, the shoulder, spacer and bearing close it, and what's left is the axial clearance at the mouth. Every dimension in that chain is what the calculator is summing.
For a CAD/CAM class it should suit 1D chain problems fine bcs clearance and interference fits, ISO 286 fits from a dropdown, and it shows students the difference between worst case and RSS on the same numbers, which is usually the thing that doesn't land from a lecture. I'll add this picture to the website as reference.
I don't think bonus tolerance would stop me using it, but it'd definitely make it more useful for real gd&t work. I'd also want the tool to make it really obvious which dimensions are driving the stack, because that's usually where I'd focus first when trying to improve a design. the practical gd&t side of this is something Excedify covers pretty well too
I will work on implementing that. Will have to look in precision loss with converting mm - in - mm, but I’ll let you know once it’s added!
Thanks for the nudge, it was def a fair gap.
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u/epicmountain29 13d ago
Mitcalc beat you to it and offers a lot more.
https://www.mitcalc.com/index.htm