Nomenclature Metric Thread Tolerances Calculation

[gregormarwick]

The ultimate end goal for now is to understand how to 2D draw a M thread. 1) basic profile (done) 2) add standard defined deviations/tols via dimensions (automated expressions in my case) - work in progress. So to gain understanding and an accurate representation (in CAD) of the true geometry I am dealing with.

For instance; here goes a true representation of a ISO965 M10X1.50 6g and the mating M10.1.50 6H. How would I go about machining this non-sense with a so called full-profile ISO 60deg insert with a tip radius of 0.22mm, or should I say how much deeper I need to dive that insert in that material to have it fully machined, or ruined.

Your Q: Why? I need validation, dims, compute on screen, a reliable method, linear analysis geometry, something/anything to ref about...

View attachment 340581

ISO 965-1 Section 11 discusses the root contour geometry. Easy enough to find a copy if you can't/don't want to buy it.

Go and download some insert models from Sandvik's website. Below is a link to their basic 1.5mm external full profile M insert. Look at the point geometry - you will see that it is not a radius but a flat with fillet radii to the flanks, as is laid out in said section of the standard.

Note that the min/max root radius (the flank-root flat fillet, not a full radius fillet) of an M10 6g/6H is .188/.216mm

Sandvik Coromant

 

[dian]

file:///L:/Gewinde/schroefdraden.pdf

sfriedberg: specifying the angles would overdefine the system.

 

[mhajicek]

Do you actually need to 3D model the actual thread?

In the old days, I'd agree, you just don't model the thread, because it'll bring the computer to it's knees. These days computers handle it fine, and I've seen lots of cases where not modeling the thread results in design error or ambiguity, where the thread intersects other features.

 

[Conrad Hoffman]

Yes and no. If your interest is in fastening things together it doesn't matter too much. If your interest is in contact area, stress and dynamic friction, the angles matter a lot. If the angles are wrong, what are the definitions of pitch diameter and such? Where's the 50% point?

 

[sfriedberg]

As I mentioned earlier, and dian reinforced, this is something that frequently takes people by surprise. The flank angles are covered by the profile tolerance. I.e., if it fits within "the box", it's OK. Admittedly, the box is shaped like a helical screw (thread!) rather than a simple rectangular solid.

 

[Human]

And so just like magic, one fine and experienced individual on Practical Machinist solved this thread's question!
I am eternally grateful to Mr Conrad Hoffman for sharing his work. Everything in there, and beyond.
Anyone with similar 2D/Standards goals, get in touch with Conrad and he'll tell ya what to do.

Formulas are validated; functional and accurate by grade so all I have left to do is to convert this into expressions and tada. Can get standardized/graded geometry out of this (subject to CAD's points tol of course), all up to validating designs' stresses & strains max and thermal expansion by material properties. Solved!





And now, to cutting M threads! to all who've contributed. Thank you for all the help guys, really appreciated.

 

[gregormarwick]

And so just like magic, one fine and experienced individual on Practical Machinist solved this thread's question!
I am eternally grateful to Mr Conrad Hoffman for sharing his work. Everything in there, and beyond.
Anyone with similar 2D/Standards goals, get in touch with Conrad and he'll tell ya what to do.

Formulas are validated; functional and accurate by grade so all I have left to do is to convert this into expressions and tada. Can get standardized/graded geometry out of this (subject to CAD's points tol of course), all up to validating designs' stresses & strains max and thermal expansion by material properties. Solved!

View attachment 340643

View attachment 340644

And now, to cutting M threads! to all who've contributed. Thank you for all the help guys, really appreciated.

From your screenshot of your model it appears that you are still using a full radius root, just in case you missed my previous response, that is not the correct root geometry.

 

[Human]

Interesting, gregormarwick. I'll have a look to see if I can find a way to get into that ISO 965-1 Section 11 as you've proposed. Will probably need to procure this documentation eventually (+ a quality thread micrometer!).

On the ext insert I already have a ER16-1.50ISO with a tip radius of 0.22mm and length of 0.92mm on order. Perfect full-profile match to DIN13 6g, which is what I've based the model you are seeing here. Although I bet I'll have to stock with several other types of inserts, some probably custom in the future, but for now all I'm interested is the how-to automate deviation/tol "maths/formulas" (wip).

 

[Mechanola]

The ultimate end goal for now is to understand how to 2D draw a M thread. 1) basic profile (done) 2) add standard defined deviations/tols via dimensions (automated expressions in my case) - work in progress. So to gain understanding and an accurate representation (in CAD) of the true geometry I am dealing with.

For instance; here goes a true representation of a ISO965 M10X1.50 6g and the mating M10.1.50 6H. How would I go about machining this non-sense with a so called full-profile ISO 60deg insert with a tip radius of 0.22mm, or should I say how much deeper I need to dive that insert in that material to have it fully machined, or ruined.

I need validation, dims, compute on screen, a reliable method, linear analysis geometry, something/anything to ref about.

Do you? M 10 × 1,5 you drill, tap, and cut with a die, respectively. I don’t understand what validation could be good for this. Larger threads, okay, but for sizes up to M 100 for instance you can buy tools. I remember a nutty production manager who forced us mechanics to make 40 mm long nuts with a Tr 28 from hex bars, turned, while two transfer machines stood around unused on which we could have done the job ten times faster using sets of taps.

CNC equipment does not preclude the use of traditional tools.

 

[Human]

Do you?

Sure can thread. Give me a 60deg-anything-cutting and I'll thread you today's best thread fit within 30~25um by the hundred quantity on literally anything you can possibly imagine (excluding glass lol). Given time and parts to scrap I promise it will 'eventually fit' any mating parts you need it matting on. Anything tighter than 30um will just cost a whole lot more but equally doable and better.

Do I theoretically understand and master the M thread standard(s) and calculations? I didn't, until very recently. The purpose of this discussion (and question) was answered by Conrad Hoffman though. I now know how and have proven/functional reference formulas to validate against. Cool of him for having put up the knowledge, recommend.

haha never had to deal with nutties, sounds fun! However I do have to be compliant to Mechanical Engineers and their specifications though. Pretty serious stuff (e.g. liabilities/legal/ect)...

 

[kenton]

I might be miss interpreting what you are saying but, if you are trying to only have 30um clearance between your male and female thread, that is your issue. You need more clearance if you want to have a functional thread that can be disassembled and reassembled more than a few times.

I make a series of parts for research that have large fine threads ex M50X1. I generally cut the male threads to the top of the thread tolerance a then use it as a gauge for the female thread. When I first started I would cut the female thread so it was a nice snug fit, almost dragging a bit as I assembled the parts. All the while thinking of what a skilled and talented machinist I was. The trouble started almost as soon the the parts left the shop. Eventually that whole first assembly was brought back to the shop piecemeal with seized and damaged threads. Apparently if any dust or debris got on the threads or the threads got the slightest ding the whole assembly would lock up.

Now I aim for enough clearance that the parts thread freely together and have significantly less issues.

 

[Human]

I might be miss interpreting what you are saying but, if you are trying to only have 30um clearance between your male and female thread, that is your issue.

Ignore that. I was just trying to say (brag?) that I can cut a precision thread on whatever material, at whatever tol. As mentioned earlier in the discussion I've always used the generic/commercial lookup tables and aimed at those crests and roots. Those same static minor/major/pitch tables everybody use I'm pretty sure. Always worked pretty well, sort of.

Without necessarily, and theoretically, understanding or mastering the M thread standard(s) calculations enough to pull off my own automated thread profiles in CAD though. Works now though - I can type in any allowance grade codes and it automatically draws the entire profile, even generates the referenced solid geometry.

From that geometry e.g. I can validate let's say linear displacement and stress-max of 600N on a 6 threads engagement surface contact in 304SS, or 7075AL, and validate if this is still within max stress/displacement tolerance for a particular mat/design. Every CAD designer & analyst dream method for a M thread!

Cutting a minor & major. That's the easy part thankfully

 

[Human]

Hell I can even have in-house standard; add oxidation thickness of any given anodizing method, validate a surface contact stress/strain max's safety tol, and adjust that thread crest & root to be machined <30um for any given problem (e.g. aerospace). This is Mechanical Engineer's dream territory though, and probably more than I'll ever need to deal with in real-life.

You need to refer to the discussion title and context (calculations). This discussion is generic for designers/analysts more than machinists I would guess. Thought you all knew better than I'll ever do, and all great mathematicians already, hence why I've asked here.

Anyway. On my front I'm sorted (again, thanks to Conrad Hoffman for passing reference eq, really helped).

 

[Conrad Hoffman]

Thanks for the vote but remember, I'm more hobbyist than anything! Hint on standards. You can get free on-line copies of the British and Indian standards, which are near carbon copies of the ones you pay for. They may be a few years old, but it rarely matters. Use your Google-Fu. Example- http://www-eng.lbl.gov/~shuman/NEXT/MATERIALS&COMPONENTS/Pressure_vessels/TEMA_thread.pdf

 

[Human]

Thanks for the vote but remember, I'm more hobbyist than anything!

With all the endless stuff I (we) need to learn on-a-daily-basis that would make me pre-junior. Bet I'll remain as such until the end. So much to learn, so little time...

Thanks to you rather