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Metric thread web calculator variances

P

PeterT

Ultra Member
Premium Member
I thought I made a prior typo error, but now that I input the exact same (custom) metric thread into 3 different web calculators I've bookmarked, I see they are giving me slightly different answers.
Has anyone had this same issue? For example M30 x 1 6g (external) just comparing major diameter & pitch diameter to spot check. If the calculator provides a min/max I averaged the two just for spot check

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Metric screw thread: M Profile calculator

theoreticalmachinist.com theoreticalmachinist.com


Metric Thread Calculator

Calculate external and internal metric thread dimensions including major diameter, minor diameter, pitch diameter and thread tolerance according to ISO 724 and ISO 965 standards.
amesweb.info
 
Ok, here goes: using the M Profile Screw Thread limits from the MH 29th edition, pages 1878 to 1900, and comparing with tabulated values for the standard M30x1.5-6g thread size, we get the following values for:

M30X1.0-6g

MAX MAJOR DIA.: 29.974
MIN MAJOR DIA.: 29.794
MAX PITCH DIA.: 29.324
MIN PITCH DIA.: 29.199

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Thanks.... I think! :/
I made a typo on the Ames PD, now corrected, so this how they compare. I would never expected any discrepancy, but obviously there are subtleties to the standards or sources?
Close enough for what I need but I'll have to pay attention to this. Might explain when I was doing my CAD generate threads from formulas, they were a bit off.
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Major Dia=nominal dia - 2*(.125*(pitch*.86603)) for metric and UN threads. TR Fastener table is out right wrong. Bible ISO is closest.
 
lucsimoneau said:
Ok, here goes: using the M Profile Screw Thread limits from the MH 29th edition, pages 1878 to 1900, and comparing with tabulated values for the standard M30x1.5-6g thread size, we get the following values for:
Click to expand...
Thanks for this. Are you saying you used the formulas to validate what they show in the tables for M30x1.5 & then applied to M30x1.0 because they don't include x1.0 in the tables?
I have MH 29th too. When I didn't see M30x1.0 in tables & was too lazy to do the math opting for online calculator.

I bet the devil in the details of 'es' & 'Td' factors. I'm sure I wrote an Excel app to do this once upon a time & subsequently lost it.


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gerritv said:
Major Dia=nominal dia - 2*(.125*(pitch*.86603)) for metric and UN threads. TR Fastener table is out right wrong. Bible ISO is closest.
Click to expand...
Yes, that confused me too. Unless they mean 'nominal diameter' but they say Major Diameter. The insert sketch shows d4=major diameter (inferring some class reduced OD) so ???? I guess avoid this source.
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PeterT said:
Thanks for this. Are you saying you used the formulas to validate what they show in the tables for M30x1.5 & then applied to M30x1.0 because they don't include x1.0 in the tables?
I have MH 29th too. When I didn't see M30x1.0 in tables & was too lazy to do the math opting for online calculator.

I bet the devil in the details of 'es' & 'Td' factors. I'm sure I wrote an Excel app to do this once upon a time & subsequently lost it.


View attachment 59235
View attachment 59236
Click to expand...
That's exactly what I did - took the tabulated values for M30x1.5-6g, dug out the formulas and factor's like es and Td, then applied same logic to the 1.0 pitch that was not in the table. My years of teaching might be a bad habit but I like to sort out this type of detail.
 
I’ve noticed similar small variances between different online thread calculators before, and I think a lot of it comes down to rounding and slight differences in the formulas they use. Even minor rounding inconsistencies can add up, especially when working with fine threads.
 
ok, finally getting back to this. My table is expanding to the right. Maybe I should take the average? LOL

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@gerritv if I use your equation I get major dimeter = 29.783. Looks reasonable to me, but doesn't match the others. What is it based on?
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@whydontu thanks for dropbox link, I found direct ISO 724 link here. Now I'm more confused. They show D = d = Nominal Dia = Major dia = 30.0mm.
But that is correlating to the truncated thread section, as opposed to the sharp point (coincident with H) where i typically understood 'nominal' to be. Maybe a terminology thing but there is no tolerance class reduction to nominal in the in ISO 724 document. It does tabulate Pitch diameter & Minor diameter, but the Major diameter is suspicious.
Also if you use their formula D2 = D - 0.6495 * P D2 = 30 - 0.6495*1 = 29.3505 = what they show in table, but I'm saying uses 30.0mm as major diameter.


https://cdn.standards.iteh.ai/samples/4958/a73f8e6490d34e8d87367cc863514fcf/ISO-724-1993.pdf
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Seems to me when I generated this in CAD from base principles from Theoretical machinist, M (30 in this example) correlated to the theoretical sharp V point. I was also able to correlate their major diameter & crest flat. And by adjusting class of fit, you could see changes to Major diameter. But in this example typing in the custom Basic diameter & Pitch combination, the crest flats are shown as 0.000 so something amiss there? But the major diameter of 29.974/29.794 looks about right for 6g
And here I thought metric threads were pretty straightforward LOL

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