I’m curious what others are doing for accurate design profiles for threads, internal and external. I know some use a thread tool, I’m not asking about this, I’m aware of it (in SolidWorks) and know how to modify the profiles and use it. I’m looking for machinable or accurate design profile threads.
Assuming a swept profile around a helix, how are you dimensioning the thread sketch profile using the data form a calculator or Machinery’s Handbook? I get the form is simple, it’s a truncated triangle or a triangle with a radius, but it really depends on the tool making the threads, right? Assume machined thread with root radius for the moment. There are several ways to ‘define’ the sketch using the values provided in the book or from the calculators.
dimensioning the pitch diameter + root radius
dimensioning to the root radius + tangent of the root radius to be the Minor diameter?
dimensioning to height of the profile or width of root, truncation of triangle…etc. etc.
It seems the ‘proper’ way to measure the threads is based on the pitch diameter over wires. But the machinist only knows the tip of his tool position and it’s radius. So is the ‘proper’ way to dimension the sketch to the tangent of the root radius with the root radius specified?
If anyone has a sketch or nut + bolt thread assembly (SW) they could share containing proper design profiles using values from a published source, I would really appreciate it!
Here’s an example of an M28x1 thread I’m working on. Calculator is METhreadPal. The sketch shows the full root radius 0.144*P and the Minor Diameter (max) used to define the thread with a driven dimension showing the Pitch Diameter to ensure it falls in the range specified.
I call out the thread and the machine shop does the rest. They neither need nor want accurate threads in the model. The machine shop owns the proper metrology equipment to ensure the threads meet the standard.
Thanks for the replies so far. I’ll also state that I know how to call out threads on a drawing but the intent here is to draw threads as machined. I know there are many people that do not need do this but I often combine molded and machined threaded parts and would like to understand the ‘proper’ way from a machinist’s perspective or someone who’s been bitten by doing it wrong lol.
Not really taboo.
More like don’t reinvent the wheel. Don’t try to make a better wheel unless you really have a really good reason to.
Repairing old press will get into odd thread and spline/gear teeth.
‘Standard’ threads are straight-forward, it’s when you take a look at ones
used in astro-photography and equipment when the fun starts
Apparently, it’s kind of a mess
All great resources for calculating the numbers, the challenge is choosing which numbers to use for defining the sketch for both mating threads. It’s relatively easy when we’re talking about a basic thread profile but we’re not here, we’re provided ranges of min/max where you have to choose ‘a number’ when sketching. So which is the ‘driving’ dimension?
Pitch, pitch diameter and thread angle. They’re the same for Internal and external.
Minor and major diameters are cut off the sharp points and clearance.
If you can get your hands on a copy of Machinerys Handbook, it goes into the math that describes an American Standard thread. I would take those equations (or similar ones for a metric thread) and apply it to whatever it is you are trying to manufacture.
On the rare occasion where I need to show threads for a drawing it’s only to show the length. I still call out the thread type with a note, and I never use the Part with threads in an Assembly. I use a configuration with the threads suppressed for that.
