Thread depth

[4GSR]

Tony didn't mention, you can buy the Gagemaker software for about $125 if the price has not gone up. You cannot duplicate the software easily, I know it very well. But for this price, it's well worth paying the price if you deal with lots of threads like I do. I have my own excel spread sheet that I use for most of the threads I deal with in the oilfield. Lots of Acme and Stub Acme threads. BTW a copy of my excel file is in the download sections of the Forum. My program does not deal with Metric threads. That's one nice thing about the Gagemaker, it deals with all types of metric/ISO thread forms and for $125 not a bad investment in my opinion. Ken

 

[Tony Wells]

I like the Gagemaker software, because it gives dimensions for making gages, and includes data on various pipe threads and most of all, it is not simply a list of standard threads. It uses the appropriate formulas to derive the dimensions from what you give it. You want to cut a 1.900-32? It will give you all the data. And if you don't have the recommended wire, you can alter that and it will provide MOW numbers for the wires you do have, provided you accept the fact that they don't hit the pitch line. And of course, if your choice is too small it won't stand out over the major so you can't really measure it very handily. I recommend it too, and have known the main distributor for about 20 years I guess....other than a friend, he's been a good vendor for me.

Although it won't do RSC or API style threads, unless the newer version does, that's the only drawback I can see. The company also offers tools for measuring those threads, but I believe it is in a different software package, although I'm not certain about that.

Their whole claim is that you do not need solid plug and ring gages. You can inspect each thread element independently and make a determination of acceptance or rejection. If that is true, and I won't say it is or isn't, even though their system is expensive, so is a complete set of solid gages. Even more expensive, by a long shot.

 

[pstemari]

How do you calculate the compound depth for a given pitch? Trying to figure out the calculation is kicking my ass.

For a sixty degree UN thread, it's 5/8 * the pitch. E.g. for a 20 TPI thread, the pitch is 0.050" inches and the compound travel is 0.03125.

It's not a particularly useful measure, though, since any error in the width of the flat on the end of the thread tool will get reflected in the pitch diameter. Better to measure the PD using a thread mic or thread wires.

...Their whole claim is that you do not need solid plug and ring gages. You can inspect each thread element independently and make a determination of acceptance or rejection...

Simple Go/No-go plug and ring gages can't measure all of the thread elements, although arguably they measure the ones that matter. For example, if the pitch diameter of an external thread, is ok, but the root is cut too deep, a simple no-go gage won't fit. Same is true of a internal thread whose minor diameter is too large. You'd need three no-go gages to test the usual thread parameters.

 

[BGHansen]

When I cut Threads, I mount my Dial Indicator on the Back of my Crossfeed and have the indicator measure off the back of my QCTP. As I feed in the compound, the indicator gives me the depth without having to calculate based on angle and compound depth of feed. I just have to remember to divide the difference between the Major and Minor Diameters by 2. (Almost forgot on the last one )
View attachment 155936

Great idea, wish I'd have thought of that!

Bruce

 

[mikey]

In my mind, the only measurement I can take from a female nut is to just caliper the major diameter and calculate from there to decipher the male thread.

What I'm trying to sort out is, when you go to make the new male thread, what do you do with that female major diameter? How much smaller do you go to make the male thread? Is there a rule of thumb? Do I just refer to the charts and use the min/max? What do you guys do?

Shawn, I just re-read my responses to this thread and I recalled that I saw something about how to figure out the size of a male nominal OD when only the female part is known. It bugged me that I didn't answer you accurately so I went looking for it and found it: http://mdmetric.com/tech/tict2011.htm#cht8

I read this years ago but forgot about it. Don't laugh; when you get to be my age you'll be happy just to remember to get out of bed in the morning. Anyway, scroll down to the bottom of the text section and you'll see Chart VII: HOW TO CALCULATE THE APPROXIMATE NOMINAL MAJOR DIAMETER (O.D.) OF THE METRIC MALE (EXTERNAL) THREAD WHEN ONLY THE FEMALE (INTERNAL) METRIC THREAD IS AVAILABLE FOR MEASUREMENT.

Take a look at the instructions and you'll see how to size the male part. This is for a metric thread and I don't know if the Factor Value, R, applies to imperial threads. I have sent an email to Maryland Metrics about this and will put their answer in this thread if they ever respond.

So, from the ID and pitch of a female threaded part, you can determine the nominal OD of the mating male part. You then cut the external threads on the male part using the tolerance specs you choose and the parts should fit. Hope this helps.

 

[Hukshawn]

Now there we go...
you said before, the collet cap will likely be metric anyways, so this should help with this project.... whenever that damn thing shows up...

 

[KBeitz]

You would thing that someone would make a Dial Indicator that would read half
for things like this...I would think it would be a HOT selling item...

 

[pstemari]

The ideal major/minor diameter have the same proportions for ISO metric and UN inch threads: major diameter = minor diameter + 2 × ⅝ × (the sharp v height), where the sharp v height = (cos 60°) × ½ × pitch.

That said, those instructions will only get you sort of close. The minor diameter of an internal thread varies depending on the amount of thread engagement, and frequently the minor diameter is drilled oversize to make tapping easier.

Going back to the OP's question, the depth on the compound would ideally be ⅝ × pitch = 0.625/TPI, but that typical isn't a useful measurement since it depends on the tip of the tool having a flat of exactly ¼ × pitch. If the flat is narrower, then the cut must be that much deeper. If the tool is perfectly sharp, then you would go in ¾ × pitch = 0.75/TPI.