Thread: Stub Acme - help :)

I'm trying to help a customer who's been asked to make some parts with an external and internal thread to the following spec.

2.500-10 Stub Acme - 2G

The customer's customer has given them specs with all thread diameters and the tolerances.

My problem is that I don't arrive at the same numbers as on the applicable specs. When my customer (on my advice) asked his customer to check the specs the reply was in effect "make it to our damn specs" so it's mostly just a question of whether I'm right or wrong for my own peace of mind

I'm looking for d, d2, d1 and D, D2 and D1 with tolerances.
For what it's worth I get the nominal pitch diameter (d2/D2) to 2.470"

If Mrainey reads this I'm sure he can answer but I'm open to all responses.

Gordon (with his fingers crossed)

When (if?) I get an answer I'll let you know if I was right or wrong

This is the ThreadPal output.

Inch Units

2.5000-10-STUB ACME (External)
Allowance,0.0126
Major Diameter Max,2.5000
Major Diameter Min,2.4950
Pitch Diameter Max,2.4574
Pitch Diameter Min,2.4384
Minor Diameter Max,2.4200
Minor Diameter Min (Ref),2.4010
Crest Radius,--
Root Radius,--
Flat At Root,0.0403
Thread Height (Basic),0.0400

2.5000-10-STUB ACME (Internal)
Allowance,--
Minor Diameter Min,2.4400
Minor Diameter Max,2.4450
Pitch Diameter Min,2.4700
Pitch Diameter Max,2.4890
Major Diameter Min,2.5200
Major Diameter Max (Ref),2.5390
Flat At Root,0.0371
Thread Height (Basic),0.0400

Pitch,0.1000
Lead,0.1000
Starts,1
Lead Angle,0.742

Included Angle,29.0000

Originally Posted by mrainey

This is the ThreadPal output.

A million thanks. I'll check it against what I came up with but I have no doubt you are spot on

You've made my day

I've checked my figures and they are very close to yours. Given the choice I believe yours The specification my customer has though isn't the same as either of us and much further off.

I have the guy that made the specs suspected of inventing his own sizes and tolerances. To make things worse all the pitch diameter diameter tolerances are given from measurements over thread wires and balls.

As my customer wants to measure with my thread inserts (and what you see is what it is) then what he needs are the thread max/min pitch diameter tolerances as they are on the finished thread. It's this information the customer refuses to give. I suspect that the guy that made the original spec has left the company and those left haven't a clue

Maybe your fantastic program could tell me the max/min pitch diameter tolerance if the thread was measured over 1.35mm thread wires? I don't even know how much they've compensated the lead angle by, not that it'll make much difference here.

Max over 1.35 wires = 64.249
Min over 1.35 wires = 63.767

I've done threads all kinds of ways for the oilfield. Standards aren't always applicable, sometimes it is a 4g when it doesn't specify, sometimes it is the way they have always done them, simple for the machinist, i.e. major and minor with a thread height. I just ask the guy, tell him what I think is expected, if he says different, it is how it is. The customer is always right if he pays for it.

Originally Posted by mrainey

Max over 1.35 wires = 64.249
Min over 1.35 wires = 63.767

And even in mm Again 1,000 thanks. I owe you

That's only 0.004 to 0.005mm from what the customer writes it should be I regard that as insignificant as the company making the threads have no problem keeping well away from the tolerance limits.

Originally Posted by mrainey

Max over 1.35 wires = 64.249
Min over 1.35 wires = 63.767

If you have no objection I'm going to put a link to your website on mine under "Useful links".

I get on average about 75 visits a day (and of course many more hits) but of course can't guarantee anything It'll be your ThreadPal in English and German that'll get a special mention.

I won't do it until I get your OK

Gordon

Originally Posted by Mydrrin

I've done threads all kinds of ways for the oilfield. Standards aren't always applicable, sometimes it is a 4g when it doesn't specify, sometimes it is the way they have always done them, simple for the machinist, i.e. major and minor with a thread height. I just ask the guy, tell him what I think is expected, if he says different, it is how it is. The customer is always right if he pays for it.

I wouldn't have any problem with that either but the minimum requirement is that the customer knows what he wants and says so. Either that or be open to suggestions. Neither IMO were the case here

If you have no objection I'm going to put a link to your website on mine under "Useful links".

I get on average about 75 visits a day (and of course many more hits) but of course can't guarantee anything It'll be your ThreadPal in English and German that'll get a special mention.

I won't do it until I get your OK

Gordon

That would be an offer I truly cannot refuse.

Originally Posted by mrainey

That would be an offer I truly cannot refuse.

If you click on my name and open my website you can see I've got it on the 3 language versions I have on my website
Third column near the bottom.

I've only put your ThreadPal segment in as a link but that should at least convince inquirers that you know your business with the other stuff you have

Gordon

Looks good. Thanks, Gordon.

Mike

Originally Posted by mrainey

Looks good. Thanks, Gordon.
Mike

I had a company (Danish) today on the phone that seems interested
Let's hope you get orders from Denmark although there are many other countries looking at my website.

I'm not looking for percentages LOL

Gordon

Originally Posted by mrainey

This is the ThreadPal output.

Inch Units

2.5000-10-STUB ACME (External)
Allowance,0.0126
Major Diameter Max,2.5000
Major Diameter Min,2.4950
Pitch Diameter Max,2.4574
Pitch Diameter Min,2.4384
Minor Diameter Max,2.4200
Minor Diameter Min (Ref),2.4010
Crest Radius,--
Root Radius,--
Flat At Root,0.0403
Thread Height (Basic),0.0400

2.5000-10-STUB ACME (Internal)
Allowance,--
Minor Diameter Min,2.4400
Minor Diameter Max,2.4450
Pitch Diameter Min,2.4700
Pitch Diameter Max,2.4890
Major Diameter Min,2.5200
Major Diameter Max (Ref),2.5390
Flat At Root,0.0371
Thread Height (Basic),0.0400

Pitch,0.1000
Lead,0.1000
Starts,1
Lead Angle,0.742

Included Angle,29.0000

Min pitch dia & min minor dia.
External, have not done internal yet.

Min = Max/pitch/minor/dia (-) class 2G tol from table 5 (.006xsqurtD) =(.00949), would give pitch min dia of 2.4479 and min minor dia of 2.4105?

Cheers,

[QUOTE=LESAWHARRIS;1744017Min pitch dia & min minor dia.
External, have not done internal yet.

Min = Max/pitch/minor/dia (-) class 2G tol from table 5 (.006xsqurtD) =(.00949), would give pitch min dia of 2.4479 and min minor dia of 2.4105?

Cheers,

[/QUOTE]

I'm not quite following you.

Table 5? Which standard are you referring to?
ACME SCREW THREADS ASME/ANSI B1.1 or
STUB ACME SCREW THREADS ASME/ANSI B1.8

Remember too that the OD is 2½". That with 10TPI makes it an unusually fine Stub Acme thread.

Gordon,
Machinery's handbook 24, page 1624 Stub ACME, Table 13a page 1624, ASME/ANSI B1.8-1988, formulas for determining Diameters. No 6 Minor dia -Min = Minor dia max, minus Class 2G pitch dia tolerance from table 5, (page 1613) 2g tolerance = .006x SqrtD, D=2.5" the O.D. book table lists 0.00949, as calculated 0.009486833.

Just checked my old 19th edition, ASA B1.8-1952, same deal different page #'s. Min minor dia = Max minor, minus 2G tolerance = .006 x sq rt D,

Did not want to create confusion, was curious, ran through the numbers, and tilt!

Cheers,

Looking at the Twenty-Seventh Edition of MH, Table 5 has some fine print at the bottom:

"For any particular size of thread, the pitch diameter tolerance is obtained by adding the diameter increment from the upper half of the table to the pitch increment from the lower half of the table."

In Gordon's example, the diameter increment is 0.00949 and the pitch increment is 0.00949, for a total tolerance of 0.0190

[QUOTE=LESAWHARRIS;1744757]
Gordon,
Machinery's handbook 24, page 1624 Stub ACME, Table 13a page 1624, ASME/ANSI B1.8-1988, formulas for determining Diameters. No 6 Minor dia -Min = Minor dia max, minus Class 2G pitch dia tolerance from table 5, (page 1613) 2g tolerance = .006x SqrtD, D=2.5" the O.D. book table lists 0.00949, as calculated 0.009486833.

Just checked my old 19th edition, ASA B1.8-1952, same deal different page #'s. Min minor dia = Max minor, minus 2G tolerance = .006 x sq rt D,

Did not want to create confusion, was curious, ran through the numbers, and tilt!
Cheers,
QUOTE]

Les (?), I hope you and other PM members are sitting down as you read this but I don't have a MH. What I do have is a rather large amount of official thread standards and norms. As I have the two relevant (mentioned in post #15) and they both have a Table 5, I never for a second dreamed you were referring to something else
Gordon

Gordon,

I've been following this thread since you started it and what mrainey has said I agree with, too.

Let me add one thing to this discussion that I ran into almost twenty years ago with stub acme threads in general. I deal with lots of stub acme threads from small to large diameters in various pitches, especially 8 pitch in general.

Given your example of 2.500-10 Stub Acme-2G thread. When you get into the fine pitches like 10 ptch and finer on larger diameters such as this, the root width gets rather wide on external threads when the OD get big. With this happening, I've see thread measuring wires "bottom" out in the root of a thread without touching the "flanks" of a thread, giving a false reading of the "measurement over wires."

This same seneria exists with Gagemaker roll system, too! So you have to be very careful how you check thread pitch diameters.

Having said that, I wonder if your customer has this issue and has not been able to identify it or live up to it?

Ken

I've see thread measuring wires "bottom" out in the root of a thread without touching the "flanks" of a thread, giving a false reading of the "measurement over wires.

I noticed that too. In order to get a useable min wire size, I made CAD drawings up for each pitch and used them instead of a formula.