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Old 07-28-05, 09:52 PM   #1
phantomcow2
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If you have a 16tpi screw...

Okay im trying to modify something here. Is there some mathematical way to calculate this?
If you have got a 16tpi screw and say you had a nut on there. One revolution would advance the nut how much?
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Old 07-28-05, 10:12 PM   #2
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16tpi = 16 threads per inch.
So if you have like, a 3/8-16 screw, for every inch along the length, it makes 16 threads. Each thread is 1 revolution which brings it 1/16th the distance of 1 inch.

y=(d/360)(1/t)

d=# of degrees of revolution
y=distance advanced
t=tpi

It's basically how a mic works. If you can control and fine tune the turning of the nut to 5 degrees per second by hand, then you're basically advancing it by 0.000868 inches per second.

I think the electron microscope we had had the specimen mount on a couple of pivots that used some really long 50tpi bolts. We were able to control it to 1/8 a degree at a time. Which turns out to be like 0.000007 inches of precision by hand, or 0.176 microns.

Last edited by slvoid; 07-28-05 at 10:19 PM.
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Old 07-29-05, 04:03 AM   #3
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This is a trick question, right?
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Old 07-29-05, 06:11 AM   #4
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Hmm.. actually, with a double helix, wouldn't 16tpi really mean 1/8th per revolution? I'm gonna have to test this at work...
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Old 07-29-05, 07:05 AM   #5
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oh yea, its 1/16, i dont know why I did not remember that.
I think i need to go to bed, thanks Slvoid.
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Old 07-29-05, 07:09 AM   #6
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Quote:
Originally Posted by slvoid
Hmm.. actually, with a double helix, wouldn't 16tpi really mean 1/8th per revolution? I'm gonna have to test this at work...

Dont think so... 1, 2 or 4 threads, if you have 16 of them per inch, per thread one revolution will result in 1/16" of travel
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Old 07-29-05, 07:24 AM   #7
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Quote:
Originally Posted by slvoid
16tpi = 16 threads per inch.
So if you have like, a 3/8-16 screw, for every inch along the length, it makes 16 threads. Each thread is 1 revolution which brings it 1/16th the distance of 1 inch.

y=(d/360)(1/t)

d=# of degrees of revolution
y=distance advanced
t=tpi

It's basically how a mic works. If you can control and fine tune the turning of the nut to 5 degrees per second by hand, then you're basically advancing it by 0.000868 inches per second.

I think the electron microscope we had had the specimen mount on a couple of pivots that used some really long 50tpi bolts. We were able to control it to 1/8 a degree at a time. Which turns out to be like 0.000007 inches of precision by hand, or 0.176 microns.
I wouldn't presume to debate your math, but I think the TPI in question is actually TURNS per inch, not threads. It's almost the same thing, and the terms are sometimes used interchangably. That tells you how many revolutions it takes to travel and inch, regardless how the threads are formed. A 16 tpi double helix thread will still take 16 turns to go an inch. A 20 tpi screw will give you .050" movement for every revolution. The exception to that is if you have a right handed thread on one end, and a left handed thread on the other. When you turn that shaft, the nuts on each end will move away (or toward) each other at twice the distance a single thread would give you. Using the 20 tip screw for example, the individual nuts would only move .050" per rev, but since both of them move, so you'd get a .100" change in the distance between them.

Have a good day, I'm off for the weekend!
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Old 07-29-05, 07:24 AM   #8
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I think it is 1/16 an inch. Im trying to make a handwheel to turn the leadscrew on my lathe for finer movements, and while im at it I would like a little dial that tells me how far I have moved the carriage.
I know a 20TPI screw moves whatever in .050" so that sounds right
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Old 07-29-05, 08:05 PM   #9
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If you're not sure, turn it 16 times and measure (to minimize the % error).

Anecdote: There is a story that Thomas Edison wanted to know the volume of one of his light bulb designs, so he handed it to mathematician and asked him to figure it out. A couple hours later, he returned to find the man still busily calculating by attempting to integrate approximated curves. Impatient, Edison filled the light bulb (which had was not closed off on the end) with water and poured it into a beaker. Moral: sometimes you've got to get your hands dirty (in this case wet) in order to figure something out.
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Old 07-31-05, 09:08 AM   #10
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Quote:
Originally Posted by iamlucky13
If you're not sure, turn it 16 times and measure (to minimize the % error).

Anecdote: There is a story that Thomas Edison wanted to know the volume of one of his light bulb designs, so he handed it to mathematician and asked him to figure it out. A couple hours later, he returned to find the man still busily calculating by attempting to integrate approximated curves. Impatient, Edison filled the light bulb (which had was not closed off on the end) with water and poured it into a beaker. Moral: sometimes you've got to get your hands dirty (in this case wet) in order to figure something out.
You ever heard that story of the scientists at the conference who were having breakfast at a restaurant, there was a salt shaker and a pepper shaker on the table but it turns out that the salt was in the one with the cap labeled "pepper" and vice versa. While they were busy trying to figure out a way to transfer the contents back to their appropriate containers with mimimal waste, the waitress comes over and switches the caps on the shakers.
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Old 07-31-05, 04:21 PM   #11
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over-engineering is one of my biggest complaints.

We have a guy at work here who does this all the time, it's funny to see him nearly bust a vein in his forehead over figuring out how to secure a nut onto a bolt that has varing tension between the inner edge of the nut and the inner edge of the bolt head. I just went to the supply rack, got some red loctite, and dabbed some inside the nut and put it in place.

...even more amusing was he got pisse off over it since he couldn't figure it out...(I like giving him a hard time since he always brags about his monstrous IQ number...he's great at math and electronics especially, but he's not the best at mechainical issues, and with an ego like that...it's hard not to see him imitate a steam whistle from time to time. )
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Old 08-02-05, 05:47 PM   #12
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Quote:
Originally Posted by phantomcow2
I think it is 1/16 an inch. Im trying to make a handwheel to turn the leadscrew on my lathe for finer movements, and while im at it I would like a little dial that tells me how far I have moved the carriage.
I know a 20TPI screw moves whatever in .050" so that sounds right

You can buy those dials already graduated at some of the industrial supply stores. In fact, you can get the lead screw material with UNF, Acme or Browne & Sharp threads there too. Look at MSC or Reid or one of those. The crank handles are available there too.
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Old 08-03-05, 06:27 AM   #13
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Quote:
Originally Posted by slvoid
Hmm.. actually, with a double helix, wouldn't 16tpi really mean 1/8th per revolution? I'm gonna have to test this at work...
Pitch: The axial distance between two adjacent thread forms.

Lead: The axial distance moved in one complete rotation.

(Simplified definitions from Machinery's Handbook)

You are correct, slvoid. Normally, pitch and lead are the same.

For a double thread, 1/16 Pitch would be 1/8 Lead. Triple thread, 3/16 lead.

In many cases in my work (I design valves and actuators), I need to design multiple lead threads on a shaft to meet the speed requirements of whatever I'm driving. You just have to be careful with multiple lead threads; you may have a situation where you can back-drive the motor if the weight you are trying to move is too great.
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Old 09-13-17, 03:45 AM   #14
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Interesting facts

Quote:
Originally Posted by phantomcow2 View Post
oh yea, its 1/16, i dont know why I did not remember that.
I think i need to go to bed, thanks Slvoid.
What's great about the 16 tpi is, you can control a all thread like a 3/8 rod, to move a table saw or metal saw... fence 1/6" left or right per 1 full revolution of the attached rod handle. 1/2 turn is 1/32". That helps when you want high accuracy of cuts.Just check the fence with a square to make sure its square when setting it up.
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Old 09-13-17, 05:19 AM   #15
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Originally Posted by VideoTracx View Post
What's great about the 16 tpi is, you can control a all thread like a 3/8 rod, to move a table saw or metal saw... fence 1/6" left or right per 1 full revolution of the attached rod handle. 1/2 turn is 1/32". That helps when you want high accuracy of cuts.Just check the fence with a square to make sure its square when setting it up.
That's just great. These folks have been waiting 12 years for you to show up and set them on the right path. Now they can rest easy.

What took you so long? Bus running slow or what?
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Old 09-13-17, 12:51 PM   #16
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A micrometer uses a 40 tpi thread which results in 4 turns to .1 inches or 1 turn = .025 or 25 thousandths. A micrometer barrel is divided into 25 sectors so that 1 sector rotation is 1 thousandth .001. My micrometer has a vernier scale on it to divide that thousandth into 10, making it can read to .0001.
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Old 09-13-17, 01:01 PM   #17
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Quote:
Originally Posted by slvoid View Post
Hmm.. actually, with a double helix, wouldn't 16tpi really mean 1/8th per revolution? I'm gonna have to test this at work...
True but a standard bolt is a single helix.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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Old 09-13-17, 01:04 PM   #18
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Quote:
Originally Posted by slvoid View Post
Hmm.. actually, with a double helix, wouldn't 16tpi really mean 1/8th per revolution? I'm gonna have to test this at work...
I believe that double helix screws are referenced by the true pitch of the thread. So a 16tpi double helix thread would still advance 1/16" per turn. But it would look like a 32tpi screw.

Just checked. The pitch on a double helix refers to the distance between the two adjacent crests. And the movement of the nut would be called the lead.

So a 16tpi double helix screw would have a pitch of 1/16" and a lead of 1/8". But what I said originally is right for metric screw nomenclature.
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Old 09-13-17, 01:05 PM   #19
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N threads per inch means it moves 1/n inches per turn.

You can't overthink that.
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Old 09-13-17, 01:10 PM   #20
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Quote:
Originally Posted by catatonic View Post
over-engineering is one of my biggest complaints.
Early on in my career, I switched from a company that made aircraft parts to one that made heavy machinery. I had to mount a linking and had designed a bracket to hold one of the pivots. I used thin sheet metal and was doing some calculations to make sure it wouldn't flex too much under load. My lead walked up behind me and asked, "What are you doing?"

I explained, and he followed up with, "You're not working on aircraft anymore. Make the bracket 1/2" thick. If it breaks, make it an inch thick!"



I guess I was over-engineering the bracket.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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Old 09-13-17, 01:32 PM   #21
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Giggle

This completely reminds me of the "if you are travelling 60 miles per hour" question that gets posed on the late night comedy shows from time to time.

Don't you love when you answer your own question in the wording?
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Old 09-13-17, 04:18 PM   #22
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.....................................1/16th the distance of 1 inch.

(brevity snip)

.
correct
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Old 09-13-17, 06:51 PM   #23
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A legit necro bump on account of my old buddy Stacey.

If there's a foo heaven, you know she's got a hell of a pet rat herd.
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Old 09-14-17, 05:49 AM   #24
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A legit necro bump on account of my old buddy Stacey.

If there's a foo heaven, you know she's got a hell of a pet rat herd.
Wow. It got us all. '05 is a long time back.
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Old 09-15-17, 07:09 PM   #25
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Wow. It got us all. '05 is a long time back.
For fun, lookup some more phantomcow threads.
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