Using thread wires

[Holescreek]

I did a search in the forum for " thread wires" and didn't get any hits so forgive me if this has been discussed already.

I have to make an odd sized tap to make some replacement parts for an old steady rest I am adapting to my lathe. The thread size is 7/16-10 LH (not ACME). While I was out there finishing the threading portion I remembered all the times I have heard coworkers complain that they didn't like using thread wires because they are too hard to hold while measuring. I thought this might be a useful tip for anyone that is curious about using thread wires.

Thread wires are cheap. For $12 they are the cheapest tool you can buy to measure threads for size (pitch diameter).

Each set contains several sizes of wires in matched sets of 3 wires each and a chart which tells you what size wire set to use for the pitch of the thread you want to measure ie 10-32 = 32 pitch. The chart also ists an "add" and "constant" number for each pitch/wire combination.

The way thread wires are used is to place 2 wires on one side of the thread and a single wire on the other side of the thread and measure over the wires with a micrometer. The "trick" is to hold all those wires in place while you fumble with a micrometer to get the measurement. Good luck finding those wires in your chip pan! I wrap tape around 2 wires then leave a bit hanging off to attach to the third wire.

With this setup you can place the wires into the V of the thread and hold them there by pinching the loose end. This leaves a hand free to measure with.

 

[Holescreek]

Once you get your measurement over the wires, add the number in the "add" column to it then subtract the number in the "constant" column from the total. Compare this total with the pitch diameter specified for your thread. The pitch diameter can usually be found in the machinist handbook, on the web, or in a computer program. Once your pitch measurement is in the range specified, you are done. -Mike

 

[rake60]

Nice tutorial Mike!

Thanks for taking the time to document the use of
thread wires.

Rick

 

[te_gui]

Nice documentation job. I might add a little grease can help hold them in too. Lots of folks have never seen them. I just used them earlier this week to measure an o-ring groove depth as well.

Brian

 

[BMyers]

nice, is that chart down loadable from anywhere ?

 

[Maryak]

Mike,

What a neat trick with the tape to hold the wires. :bow: :bow:

Best Regards
Bob

 

[Holescreek]

nice, is that chart down loadable from anywhere ?

Don't know. There are actually 3 charts; metric, Acme, and U.S. I believe that the wire set is made by Fisher Machine in CA. A quick google search told me that I bought my set a long time ago, new price from Fisher $22. I have only had this set about 9 years.

I have a computer program I purchased for $50 (ME Threadpal) which has all of the standard and international thread specs and allows you to enter your own sizes and it will calculate all of the data for you, including entering the diameters of the wires you actually have vs. what sizes are called for. I bought a copy for work as a large part of my job involves non-standard threads used in automotive.

There are a few gadgets that are made for holding the wires for you. None as cheap as a piece of tape. :hDe: -Mike

 

[mklotz]

There's a free program on my page (3WIRE) that will function in lieu of a table. Here's an example output...

THREE WIRE THREAD MEASUREMENTS (60 degree threads)

(M)etric or [I]mperial threads?
Thread pitch [20 tpi] ?

Most common threads are single start.
Number of starts [1] ?

Best wire diameter to use = 0.7332 mm = 0.0289 in
Wire diameter used [0.0289 in] ?

For American National Thread form, subtract 0.0325 in from
major diameter (assumes p/8 flat on crest) to obtain pitch diameter.

Major diameter of thread [0.25 in] ?

pd = pitch diameter, mow = measurement over wires
Calculate pd from mow (p) or mow from pd [m]?
Pitch diameter of thread [0.2175 in] ?

Measurement over wires = 6.6279 mm = 0.2609 in

 

[kvom]

We just had a unit on this topic at school. Rather than calculate the PD from the wire measurement, we took a slightly different approach.

For each given thread, Machinery's Handbook lists a max. and min. PD. Given a wire size, you can calculate the range of measurements that fall within the PD range. Then you just measure across the wires and see if you're within the range.

 

[Davyboy]

Great tip! :bow: In 30+ years in the trade, I've taped 2 of the wires together, but not all 3, and I never thought to put my fingers on the other side of the part

One thing I do is to put a shop rag or towel across the ways, so when I drop the wires, they don't go into the pit. The towel catches them.

DB

 

[lugnut]

Thanks for sharing. And now there is another tool to buy.
Mel