Al's correct. For any who want to try it, the way I used to chase threads on a
lathe was as follows. First, mount the shaft and bring it into round with your
dial indicator using a 4 jaw chuck. Next, bring the carriage up close to the
work, and engage the half nut lever while watching the thread dial for the
proper place for even and odd number threads. Let the carriage run until the
tool holder is in front of the thread. Stop the lathe and mount the V-tool in
the tool holder. Push it into the thread until it bottoms out. Make sure it is
aligned straight into the thread. Note what number you dropped the half-nut in
on. Back the tool out of the thread and watch how far out it takes to clear
using a dial indicator behind the cross-slide (for example 0.1"). Release the
half-nut and back the carriage back towards the tailstock out of the thread.
Run the tool in the amount you noted on the indicator before (0.10" example).
Start the lathe, and watch for the same number on the thre
ad dial you recorded. Drop the half-nut in on this number and try to clean it
up first with the tool just tipping the bottom of the thread. If this dont work
try taking about a 0.0005" to 0.001" deeper cut than what the bottom depth is.
This being add that to the 0.10" example you backed the tool out by. 0.005 to
0.001 inch will make the fit of the thread looser but will clean it up.
Remember, what you take on one side reduces the OD by two times. Keep a set of
thread wires and a mic handy too. That's about all I can think of but using a
good cutting fluid sometimes helps.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/13/06 at 5:59 PM Al Tanner wrote:
>>Some years ago in the dim past when production and shop machinery was
>gear driven, it was somewhat common for companies to use odd ball threads
>that were not "standard" to the industry. Another example would be the
>threads used on gasoline pumps and hoses. These were threads that fell
>"in between". This meant that the average feller could not run down to
>the local machine shop and have parts made or repaired. Instead, a new
>"factory made" part would have to be ordered and purchased. Today with
>the use of CNC lathes (computer controlled) all threads are generated by
>using the "lead" (pronounced leed) method. This is 1 divided by the
>number of threads. So a 20 thread per inch screw would have a "lead" of
>.05 of an inch, or 50 thousands of an inch. (Note: Metric threads are all
>given by "lead", not threads per meter, or anything like that). This
>"lead" system is true regardless of the diameter of the shaft. Usually
>the decimal accuracy is carried out to 5 or six places, so the 23 TPI
>would have a lead of .043478 inch. The error by rounding at this point is
>insignificant. Modern machines have no problem running ANY thread on ANY
>shaft because of this. BTW...I researched and could find no "known"
>source common to industry that makes a die of this size. Re-cutting an
>existing or damaged thread is expensive due to the time involved in
>setting up. The thread cutting tool must be perfectly aligned with the
>existing thread. This is true of ANY rethreading job, manual OR CNC.
>That's my 2 cents worth. I will now fade back to the rear of the
>room.........W8FAX
>
>
>----- Original Message -----
>From: "Rich" <rdjmgmt@socket.net>
>To: <amps@contesting.com>
>Sent: Monday, March 13, 2006 3:58 PM
>Subject: Re: [Amps] Proof of idiocy
>
>
>
>>
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