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Ken_Shea
06-07-2008, 09:54 PM
Have turned my share of inch threads but never a metric, I have a 22x2.5 to turn tonight.

Had to change a couple gears and the dials are set but I see no pitch settings on the thread dial placard.

Any ideas on which and/or what to use :confused:

Ken

garyphansen
06-07-2008, 10:58 PM
If you have an inch lead screw, you need to leave the half nuts engaged until you are done cutting the thread. Make a pass, stop the lathe, back up the cross slide reverse, and repeat. Gary P. Hansen

Ken_Shea
06-07-2008, 11:52 PM
Found the lathe owners manual and that is exactly right Gary, you have to be kinda quick on backing out the cross-feed too. It is done and came out very nice, I learned a thing or two tonight so that is a good thing.


Thanks
Ken

dp
06-08-2008, 12:20 AM
Evan made and excellent cross slide stop for threading, and I copied it. Works perfectly:
http://vts.bc.ca/metalshop/tstop/tstop.htm

As awkward as metric threading can be, this little gadget helps to pick up the pace.

oldtiffie
06-08-2008, 12:36 AM
There is another way (2 actually) as per the excellent set of utilities my Marv Klotz, a long-time member of this board.

It is at:
http://www.myvirtualnetwork.com/mklotz/files/stick.zip

Open the stick.txt file in the stick.zip archive which will explain it all.

The "intro" can be found at "Stick" in Marv's utilities at:
http://www.myvirtualnetwork.com/mklotz/


Tired of running the lathe in reverse when cutting metric threads on a lathe with an Imperial leadscrew? Peter Lott, writing in Machinist's Workshop (6/01, vol. 14, no. 3) outlined a technique for getting around this annoyance. I programmed the calculations involved in his approach. As a bonus, the program also allows the technique to be applied to any combination of metric/Imperial leadscrew/thread-to-cut, a feature not covered in Peter's article.
Marv's utilities are a gold mine.

Ken_Shea
06-08-2008, 12:52 AM
Dp, I had seen that and also forgotten it, I have cut so many threads that my back off cranking distance is almost precise :) so while that does look useful I am not sure how beneficial it would be at least with Inch threads, probably more so with the metric that I am unaccustomed to cutting.

oldtiffe, that looks very interesting, unfortunately, I can never get those programs to work, they run and then just close immediately after getting the results.

Ken

dp
06-08-2008, 01:34 AM
Dp, I had seen that and also forgotten it, I have cut so many threads that my back off cranking distance is almost precise :) so while that does look useful I am not sure how beneficial it would be at least with Inch threads, probably more so with the metric that I am unaccustomed to cutting.

When I first got my lathe it didn't have a thread dial, so the first solution for me was Evan's stop. I fortunately don't have a big need to turn metric threads, the the last time I did, out came that stop! :)


oldtiffe, that looks very interesting, unfortunately, I can never get those programs to work, they run and then just close immediately after getting the results.

Ken

You need to open a Windows command line (DOS) window and run them from that. The window will then stay open for you.

oldtiffie
06-08-2008, 06:36 AM
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oldtiffe, that looks very interesting, unfortunately, I can never get those programs to work, they run and then just close immediately after getting the results.

Ken



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You need to open a Windows command line (DOS) window and run them from that. The window will then stay open for you.

Thanks Ken and Dennis.

Dennis almost has it right.

"Windows" has an excellent "DOS" (pre-Windows Disk Operating System) - all-be-it somewhat restricted - but it works very well.

Marv Klotz has made it very clear that his utilities are made (mostly) to operate under/in a "DOS environment".

First of all, create a new folder for the utilities, say C:\hsmutil

Then insert the utilities into this folder as advised in Marv Klotz' instructions.

To use this feature, go to "Start" (lower left of screen)

Start>Run>Cmd>Browse select c:\hsmutil

Then type the name of the executable file (usually *.exe or *.com)

Follow the prompts to fill in the required values and press "return" to execute the command.

"DOS" is a "command-line" driven system that is not the least bit forgiving for errors in/of syntax or "typos" - so be careful - you may use the "backspace" and "delete" keys more than you will imagine!!

It can be as frustrating and (for Windows users) as difficult as ...........................

But once "on top" of it all, the system is very fast.

Once on top of it, try more of Marv's utilities as they are gems.

Read the *.txt files as they contain a lot of information.

deltaenterprizes
06-08-2008, 06:46 AM
What is the purpose of the stop?

ptjw7uk
06-08-2008, 07:22 AM
The stop is so you can vary the length of the threaded section as I believe Evan uses a handle to turn the headstock when threading.
I have been thinking that it should be possible to add an intermediate gear between the indicator gear and the threading screw although not done the maths although the 25.4 to 1 is not easy in small sizes.
Just a thought.
Peter

oldtiffie
06-08-2008, 07:38 AM
Not that I think its relevant in this case, but as it is mentioned, there is at least one set of gears that will approximate 2.45 very well.

47/37 x 2 = 1.2703 x 2 = 2.504

The 127 gear used in many gears trains for conversion between metric and inch threads is:
25.4 x 5 = 127

Either will work if you keep the half-nuts engaged.

127 is preferred as it is an exact multiple of 25.4

47/37 x 2 x 10 = 25.4054

Which is: ((25.4 - 25.4054)/25.4) x 100/1 = ((-0.0054)/25.4)) = (-.0213)% which in most cases is negligible and can be safely ignored.

Ken_Shea
06-08-2008, 10:02 PM
Dennis, the dos window took care of that problem.

oldtiffe, your suggestions would surely speed thing up as I had that file buried in a directory and sub directories.

All I can say is long live imperial :D

Of course the guys with the metric gear box will have the same fun turning inch threads, so I guess we all get caught sooner or later.

dp
06-08-2008, 10:47 PM
What is the purpose of the stop?

When threading it is necessary to back the tool out of the thread so you can move it to the start of the thread for the next pass. This stop allows you to use the cross slide for this purpose. The stop is there to allow you to put the cutter exactly back to the same depth it had at the end of the previous pass. At this point you advance the compound to increase the depth of cut along the 29.5 degree angle and make the next pass.

The stop works going in, not out. The center screw is screwed into the cross slide and the bolt head is the stopper when it contacts the dovetail clamp.

Paul Alciatore
06-09-2008, 02:55 AM
Most threading dials on lathes with English lead screws are based on a four inch distance - that's the distance the carriage or tool moves along the work. The four numbers on the dial are actually inch divisions and the lines between them further divide those four inch distances into halves, quarters, and eights. Most, if not all English threads will repeat in that four inch distance. Many will repeat in shorter distances so the dial can synchronize them.

A metric thread may require distances up to 100 inches to synchronize so the four inch dials will not work. A 100 inch dial would work, but you would wait a long time for that to happen. For instance, a 1.5mm thread would require 15 inches or 254 revolutions to sychronize. At 100 RPM that is two and a half minutes. Others would take more or less time to synchronize but all would take a long time compared to what we are used to for English threads.

oldtiffie
06-09-2008, 03:15 AM
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For instance, a 1.5mm thread would require 15 inches or 254 revolutions to sychronize. At 100 RPM that is two and a half minutes. Others would take more or less time to synchronize but all would take a long time compared to what we are used to for English threads.

That will be the case in a "dynamic" ("non-stop") scenario.

In that case, stop the lathe at the end of the thread-cutting, disengage the half-nuts, move the carriage 15 inches toward the tail-stock, re-engage the half-nuts, set the tool to depth and switch on. If as in this instance, time was a concern, I would set the head-stock speed to say 400 RPM, close up to say 1", reduce speed to 100 RPM again and get going.

This is only one of several options.

Using the "usual/normal" approach of keeping the half-nuts engaged for the entire screwing session and reversing the spindle is still quite valid if it suits better.

It is entirely up to the machinist to know all his options and to make a value judgment based on circumstances as he sees it on the day.