# Threading dial question



## SmoggyTurnip (Aug 12, 2008)

I have done some threading - not much. I have not yet used the threading dial. I always left the half nuts engaged. I want to try using the threading dial but something is bothering me. I know that when I engage the half nuts if the half nuts are half way between two threads on the lead screw the carrage could move a little to the left or right - a 50-50 shot. So what happens when you disengage the half nuts and the gear on the threading dial lands on one of those spots where it does not fit nicely into the lead screw, is there not a 50-50 chance that sycronization will be lost. I guess not because machinests aren't gamblers, I just don't understand it yet.


----------



## kvom (Aug 12, 2008)

Once you make the first cut the leadscrew is synchronized to the work as long as you don't rechuck or move the toolpost. You should be able to feel when the halfnuts engage fully. Start with the tool away from the work and use a slow speed; if the halfnut doesn't feel like it engages properly disengage and start over.

You need to be looking at the threading dial and engaging on the proper mark(s).


----------



## SmoggyTurnip (Aug 12, 2008)

My concern is not with engaging the half nuts, it is disengaging them. This is when the threading dial gets engaged and I wonder how it can always get in the right place.


----------



## Bogstandard (Aug 12, 2008)

Smogs,

A bit of confusion here, so I will try to talk you thru it.

The threading dial should, when screwcutting, be permanently engaged onto the leadscrew. The threading dial tells you when the threads on the leadscrew are in the correct position for you to engage your half nuts.

When just starting out in thread cutting for the first time, it is best to disregard all the numbers on the threading dial except for one, and I would make that number No.1.

As kvom says, if you don't move the job in the chuck jaws, whenever you put the lever for the half nuts down, as long as that number you have selected on the dial is lined up with the pointer, the tool tip will be in the correct position for staying in sync with the thread you are cutting.

As I suspect, where your query comes from is when do you retract the half nuts when coming to the end of threading.

If you are a beginner to it, the usual thing is cut a runout section on the part for your cutting tip to enter before you uncouple the half nuts. Then you retract your cutting tool using the cross slide, wind it back past the beginning of your start, put your cut on again and engage the half nuts at the chosen number.
A sketch at the bottom shows what a runout area might look like.
As you gain experience, the runout area will get shorter and shorter, until after a time, you will find you should be able to do without it. Even now, I still usually put a small runout area for my threads as it allows nuts to run right up to the shoulder on the job without any binding. It is no crime to have a runout area.

I hope that this has answered your question.

John


----------



## Lew Hartswick (Aug 12, 2008)

It dosent matter when you dis-engage the half nuts, but it should be in a thread stop grove or it will 
make one of its own. 
  ...lew...


----------



## kvom (Aug 12, 2008)

The technique I learned to make coordinating the process easier is as follows:

1) When first touching off to the work, arrange it so that the crossfeed handle is on top. Then set the moveable dial to 0 on the crossfeed.

2) Watch the cutting tip closely as it nears the thread relief area, with left hand on the crossfeed handle and right hand on the halfnut lever.

3) As the tool tip clears the threaded area first make a fast movement of the crossfeed handle to clear, and then disengage the halfnut lever as fast as possible.

4) Move the carriage back to beyond the start point, and return the crossfeed to its zero position. Then advance the compound for the next cut. Remember that the deeper you go in the thread, the more material is being cut, so reduce the DOC as you go.

My first few tries at this I ran the lathe at 50 rpm; after getting used to the motion I moved up to 80 rpm.

The diameter of the thread relief area should be equal or greater to the minor diameter of the thread.


----------



## SmoggyTurnip (Aug 12, 2008)

Bogstandard  said:
			
		

> The threading dial should, when screwcutting, be permanently engaged onto the leadscrew.
> John



I am not always that good at explaining my thinking so I'll give it another try.
As I understand things the threading dial is only engaged with the lead screw when the half nuts are not engaged. So the sequence of events goes something like this.


1) Half nuts are not engaged but the threading dial is engaged. 
2) Stand around waiting untill the dial comes up to the number 1.
3) Engage the half nuts - now the dial stops turning thus staying at the number 1.
4) Watch the carrage move to the left and cut some threads.
5) When the cutting tool gets as far to the left that you want disengage the half nuts.
  This causes the dial to engage the lead screw with the dial still at the location 1 so that 
  sycronization can be maintained.
6) Retract the tool bit and move carrage to the right
7) Move the cutting tool back plus some.
8) Go back to step 1 untill done.


My question is about step 5.
Since the threading dial is not turning and the lead screw is turning 
it is possible that a tooth on the dial may not land inbetween 2 threads 
on the lead screw when disengaging the half nuts.

In this situation the threading dial needs to turn a bit to get back into 
the lead screw - how does it know which way to go?


----------



## Bogstandard (Aug 12, 2008)

Smogs,

I now think where you are coming from.

Before you engage the half nuts, the leadscrew is driving the dial because the saddle isn't moving, when you engage the leadscrew the saddle then moves in sync with the leadscrew, so in effect the dial is not being driven any more, just one tooth is following the thread, so the dial actually stops turning. When you disengage the nuts, the saddle isn't moving in sync with the leadscrew any more, so with the saddle stopped the leadscrew is then driving the dial again.

The dial isn't disengaged at all during any cutting or moving back to the start. If you look at the dial as you go back to the start, it turns backwards, so showing it is still engaged with the leadscrew.

Total gibberish, but I hope that has explained it.

John


----------



## biometrics (Aug 12, 2008)

???

Step five is not very clear to a newguy. &#160;

The threading dial is engaged to the leadscrew even before threading starts, and once engaged remains engaged through the entire threading process. &#160;This synchronizes the threading dial to the leadscrew. &#160;You only disengage the half nuts, not the threading dial. 

Have your hand on the half-nut lever...The first thread cutting pass begins when the number 1 on your threading dial comes to the reference mark on the dial and you quickly engage the half nuts. &#160;

When the first pass is finished, your tool point will be in the relief area... and you quickly disengage the half nuts, thus ending your first pass.

Then you back off on the threading tool point far enough to miss the newly cut thread diameter on your move of the carriage back to the right of your work. 

Reposition the tool point to some random point to the right of your threaded section, then increase the depth of the tool point what ever increment you want to deepen the thread cut on this next pass (a couple of thousandths). &#160;

Observe the threading dial (which is still engaged to the leadscrew and turning) and when your number (1) approaches the reference mark on the dial, quickly re-enage the half nuts for your next threading pass.

Repeat this process until your threads are cut to the diameter that was your target size.

You can even turn your lathe off for incremental measuring of the thread diameter, and as long as you don't disengage the threading dial, or move your carriage, you have not lost synchronization required for the threading process when you turn the lathe back on.

I hope this explanation of the single point threading process has been helpful.


----------



## SmoggyTurnip (Aug 12, 2008)

Bogstandard  said:
			
		

> The dial isn't disengaged at all during any cutting or moving back to the start. If you look at the dial as you go back to the start, it turns backwards, so showing it is still engaged with the leadscrew.



THE LIGHT JUST WENT ON! All this time I thought since the dial stopped turning that it was actuall not in contact with
the lead screw. It is just an illusion, the threads on the dial might as well be the half nuts when the half nuts are engaged.


----------



## biometrics (Aug 12, 2008)

> THE LIGHT JUST WENT ON!



That's great! Throw a piece of scrap in the lathe and give her a try! Its a piece of cake.


----------



## mklotz (Aug 12, 2008)

Now that you understand the use of the dial, you'll soon get tired of "waiting for your number to come up". That's why all those other numbers and lines are on the dial. Puzzling out what to do with them can be a challenge for the beginner. To that end, I wrote a brief explanation for our club which may help you to start using the dial the way it was intended to be used.

===============================================	

											USING THE THREADING DIAL

Some folks are confused by which marks to use on the threading dial on their
(assumed Imperial) lathe. Of course, you're always safe restarting on the
same dial mark on which you started but that means you'll spend a lot of time
'waiting for your number to come up'.

It's pretty easy to think through. Most dials have four numbered marks
labeled, unsurprisingly, 1-4. Between these marks are smaller, unnumbered
marks.

[Aside: A consequence of the four numbered mark dial is the fact that the
gear that meshes with the feed screw will have a number of teeth which is four
times the tpi of the feed screw, i.e., an 8 tpi lead screw will have a 32
tooth gear on its thread dial. This is worth knowing if you intend to build a
threading dial for a lathe that lacks one. Since there's no load on this
gear, a perfect match to the helix angle of the lead screw is not needed. Any
old gear with the right number of teeth can be pressed into service.]

The numbered marks almost always correspond to a carriage movement of one
inch. (However, you should confirm this by actual measurement on your lathe.)
By deduction, the unnumbered lines must then correspond to a carriage movement
of one-half inch.

Now, suppose I'm cutting an even-numbered thread (e.g., 32 tpi). If I move the
carriage by one-half inch, the tool will reenter the thread perfectly. If I
move the carriage one inch, the tool will also reenter. Therefore, I can
reengage the half-nuts on ANY line on the threading dial.

If I'm cutting an odd-numbered thread (e.g., 13 tpi), the tool will not reenter
the thread if I move one-half inch - I have to move one inch. Therefore, I
must reengage the half-nuts on ANY NUMBERED LINE on the dial. (If I started
the thread on an unnumbered line, I would then reengage on unnumbered lines but
that is generally too difficult to remember in the 'heat' of thread cutting and
should be avoided.)

If I'm cutting a half-fractional thread (e.g., 11-1/2 tpi), the tool will only
reenter the thread every two inches. Therefore I must reengage the half-nuts
on ONLY THE ODD NUMBERS ON THE DIAL (1 and 3) or on the even numbers (2 and
4). It's a good idea to decide on one of these options and always stick with
it. I always start the thread on 1 and then use either 1 or 3 to reengage.

Rarely, a lathe can cut a 1/4 thread (e.g., 1-1/4 tpi). This thread will only
repeat every four inches so, in cutting such a thread, one would reengage the
half-nuts on the same mark one used to start the thread.


----------



## SmoggyTurnip (Aug 12, 2008)

Thanks mklotz. It is comming together now.


On my lathe there are 12 numbers on the threading dial.
I just got a measuring tape out and did a little test.
It takes 4 inches of travel to make the dial go once around.

So I guess that would mean there are 48 teeth on the dial?

Some time this week I want to do a 8tpi thread.

So if I want to do an 8tpi thread the tool must move 1/8, 2/8, 3/8 ... to reenter perfectly.
as each number on the dial goes by it is 1/3, 2/3, 3/3 ... etc
The only numbers that work as both 8ths and 3rds are 0=0, 3/3=8/8, 6/3=16/8 ...

So I could ust 1,3,6,9, or 12 - Is this correct?

 Threading at 8tpi on my lowest speed (150 rpm) means:

 150 reveloutions x 1/8 inch = 18.75 inches/minute or .3125 inches/second


(.3125 inches/sec) * 48 teeth = 15 teeth /second

Thats pretty fast.

So how does one ensure that they are engaging the half nuts at 1 and not 1.25 or .75 at that speed.


----------



## tel (Aug 12, 2008)

Practice.


----------



## biometrics (Aug 12, 2008)

Seriously... *practice* is the answer. You will find that you will develop a feel for when to engage the half-nuts... and you will have to be pretty far off to screw up your threads.


----------



## mklotz (Aug 12, 2008)

Smoggy,

I must admit I've never seen a lathe with twelve numbers on the threading dial. (Would love to see a picture of that.) Are you sure you've got an Imperial lead screw? Twelve, with your indicated third of an inch per division, sure doesn't sound very convenient for cutting Imperial threads.

One way to check your understanding is to chuck up a piece of broomstick and "thread" it using a pencil as your threading tool. Try engaging on the (thread dial) marks you believe will work and see if the pencil marks on the workpiece track.


----------



## Bogstandard (Aug 12, 2008)

Marv,

My new lathe when it gets here, has a weirdly marked threading dial.
As far as I can remember it has 3 major marks, with smaller ones in each third division, and it is massive, if I remember rightly, about 2" across. It is a metric machine.
I noticed it, but never thought to ask.

John


----------



## SmoggyTurnip (Aug 14, 2008)

mklotz  said:
			
		

> I must admit I've never seen a lathe with twelve numbers on the threading dial. (Would love to see a picture of that.)








My first try at posting a picture, hope it works.


----------



## SmoggyTurnip (Aug 14, 2008)

This is what it would look like if I was trying to engage it at 12 but missed by 1 tooth: (the first picture shows the dial at 12)







So you have to courage to use this if you are putting 8 threads per inch on a part that you have spent hours on already.


----------



## mklotz (Aug 14, 2008)

Dang, I really don't understand what's going on there.

Three more questions...

Yours is definitely an Imperial lathe?

What is the pitch of the leadscrew?

Does your lathe manual have anything to say about using the threading dial?


----------



## SmoggyTurnip (Aug 14, 2008)

mklotz  said:
			
		

> Yours is definitely an Imperial lathe?
> What is the pitch of the leadscrew?
> Does your lathe manual have anything to say about using the threading dial?



Yep it is imperial - no question about that.
The leadscrew is 12 threads per inch.
The only thing the manual says about threading is how to change the gears.


----------



## GailInNM (Aug 14, 2008)

Is it possible that the thread dial is not fully engaged? On the old Southbends the thread dial could be pivoted to disengage from the lead screw to save wear and tear on both the lead screw and the dial gear. A bolt was loosened to move the dial ant then tightened after engagement  When engaging the gear you had to make sure that the gear was fully engaged or this sort of funny thing could happen. I don't know if yours is built the same way or not.
Gail in NM,USA


----------



## Lew Hartswick (Aug 14, 2008)

I'm curious. If you (with the lathe stoped) move the carriage exactly 1 inch, how much does the 
threading indicator wheel turn?
  ...lew...


----------



## mklotz (Aug 14, 2008)

Lew,

He's already said that one dial revolution corresponds to a measured travel of four inches.

So, one inch of travel should correspond to three marks on the dial.

That's what is hard to understand. I can't see why anyone would want such an unusual relationship on an Imperial lathe. Where's the benefit? Four inch travel per revolution is normal for most thread dials but they're usually marked with only eight (four numbered and four unnumbered) lines.


----------



## GailInNM (Aug 14, 2008)

Marv,
I think it has a 12 pitch lead screw, therefore 12 numbers on the dial. Look a the lead screw in the photos. I think this was done so a lower gear ratio could be used in the change gears and therefore make the gears smaller in diameter on light duty lathes. The maker probably assumed that no one would try to cut a coarse pitch thread with a smaller lathe, so the gears would not get overstressed. 
Gail in NM,USA

Edit: I missed that he stated that it has a 12 pitch lead screw.


----------



## GailInNM (Aug 14, 2008)

Looking at photo 2, I don't think you are missing by one tooth. I think all you are seeing is backlash in the thread dial gear to the lead screw and maybe some contributed to the backlash in the half nuts.  One index line on the thread dial will equal one tooth on the thread dial gear. If you disengage the half nut and then move the carriage while putting a little pressure on the halfnut engaging lever, you will see the dial move one division before it will drop in. If you do the same thing in moving the carriage in the other direction you will see the same thing, but because of backlash in the system the indexes will not line up perfectly with the pointer. Same sort of thing that happens with the cross slide lead screw where the knob has to be turned a bit before the slide moves when reversing the travel direction. 

Engage the half nuts, and turn the spindle forward a couple of turns and note the thread dial position. Now without changing anything, rotate the spindle in reverse a few turns. The dial will have changed because of the backlash, but the half nuts are still engaged in the same thread on the lead screw.
Gail in NM,USA


----------



## SmoggyTurnip (Aug 15, 2008)

GailInNM  said:
			
		

> Looking at photo 2, I don't think you are missing by one tooth. I think all you are seeing is backlash in the thread dial gear to the lead screw and maybe some contributed to the backlash in the half nuts. One index line on the thread dial will equal one tooth on the thread dial gear.



Nope - there is 48 teeth on the dial gear so 1 tooth is 1/48 of a revolution or 1/4 of a mark.

Last night I actually used the threading dial successfully for the first time making 8 threads per inch.

At first I just stoped the motor after I returned the carrage and then aligned the dial to 1 by moving the carrage while the motor was stoped. Once it was aligned I started the motor and it cut in sync.

After I gained some confidence with that I started engaging the half nuts with the motor running - it wasn't half as bad as I thought it would be. I never missed once. Tonight I will try it again using 1, 4, 7, 10 and see what happens.

On the the lathe there is a table that gives the numbers that can be used for different pitches.

For 9, 12, 18, 24, 36 48, and 72 tpi you can only use the number 1.
for 9.5, 11.5, 13.5 tpi you can use 1 or 7
All other threads you can use 1, 4, 7, or 10.


----------



## SmoggyTurnip (Aug 15, 2008)

GailInNM  said:
			
		

> Is it possible that the thread dial is not fully engaged? On the old Southbends the thread dial could be pivoted to disengage from the lead screw to save wear and tear on both the lead screw and the dial gear. A bolt was loosened to move the dial ant then tightened after engagement When engaging the gear you had to make sure that the gear was fully engaged or this sort of funny thing could happen. I don't know if yours is built the same way or not.
> Gail in NM,USA



Miine is the same way but it is defininitly engaged all the way - I checked this several times.


----------



## SmoggyTurnip (Aug 15, 2008)

Lew Hartswick  said:
			
		

> I'm curious. If you (with the lathe stoped) move the carriage exactly 1 inch, how much does the
> threading indicator wheel turn?
> ...lew...



3 divisions


----------



## SmoggyTurnip (Aug 15, 2008)

mklotz  said:
			
		

> Lew,
> 
> He's already said that one dial revolution corresponds to a measured travel of four inches.
> 
> ...



I was thinking about changing the faceplate on the dial. - As you can see ini the picture it is only held on by a Phillips head screw.


----------



## SmoggyTurnip (Aug 15, 2008)

So what would this table:

For 9, 12, 18, 24, 36 48, and 72 tpi you can only use the number 1.
for 9.5, 11.5, 13.5 tpi you can use 1 or 7
All other threads you can use 1, 4, 7, or 10.

look like if I used a dial with 4 marks with lines inbetween?


----------



## Lew Hartswick (Aug 15, 2008)

>For 9, 12, 18, 24, 36 48, and 72 tpi you can only use the number 1.
for 9.5, 11.5, 13.5 tpi you can use 1 or 7
All other threads you can use 1, 4, 7, or 10.<

If you can never use 2,3,5,6,8,9,11,12 Then what use are they? Make teh dew dial face. 
  ...lew...


----------



## mklotz (Aug 15, 2008)

For 9, 12, 18, 24, 36 48, and 72 tpi you can only use the number 1.
for 9.5, 11.5, 13.5 tpi you can use 1 or 7
All other threads you can use 1, 4, 7, or 10.

1,4,7,10 correspond to carriage movements of one inch. Since 9,12,18,24,36,72 tpi threads (and all other integer tpi threads) repeat every inch, I see no reason why they advise you to use only 1. Furthermore, 12 tpi corresponds to the pitch of the leadscrew. When cutting a thread with the same pitch as the leadscrew, you can engage the halfnuts anywhere.

[Aside: You can verify this by cutting a "scratch" 18 tpi thread, engaging at, succesively, 1,4,7,10. The thread should track on all four engagement points.]

The half threads (9.5, 11.5, 13.5) repeat every two inches so the advice to use 1 or 7 (carriage movement of 2") seems correct.

Like Lew, I still don't see why they have twelve marks. Since one revolution of the dial is four inches, I can see no reason to not just have the traditional eight subdivisions, used as indicated in my writeup. What is gained by having the extra marks?

Idle speculation here... The Chinese reverse engineers saw that there were 8 marks on the dial on a 8 tpi leadscrew lathe so they figured that a 12 tpi leadscrew needed 12 marks.


----------



## NickG (Aug 15, 2008)

This can be a disadvantage with some of the modern lathes .... they have no back gear, so it's difficult to get a low enough speed for screwcutting, especially with variable speed drives. Also, unless it's got a whopping motor, they will struggle to get the torque required to screwcut harder materials, or larger diameters. You may be able to get away with taking very small cuts though. I nearly bought a C4 and know they have a powerful motor though so you should do OK with that particular lathe. My old Harrison can go down to 30rpm which is one of its advantages. 

I tried (for the first time) cutting a screw thread on my lathe for the hot cap on my stirling engine. The two parts sort of screw together but not very well, and at the dimensions I originally went to, they were nowhere near assembling! It seemed like I had to take miles more off the female thread than I originally planned, but I think I messed up re-engaging the lead screw in the wrong place or something.

Was just trying to remember how I did it and to be honest, I can't remember! I think I just ground the tool to as near as I could 60 deg, with a thread gauge I think (this was probably quite bad). Have just worked out that for a flank angle of 60 deg and a 32tpi thread, my depth of cut should have been about 0.0135 to leave the 5/8" major diameter. Can anyone tell me if that is right?! Or does anybody have any information on M.E. threads, major and minor diameters etc, what clearance there should be between male and female for the correct fit?

Think I need to practice as it would be very useful to be able to cut threads properly to the size I want. It keeps everything nice and concentric and straight doing them in the lathe. Need to make use of my screwcutting gearbox too!

Thanks,

Nick


----------



## mklotz (Aug 15, 2008)

Nick,

Download my DOT (Depth Of Thread) program and it will tell you more than you ever wanted to know.


----------



## kvom (Aug 15, 2008)

For a 32 tpi 60 degree thread:

pitch is 1/32 or .031"
slant depth = .75 x pitch = .023"

The slant depth is the amount to advance the compound when it is set to 29.5 degrees.


----------



## NickG (Aug 15, 2008)

Cheers Marv & Kvom


----------



## NickG (Aug 15, 2008)

marv, just tried the program, something flashes up very quickly (milli seconds!) but the screen goes before I can read it! What am I doing wrong?!


----------



## mklotz (Aug 15, 2008)

Read the very first line in the Introduction on my page.


----------



## NickG (Aug 15, 2008)

thanks


----------



## SmoggyTurnip (Aug 16, 2008)

Well I guess I made a mistake. When I said I was sucessful at doing 8 tpi with the threading dial I had only done 2 passes and it looked like each pass was aligned. I had to leave after that and in my mind I thought I had it all sorted out. Last night I went to finish the job and iafter a few more passes I started to notice that all was not right. It seemed that the thread was gradually moving to the left a little on each pass. When I came to notice this I stopped to think for a minute - is it really out or are my eyes just getting worse. Then I thought I' do a couple more passes. I waited for the "1" to come up on the dial and engaged the dial and then engaged the half nuts. On this pass the cut was no where near the right place. What am I doing wrong I thought. I couldn't figure it out so I went to bed and slept on it.

Today is a new day and I think I understand what went wrong.


Several month ago I was doing some threading without using the threading dial. I do not remember what pitch I was doing as it was not for anything important - I was just trying to teach myself how to do threading on the lathe. The threads wer cominig out slightly off (the pitch was not quite right). I checked the gears that I had installed and they wer right acording to the chart that is printed on the lathe. Here is the chart:








It took a couple of days playing around with it and thinking before I decided to calculate what pitch I should get using the gears I had set up. I didn't do this at first because I thought that was what the table was for. To my suprise the table was not correct It was full of aproximations. So I wrote a little program to calculate all the possible pitches I cut cut with the gears that I have - it even ruled out combinations that would not fit for one reason or another. It created a text file and sorted it by pitch so now when I want to cut a thread I just look in that file and find the pitch I want and use the gears that were calculated. 


So when I set up to do 8 tpi I looked up in the table - the closest thing there was 7.988166 tpi. I thought that was close enough and it would be if I wasn't using a threading dial. I was cutting about 1 inch of threads so on each pass I was comming up short by .002 inches. This can easily be missed on the first 2 passes by a rank amature like me. It also explains why the last cut was so bad. As I stood there thinking about what could be going wrong the lathe was still turning and the spindle was getting more and more out of sync with the leadscrew. So anyway it looks like I can not use the threading dial for 8 tpi on this machine or 9 tpi or 10 tpi or 11 or 11.5 or 13.5 or 14 or 16.

As an example of how bad the table is on the lathe look at this.

The table says for 8 tpi use the gears 40/60 45/120 127/40 and put levers in B and I.

(40/60) X (45/120) X (127/40) = .79375

Levers in B I multiplys this by 2

this gives 1.5875

divide by 12 (lead screw tpi) gives .13229166

the recprical of this gives the threads per inch = 7.559.

7.559 is a long way off of 8.

My program calculated the closest possible set of gears to be 40/60 52/120 127/44 with levers in B and I.

this gives 7.988166 tpi - much closer but still impossible with a threading dial.


The thread I want to make is to a shoulder so it is going to be difficult without using the threading dial.


----------



## SmoggyTurnip (Aug 16, 2008)

I uploaded the new chart that I made for threading on the C6. If you happen to own a C6 AKA Grizzly 0602 you should download this file. The table on the lathe is really bad and should be painted over. The file is just a text file and it gives the gears for imperial and metric threads.


----------



## Stan (Aug 16, 2008)

I don't know anything about your Grizzly 06 but when cutting threads, you usually advance the cutting tool with the compound set at 30° (some prefer 29.5°) so that the tool advances in and to the left at the same time. With this method, you are only cutting with the left edge of the tool and the crest of the thread is moving to the left with each advance of the compound.


----------



## mklotz (Aug 17, 2008)

More confusion.

Look at the picture on your chart. According to it, 40 meshes with 60, then "a" meshes with "b" - the 127 is used only as an idler so doesn't figure into the final answer.

Thus...

(40/60) * (45/40) = 45/60 = 3/4

(3/4) * 2 = 3/8

(3/8) * (1/12) = 1/8

Take the reciprocal and you've got 8 tpi.

I'm not questioning that your threads are coming out wrong but I do think you need to check your calculations and understanding. For instance, you include the "120" gear in your calculations and, according to the diagram, it isn't in the indicated gear train. [It's probably used when cutting metric threads.]

Just as a sanity check (mine, not yours) let's try for 10 tpi. We have:

(40/60) * (36/40) = 36/60 = 6/10

(12/10) * (1/12) = 1/10

and the reciprocal is, yup, 10 tpi.


----------



## SmoggyTurnip (Aug 18, 2008)

Thanks mklotz for taking the time to read the details and figure this thing out fore me
Now another light has come on. 

I was looking at the diagram wrong. I thought the 120 tooth gear meshed with b, after all why would the 120 tooth gear be there if it doesn't mesh with anything. I guess it is just used as a spacer. I wish I had of read your post before I spent all afternoon yesterday using the wrong set up. But in the end I learned something.


----------



## SmoggyTurnip (Aug 18, 2008)

This is what i managed to make yester day. I used the gears setup to make 7.988 TPI since I didn't know how to set up for 8.000 TPI. The procedure I used to turn to the sholder I used was as follows.

With the carrage to the right and the half nuts disengaged I turned the spindle until the number 1 was indicated on the threading dial then stoped the carrage and engaged the half nuts. Also zero the cross slide dial. Now I am set up and will repeat the following steps.

1) Use the compound slide to set the depth of cut.
2) Turn motor on with the half nuts engaged and let tool cut as carrage moves to the left.
3) When the carrage gets to the thread relief area disengage the half nuts and then turn off the motor.
4) Use the cross slide to bring the tool out of the threads.
5) Run the motor in reverse and engage the half nuts when the dial gets to 1
6) Let the carrage go to the right untill it is in the same place as it was when you started in step 1
7) Dial the cross slide back in to 0
8] Go back to 1 and 'repeat till done.

It worked perfect and should work for making threads of metric pitch on an imperal lathe.


----------



## mklotz (Aug 18, 2008)

Smoggy,

Now that we've established that the lathe gear chart is indeed correct and the chart you uploaded is based on erroneous observation, you may want to think about asking one of the administrators to remove the upload so it doesn't cause confusion in the future.

Your latest procedure for thread cutting looks ok except for the fact that, by always engaging on the same number, you're not using the threading dial the way it was intended to be used. I strongly encourage you to try the experiment I've already described. On a piece of scrap, set up for 18 tpi and then try tracing the threads while reengaging at 1,4,7,10 on the dial.


----------



## SmoggyTurnip (Aug 18, 2008)

mklotz  said:
			
		

> Smoggy,
> 
> Now that we've established that the lathe gear chart is indeed correct and the chart you uploaded is based on erroneous observation, you may want to think about asking one of the administrators to remove the upload so it doesn't cause confusion in the future.



Actually the chart I uploaded is correct. It uses a different setup in the gear train than is shown on the diagram in my picture. On the picture the 120 tooth gear does not mesh with anything. In the table that I uploaded the b gear would mesh with the 120 tooth gear rather than the 127 tooth gear. So the table that I uploaded gives thousands of other possible spindle to leadscrew ratios shuch as the one that I used that resulted in 7.988 TPI. It may not have any be practial use but it is correct.


----------



## SmoggyTurnip (Aug 18, 2008)

mklotz  said:
			
		

> Smoggy,
> 
> Your latest procedure for thread cutting looks ok except for the fact that, by always engaging on the same number, you're not using the threading dial the way it was intended to be used. I strongly encourage you to try the experiment I've already described. On a piece of scrap, set up for 18 tpi and then try tracing the threads while reengaging at 1,4,7,10 on the dial.



The threading procedure that I posted was for threading to a sholder when using pitches that don't divide into the leadscrew pitch for example 7.988 TPI. When I made my part I had the gears set up for 7.988 TPI which makes it impossible to use the threading dial the way it was intended to use. I thought I would post the procedure because it gives a way to thread to a sholder when doing metric threads on an imperial lathe. Anything I have read on the net says that you need to leave the half nuts engaged all the time when doing this - but you don't as I have just shown.

Now that I now how to set up the gears the way they were ment to be set up, I will be trying to use the dial the way you explained. I can't believe how long I have been confused about all this but now it is all perfectly clear. I would have been a long long time figuring this out with out your help - so thanks again.


----------



## SmoggyTurnip (Aug 18, 2008)

I have updated my program. It now generates all the combinations that were missing from the first program. It now gives all the combos that are listed on the lathe plus more. The complete list results in 9,018 combinations (counting the gearbox settings). This rtesults in 3,370 different spindle to lead screw ratios. Now if someone could explain how to replace a file in the upload section I would go ahead and do that.


----------



## NickG (Aug 25, 2008)

Hi all,

Just about to try some screw cutting as I need some 1/4" x 32 bungs for a model loco boiler that needs hydraulic test and don't have taps or dies!

Got another question, applogies if it's been covered. Why put the compound slide at 29.5 degrees? I've heard it's so there is only load on one face of the cutter or something? Don't get it. Also, why 29.5, why not 30?!

Cheers,

Nick


----------



## kvom (Aug 25, 2008)

With the extra .5 degrees, the non-cutting edge burnishes the back face of the thread.


----------



## NickG (Aug 29, 2008)

Still don't understand this putting the top slide over stuff, someone will need to get crap-o-cad out to show me I think!


----------



## SmoggyTurnip (Aug 29, 2008)

The diagram on the left shows what happens when the cutting by going straight in. As you can see the tool is cutting the same amount on both sides of the cutter on each pass. The diagram on the right show what happens when you advance the cutter using the compound at an angle. The angle the diagram is exagerated to make the effect stand out better. At 29.5 degrees the tool is cutting almost entirely on the left side of cutter. On the final pass the tool needs to be advanced straight in to remove the zig zag left on the right hand side of the cut.


----------



## NickG (Aug 29, 2008)

Thanks for the diagram but I still don't understand why that is necessary. The way I thought to cut the thread was to put on my cut further along where there is no material then let the saddle go into it, rather than plunge into the work piece with it all running?


----------



## SmoggyTurnip (Aug 29, 2008)

NickG  said:
			
		

> Thanks for the diagram but I still don't understand why that is necessary.



I don't think it is necessary. It is just easier on the machine and requires less power to go the same depth. Threading on small bench top lathes can push the machine to it's limit in very small depths of cuts, so to complete a thread will take alot of passes and therefore alot of time. Advancing the cutter on an angle will alow you to go deeper on each pass so in the end the it is faster. Of coarse I am no expert on the subject as I have only have about a total of 4 hours of experience in actual threading with about 3 hours and 50 minutes of total screw ups. I am only giving you my interpretation of what I have read about it and what I have learned in that short time of trying it myself.


----------



## kvom (Aug 29, 2008)

You need a sharp point to cut 60 threads. If you go straight in you are very likely to chip the point.


----------



## Stan (Aug 29, 2008)

NickG: In the beginning (Noah's lathe) there was no compound on lathes and threading was done straight in. As Smoggy pointed out, on a coarse thread, when you get in deep, there is a high load on the lathe and you quickly develop chatter.

If you have enough rigidity and horsepower there is no reason not to go straight in but if you try it both ways, I think you will find the compound advance easier to do. Back out at the end of the thread with the cross slide handwheel, move the carriage to the other end, return the cross slide to your zero and then advance the cutter with the compound.



> Thanks for the diagram but I still don't understand why that is necessary. The way I thought to cut the thread was to put on my cut further along where there is no material then let the saddle go into it, rather than plunge into the work piece with it all running?



I'm not sure what you mean by this, but the correct procedure is to advance the cutter with the cutter away from the workpiece thread before you engage the half nuts.


----------



## rake60 (Aug 29, 2008)

At work I've cut threads that were 2" pitch and 1-1/32" deep.
To cut them the tool was obviously advanced on a 29.5 degree angle.
Even at that it was a battle with chatter.

For a hobby scale thread, even up to a 1"-8 pitch, straight in will cut just fine.
People will be lining up to tell you how wrong that is. 
All I can say is it's worked fine for me for the past 20 years. 

When you start into a 2" pitch thread and see a 9" boring ram flex under the tool
pressure but the thread still ends up being perfect, you kind of loose your fear of
going straight in on a small thread.

Rick


----------



## Stan (Aug 29, 2008)

rake60: I defer to you knowledge and experience cutting threads straight in but I have had trouble cutting 1 1/2 x 8 inside threads on a 9" Southbend even when advancing the compound. When the biggest boring bar the lathe will hold is 1/2" the bottom of that 8 TPI thread is tough to do without chatter. 

I am sure the professional machinists can do it, and probably do it all day every day, but for the amateur model maker who does it once a month, it is tough.


----------



## rake60 (Aug 29, 2008)

An internal thread changes the game completely!

A threading bar takes away the rigidity.

No professional machinist machinst could cut an internal 1 1/2-8 thread straight in
unless they were sound asleep in a sweet dream. 

I won't be turning a machine on in my hobby shop this long weekend for just that reason.
In the past 2 days at work I made 6 high pressure caps that called for a 4 pitch internal
Acme thread. The only way to get the machine to cut that thread cleanly was to open 
the machine doors at that process and push a length of 2 X 4 wood against the tool holder.
57 passes. I have a bruised hand and chest from making that work out, but I also have
6 high pressure caps that fit perfectly with no chatter in the internal threads to be
delivered to the customer on Tuesday morning.

Rick


----------



## chuck foster (Aug 29, 2008)

years ago i did some internal acme threads (not sure what they were for) but i made a wooden piece that went on the backside of the boring bar and i kept the bar from springing and chattering............if i remember right the pitch was about 1/2 thread per inch.
it was a rotten job but i got it done.............but the worst part was since i could do the job i got about 60 more of them to do, they were big brass castings. 

one of the scary things i did was a huge bronze bearing, and i mean huge, it had a 6' o.d and a 4' i.d and was 7' long.
it was something for the mining industry, it had a grease groove from one end to the other and in the 7' length the grove went one turn. if you think the carrage on rick's lathe was moving fast in the video you should have seen this one go 
the grove was about and inch deep and an inch wide, i had to make about a hundred passes to get it to the right depth.

any way rick............hope you heal fast and get back in the shop..............but wasn't it you that said the body is not a machine :-\

take it easy my friend and rest well cause monday will be another work day

chuck


----------



## rake60 (Aug 29, 2008)

LOL

Yes I did say a body is not a machine.

But, pride in your work sometimes intervines.
Bruised ribs will heal, but when some redneck oil field worker is standing
at a well head and that pressure cap spins on before he gets hurt....
Well it's all relevent.

Knowledge is a wonderful tool!
When you actually know what HAS to work the very first time you add a little 
extra effort to it.

What we do at home is a different story.
If it doesn't work the first time we are not happy but we can fix it.

Try telling a pipeline rough neck, "Oh I'm sorry, bring that back and I'll fix if."

Drill pipe joints are 50 feet long. 
Not something I'm willing to be shown where it should fit!
 :big:

Rick


----------



## NickG (Aug 30, 2008)

Thanks for all this information, but I still am not understanding the swivelling over of the compound slide! , is the tool is still at normal angle to the lathe spindle axis when you set the compound slide at 29.5 deg, i.e. you have to swing the tool post back 29.5? If so what difference does it make using that slide or the cross slide? The tool still ends up in the same position for each cut? Or do you set it all up at 0 degrees to cut the thread, then just move the compound slide over? Then you don't get the right thread form!

 ??? :-[ :-\


----------



## Circlip (Aug 30, 2008)

When you have set the Top slide over to half the thread angle Nick, you set the cutting tool point at right angles to the workpiece using a thread gauge or whatever you use. Wind the tool in to touch the job and zero the top slide dial. Now, by feeding in using the top slide, you are only cutting on ONE face of the tool. As posted by someone else, this " Old wives tale b--l s--t " method is a lot kinder to the cutting tool AND machine when cutting large pitch/any threads on smaller machinery. Other members have given a far more in depth ( ;D ) description than mine, but NEVER be afraid toask.
 Regards Ian.


----------



## kvom (Aug 30, 2008)

With the compound at 29.5, you align the tool with the gauge like this:


----------



## NickG (Aug 30, 2008)

Thanks again, I can see this point, but you would apply the feed when the tool is clear of the work anyway, so you're not plunging into the workpiece. When you engage the half nuts the forces on the tool / workpiece are exactly the same?


----------



## lathe nut (Aug 30, 2008)

Rick, hats off to you fellows, I work in the Oil Field, for several years when I was doing the pumping at well sites, would often think when we pumped from five to fifteen thousand PSI, sure hope the threads are right, 8R, Weco, or what ever we were pumping through if not we won't live to complain, sometimes they would drip but never had one blow out, we did depend on you fellows without fail, thanks, Lathe Nut


----------



## Stan (Aug 30, 2008)

NickG: It would be so easy to show you on a lathe but hard to put into words. When you advance the tool straight in and start the carriage moving into the thread, the tool will be cutting an equal amount on both sides of the tool. Do you understand so far?

When you make your first scratch cut you have a spiral line going down the work. If you use the compound set at 30° to advance the following cuts, you never touch that first scratch cut again. Each time you advance the compound it moves the tool toward the work and toward the headstock It is a long time since I did math but I think the relationship would be the distance advanced into the work is the cosine of 30 times the amount you advance the compound handwheel.

If you now visualize the work when you have a nearly completed thread, the point of the tool is going deeper into the work a bit to the left of the previous cut and the left side of the tool is cutting metal. The right side of the tool is just going along for the ride. 

The end result is the right side of the thread is at the point where you started but the bottom of the thread has moved toward the headstock. Why don't you try cutting a coarse thread on a piece of material and see what happens.


----------



## NickG (Aug 31, 2008)

Stan,

Thanks for that. I think it was just me being a bit thick! I needed it spelling out step by step! 

Just drawn a little sketch for myself and understand it fully now! I guess setting it at 29.5 degrees just lets it cut a small amount on the right hand tool flank to clean it up each time you advance the tool for the next cut. Will have to give it a go!

Thanks to everyone for trying to explain this, you've finally cracked it! ;D


----------



## Circlip (Aug 31, 2008)

If you want to prove it for yourself without the BANG Nick,( this occurs when you put the last cut on,and is the sound JUST before you need to resharpen) get a piece of PVC or some other "Hard" plastic rod/bar to gain confidence threading. It might not be useful for a project, but it sure gives Friends and neighbors something to talk about when they see it on the coffee table. To explode another myth, It's best not to take the tool out of the tool post until you've finished, yes that's right BUT, if you need to, to resharpen, or regrind ( after a bang ) providing the tool is square in the toolpost and when winding the tool back in to line up with the job that you take up the backlash you find It's not difficult at all and takes far less time to do than read my explanation.
 Regards  Ian.


----------



## Stan (Aug 31, 2008)

NickG: Glad you understand the principle. Single point threading is primarily a hand-eye coordination thing and practice is the only way to get good at it. Since I use DC drive, I can run as slow as I need for any particular job.

 If it is critical that the thread end at a particular spot, I mount an indicator on the bed so that the carriage hits it about an inch before where I want to stop. I then watch the indicator to know when to disengage the halfnuts and back out. If you always stop at he same mark on the indicator, the thread will end one thead pitch past where it was on the first pass. If it is really critical, you can do the math so that you have each cut end short of the previous cut to eliminate any stress riser at the end of the thread. 

Circlip has a good suggestion to practice on plastic. ABS sewer pipe is beautiful stuff to machine and it is big enough that you can watch the progress of the thread.


----------



## NickG (Sep 3, 2008)

I did a few 1/4" x 32 bungs the other day for that boiler. I noticed that if I took the depth all the way to 27 thou , it was too much, but i guess that's not accounting for any radii, assuming a totally sharp crest and root. Just experimenting a little about 20 thou gave the best threadform. However, this could be down to my tool, it probably wasn't very well ground.

Nick

ps am going to practice with some larger pitches and try setting the compound slide over though


----------

