------ Original Message ------
From: "DJ Delorie" <dj@...>
To: [email protected]
Sent: Thursday, 16 Feb, 23 At 18:48
Subject: Re: [SouthBendLathe] Metric threads/Imperial threads

"Andrei" <calciu1@...> writes:

All this discussion of metric threads has raised a question in my mind. Sorry for being simple, but the only metric threads I ever cut were small enough that they were done with a tap or a die, never on the lathe.

Did you know that spark plug threads are always metric?



That's a spark plug plug for servicing chain saws. I don't recall the
exact thread, but finding a die for it would likely be impossible.

Part 1 - Metric leadscrew. How do you cut imperial threads? Part 2 - Metric leadscrew. How do you cut metric threads? Is it as straight forward as imperial on a imperial lathe? Part 3.- Imperial leadscrew. Allan had a great explanation for how to cut metric threads. Thank you.

The key thing to understand is what the thread dial does. It indicates
the *difference* between the cut thread and the tool. In general, it
does around once per four inches of leadscrew (and thus tool) travel.
The gearing determines how many times the spindle goes around in those
same four inches; an 8 TPI thread would go around 32 times in 4 inches.

A metric lathe would have a thread dial that goes around, for example,
once per 12cm.

When doing "matched" threading (imperial-on-imperial or
metric-on-metric) you can disengage the thread dial, move the carriage
by some whole number of threads, and re-engage the thread dial; without
messing up your threading operation. The key is "whole number of
threads". If you have a whole number of threads in 4 inches, starting
on the "same number" always drops you into a thread, etc. Same for a
whole number of threads per 12cm for metric lathes.

The problem with mis-matched threading is that there is no metric thread
that is a whole number of threads per 4 inches (or the reverse) so
there's no way to move "a whole number of threads" away. Hence the
extra effort taken to keep the thread dial in the "same leadscrew
thread" so that it stays on the one cut thread you started with.

If you had a leadscrew with 9 threads per attoparsec (tpap), you could
turn any thread that was a multiple of 9 tpap (like 27 tpap) but you'd
need to use the "mis-matched" method for either inch or metric threads,
assuming the change gear fit in your local spacetime.

I suggest using an electronic leadscrew for those ;-)

I doubt whether spark plug manufacturers nowadays use dies, more likely thread milling or some such, but surely you can get the taps for cylinder head repairs?

Eddie

------ Original Message ------ From: "DJ Delorie" <dj@...> To: [email protected] Sent: Thursday, 16 Feb, 23 At 18:48 Subject: Re: [SouthBendLathe] Metric threads/Imperial threads "Andrei" <calciu1@...> writes:

All this discussion of metric threads has raised a question in my mind. Sorry for being simple, but the only metric threads I ever cut were small enough that they were done with a tap or a die, never on the lathe.

Did you know that spark plug threads are always metric? That's a spark plug plug for servicing chain saws. I don't recall the exact thread, but finding a die for it would likely be impossible.

Part 1 - Metric leadscrew. How do you cut imperial threads? Part 2 - Metric leadscrew. How do you cut metric threads? Is it as straight forward as imperial on a imperial lathe? Part 3.- Imperial leadscrew. Allan had a great explanation for how to cut metric threads. Thank you.

The key thing to understand is what the thread dial does. It indicates the *difference* between the cut thread and the tool. In general, it does around once per four inches of leadscrew (and thus tool) travel. The gearing determines how many times the spindle goes around in those same four inches; an 8 TPI thread would go around 32 times in 4 inches. A metric lathe would have a thread dial that goes around, for example, once per 12cm. When doing "matched" threading (imperial-on-imperial or metric-on-metric) you can disengage the thread dial, move the carriage by some whole number of threads, and re-engage the thread dial; without messing up your threading operation. The key is "whole number of threads". If you have a whole number of threads in 4 inches, starting on the "same number" always drops you into a thread, etc. Same for a whole number of threads per 12cm for metric lathes. The problem with mis-matched threading is that there is no metric thread that is a whole number of threads per 4 inches (or the reverse) so there's no way to move "a whole number of threads" away. Hence the extra effort taken to keep the thread dial in the "same leadscrew thread" so that it stays on the one cut thread you started with. If you had a leadscrew with 9 threads per attoparsec (tpap), you could turn any thread that was a multiple of 9 tpap (like 27 tpap) but you'd need to use the "mis-matched" method for either inch or metric threads, assuming the change gear fit in your local spacetime. I suggest using an electronic leadscrew for those ;-)

I doubt whether spark plug manufacturers nowadays use dies, more likely thread milling or some such, but surely you can get the taps for cylinder head repairs?

Eddie

------ Original Message ------ From: "DJ Delorie" <dj@...> To: [email protected] Sent: Thursday, 16 Feb, 23 At 18:48 Subject: Re: [SouthBendLathe] Metric threads/Imperial threads "Andrei" <calciu1@...> writes:

All this discussion of metric threads has raised a question in my mind. Sorry for being simple, but the only metric threads I ever cut were small enough that they were done with a tap or a die, never on the lathe.

Did you know that spark plug threads are always metric? That's a spark plug plug for servicing chain saws. I don't recall the exact thread, but finding a die for it would likely be impossible.

Part 1 - Metric leadscrew. How do you cut imperial threads? Part 2 - Metric leadscrew. How do you cut metric threads? Is it as straight forward as imperial on a imperial lathe? Part 3.- Imperial leadscrew. Allan had a great explanation for how to cut metric threads. Thank you.

The key thing to understand is what the thread dial does. It indicates the *difference* between the cut thread and the tool. In general, it does around once per four inches of leadscrew (and thus tool) travel. The gearing determines how many times the spindle goes around in those same four inches; an 8 TPI thread would go around 32 times in 4 inches. A metric lathe would have a thread dial that goes around, for example, once per 12cm. When doing "matched" threading (imperial-on-imperial or metric-on-metric) you can disengage the thread dial, move the carriage by some whole number of threads, and re-engage the thread dial; without messing up your threading operation. The key is "whole number of threads". If you have a whole number of threads in 4 inches, starting on the "same number" always drops you into a thread, etc. Same for a whole number of threads per 12cm for metric lathes. The problem with mis-matched threading is that there is no metric thread that is a whole number of threads per 4 inches (or the reverse) so there's no way to move "a whole number of threads" away. Hence the extra effort taken to keep the thread dial in the "same leadscrew thread" so that it stays on the one cut thread you started with. If you had a leadscrew with 9 threads per attoparsec (tpap), you could turn any thread that was a multiple of 9 tpap (like 27 tpap) but you'd need to use the "mis-matched" method for either inch or metric threads, assuming the change gear fit in your local spacetime. I suggest using an electronic leadscrew for those ;-)

I doubt whether spark plug manufacturers nowadays use dies, more likely thread milling or some such, but surely you can get the taps for cylinder head repairs?

Eddie

------ Original Message ------ From: "DJ Delorie" <dj@...> To: [email protected] Sent: Thursday, 16 Feb, 23 At 18:48 Subject: Re: [SouthBendLathe] Metric threads/Imperial threads "Andrei" <calciu1@...> writes:

All this discussion of metric threads has raised a question in my mind. Sorry for being simple, but the only metric threads I ever cut were small enough that they were done with a tap or a die, never on the lathe.

Did you know that spark plug threads are always metric? That's a spark plug plug for servicing chain saws. I don't recall the exact thread, but finding a die for it would likely be impossible.

Part 1 - Metric leadscrew. How do you cut imperial threads? Part 2 - Metric leadscrew. How do you cut metric threads? Is it as straight forward as imperial on a imperial lathe? Part 3.- Imperial leadscrew. Allan had a great explanation for how to cut metric threads. Thank you.

The key thing to understand is what the thread dial does. It indicates the *difference* between the cut thread and the tool. In general, it does around once per four inches of leadscrew (and thus tool) travel. The gearing determines how many times the spindle goes around in those same four inches; an 8 TPI thread would go around 32 times in 4 inches. A metric lathe would have a thread dial that goes around, for example, once per 12cm. When doing "matched" threading (imperial-on-imperial or metric-on-metric) you can disengage the thread dial, move the carriage by some whole number of threads, and re-engage the thread dial; without messing up your threading operation. The key is "whole number of threads". If you have a whole number of threads in 4 inches, starting on the "same number" always drops you into a thread, etc. Same for a whole number of threads per 12cm for metric lathes. The problem with mis-matched threading is that there is no metric thread that is a whole number of threads per 4 inches (or the reverse) so there's no way to move "a whole number of threads" away. Hence the extra effort taken to keep the thread dial in the "same leadscrew thread" so that it stays on the one cut thread you started with. If you had a leadscrew with 9 threads per attoparsec (tpap), you could turn any thread that was a multiple of 9 tpap (like 27 tpap) but you'd need to use the "mis-matched" method for either inch or metric threads, assuming the change gear fit in your local spacetime. I suggest using an electronic leadscrew for those ;-)

<eddie.draper@...> writes:

but surely you can get the taps for cylinder head repairs?

Well, probably, but I wasn't fixing a cylinder head.  I was making a
spark plug plug tool.  You take out the spark plug, insert the tool, and
it prevents the piston from passing TDC so you can remove the crank
shaft nut.  Not something most people would be aware of.

Having said that most modern spark plugs are 14 and 18mm, that was not always the case. Back in the model T days there were common spark plugs with 1/2" pipe threads as well as 7/8" - 18 threads. As a mater of fact I believe that is what my 1944 IH tractor uses. I have a small collection of spark plugs which I started collecting when I was a kid.? I didn't go out of my way to do so but picked up odd balls as I came across them. I have a bunch of Spark plug collectors magazines and there are some pretty weird shaped plugs in there. Even some with what looked like a 1/2" course thread. And then there are tiny spark plugs for models and I have seen several sizes there too.
Just thought I would add another 2 cents worth, Nick

On 2023-02-16 3:16 p.m., eddie.draper@... via groups.io wrote:

I doubt whether spark plug manufacturers nowadays use dies, more likely thread milling or some such, but surely you can get the taps for cylinder head repairs?

Eddie

------ Original Message ------ From: "DJ Delorie" <dj@...> To: [email protected] Sent: Thursday, 16 Feb, 23 At 18:48 Subject: Re: [SouthBendLathe] Metric threads/Imperial threads "Andrei" <calciu1@...> writes:

All this discussion of metric threads has raised a question in my mind. Sorry for being simple, but the only metric threads I ever cut were small enough that they were done with a tap or a die, never on the lathe.

Did you know that spark plug threads are always metric? That's a spark plug plug for servicing chain saws. I don't recall the exact thread, but finding a die for it would likely be impossible.

Part 1 - Metric leadscrew. How do you cut imperial threads? Part 2 - Metric leadscrew. How do you cut metric threads? Is it as straight forward as imperial on a imperial lathe? Part 3.- Imperial leadscrew. Allan had a great explanation for how to cut metric threads. Thank you.

The key thing to understand is what the thread dial does. It indicates the *difference* between the cut thread and the tool. In general, it does around once per four inches of leadscrew (and thus tool) travel. The gearing determines how many times the spindle goes around in those same four inches; an 8 TPI thread would go around 32 times in 4 inches. A metric lathe would have a thread dial that goes around, for example, once per 12cm. When doing "matched" threading (imperial-on-imperial or metric-on-metric) you can disengage the thread dial, move the carriage by some whole number of threads, and re-engage the thread dial; without messing up your threading operation. The key is "whole number of threads". If you have a whole number of threads in 4 inches, starting on the "same number" always drops you into a thread, etc. Same for a whole number of threads per 12cm for metric lathes. The problem with mis-matched threading is that there is no metric thread that is a whole number of threads per 4 inches (or the reverse) so there's no way to move "a whole number of threads" away. Hence the extra effort taken to keep the thread dial in the "same leadscrew thread" so that it stays on the one cut thread you started with. If you had a leadscrew with 9 threads per attoparsec (tpap), you could turn any thread that was a multiple of 9 tpap (like 27 tpap) but you'd need to use the "mis-matched" method for either inch or metric threads, assuming the change gear fit in your local spacetime. I suggest using an electronic leadscrew for those ;-)

In my 55+ years as a mechanic I have never heard of that. I always used an impact gun and never had one that wouldn't come.
Nick

On 2023-02-16 5:02 p.m., DJ Delorie wrote:

<eddie.draper@...> writes:

but surely you can get the taps for cylinder head repairs?

Well, probably, but I wasn't fixing a cylinder head.  I was making a
spark plug plug tool.  You take out the spark plug, insert the tool, and
it prevents the piston from passing TDC so you can remove the crank
shaft nut.  Not something most people would be aware of.

I have a spark plug tool that I made and I just used an old spark plug and cleaned the ceramic out of the middle. I then tapped the inside and put a bolt in with the head cut off and then the end rounded over. I use it as a positive stop for determining TDC (along with a degree wheel). I would not consider it for breaking loose stuck crank bolts - too big of a chance of poking it right through a piston.

------ Original Message ------
From: "Nick Jonkman" <njonkman@...>
To: [email protected]
Sent: Thursday, 16 Feb, 23 At 22:13
Subject: Re: [SouthBendLathe] Metric threads/Imperial threads

In my 55+ years as a mechanic I have never heard of that. I always used an impact gun and never had one that wouldn't come.
Nick

On 2023-02-16 5:02 p.m., DJ Delorie wrote:

<eddie.draper@...> writes:

but surely you can get the taps for cylinder head repairs?

Well, probably, but I wasn't fixing a cylinder head.  I was making a
spark plug plug tool.  You take out the spark plug, insert the tool, and
it prevents the piston from passing TDC so you can remove the crank
shaft nut.  Not something most people would be aware of.

?

??? ??? I had a store bought tool along those lines , I loaned it to a guy that took it with him when he moved . It had a micrometer body that threaded into the plug hole & a adjustable shaft that would hit the piston top . It's been so long I cant fully remember just how it worked . I thought it was called a " micro timer " but it has not come with a google .

??? ??? animal

I have a spark plug tool that I made and I just used an old spark plug and cleaned the ceramic out of the middle. I then tapped the inside and put a bolt in with the head cut off and then the end rounded over. I use it as a positive stop for determining TDC (along with a degree wheel). I would not consider it for breaking loose stuck crank bolts - too big of a chance of poking it right through a piston.

Mike,

Here is one I made for my Grandson’s IAME KA-100 Racing Kart.

Steve

?

?

From: [email protected] <[email protected]> On Behalf Of mike allen
Sent: Thursday, February 16, 2023 8:27 PM
To: [email protected]
Subject: Re: [SouthBendLathe] Metric threads/Imperial threads

?

??? ??? I had a store bought tool along those lines , I loaned it to a guy that took it with him when he moved . It had a micrometer body that threaded into the plug hole & a adjustable shaft that would hit the piston top . It's been so long I cant fully remember just how it worked . I thought it was called a " micro timer " but it has not come with a google .

??? ??? animal

On 2/16/2023 5:16 PM, d6crawler via groups.io wrote:

I have a spark plug tool that I made and I just used an old spark plug and cleaned the ceramic out of the middle. I then tapped the inside and put a bolt in with the head cut off and then the end rounded over. I use it as a positive stop for determining TDC (along with a degree wheel). I would not consider it for breaking loose stuck crank bolts - too big of a chance of poking it right through a piston.