Help with Lathe Thread Dial

macardoso

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Hi all,

I own an Enco 110-2033 (12x36 lathe similar to the G9249 from Grizzly). I was trying to cut a 1.125-18 thread this past weekend and couldn't figure out how to disengage and re-engage the halfnuts for this 18 TPI thread.

Here is the thread chart. My machine have a thread dial with 4 large ticks labeled 1,2,3, and 4 with shorter ticks in between each of the large marks.

If I started on the line marked "1" and then later re-engaged the thread on "1", the threads didn't line up. I ended up keeping the half nuts engaged the whole time and cutting the thread like I would a metric one. Any tips for what the 1/2 3/4 means on the 18 TPI entry in the table?

Thanks!

-Mike



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Boswell

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I have not done this so my answer is only hypothetical. but I think it means that you can engage on 1 or 3 OR you can engage on 2 or 4
So if you do you first pass on 1 then you can use either 1 or 3 going forward. If you use 2 on your first pass then you can use 2 or 4 going forward.

I believe that you can always use the same number for any thread so no matter what number you start on, always use that number. I realize that this contradicts the experience of Mike so not sure about that.
 

Bob Korves

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It means that you can use 1 and 3, or 2 and 4 to engage your half nuts. The reality is that you can use any 2 places that the half nuts engage in, as long as they are 180 degrees apart on the threading dial and you always use only those 2 places while making your thread. The easiest thing to do is to use the same spot on the threading dial every time, doesn't matter which one, as long as you use the same one each time. Just takes a little more time for it to come around. A felt pen (Sharpie) can be useful for marking the threading dial and housing and making sure you always engage in the same place, or in multiple places where applicable.
 

macardoso

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Huh, I must just suck at threading then :)

I ended up with a great 18TPI thread at the end but I hate having to keep reversing the lathe if I don't need to.

My halfnuts are in good condition but always feel like they're clamping onto putty rather than a crisp snap into position. Makes it hard to really be sure you have engaged in the right position.
 

benmychree

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Generally speaking, even # of threads can be cut on any number or line, odd # on opposite numbers, 1/2 threads on a specific number, and 1/4 threads on the same number.
 

Bob Korves

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If you are doing metric threading on a lathe with an imperial lead screw, or imperial threading on a metric lead screw, then the threading dial will be totally worthless.

It also turns out that the quaint old fractional system used on imperial lathes works well for using a simple threading dial to keep the cutter in sync with the developing threads. On metric lathes the threading dials are much more complicated, and neither system covers all the possible threads the lathe can cut, much less all the ones that exist. At some point we all need to use the "leave the half nuts engaged for the entire sequence of making the thread" method. Electronic controlled powered lead screws can make many or all of the problems go away, and do both metric and imperial threads on any lathe seamlessly, but are not necessarily easy or cheap to retrofit to existing thread cutting lathes. I know little about the nuts and bolts of electronic lead screws, but I do understand the concepts.
 

macardoso

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Thanks all. I need to sit down and just practice cutting some different pitches of threads again. I do it often but this is the first time I've had issues.
 

RJSakowski

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Generally speaking, even # of threads can be cut on any number or line, odd # on opposite numbers, 1/2 threads on a specific number, and 1/4 threads on the same number.
Thread dials are machine specific.
]
My Grizzly 602 has a 12 tpi lead screw, 36 teeth on the thread gear, and twelve numbered marks on the thread dial. I cuts any thread with a tpi divisible by three on any mark. All other whole number threads are are cut using every third mark (1,4,7,10 or 2,5,8,11 or 3,6,9,12). Half numbered threads like 11-1/2 tpi are cut using every sixth mark (1,7 or 2,8 etc.)

My Atlas Craftsman 6 x 18 has a 16 tpi lead screw, a 32 tooth thread gear, and four marks on the thread dial. Even numbered threads are cut using any two opposing marks while odd numbered threads are cut using the same mark. Half numbered threads cannot be cut using the thread dial.
 

rzw0wr

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I have a Bolton lathe that hates to thread.

I start by shutting off the lathe, picking a mark, engage the half nut and turn on the lathe.

Then I disable the half nut and run the carriage back to the start, pick the same mark on the half nut and do it all over again until I get the thread to what I want.

On my lathe you can not select a mark while the lathe is running. You will always miss.

About 1/2 of the make line will mess you up.
 

Cadillac

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I have a Bolton lathe that hates to thread.

I start by shutting off the lathe, picking a mark, engage the half nut and turn on the lathe.

Then I disable the half nut and run the carriage back to the start, pick the same mark on the half nut and do it all over again until I get the thread to what I want.

On my lathe you can not select a mark while the lathe is running. You will always miss.

About 1/2 of the make line will mess you up.
The half nuts may be adjustable most are.
 

Tozguy

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My halfnuts are in good condition but always feel like they're clamping onto putty rather than a crisp snap into position. Makes it hard to really be sure you have engaged in the right position.
Just a thought that maybe a squirt of heavy oil to the half nut dovetails might improve the feel on the lever.
It is a place that is difficult to access and might be neglected on lube day.
 

Janderso

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I was having trouble on my old South Bend thread dial after I took it apart to clean and oil.
The dial will move on the shaft. If the numbers do not correlate with the timing on the lead screw the dial will need to be loosened and adjusted to line up with the corresponding fit between the half nuts and the lead screw.
In other words, when the half nuts were engaged, the dial never aligned with a number, always off by a matter of degrees until I corrected it.
Does this make sense at all?
Made all the difference in the world.
 

machinistmarty

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If your lathe has a metric leadscrew (which it sounds like it does) then you must leave halfnut engaged just like threading metric with an american leadscrew If threading to a shoulder you can disengage as long as you reengage on same line without skipping it and then reversing lathe
 
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