Crazy Threads...

If lathe has neutral place it there or in highest speed to turn by hand but remember to shift back.

Regarding thread dial...

We are not pros and never remember processes but it seems that some operations require any number while others require odd and others require even.

So get some junk scrap and some dykem or felt tip pens.

Turn the scrap clean then paint it with the ink.

Place a scribe in your tool post such as a spring so it can give a bit.

Now you are cutting "virtual" threads.

Repeat cuts should land on the same mark.

If a washer is missing from under the thread dial or one added it may change the relationship to the 1/2 nuts.

Also if the 1/2 nuts are upside down it may change the relationship with thread dial.

Focus on why the nuts cannot engage exactly in a mark.

Slop elsewhere cad wind itself out via engaging ahead of time but the 1/2 nuts need to be proper to the thread dial

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
My thoughts/questions are along the same thread as dave2176...... On my lathe, depending on the pitch of the treads being cut, only certain numbers on threading dial will result in the cutter being indexed properly. For example when cutting a 10 TPI thread, I can only use 1 or 3 on threading dial. But when cutting 24TPI treads I can use 1-8 on dial. Could this be a similar situation with your lathe?

As a way to check the Half Nut and everything else is working properly, could you do it old school, as if you didn't have a treading dial? At the end of a threading cut, turn off the lathe leaving the half nut engaged. Then physically spin the chuck backwards until the cutter is back at it's starting position and try to cut a second pass. If the second pass is aligned as it should be then your issue is probably with the treading dial.

Attached are the Threading Dial Instructions for my Lathe, which describe the use of certain numbers on the Treading Dial for specific tread TPI's.

Hope this helps,

Chris
 

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My thoughts/questions are along the same thread as dave2176...... On my lathe, depending on the pitch of the treads being cut, only certain numbers on threading dial will result in the cutter being indexed properly. For example when cutting a 10 TPI thread, I can only use 1 or 3 on threading dial. But when cutting 24TPI treads I can use 1-8 on dial. Could this be a similar situation with your lathe?
If you always start on the the same number it will always work. For some threads you can also start on other numbers as well. Which ones depends on the TPI of your leadscrew and the number of teeth in the thread dial gear.
 
Rather than trying to guess where to engage assuming the hash marks are off, draw a mark with a sharpie when the half nuts are engaged and use that mark exclusively. Practice engaging it at the speed you run when threading until you can hit it perfectly every time. If you still have issues check your lead screw. You can use a thread pitch guage to determine if your lead screw is metric.
 
Rather than trying to guess where to engage assuming the hash marks are off, draw a mark with a sharpie when the half nuts are engaged and use that mark exclusively.
Or simply adjust the threading dial.
 
i was playing with this last night. i pulled some gears off to try to have a better look, and a flashlight to see under/inside the gear box. that slack seems to be in a union. much like a hydrolic pump union as if the nylon spacer had worn away between the cogs. HOWEVER, once the half nut is set with the machine is running, all the slack is taken up within the first half revolution... i cant see this being the issue. i could understand it causing some kind of chattering, but thats not the issue here. each pass is true and even, its just in a different spot each time.
It's your machine, but I'd fix that coupling before tearing into the apron. You're having trouble threading and you've found something wrong that could impact threading. Why not fix it?
 
home finally. took the kiddo to the santa clause parade... its zero degrees here with a wind chill of minus 10 with 35 mph winds... we froze...

i did take a video. im not going to tear the apron off just yet, as im not 100% sold thats the issue. i have the video uploading now, it still has 30 mins to go. ill post it as soon as its done. i ran through the setup and the exact procedure i took to thread. youll see pretty clearly what the problems are. i do not believe it has anything to do with slack or play in the machine. i did count the gear teeth to make sure the gears were correct according to that gear set up diagram.
hang tight for 30 more mins. then i hope many of you will have a clearer picture of what im experiencing.

again, thanks everyone!
 
OK, at the risk of restating what may have been stated before. A little detective work:
First off, the setup for the compound and the threading tool look correct from photos 2 & 3.
Second, the OP stated that the lathe was new to him within a month but there is evidence of much use from photo #2, indicating a previous owner.
Third, From threading table in photo #4, the lathe was originally set up with an imperial lead screw.
Fourth,there appears to be an asymmetric thread as well as what looks like a double cut thread.

If the OP is using the same index mark on the thread dial, he should be cutting a proper thread, regardless of gear setup unless:
1. there is a broken shear pin (already suggested).
2. The PO had replaced the gear on the threading dial with a gear with a different tooth count.
or 3. The PO had replaced the Imperial lead screw with a metric lead screw.

I would lean toward #3 which would explain why the multiple start asymmetric threads and why it was difficult to get the half nuts to engage properly.

You can verify the lead screw by hand cranking toward the headstock and stopping when a particular index number on the thread dial is aligned with the index mark. Measure the distance from the headstock to the carriage. Now continue cranking towards the headstock until the index number is again aligned. Remeasure the distance from the headstock to the carriage. If it is an Imperial lead screw, the difference in distance will by a whole multiple of 1 inch. Most lathes are multiples of 2" but for my Grizzly 602, i6t is 3". If it converts to a nice round metric number, it is a metric lead screw.

If you have a metric lead screw, the method suggested by several above of not disengaging the half nuts but reversing the lathe to back up to make another pass will work. You should be able to cut perfect threads. They may not have the correct pitch, however. Offhand, I would not expect to be able to use the threading chart, depending upon how the change gears were set up on the lathe.
i went #1 to #1 and it gave me aprox 1.75".... ?
 
ok. heres my first ever youtube machine video... hand held phone, so extra shaky... let me know what you think... i can take more videos if anyone wants a better look at anything specific.




sorry about the vertical video.

edit - i meant to say gears 74 and 51 are engaged, not 34 and 51...
 
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