# Another Threading Question



## SteveM (Oct 24, 2014)

I'm a newby who's been at this a couple years. I can cut standard threads pretty predictably but recently needed to cut metric thread and it's been a total shambles. I have a 12x36 Shop Fox lathe with quick change gear box and it's approximately a year old and hasn't been crashed yet) The problem is I'm trying to cut a 1.5mm thread and that is definitely what I get. Have read the manual over and over, pulled up the manual of similar machines, but nothing seems to help. Has anyone else run into this? Yesterday I changed back to standard and cut a good 1.0 x 12 thread first time, no problem, just to be sure it wasn't a basic machine problem. Any suggestions will be appreciated.In the meantime I'm going to count teeth to be positive the gears are correctly marked.


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## MarioM (Oct 24, 2014)

Even if you have a quick change gear box, you need to change some gears in the transmission for changing it to metric. This is how mine works..... I do not really know about your lathe but I am pretty sure it should be the same.


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## MarioM (Oct 24, 2014)

I am sure somebody in the forum will be able to help you with that particular lathe


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## Chucketn (Oct 24, 2014)

"The problem is I'm trying to cut a 1.5mm thread and that is definitely what I get."

I'm not understanding you. You get the thread, or you get shambles? What is the problem with the thread? Are you using the correct gears for the desired thread?

Chuck


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## John Hasler (Oct 24, 2014)

I assume that the word "not" is missing from that sentence.


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## SteveM (Oct 24, 2014)

I've done that according to the manual but.................I get a very pretty thread which is incorrect Am totally bumfuzzled as to what's going on. The Grizzly version shows the 86 & 91 tooth gears reversed but my change gears are made with the opposite position designed in so that's not any option.


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## SteveM (Oct 24, 2014)

Yes, reversing the 86/91 tooth gears is not an option. Per the manual I'm not releasing the half nuts although I've read several different opinions on the subject. I'm ending up with a great looking thread with incorrect pitch.


John Hasler said:


> I assume that the word "not" is missing from that sentence.


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## MarioM (Oct 24, 2014)

http://pics.woodstockint.com/manuals/m1099_m.pdf

Is this your lathe manual?


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## MarioM (Oct 24, 2014)

Sorry.....you said 12x36.....it is not in the web page.....


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## SteveM (Oct 24, 2014)

It's this one. http://pics.woodstockint.com/manuals/m1112_m.pdf


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## John Hasler (Oct 24, 2014)

According to that manual you must install the 86/91 gear with the 86 tooth gear on the outside in order to get a 1.5mm pitch.  Can you explain why you have been unable to do that?


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## SteveM (Oct 24, 2014)

I can do that and have without success. It's possible it's operator error? I will give it another try. Thanks for the input and I'll report back.


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## Wreck™Wreck (Oct 24, 2014)

If the machine will allow it, put the lathe in the gear of choice, engage the half nuts, put a dial indicator against the carriage and rotate the spindle by hand.
The distance moved in 1 revolution is the lead of the thread. Do this before turning any threads of course (-:

Some machines do not make this possible.


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## John Hasler (Oct 24, 2014)

Note that you also must install the G gear so that it engages the 86-tooth gear.  This means reversing it from the position shown in fig. 47.


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## SteveM (Oct 24, 2014)

I'm working my way through this. The 86/91 tooth gears can be reversed. I knew that but had not accepted them as part of the change gear equation. I roughed out another blank this afternoon and will have another  go tomorrow. Worst case I'll take the blank to an experienced friend who offered his machine and expertisee while I sort it out.


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## John Hasler (Oct 24, 2014)

Secure a Sharpie to your toolpost instead of a cutter.  That way you can find out if you've got the gearing right without using up any material.


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## Chucketn (Oct 25, 2014)

Steve, when cutting mertic threads on an imperial leadscrew lathe, you must leave the half nuts engaged, and reverse the lathe to return the carriage after each pass. Same thing if cutting imperial threads on a metric leadscrew lathe.
Don't give up. You'll get it. The gear train needs sorting out and the technique will come.
Do you have a metric screw pitch gage? It will help.
Lots of folks advise practicing cutting threads on scrap pvc pipe until you get the technique down. I did that myself. Coat the pvc with a colored sharpie to make the threads stand out.

Chuck


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## SteveM (Oct 25, 2014)

John Hasler said:


> Secure a Sharpie to your toolpost instead of a cutter.  That way you can find out if you've got the gearing right without using up any material.


 Great suggestion John. DUH...Too simple.Lol.


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## SteveM (Oct 25, 2014)

chucketn said:


> Steve, when cutting mertic threads on an imperial leadscrew lathe, you must leave the half nuts engaged, and reverse the lathe to return the carriage after each pass. Same thing if cutting imperial threads on a metric leadscrew lathe.
> Don't give up. You'll get it. The gear train needs sorting out and the technique will come.
> Do you have a metric screw pitch gage? It will help.
> Lots of folks advise practicing cutting threads on scrap pvc pipe until you get the technique down. I did that myself. Coat the pvc with a colored sharpie to make the threads stand out.
> ...


 another great suggestion Chuck.


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## bfd (Oct 30, 2016)

when you aren't sure what thread you are getting do this: set your lathe up as normal. dykem blue the part and take a .002" cut measure with a thread pitch gauge. this will tell you what thread you just cut. if its right then continue if its wrong reset your lathe reblue and take another skin cut this slight cut will not show up on you finished thread. and you wont need to remake the whole part. plus it might lead you to figuring out where you are making your  error. bill


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## Tozguy (Oct 31, 2016)

SteveM said:


> I'm working my way through this. The 86/91 tooth gears can be reversed. I knew that but had not accepted them as part of the change gear equation. I roughed out another blank this afternoon and will have another  go tomorrow. Worst case I'll take the blank to an experienced friend who offered his machine and expertisee while I sort it out.



From what is shown on p.33 of the manual, the 86/91 gear doesn't need to be flipped at all for metric threads.
The smaller gear (G) on the bottom front of the set up needs to be shifted out to mesh with the 86 gear as John mentioned above.
Isn't it all in understanding the metric gear chart fixed to the front of the lathe?


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## atunguyd (Oct 31, 2016)

If you have a DRO on your lathe or is even easier to test what pitch you are cutting. Engage your half nuts and turn the chuck a few turns to take out any backlash. Now zero your DRO Z axis and then your chuck exactly one turn by hand. The DRO  should indicate the carriage travel and hence your thread pitch. 

If you are cutting a particularly fine pitch it may be hard to get a decent result as your can't turn the chuck exactly 360 degrees, then try for ten turns and divide the dro amount by 10.

Sent from my SM-N920C using Tapatalk


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## epanzella (Nov 1, 2016)

According to your chart, you need to mesh the upper 45T to the 91T and the 86T to the lower 60T with the transmission in B6. This gives you the wrong pitch? If you can't mesh that combination you may have to fab something or reverse the lower gear to mesh further out.  When I got my 12 x 36 grizzly the first time I tried to cut metric threads I couldn't get the correct combo of gears to mesh up. I ended up making a spacer or two and keep them in the box with the change gears.


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