# What Am I Doing Wrong



## Fortis64 (Jan 8, 2017)

I've tried threading a few times with some success but more failure . I set the lathe up as is shown all over the internet and youtube . . My threads always seem to lean to the right as I'm looking at the lathe ,the thread is formed just doesn't look right. I spent a good couple of hours making a backplate for my 4 jaw ,everthing was perfect and then i started threading the 7tpi 1 3/4 " bore ,then the problems started . The back plate is junk now  . I should've taken photos . My thread dial doesn't line up bang on the mark ,it's more like a 1 1/16th of an inch either side ,i can never get my half nuts to engage right on the line . I'm staring to think it's not the correct tread dial .   . Any advice welcome .....

Sean


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## Billh50 (Jan 8, 2017)

Without photos it is hard to tell what is wrong. But as far as the dial not lining up on the mark. The dial could be the right one but the housing for it may be off a bit. Mine was just a bit and I made a shim for the housing so now it reads right at the mark when engaged. It is still usable the way it is as long as you keep engaging at  the same place. It shouldn't matter if it is before or after the mark as long as it is the same. So if your first engagement is just before the mark you should always be just before the mark when engaged. Other than that I am not sure why your threads may be off without photos.


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## Tozguy (Jan 8, 2017)

The thread dial can be adjusted to engage on the marks. Usually by moving the index mark or by rotating the gear on the shaft.

Threads leaning right; using method shown all over the internet(?); need more details on this.
Are you are feeding with the compound set at 29,5 deg to the spindle axis or 29.5 deg from the cross slide axis?

As Bill said, pics would help a lot.


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## Fortis64 (Jan 8, 2017)

I  set the compound off the chuck to 29.5 deg .

Sean


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## Tozguy (Jan 8, 2017)

Sean,
Could you supply photos of your set up please?


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## brino (Jan 8, 2017)

Hi Sean (@Fortis64)

Do your threads look like this:
http://www.hobby-machinist.com/threads/threading-help.49488/

That problem was caused by setting the angle of the compound slide wrong.
It is easy to do, because some machines measure it relative to the lathe axis (the imaginary line from headstock centre to tailstock centre), while some measure it with respect to the cross-slide motion (ie. 90 degrees perpendicular to lathe axis!).

You need to know which kind of machine you have.

Hope this helps,
-brino


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## higgite (Jan 8, 2017)

Maybe this will help.




Tom

Edit: Just noticed that this is in the thread that Brino posted a link for. Great minds....


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## Fortis64 (Jan 8, 2017)

Yeh that's how they look ,a bit worse than that . Maybe I need to try the 90deg method then I'll find out I suppose. 

Thanks guys .

Sean


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## BGHansen (Jan 8, 2017)

I set the compound to 29.5 deg. as mentioned above for external threads.  If I'm reading your post correctly, you are threading internally.  In that case the compound is swung so the crank will be under the work at the 29.5 deg. angle or whatever the protractor reads on your lathe (if that makes sense).  You'll want it to be slightly under the 30 deg. angle from square so one edge of the cutting tool is doing all of the heavy work, other side is just scraping the opposite side so you don't have steps in the thread from multiple passes.

Sounds like your tool is not square to the work or you are getting deflection while threading.  I verify the tool is set at the proper angle to the work with a center gauge like the one pictured below.  Set the flat edge on the work and set the 60 deg. V of your tool into the V of the gauge.  Adjust the tool post (not the compound) so the tip of the cutting tool fits into the gauge V.  For internal threading, you'll set the gauge on the back side of the work, front side for external threads (assuming you have a cylindrical part in the lathe).

If you don't have a center gauge, you can use a hardware store bolt.  Lay it on the work same as the center gauge and set your tool bit into the threads of the bolt.

If you are square but are still getting an off-angle thread, you might try less depth of cut.  I usually go around 0.002" - 0.003" on the radius per pass.  Others may go 0.005" - 0.010", but I'm conservative when it comes to depth of cut.  The deflection could also be from the boring bar sticking out too far from the tool post.  

Hope that helps, good luck with the backing plate!

Bruce


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## Tozguy (Jan 8, 2017)

All might not be lost with your backplate. By installing a threaded bushing in the back plate might be salvaged. It would be a threading exercise for you.


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## Fortis64 (Jan 8, 2017)

Bushing sounds good ,because everything else with the backplate was perfect.  I made a sacrificial register to test fit when I was turning the actual part and the fit was perfect 

Sean


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## epanzella (Jan 8, 2017)

Feed with the xslide.


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## Fortis64 (Jan 8, 2017)

Went  out to the lathe for 5min.... I reckon I've had the compound setup  totally wrong .I was reading the protractor wrong .I had it set to too much of an angle ,and yeh i forgot to take a photo ... That'll explain why it was catching the top of the thread after about 3 passes and there after . This all marries up to the setup images I've been looking at today .... Feel such a fool now and annoyed with myself ... All the time in getting the backplate right in ever other aspect .. 

Sean


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## T Bredehoft (Jan 8, 2017)

That's how we all learn, If you do it right, you won't remember it, do it wrong, study, figure it out, then you'll remember it.


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## Fortis64 (Jan 8, 2017)

Learn by them ... is what i was always told ...

Anyways ,looking like i have a bushing/slug to make ....This'll be interesting


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## HBilly1022 (Jan 8, 2017)

epanzella said:


> Feed with the xslide.



This is the way I do it most of the time because it is easier, if the machine can take the heavier cut. That way the compound setting is not important. I'm relatively new to this hobby (about one year of hobby use) and was confused by the need to set the compound at 29.5* until reading some reference material. From my understanding, the basic difference between the 2 methods is that using the compound and advancing it at 29.5* only cuts on one side of the tool tip. Using the cross slide (plunge cutting) will cut on both sides of the cutting tool and requires more power and exerts more force on the equipment. With my first lathe (10 x 22) I had to take very light cuts when plunge cutting and the machine would struggle, sometimes stalling and jamming in the cut, even with cuts as shallow as 0.001". It was easier to use the compound but the setup was important. I did the same thing you did and set it off the wrong reference. Oh well its all a learning experience. With my new larger lathe, I can take much deeper cuts while plunge cutting and there is no issue with lack of power or rigidity.

Not sure what size lathe you have but you could try plunge cutting and see how that works for you. Good luck.


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## Fortis64 (Jan 8, 2017)

It's a fortis/Clausing derived  12" swing with a 1 1/2 hp motor .  When i was turning down the back plate i experimented in seeing what the lathe would do ,and i stopped (chickened out) at 60 thou on a 7"od interrupted cut . It's a tough old girl and that was tough on it too,  I wont be doing that again .

Sean


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## JR49 (Jan 8, 2017)

Fortis64 said:


> It's a tough old girl and that was tough on it too, I wont be doing that again .


Fortise64, please don't stop experimenting.  That's how we learn.  I think your "experiment" was skewed by the large dia. and interrupted cut.  I'm also new to this, but would bet that without the interrupted cut, your lathe would have been perfectly happy.  Happy Machining,  JR49


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## Whyemier (Jan 8, 2017)

Yes, making a mistake makes an impression and you remember...unless your me then you have to do it at least one more time.  
So learn by them...unless your were referring to "THEM!", the 50s movie...big ants and all that.


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## Tozguy (Jan 8, 2017)

Feeding in at 90 deg (as when using the cross slide) for a 7 tpi thread is going to take a heavy cut at full depth. Why not stay with feeding the compound at 29.5 deg. for such a coarse thread now that you have it wired?


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## dulltool17 (Jan 8, 2017)

First off- darned near everyone has mis-calculated an angle or two.   This mistake is way more common than folks will admit.
Second- those that make no mistakes generally aren't doing much, at least in my experience.

Keep at it!


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## AGCB97 (Jan 9, 2017)

First    on setting the compound to 29.5 on my lathe that is 60.5 degrees on the dial. Check that on yours.

Second     I had to put a magic marker line on the thread dial so it would engage on the mark. It's only a little bit different than the stamped mark


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## ddickey (Jan 9, 2017)

A quick way to tell if you have your angle correct is to set your tool on the compound with one cutting edge parallel to the side. Your tool should point straight ahead, perpendicular with the axis.


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