Single point threading on mini lathe

[GeneT45]

What is the cutting depth per pass that you guys recommend for a thread?


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You really just have to get a feel for it. Everything changes with the machine and the workpiece. Generally though I'll take a 'scratch pass' to verify that my pitch is correct and that nothing else is wrong with the setup. Then I'll take a pretty deep first cut (maybe 0.025" as long as the workpiece can take it) and take a bit less per pass, getting to just a few thou dialed (I use the compound for infeed) in the last passes. As I approach final dimensions I make a spring pass before stopping to measure or test the thread. If the workpiece is long and/or thin, I'll take lighter passes to reduce deflection.

Watch for chatter or part deflection and reduce your infeed if it occurs. If in doubt, just take light passes. In a hobby shop you don't have to 'make time'.

GsT

 

[Smithdoor]

Hi,
Here's what I'm doing...

First some history...
I have a HUGE problem with raccoons in my yard due to a large sprawling park less than a 800 feet from my house. They deficate on my pool deck, go for late night swims in my pool, tear up my solar cover, tear up my lawn looking for grubs, eat my vegetables and do other things that raccoons do. Quite annoying.
I have tried everything imaginable and other suggestions through advise like cayenne pepper, mothballs, mint, and other solutions recommended by nature enthusiasts but the only thing that has worked is motion sensor sprinklers.

I have run a dedicated water line around my yard with taps at strategic locations where I setup these devices and control them globally with a water timer, on at 10PM, off at 6 AM. However, these devises are designed to cover a large area, like a lawn not a 10-12' x 25' pool deck and they spray high and far.

So, I have endeavored to make a more suitable 'sprinkler' or 'water application device' triggered by the motion sensor of these devices, that keeps the stream low and confined. (Neighbors complained about sudden streams of water coming over their my fence during their late night parties. Sheesh!) To do this I had to determine the thread used to hold a sprinkler head which is 25/32" - 14 (to my best measurement) which means I need to SP it.

Now here's the reason for this post....
When I set up my mini lathe to cut the appropriate TPI after turning the correct diameter and set the compound to the traditional 29.5 degrees, cross slide to zero after touching off, thread cutting tool bit mounted and set correctly, everything looked good on the scratch pass but, when completed, the threads had a saw-tooth shape rather than the nice V that I was expecting.

What did I do wrong?

PS: apologizes for the long story but the wife found it very funny so I thought you would too.

Michael.

Most of my threading I only use the cross slide.
But on mini lathe for corse threading it may take to heavy of cut.
So use the compound set at 29½°.
This from a data from about 1900.

Other thread like acme use different angle.

Dave

PS
Some will cut all threads at 29½° nothing wrong just takes longer.
When first started I use 29½ and change in 1976 to cross-slide

Until purchased my mini lathe I cut all threads using just the cross-slide for speed.

 

[GeneT45]

Other thread like acme use different angle.

Which is half the included angle, minus 0.5*. So for acme (29* included angle) set to (29/2): 14.5* - 0.5* or 14*.
Hope that makes sense.

GsT

 

[redvan22]

I have become a single-point thread cutting freak! Every external thread I need now, I SP. Takes a little time to change the gears on my mini lathe and do the necessary setup but I really enjoy it. I do it the old fashioned way, cutting towards the headstock. I don't see the issue so many complain about, the "white-knuckle" syndrome of possibly crashing into the headstock or ruining the piece. I haven't yet and really don't see how it can happen, if you're watching what's happening. Albeit running the machine faster to overcome the issues of a mini lathe (low torque) compared to a larger lathe does present a challenge to not ruin the piece, like I said, if you're paying attention, I don't see an issue.

 

[GeneT45]

Now go try an internal thread. The only surprise should be that it's just more of the same (albeit you need to crank the tool out of the cut in the opposite direction. After a few goofs when I was learning I started making a sharpie arrow on my cross-slide when cutting internally (the mark wipes right off with a bit of solvent when you're done). Other than that, it's just more of the same, and it's well complements your new-found external threading skills.

cheers,
GsT

 

[Larry$]

Which ever method you use, practice until you feel confident. I started by using the traditional 29.± method. Watched Joe Pie's videos on the subject and found it was easier. ½ the # of moves, less chance of a mistake. The use of some lubricant also helps. I also find that threading away from the chuck has fewer risks.
Side note: Joe Pie's use of thread wires also makes life much easier. No need to juggle 3 wires.

 

[Cadillac STS]

Standard thread pitch for garden hoses is 11 and 1/2 tpi.

Different here but wanted to toss it in the “thread” on turning threads

 

[verbotenwhisky]

I have become a single-point thread cutting freak! Every external thread I need now, I SP. Takes a little time to change the gears on my mini lathe and do the necessary setup but I really enjoy it. I do it the old fashioned way, cutting towards the headstock. I don't see the issue so many complain about, the "white-knuckle" syndrome of possibly crashing into the headstock or ruining the piece. I haven't yet and really don't see how it can happen, if you're watching what's happening. Albeit running the machine faster to overcome the issues of a mini lathe (low torque) compared to a larger lathe does present a challenge to not ruin the piece, like I said, if you're paying attention, I don't see an issue.

All my sprinklers use NPT threads on their base.

 

[Cadillac STS]

Is it raccoons like this?

 

[Janderso]

Do you have a pic of your setup?
Sound like your 29.5 degree setting may have been the incorrect orientation.

Yep, the angle is not 29.5. I have two protractor or my lathe. One is correct for threading the other isn’t right.
You’ll get it.
Been there.