Single point threading on mini lathe

Compound angle is off, as noted above. Also, the threading tool is ground the wrong way, at least for threading to the chuck. It obviously will work, but usually the short part of the vee is towards the chuck. Having the left side being the shorter side allows one to thread closer to the chuck or shoulder.

Edit: More like this. Yours will work, but it might be hard to get close to a shoulder. Photo is a 3/8" HSS threading tool in an OXA holder.

PXL_20240707_010342553.jpg
 
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rotate it clockwise 30 more degrees.

your tool bit will work, but a smaller one is better.
 
try going in at 90 degrees, I always thread at 90' with no problems.
I'm assuming you used a fish tail gauge to ensure the tool bit is at the correct angle.
Also the tip is dead nuts on the centre line.
Does the tool bit have relief on both sides.
 
WobblyHand said:
Compound angle is off, as noted above. Also, the threading tool is ground the wrong way, at least for threading to the chuck. It obviously will work, but usually the short part of the vee is towards the chuck. Having the left side being the shorter side allows one to thread closer to the chuck or shoulder.

Edit: More like this. Yours will work, but it might be hard to get close to a shoulder. Photo is a 3/8" HSS threading tool in an OXA holder.

View attachment 495922
Click to expand...
Tried grinding my own but didn't have the patience and the bit was getting short so I bought a double-ended threading tool bit. It seems I used the wrong end.
 
savarin said:
try going in at 90 degrees, I always thread at 90' with no problems.
I'm assuming you used a fish tail gauge to ensure the tool bit is at the correct angle.
Also the tip is dead nuts on the centre line.
Does the tool bit have relief on both sides.
Click to expand...
I just watched a video where the operator doesn't use the 29.5 method but does like you suggested, 90. Going to try that.
And to your other questions... yes, yes, yes.
 
I have always just gone in at 90deg for single point threading. It might not be ideal, but it sure has been good enough. Never had a problem with this and much easier to setup.

I am also surprised that the sprinkler threads are not a standard NPT size.
 
The 29.5º setting is used for lathes where 0º means the compound advances on a line perpendicular to the spindle. Many Asian lathes have the the zero setting so the compound advances parallel to the spindle and the correct setting is 60.5º for those lathes. Note that any angle less than 30º (greater than 60º for Asian lathes) will work.

If this is not the case, the right flank of the thread will have an angle equal to the compound setting.rather that of the form tool used to cut the threads. If the angle is set at 60.5º relative to the cross slide travel, a sawtooth thread where the left flank is the proper 30º is cut but the right flank is 60.5º. Depending upon the amount of advance of the compound, the right flank will also have a jagged surface.

The purpose of the slightly less than 30º setting is so that the primary cutting occurs on the left flank while the right flank just receives a skim pass. Cutting both flanks equally can result in chatter, especially on smaller less rigid lathes, leading to rough threads.

Good luck with the raccoons. They actually are rather fond of water and once the surprise wears off, I expect they will pretty well ignore your sprayer. A good coon hound is an effective deterrent although the neighbors might not appreciate late night barking.
 
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FWIW
George H. Thomas in the posthumously published The Model Engineer's Manual talks about the "plunge" in method, with a perpendicular compound. He is not enthusiast about it noting that the tool can't have any side rake. I picked up somewhere else that a method to reduce right side cutting is moving forward toward the headstock ~ .0005 after three or so passes. I have seen this method brought up by several British modelers, once in quite the urinary olympics on a Joe Pi thread on SPT. So my casual observation is that it's a common technique in England.
 
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The 30 degree method reduces the area being cut by 1/2 => less part deflection.

If your L/D is less than 4 probably not an issue. If you get up to 8, this could matter a great deal.

For those 8+ L/D situations, I have found giving the tool a lot of top rake helps a lot. Top rake is 0 on most cutters, but this lets one use the 29.5 and skin cut on back side.
 
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