Cutting course external thread on a lathe?

Use a thread cutting lathe and a 60 degree tool. Other than that it depends on the lathe. Make the thing from aluminium if possible and use parafin as cutting fluid if you don't have proper suds. RDG Tools stock cheap thread cutting tools ground to shape. What lathe do you have?
 
nigelmercier said:
This is the thread dimensions of a Raymarine ST60 Wind Vane. I plan to find out what frequency they produce for a given speed, so I need to make a handle.

I wonder if I can make this on my lathe? Any tips or suggestions?
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The thread which matches these dimensions is M22x3 in the Metric Thread - Extended Thread Size Range. See http://mdmetric.com/tech/M-thead%20600.htm

Depending on your lathe, a course thread like this may require the lathe to be turned by hand.

Paul
 
If this is just for experimentation, turning a screw-on handle seems a bit OTT. Slide some contacts over the pins and tape a stick to the pole?

Pete
 
If you've got the right back gears, you should be able to do it.
You should be able to grind a form tool near enough to the thread profile for it to work, I guess it does not need to meet the theoretical strength of an M22 thread.
 
Use a turning handle and set the compound slide to 29 degrees. Feed in tiny increments using the compound slide and repeat each cut at the same setting, several times when approaching the finishing. Copious amounts of paraffin. Watch out for material build-up on tool and remove as necessary.

Since you have a lathe, one simple but very useful project that you should make is a turning handle.
Find a short length of pipe that is a sliding fit in the bore of the spindle; turn a slow taper in the bore of the pipe.
Split the tapered end with three or four lengthwise cuts using a hacksaw.
Turn a matching outside taper on a short length of round bar that is slightly less than the bore of the spindle.
Drill and tap to take whatever length of studding you have handy (e.g. M8 or M10 if it's a small lathe).
One end of the stud is threaded into the male taper and fixed in place with Loctite; the other end exits from the back of the spindle and is used to hold the handle. (length of flat bar with a hole for the stud at one end and a loose handle at the other).
Tightening a nut on the stud holds the handle in place while it pulls the male taper into the pipe and locks it to the spindle (like a Rawlplug).

Very easy to make and very useful. I would say that it is essential for cutting threads on a small lathe.
 
nigelmercier said:
You don't know me very well, do you. :)

Lathe is one of these: www.amadeal.co.uk/acatalog/----span...--Metric-----span-----AMA_LA_CJ18_M_3JRB.html

Buggerit, just seen "Range of Metric Threads: 0.5 - 2.5mm"
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It should be possible to cut a 3mm thread. First of all what is the leadscrew pitch? If it is 3mm then it just has to turn at mandrel speed, i.e 1:1 gearing. If it is 2.5mm then you need to gear it up from the mandrel 6 turns for every five of the mandrel. If the change wheels are in 5 tooth increments that should be easy enough. If that fails then look up the changewheel combination for a 1.5mm thread, then see if you have a pair of gears that will make a 2:1 increase in that. If that fails try the 2mm pitch combination and a 1.5:1 step up pair. Puff the magic Dragon gives good advice re making and using a crank handle which is the only safe way to cut coarse threads on a small lathe.
 
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