Cutting wood threads on the metal lathe

[Don Wattenhofer]

This is a response to some comments in a discussion post about thread chasing that morphed into threading jigs.
The comment I made was that if you owned a metal lathe you had the best machine for threading wood.
I started experimenting threading wood in 1990 and succeeded in making a 2 1/2" - 2 maple bench screw and nut plate and that was enough to get me started.
I will start with photos and explanations in installments of the current method I am using.

This photo shows a rough turned walnut urn and a blank for a lid along with male & female threaded chucks plus a box full of chucks in various sizes. The rough opening is about 2 1/8" diameter so I chose a set a nominal 2 1/2" - 10 (10TPI) (Metric terms 63.5MM X 2.54MM). The opening for the female thread was cleaned up to about 2.25" then it was taken from the wood lathe with the chuck to be mounted in the metal lathe.

These 3 photos show the modifications necessary to the metal lathe. The first & second show how the 1 1/4 - 8 adapter is mounted to my LaBlond Regal lathe: The large threaded collar protects the spindle thread and is also used to remove the collet holder. The next piece is the 4C collet holder that fits into the headstock morse taper and adapts to the 4C collet. The third item is a 4C shank with the 1 1/4" - 8 adapter attached. Note the 4C collet system is no longer available, but it came with the lathe so I used it. The third photo shows the router mounted to the top slide with a 2 flute custom made carbide tipped 60 degree 1/4" shank bit.

I will try for the next installment tomorrow maybe.

 

[Don Wattenhofer]

The First installment talked about how I made the adapter to mount the wood turning chuck in the metal lathe but the actual adapter that someone else would make depends on the metal lathe you have and I am assuming that if you have the metal lathe you can figure out how to make an adapter that works for you.
This photo shows the trued up form ready to cut the female thread, however there are some settings to do on the metal lathe.
This is a view of the Thread pitch settings: The chart on there details the settings necessary to set up for 10 TPI: The fine / coarse lever ( not shown above the chart) is set to coarse, The prominent round lever is set pointing to 10TPI. The bottom lever has 3 positions and the chart says to put it in the middle. The final setting is engaging the lead screw which is the upper shaft coming out of the righthand side - the slide is moved to the left to engage.
The top slide is set to 29 degrees.
The hand wheel on the top slide is used to feed the cutter into the thread so to start set it to zero then use the Y axis to move the cutter to just barely touching and back the cutter out of the work piece.
This is the chasing dial and it is used to determine when to engage the lead screw for 10TPI that is an even thread so any line will work. Set the top slide to 100 thousands or 0.1" (the thread does not need to be cut in one pass I usually do it in multiple passes to sneak up on a good fit and you may want to soak the partial thread with CA). Start the lathe at it's slowest speed ( I have added a VFD to slow it down even more if I desire). Start the router then with the threading handle on the cross slide gear box engage the lead screw when the chasing dial is on any one of the lines Note if you miss a line wait for the next one. The thread will be cut as soon as the bit reaches the opening then when the bit clears the inside or where ever you want to stop disengage the lead screw. Stop the lathe and the router then if using the double angle mill note the setting on the top slide and back it out of the vessel. If you have a 2 flute bit just turn it so both flutes are clear of the thread. The size of the X axis will determine how far you can back up to test fit the thread. The final fit should be fairly loose to account for seasonal changes and don't use a fine thread because there will be less tolerance available for the inevitable wood movement.
I welcome questions if I have not explained any of these points