Cutting very fine threads

[funkychicken]

Not sure where this thread should go but I'll stick it here.

I'm wanting to cut some very fine threads in (hard) Hardwoods for some custom pen kits. Would a metal lathe be the go? I've been wanting to grab one for a while, this would be the perfect excuse:D

[weisyboy]

get a cheep tap and dye set

[funkychicken]

Nup, wouldn't work

[Woodlee]

I'm not sure that a fine thread would work in wood ( no pun intended).The wood fibres would just tear and break away I reckon.But a metal lathe would certainly cut it if fitted with the appropriate gearing ,but have never tried .I don't like wood dust near my lathe anyway.

I don't know any thing about making pens ,but would think that you would use a metal ferrule with the fine thread in or on that .

Kev

[.RC.]

What is your definition of a "fine thread"??????

[funkychicken]

The bit on the right will screw into the bit of timber which should look like the bit on the left

[Kody]

Fine threads in wood can be cut with relative ease. The secret is to use a fly cutter mounted in the toolpost. The metal lathe is set up to cut the TPI and the fly cutter is rotated at very high spped to then cut the thread, The leadscrew is engaged and the chuck is very slowly rotated by hand. The flycutter will advance along the bed and machine the threadform. To cut a perfect thread, the cutter needs to be tilted to the angle of the thread "slope". This can be determined with a simple trig calculation. The spindle that the flycutter is mounted on must be very ridgid. I used a sewing machine motor to drive my cutter but an air driven grinder can also do the job. The drive from the motor was via a light belt. Be very careful not to engage the precious pinkies in the rotating cutter. The slower the rotation of the chuck, the better the finish of the thread. It is best to swing the toolpost to 30/60 degrees so the cutter only cuts on one face, same as when cutting a thread on metal. A deep thread (1/4") can be cut in this manner. With a razor sharp cutter, the result is outstanding.
The only way an internal thread can be produced in wood it to use a brand new tap and even then, the thread wont be of high quality. If the ID of the internal thread is large enough, the fly cutter (if made small enough) can reproduce an internal thread. Its slow work but it is very satisfying in the end.
The best and quickest way to make the threads is to make two sleeves of brass and thread these to fit. The best part about the brass is that the threads dont wear out like a wooden thread will.

Kody

[funkychicken]

Rightio

Rethink: Cut the thread in brass. Will a small tap (http://www.carbatec.com.au/metalworking/metalworking-accessories/micro-hss-tap-die-set) work?

[Kody]

The quick answer is.. NO!
A "small" tap, about 6mm or 7mm in dia or even less, may still have a thread that is too coarse for what you want. If you want to use a tap, explore the standard sizes available and work from there. A 1/4" UNF might do the job (28 tpi) or maybe a 5/16 UNF. There are some very fine thread metric taps listed as standard but these are as common as chooks teeth to find and they are very expensive. If I was doing what you intend to do, I would screwcut the od threads at 32 tpi and make a tap from silversteel to thread the internal parts. Because you would be making lots (?) of these, I would also screwcut the internal threads as well as the external ones, but thats me! Making a tap to give a good finish and consistant size can be a pain in the neck. keep in mind that a sloppy thread will reflect on the finished quality of the pen you are making. You can a glorious grain patern, highly polished timber, perfect shape to hold and look at but if the thread is sloppy, it will look like a cheap piece of Chinese junk. It's just a thought.

Kody

[weisyboy]

take the piece with the thread in to a mob that specialize in fasteners they will be able to give you exactly the right tap.

[funkychicken]

Okay I'm clueless when it comes to Metalwork. Whaddya mean by screwcut?

So are you saying I should make my own tap?

[Woodlee]

You might try Model Engineers thread 32 tpi and 40tpi or British Standard Brass threads 26 tpi.
Taps and dies are available for these threads .

Kev.