from a previous post i was wondering how possible is it to cut threads into acrylic acetate and ebonite if,

1. you are only using a mini lathe, a wilton.

2. you have limited funds.

3. and, how do you finish the cut threads so they are polished and as shinny as the rest of the pen.

i know nothing about cutting threads.

much appreciated.

You said you know nothing about cutting threads so:

Cutting threads on a lathe requires that the lathe be set up to allow this.

A thread is an inclined plane, wrapped around a cylinder. There is a unique place at the intersection of the face of the cylinder and the diameter, where the thread starts. You must be able to start your cut repeatedly at that unique place. This requires that the lathe have thread cutting capabilities. This is usually evident by a seperate handle to engage what might be interpreted as feed, and a wheel with some numbers and or lines on it that turns when the carriage is motionless. What all this does, is allows the spindle of the lathe to be synchronized to the carriage.

Does your lathe have these features? Good.

Threads are "V" shaped with the "V" being a 60 degree inclusive angle. I highly recommend you purchase a thread cutting tool holder and carbide inserts if you plan on cutting threads. Believe me, it is easier and cheaper than grinding your own cutters. If your not going to do that, then at least buy a "Centering Gage" that is a small piece of metal all about that angle. $7 or $8. You will also need an internal thread cutter of course. It is imperative that the cutter be set to the cylinder, such that the thread angle is equal on each side of a line drawn perpendicular from the cylinder. Imperative!

Pens often use multi-thread threads. This means that the diameter of the threaded portion may have two, three or even four threads cut inside of one another. Overlaping, if you will. This allows for a much faster pitch (the distance the thread "moves" linearly per revolution) without giving up the surface contact of the thread(s). This requires either your lathe be set up to cut multi-threads or you have a way of rotating your piece accurately between thread cutting processes. You can "trick" the lathe by setting the compound parallel to the longitudinal axis and back up exactly one half the pitch of the thread. This will cause the start to be 180 degrees from the initial start.

You cannot cut a thread to just any specifications you dream up. Okay, you can, but it doesn't work out well. The ratio between pitch and diameter and depth of thread needs to be correct. I suggest you look up the numbers in The Machinery's Handbook. There is a lot of information on Threads in The Machinery's Handbook.

Now then, I've prattled on long enough for now. If your machine will do it, and what I've written doesn't scare you off, I'll tell you the secrets of machining threads in lesson two, upon request.

i only have a mini wood working lathe, i was thinking more about a tap and die set

still your post was very informative and i appreciate the time you spent. i guess i wont need part two, well not for now anyway.

Hi Clydesdave,
My sincere congratulations on your simple & clear primary explanation on thread cutting.
I expect you are a technical teacher or an engineer !
regards, Francis

aurrida,
Commercially available taps & dies are not really suitable for pen making. Pens really want very fine pitch threads with multi starts and standard threads look a little odd. I put an M10 coarse thread on a connector I made for a Parker 61, as shown in the picture below. Even I'll accept it looks odd.

Regards

Richard

thanks everyone, i think i will go in a different direction. i dont really have the resources needed to get into the engineering side but its been interesting finding out.