"Vincent Coppola" wrote in message
om...
Hello,

I am rehousing a webcam for use in astronomy and I turned down on my
minilathe a simple adapter tube out of aluminum to fit the standard
1.25" diam eyepiece holder.
I now have to turn an inside thread to hold
a standard filter. The filter requires a 1.125" x 40tpi thread. I am
trying to grind my own highspeed steel tool and having some difficulty
getting the threads to look right. They are there but look flattened.

DoN has mentioned the necessary amount of clearance on the threading tool,
but there's one thing that you may be missing, and it's easy to do. The way
you describe your thread leads me to believe that you have your compound set
improperly. The markings on compounds are not all the same. What is 30
degrees on one is 60 degrees on another. To set your compound properly,
assuming you are threading a right hand internal thread, cutting from the
outside towards the headstock, you should start with your compound parallel
to the cross slide, with the handle towards you. At that point, you should
turn the handle TOWARDS the headstock until you've gone almost 30 degrees.
I like to use 29, which makes sure you keep cleaning up the back side of the
thread. It may not read 29 degrees, but 61 instead. Don't let that worry
you, it's the way the machine is marked. Setting the compound as I've
suggested is important to a good end result. Don't set the compound the
same way you do for an external right hand thread.

If you're not comfortable with your compound set as I've suggested, the next
best way is to set it exactly 180 degrees opposite, with the handle on the
far side of the bed, and pointed towards the tailstock. That way you always
feed such that you keep the leadscrew loaded by the cut. I tend to harp
on this subject endlessly, but it's a good lesson to learn and remember, and
it ALWAYS applies when threading, regardless of the type of thread.

Hope this helps. If you're still having trouble, feel free to contact me
on the side and I'll try to carry you through the proper threading tool
configuration. There's no real reason to NOT hand grind this tool, it's
quite simple to do.

Harold





Does someone have a dimension or procedure for grinding such a
tool to work with aluminum? Would the same tool work for delrin? I
have searched the web many times and I can turn up very little on this
subject.

Please advise,

Vince Coppola