Wednesday, January 11, 2012

PD400 - Cutting the Threads

No appointment at tonight.  So I left office after the system was shut.  Was quite a busy day and a little tired.  My dear wife was called last minute for a visitation with Pastor, therefore, this is the night to complete where I left off in the previous session - threading.

I checked my setup once again to make sure I've not forgotten anything that will screw up the hours spent so far.  The thread cutting tool was installed on the tool holder and the compound was set square to the movement of the bed.  I "fished" out the fishtail gauge (or centre gauge) to make sure that the tool is held perpendicular to the workpiece.

Don't know if I'm using it right.  Comment please?
Once I have everything setup, I ran through the process from the manual again to make sure I have the steps in my head.  I advanced the cutter by 0.1mm into the work and started the lathe.

Right or wrong, we'll find out soon.
First time running the lathe at 80 rpm. The steel was just peeling off the workpiece.
After 2 passes of 0.1mm each.
Checking against the thread gauge.  Right on!
Just about done.  A couple of light cuts should complete the job.
This has to happen at the very last pass... I was trying to get close to almost the should, turn off the lathe and reverse the leadscrew. But I turned the switch to the wrong direction... The tool crashed into the shoulder causing the shoulder to be sheared off and knocking the part out of alignment.  Should have been more careful...
Inspecting the damage.
I rechucked the workpiece and to my amazement, there isn't any visible run-out of the part when the lathe was turned on!  The right hand tool was installed to clean up the mess at the shoulder.

I tried chasing the threads with an M8 die but the die simply refused to go on it.  Frustrated, I took out an M8 flange nut and it threaded on nicely though I can feel a little tightness.

You can see the cleaned up shoulder from this piece.  The nut can be turned all the way up to the shoulder.
Closer view of the almost done work.
Can't really see much from this pic but it is showing the part off turn in use.  I chose the wider Proxxon part off turn rather than the Sherline's or AR Warner's to see how well it work.  The cut was effortless and I didn't experience any binding of the tool during cut.
Almost there.
Look at the long nip... Rechucking the part with the jaws gently pressing on the threads.
After cleaning up.  It took me so long just to make a... bolt... The head (or cap) was chamfered to break the hard look.

Now for the test before drilling the hole for tommy bar.  The clamping plate was taken off the tailstock to make testing easier.

This is the max I can get the bolt into the clamping plate. I measured the diameter of the original blot (the black one  on the foreground.  It is only 0.01mm smaller than the one I made.  Could the bolt I made a little too big?  Checking against the thread gauge confirmed that the thread pitch is correct.
Got to stop here.  Wife is back with dinner.  If anyone know of a way to remedy this, please drop me a note.

Be blessed.


GeneK said...

Wong, some simple observations, first hitting the should need not happen. You did not need to thread up to the shoulder. The portion of the bolt that goes through the tail stock does not need threads, only the part that actually thread into the clamp plate. That will give you more time to stop the threading without hitting.
For the times you need to thread close to the shoulder, turn your tool upside down and run the spindle in reverse, that way you will thread away from the head stock.
My eyes are getting old and your pictures are small enough that I can't see for sure, but some times when I cut threads it raises a burr on top of the thread, so I run a flat file over the threaded portion to knock off the burr, probably about the amount you say is the difference in size of your bolt. Also If you have a tap of the correct size, run it through the clamping plate, their tap may have been getting worn out by the time they tapped yours.


Wongster said...

The problem was solved this morning when I dug out a set of Indian taps & dies bought when I first started. This set came with a slit to open the dies up slightly. I've successfully completed the threads with the die. Wrote a post while waiting for client but what I wrote disappeared when the uploading fails...

Cutting in reverse is something I didn't think about. Should try that sometime. I realized that I don't need to cut all the way to the shoulder. Wanted some practice.

Will see if I have time to complete this small project tonight. Am having fun. I now have a bolt that I made myself! Lolz... But I won't be going into production for Wongster's bolts and maybe nuts. I'll be nuts in no time...