Threading problems

[Delw]

I have a sharp 16-40l its been sitting for 5 years(not used) its 8 or 9 years old, we only used it for chamfering bars for our cnc lathes or an ocassional goverment job.

so I needed to do an Id thread the other week in alum., the finish was terrible, burrs everywere to run a clean up pass it made it even worse.

first thought was the usual operator error, tool problems blah blah blah, everything checked out fine. so in playing with this for a few days I am thinking its slop in the z axis? I did put the z lock to it slightly when it was feeding but it didnt make a difference in the thread.
is there an adjustment? the z axis doesnt feel sloppy ( I tightened up the x axis just to be sure it wasnt the x)
I tried other thread pitches both metrix and standard they all come out the same.
I used to do threads on gun barrel for it with no problems or a fixture for the mill but that was years ago.

I have no clue about manual machines on what to look for when it comes to tuneing up so to speak, on cnc's I can do anything as far as repair, Plus I have no maintenance book on the sharp.

anyone have any idea's?

Thanks
Delw

[Delw]

Just a heads up.

I talked to the tech at sharp industries today, they said it was a half nut, so I ordered one and we will see what happens.

Delw

[Shawn1111]

Originally Posted by Delw Just a heads up. I talked to the tech at sharp industries today, they said it was a half nut, so I ordered one and we will see what happens. Delw

The only problem slack in Z would cause would be to twist at reversal when the half nut picks up which would cause the root of the thread to be wider than desired at finish depth gib adjustment maybe tool above or below center the cut is too heavy ,cutting the thread dry if there were slack in the x this would allow the tool to be pulled above or below center
Typically the half nut just works until the threads wear out and then it will jump lead altogether and will no longer thread or skip during a heavy cut
if the threads in the half nut are done you should be able to make it jump past the lead by hand also it will sometimes lock up and be very hard or impossible to disengauge

Is the bore too tight to clear the chips this will also cause the problem

are you threading into a shoulder or out from a grove some threads finish better from the opposit direction with the tool upside down
one other problem could cause this is if the spindle bearings are loose
These Items would be my first point of inspection
hope this will help you
Shawn

[Delw]

Shawn
the thread is bad enough you can't tell its a thread any pitch that I do.

The finish when not threading is perfect, size tolorance is perfect on turning as well as repeatability.
its just in threading Lets say I make one pass .015 deep per side the thread is close to telling its a threads, when I make another pass at that same setting it destroys the thread.

I to thought it was tooling, center height something loose, threading insert bad etc etc. to no avail. Its got to be mechanical.

One thing I did notice today cause I was playing with it is that when you engage the thread on the proper dial setting that if your off just a degree the level tends to stick then go down all the way, it used to be if I remember correctly that if I was off a degree or 2 the level would have some light pressure then catch smoothly.
I need to fix the oiler anyhow it decided not to work a few weeks ago so I'll replace the half nut as well and hopefully that will work

the bore on the part is 6" dia. even on an od thread I get the same problem. no shoulder no groove just a straight thu one.

[Shawn1111]

In the end you have change gears and it might be that the key is missing or sheared from the drive or driven gear pull them off and check them
During the threading operation have someone watch the lead screw and see if it stops turning this will be also related to a sheared key

Shawn

[Delw]

Shawn
I think your onto something, I read your thread this am, and had never looked in the back of the machine where the gears are, Its not a change gear machine as I was thinking.(meaning you don't have to manually take a gear out and replace it with another for a different pitch like the old school lathes, this one is all built in)

so I popped that cover open, and was seeing if a key way could be bad, like you suggested.
I moved the gears and there was alot of slop, upon further looking there is an adjustment.
you have three gears a small one that goes to the spindle part, then on the adjustment end you have 2 gears one that goes to the levers for the pitch selection and an idler.

the idler was barley touching the head stock gear( small gear) like right at the tips lossened the nut and tightened it up a tad tighter and everything seem to go ok. only about .002 backlash from what I can tell, I didnt know if I needed it tight or not. but could only imagine if it was to tight it would break something.

so now the gears are meshing properly .
I havent tried it yet as far as threading but will and let you know the results.

after sleeping on your first post about the spindle slopping around for a couple of days, I started thinking everyonce in a while at highspeeds 2000 rpm I hey a tinging noise. when I pulled the head stock cover everything seemed fine and tight. so I never thought a second note about the noise. then I put the face plate on yesterday and hear it again. then this morning It dawned on me the noise soundly like gears.

I mainly run a 5c collet and only heard the noise when with the chuck or face plate ( Inertia? sp)

Anyway thanks alot for that post this am. hopefully that will fix the threading problem.

Thanks
Delw

[DareBee]

Have you tried doing this thread without disengaging the half nut?
This is the safest way to thread.
At the end of the thread crank the X clear and reverse the lathe (without disengaging half nut) when you get back to the start stop the spindle, reset X for the next cut and turn to forward.
This should eleminate all slop errors.
If the thread is still bad then I would say it is spindle or tooling problems.
I assume you are using lots of tapping fluid as well.

[Shawn1111]

Your change gears will be fine if they have between .007 too .015 backlash as long as you can move them back and forth smoothly with your hand

Originally Posted by Delw Shawn I think your onto something, I read your thread this am, and had never looked in the back of the machine where the gears are, Its not a change gear machine as I was thinking.(meaning you don't have to manually take a gear out and replace it with another for a different pitch like the old school lathes, this one is all built in) so I popped that cover open, and was seeing if a key way could be bad, like you suggested. I moved the gears and there was alot of slop, upon further looking there is an adjustment. you have three gears a small one that goes to the spindle part, then on the adjustment end you have 2 gears one that goes to the levers for the pitch selection and an idler. the idler was barley touching the head stock gear( small gear) like right at the tips lossened the nut and tightened it up a tad tighter and everything seem to go ok. only about .002 backlash from what I can tell, I didnt know if I needed it tight or not. but could only imagine if it was to tight it would break something. so now the gears are meshing properly . I havent tried it yet as far as threading but will and let you know the results. after sleeping on your first post about the spindle slopping around for a couple of days, I started thinking everyonce in a while at highspeeds 2000 rpm I hey a tinging noise. when I pulled the head stock cover everything seemed fine and tight. so I never thought a second note about the noise. then I put the face plate on yesterday and hear it again. then this morning It dawned on me the noise soundly like gears. I mainly run a 5c collet and only heard the noise when with the chuck or face plate ( Inertia? sp) Anyway thanks alot for that post this am. hopefully that will fix the threading problem. Thanks Delw