5641
General Mach Discussion / Re: Problems threading on the lathe
« on: October 05, 2009, 07:43:36 PM »
ART,
Did a few more test pieces today. Same 115 rpm, 40 passes @ .0001" deep for 10,20,40 TPI.
I used the standard lathe screen and threading wizard.
Now we know that the tracking was good but the lead was decreasing. So i tried the tests with adjusted lead.
The rounded lead error was a decrease of .008" / inch. So I just changed the lead to be used in the wizard as follows:
TPI TRUE PITCH MODIFIED PITCH
10 .1 .1008
20 .050 .0504
40 .025 .0252
The Gcode provided by the wizard will post the modified feedrate ( namely .1008 / .0504 / .0252 ) even though it rounds it in the wizard screen.
The lead error in 1" was almost un-measurable ( including each crest / root distance ............ 0 or under .0005" / inch. That's about as perfect as you can get! Heck, what are you measuring, the lead screw accuracy if you know what i mean.
You can also decrease the inputed lead if you want to take care of an advancing cut lead. I haven't tried a 0-80 to see if the lead should be modified to .01256 ( don't cut to many 1" long 0-80's ).
Will relative / ratioed numbers hold true for other rpm? I don't know.
So, if you left the threading code alone, and a user tested ie; cut a scribbed test piece at .1" pitch for 1 or 2" long and very accurately measure the lead, then adjust feedrate accordingly, they may just solve their problem.
It's a work around, an easy one, but users must remember that there are a lot of other influences that can play into threading.
Is John S doing any testing?
RICH
Did a few more test pieces today. Same 115 rpm, 40 passes @ .0001" deep for 10,20,40 TPI.
I used the standard lathe screen and threading wizard.
Now we know that the tracking was good but the lead was decreasing. So i tried the tests with adjusted lead.
The rounded lead error was a decrease of .008" / inch. So I just changed the lead to be used in the wizard as follows:
TPI TRUE PITCH MODIFIED PITCH
10 .1 .1008
20 .050 .0504
40 .025 .0252
The Gcode provided by the wizard will post the modified feedrate ( namely .1008 / .0504 / .0252 ) even though it rounds it in the wizard screen.
The lead error in 1" was almost un-measurable ( including each crest / root distance ............ 0 or under .0005" / inch. That's about as perfect as you can get! Heck, what are you measuring, the lead screw accuracy if you know what i mean.
You can also decrease the inputed lead if you want to take care of an advancing cut lead. I haven't tried a 0-80 to see if the lead should be modified to .01256 ( don't cut to many 1" long 0-80's ).
Will relative / ratioed numbers hold true for other rpm? I don't know.
So, if you left the threading code alone, and a user tested ie; cut a scribbed test piece at .1" pitch for 1 or 2" long and very accurately measure the lead, then adjust feedrate accordingly, they may just solve their problem.
It's a work around, an easy one, but users must remember that there are a lot of other influences that can play into threading.
Is John S doing any testing?
RICH