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Author Topic: Conventional CNC Threading  (Read 2762 times)

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Conventional CNC Threading
« on: September 08, 2008, 11:34:52 AM »
Hello Graham and Others,
I have a threaded sample from a commercial CNC lathe, make and model unknown. I will duplicate this part using Mach and my lathe.
Upon close inspection with a microscope, the thread was cut in at least 4 passes.
I can clearly see that each successive pass retracts approximately 30 degrees (of Rotation) prior to the previous pass.
Are some controls designed this way for the G76 cycle ?
Do you know which systems use this technique ?
Also, there is absolutely NO pitch variation during the extraction as it is with Mach.
Curious as always,
RC

Offline Graham Waterworth

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Re: Conventional CNC Threading
« Reply #1 on: September 09, 2008, 06:42:42 AM »
If you think about how a thread is cut, you have to stop at the same end point for each pass of the thread.  The only way to do this as the thread depth increases is to jump out of the thread sooner.

Graham.
« Last Edit: September 09, 2008, 06:48:42 AM by Graham Waterworth »
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Re: Conventional CNC Threading
« Reply #2 on: September 09, 2008, 07:13:18 AM »
Graham,
In this example, the thread does NOT stop at the same end for each pass. The actual jump out for each pass takes place over a very short distance...almost instantly. Then each successive pass jumps out at least 30 deg. sooner. Different than Mach for sure.
Thanks,
RC

Offline Graham Waterworth

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Re: Conventional CNC Threading
« Reply #3 on: September 09, 2008, 07:26:16 AM »
I did not explain that too well.

The Z axis is programmed to stop at a given point e.g. Z-25.0  If the X axis was to jump out at the same point on each pass the lead out would end up as a ring around the job, so they jump out sooner as the depth increases. The amount of lead out is programmed in degrees of rotation in Mach, the reaction time of your set up determines how accurate this is produced.   

Dose that make more sense ?

Graham.
America gave us powered flight, England the steam train and Germany the car.  Who invented the first boat?
Re: Conventional CNC Threading
« Reply #4 on: September 09, 2008, 07:57:30 AM »
Yep...sure does. So this sample was evidently done on a machine with a very fast response to the lead-out and/or was run at a relatively slow spindle speed.
Thanks Graham,
RC