thread cutting on fagor cnc mill 8055i

[toolmaker_79]

hi to all
i am new to this web site,i am working in a work shop where we do all rough machining for mining equipment.we got a fagor cnc mill which is 8055i model.we had a job which is thread cutting has to be donein a rectangular piece for the thread size of 56 mm by 4 mill pitch for 100 mm long.i am not sure we got an rotary encoder r not.as per the manual i did a program using g 33.problem is when i finish one cut instead of the spindle orentation i am moving the tool out for every cut and passing the cut but i know this is not the right procedure.any one can give me any better ideas,and how to do it in the right way.
thanks for u r time and help

[Kiwi]

toolmaker79
I'm not conversant with G33. Does this mode cut the thread as done in a conventional lathe?
For a coarse thread like your 4mm pitch, I would use:

G02 (clockwise starting from top=conventional milling)
G02 X??.? Y0 I-??.? J0 Z-100 K4 (??.? figure to suit the diameter cutter being used)

OR

G03 (counter clockwise starting from bottom=climb milling)
G03 X??.? Y0 I-??.? J0 Z0 K4 (??.? figure to suit the diameter cutter being used)

This method the cutter rotates as the tool travels the helix and can be done with one pass.

[toolmaker_79]

thanks for u r reply.i understand what u mean,but i am not sure we can do it in one pass,b coz its a 4 mill pitch thread,and we got the tool like a boring tool with a thread cutting tool clamped for there is no way that we can move the tool bit diametrically.for increasing the thread depth after each pass to suit the bolt.(if its not possible to cut the thread in single pass b coz its a pretty big thread 56 mill by 4 mill pitch)but as per the manual with g33 we can perform thread cutting if we got a rotary encoder.but i am not sure if the machine i am working on got that r not.i am still learning on it.i try to work with the function g33 its not cutting as the manual says.like u have to adjust the tool for each and every pass.any way thanks for u r time and u r help.

[Kiwi]

toolmaker79
Doing it the way I suggest, the cutter rotates the same as a milling cutter and the full depth of the 4mm pitch is cut with one pass.
You will need a tool like a lathe boring bar with a round shank.
The cutting tip will need to be ground to the 60deg thread angle with rotational clearance. Bore a hole with it to determine the diameter.
There are special tool holder which will hold inserts which could be used. Using this system you will not need to travel the full 100mm as these inserts cut more than one pitch with each circulation.

[toolmaker_79]

hi kiwi,
thanks for u r time and u r reply,i will try the way as u said and see how i go any way once again thanks for u r help