View Full Version : G70 &G71 problems

Stephen Beecroft
03-07-2004, 12:59 PM
A friend recently bought a TL-1 (Haas) CNC lathe. I've been writing a few programs for him, but have been having a few problems.

I'm trying to machine a socket -0- a 2" ball with two shafts on either end and a 3/4" hole through the center. I had no problem with the circular intepolation part of the programming, but when trying to use the g70 and g71 to rough and finish the part i incountered a problem. The roughing cycle does the appropreite job, but the finishing cycle does not finish the radius ball and just leaves the roughed out shoulders..

03-07-2004, 08:15 PM
Look for a repeating shape / pattern canned cycle. You are using straight turning cycles meant to primarily turn from one direction or another. Your plunge is probably from the front of the part and to the chuck, retract then return and cut that way again. The repeating pattern cycle will do the same, but will cut the pattern in increasing depths. On my lathe this is G73. You program the points like a G71 and such, there is no G72. The part will cut the pattern in increasing depths, you specify the start distance away from the part, and number of times to cut.

I make candlesticks with this method. It is the only way to do it.

The alternate way is to program 1/2 of the ball from the front with the first G71, front to chuck, the second half of the ball from chuck to front. Finally cutting the ball with a specific G01 / g02 / g03 finish sequence.

I have programmed many of these "balls" before, I prefer the "repeating pattern" methiod.

Be sure you have proper back clearaice on the tool, and that your Nose radius comp is correct. Even then, you wil have to "cheat' the back side on the finish as the back of the tool does not properly "comp" unless you are using a ball end type of tool - "convex" Dog bone or a complete rounded tip.

03-08-2004, 02:03 AM
The Haas Factory Outlet that your friend purchased the machine from can be called and they will assist you with the problem - it is a resource that you are entitled to use as a customer - use it. They have lots of neat tricks that they can help you with that you would never have thought of - get used to calling them first, that is what the HFO's were set up for in the first place, to give superior quick service to their valued assists - you, the customer. You have a great machine, BTW