4th axis feed rates

[SVO]

Doing some 4th axis milling in 17-4 mat'l with a .031 endmill. I don't understand what determines the feedrates or how their calculated. Machining with the "x" and "a" axis the post puts differant feedrates on several lines. I realize the feedrates and in degrees/min, but their forever changing throughout the program. Could someone explain how and why? I'm having trouble keeping a constantload on the tool.

Thank you.

Dan

[Mike Whitten CAD/CAM Contractors]

I am not sure what you are doing but the best way to go is to run "Inverse time" feedrates.

 

Many machines have this option at no charge. We have it here on are Haas and Fadal machines and also enabled on a few of our Matsuura machines.

 

You may have to set a switch or two in the post.

 

When getting into stuff like this, it is always better to consider using a modern day post such as Mpmaster.

 

Mike

[SVO]

Thanks Mike, I'll have to look into this a little further. I am using a post that's about 3 years old. It has worked great in the past. Maybe now is the time to change.

 

Dan

[SVO]

Can you explain what "Inverse time" feedrates are and what they do?

 

Thanks

 

Dan

[gcode]

Invesre time is a feedrate used for simultaneous

multiaxis machining. Linear axis feed in inches

(or MM) per minute. Rotary axis feed in degrees per minute. To get all axis feeding correctly together they use inverse time.

I've got the formulas to calculate inverse time at work. Basically, its a time value that detirmines how long it wll take all 4 or 5 axis to reach a programmed point.

 

edit:

That's one of the nice things about Haas rotary products. There is a setting in the control where you input the workpiece diameter. You use regular ipm feedrates and the control does the rest.

[SVO]

Thanks gcode, that explains a lot. I will definetly look into inverse time feedrates.

 

Thank you

 

Dan

[Travis_Buchanan]

Feed rate controls the center of rotation on most machines. So if you are moving X & A the speed of the tip of your tool is either increased or decreased by this A movement. The reason for different feed rates is so that the tip runs at the programed feedrate and the center of rotation speeds up and slows down as needed. Inverse time is simply (1/time in seconds to complete that line of G-code). Inverse time seems to work better on Fanuc controlled machines, because the feedrate always applies to the longest axis movement. If A>X the it interpets the feed as deg/min if A is less than X then it interpetes it as in/min. This makes for some very tricky post caculations but time is time no mater what, this is why I recomend inverse time.

[Mike Whitten CAD/CAM Contractors]

Thanks guys,

 

 

When I switched over to Inverse time, I was very impressed! Mastercam seems to report perfect Inverse time calculations for me.

 

Mike

[SVO]

Thanks guys,

I posted with the mpmaster and the code looks good and the tool movements are a lot smoother.

Thank you for the explanation and information. There'a always somrthing new to learn.

 

Dan

[Allan Brown]

If your machine handles combination linear/rotary feeds the same way Mpfan assumes (and performs its tangential velocity calcs), there should be little or no difference between inverse time feeds and regular feeds. Mpfan basically slaves the XYZ axes to deg/min feeds - using the change in C in proportion to the entire span length of the tool tip travel in XYZC.

 

The post actually needs to go through the tangential velocity calcs on the way to calculating the inverse time feeds... Having said that, G93 (inverse time feed) may be easier for the control to process - there is no assumption regarding deg/min vs. in/min here - it's all 1/sec or 1/min.

 

[ 05-10-2004, 03:31 PM: Message edited by: Dave Thomson ]