Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: polycut on October 13, 2015, 04:41:40 AM

Title: Fundamental issue with the Tangential Knife Cutting option
Post by: polycut on October 13, 2015, 04:41:40 AM

Hi guys,

I'm using tangential cutting option on Mach 3, on a knife cutting table.
However, there appears to be a fundamental issue.

I am cutting plastic material which is approximately 35mm thick. My Gcode is simple:
G0 X100  Y100     -     move to position
G1 Z1         -     plunge knife
G1 X10  Y10     -     Cut to end position

I am using 2.5D Z control to plunge the knife in and out, hence setting the Z to positive 1 to activate the output.

However, what I expected to happen was for the knife (rotation axis A) to rotate to the correct angle PRIOR to plunging into my material. But it didn't. It rotated after plunging and therefore made a big mess of the material as it rotated.

Now, I can understand the logic behind the action. It can't know which angle to rotate the knife until it reads the G1 X & Y line.

I then tried adding the Z motion to the Cut command:

G1 X10 Y10 Z1

But as you can imagine, the knife rotated to the correct angle as the machine was cutting in the XY direction, and because Mach3 set the speed of the Z movement such that it reach 1 at the same time as X and Y reached 10, then the knife only plunged half way through the cut.  

Anyone know a way around this?

Many thanks

Mark

Title: Re: Fundamental issue with the Tangential Knife Cutting option
Post by: TPS on October 13, 2015, 05:34:11 AM

Hi Mark,

i know tangential cutting from cutting glas.

i allway did a smal move "in the air" to get the wheel orientated
like this:

G0 X110  Y110     -     move to preposition
G1 X100  Y100     -     move to position to get knife orientated
G1 Z1                  -     plunge knife
G1 X10  Y10         -     Cut to end position

Thomas

Title: Re: Fundamental issue with the Tangential Knife Cutting option
Post by: polycut on October 15, 2015, 06:17:18 AM

Hi Thomas,

That makes sense, although it is a bit of working out to include this pre-position in the GCODE. Especially when working with odd angles. Eg is the start position was X100, Y100 and the finish point is X43, Y28, what would be pre-position point on that vector? 

Don't suppose you know the formula for working this out?

Many thanks
Mark

Title: Re: Fundamental issue with the Tangential Knife Cutting option
Post by: TPS on October 15, 2015, 07:36:38 AM

Hi Mark,

attached a small excelfile, try it not tested in all conditions.

m = (YEnd-YStart) / (XEnd-XStart)
q = YStart - m * XStart

XPre  =  XStart + 10
YPre =  m * XPre + q

Thomas