Same Lathe Programmer STILL needs help!

[lydokane]

Thank you to all who helped me with my hex homework over the last two weeks.

See this thread:
http://www.practicalmachinist.com/vb/cnc-machining/lathe-programmer-needs-help-306908/

I still don't know yet how much credit I was given for this assignment but after speaking with the instructor I believe it will be about 70%.

After going over all the replies I am still quite confused (I wish I had a simulator). Using the first explanation that angelw gave me; I created a spreadsheet to calculate some trig. I made the spreadsheet so that when I enter the number of sides of the shape and distance across the flats. The spreadsheet calculates start angle, hypotenuse (see CAD drawing in above post), incremental angle and X & Y positions. I used this spreadsheet to calculate my homework. The spreadsheet was not setup to calculate the .25 radii at the points.

After reading the second post from angelw I became a bit more confused as the tool path that was presented didn't match what I had calculated. I attribute this to the fact that my spreadsheet doesn't calculate the radii. However, when I calculate the distance from the point of the hex to the tangent point of the .25 radius I get .1082. This figure doesn't seem to 'fully fit' with angelw's tool path. When it is doubled (.2164), it works for some parts but not all.



What I would like to do is this: use my spreadsheet to calculate X&Y on an example hex and write some code then let the group critique my tool path.

In this example I have a part that was turned to a 5.0" OD. The hex is 4.0" over the flats with no corner rounding. The hex extends one inch back from the face of the part. The tool used is a .500" four flute EM.

When I enter 6 sides and 4.0" (distance over flats) into the spreadsheet this is what I get:

Hypotenuse: 4.6188
Incremental Angel: 60

ANGLE:	30	90	150	210	270	330
X:	5.0000	0	-5.000	-5.000	0	5.0000
Y:	2.8868	5.7735	2.8868	-2.8868	-5.7735	-2.8868

From the table above I wrote a tool path in the program below. Is this remotely correct?



N14 (MILL HEX LEFT SIDE)
G99 G40 G20 G18
G00 G28 U0 W0
T0800
M05 P11
M35 (C AXIS ON)
G28 H0
T0808
G97 S1900 M03 P12
G17 U0 H0 (X/Y PLANE)
G112 (POLAR ON)
M89 (BRAKE ON)
G55 X6.5 Z.5
G42 X5.8 Z-1.0
G01 X5.0 C0 F.01
X5.0 C2.8868
X0 C5.7735
X-5.0 C2.8868
X-5.0 C-2.8868
X0 C-5.7735
X5.0 C-2.8868
G00 X5.1
G40 X6.0 Z1.0
M09
G113 (POLAR OFF)
G18 (X/Z PLANE)
M90 (BRAKE OFF)
M05 P12
M34 (C AXIS OFF)
M01


Again, thank you all for your help.

PR

 

[angelw]

Hi lydokane,

The AF of the hex is 4". Accordingly, even if you're programming the centre of the cutter (calculating the tool path taking into account the 0.25" radius of a 0.50") and not using Tool Radius Comp (G41\G42) at the control, the X coordinates for the flats will not be X5.0. If the 0.25 Cutter Radius was incorporated into the calculations, the X coordinates for the flats will be X4.5 and X-4.5; therefore, you have a problem with your Spread Sheet.

You're using Cutter Radius Comp in your program example. Accordingly, unless you're using what is referred to as partial Tool Radius Comp, where the geometry of the program takes into account the radius of the tool, and Tool Radius Comp at the control (G41\G42) uses a Zero, or close to Zero Tool Radius value, then the X coordinates will still only be X4.5 for the flats. If the whole Radius of the cutter is registered in the Tool Radius Offset Registry, the X coordinates for the flats will be 4.0" as shown in the example program below.

I doubt that you will need the Brake on (M89 (BRAKE ON)), as the C axis must be free to rotate during the Polar Interpolation exercise.

Following is a correct Polar Interpolation Program based on the data listed in you opening Post, using Tool Radius Comp at the control to use as a comparison.

Regards,

Bill

G00 X6.2000 C0 Z0.2500 (Positioning to start position)
G01 Z-1.000 F_ _
G112 (Start of polar coordinate interpolation)
G42 G01 X4.0000 C0.0000 F_ _
G01 X4.0000 C1.1547
G01 X0.0000 C2.3094
G01 X-4.0000 C1.1547
G01 X-4.0000 C-1.1547
G01 X0.0000 C-2.3094
G01 X4.0000 C-1.1547
G01 X4.0000 C0.0000
G40 G01 X6.2000 C0.0000
G113 Cancellation of polar coordinate interpolation
Z 0-.2500
X_ _C_ _
M30

 

[angelw]

Hypotenuse: 4.6188
Incremental Angel: 60

N14 (MILL HEX LEFT SIDE)
G99 G40 G20 G18
G00 G28 U0 W0
T0800
M05 P11
M35 (C AXIS ON)
G28 H0
T0808
G97 S1900 M03 P12
G17 U0 H0 (X/Y PLANE)
G112 (POLAR ON)
M89 (BRAKE ON)
G55 X6.5 Z.5
G42 X5.8 Z-1.0
G01 X5.0 C0 F.01
X5.0 C2.8868
X0 C5.7735
X-5.0 C2.8868
X-5.0 C-2.8868
X0 C-5.7735
X5.0 C-2.8868
G00 X5.1
G40 X6.0 Z1.0
M09
G113 (POLAR OFF)
G18 (X/Z PLANE)
M90 (BRAKE OFF)
M05 P12
M34 (C AXIS OFF)
M01


Again, thank you all for your help.

PR

Hello lydokane,
I've just had a closer look at your numbers, and you clearly have some issues with your Spread Sheet Program and your Polar Interpolation program. For starters, the hypotenuse of 4.6188" will result in a Hexagonal with 8.0" AF dimension. The hypotenuse used in the equation is the Radius from the centre of the Hex to the point described by the intersection of two adjacent sides, or the PCD/2 of the points of the Hex.

The points in your program of X0 C5.7735 and X0 C-5.7735 will require the AF of the Hex to be 10.0". Accordingly, because Polar Interpolation uses X addresses expressed in terms of diameter on a lathe, the X5.0 coordinates in your program should be X10.0. Therefore, the shape being described by your Polar Interpolation Program is not a Regular Hexagon with all side dimensions and angles between adjacent sides being equal. Your shape is an Irregular Hexagon that is tall and skinny.

Regards,

Bill