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oval circle
« on: December 17, 2016, 01:35:56 PM »
Hello,  New to this forum and the world of CNC and Mach3.

I'm trying to gut a test circle of 49mm but it turns out slightly oval,  to eliminate as much as possible i've made the circle in the mach3 wizard.

when i measure the circle it is only 48.5mm on the Y and X axis. but when i meassure on 45 degress to x or y it is the correct Dimension.

What am i missing or where should i look to correct this?

here is the g-code

(Code by Newfangled Wizard, 17.12.2016)
(Version 2.86)
(Program Posted for Wood )
G0 G49 G40.1 G17
G80 G50 G90 G98 
G21 (mm)
(***** Circular Groove/Cutout *****)
M6 T7
M03 S24000
M9
G00G43 H7 Z1
G00 X20 Y-2.25
G41 P1.5
G01 X22.25 F1000
G03 X24.5 Y0 R2.25 F1000
G01 Z-0.5 F500
G03 X-24.5 Y0 R24.5
X24.5 Y0 R24.5
G00 Z1
G03 X22.25 Y2.25 R2.25
G40
G00 X20 Y2.25
M5 M9
M30


John

Offline Tweakie.CNC

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Re: oval circle
« Reply #1 on: December 18, 2016, 01:51:15 AM »
I never use tool radius compensation within Mach3 (it's easier for me to let the CAD/CAM software take care of this) so my knowledge is limited.


First, check that you have your tool table set up correctly then try running your code again but first change the G40.1 to G40
Does this produce better roundness and dimension ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: oval circle
« Reply #2 on: December 18, 2016, 05:55:54 AM »
Thank you for your answer.

Changing from g40.1 g40 doesn't change the Dimensions.

if i try the set steps per unit wizard  and ask for 100mm i the lengtht is correct in both x and y.
I tried to make a 50x50mm Pocket With the mach wizard and it turns out square but only 49.8mmx49.8mm 
John
Re: oval circle
« Reply #3 on: December 18, 2016, 06:14:27 AM »
initially i tried make the circle in fusion 360 and had the same results. With fusion doing the tool comp.
John

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Re: oval circle
« Reply #4 on: December 18, 2016, 06:34:51 AM »
Hi John,

By trying Fusion 360 doing the tool comp. and the same error persisting has, I think, shown that it is not a Mach3 error.

From the information you have given I would suspect the problem is a mechanical issue with your machine, perhaps backlash, a loose set screw, etc.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: oval circle
« Reply #5 on: December 18, 2016, 06:35:51 AM »
+1 on checking the backlash.



Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: oval circle
« Reply #6 on: December 18, 2016, 09:49:35 AM »
I suspect its tool deflection especially as your movement check without cuts is correct. Have you tried re-cutting the original machined hole with the same program to see if it takes off more material and corrects the dimensions. When doing a circle the machine constantly changes direction in two axis with no pause hence different pressures on the Z axis spindle. That's why I usually do a finishing cut of say 0.5mm to give me a perfect circle as hobbyist machines are not that ridged as production machines.
« Last Edit: December 18, 2016, 09:51:22 AM by jimthefish »
Re: oval circle
« Reply #7 on: December 18, 2016, 10:01:38 AM »
Ok, thank you.

played with backlash and that definitely helped but in (0.47mm for x and y, measured with dial indicator giving x-10, x0, x8,x0 ),  but when i try to make a circular pocket I'm getting a small ridge right when it changes direction on x or y
John
Re: oval circle
« Reply #8 on: December 18, 2016, 10:02:23 AM »
yes i think tool deflection might come in here also,  will try as you suggested
John
Re: oval circle
« Reply #9 on: December 18, 2016, 10:16:07 AM »
if your getting a small ridge its got to be tool deflection. If your a hobbyist machinist and time is not a problem always do a finishing cut. as the tool wears over a period of time your deflection will increase hence the finished component size reduction. Some of us if we want to maintain a size on a batch of components have a finishing tool which does very little cutting so can be relied on to keep its size.  Just for reference I'm talking about cutting metal but the same applies for wood on a reduced scale