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Re: oval circle
« Reply #10 on: December 18, 2016, 10:21:24 AM »
ok, so this is my result

the original circle  is now 49mm measured on  the x and y axis, and 49.4mm in the 45 degree angles whitout backlash comp.  
with backlash comp it is 49.4mm on all dimensions, but i get a small ridge just where the compensation is happening. and i can se the router is jumping right when its making the adjustment.

running the same program twice doesn't change anything.

i have adjusted the steps some from when i first started and used a dial indicator for measuring.

yes this is a hobby machine Openbuilds OX, my cutter is brand new. and i only make 1-2mm deep cuts in mdf right now when i try.

I will try to make a circle in fusion with a very light finnishing pass.
Re: oval circle
« Reply #11 on: December 18, 2016, 11:03:32 AM »
just to clarify, when i said that i can se the router jump, it's the hole gantry moving. if i hold on to the gantry you can feel it's the steppers making a quick change.
« Last Edit: December 18, 2016, 11:17:53 AM by jajohnsen »
Re: oval circle
« Reply #12 on: December 18, 2016, 11:17:27 AM »

Offline Davek0974

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Re: oval circle
« Reply #13 on: December 18, 2016, 11:27:02 AM »
Whatever you do, try to run without backlash comp - it can cause more issues than it fixes sometimes, jerks and steps would be two of them.

I was chasing an off-sized result for some time when it turned out to be the tool slightly worn.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: oval circle
« Reply #14 on: December 18, 2016, 11:31:55 AM »
Yes, i have seen that.  I have checked my grub screws and they are as tight i can get them. I had problems with flat spotting like he mentions and that was because of one loose screw. But that is fixed now.

With backlash correction on,  the circle looks round now, but with the noticable jump each time it corrects itself. I'm using wery shallow cuts 1-2mm and feed rate of 1000
Re: oval circle
« Reply #15 on: December 18, 2016, 11:54:53 AM »
One last check to confirm if you cut an internal square or circle then an external square or circle just cutting on one edge do you get the same size errors. if the inner one is smaller and the outer on bigger its tool deflection. If they are both the same size its your step settings or backlash.
« Last Edit: December 18, 2016, 11:59:16 AM by jimthefish »
Re: oval circle
« Reply #16 on: December 18, 2016, 03:11:43 PM »
ok thank you for the suggestions,

tried to cut 49mm cirkel

inner one Y48.7 x48.65  45degreo 49mm
outer one y48.5 y48.4    45 degree 48.8

this is whitout backlash comp.

i think there is a compination of  backlash and deflection going on here.  i just redid my my step settings measuring off the gantry with my dial indicator and it's dead on. but if i touch it slightly i can se neadle deflection and if i push some there is no problem getting the nedle move +- 0.3-4 mm


« Last Edit: December 18, 2016, 03:16:13 PM by jajohnsen »
Re: oval circle
« Reply #17 on: December 23, 2016, 03:13:24 PM »
Hi jajohnsen,
I remember when I was a boy my uncle teaching me to use the lathe. He set up a dial gauge between the two lathe rails then asked
me to grab the rails and try to spread them apart and lo and behold I got about 1-2 thou of movement. I was gobsmacked, how could
I at nine years old deflect such a beefy casting! The concept of flexure of what appears a rigid component has stayed with me ever since.
I am inclined to forget the lesson until I try to work out why some operation that didn't go as I'd hoped only to realise I was relying on components
being absolutely rigid and unless Hookes law is repealed that's never the case.

My wife left with my best friend...
     and I miss him!