Circle Cutting Problem

[csbrads@comcast.net]

I am experiencing problems cutting true circles when using my prt. For instance, I am trying to cut a circle that is 30" in dia. using a 1/4" bit. The circle cut correclty in the y axis but cuts 1/8" oversize in the x axis. I have redrawn and cut the file to compensate for this and it cuts correctly. Does anyone have any idea as to what may be causing this?

Thanks,

Carroll Bradshaw

[Mike Windsor]

check your unit values ( VU ) for X and Y should be the same

[fleinbach]

How deep a cut are you taking on one pass? Two deep a cut will pull into or away from the intended line particularly on the X axis. The only way to stop it is make lighter passes, no more then .25" at a time.

[bill.young]

Carroll,

Look for slop too...maybe a loose pinion gear or a pinion gear that's not meshing with the rack correctly. That sort of thing will show up in one axis and not the other.

Bill

[bob buttons (Unregistered Guest)]

this is a real problem and i would like to know how to fix it too, is it grain is it deflection?? if i throw a pen in the bot runs super. when i cut it is off. have not come up with a real solution here. cad compensationg for errors is time consuming but does help. problem is you have to cut one to see where the problem will be on each project. any one have any insight on how to fix this?? perhaps there is no answer when that bit hits the wood so many factors are in play that cause errors in sizing. i wish it didnt happen.

[csbrads@comcast.net]

All,
Thanks for the suggestions. I will check out my gears and my values. I will cut a rectangle too to see if the problem just pertains to cutting circles. I was making a practice cut in a piece of foam insulation prior to making my final cut. Glad I did. I made my final cut in 1/4" lexan and it cut perfectly with the offset.

Carroll

[wmcghee]

I had this problem and it was loose pinion gears on the motors as Bill suggested above.

[csbrads@comcast.net]

I checked my unit values and they were different. My x was set at 128 and the y was set at 127.324.
I change the x and the circle cut correctly.

How do you know what the settings are suppose to be?

Thanks to everyone for your help.

Carroll

[garyb]

Carroll you have mail

[gerald_d]

Look halfway down this thread (http://www.talkshopbot.com/forum/messages/312/5263.html). 127.324 is the correct value for both your x and y in your case.