Carving Concentric Circles

[RWBess]

I believe this topic was addressed previously, cannot find it in the Forum but I remember some of the advice and
tried following it. Sprayed the rails and screws with silicone, installed Bits 'n Bits collet, tried different .25 downcut
carbide bits and I still do not get concentric circles. Anybody have an idea about what else to try. Also carving in smaller
steps. I have to say it, for the cost of this cnc machine, it ought to be able to carve "round" cutouts.
Frustrated, guess I will have to try my Carvewright.
RWBess

[jeb2cav]

Hi RW,

Can you post your project or an example project? I'm sure one of the members will be able to look...

[RWBess]

I meant to say that I also tried tightening the screws on the motors, although I didn't do that for
the Y -axis as I didn't want to have to take the bed off as it seems you must or have very
skinny long arms. The ones I checked were very tightAll I am trying to do is carve a 4 7/16" circle
pocket about 1/8" deep and it always turns out- not round, but slightly oblong, will not do. I also
tried the "Cookie Stamp" project that was available via the Vectric Forum and they also were oblong.
Those cutouts were about 2" in diameter. Other than the circles, the Shark is so easy to use and
generally does a fine job.
The z-axis travel could be improved, can't seem to be able to adjust it to the exact same
position every time.

[jeb2cav]

Hi RW,

You may want to try fine tuning the G64 setting in the post processor you are using. Open the post processor you are using with Notepad or Wordpad for example (open Notepad or Wordpad), typically found in Programs, Accessories from the Start menu, then use File, Open, navigate to the folder where this post processor is, set the file type to 'All Documents' (otherwise it won't show as a choice), and select the post processor you want to fine tune).

I'd next do a file save as and change the name slightly. Be sure it retains a .pp file extension. In the post processor file itself, you'll want to adjust the POST_NAME line to something you'll recognize as the fine tuned one in VCarve Pro.

Then, find the G64 Px.xx line. If you delete it, the Shark should attempt to follow the toolpath explicitly. I'd try a setting of 0.001 or 0.0005 instead though. For an explanation of this command setting and a picture of what it looks like in the post processor file, look at pp. 8-9 in the CNC Shark Post Processors document found on the NWA Downloads page.

If this fine tuning does not cure the oblong circle, then perhaps something to ask NWA about.

I've attached 2 post processors in the zip file - one using G64 P0.001 and one using G64 P0.0005. I'm sorry I'm not able to go and experiment with this right now myself. I look forward to hearing the outcome.

[RWBess]

Joe, thanks for the response, I will try the G64 adjustment as soon as I can
get to it and let you know. With all that you have been doing for folks on the
Forum, I thought you might have a potential solution.
Bob

[RWBess]

Joe,
No problem in changing the PostP, used the .0005 version and my circle was 4 7/16" diameter but if I
turned the job 90 degrees the measurement was 4 17/32", not good enough by a long shot. Seems to be elongated
in the y-axis direction. Guess I will have to get ahold of T.Owens. What exactly is the G64 G-code, I do a little
G-code coding for a pen making lathe. Have not come across it. Anyway thanks for all the help you offer all the guys
on this Forum.

I'm not giving up, this expensive machine certainly should do "round" circles, everything else I have done seems
to have turned out as specified in VCarvePro.

[sk8nmike]

Is the 3/32' difference constant or does it change with the size of the circle? Do squares do the same thing? Have you checked the play in your Y axis?

Sorry for no anwser but maybe the questions will get us some where. I'm going to try this when I get home tonight..

[Kryptik]

One quick thing to try, halve your feed rate and run a circle.
The Shark Pro Plus really doesn't like going too fast in the Y, the router will easily rotate some around the X axis if the bit "drags" through the material.
It took a bit to realise that I actually had to take my fingers off the Z screw when setting Z0 with paper, it was causing issues doing fine lines in acrylic..
I also notice a vertical line running from the centre of a job running Y- when carving a dished shape, right on the line of the Y shift to the next pass, which my preliminary thoughts are that it is caused by the same issue.

$0.05
Marc

[drueth]

I have done severial clock gears that are 7.75 in. dia. and also 1.00 in. dia. , in 1/4 ply. using a .125 end mill. I did slow the feed rate down to about 60 and they came out ok. So I would have to say my HD PRO at least can do it.

dar

[RWBess]

Thanks, guys, I thought I slowed the cutter down, but will try even slower. As I mentioned earlier, I tried carving the parts
for the Cookie Stamp project available on the Vectric Forum and the bottom and top of the stamp handles were badly warped. The handle end circles were 2.25" and 2.50". They ended up almost oblong, very disappointing. The fact that they
were out of shape was very obvious, it was not quite so with the larger circle until I checked it with a micrometer.I guess I had better do some serious checking of the y-axis. Will keep you posted.

I haven't tried squares and will do that.

By the way, Joe, I checked the G64 best possible speed code.