View Full Version : Cutting Circles? Help please!

03-10-2002, 08:41 AM
I'm having problems cutting circles (Drawing in AutoCad, Post in Rams 1.6). The following are two of the circle cut instructions generated. The first functions correctly - it plunges buzzes arround and then pulls up, the second plunges and then immediately pulls up again (no circle). In reading the documentation on "CG" it seems that both should work. HELP!?

First circle,
J3,15.125 ,18 ,0.5
M3,15.125 ,18 ,-0.76000005
CG,,14.875 ,17.75 ,-0.2500,0.0000,,1
CG,,14.625 ,18 ,-0.0000,0.2500,,1
CG,,14.875 ,18.25 ,0.2500,-0.0000,,1
CG,,15.125 ,18 ,-0.0000,-0.2500,,1
J3,15.125,18.0, 0.5

Second circle
J3,13.125 ,16 ,0.5
M3,13.125 ,16 ,-0.76000005
M3, 13.125 , 16 , -0.76000005
J3,13.125,16.0, 0.5

03-10-2002, 07:03 PM
It looks like the problem is in the Xendpoint and Yendpoint specified in the second circle CG code. Specifically the code for the second circle is asking the machine to:
1) Move to the start point (X=13.125,Y=16)
2) Plunge from Z height of 0.5 to depth of -.76
3) Cut a tiny arc clockwise from the starting point of 13.125,16 to an ending point of 13.1244,16.016 (a distance of only about 1/64inch)
4) Move back (at depth) from arc end point of 13.1244,16.016 to arc starting point of 13.125,16
5) Pull up
On a running machine with a whirling bit that would look like it merely plunged down and pulled back out.

03-11-2002, 10:58 PM

Thanks for your answer but it seems to raise more questions than to solve the problem.

The bit is starting at position 13.125,16 and moves CLOCKWISE to position 13.1244,16.016 (a position slightly to the left and above the starting point).

.............x <- ends here (13.1244, 16.016)

...............x <- starts here (13.125, 16)
...............V <- clockwise be thisaway, Help!

Ted Hall, ShopBot
03-12-2002, 02:51 PM
Hi Guy,

The second circle works for me both in Preview Mode and on the tool. I'm thinking there are 1 of 3 possible problems:
1. You may not be using version 2.28 or 2.29 of the software ? (We did have some earlier problems with CG.)
2. Your circle segment resolution may have gotten set too high. It is the 5th parameter of VU and should be .05 or less.
3. There may be something else funny in the file, and it is just getting expressed in this line ... if #1 or #2 don't fix it, send along the Part file and your PROBLEM.LOG file.

Guy Hilliard
03-12-2002, 06:55 PM
Thanks Ted U got it in 1. I had version 2.25m. The file cuts perfectly now.

03-12-2002, 11:08 PM
Guy and Ted,
The file does work fine in version 2.28, and I would have known that if I had run it *before* proposing an answer based on the numbers alone! In this case the numbers didn't support my answer either, because, as you correctly pointed out, an ending position of 13.1244,16.016 will always be slightly to the left and above the starting point of 13.125,16. I definitely got this one wrong -- my apologies for the extra confusion that it caused. I'm glad you were able to resolve this one.

04-21-2003, 12:05 PM
Off-shaped Circles.

I am gettig off shaped circles out of my PRT96.
Just installed version 2.35, and I use Vector cad to output sbp. files.
Everything rusn fine, but when it comes to cutting, the circles come out off-shaped, Why is this happennig?
VU values for my PRT96 are
X AND Y VALUES: 5.56972
Z: 44.5579
ACC: 78.7406
Are there any adjustments to correct the problem?

04-21-2003, 01:01 PM
Pedro, what is "Off-shaped"? Is your problem on both x & y directions? What size circles are you cutting and how far "off" are they?

04-22-2003, 07:27 AM
Most likely your machine needs to be re-calibrated. Really easy to do - its built right in to the Shopbot software.

Go to Utils > Calibrate X and Y axis.

If you have one of the cheapy laser pointers this is duck soup. Just tape it to the Z axis and lay a yardstick on the table. If you want to get really anal (Like we do) put a piece of sharpened steel rod in the chuck and use a machinists steel rule. We have also used a dial indicator but the advantage of having thousandths to read is lost by the disadvantage of having less than one inch of travel.

Remeber that the Shopbot is going to think in decimal inches, so don't forget to convert.

Before you actually calibrate practice a time or two. Move the Z axis up a couple of inches and run through the program. It gives you a choice to bail out at the end without saving the results.

04-22-2003, 10:52 AM
Hello gerald
When I say off sahape, I mean oval like circles,
sometimes the ends do not meet.
I will Try Tom's suggestion to see if it works.
Thank you guys for answering.

04-22-2003, 11:42 AM
Pedro, I think that you have a mechanical problem. Something is moving while you are cutting. The router could be shifting around where it is mounted to the z-axis. Or the gears have come loose on the motor shafts (grub-screws) on the x and y axes.

04-22-2003, 11:47 AM
I just had a similar problem, check to see if your pinion gears are tight on the motors, the allen screws do come loose. Just push/pull the gantry with power on

04-23-2003, 07:15 AM
Sorry - see the next post!

04-23-2003, 07:18 AM
I wouldn't show this to just anybody, but here is a gear that I cut with the machine out of adjustment. It is not stretched or manipulated, it really is an oval.
We keep it around cause it gives rise to a lot of discussions about Rube Goldberg and his machines.


04-23-2003, 08:38 AM
Tom, you may want to sub-contract to a company like this (http://www.cunningham-ind.com/ellipt.htm) or this (http://www.customstockgear.com/html/g08.html).

04-23-2003, 08:20 PM
Tom Gerald's right if you just leave your machine alone you could do work for those guys [
] and you could even set a new standard for the Rube Goldberg thang, post back to let us know if the problem is fixed or, and what the problem was,is etc. David in Wyoming

04-24-2003, 07:01 AM
I came heir to a MONONGOUS Oriental Motor that I wanted to put in to the X axis. (The MORE POWER theory at work here!) Obviously it changed the ratio at which the X axis was operating.
On my machine, which is largely home made, the X axis moves while the Y and Z axis are on a gantry.

04-24-2003, 07:43 PM
Tom are you sure your name isn't Tim Taylor RRR [
] You know i bought a Tim Allen signature finish hammer once used it and on the secound swing the head came off!!!!! just to show you about MORE POWER RRR Dave in Wyoming

06-30-2003, 03:54 PM
I would like to know how the SB cuts Circles. Does it do it with point-to-point lines, by creating a Polygon? How many sides to the polygon if it uses a polygon?

06-30-2003, 04:01 PM
Circles appear to be completely smooth. Obviously they must be slightly stepped, because they are made by stepper motors, but this is invisible.

07-02-2003, 05:55 PM
I did a 10"dia. circle on partwizard, converted it to shopbot code. It had 513 sigments around the circle each aprox. .06 long. Like Gerald says, they appear completely smooth.

07-02-2003, 07:10 PM
I did the same test with a 1" circle. It had 129 sigments @ .024" each.

07-02-2003, 11:40 PM
Scott, did PW give you 129 or 513 straight lines for a 1" and 10" circle? That's strange to me. How did you see the segments? As separate lines of code?

07-03-2003, 02:31 PM
Pw outputs to the sbp file with M3 commands. I simply edited the sbp file and added up the M3 lines.
Yes that means the simple 10" circle file was over 13 pages of code. That's the one thing I do not like about pw. Pw will use 4)GC commands if you select shopbot[arcs][inch] when you output the sbp file. This makes the file about 12 lines long. This format is much easier to deal with but is still very difficult to edit if you want to make a quick change to the file in the shop. It would be nice if pw would output a CP command. That way if you needed to edit a hole you could simply change the center point or diameter. Just a gripe of mine.

07-03-2003, 02:37 PM
A very valid gripe. Surely Scott must be doing something wrong if he can't get one line of code per circle - would the PW experts please step in?

07-03-2003, 02:58 PM
Yes please,

Any suggestions will be greatly appreciated.

07-03-2003, 04:47 PM
This is a valid gripe. The file sizes out of PW can be a bit large and hard to make changes to. The Arc version of the post does create some CG commands in the part file making the file size smaller, but there are still going to be a lot of M3's. This is happening because PW circles and arcs are actually splines that are interpolated by the toolpath generator.

The reason the CP command wasn't used is because it is very different from the format used within PW. The CG command has a ver similar format to a G-code style circle command that allows us to output circles from programs that were traditionally G-code output only.

The length of the segments that are generated can also be a bit mysterious also. The length of the moves created are controlled by the tolerance in the toolpathing tool. This tolerance represents the maximum length between the cord of a line drawn between each end point of the line and the circle. The larger this gap the larger the line segments, avoid using zero it causes the toolpathing to take a long time. This is a fairly simplistic explanation of this so I hope it makes sense.

07-03-2003, 11:44 PM
Just for the record, Vector always gives only one line of code (CG or M3) for any arc, circle or straight line.

07-04-2003, 01:09 AM
Therefore, to answer Lou Jiron's question: "I would like to know how the SB cuts Circles. Does it do it with point-to-point lines, by creating a Polygon? How many sides to the polygon if it uses a polygon?", it depends on the software that you are using to drive the SB.

07-31-2003, 11:45 AM
CHATTER; I get chatter on as I start in a turn in mdf no one at SP able to fix this problem has any one gotten rid of this an may I ask how

07-31-2003, 12:23 PM
What speed, bit style and cutting depth...All neccesary factors to unravel this mystery