Problems cutting on a vector

[jbworden]

I'm trying to cut several pieces out of a sheet of plywood that are 2.75" in width and the full length of the plywood sheet. Sounds easy. I laid out the sheet in CorelDraw simply by drawing vectors on a 4'x8' rectangle with the vectors exactly 3" apart. I then imported the file into VCarve Pro (as an EPS) and used the 2D profile tool to cut "ON" the vectors. Since I'm using a 1/4" bit that should give me a series of 2.75" planks. It should.

What I actually get is a set of planks that are alternately 2.37" and 3.13" in width. Given the rounding there is exactly 3/4" difference in the width of the planks. I've double checked the Corel file and the VCarve file and both have the vectors at exactly 3".

Any idea what I'm doing wrong? I'm also carving some pokets in the end of the planks and those seem to be dead on.

[conceptmachine]

Jim,
That's strange i've done this before and i had good results.if you want to send me your crv file i'll run it on my bot and see what happens.
conceptmachine@bellsouth.net (mailto:conceptmachine@bellsouth.net)
shawn

[Brady Watson]

Jim,
Sounds to me like your material might be moving. How are you holding it down? Does it lift when cutting?

-B

[srwtlc]

Jim,

I tried it with a .dxf from TurboCad and VCPro with no troubles. You can't choose a toolpath setting other than "On" the vector for this without VCP warning of unsuitable vectors, so you can rule out mistakenly choosing in or out.

Check the resulting .sbp file and look to see if each pass has been processed as 3" apart.

VCP comes back to the beginning for each pass instead of zig zag, so you shouldn't have compounded bit deflection (I've had that happen) unless yours happens to do it in a zig zag manner. Even then, that would be more deflection than possible.

I'd check that CorelDraw file and verify that the lines are indeed 3" apart or that you don't happen to have a outline applied to the lines other than "Hairline".

You don't happen to have some relation from Wisconsin, do you? Maybe I asked you that before and forgot.

[fleinbach]

This happened to me when I first got my PRTAlpha and that prompted me to look into what was going on and may be whats happening to you.

I was cutting 3/4 MDF in a single pass. I had set it up to cut down the sheet and then back up. What is happening is the y-car will always pull into the cut due to flexing. This flexing takes place because only one motor holds the Y-car in position. No matter how tight your V rollers are there will be movement. Of course it will be worse if they are not as tight as possible. What is happening is when going in the first direction the bit is deflectining into one piece and away from the other. When it comes back up the other side it is pulling back into the same piece but away from the adjacet piece. My descerpancey was 1/2 inch differance in size. You can eliminate the problem if you make all cuts in the same direction then only the first piece will be differant in size.

[fleinbach]

Jim,

I previously posted the cause of this issue 2 years ago. You can check it out here for more details. http://www.talkshopbot.com/forum/show.cgi?tpc=29&post=24475#POST24475

[jbworden]

Thanks for all the responses. I've done a bit of investigating and here's what I've come up with so far in no particulare order because my brain, when it works at all, works in no particular order.

1. The vectors in the Corel file are hairline strokes and are dead on 3" centers. I imported the EPS file back into Corel (X3) and also into Illustrator CS3 and got perfect results both times.

2. I imported the exact same EPS file into Part Wizard and it screwed it up badly. For some reason one vector was at y=36" and looked exactly right. The entire remainder of the drawing was shrunk down to about 25% of it's actual size. I was never able to acurately import an EPS in PW.

3. Looking at the original SBP file out of VCarve shows that while the vectors are imported at 3" centered the Y coords being generated are spaced alternately by 2.625" and 3.375". The problem is definitely software related.

4. Generating the same EPS file in PW (after manually resizing it results in a SBP file with spacing extremely close to the 3" mark. Since I manaully resized the drawing I think the .017" variations I was getting are acceptable.

5. I recreated the Corel file by removing the vectors and recreating them as boxes 3" in width and 96.5" in length. The resulting SBP file has Y offsets within .000028 of 3" centers. Certainly close enough for my purposes.

6. PW still shrunk the new EPS file when I attempted to import it so I abandoned PW for this project.

My conclusions are that 1) VCarve doesn't handle vectors very well, and 2) I probably need to take this over to the Ventric forum.

[Brian Moran]

Hi Jim,

Are you saying that the vectors seem to import with the correct 3" spacing into VCarve but after machining ON the vectors, the toolpaths are at a different pitch?

Can you send the original eps file from Corel AND the .crv file from VCarve to support@vectric.com (mailto:support@vectric.com) so we can find out what is going on? Please make sure the .crv file from VCarve Pro has the toolpaths calculated just as you had them when you saved the .sbp file.

Thanks

Brian

[jbworden]

Okay! I confess. I can't make this happen again. I have the .SBP file I used to make the original cut but when I go back to regenerate everything just to eliminate any possibility of getting a bad file mixed in I can't duplicate it. The largest variation I can get now is .000028". I'd get more variation than that by breathing hard on the router. The same input with different results. As we used to say back in my programmer days, that sounds like a hardware problem, a nut loose on the keyboard. :-(

I'll keep an eye on things to see if it happens again.