Cut passes not tracking right on circular end cuts but ok on linear cuts.

[gregsolano]

Ok, what should I look at adjusting on my machine for this problem. I was making a boat quarter board sign as a gift for my father in law. I decided to try and carve it out of vinyl, (similar to azek but they don't sell azek where I live so I carved out of 3/4 vinyl trim I bought at lowes. I thought the water proof quality would make it ideal. It carved nice, no melting, gumming up bit etc. But when It carve the cut out which I put at .200 per pass it carved the straight lines perfect but the curved at the end cut out about 1/8 inch per pass on the outside on one end of the quarter board and about 1/8 of and inch per pass inside on the opposite end of the sign. In other words , major stair stepping.

I am attaching pics. I am going to salvage the sign by using my band saw to trim each end to match, but I am not sure why this happened? I make clocks, octagonal and round all the time and those cut outs seem fine although its been a few weeks since I made any.

Any suggestions? And yes I know I probably should have just cut it out with my band saw but I also wanted to see how this vinyl would cut and carve.

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[Kenm810]

A few thing come to mind.
Did you put masking tape on the bottom of the Vinyl for traction
Is your head pressure to low
Did you leave enough stock at each end of the project,
or sled to stay under the pressure rollers

[AskBud]

1) How long was you actual project board?
2) If you used a sled, how long was it?
3) If on a sled, how was it secured?
4) Did you use masking tape on the bottom (where the Brass Roller tracks)?
5) Did you use extra support rollers on each side of the CW?
6) How do the Brass Roller teeth marks look on you failed carve?

Last:
As I compiled your project, I got the attached warning.
It warns about the top of your cut-out is too close to the Brass Roller contact. It further warns about the board leaving the top rollers, if you have not added at least 7 inches to the actual board/sled you used.
AskBud
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[gregsolano]

I knew I left stuff out. It was securely attached to a sled with four inch boards on each end of a 37.5 inch x 5.5 inch project board giving it more than 4 inches on each end. I did not have extra support after outfeed tables. My sled is 4 feet long and made from 1/2 inch mdf. I use tape under the sled. 95% of my stuff is done on this sled which has adjustable ends and side pieces. I have not checked my head pressure in a while so I will check that. The teeth marks look consistent on the sled tape. and the mdf is straight and flat. The cut through always slightly cuts into the sled so I know there would be no damage to rollers or anything due to cut through.

[AskBud]

I knew I left stuff out. It was securely attached to a sled with four inch boards on each end of a 37.5 inch x 5.5 inch project board giving it more than 4 inches on each end. I did not have extra support after outfeed tables. My sled is 4 feet long and made from 1/2 inch mdf. I use tape under the sled. 95% of my stuff is done on this sled which has adjustable ends and side pieces. I have not checked my head pressure in a while so I will check that. The teeth marks look consistent on the sled tape. and the mdf is straight and flat. The cut through always slightly cuts into the sled so I know there would be no damage to rollers or anything due to cut through.
1) Do you replace the tape, for the Brass Roller, prior to each carve?
2) How did you secure the project board (Tape is probably not the answer)?
3) Extra support/outfeed rollers are needed!

From a closer look at the stairsteps, I can see the movement with each cycle of the cut. Any one of the of the above, or a combination, may be your source.
AskBud

[gregsolano]

Thanks bud, I do replace the tape each time, and my sled is made with adjustable ends and side rails which encase the item and then I tape it down. The only conceivable movement could possibly be up and down but no side to side or end to end which is what would have to happen with that kind of stair stepping. With the length of this item maybe I needed additional outfeed support but I use the same sled for 15 to 18 inch items all the time with out any cut out problems. I will check the head pressure which I have not done for months and many carvings have happened since my head pressure check. Funny thing is now that I think about it a three foot bench I made did the same thing months ago. So the problem seems to be only on long items with curved cut through. The bench had angled and curved cuts that messed up also. This is a version C with rubber belts but when I did the bench it still had the sandpaper belts so it was not the change of belts that caused this. Thanks for the suggestions I just still not sure we have figured it out. I am still going to use this quarter board but I will check everything and wait until I have another large project to see if it worked. If anyone thinks of anything else I should check please chime in. Thanks Bud and Ken.