Plotter SC-14000 - circles not closing...

[Signsforwhile]

For a couple of months now, and it seems like it's getting progressively worse, our Mutoh SC 1400 plotter doesnt close circles correctly. On larger stuff you dont even notice, but the smaller the circle, or even insides of capital 'A' don't close and you either tear the vinyl while weeding or have to go in before with your knife and complete all of your circles.

We have one customer in partictular who constantly notices even when work has been corrected because a tiny portion of the circle is flat or off. And I'm sick of hearing about it!!

Not sure if this is a software or hardware issue...

 

[S'N'S]

Don't know about either machines but on my Roland it's usually blade offset, try adjusting that.

 

[sgraves]

Offset adjustment

Attached is an image showing why there is an offset adjustment. In my experience, there can be a number of things that will cause the offset to need to be readjusted. A knife with a different angle and a change in the depth of cut are the most common. A change of the depth of cut can happen as a knife gets dull as well as a depth adjustment.

After post I realized that the image didn't make one thing clear. The knife always cuts slightly behind the center of rotation. This allows the knife to act like a shopping cart wheel and swivel in the direction of travel. The offset is the distance between the center of rotation and the point where the knife is cutting. As discussed, since this distance can change depending on knife, etc. the offset must be adjustable.

I have heard that some people control the cut depth by adjusting force, in my experience that is an imprecise method. It is more accurate to adjust the depth by exposing the right amount of the knife and using a little more than enough force to cut to the exposed depth. One gets much less variation in cut depth as the knife gets dull. One may still need to increase force as the knife gets dull and maybe increase exposure as well. One still has a more predictable response using this method. In fact I have created tools (using a dial indicator) that allow me to measure knife exposure to a high degree of accuracy.