Improving V-Carves on weak machine

[Sandy H.]

I'm using a wooden DIY 10x9 skate bearing design to try some v-carving. With more utilitarian stuff (i.e. making parts to build things) I would set-up tool paths to cut a rough quickly and a finish slowly, slightly offset from the rough pass. I've improved the carriage and Z-axis strength, but when v-carving I get little steps in various locations based on pass depth.

I was wondering if there was an automated way to do a rough tool path and then a finishing pass with the standard v-carve method. It appears that the step over doesn't really have much to do with v-carving.

If there isn't an automated way to accomplish this, would it be wise to make 2 identical tool paths with different setups?

#1: Roughing parameters (fast feed and multiple depth passes) where the Z zero is set 0.02" above the material (to fake out the carving depth allowing a 'finish' pass).
#2: Exact same vector, but Z zero is set correctly at the top of the material and the depth of cut is as deep as practical.

I do intend on building a stronger machine when shop space becomes available, but for the near future, I'd still like to do some high quality v-carving with what I have.

Any other thoughts are appreciated

Sandy.

[oxenham1]

You should be able to control the depth of cut when you select the cutter. You could also offset the vector inwards a small amount and used that vector for the roughing portion. Then select the final vector for the final pass at full depth.
Does that make sense I hope

[Sandy H.]

I initially tried offsetting the vector since it was the same thing I had been doing with simple shapes. In the preview, the offset showed the letter 'y' to look wrong. I chose 'offset to the inside' but the loopback also offset to the inside so more material was removed. Hope that makes sense.

The particular project I'm working on is a nameplate for our house, so it is only text/numbers. I chose a script like font and the project looks pretty good except for the actual finish on the letters. If I go very slow (15 IPM or so) it is almost unnoticeable, but if I go faster (100 IPM is the approximately correct rate for the correct chip load) I get steps.

I thought changing the Z height for the roughing pass so that it was slightly above the material would basically result in slightly less material being removed, but along the proper path. Then, the finish pass would be at the proper height, but with much less material to remove.

Sandy.

[Paul Z]

Sandy,

Congratulations on building your own machine!!!

There may be a way to improve your machine's performance without altering the existing hardware. You might try "fit curves to selected vectors" (smoothing) before creating the toolpath. When toolpaths are created from these smoother vectors, they have less up and down movement which should help reduce the number of "steps" that you see in the final product. I have a shopbot PRT Alpha which is a reasonably accurate and tight machine. I use this type of smoothing and it makes quite a difference.

If you are doing text, you'll need to convert it to vectors using the "convert object to curves" before smoothing it. For smoothing I'd suggest using Bezier curves and a 0.005" tolerance in the smoothing process. Remember to select "replace existing vectors" or you'll get a second set of vectors laying on top of the first set.

To be sure there is an improvement, cut both the original and the smoothed versions on a piece of scrap. If you can, please post a picture the results. I'd be very interested in seeing the difference on your machine.

Paul Z

[Sandy H.]

Thanks for the input. I converted the text vector to a curve and applied smoothing as you said. It took me a few minutes to figure it out, as I'm new to VCarve Pro, but once I understood the interface, it was a snap.

Regretfully, I managed to run into a problem on the machine, so I couldn't give it a fair test. It didn't appear to help, but as I said there was a machine problem, so I'm not abandoning the idea at all.

Hopefully tomorrow I'll be able to solve the issue on the equipment and give it a fair try.

Thanks for the help.

Sandy.

[jhop]

I had several issues when I built my machine. Since you didn't mention driver software, I assume you are using Mach3. There are many set up options in the program. My machine is made of aluminum with xylotex steppers. They run very well, but I find 80 ipm is the best speed for good results. The machine is tight and accurate, but the motor tuning has to be right. You talk about chip load so that with the fact that you built your machine tells me you understand what makes it run properly. I just remember getting impatient and trying to cut items expecting good results without taking the time to fine tune things.
My test which resulted in my logo was to carve a star inside a circle. This will show the accuracy of your machine. I ran that file about 8 times before I started to see the carving look like it was not exactly in the same place. I wish I remembered all the different tuning settings, but it has been a long time and I'm happy with the results.
Sorry for the long winded editorial.

Jim