Carving Advice

[Jerome]

We are past the holidays now and I can take a break from the mdf kids furniture we have been making on the bot.

The last few days I have been trying some carving and could use some advice.

What are the advantages of Rastering versus offset when doing a finish carving?

I am using the 1/8 inch ball nose bit from the Shopbot starter kit. What do you suggest for the stepover value and feed rate. I am using hard Maple and Cherry.

I know there are no hard and fast rules about these questions but the advice I have been given has been very valuable to me in learning to use the bot. So any suggestions will be appreciated.

By the way, I am having way too much fun with the bot.

Thank You
Jerome

[butch]

Here are a couple of numbers - I use this for Cherry and Maple.
1/8 ball nose bit
RPM - 10,000-12,000
Step over 10%
FR 2.5 inch per second

I do not do a roughing cut, but do a raster cut on the finishing path.

[dlcw]

Jerome,

I do the following for 3D carvings. Depending on the size of the carving and how smooth I want it to be when I'm done I will add 2 finishing passes. First pass will be 12000rpm, 3ips feed, 12% stepover, leave 1/64" material for 2nd pass. 2nd pass 12000rpm, 3ips feed, 6% stepover (leaves a very smooth finish).

When I use this combination the results are so good, very little sanding is required. The trade off is machine time goes up. But it is a good tradeoff for a project where I can be doing another piece of it while I'm getting the carving done. I'd much rather be building something then sanding something - but that's just me. :D

[ken_rychlik]

From my 3d cutting, Cherry is on the verge of being to soft. It leaves more clean up than harder woods.

Hard maple is good, Euro beech is one of my favorites.

My settings are close to Don's, but I go with 8% step over on the finish pass.

[Jerome]

I carved the horsehead that came with bot and it was set to offset. the resolution wasn't very good. Based on suggestions from the forum I carved it using raster with 10 degree stepover and it turned out much better.

Thanks to everybody who responded.

Jerome

[blackhawk]

I always raster in the Y direction. This way you are only working one motor instead of two for most of the time. Less wear and tear on the machine and should save a little electricity.

[michael_schwartz]

I try to raster with the direction of the grain when I can when working with solid wood. Occasionally I go against this for various reasons that I have encounters.

I always raster along the Y axis when I can, as I find the cut tends to be smoother. Of course this also contributes to less wear and tear on the rails, and drive components on the X axis.

These days I have been using offset 3D finishing toolpaths quite often. A recent example would be a situation where I had an arched 3D molding framing a relief which was cut with a pocketing tool path.

As far as step over I tend to aim for about 6-9%. One time I wasn't in a rush and didn't have anything else to cut so I cut out a carved plinth block with a 2% step over for the heck of it.

I would check out the following article authored by Brady Watson on tuning ramp values for 3D.

http://www.shopbotblog.com/index.php/2008/03/a-ramping-the-vr-command-and-how-to-tune-
your-tool-for-maximum-performance/