How fast do you cut in 3D?

[blackhawk]

Hello All - Here is a piece that I just machined out of Mahogany. (My customer calls it mahogany, but I expect that it is Sapele.) I cut this on my PRT Alpha (7.2 upgrade) and PC router at 2.5 IPS on X and Y and 1.8 IPS on Z, 19,000 rpm. I have optimized my VR sheet based on Brady's article. I am happy with the results, just wonder if I could go faster. This piece was about 12" tall and 40" wide and took about 3-1/2 hours with an 1/8" ball nose.

With this type of 3D work, I think that you are going to reach a point where the speed is limited by your ramping and Z moves.

[steve_g]

Nice work! I suspect that you have already maxed out the speed you're going to get due to ramping... It won't hurt to try ridiculous speeds and see if any time improvement is realized...

SG

[dlcw]

I 3D carve on my PRSAlpha at about 3-4ips. Any higher and I think you just beat the snot out of your machine. This seems to be the sweet spot for my carving. I cut plywood at around 6-7ips.

[blackhawk]

I just cut out two identical panels tonight. I ran the first one with all the same settings above except I had my X,Y speed at 2.6 IPS. It took 2:15:45 to run. I cut the second one at 2.8 IPS (about 7.5% faster). The second one cut at 2:15:10. I only gained 35 seconds or about 0.4%.

It probably makes a bigger difference if you have a lot of open areas with no Z moves.

[cowboy1296]

I am always looking for a way to speed up my 3-d. Currently I am at 3 ips feed rate and 2.5 on a plunge. I use a 7% step over and my rpm is 10k. I cut primarily black walnut and alder.

[Brady Watson]

She'll go as fast as she'll let you go...Every relief is different & tweaking ramps will let you gain some speed, but not gobs more.

Three areas are going to influence your 3D cutting more than anything else:

1. Slow Corner Speed; simply explained, the percentage of your move speed that sets how fast it will go around a corner, in XY OR YZ OR XZ (and XYZ) - so if your SCS is at 30, it will slowly climb over details. Jack it back up to the stock 65 setting, unless you are getting rough movement or 'banging' - think of SCS as a cushion. The higher it is, the harder it is.

2. 3D Ramp Rate, this reduces the sensitivity of ramping in the Z axis. Stock is 100, I like 150 for most things, up to 300 is useful, more than this is a diminishing return. If Z bangs, pull it back.

3. Often overlooked, one of the most important things is machining at a 'good speed'. The XY to Z speed ratio is important, so go check out the speeds I posted in the article and try running at one of those. On that relief, it isn't that detailed, so you should be able to run maybe 3,2 or 3,3. I don't like running the Z faster than 3 because it will result in a poor finish...it is asking an awful lot from the Z motor to move that fast while lifting a 20-35 pound gyroscope. Running at the speeds I recommended will make tuning the other 2 settings easier.

-B

[hespj]

Are you guys not worried about breaking your 1/8" bit at too high a speed?

Brady, where can I read your article?

John

[jerry_stanek]

After the first cut you are only taking just small bites

[Brady Watson]

http://www.shopbotblog.com/index.php/category/bradys-tricks/

[hespj]

Thanks Jerry, Brady.

John

[joe]

Don't hear much about quality when cutting a variety of materials. For example I'm using 1" PVC as well as considerable amount of HDU and Yellow Pine. Each of these materials cuts differently. However when I'm doing a 3d woodgrain background and pocketing for my letters the quality of cut isn't very important. You're just hogging it out. But when doing detailed, fine work in Duna, it's best to take your time. For the most part this is a business of quality not speed.

We usually start our long runs in the afternoon and let it run through the evening. This isn't a good idea when using a router or older equipment.

I do my dead level best to stay away from 3d as much as I can. What I've made my living of off is 2.5d. Most people call it 3d. I don't mind.

Joe Crumley
www.normansignco.com (http://www.normansignco.com)

[joe]

I've also learned when doing delicate critical work with the combination of 3d passes, it's best to profile cut my smaller letters and dignbats in advance. This technique gives much more control. For example if the material is wood a small 1/8 or 1/16 down spiral bit can is good. If you're worried about tear-out a person can make small Z's to keep it all together. Then start the 3d process.

All that said, I could easily live without 3d. It's never as sharp or a clean as 2.5 or V carving.

Joe Crumley
www.normansignco.com (http://www.normansignco.com)

[Mayo]

This was my first attempt at duplicating a sign with wood grain background. The original was broken by someone.

I had intended to sandblast it but my idea to use PVC shower pan liner as masking failed miserably. I was afraid to use contact cement because I thought it would be a permanent bond, so I sprayed 3M Super 77 on both the PVC liner and the wood, let them tack up, put the liner on and rolled it down. When cutting the liner with a 1/16" bit, it easily lifted off the board and got tangled in the bit so I trash canned that idea. All the adhesive came off the liner and stayed on the board.

My 2001 PRT cut this 18x36 inch Douglas Fir sign at an amazing speed.
I'm so amazed that I don't think I'll ever machine a textured background like this again. 8 hours and 16 minutes. Cut speed about 2.5 inches per second, jog speed 3.5, 1/8 inch tapered ballnose bit for the texture and lettering. 10% stepover finish cut. No roughing path cut because it didn't decrease the machine time shown in the toolpath details area.

Sorry for the less than great photos - taken as stills on a video cam.
The wood grain texture was done from a photo, brought into Aspire and sized to fit within the inner border. The text was approx. 1/8 inch higher than the wood grain.

My original selection of wood took into account that I was going to be sand blasting it so I tried finding straight grain. I doweled and glued up several boards to make the sign blank and in spite of alternating the grain you can see that after machining the sign has developed a significant cupping or warping. I guess that particular piece was too close to heart wood.

I hope I don't have to cut this again...
My attention to detail was lost in space and I created rounded corners where they should have been square! My creative license allows me to do stuff like that.