Still No Solution...Help me please! :)

[sevans]

Hello All. Check out the quality of this V Groove. I've posted this before but still have not solution. Anybody got thoughts? Many thanks for looking! -Sarah Evans17713

[srwtlc]

Hi Sarah,

Assuming that your machine is mechanically sound, attach the file for us to take a look at. Could the chosen font be of poor quality? Meaning that it may have a jagged outline that can't be seen until you zoom in on it. Does it have many nodes instead of just a few (in node edit mode)?

Is the material held securely or is it vibrating slightly under the cutting forces.

Cutter quality. Dull, not exactly the angle degree that it should be.

Worn collet.

Is that blue foam? How's the cut in another material?

[dlcw]

Hi Sarah,

Assuming that your machine is mechanically sound, attach the file for us to take a look at. Could the chosen font be of poor quality? Meaning that it may have a jagged outline that can't be seen until you zoom in on it. Does it have many nodes instead of just a few (in node edit mode)?

Is the material held securely or is it vibrating slightly under the cutting forces.

Cutter quality. Dull, not exactly the angle degree that it should be.

Worn collet.

Is that blue foam? How's the cut in another material?

I would be looking closely at the material vibrating while being cut. Does every letter show the same characteristics? If so, that would lead me to possible material hold down.

Try some MDF to see how that cuts.

[gene]

are you using a router or spindle? if its a spindle id the collet locked in the nut before its put on the spindle?

[sevans]

yes, of course.

[sevans]

I gotta tell you, I just can't see how it could be vibrating. You can barely pull it off the table after you turn the vacs off.

[sevans]

Are there physical indications of a worn collet? Something in particular I can do/see to tell if it is worn?

[Chuck Keysor]

Sarah, how large are those letters? And what cutting speeds are you running at (Inches per second)?

The smaller the letters, the slower the IPS seems to be for me to keep the vibrations down with my heavy 5hp Columbo spindle. Just watch your machine as it is reversing directions, it is really quite amazing to see this huge weight of the spindle getting jerked this way, then instantly being yanked that way. If everything is not tight and solid, it is easy to see how your entire spindle bit assembly would be vibrating after each instantaneous direction change!

For my finest letters, 1/4 high, 1IPS to 1.5 IPS is where I usually run. Someone else posted the other day, running WAY slower than I am in order to get clean results.

And I was not even able to experiment on this level until I had tried a couple of other brands of bits. In my case, I hadn't needed to do any added fixing, just figure out how fast I could run (IPS) before I had pushed the shakiness of my machine too far!

Chuck

[sevans]

That does make sense. It is jerky for sure. These letters are 1.5" or so in height. I used a 120 degree her saf bit and fed it at 1.2. Spindle 18000 rpm's. how slow can you feed? Or should I?

[bill_l]

Sarah,

If I understand, you're feed is 1.2 ips? If so, slow it down and cut your spindle speed back. When carving letters I use the 90 degree her saf and use a feed of .5 to .75 ips feed and almost never exceed 10-12K rpm on the spindle. If the letters are really small I move slower still.

By running some tests you can find the "sweet spot" that will net the best results.

Bill

[srwtlc]

Have you tried a different bit? I've had a couple of Her-Saf bits (replaceable cutter type) and they were the worst bits I have ever seen! One that I returned for replacement, a 90º v-bit, that was supposed to be ground for zero rounout at the point was way off and you had to try adjusting the cutter to get it to run even close to true. As far as I'm concerned, Her-Saf bits are junk and you'll never get them to run true. If you place a piece of material under the cutter and bring the tip of the cutter down to just touch the surface and give it a spin. If the tip cuts a circle or an enlarged hole instead of just a point, you'll never get a good cut out of it. Corners are going to be rounded out, the cut will be wider than expected, and the valley won't be sharp or crisply defined, but have somewhat of a flat bottom (which it looks like your image does) . Save yourself some grief and dump the Her-Saf bits.

If you learn about ramp settings and play with them a little, you can create a softer ramping scheme for small to medium v-carving jobs that will alleviate some of the abrupt jerk seen with the short sharp corners cuts. You can save this ramp scheme and load it when needed and then revert to the original ramps when not. Good information on ramping can be found here.... http://www.shopbotblog.com/index.php/2008/03/a-ramping-the-vr-command-and-how-to-tune-your-tool-for-maximum-performance/

[Chuck Keysor]

Sarah:

a) Scott's comments about bits are 100% correct. I did the same test he described with two other brands, and found that I got small circles, instead of a point when spinning the bit in the spindle. One brand that seems to have universal approval for the sharpness and alignment of its tip is the CMT 60 degree "Laser" bit. Even if 60 degrees is too steep for your need, buy one for testing and to eliminate the bit as a variable in your investigation.

b) It is good that you supplied your feed rate (inches/second). As noted, I have found I can run at 1 and even 1.5 inches/second with tiny letters (.25" high). But others have said they need to run at .2 or .5 inches/second. After you get a new bit, you will need to experiment, and at least find if there is any speed that produces a chatter free cut.

c) In terms of your spindle RPM, it seems to me as the entire question of the dynamics of moving a big weight (your spindle or router) and instantaneously reversing its direction are will overwhelmingly dominated by your inches/minute feed rate. That set of variables will be affecting your chatter. The RPMs of your spindle or router would seem to be connected more to just the quality of your cut as a constant characteristic around your cutting path, which would show up in fuzziness, chipping and bit heating, but not affect your chatter. At least when I was fighting chatter, my RPM settings seemed to be unimportant.

Go buy a CMT Laser bit as your first move! Thanks, Chuck

[paul_z]

Sarah,

I'd suggest that you create two 3" x 1" rectangles and calculate the V Crave toolpathfor each one seperately. Run the toolpath for the first rectangle just once and for the second rectangle run the toolpath twice.

Then look closely at the results. The corners should be very clean. The corners in your photo show little "blobs". It looks like the actual bit angle is less than advertised.

The purpose of running of the toolpaths twice is to reduce the force on the bit during the second pass. I think you will see a much smother result on the two pass rectangle.

If you try this, please post a photo of the results.

Paul Z