"Waterline" marks and VBit angle

[scottp55]

Finally got a chance to repay the guy who picked my Desktop up from the shipping terminal in his truck and helped me uncrate.
Bedroom door sign for a 6yr old girl who likes snakes and frogs(Yuck).
Decided to dial in a new Kyocera .25" 90VBit- quite dismayed to find "waterlines" I could catch a fingernail on(barely).
Remembered a thread by Paul Z for testing the actual angle of a VBit and downloaded the file. Had scrap on right of Cherry for the test if I re-arranged them.
Cut first at an included angle in tool database of 90 degrees and got the same as the carving. Then changing only the angle of the bit in the database, I went from 85-92 degrees. 88 degrees was better.At 86 degrees I was getting toolmarks from the outer diameter of the bit when it went to clean up the corners. at 92 degrees waterline was worse.
Also tested at 40% faster feed/speed and pass depth as I always feel I'm cutting slow compared to you guys even though chips and bit temp say otherwise. Didn't like the idea of sanding this kind of thing though--so just letting the machine do the work while I do other stuff.
I thought the 87degree included angle looked best, so changed that in the database and decreased pass depth 30%( so any new marks would be at a different height from originals) and rezeroed .006" (not enough to eliminate old marks:( )lower.
Only "waterlines" were the originals MUCH reduced and NO new ones:) BUT it's a much more intricate cut than the test triangle and many more passes, so you'll see toolmarks in corners so I'm TOO steep now. I'll change to about 78.8degrees next time I use the bit.
By then it was getting late, so was going to recut this morning BUT idiot me shut down, and any cut now would have been a hair off--Oh well next time.
Interesting though are the toolmarks from 85-87 degrees as they are the same exact marks I get from my Vortex .25" 60 VBit that drove me so nuts doing deep cuts I stopped using it and used an Onsrud 60 engraving for those cuts. I bet if I dial in 62-63 degrees on the Vortex they'll disappear:)
I KNOW the right way is to have a VBit that is large enough to do a full pass afterwards, but money is tight and working with what I have.
Hope this is of some help to somebody.
Thanks Paul--You helped me!!! Again :)
scott

http://forum.vectric.com/viewtopic.php?f=3&t=2164

[Burkhardt]

What I learned from my own experiments....
- the waterlines are "normal" when using a very sharp tipped bit and you match the v-bit angle precisely. The surface speed of the very tip at normal spindle rpm and feed speed is just too low to cut properly.
- using a rounded or blunted tip helps some but won't leave a sharp edged bottom.
- my own best recipe is roughing the v-carve about 0.02" high in depth steps like you did an then doing a full depth finish cut (may require a large diameter bit) at proper depth. With that method and a 1.25" dia cheap eBay bit I got the cleanest results.
- I measured the resulting groove angle of several bits and found they all were pretty much on the money. Only the CMT laser point was way off (56 instead of 60 degrees).
- i did not try cheating with the specified angle intentionally. Looks like that may work, too.

[Joseph clements]

I used Onsurd bits. And don't have this problem

[Burkhardt]

I used Onsurd bits. And don't have this problem

Please let me know which bit, speed and feed as well as depth of cut. So far I have take it as given that a sharp tip does not cut (because the circumferential speed is very low) but drag and rip some fibers. But I would be interested to try if the Onsrud folks found a way around that.

[scottp55]

G. , So you never dialed in 56degrees?
What method of measuring bit angle did you use? Just wondering if we could afford it and how accurate it was.
Going to dial in the Vortex .25"60 today and will run my .5"90 Onsrud in same test with same pass depth as the 1/4's.
also going to do a before after test with that Kyocera .25"90, got a sintered diamond lapping plate in 1200G and get a flat on that bit that can only be seen 10X to start and check that effect---nice thing is the lap was made for my Diamond Pacific Pixie so has a 1/4X20 bolt on the backside. If I make a pocket in my most stable wood I should be able to get repeatable custom flats for inlays.
I'd be interested if changing the CMT to 56 made a better deep cut. VCarve depth on the sign was .524"

[Burkhardt]

G. , So you never dialed in 56degrees?
What method of measuring bit angle did you use? Just wondering if we could afford it and how accurate it was.
Going to dial in the Vortex .25"60 today and will run my .5"90 Onsrud in same test with same pass depth as the 1/4's.
also going to do a before after test with that Kyocera .25"90, got a sintered diamond lapping plate in 1200G and get a flat on that bit that can only be seen 10X to start and check that effect---nice thing is the lap was made for my Diamond Pacific Pixie so has a 1/4X20 bolt on the backside. If I make a pocket in my most stable wood I should be able to get repeatable custom flats for inlays.
I'd be interested if changing the CMT to 56 made a better deep cut. VCarve depth on the sign was .524"

Scott, I found that the CMT made actual stair-steps when vcarving in layers at 60 degrees, unlike all other bits where the "waterline" is basically only a scratch line. Then I started measuring which is tricky as the CMT bit has 3 flutes. I ended up cutting deep v-grooves into a maple board and taking the result to work and measure the groove angle with an optical comparator. Pretty much all bits (even the cheap ones) left a rather precise 60 degree notch except that CMT bit. You surely don't want to buy a $6000 comparator but if you make such a notch deep enough you can probably measure this with a protractor or make a 60 or 90 degree wedge to check the fit.

Other than that, the CMT bit cuts very clean and I may use it again but dial in the proper angle. It is anyway very different; most such bits have 2 brazed carbide flat flutes but the CMT bit has a solid round carbide plug brazed into a steel receptacle and then 3 flutes ground in.

Sometime I may have some custom v-bits made where to tip is not just blunted but is truncated a little (maybe 0.02") with a large radius (maybe 0.5") so that it still has a sharp tip. Hope that makes sense. That might be a compromise to get a crisp bottom and still be able to machine the layer marks away with the next depth step. But that is a project for another day.

[scottp55]

Nope, $6K is out. I'll stick with my $15 General #17 protractor. Funny that it says the Kyocera is 88 instead of 90, and the Vortex at 61+ instead of 60---same as that first test cut and what I was expecting to see in the Vortex.
Got sidetracked with a Desktop problem, may not get to do other testing today.
Yep, the extreme tip of the bit would be almost a "Flame tip" like I use for freehand diamond carving in gems.

[shilala]

Scott, when I get that goofiness, I just bump down like .008 and hit the whole thing again at a full depth pass. You might have to nudge it a little more till it gets clean.
I've pretty much done away with the steps by doing one aggressive pass, then one small finish pass, rather than the 5 or 6 passes you have there.

The Onsruds I have were only about 30 bucks each. I can't remember where I got them, but I posted the source here.
I use 1/2 shank 1" 60's, mostly. The 90 I have I've not used yet. It's so big around I'm not sure where I'll use it, but I'll get around to it.

My bad, I just realized you were using a 1/4 bit. You're kinda screwed.

[scottp55]

Scott, Rarely do stuff like this nowadays and usually only using .006-.009" of tip and seem to be working on woods with"moderate" to"severe" blunting effect so trying to see how the $4-11 Kyocera's work out(seem excellent so far and I don't get tempted to use a bit past it's prime).
Just thought it was worth pointing out that changing bit angle 1-2degrees can make so much difference. Looking forward to dialing in the Vortex 60 .25" as I seem to remember that was $37, but I had stopped using it except for shallow single pass stuff as the shoulder of the bit was leaving marks.
Thanks
scott