Odd Blemishes while v-carving

[rcnewcomb]

I'm getting odd blemishes while cutting this pattern. I resized it to 9.375"x15". I used a 1.25" V120 Gerber bit at 3ips (1ips plunge) at 13K. I believe the router (Porter Cable) was bogging down a bit during the initial plunges. The material is red oad what was being held with a vacuum puck. Any thoughts as to the cause of the blemishes (circled in red)?
V-Carve Blemishes (on another web site) (http://www.222artisans.com/images/Blem24Oval.jpg)

[steve_wms]

That looks like a toolpath issue to me.

[paco]

Check the toolpath tolerance if there's any (ArtCAM or VETRIC or else?).

If you have a good (VERY) protractor, check the included angle of the bit; it's not so rare that it's off by 1-3 deg. You can check this with a series of test with simple shape where you change the included angle (by +/- 1-3 deg.) until it leave NO such tool marks. Start with the protractor check first... After messing around with many brands of V bits, my heart as felt for Her-Saf!

Next would be vibration from the machine; hold down, plunge speed and feed speed, ramping settings...

I assuming you have ruled out the design quality aspect.

[rick_woodward]

Thought i had reading your post was this. The porter cable seemed to bog a bit.... Red oak is tough stuff. The porter cable likely couldnt maintain the rpms/torque it needed for the feed speed. When it bogs an tries to recover it will waver in its cutpath. Bearing slop causing a slight harmonic imbalance. Try reducing your feed speed in tougher woods. I know for a fact Paco has more experience than i do, but no matter what angle a bit is. It would cut the whole path at that angle. Not suddenly dip an waver in its path.Porter cable routers where not built for use on a shopbot, they work, but there will be issues like this. The bogging down shows where it starts to make its cut til it slows down near the end. Then it momentarily stops , making that indention, and proceeds to cut the end of the path. If your bit is new or sharp, i'd reduce feed speed. Just my thoughts, rick

[paco]

V Carving strategie use the included angle of the said bit to calculate the toolpath. If the Included angle is not as entered in the tool data base, the it can't perform as intended (as calculated by the program). Say it's wider than entered in the tool data base, it'll over shoot the 3D corner sharpening with over cuts just around the corner sharpening. It may not be very obvious, but 3D moves (corner sharpening) sometime are create in curves too (check the toolpath in preview mode) like in the pix shown above hence create those over/under shoots...

Vibration/chattering would be the first I'd look at too though... hoping I have a good V bit...

[paco]

I "almost" can see this kind of over cuts here...


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Here part of the design (I assume)...


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Here you can see the 3D moves create for both the corners and the very gentle corners at the curve...


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[Brian Moran]

Hi,

Randall posted this query on the vectric forum at the same time as this post and I believe we got to the bottom of the problem pretty quickly in that the cutter geometry was incorrect.

As Paco said above it is not unusual to find that even new bits aren't ground particularly accurately. If you look at this thread http://vectric.com/forum/viewtopic.php?t=317 on the Vectric website, about half way down the page you will find the discussion.

There are some images in that thread which show the errors which arise with just a 1 degree error on the tool geometry - 119 degrees instead of 120, it looks as though Randall's tool was actualy about 118 degrees.

It really is critical when vcarving that the geometry of the tool matches exactly the geometry you have told the program when calculating the toolpath.

Brian

[rick_woodward]

SCORE ! Paco ! Good call. I learned a thing or two on this thread. Mucho Gracias, Paco, and Brian.

[superior]

Isn't this forum just the berries? Imagine, help from around the world, and FREE. What a bargain!
While re-reading this, I couldn't help but wonder where this file originated. It is a really great file. Is there any way to access and download it? Sure would make a good "show and tell" for our customers.
Any help available? Web site mabye?
Thanks to everyone who so willingly shares.
Doug

[tony_mac]

Hi Doug,

One of our VCarve Pro customers kindly supplied this design for other VCarve customers to freely use, and it's available to download from the Vectric Forum (http://vectric.com/forum/viewtopic.php?p=1871#1871)


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As you say, it's truly stunning just how helpful everyone is when it comes to sharing knowledge and ideas. Long may it continue!

Tony

[superior]

Like I said, just the berries. Seems as though someone ALWAYS comes through on the forum. Bryan and Tony have been a Godsend to me since I first became aquainted with them. Wonderful products, better people. Keep up the good work, long live 'Botting
Doug