using VCarve w/Flat bottom tool path - Star w/Sharp points

[Ton80]

Hi,

I ran a job a while back in which I machined away the background using a VCarve tool Path and Flat bottom. My desired effect was to create a 2.5d image. In the PREVIEW of the tool path, everything looks like I wanted it to and my 5 pointed star has nice sharp points. However, when the job ran the external points of my star were rounded and not showing the sharp point the preview showed me.

Here are screenshot of that previous job - I ended up going in with a hand held router and fixed this

the resulting star

This is what the tool path preview said I would get

notice my star shows the sharp points

I have another project ready to run and I there are some stars which are having the area around them carved away using a V Carve with Flat Depth. Preview is showing me the pointed outside profile but I know that is not what I will get. I notice the 2D Profile tool provides some control over CORNERS... So, I guess there is a reason that same control is not provided here but in my head, the fact I chose a V CARVE strategy should create these sharp points...



This is the job I am about to run. I have the top area with the stars and the bottom area with the Deer set up together using a V CARVE w/FLAT DEPTH tool path.

stars show the sharp outside points in preview.

DO I need to scrap the V CARVE strategy for this and go with a 2D Profile? What happens when I truly need a VCarve Strategy but there is a STAR involved somewhere? You can see the Deer in the bottom area NEEDS the V Carve strategy - at least I think it does.

[Adrian]

If the preview doesn't match what you're seeing on the machine then 99.99% of the time it's a problem with the machine either physically or with the control software.

Generally when there are rounded corners where sharp ones are expected it's because the deceleration/acceleration (CV) settings in the control software are wrong for the job.

The other causes could be inaccurate z-zero setting or the v-bit doesn't match what the program has been told it is.

[Ton80]

hmm. Ok. Well I know it was not an issue with the V Bit I loaded and the Zero was not the issue either. I'll post this on the Shapeoko forums since that is the machine and it's their Control software running my machine.

Thanks

John

[martin54]

hmm. Ok. Well I know it was not an issue with the V Bit I loaded and the Zero was not the issue either. I'll post this on the Shapeoko forums since that is the machine and it's their Control software running my machine.

Thanks

John

How do you know it isn't an issue with the v bit ? Have you checked the actual angle of the bit is the same as it says on the tin There is a thread on the forum about checking v bit angles because they are often not exactly the angle they claim to be, this can lead to errors with carving.

The toolpath preview is very accurate so as Adrian has said if what has been machined doesn't match then most of the time the fault lies elsewhere. Can't help with control software as I have absolutely no idea what your machine uses

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

[Ton80]

I am going to verify my bits now... Vectric support came back with the same assessment. Looking at my tool database right now and it supposedly matches my bit. Going to examine the bits now.

[Adrian]

It looks like you're cutting oak so another possibility could be that you're pushing the machine too hard with the feed rate/pass depth you're using.

[martin54]

The link I posted has a downloadable file that can be used to check the angle of your v bits

[Ton80]

Thanks... I just went and read that thread. I'll test my bit out.


The width of the bit is off a slight amount ( .50" but calipers show .493 ) so I guess it's safe to assume my angle might not be perfect either and on such an extreme angle that is going to show up.

[Ton80]

Well I screwed up that test to determine the angle of my bit... I didn't use the toolpaths there.. doh. I just selected everything and applied my V90 and created a toolpath for all of them... dumb. However, I did go out and pick up a semi-decent protractor and the Angle under magnification does appear to be very close to 90deg.. certainly close enough that I can't see changing anything in the tool database.

I did run the star on the same test board though, this time with my V90 width changed to .492 ( actual ) rather than the .50 spec and wouldn't you know, that was the problem.

Another valuable lesson learned today, Thanks once again gentlemen!

I do plan on running that angle test again the proper way, using the toolpaths already programmed and just using my tool in the spindle.

[Ton80]

Can't edit my post above.. odd. Well maybe the diameter difference was not the cause afterall. A member of the Carbide 3D forum pointed out that the diameter difference would not make that become an issue unless I went full depth and that was not the case. Maybe it was all do to a zero issue. I'll never really figure that out now but I'll just be much more careful with zero and double checking my tools before assuming the info provided by manufacturer is right.

[martin54]

The guy on the other forum is correct, the actual diameter won't come into play unless you are carving something wider than the stated diameter of the bit
Still doesn't mean you have fixed the problem though (sorry) if it is a problem with CV settings this is something that will need to be addressed. It might be that with this particular job the machine is not reaching a speed that would cause the corners to round
I would still speak to people on the forum that deals with your machine & its control software to see if there is any tuning you can do with the control software settings.

[adze_cnc]

Don't some machine's controlling software have a g-code setting to determine how quickly it goes around corners? It seems to me there have been similar post where corners get rounded because of that.