Whay I'm Geting This Cuts

[german]

Hi every one, My concern today are the "MARKS" that you can see on the cuts, specialy "V" cuts on mdf and wood, the one on the picture is a base for a trophy I did today out of .75 mdf and the size is 4x3. I did a profile toolpath for the edge with a 120 deg. V bit at 1 ips move speed, 16000 rpm, .5 of Z plunge. I think the toolpath is preatty slow to get these kind of marks. I have been getting these marks on all the V cuts that I make.
Any advice or any clue on fixing my problem will be greatly appreciated.

German.

3787


3788


3789

[Gary Campbell]

German...
Things to check:
Test that the bit is exactly 120 degrees..
Try cutting the same file with less stepdown
Check to see that the bit is not damaged
Make sure that you are not exceeding the cut depth of the bit with your pass depth.
Good luck, Gary

[pfulghum]

Will your cutter, make that cut in one pass?

Do your rough cut with an offset of say .01.

Then make another toolpath where you want but "edit" the bit to have a stepdown of 1" to force a single pass.


Make sense?

-- pat

[myxpykalix]

make sure you have good sharp bits. Look at the angles on these, they are right on the money. Check out www.centuriontools.com (http://www.centuriontools.com)


3790

[srwtlc]

Is that bevel cut in one pass to get the depth or two passes? What software? I cut something awhile ago that left that type of a mark, but VCPro also showed it in the 3D preview. I was told by Vectric that it was on purpose (only during a double pass situation). Don't know why.

If it's cut in one pass, I'd say that your tool is damaged. Hit a screw lately? ;-)

[german]

Ok guys, first of all thank you for take the time and respond to my question.

Gary, this is a new 2 1/4, 120 deg bit, with out any damages, stepdown for this toolpath is .375,
thiis the second time I use this bit, the first time was with a HDU sign cuttin just a couple letters.

Pat, Scott, yes is one pass, and the software is partworks, the bit is like new, it only has been used twice, and the marks are in every V cut I make, and with any V bit I use, 90, 60, 120...

[german]

Here are some pictures of diferent files with the same problem, in the scuare one you can see the marks at the lower right corner, both of them are made with a 90 deg. bit at .5 ips, .375 stepdown, .5 on Z, and partworks software, the material is MDF, and if it is relevant, my machine is a prs standar.

German.
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[cnc_works]

Is it always in the same batch of material? Is it possible that the material has different densities at different levels in thickness?

Donn

[german]

I always use the same material, trupan mdf

German.

[pfulghum]

German,
Send me one of your PartWorks files that have the toolpaths already created. Let me see how you are creating the toolpath. If I see problems I will create new toolpaths and send it back...

-- pat

[jeffreymcgrew]

I'd double check your Z-axis, as well as your spoilboard, and make certain there is no unintended movement there.

I had some weird issues along these lines once and it turned out that the pinion on the Z-axis wasn't tight against the rack, allowing for a 1/32" or so vertical play. But then mine's a PRT, don't know if that makes a difference.

But if your spoilboard is able to move (i.e. flex) when the cutter is plunging or the material itself is able to 'relax' up while cutting it could cause very slight Z-axis issues as well.

[jhicks]

I'm surprized folks find this unusual. It happens to me all the time so I've basically taken it for granted as "the way it is" but my belief is that this could be caused by one or more variables.
1) yep, those 120 V's are not always a pure 120 degrees. Maybe 119, maybe 122 but when one sets up their library at 120, any variation will/could generate this "step over/down mismatch".
2)X,Y, or Z on my PRT simply isnt absolutely dead on or dead tight. Things do tend to move over time or flex when cutting. These inherent mechanical issues also contribute or cause this type of result.
Material can certainly also relax after cutting so just one more reason.
The question i would ask is; do others not experience this? Because from those I have discussed with, it seems to be something we just live with and sand out. Especially with Trupan or HDU. Easir to hit with a piece of sandpaper or sanding sponge and wipe away the machine marks.
Hope someone has the answer but when I look at the results on "more robust" machines, this does not occur so to me its mechanical stabilty or bit geometry.

[pfulghum]

I almost always run a final pass at full depth to avoid such problems. Keep the intermediate passes 1/32 (.03) away and then do one pass at full depth. This will overcome all the symptoms you just talked about.

-- pat

[prolitesigns]

That looks like the marks my machine leaves, when the tool is making more than one pass because of the stepdown depth not being enough.