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View Full Version : Need Help! 3D milling of a part. Tool path don't look right.



FoxCNC1
06-05-2015, 11:16 PM
hello gents.

I am not very experienced in milling 3D shapes with my router but I would like to learn. I am having a bit of a hurdle here and I am hoping to get some help.

I am trying to make a cylindrical part by splitting it into two halves the same way some people make guitars.

This is the original part:

http://i10.photobucket.com/albums/a146/Profoxcg/Part_zpsupl6dfqh.jpg (http://s10.photobucket.com/user/Profoxcg/media/Part_zpsupl6dfqh.jpg.html)

This is the same part after a horiz. Roughing pass with an endmill (or whatever tool).
Notice how their stock left at the 90 deg corners.

http://i10.photobucket.com/albums/a146/Profoxcg/Horizontal%20Roughing_zps8wxheaxv.jpg (http://s10.photobucket.com/user/Profoxcg/media/Horizontal%20Roughing_zps8wxheaxv.jpg.html)

This is the result of a Parallel Fin Pass... same deal. The cutter doesn't seem to clean up along the vertical side of the larger cylinder.
Take a look at the tool path. This happens everywhere there is a vertical transition.

http://i10.photobucket.com/albums/a146/Profoxcg/Parallel%20Finishing_zps1jyewaho.jpg (http://s10.photobucket.com/user/Profoxcg/media/Parallel%20Finishing_zps1jyewaho.jpg.html)

What am I doing wrong? Or am I mistaken in thinking that what I am going in the right approach to make this part? - I do not have a lathe, but I run into this problem regardless very frequently.

Also as a result of all my machining operations, the part is now floating....
I appreciate any guidance in advance.

FoxCNC1
06-06-2015, 01:12 PM
Guys I wanted to update:
I changed the object to he cut thinking it was maybe a limitation caused by the object I'm trying to cut but I get the same material left over whenever there is a vertical face. It's clear that the tool path extends part the vertical edge rather than plunging down to mill the vertical fetuses properly. I tried this same workflow in Aspire and the preview seems to show more of the results I am after...

I keep thinking that this can't just be a software limitation l. It just seems dumb of such expensive software. Please help.

brian257
06-06-2015, 07:47 PM
It looks to me like you are using a square ended end mill for the tool instead of a ball mill that you will need to get the round object. Either way though you will not get into the corner between the small diameter shaft and the large diameter one.

If you really have to machine this part on something other than a lathe you will get a much better shape a whole lot faster if you turn it on its end. Much easier for an end mill to just circle around the part than to keep making passes to reduce the scallops the way you are doing it. It will also allow the sharp corner between the two radii with a square end mill.

What I would do is cut it vertically with the smaller radius end at the top. This would be a 2.5d operation. Cut the smaller radius first then step down and cut the larger one. Then turn the part over and face off the back side.

You are probably going to find that you rarely need to do 3d cuts. 2.5d cuts nearly everything I ever need.

victorofga
06-06-2015, 08:25 PM
use first a 1/4 endmill, cut the endsurfaces to size, rough the arched tops with excess, about 1.16 then finish with a 1/8 ball end mill

with ball end mill you need ""overcut"" as much as the ball end mill radius..

Zorbit
06-15-2015, 03:47 PM
How is your tool / holder defined ? It looks like RhinoCam is stepping away from the vertical face when the cut is a certain depth - possibly to avoid crashing the tool holder.

tr1k
07-07-2015, 03:25 PM
I think you are missing the length of the cutting edge of the tool or instrument to the departure of the collet.

FoxCNC1
07-26-2015, 10:43 PM
How is your tool / holder defined ? It looks like RhinoCam is stepping away from the vertical face when the cut is a certain depth - possibly to avoid crashing the tool holder.

I will check into that.
Sorry for the delayed replies for some reason the forum never e-mailed me about you guys posting..

I appreciate all the feed back.

@victor What do you mean "overcut"

FoxCNC1
07-27-2015, 12:21 AM
I looked at the file and changed the tool to a longer endmill (by the way it was an endmill all along).

I programmed a parallel finishing with a 5% stepover. The simulation seems to clean the front face in question much better. After if I add a pencil trace and profile the cut stock seems to match the part pretty closely.
The one challenge I am still having is shown in red. The only way I can think of to get rid of that if to PROFILE the part as shown.

- Once you start to get into 3D milling you realize its a whole different ball game compared to 2D/2.5D.

Guys, when I cut (profile) 2D parts I use the tabs functionality in the software to place them (advanced) to hold the parts in place. I noticed that all these 3d operations are pretty much leaving my part floating. Can some one give me some advice?
The scenario here is that this part is one of two halves so I can't really move it up in the Z axis. The only thing I can come up with is to MODEL my own tabs. Is this realistic?

Horizontal Roughing:
http://i10.photobucket.com/albums/a146/Profoxcg/HR_zpsthvedy21.jpg (http://s10.photobucket.com/user/Profoxcg/media/HR_zpsthvedy21.jpg.html)

Parallel Finishing:
http://i10.photobucket.com/albums/a146/Profoxcg/PF_zpsjy3dds2v.jpg (http://s10.photobucket.com/user/Profoxcg/media/PF_zpsjy3dds2v.jpg.html)

2D Profiling:

http://i10.photobucket.com/albums/a146/Profoxcg/Profile_zps8dgxrfyo.jpg (http://s10.photobucket.com/user/Profoxcg/media/Profile_zps8dgxrfyo.jpg.html)

Zorbit
08-02-2015, 03:33 PM
I make similar parts to yours, from hardwood. Rather than use tabs, I prefer to cut almost through the material and either break the part out or plane it out in a thicknesser. The thicknesser method requires practice, you want to leave a small bulged skin of wood holding your part in place or the thicknesser blades will pull it out and mince it up. Annoyingly, this method works best with blunt blades, they are more likely to leave that bulged skin of wood. If you need to remove a fair bit of stock before getting to your part, machine some holes in waste wood slightly deeper than your part is cut, that way you get a warning when you are getting close.

I regularly use these methods with Oak, Mahogany and Teak.

FoxCNC1
08-02-2015, 07:50 PM
so you don't cut all the way is that you are saying.

Zorbit
08-03-2015, 02:22 AM
so you don't cut all the way is that you are saying.

Yes, for hardwood parts. If I use the planer / thicknesser method to get the part from the waste the wood actually moves away from the blade where the routed cut is, so it holds the part in place yet still breaks out at almost the exact size I wanted. If I make long parts it works better, the thicknesser can't grab them so I can cut them right out.

victorofga
08-03-2015, 08:57 AM
first off, could you post the pictures here? it is impossible to zoom in when you post on a kinky website and link over here..

for the outline you mentioning on the second picture, I think that is the result of the setting """stock offset (pocketing) """

when I say ""overcut"" means your ball end mill , ""ball""center need to reach the bottom level, means tip will be lower by the radius..

if you want to leave tabs, similarly than 2d cuts, then you have to model those tabs.., so finish cut going around the tabs..

Zorbit
08-03-2015, 03:44 PM
288760

I'm not sure I explained well, so here are some pics of some teak parts I made today, showing the "blisters" left by the thicknesser.

288762

ger21
08-03-2015, 04:09 PM
Boy, that looks really risky. :)

I leave about .005-.008 and just break off the scrap, and clean up the edge with sandpaper.

FoxCNC1
08-03-2015, 04:55 PM
Sorry I am having and hard time understanding the thicksenner workflow.
BTW, there is nothing Kinki about photobucket who I have used for years to host my photos. Not sure what Victor is seeing. But I see my images full size.

Greg, 0.005" will hold the piece in place?
I think I need to set a bottom Z offset to keep the cutter from going all the way. Again I guess there is not "simple" solution for these types on parts specially the 3D type which use 3D model geometry to know where to cut and stop. - Now a video I saw a while back makes total sense. The guys was using "fake" geometry to keep the cutter from going all the way down.

Regarding holding, sometimes I guess you just have to model tabs etc.

I have to say that I started I was using aspire and that program got me spoiled with its automatic tab generation.

Zorbit
08-03-2015, 05:31 PM
Boy, that looks really risky. :)

I leave about .005-.008 and just break off the scrap, and clean up the edge with sandpaper.

The thicknesser leaves enough to hold the part in the plank until I break it out, the advantage is that I can have more depth of wood holding the job steady whilst it's on the router. It's just the method I have drifted into using, works well for me as long as I keep the MDF sacrificial router bed in reasonable condition ( so that my Z depth is consistent in the plank ).

The parts in the pictures are quite long, I could have used the thicknesser to cut them right out without problems but wanted a photo of the "blisters" that I use for smaller parts.

FoxCNC1
08-03-2015, 08:21 PM
Now I get it Zorbit !! Thank you for you last post that make it clear. Well I don't see myself getting a thicknesser but its another way to skin I cat I just learned. !!