Roughing pass taking extremely long time

This section is for useful tips and tricks for Aspire
relayerbob
Posts: 31
Joined: Sat Oct 27, 2018 4:56 am
Model of CNC Machine: Shark HD4

Roughing pass taking extremely long time

Post by relayerbob »

I am trying to make guitar necks, but since they are too long for my machine's X or Y, I prefer to run them at a 45 degree angle (Yes, I klnow I can tile it, but that adds more realignment error possibility). I can make a really nice neck, but the roughing pass takes forever, mostly because Aspire only allows the roughing pass to be in x- or y-, and not at the 45 degree angle of the actual model.

The final pass doesn't have a problem, it runs happily at the 45 degree angle I need. I currently program the final pass as an offset that starts in the middle of the enck and works it's way out. This takes about 40 minutes with current feeds and speeds. I can probably cut that time down, but that isn't an issue at the moment. My stepover is 7%, using a .25" ballend mill, climb milling. Very nice and clean finish, almost no sanding required.

The roughing pass, however, using 1/4" EM takes some 4 hours to complete!! This is a pass depth of only 0.05", but I found that a pass depth of .10" left some artifacts here and there, especially on the top of the neck, as the final pass of the BE mill reaches the "dropoff" to the next level, so I get a better result with this lower pass depth. I also currently use a machining allowance of 0.25mm, to also help with any artifacts. I can go with the larger pass depth, and cut the time in half, but still: 2+ hours!!??? Sorta defeats the quick roughing aspect of roughing. So, multiple questions:

1 - Do I even really need a roughing cut? I see alot of variation in people's opinions, but curious about other people's experiene before breaking bits and damaging wood. The finish bit is not taking much off per pass, but at the end of the process, it's plunging to the full thickness of the blank (and yes, the BE mill is long enough to do the job). Is this recommended at all? Should I always plan to use a roughing cut for this sort of thing, or do others just do a final pass?

2 - Is there a way to get Aspire to effectively cut a roughing "pocket", short of designing my own using the pocket toolpaths (which also run at 45 degree angles with no problem) that runs the tool at a 45 degree angle - I believe the thing that takes so much time is the constant turning around, it rarely gets to anywhere close to full speed during roughing, since the roughing path is always at a 45 degree angle to the actual model edge (swapping X and Y on the roughing only makes a small difference in time). The distance actually travelled is very small, towards the bottom edge, it's only moving 1/2" and turning around, if it ran close to parallel to the neck itself, it would have far fewer reversals of direction, and would be able to maove at much higher speeds.

3 - Is there a way to greatly accelerate the roughing strategy (deeper pass depth and machining allowance, for example) that I am misunderstanding? Idea on how to accelerate this? What am I missing?

In my mind's eye, I would expect the roughing process to be much faster than the final cut on something that is more or less a straight (if angled) line. But instead, it's 5 or more times longer.

Hope this makes sense.

Thanks!

Bob

User avatar
gkas
Vectric Wizard
Posts: 1286
Joined: Sun Jan 01, 2017 3:39 am
Model of CNC Machine: Aspire, Axiom AR8 Pro+, Axiom 4.2W Laser
Location: Southern California

Re: Roughing pass taking extremely long time

Post by gkas »

A look at your file will help much more than just a long description. There are plenty of folks here willing to help optimize the toolpaths.

Instructions: How do I upload files or photos to the forum?
If the file is too large to upload here you can place it on a site like drive.google.com, dropbox.com, or onedrive.com.

Make the file shareable, and then provide the link to the file here. Instructions: How do I upload files or photos to the forum?https://support.vectric.com/faq/vectric ... -the-forum

User avatar
Adrian
Vectric Archimage
Posts: 11937
Joined: Thu Nov 23, 2006 2:19 pm
Model of CNC Machine: ShopBot PRS Alpha 96x48
Location: Surrey, UK

Re: Roughing pass taking extremely long time

Post by Adrian »

You don't say what your stepover is on the roughing pass. 40% is typical.

Generally you can only get away without a roughing pass when machining concave type designs like bowls as the first cut on the edge is very, very shallow and every pass after that is side loaded with a small stepover. As finish toolpaths always run in a single pass you can end up with very deep, full contact plunges which will snap a finishing bit in an instant as you can't control the pass/plunge depth.

You could experiment with a 45 degree raster pocket toolpath with the Project onto 3D surface checked. Never tried it myself but you can easily see what the result would be using the preview and get relative time differences.

chemstock
Posts: 41
Joined: Wed Sep 18, 2019 2:05 am
Model of CNC Machine: laguna swift 4x8 w/ 11" 4th Axis
Location: Calgary, AB

Re: Roughing pass taking extremely long time

Post by chemstock »

I ran a tapered cylinder at 45 deg to mimic a guitar neck. with a 1/2" bit at 40% stepover, I found 2.52 hrs using a Y raster cut and 1.01 hrs with a Z level cut. This was done with the time estimate on the toolpath tab.
I have found the Z level almost always takes less time but the caution is that it will leave more material. Be careful that the pass depth in the tool database is small enough so the tool used on the finish path does not break.

relayerbob
Posts: 31
Joined: Sat Oct 27, 2018 4:56 am
Model of CNC Machine: Shark HD4

Re: Roughing pass taking extremely long time

Post by relayerbob »

1 - I use a 40% stepover on the roughing pass
2 - The two hours is about what I get if I increase the pass depth, but it leaves minor artifacts that I can avoid with the lower pass depth. If the roughing path was able to run at a 45 degree angle, there should no reason for it to take that long.
3 - I figured doing no roughing was a bad idea, but thought it worth asking.
4 - Can't post it, the design is proprietary, and the question is more generic than that, it affects everything that requires a product that is longer than the bed of a CNC machine (in my case, 25x25). I wish (and don't really understand why not) the roughing pass doesn't have the ability to run at an angle, since other tool paths, including the final pass, does.
5 - I hadn't thought of trying it with pocket tool path projecting the 3D model on it (which I see now, I had thought I would have to build a bunch of small pockets to clear). I will try that and see what happens.
6 - I am currently using the Z-level cut.

Thanks!

wb9tpg
Vectric Wizard
Posts: 333
Joined: Tue Sep 04, 2018 2:49 pm
Model of CNC Machine: Shapeoko 3 XL

Re: Roughing pass taking extremely long time

Post by wb9tpg »

Doing pistol grips I found that Z level speed it up a lot for me. Seemed to do unneed passes
Gary Mitchell
Kentucky, USA

User avatar
adze_cnc
Vectric Apprentice
Posts: 1647
Joined: Sat Jul 27, 2013 10:08 pm
Model of CNC Machine: AXYZ 4008
Location: Vancouver, BC, Canada

Re: Roughing pass taking extremely long time

Post by adze_cnc »

relayerbob wrote:
Sun Nov 15, 2020 9:00 am
I can go with the larger pass depth, and cut the time in half, but still: 2+ hours!!???
Sure, 2 hours is quite a reasonable amount—given that you never told us your roughing cutter's feedrate.

I'd say that the bulk of the original 4 hour slowness is due to the 0.05" pass depth and 0.25mm (0.0098") machining allowance at a slow feed rate.

relayerbob
Posts: 31
Joined: Sat Oct 27, 2018 4:56 am
Model of CNC Machine: Shark HD4

Re: Roughing pass taking extremely long time

Post by relayerbob »

The point is that it never gets anywhere close to a nominal feed rate, since it moves only in x and y, it only moves about half inch or less at time though most of the process. It never fully accelerates before it has to turn around 180 degrees. Even with those depth and stepover values, it can completely clear the space as a "pocket" in under 30 minutes, precisely *because* it reaches nominal feed rates. That's the point of my question - how can I get it to run the roughing pass properly at the correct angle.

Btw, the pocket toolpath with projecting the pocket onto the 3D object works ok on screen, although it is a bit tricky to get the final pass to look good on screen. In actual reality, it may not work correctly though, as it doesn't like to use pass depth properly when using the 3d object projection and plunges to the bottom of each path.

Sigh. Would be so much easier if Vectric would simply allow roughing paths to be placed at the same angle as the final pass and pocket functions do.

User avatar
martin54
Vectric Archimage
Posts: 5580
Joined: Fri Nov 09, 2012 2:12 pm
Model of CNC Machine: Gerber System 48,Denford Triac Modified
Location: Crossgates, Scotland

Re: Roughing pass taking extremely long time

Post by martin54 »

How bad are the artifacts the deeper cut gives you? Whole point is that the finish doesn't have to be brilliant if your then going to run a finish pass. Understand you can't post the file but you could post some screen shots which might help people understand better & offer advice. Can you use a bigger bit for roughing? Your using a 1/4" ball nose for finishing so a bigger roughing bit might be a good option.
What do you have the plunge rate for the bit set at? Increasing the plunge rate can often reduce machining times especially if the plange rate is set at a very low value.
Screen shots of your settings may help

relayerbob
Posts: 31
Joined: Sat Oct 27, 2018 4:56 am
Model of CNC Machine: Shark HD4

Re: Roughing pass taking extremely long time

Post by relayerbob »

As someone else noted, if the pass depth is too large on a z-level rough, it can (and does) cut through the finish pass planes, in certain specific locations. I don't care what the roughing pass looks like, only what it looks like after the finish pass. if I go too far one way on pass depth, the roughing bit cuts into the surface a bit, and if I go the other way, there are minor chatter marks. Both require me to sand them away, and mars my otherwise smooth and clean surace. Either way, I know the settings I need to give me a near perfect surface, it just takes forever, due to the orienation of the roughing cut.

The spindle doesn't plunge much, the machine only goes back and forth in either the z or y plane at only 0 or 90 degrees to the material edge. Because it has shorter and shorter paths as it cuts into the wood on either side of the model, if never gets up to any significant speed. It moves in the z-plane only at the end of each roughing layer, as it steps down, so less than 0.1% of the time is spent moving in the z-axis at all. It takes many minutes for it to get to the end of a level and a fraction of a second to drop the bit.

Projecting a pocket toolpath onto the model only allows me to make something that looks good on screen, but won't work in reality, as the depth of cut is the same depth as the top of the model. The software ignores tool database depths of cut, unless I'm missing something - it assumes all the wood has already been removed, and that the pocket is simply being laid on top of something that's been prepped. Which is fine, if that is what you want to do.

My design is at a 45 degree angle, and must remain that way. All the parameters I have for making the final product work fine, except it takes far too long for it to complete roughing - it literally takes longer to do roughing, than the many other steps, both sides, to do this combined - because the roughing path does not track the finish path at the same 45 degree angle that everything else uses, for all of the various cavities I am cutting out on both sides of this device.

I am reasonably experienced in this, I am trying to figure out if someone has a trick to work around this limitation of Aspire. It's a good program, but it's illogical (and eats up a lot of time for me) to not allow the roughing path to work at a raster angle, just as the finish path and pocket paths do, easily. I presumed that others have tried to do this (make roughing cuts on models with angles) and had workarounds, but it seems not, which sorta surprises me. Anyway, I've come to the conclusion that there actually is no workaround.

I've attached a couple of screen shots to illustrate. The first is the roughing toolpath (using Z-level along X, using the Z-level along Y simply has the tool path lines vertical to the model, but is otherwise basically the same). The second is the finish pass, showing that the tool follows the model at the same basic 45 angle. If the roughing path can be made to move at that same angle, it will cut roughing time by at least 75%, probably more, based on my simulations.
Attachments
45 degree finish path.JPG
X-roughing direction.JPG

User avatar
Adrian
Vectric Archimage
Posts: 11937
Joined: Thu Nov 23, 2006 2:19 pm
Model of CNC Machine: ShopBot PRS Alpha 96x48
Location: Surrey, UK

Re: Roughing pass taking extremely long time

Post by Adrian »

relayerbob wrote:
Mon Nov 16, 2020 7:19 am
I presumed that others have tried to do this (make roughing cuts on models with angles) and had workarounds, but it seems not, which sorta surprises me. Anyway, I've come to the conclusion that there actually is no workaround.
I've not seen it as an issue before on the forum. I guess it's because the majority of 3D work done by people with the smaller machines fit along an axis and the longer pieces I've seen done are made with the moulding toolpath rather than as a 3D shape.

Or it could be as the smaller machines tend to be owned by hobbyists they just don't care that it takes longer to machine something on an angle even if they are aware of it.

Probably best to raise it as a feature request directly with Vectric (support@vectric.com) as this is primarily a user to user support forum.

ich-fräs-das
Posts: 21
Joined: Wed Oct 07, 2020 7:39 am
Model of CNC Machine: BZT PFE1000-PX
Location: South of Hamburg, Germany

Re: Roughing pass taking extremely long time

Post by ich-fräs-das »

Hi,
i found a youtube video of a bass guitar being milled. The neck is also clamped diagonally for reasons of space. I mill my guitars using the same method but not diagonally. The speed at my machine is diagonally neer the same. I have attached my job setup sheet, which applies to my machine, which is more stable. You must find out your settings. The video is also linked.


merry christmas
Eckart
Attachments
5Str Bass Neck_Back Eckart-machining.pdf
(34.3 KiB) Downloaded 44 times

User avatar
jfederer
Vectric Craftsman
Posts: 199
Joined: Tue Nov 27, 2018 1:09 am
Model of CNC Machine: CanCam D23M
Location: Horton Township Ontario Canada
Contact:

Re: Roughing pass taking extremely long time

Post by jfederer »

Eckart, thanks for that video. I'll have to watch it again and take notes.Lots of great approaches and ideas! My CNC isn't a Hammer, but the rest of my equipment is.
Joe Federer

www.fabrikisto.com incl. Tailmaker software
www.federer.ca

User avatar
jfederer
Vectric Craftsman
Posts: 199
Joined: Tue Nov 27, 2018 1:09 am
Model of CNC Machine: CanCam D23M
Location: Horton Township Ontario Canada
Contact:

Re: Roughing pass taking extremely long time

Post by jfederer »

Lots of good ideas in that video. I particularly like how they create jigs and fixtures using the CNC to get an exact match to the part being machined. Clearly precision was a much higher priority than speed. Ich denke, wir werden nicht erwähnen, daß sie keine VCarve-Software verwenden!

Danke Eckart!
Joe Federer

www.fabrikisto.com incl. Tailmaker software
www.federer.ca

relayerbob
Posts: 31
Joined: Sat Oct 27, 2018 4:56 am
Model of CNC Machine: Shark HD4

Re: Roughing pass taking extremely long time

Post by relayerbob »

Yes, My process is very similar, and my final results are fine, that's not the issue. The very good video shows almost exactly what I want to be able to do with roughing the neck, it roughs it in line with the neck angle (roughly 18:30 to 18:50 in the video). Then they do the finishing pass. Vectric doesn't do that, it insists on roughing either in the x- or y- axis, not at the angle the enck is sitting at, which adds a ton of time. It literally takes longer to rough the neck as to do the rest of the job. My finishing pass takes about 10-15% of the time as the roughing, at most. If someone knows the trick to do that (roughing at an angle), please let me know.

Post Reply