[mmoe]

Well looks like I just may have started a second buisness, it's a startup cad drafting company that does cad drafting in return for hobnobs and bacon sarnies. I shall call it cad for food, I think I now qualify I'll just have to keep a record of my eaten and un eaten accounts in case autodesk believe there's no ligitimate buisness going on.

Or, since you said you don't need all the bells and whistles of HSM Pro, you could just do the $300/year license, which should not be an issue if you're making more than $100k anyways. Just a shame you missed the early adopter! I am pretty sure we'll see 99% of what is in HSM Pro once they finally release a true "Ultimate" version, if not all of it. Bottom line is that you will want to stay on the up and up if you are a business. $300/year is still a heck of a lot better than $3500/year or whatever Inventor/HSM Pro is running nowadays.

[mmoe]

Hi guys,
what strategy do you recommend for the pocket and and round fillet ?
Attachment 296532


Thanks.

Vincenzo

Vincenzo,
I think you've already got your answer, which is to use the scallop or morphed spiral strategy on the areas that are rounded over. However, you will also need to set the maximum depth to the bottom of the roundover edge, plus the radius of the ballend mill in order to get it to cut the radius completely.

Another way to work on roundovers is to create boundaries. In the case of your part, you only need to set the maximum Z depth because they are uniform across the bottom. But what if you're round over is 3D? The problem is that then the cutter will either have to travel straight down and gouge the sides of your part until the cutter reaches the maximum Z depth, or you use the edge of the part as a boundary, but then the problem is that you won't be able to cut the full depth of the roundover and it will be incomplete. In HSM Pro, there is an option called "Flow", which I hope they introduce to Fusion at some point in the future, but it will probably be an "Ultimate Only" strategy if they add it at all. The idea is to machine the entire roundover, but not machine any more than only the roundover so that there aren't any gouges. My solution with the current available toolpaths is to generate a model that has what could be called a "drive surface".

In the case of a 3d roundover being cut by a 12.7mm ballmill (1/2"), I create the opposite of a roundover, what is essentially a fillet without anything beyond the outside edge of the fillet. The radius of the fillet surface must be slightly larger than that of the tool, so perhaps 6.5mm for a 12.7mm ballmill. If you can picture it, the ballmill would just fit into this fillet surface with a tiny bit of room to spare. The fillet must come up to the base of the roundover, creating an "S" of sorts. Once you have generated this fillet surface, you can now use it to contain the ballmill on 3d roundover operations. Just select it as part of the geometry to machine, use the outside curve of the fillet as the outer boundary, and the top curve of the roundover as the inside boundary, while selecting all the necessary surfaces including the fillet surface, roundover surface and I like to also select the surface inside of the roundover just to be sure there is something continuous beyond the fillet. I hope that all makes sense, and I'll warn that it is not always easy to create the fillet surface depending on the geometry you are dealing with. Also, Scallop machines everything a little more uniformly, but generates a lot of rapids between areas. Morphed Spiral, as shown below, generates a more continuous flow of the tool, though as it approaches the lower part of the fillet is starts to get a little less smooth than Scallop. Both produce good results, just a matter of preference.

You can also get similar results by using the "Avoid/Touch" settings, but in order to cut the roundover fully, you also have to add an "Additional Offset" of just over the tool radius. The problem with that solution is that it cuts past the edge of the roundover if you leave the upper part of the model as an area that can be "touched", but changing it to "avoid" can cause the tool not to reach all the way to the top of the roundover. Using a drive surface seems to fix the problem. I haven't tried it yet, but you may be able to create an offset geometry below the model to use as an outer boundary, again just a little more than the radius offset from the model. If that works, it might be the easiest way to do this sort of job.

Edit: Just tried adding a sketch offset from the model to use as a boundary. While it works, it didn't generate quite as good of a toolpath. For what it's worth, the drive surface method creates the best toolpath, but the offset sketch boundary method is perhaps 5 minutes faster and creates a pretty useable result if you aren't that good at generating 3d geometry such as the fillet surface shown. The last image shows the results using an offset sketch boundary, visible at the base of the model. It creates a few extra rapids where it doesn't connect as seamlessly, but otherwise is pretty good.

Attachment 296798

[Jon.N.CNC]

Or, since you said you don't need all the bells and whistles of HSM Pro, you could just do the $300/year license, which should not be an issue if you're making more than $100k anyways. Just a shame you missed the early adopter! I am pretty sure we'll see 99% of what is in HSM Pro once they finally release a true "Ultimate" version, if not all of it. Bottom line is that you will want to stay on the up and up if you are a business. $300/year is still a heck of a lot better than $3500/year or whatever Inventor/HSM Pro is running nowadays.

ipals

Lol no its the principles behind how hsm pro was sold to me.. i could have paid for ultimate fusion 360 4 times over.

[Jon.N.CNC]

Vincenzo,
I think you've already got your answer, which is to use the scallop or morphed spiral strategy on the areas that are rounded over. However, you will also need to set the maximum depth to the bottom of the roundover edge, plus the radius of the ballend mill in order to get it to cut the radius completely.

Another way to work on roundovers is to create boundaries. In the case of your part, you only need to set the maximum Z depth because they are uniform across the bottom. But what if you're round over is 3D? The problem is that then the cutter will either have to travel straight down and gouge the sides of your part until the cutter reaches the maximum Z depth, or you use the edge of the part as a boundary, but then the problem is that you won't be able to cut the full depth of the roundover and it will be incomplete. In HSM Pro, there is an option called "Flow", which I hope they introduce to Fusion at some point in the future, but it will probably be an "Ultimate Only" strategy if they add it at all. The idea is to machine the entire roundover, but not machine any more than only the roundover so that there aren't any gouges. My solution with the current available toolpaths is to generate a model that has what could be called a "drive surface".

In the case of a 3d roundover being cut by a 12.7mm ballmill (1/2"), I create the opposite of a roundover, what is essentially a fillet without anything beyond the outside edge of the fillet. The radius of the fillet surface must be slightly larger than that of the tool, so perhaps 6.5mm for a 12.7mm ballmill. If you can picture it, the ballmill would just fit into this fillet surface with a tiny bit of room to spare. The fillet must come up to the base of the roundover, creating an "S" of sorts. Once you have generated this fillet surface, you can now use it to contain the ballmill on 3d roundover operations. Just select it as part of the geometry to machine, use the outside curve of the fillet as the outer boundary, and the top curve of the roundover as the inside boundary, while selecting all the necessary surfaces including the fillet surface, roundover surface and I like to also select the surface inside of the roundover just to be sure there is something continuous beyond the fillet. I hope that all makes sense, and I'll warn that it is not always easy to create the fillet surface depending on the geometry you are dealing with. Also, Scallop machines everything a little more uniformly, but generates a lot of rapids between areas. Morphed Spiral, as shown below, generates a more continuous flow of the tool, though as it approaches the lower part of the fillet is starts to get a little less smooth than Scallop. Both produce good results, just a matter of preference.

You can also get similar results by using the "Avoid/Touch" settings, but in order to cut the roundover fully, you also have to add an "Additional Offset" of just over the tool radius. The problem with that solution is that it cuts past the edge of the roundover if you leave the upper part of the model as an area that can be "touched", but changing it to "avoid" can cause the tool not to reach all the way to the top of the roundover. Using a drive surface seems to fix the problem. I haven't tried it yet, but you may be able to create an offset geometry below the model to use as an outer boundary, again just a little more than the radius offset from the model. If that works, it might be the easiest way to do this sort of job.

Edit: Just tried adding a sketch offset from the model to use as a boundary. While it works, it didn't generate quite as good of a toolpath. For what it's worth, the drive surface method creates the best toolpath, but the offset sketch boundary method is perhaps 5 minutes faster and creates a pretty useable result if you aren't that good at generating 3d geometry such as the fillet surface shown. The last image shows the results using an offset sketch boundary, visible at the base of the model. It creates a few extra rapids where it doesn't connect as seamlessly, but otherwise is pretty good.

Scallop is not a good option at all, It is designed for roughing a part not for creating a good finish as it keeps the passes constant, so where you get two curved radius meeting where the passes need to change direction you get a point in each pass where its no longer a smooth transition but an angled direction change in all the passes in the same place so you can end up seeing the direction change in the cut part.

see scallop described here, most importantly the image noting the direction change in each pass: HSMWorks

In my experience with 3d contour and touch avoid, i use this alot, There is no requirement to add an offset, the tool if accurately set up is programmed to only touch the edge you have selected, it does that exactly, there is no overcut. I have used it with large chamfers requiring multiple passes and round overs alike where the top extent of each leads straight into another feature where an overcut would be detrimental to the finish between features and assure you i do not get this problem, and it wouldnt be part of hsm if it wasnt accurate. if you are getting this problem id say there is something not set correctly in your tool setup. Or you have selected the top surface along with the edge to touch, you only want to select the rounded over edge only. A 3d contour does not use constant parallel passes so in effect areas where there are direction along with angle changes you get a morphed pass instead of definitive point of direction change in same place of every pass.

So really there is very little difference between morphed spiraling and 3d contour when used for a roundover or chamfer. Only pretty sure setting up a morphed spiral requires a few more steps than 3d contour to generate.

A fillet or your opposite round over you may want to consider pencil as the correct strategy.

Really the correct use of each strategy is in the strategies name and you are applying a 3rd dimension which is the round over to a contour so thats a pretty big clue as to which strategy is designed for this operation.

[ger21]

I also bought in for the lower long term rate, but my recollection is that it was "Fusion 360 Ultimate for the price of Fusion 360 Standard for life", not necessarily $300/year for life. If Fusion 360 Standard goes up to $1000/year and Fusion Ultimate goes up to $3600/year (not likely given that you could get Inventor/HSM Pro for about that price), then my understanding is that we would get Fusion 360 Ultimate for $1000/year. My guess is that it will stay in the range of the $300/year, but I am prepared for the fact that it may go up a little as well.

My recollection was $300/yr for life. That's why I bought in. I haven't even used it yet.

[cyclestart]

We have not changed our commitment to early adopters. You will receive all the benefits of Fusion 360 Ultimate at the price
of $300 annual contract now and going forward.

Autodesk posted that July 30 of this year

https://knowledge.autodesk.com/suppo...aging-FAQ.html
It feels too good to be true but it sure reads as $300/yr locked in. I share some suspicions about this deal.

Anyway this has gone well off topic so I'm outa here .

Edit/ Possibly Autodesk will redefine 'Ultimate' by adding more tiers to the software.

[mmoe]

Scallop is not a good option at all, It is designed for roughing a part not for creating a good finish as it keeps the passes constant, so where you get two curved radius meeting where the passes need to change direction you get a point in each pass where its no longer a smooth transition but an angled direction change in all the passes in the same place so you can end up seeing the direction change in the cut part.

see scallop described here, most importantly the image noting the direction change in each pass: HSMWorks

In my experience with 3d contour and touch avoid, i use this alot, There is no requirement to add an offset, the tool if accurately set up is programmed to only touch the edge you have selected, it does that exactly, there is no overcut. I have used it with large chamfers requiring multiple passes and round overs alike where the top extent of each leads straight into another feature where an overcut would be detrimental to the finish between features and assure you i do not get this problem, and it wouldnt be part of hsm if it wasnt accurate. if you are getting this problem id say there is something not set correctly in your tool setup. Or you have selected the top surface along with the edge to touch, you only want to select the rounded over edge only. A 3d contour does not use constant parallel passes so in effect areas where there are direction along with angle changes you get a morphed pass instead of definitive point of direction change in same place of every pass.

So really there is very little difference between morphed spiraling and 3d contour when used for a roundover or chamfer. Only pretty sure setting up a morphed spiral requires a few more steps than 3d contour to generate.

A fillet or your opposite round over you may want to consider pencil as the correct strategy.

Really the correct use of each strategy is in the strategies name and you are applying a 3rd dimension which is the round over to a contour so thats a pretty big clue as to which strategy is designed for this operation.

We seem to disagree on a lot of things, which is fine since everyone has their own ways of doing things and there really is no "right" way. I do enjoy sharing and comparing methods, so don't take this as any kind of slight that we do disagree. I do want to share why I don't use the methods you like and why I do like the more tedious method of generating additional geometry to drive toolpaths. If I had the "Flow" option you have in HSM Pro, I would be using that over any method available in Fusion for roundovers, but we don't have that one yet (I'm hopeful it will be part of Fusion Ultimate when they finally start to delineate between levels).

I have not been able to produce a finish with 3d contour that is as good as the Morphed Spiral option, in my opinion, even when using touch surfaces. I did figure out that you can get by without adding an offset boundary if you use the "Tool Outside of Boundary" option, but my feelings on that option are that I'd rather create a boundary that I control than leave it more arbitrary. Old habits die hard, so my preference will probably always be to use a defined boundary instead of that setting in particular. It does work on the example shown (first image below), and the same method with Morphed Spiral does "work" on both the same part (second image) as well as the 3d example I used earlier (third image shown), but you can see that the drive surface concept produces a better result on the complex 3d roundover than using the "touch/avoid" combined with "tool outside boundary" method, which resulted in extra jumps up and down and a disjointed toolpath compared to a completely contiguous toolpath when using the drive surface instead (image in previous post).

The other problem I have with the 3d Contour option is that the stepovers are not uniform at all, with or without the "Machine Shallow Areas", and the toolpath never reaches to intersection between the top surface and the start of the roundover no matter how low I set the stepdown value that controls that (fourth image below has .01mm stepdown and .1mm step over, but gets no closer to the intersection than previously). In theory, there isn't much difference in Z level between where the 3d contour is starting and the Z level where that intersection occurs, but the stepover from that point is large enough that I'd expect a noticeable scallop in the finish when using a 1/2" ballend mill. 3d Contour does not seem to take that into account when it's determining where to start the toolpath, only how much the geometry has stepped down from flat to determine that. That places much more importance on how you finish the top surface in determining the actual finish quality at that intersection. If you use a bit face mill, or you use a parallel strategy with a cap over the opening in the example below (first image is one of 3d Contour), you could help reduce the impact of the way the 3d Contour operation works, but you can clearly see that the Morphed Spiral example (2nd image) provides cutting all the way up to the intersection between the top and the start of the roundover, leaving no chance that the finish will be substandard.

When you then move on to the roundover on a 3d surface edge, as in my previous example, you can see that 3d Contour produces a very undesirable toolpath (fifth image below). By it's nature, 3d Contour will machine at a Z-level, then step up to the next Z-level, etc. On any 3d roundover that follows a complex edge, this will just not work. As you can see in the image, the result would be poorly finished due to so many entry/exits and require perhaps 3 times the machine time as compared to the Morphed Spiral version.

If I've missed ways to improve these results, I'd love to learn more about the settings in HSM/Fusion. To my knowledge, I've produced about as good of a result as each strategy is capable of for the given example, and my personal evaluation is that Morphed Spiral is the go-to tool for roundovers based on the results I've been able to produce on these sample parts. Obviously, real world situations vary and some conditions will favor different methods than others. I do think these are both pretty fair examples of the kinds of roundovers I run into on a regular basis and my experience is that it works the same on most parts I cut as shown here. For example, if you want to cut a roundover on the perimeter of a Strat-style guitar, that roundover comes out closely to the same as the complex 3d roundover example I've shown here. I can get a neraly continuous motion around the guitar by linking the roundover thought the neck pocket and using a drive surface around the entire guitar as well. I have had no success machining that kind of complex roundover using any other method, though as I said earlier I'd much prefer to have the "Flow" option available which would completely eliminate the need for a drive surface.

As a side note, I have created a feature suggestion for Fusion that I'd love people here to go vote for. It is a modification to the Scallop strategy to work in a spiral manner, which would eliminate the links between passes and provide a similar continuous path that Morphed Spiral provides, with the exception that the step over is always the same instead of morphing. I've also suggested that if it's easier to develop, the same option could be made in Morphed Spiral by creating a "Suppress Morphing" option so that the stepover is a constant in that strategy. Either way, this would be a huge improvement to one or the other of those strategies. I posted a similar toolpath produced in Bobcad using the spiral with constant stepover as an example of the difference, and I'm sure that no one would argue it produces by far and away the best result for his kind of condition due to the spiraling contiguous toolpath combined with a completely constant (and therefor consistent) stepover all the way around the roundover. This would be a very powerful option in my experience. Please have a look here and vote:

Spiral Option in Scallop Strateg... - Autodesk Community


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[Jon.N.CNC]

We seem to disagree on a lot of things, which is fine since everyone has their own ways of doing things and there really is no "right" way. I do enjoy sharing and comparing methods, so don't take this as any kind of slight that we do disagree. I do want to share why I don't use the methods you like and why I do like the more tedious method of generating additional geometry to drive toolpaths. If I had the "Flow" option you have in HSM Pro, I would be using that over any method available in Fusion for roundovers, but we don't have that one yet (I'm hopeful it will be part of Fusion Ultimate when they finally start to delineate between levels).

I have not been able to produce a finish with 3d contour that is as good as the Morphed Spiral option, in my opinion, even when using touch surfaces. I did figure out that you can get by without adding an offset boundary if you use the "Tool Outside of Boundary" option, but my feelings on that option are that I'd rather create a boundary that I control than leave it more arbitrary. Old habits die hard, so my preference will probably always be to use a defined boundary instead of that setting in particular. It does work on the example shown (first image below), and the same method with Morphed Spiral does "work" on both the same part (second image) as well as the 3d example I used earlier (third image shown), but you can see that the drive surface concept produces a better result on the complex 3d roundover than using the "touch/avoid" combined with "tool outside boundary" method, which resulted in extra jumps up and down and a disjointed toolpath compared to a completely contiguous toolpath when using the drive surface instead (image in previous post).

The other problem I have with the 3d Contour option is that the stepovers are not uniform at all, with or without the "Machine Shallow Areas", and the toolpath never reaches to intersection between the top surface and the start of the roundover no matter how low I set the stepdown value that controls that (fourth image below has .01mm stepdown and .1mm step over, but gets no closer to the intersection than previously). In theory, there isn't much difference in Z level between where the 3d contour is starting and the Z level where that intersection occurs, but the stepover from that point is large enough that I'd expect a noticeable scallop in the finish when using a 1/2" ballend mill. 3d Contour does not seem to take that into account when it's determining where to start the toolpath, only how much the geometry has stepped down from flat to determine that. That places much more importance on how you finish the top surface in determining the actual finish quality at that intersection. If you use a bit face mill, or you use a parallel strategy with a cap over the opening in the example below (first image is one of 3d Contour), you could help reduce the impact of the way the 3d Contour operation works, but you can clearly see that the Morphed Spiral example (2nd image) provides cutting all the way up to the intersection between the top and the start of the roundover, leaving no chance that the finish will be substandard.

When you then move on to the roundover on a 3d surface edge, as in my previous example, you can see that 3d Contour produces a very undesirable toolpath (fifth image below). By it's nature, 3d Contour will machine at a Z-level, then step up to the next Z-level, etc. On any 3d roundover that follows a complex edge, this will just not work. As you can see in the image, the result would be poorly finished due to so many entry/exits and require perhaps 3 times the machine time as compared to the Morphed Spiral version.

If I've missed ways to improve these results, I'd love to learn more about the settings in HSM/Fusion. To my knowledge, I've produced about as good of a result as each strategy is capable of for the given example, and my personal evaluation is that Morphed Spiral is the go-to tool for roundovers based on the results I've been able to produce on these sample parts. Obviously, real world situations vary and some conditions will favor different methods than others. I do think these are both pretty fair examples of the kinds of roundovers I run into on a regular basis and my experience is that it works the same on most parts I cut as shown here. For example, if you want to cut a roundover on the perimeter of a Strat-style guitar, that roundover comes out closely to the same as the complex 3d roundover example I've shown here. I can get a neraly continuous motion around the guitar by linking the roundover thought the neck pocket and using a drive surface around the entire guitar as well. I have had no success machining that kind of complex roundover using any other method, though as I said earlier I'd much prefer to have the "Flow" option available which would completely eliminate the need for a drive surface.

As a side note, I have created a feature suggestion for Fusion that I'd love people here to go vote for. It is a modification to the Scallop strategy to work in a spiral manner, which would eliminate the links between passes and provide a similar continuous path that Morphed Spiral provides, with the exception that the step over is always the same instead of morphing. I've also suggested that if it's easier to develop, the same option could be made in Morphed Spiral by creating a "Suppress Morphing" option so that the stepover is a constant in that strategy. Either way, this would be a huge improvement to one or the other of those strategies. I posted a similar toolpath produced in Bobcad using the spiral with constant stepover as an example of the difference, and I'm sure that no one would argue it produces by far and away the best result for his kind of condition due to the spiraling contiguous toolpath combined with a completely constant (and therefor consistent) stepover all the way around the roundover. This would be a very powerful option in my experience. Please have a look here and vote:

Spiral Option in Scallop Strateg... - Autodesk Community


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Nope still think your doing something wrong or looking at it incorrectly.

Tool inside/outside boundary doesn't come into it. You shouldn't set anything other than the touch edge alone, that's it, four clicks after tool setup to be exact: touch edge selection tool, click round over, tick touch edge, generate Hsm simply uses the contour of the bit and calculates where to place the toolpaths so that the bit contour touches all of the edge contour and it does exactly that. Nothing left behind. You can even add multiple stepovers and passes to improve finish.

If you are just getting your results from looking at the toolpath and visually you see one of the contours is not on an edge line so you feel it's going to miss that bit then your not taking into consideration the contour of the bit as the software does.

Maybe try it by cutting it, but I can assure you a 3D contour does exactly what it says it does. And this operation of a round over you are doing is a 3D contour, otherwise what your saying is Hsm 3D contour doesn't work, i honestly use it with 4 click as explained above all the time with chamfer bits, round over and ball nose bits and it's always bang on with an excellent finish.

This offset you say you need to apply so you see a toolpath on the edge line is for what exactly? The bit will not be engaged and will just be cutting air, a round over ball nose or chamfer can follow a line at any point along the bits contour, I.e the line left at 99.9% engagement should be as crisp as the line at 1% engagement. Only at 99.9% your not wasting any time cutting air. Very confused as to you have settled with a more complicated less efficient operation to do a task that has an operation designed solely for doing exactly what you looking to do. There is little function for 3D contour outside of making these kinds of toolpaths so for you at the moment it has no functionality whatsoever, once you get used to Hsm you will come to realise that using the software operations for the correct operation in hand is the most efficient way to program and to cut after all this cam is called and designed around high speed machining so what you see in the toolpaths may look too simplified compared to other cams, it is that way to be efficient but the results will be the same.

As with the toolpaths you have generated seem to have many more passes than is required to generate a finish, this is because the Hsm technique that has been programmed for this task are not being used by using 3D spiralling.

[mmoe]

Nope still think your doing something wrong or looking at it incorrectly.

Tool inside/outside boundary doesn't come into it. You shouldn't set anything other than the touch edge alone, that's it, four clicks after tool setup to be exact: touch edge selection tool, click round over, tick touch edge, generate Hsm simply uses the contour of the bit and calculates where to place the toolpaths so that the bit contour touches all of the edge contour and it does exactly that. Nothing left behind. You can even add multiple stepovers and passes to improve finish.

If you are just getting your results from looking at the toolpath and visually you see one of the contours is not on an edge line so you feel it's going to miss that bit then your not taking into consideration the contour of the bit as the software does.

Maybe try it by cutting it, but I can assure you a 3D contour does exactly what it says it does. And this operation of a round over you are doing is a 3D contour, otherwise what your saying is Hsm 3D contour doesn't work, i honestly use it with 4 click as explained above all the time with chamfer bits, round over and ball nose bits and it's always bang on with an excellent finish.

This offset you say you need to apply so you see a toolpath on the edge line is for what exactly? The bit will not be engaged and will just be cutting air, a round over ball nose or chamfer can follow a line at any point along the bits contour, I.e the line left at 99.9% engagement should be as crisp as the line at 1% engagement. Only at 99.9% your not wasting any time cutting air. Very confused as to you have settled with a more complicated less efficient operation to do a task that has an operation designed solely for doing exactly what you looking to do. There is little function for 3D contour outside of making these kinds of toolpaths so for you at the moment it has no functionality whatsoever, once you get used to Hsm you will come to realise that using the software operations for the correct operation in hand is the most efficient way to program and to cut after all this cam is called and designed around high speed machining so what you see in the toolpaths may look too simplified compared to other cams, it is that way to be efficient but the results will be the same.

As with the toolpaths you have generated seem to have many more passes than is required to generate a finish, this is because the Hsm technique that has been programmed for this task are not being used by using 3D spiralling.

I have figured out that the "Contact Point Boundary" and "Contact Only" check boxes must be checked or the "touch" surfaces method you describe does not machine all the way to the bottom of the roundover surface. It still won't go all the way to the top most portion of the part, and that's about a 1.5mm offset for the first path. That's more than enough to greatly exceed the tolerance settings for surface deviation (by about 6x), so it's not that the CAM engine thinks it's within tolerance. It's simply that 3d Contour, if we are talking about the same strategy, isn't very good at machining areas that are flat, even with "Machine Shallow Areas" checked and the tolerances for that operation set very tight. After reading your last reply, I'm thinking you and I may not be talking about the same strategy anyways? Are you using a form tool or a ballend mill? If you use a ballend mill, none of the toolpaths I've shown will cut air. They cut only as far as they need to to get to the bottom of the roundover. I also have them set at a .4mm stepover with a 1/2" ballend mill around a 1/4" radius in the case of the square part. With those stepovers, you are looking at a surface deviation of around .03mm, which is getting to about the max I'd comfortable with calling a finish pass. The same stepover on a flat surface produces something closer to a .01mm surface deviation (or less), so the effect of cutting around a curved face with a ball mill is to exaggerate the scalloping between passes, which requires some compensation by tightening up the steps.

I may see if I have time to put a video together which shows why I use the offset, or as I've found you can also use the "Tool Outside of Boundary". I can probably show 4 or 5 ways to get the same result, and the reality is that none of them take more than 1 minute more or less than the others with the exception of when I add the drive surface (takes perhaps an extra 5 minutes, but provides an undeniably smoother toolpath as I've shown).

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I can provide the models for you if you want to show me what you are talking about, otherwise all I can get is that you disagree but don't provide detailed information on how it can be done better.