Spiral toolpath to machine a cone?

[Neale]

My feeling is that G1 straight-line segment approximations will be fine but you need to start with a smooth curve model, not faceted as per STL, so the CAM process can sort out better approximations. Not sure why you seem a bit "anti" G1? I know it feels counter-intuitive but having done a fair bit now with F360 I find it often produces lots of g1s where you would expect curves, but the only downside seems to be file size. I've ended up with gcode files for quite small parts which have maybe 75K lines of code which are generated by the adaptive cutting strategies, but after my initial surprise, I now just shrug! In the days when machines read files from floppy disk, that would have been pushing the storage limits but these days, even a smallish memory stick holds 10000 times that so it just ain't a problem. As long as your motion control software/hardware can then do the constant-velocity stuff to smooth out the corners and with decent MC hardware this isn't rocket science.

Or just build your spreadsheet to generate one G2 per vertical step, and calculate away! I'm sure that that will work. But my IT background says that if a machine can do the work for me, then I'm not going to spend brain cycles doing it by hand...

Good luck either way.

[Kitwn]

Or just build your spreadsheet to generate one G2 per vertical step, and calculate away! I'm sure that that will work. But my IT background says that if a machine can do the work for me, then I'm not going to spend brain cycles doing it by hand...

Good luck either way.

I was pondering along these lines as well, a good excuse to swot up on exactly how G2 and G3 instructions work and whether Excel will export files delimited with cariage returns. The arc centres are all the same and the end points progress outward in symetrical straight lines so it should not be too dificult. If the angles match then using a V-bit will help smooth the edges but that would only be possible for very short cones with most V-bits.

You're not going into competition with OMLCNC are you? http://www.mycncuk.com/threads/14408...632#post123632

Kit

[Voicecoil]

You're not going into competition with OMLCNC are you? http://www.mycncuk.com/threads/14408...632#post123632

No :-) my cones are only going to be 2...3cm tall and made of 7075 ali

Kit

[Voicecoil]

I was pondering along these lines as well, a good excuse to swot up on exactly how G2 and G3 instructions work and whether Excel will export files delimited with cariage returns. The arc centres are all the same and the end points progress outward in symetrical straight lines so it should not be too dificult. If the angles match then using a V-bit will help smooth the edges but that would only be possible for very short cones with most V-bits.

Kit

Did a bit more thinking about this and to get a smooth toolpath the arc centres aren't the same, you need to offset them ever so slightly to get the arc ends to join up and get the best approximation - as Neale pointed out, on a true spiral the radius is continually increasing, hence if you divide the circumference into a small-ish number of sections with the same centre there would be a slight bump in-between sections. In the end for prototyping I took the crude but simple approach, slicing the model to create a number of 2D toolpaths which I outputted together. Wasn't as much work as I thought thanks to the speediness of Generic CADD (actually took less time than I'd spent playing around with the maths of an elegant solution!), and has ended up greatly reducing the machining time as I've been able to include the flutes which I was going to cut into the cone as a separate operation. The 303 stainless cuts nicely on my little machine using blue-nano coated cutters, only running at 800mm/min at the mo but from the noise it feels like it could go a fair bit faster - but I'll leave pushing the limits until the development work is done!

[Kitwn]

Did a bit more thinking about this and to get a smooth toolpath the arc centres aren't the same, you need to offset them ever so slightly to get the arc ends to join up and get the best approximation - as Neale pointed out, on a true spiral the radius is continually increasing, hence if you divide the circumference into a small-ish number of sections with the same centre there would be a slight bump in-between sections. In the end for prototyping I took the crude but simple approach, slicing the model to create a number of 2D toolpaths which I outputted together. Wasn't as much work as I thought thanks to the speediness of Generic CADD (actually took less time than I'd spent playing around with the maths of an elegant solution!), and has ended up greatly reducing the machining time as I've been able to include the flutes which I was going to cut into the cone as a separate operation. The 303 stainless cuts nicely on my little machine using blue-nano coated cutters, only running at 800mm/min at the mo but from the noise it feels like it could go a fair bit faster - but I'll leave pushing the limits until the development work is done!

I was thinking in terms of a series of 2D cuts rather than a true spiral. The maths would be a lot simpler, though I can see the desire for the best surface finish straight off the machine when you're cutting stainless. Not quite as easy to sand afterwards as hardwood!

Kit

[Voicecoil]

Not sure why you seem a bit "anti" G1? I know it feels counter-intuitive but having done a fair bit now with F360 I find it often produces lots of g1s where you would expect curves, but the only downside seems to be file size.

Partly because it's counter intuitive (I like neat stuff!) and partly through prior jerky machining experiences. Also currently I have no way of generating it in CAM, F360 is out for me due to slow rural internet, OS and besides this is a work job. I will however research what UCCNC has in the way of smoothing for future reference.