Spiral toolpath to machine a cone?

Quote:

---

Originally Posted by Kitwn

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 :beer:

Kit

---

I'm watching this thread with interest (obviously not understanding it fully) but if you can sort it out, it would be of great for cone lamps.
The lengths of lamp are 150mm, 300mm 500mm. I also do standard lamps at 1500mm length but that would be a complete new machine for that project.
I have played with Fusion 360 but Vetric Aspire gives the best results so far but by modelling.
Attachment 29611

Quote:

---

Originally Posted by Kitwn

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!

Quote:

---

Originally Posted by OMLCNC

I'm watching this thread with interest (obviously not understanding it fully) but if you can sort it out, it would be of great for cone lamps.
The lengths of lamp are 150mm, 300mm 500mm. I also do standard lamps at 1500mm length but that would be a complete new machine for that project.
I have played with Fusion 360 but Vetric Aspire gives the best results so far but by modelling.
Attachment 29611

---

Mmmm, how are you machining your cones? From the height of your product I would have thought a horizontal/4th axis approach would work better than the vertical machining I'm doing - mine are only either 24 or 34mm tall. For even the 150mm high version you would need something like a 175mm cutter which is going to be neither particularly rigid or cheap I would guess.

Quote:

---

Originally Posted by Voicecoil

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

Quote:

---

Originally Posted by Voicecoil

Mmmm, how are you machining your cones? From the height of your product I would have thought a horizontal/4th axis approach would work better than the vertical machining I'm doing - mine are only either 24 or 34mm tall. For even the 150mm high version you would need something like a 175mm cutter which is going to be neither particularly rigid or cheap I would guess.

---

You are quite correct, I am working on a 4th Axis at the moment for my machine.
What I actually want to achieve is a cone with a slight twist, about half a turn over the length, but with the number of thread starts (flutes) converging to the top (small dia of cone) and fading outto a plane cone.
Hard to describe, but similar to a piece of cloth being wrung out when wet.

Probably should start a separate thread for this when I've got the 4th Axis on the machine working and just watch this thread