Tapered Rope Carving (Can't figure it out)

[chubb]

Hi all,

A fellow woodworker friend had asked me to cut a twisting rope pattern on some legs he was working on for a project.

"Sure, the machine will blaze through that". big mouth, big foot.

Next day, he hands me 4 skinny twigs pre turned on a lathe with a taper in them.

I can't figure out how to cut a spiral rope on a tapered spindle in either vcarve pro or aspire efficiently. It's not a drastic taper. From a 25mm diameter to a 35mm diameter over a 300mm length

I have been able to do a twisted rope in aspire, but it has to be cut with a tapered ball nose (a la 3d raster cut) which ends up taking about 4 hours (not too efficient).

I was wondering; is there any way to project a twisted vector onto the model and do a profile cut on the vector with a rope mold cutting bit for each strand? Would probably be 1/5th of the time and a cleaner finish.

Does anyone have any idea how this could be accomplished or something like it?

Any input or ideas would be greatly appreciated. I'm stumped.

Mark

[Brady Watson]

Pics would help...

I am not clear if you are talking about a rotary relief done in the indexer or one done XYZ flat on the table, or 4-sided?

-B

[bleeth]

Brady:
Since he posted in the indexer section I would say he has an indexer

So I guess what he is asking is can you program a reducing spiral vector for a profile bit to follow and therefore cut a twisted rope pretty much like a v-carve.

[chubb]

Pics would help...

I am not clear if you are talking about a rotary relief done in the indexer or one done XYZ flat on the table, or 4-sided?

-B

Brady:
Since he posted in the indexer section I would say he has an indexer

So I guess what he is asking is can you program a reducing spiral vector for a profile bit to follow and therefore cut a twisted rope pretty much like a v-carve.

I guess I could have been more clear.

Absolutely right Dave, Its to be cut on the indexer . It's a spiral rope pattern on a spindle. but rather than it being a traditional twisted rope pattern which is cut on a spindle that has a constant diameter along it's length, this one has a varying diameter along it's length (from 25mm to 35mm). I think Dave explained it more clearly above (thanks).

Sort of like the pictures attached (sorry, the pictures are small).

Mark

[myxpykalix]

I don't know about how to do it in aspire but since you already have the taper cut into the leg a "jerryrig" way of doing it might be to make your toolpath in aspire for your spiral then take your tapered leg, insert it into your indexer and rig up something for your tailstock to hold your leg in so that the taper is a flat 90 degrees to your bit and you fool the toolpath into thinking it is making a flat spiral?

This is a wizard i made 5 years ago and although it doesn't show it done as a taper it is i think how you want to cut as opposed to a 3dcarving toolpath.
http://www.youtube.com/watch?v=jSy8PGj2eDU

Also go thru some of the Legacy CNC videos on youtube as i know it can be done easily on a legacy. Possibly you can glean something from them. It seems to me their tailstock moves up and down for that process...
http://www.youtube.com/results?searc...orking%20&sm=3

[Brady Watson]

Sorry...I hardly ever read the 'section heading' - Indexer it is!

Yes - you can do this relatively easily using a '2D' strategy. You would need to setup a Wrapped Job using the Gadget and then create an angled plane that represents the taper. When you setup your Wrapped Job, choose the Spiral Wrap option & work out the number of turns you will need to get the desired effect.

Since the tool must taper along the length, you'll need that angled plane component to be represented in 3D first, then you'll need straight vector lines (kicked on an angle - wrapped/spiral job setup will help with this) and then you will need to add your special 'barley twist' bit profile to the tool database, setting it up as a Form Tool type. I believe that Magnate is the most popular manufacturer of these types of bits, although depending on your desired profile you may be able to get way with a roundover of the appropriate shape.

After you have added your custom tool, select all the straight vector lines and do a Profile toolpath using the ON strategy. Towards the bottom check the box that says, "Project Toolpath onto 3D Model" and the lines will rise & fall matching your taper. Be sure to Zzero to the center of the model.

If you are starting with a non-tapered blank, you will need to rough out the blank down to the taper 'major diameter' so that the form tool doesn't have to plow through extra material along the way.

Hope that gets you pointed in the right direction.

-B

[chubb]

I don't know about how to do it in aspire but since you already have the taper cut into the leg a "jerryrig" way of doing it might be to make your toolpath in aspire for your spiral then take your tapered leg, insert it into your indexer and rig up something for your tailstock to hold your leg in so that the taper is a flat 90 degrees to your bit and you fool the toolpath into thinking it is making a flat spiral?

This is a wizard i made 5 years ago and although it doesn't show it done as a taper it is i think how you want to cut as opposed to a 3dcarving toolpath.
http://www.youtube.com/watch?v=jSy8PGj2eDU

Also go thru some of the Legacy CNC videos on youtube as i know it can be done easily on a legacy. Possibly you can glean something from them. It seems to me their tailstock moves up and down for that process...
http://www.youtube.com/results?searc...orking%20&sm=3

Hi Jack,

I thought the same thing about doing a kind of rig to lift one end so the top surface is horizontal rather than inclined. I was only concerned with the accuracy and rigidity of such a setup, as well as the ability to change the height to adjust for different tapers.

Your video looks great! were you using a magnate bit? very smooth finish. How did you write the wizard? Haven't ventured that far into shopbot solutions yet.

The legacy machines seem to do tapers without a sweat using their "5th axis". Which isn't really a 5th axis but more like the jerryrig you first talked about ,although theirs "see-saws" on both ends, where as the jerry rig would only lift or drop one end.

Thanks for the ideas. I think a "See-Saw 5th-Axis project" is in the pipeline. Seems like an interesting addition.

Yes - you can do this relatively easily using a '2D' strategy. You would need to setup a Wrapped Job using the Gadget and then create an angled plane that represents the taper. When you setup your Wrapped Job, choose the Spiral Wrap option & work out the number of turns you will need to get the desired effect.

Since the tool must taper along the length, you'll need that angled plane component to be represented in 3D first, then you'll need straight vector lines (kicked on an angle - wrapped/spiral job setup will help with this) and then you will need to add your special 'barley twist' bit profile to the tool database, setting it up as a Form Tool type. I believe that Magnate is the most popular manufacturer of these types of bits, although depending on your desired profile you may be able to get way with a roundover of the appropriate shape.

After you have added your custom tool, select all the straight vector lines and do a Profile toolpath using the ON strategy. Towards the bottom check the box that says, "Project Toolpath onto 3D Model" and the lines will rise & fall matching your taper. Be sure to Zzero to the center of the model.

If you are starting with a non-tapered blank, you will need to rough out the blank down to the taper 'major diameter' so that the form tool doesn't have to plow through extra material along the way.

Hope that gets you pointed in the right direction.

-B

Hi Brady,

I had a go at it as you outlined above.

created the wrapped job setup, created a profile of the taper shape, ran 2-rail sweep, generated spiral vectors (using the gadget), and that's about all that was easy

when it came to projecting the toolpaths onto the model, aspire just wasn't having it. After some head scratching I figured it was because it generates the spiral vectors beyond the material boundaries (when viewed flat) so none of the vectors were actually above the surface, so as to be projected onto it. So I shifted the vectors onto the material and mirrored them so the entire surface of the material was covered in the spiral vectors. When i then projected the toolpath onto the 3D surface it worked. But not without some trade off. Some of the spiral vectors were cut short and won't be cut continuosly in one sweep but rather in two. It's just a minor detail that would probably require a bit more sanding but thats about it.

I've attached some previews to illustrate what I mean with the "cut-off vectors".

I found the whole process to be quite tedious, not difficult, just tedious (especially the spiral vector gadget), not difficult. there were so many numbers to put in and keep track of from start to finish. I definately see myself messing up some legs by putting in wrong values.

I wish there was a more.............elegant solution

I think maybe like a simplified specific gadget or a wizard like the one Jack has.

Nonetheless it is a solution. I'm sure all the tediousness of this process just adds to the flexibility of what you can do and create with it, so can't complain much

Thanks for the push in the right direction. Got to learn a couple new processes while taking on your advice that I can definately use on other projects.

Will give it a go tomorrow and probably upload a photo of the result.


Thanks again all.

Mark