For those of you with indexers....Nested Helixes

[myxpykalix]

This looks really cool and basically you could hook up your scroll saw to cut while using your indexer. I think it warrants further investigation and thinking on how to adapt....:cool:
http://www.instructables.com/id/Nested-Helix/?ALLSTEPS

[Burkhardt]

I did not read it all but why use a scroll saw? With the indexer and a ballnose bit you can machine that directly. I know you can do the ones with solid core, I made some wooden lead screws a few years ago, see pic and clip below (no special purpose, just to show it can be done). I believe the hollow core corkscrews can be done as well but not sure about that (I hope you just did not initiate my next project...).
https://lh3.googleusercontent.com/KxAg1lxPZdkFACVtgQxnkTw8AjVlNPgy3LAXiOuyYh1dnVzz5x 69rVf5WDhCjPvKC7X4FWyBQlarP09C2FfMprBu4ud5XSJO5Eb9 fK-JLusi1Zr7W6Vq1TobpClfot4NianAA9EgLAezVBLcc69ZX-7PV031cz6LGGxjZ9aiX5KB-ZN5A9u21DVvs7JuC68niuE0Vm-rE1Q5MTRL8TFMxrBdjbHPufzIFxeffm0dTGljjg7e47TkLt3HC DVzjMkxeATJGdBsYMJFQlnc6HYubLCx6nsAK751kS-0WWbdnV9unoevq_dTITzgF0eHivoNx37a2SLGwsCa5b_RWfWLX xTGvTCxGVQNQgLT2owGQz-efEs1I5Uf975DKOKN6W47SVL2YZeF79OOXTT0lHsNSd7dYjgnp 7bvS3ZC-NJSChzt0X3iVcUGv0cNuBnTUBhBSHpZ9qYj9J0J7o9ZtG4DRa9 U5y7fTH9jUSC1FtoZjDn3_Q7sm4QH7Pa7x8jzDxRwg_-HOrSVVmrqa8lXq3G30rvPonSVXz6gSiM3f5ns-T7zrqQ-qcbH3beMGhwmArmawineIAjxOL-xBkepGIuMq3kHUPbNEDmqcbk7eO8hP9azo35q=w1024-h452-no


https://www.youtube.com/watch?v=DoMhAm-JZUw

[myxpykalix]

NO...I don't mean to get you hooked on a project...especially since it's already been done. lol
Here is a tutorial i contributed to and the relevant part for hollow spirals is close to the bottom of the page.
The simple explanation for a hollow spiral is, you take a long square board, carve a U trench in it, cut it, glue the two halves together to make your hole in the center. Reinforce that with a dowel. Carve your spirals from there. The tutorial goes into great detail with pictures...you'll get it when you see pics.
http://www.humblesticks.com/cnc-rotary-tutorial.html
Randall Newcomb did a great job putting this together.

[Burkhardt]

NO...I don't mean to get you hooked on a project...especially since it's already been done. lol.......

Thanks for the link. This is interesting. But I was not really thinking of a prepared hollow rod but was wondering to cut the hollow screw directly from a solid rod. As long as the ballnose bit diameter fits in between the gaps of the spiral windings that should be geometrically possible. Not very practical with the usual CAD programs from a 3d-model but maybe some custom piece of software. It is just the kind of mathematical challenge that I find interesting....But I can see the problem mentioned in your tutorial that the hollow spiral screw will get rather fragile and in need of some kind of support.

[Burkhardt]

Oh well, it did become a mini project...but good fun. I wrote a piece of software to generate indexer tool paths for cutting spirals with circular or elliptical cross-sections and varying "swing" radius using a simple ballnose bit. Not sure yet what to use it for but another tool in the box. Maybe I start a business in prosthetics for unicorns.

So far I did only 3/4" rods for testing but there is no size limitation. However, cutting a hollow spiral is indeed a challenge. At some point the wood coil becomes so flexible that it starts vibrating. When such chattering occurs, the bit will catch and the tear the part even at moderate feed rates and stepover. But depending on the length it works down to a cross-section diameter of 1/3 of the dowel.

Cutting time is actually quite short, since no complicated 3d movements are necessary. About 10 minutes for such a small dowel with a resolution of 200 facets on the circumference. At this resolution, very little sanding is required.

https://lh3.googleusercontent.com/X_02F-PP-P7xNOt4HkJQ9VKCVnFzbXAR_zKXZhVfHsf3rIXdNrXgBzNwUvt v0E3v1Z_3lebeVw=w1920-h1080-rw-no

https://lh3.googleusercontent.com/3ayiTyeqfmfrZHBEvgkWoR0iRHZpQFGSVSnfXT1Mo-TLCZeXXkmr4rDunWHvGU19rtLI5Lr_Pg=w1920-h1080-rw-no

https://lh3.googleusercontent.com/CacToBjHxryU2MiibYO5mZyuL0AhcWDzl9zffPsnHv0fkVRKnw ob8-PkT-TmUhIpZJTrxF8qkg=w1920-h1080-rw-no

[tri4sale]

If I had an indexer on my 'bot I could so use this for a project!

[Burkhardt]

If I had an indexer on my 'bot I could so use this for a project!

Really not that expensive. I got something like that (http://www.ebay.com/itm/CNC-4th-Axis-Router-A-Axis-100MM-Chuck-Gapless-Harmonic-Drive-Reducing-Gear-Box-/261858842965), Chinese Harmonic Drive clone 1:50 with 4"/100mm 4-jaw chuck for $400. A 65mm tall tailstock (http://www.ebay.com/itm/Alive-CNC-Wood-Lathe-Tailstock-65MM-For-Router-Axis-A-4th-Axis-Engraving-Machine-/251911934273) is another 60 bucks.

[bleeth]

Absolutely outrageous walking sticks, canes, lamp posts, stair newels, chair/table legs/spindles.
Let your mind go free!

[tri4sale]

Really not that expensive. I got something like that (http://www.ebay.com/itm/CNC-4th-Axis-Router-A-Axis-100MM-Chuck-Gapless-Harmonic-Drive-Reducing-Gear-Box-/261858842965), Chinese Harmonic Drive clone 1:50 with 4"/100mm 4-jaw chuck for $400. A 65mm tall tailstock (http://www.ebay.com/itm/Alive-CNC-Wood-Lathe-Tailstock-65MM-For-Router-Axis-A-4th-Axis-Engraving-Machine-/251911934273) is another 60 bucks.

Isn't the cost thats prohibitive, its the complete and utter lack of know how to get that hooked up to my ShopBot.

[myxpykalix]

I wrote this in '08 with a lot of help from a coder. That's what i've used.

[Burkhardt]

Sorry if that thread is going a bit off....

I continued playing with my new software. I can now cut helixes with varying cross-sections, either circular/elliptic or polygons as well. Besides the previously shown simple helix and the unicorn style conical ones, here is one that could be used as a finial for posts or similar (see video clip below). I am beginning to think this could be useful for other people but how many CNC users do actually have an indexer?

https://lh3.googleusercontent.com/N7kja4xNbGK6LH8okKNLWygE9UN0tGWIznyOnQXyCUW-iw5-6e3y7_oLSykVQp4Q8axJk3VeXQ=w1920-h1080-rw-no

https://lh3.googleusercontent.com/OQwrldP1iC_tjPSWozb-G_fGBUVzu7MGPCK4QbOQ7dQIZLCkfEdLWSv_LNkIsQq-VfekaxKbjQ=w1920-h1080-rw-no


https://youtu.be/Dm5SrtTiL_U

[myxpykalix]

I do! Would you be selling this app? How much? Many of these indexer users need inspiration and motivation to get their indexers hooked up.This would do it... Very cool!

[Bobtail Farms]

Ditto. Thanks.

[tri4sale]

Be great addon to the Dovetail program :)

When I get my indexer I'd love to have this.

[Burkhardt]

Hm, got to think about that a little. Right now this is a barebones program without any user interface, only good enough to test the tool path calculations and use it for myself. Writing the user interface including some meaningful visualization of the intended results would be a few weeks of evening work. No promises and no timeline but I will get back here in case I have something.

[JimmyD]

That's excellent, shows lots of promise for some creative work. I'd buy it.

Jim

[Burkhardt]

So, I made a little progress over the holidays, allowing a Bezier curve outline of the helix, fluted polygon surfaces and fixed a lot of bugs. Unfortunately still not much of a user interface.
But to keep me motivated, I practiced a little today. To save a tree, the experiment was really small, that means only 2.5" long. Made from a 5-ply laminate of 2xmaple and 3x(looks like lauan?). For the left/right twist effect, the helix pitch number was reversed. Machined with an 1/8" ball end mill at 4.5ips.

https://lh3.googleusercontent.com/oli1yYbEFPkC6cOp4XSAOlBuWHfi4X5U8E_fS5WyI6K4TXY9ei i8zlWQ38nqyt7JmtnDU-4-DRdYmw=w1920-h1080-rw-no

Simplified tool path display (from my machine controller). This is only 40 facets on the circumference to show the way it machines. The actual parts was machined with 400 facets to avoid any sanding.

https://lh3.googleusercontent.com/e7-QVo_pDBztFmbrV04-nA2TbeBNb7K-XOIsYje9j8JHfLBPqJbviSKdtjMhvQWUZ-m4iCfZKzSb7Q=w1920-h1080-rw-no

[myxpykalix]

How are you able to carve this without destroying it? I know 2.5" isn't much but it still needs a way to hold it?

[scottp55]

No pic G. ?

[Burkhardt]

How are you able to carve this without destroying it? I know 2.5" isn't much but it still needs a way to hold it?

Maybe the picture below of another test part shows it. There are 3 reasons it holds up:
- there is still a small dowel left on both ends to hold the part, although the one on the right hand side is only 0.08" diameter. This can only be done with a live center on the right or it would flex too much. A short thick part could be held by the chuck alone.
- The helix is a symmetrical 2-start thread. That leaves a center chord intact to stabilize the whole thing. I noticed the biggest trouble happens when machining a single start hollow helix. In that case, when the center is being machined away the remaining spring shaped carving becomes so flexible it will vibrate and eventually shatter.
- The earlier shown tool path is only the finish path with very small stepover and very small machining forces. That (and the minimal y-z-movement) allow for the high machining speed. Before that it has to be roughed out with a remaining skin. This is also done with the ball end mill but much coarser stepover and cutting depth. While roughing there is still more material left and the part more stable. The second pic below is the roughing tool path which is a similar spiral trace as the finish path but harder to see due to multiple depth layers. The roughing also creates a sloped lead-in and lead-out on both sides to prevent the bit from broadside slamming into the material at full depth.

https://lh3.googleusercontent.com/NcG6LlTiZN9oRo-XnK-swcBL7emcXrcM3HpVHKglw6B4bShOwV8DnJI5A62o-vjvE7UvRIvZNgJmRw=w1920-h1080-rw-no

https://lh3.googleusercontent.com/tZWPsILRvXRcWhT33xE7pZC4aARHvZFyi9fJ5Pbwvwup3cyDod 8q-Qwroig7ap3n8R9aFjp_2abv6zHFF2ixul1y3AOn97wUyAzX37J B4c6Sv5cEDUmbroG38r2i4W_oOMjERn6qF2mWuajHI1eAeoVNX FOkNf1vCJaIeLEXjgkQuO6dtQIPDGNax_9rdcIwGYOVTEWz3xf xTxQ0BU3GEfi2FtT4hTttCDJ4dxkRZcXwA15xbNtKldFk-bi2IpHZ5mBgfn2dLeocVJLtjz96_nR98U95lZkyN39wxDVPxRB nmYpuuxCUrMpd2VHAtD6oupHTAokoo-1mosP56UCzDN39kLGUy2H71GWdCxYqZG1qFuA_wLZEtnjQoF8K ydREChX5qWWpIeSGvkY-CVSGGOWS-R8uisCM8gW7rkeu_UBUhkEY-NyB2atZTsGJ1hkwGn1A-bdi9M1kHpYQkNf1siBBV9jRqvW-oecRM5emdtmplEkRsc1grTD1e_RjyWV9MMygrIaTNVtK0Wy2zw lyS-0taHJKn9z8md5yOAOIjtCssqD9gGyW0xVGKyAv5q4x1Ucolfxz BNrD0usAG57wnrYOj1b-Jal7FXqJP1H800aUT7sra508=w1165-h694-no

[Bobtail Farms]

[I do not see a picture]

[dmidkiff]

I see 2nd pic but not 1st.

[steve_g]

Gert…
This is how I see images you’ve posted… I thought it was just me.
SG

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29488&stc=1

[scottp55]

I see 1 pic in #20, and not even the icons Steve shows in #17.
Using latest 10 update, and Firefox latest.
No plans for an indexer yet, but always like looking at Gert's "Projects" :)
scott

[waynelocke]

I have been following this thread and have just reread it. Aspire and Carve Pro both do rotary wrapping and can do spirals effortlessly and easily. A hollow spiral would be difficult but only because of the machining difficulties described by Burkhardt. Am I missing something?

They are very cool.

[Burkhardt]

I have been following this thread and have just reread it. Aspire and Carve Pro both do rotary wrapping and can do spirals effortlessly and easily. A hollow spiral would be difficult but only because of the machining difficulties described by Burkhardt. Am I missing something?

They are very cool.
The rotary wrapping is just that: wrapping a 2-d tool path around the x-axis. That works for simple things with modest depth but fails when the part becomes very "3d-ish" because the target position for the ballend mill tip will change when the surface is folded much by twisting or has steep radial walls. It took me quite a while to work out the math for that. The simple wrap method can not do that and would also have trouble with a changing outline like conical spirals.
For my software you can define a number of cross-sections along the rotation axis which can be circles, ellipses or polygons with varying vertex count and the additional option of fluting. These cross-sections can be centered (like the slim ellipse cross-sections for the earrings) or off-center for a real spiral. The toolpaths are then created to cut a surface that conforms with these cross-sections and twist with selectable pitch.


I see 1 pic in #20, and not even the icons Steve shows in #17.
Using latest 10 update, and Firefox latest.
No plans for an indexer yet, but always like looking at Gert's "Projects" :)
scott

Now that is weird. The pictures are not uploaded but linked to my Google Photo account. That has always worked in the past and I can see the pictures myself at home as well as in the office (with a Chrome browser, that is). I will try and upload smaller pictures tonight.

[myxpykalix]

If you look at the excellent tutorial put together by Randall Newcomb, i contributed to it re: issues on hollow spirals. I solved that problem. About 3/4 down the page where you see this pic.
http://www.humblesticks.com/cnc-rotary-tutorial.html
So you can do a hollow spiral as you'll see easily....(well not that easily!)

But i actually think it is a bit different then G's example. The fact that it is short helps negate the need for support.He's definitely got the right ideas...

[Burkhardt]

Well, this is indeed strange. When I read this thread with the Chrome browser all the pictures are there. But when I try Microsoft Internet Explorer I see only one of them, otherwise just the little error icons.
Maybe I really need to upload the images to the forum server or I try a link to Dropbox Photos.

[Burkhardt]

I think I know now what that is...I posted the links while logged onto Google+ Photos and that seems to have created short links that also required my Google credentials. Well at least this is my explanation.
So here I try this again with long links (reposting the pics without further comment) using the Edge browser and hope it works...
https://lh3.googleusercontent.com/Xx8iCpE03FdyvXKeIQIgRmpDfTjXZL_qCIJDT8P4pGQ60Aaru2 jjE4dDSBCXFqTTA5SQDvU4RHPoDSUUGr7kW1ottCXnql7aMjZH 1gXoniiVJylJFIq9hpHhBuVl-A5AK5ZZN5YD7WcVlSiXfBWILETP_qCecvhKA2Ye20Gvs1OZ6gz n2SHTHIlB-KoFtGd5NM5r1ZZwudon7bFRNwrQlH8ZhmdepkWPNLS8W-O21lWaP5syKPeLxS_pmL-iVtFMT8Ncm-4BUX2NdvCcYZqN8vCfRVFISgpPXq7iEc7sqA3jDo4CFEsD-Tq3wFKn1ju56ObrYxl_WTniW6e9-G5lyyzEMgvu4H1f_yzZPuOFzE9o-5eI5EE5a1yn7_lHTi5OKNHhmz6zo_nWvp7Le4EHkBZs8iEpSyS ZfQoqvfdXZh4vMsAjvu3f-RBN6Np_z6gthcsMyFDBP8yQuV5ZsDZEZVSW9TBUyuyyFmfjxjv IOgLM23aVvnFapeqb_yrvCaMMFIqAvUx_m0RhkqO3PhT9ZQInG 8rxylIKIvMtO5ez-kgJ75Ipu4a6TempP_9tt6bAnf1fA0bC6wvhiL7Ogvha7Qw2DIn Qh4KW9p7PtMqT9QWAq1RU=w1024-h780-no

https://lh3.googleusercontent.com/7hnNFsQhrbh1GcJJOcxYHfinrHtXDHRvJbXoatRCCKXT0mZ-mQGS8eXXfqFm8ZZ7pGSOcT3D-oJvXv8QADNW8YG17cfvwP-QjToA6T_9isEaKhURvwa5d3qz_Zujoa3nYBGGcEfCaoIVsT4gC xvVOq9UR1NnxlYCwj3B8hu-UIjnaXtqY1vGh7fiF2ba68xkghQ0hsOFMTlO-Yrd71UJzycImLMo3mIWis1_eejJJlxSaReFJdQDDyPTYMhhM9M 8VVyhqRAj862-vJK5U9fu7sXRYjfr4c-qs_fP2pIJyU5SS7zqk93zywPXmfThkBdXhfBQtHF4AmWeODQL0 FvdFC8pZzhkNYuKPwExQVRA2Ul-eqn-o7qd61QNQTQh19Cj7H30llwMOQrSzUbRs0nOKbymH0lSZK3C2-4zTTb31skeBJ19uzZYa_a8roP9wgdcVXek2vkpTkXwhfF3E-HCbZ4zsfYYhllqkQxar6zaNm9QYeHvCK5atWSR-nNCIVAVDOdPR3Pt_mdxCvSvt-vif1MAzvYpSPO1RNuzBvTMd-EqgWw1c7mKsi03RBrVbFs6Nh4mH6KaOmu4SRakWsMzTFUyaDzA xg0dkHwjRKhrskCp9j1n=w800-h533-no

https://lh3.googleusercontent.com/mjIzl6uxoEcXBS7RUkWeg0jLh-14yrY0uudT6xtGhKOqSjXTrHOjQcoU7gHI9iCdtjdp5uHBnQ3o 9S0nv7Co7bX8YQpvqZVxoYOe57P7v0PcpiqiFO3lhj7t_su2Xv Nqn4ZtAdGtpxhorwLA5QTgJ2g0Stkemy5s4m-Yl25amg7hJ51OEMQjuuMFYi4oMyIh0DYlXKLOounZr5FfgngAy XRxMB7wun18vZS9eN2mDJFQAYtdwHqrmwWsFQ_i38SY9Da5-0-3HI2meVG2jFSD8hNrKaStL1IBma3WpJ-4DQPZqliJstNrNW8l1w9zKVHPoBU4Jr_WBRfg5z3rG3Hxd7oDl 5n_nR_-HEswd_03KzQGa5gNbENVapHJtEFWx5DzzkKi3G2ifIxrxubu4t ZKEILMDDnF0FKt19OkdBl6ykdmkZZ17mryW22Qn641IzlVOI4F l0k6U6oCzE441kvF4GXU3YbTsTPhBxattxyO4j4I4kgO6svfe8 i3a37ADjyXqvqSCQtz6lGaff9t0WAqYgmovwPMM2DtiJEBO5V2 WBkyRyEDlr1hG7vyBJpEj8wDmawBCzSf9QzGGy-m-pTskFmvRDNwYN9xE5wGzKjG5oNTmhkv=w696-h950-no

https://lh3.googleusercontent.com/eGelgSQroDCxszPem9NjXFsrSRilatKqLzSO11AgNa5jFXjnub-2ZqN0GkefeZRPMl_ZBqB8XvqrTjmZpfXMuB1CW7E2kM1PAP6Ag uEuF-rghgrBE7KhWkR4XpgQEwaY3373KOJ7uXCfLPaZKQyBeqBO0f3B bW8KPxWlNhdA7pcKE-VS82EzlZAlUidE-a4fjM52YIPu3CPoouwnF05kl0OgLDgEc-RLPAd89vBfMnTqkS1ag5ZtmNWfgKRKXSvPhjaamW1RM7DRfCQx RB4GeqP2pSxvqDtGQfNOJit3G3rMR_kP_6VHxSNT9PK0v5spy8 kmvzjKVXCjI4wRr1oF2d7T9kfWYX1TdlHXMwwuZXG02Pk3Kj8X LiBUw5s4aX3LOKiA4Kp_SJH-h2KJoncyAuNV2P6gQUl_eAMMYrB5PEV47h8B9Fpd8N2mMCYOry UP_vcBjoQ52IQV1gzp82kSOteLp2H_PFZG_CjKn18UTb2sxS1H 2PTkr2-NNTlOCwjqJ_yIltua3wxs72VlFBdYCglj8bXpFj5fEYNZSisL8 F2slfgWyvbxQ22NcgfKb3nYFisX1N9Fx7SRmBFcGKnA2cIHXHI DzSTWI5eZhhqQq_2HDr41=w1140-h738-no

[Burkhardt]

And the remaining 2 pictures....

https://lh3.googleusercontent.com/YQ4WqZ8K1PrMWlc4daCKD3VRSAA9XjazueRABhmrz5DZ_ojL22 udN5VMeFRcUHBxEvXFJ6b5w5AI11t1QC-qEBcR2pcZg7BLd2S98WPpe9E1GVC9yRUgVZ7cza5YWXiBfDSTt 4ylKVliMQETRgO_mAbmdUrtTClK3xr8MNnjU4i79R5FPbUV-hEh6kHMbn6xMK1h1CD5scs2d-t4gtBJmypEeMncw7n0qeBmKQQL2zOX7kiDSnajgaUmFhkJsqSe WHc9q2u_Cmjpuz6ALRS55ybQ4j8KLR3aIxPUm45wNGiLredjYb 4htpq0YZYA6S4HI2CEySTlVPkCmPA9-PLjf5TeXOZ-Rh63fYXZiSh_xDTp6rv8fGEc5_GSHrF-OMLRvNC0SvvKTmePTGsczvQJ5C8w3oTh03ffM9PO_18MY4MMcA SkWvh0tyHQSTn-jXHHW2aMb7QZYBEZYTmrGQ7ffIEirDXBx9w44nAiJcVqH1ZdEZ fGJh-0_EjZS5pCpuHU8_XetHaNHvS1f_6JOwS7tUyrm73_5REjy_ni1 ThoV_oZD_vNK-caMV9VB24mf-3n2kKF6ioJIcMkWjVY9aNEVNOv0lw6Z3o-YS2HXPoNGo6p0IDG=w1200-h669-no

https://lh3.googleusercontent.com/xjZHDNjcQ9zjyufHjtSkeTN-R9D8H55OY0f-SnHCtPSaD7ANaCoB0lSu8HQF8sERWXyBmVu18DugGXIuitK4tV LxiyRXBgptSpCwbvuiJl53fAiZ3Xw9IzDR5LGlPygPIuGFb1Cd T1octS1kpemYzPF_bHuKjbzAY7pW4L3HrkVhvkX2O1KCpPx7ZD H7Ura4_dcf1cF_oh70Iu0Zm335Y4NNMmmhoL82k4G-v7H4Z4kmMbHNxoYcmwY_s0IRTkLTiObnxrMqmxZj6turJ5UUyc c60zJuHvHXqlZZHWmzjfPRVfeXbqo7ywQGRs-Pw_yi-fTR39vopBA-gbVbcQ8BjYUny1zmbu6BQtzNGRzTbzHrUzHMOFOFo2tQyry0JP FWEc4mBEgpYCnGgyjkgBsROWzEFexa4pp35HxnNWwtHKmA9U-ymMn7ZXYbD-b54iMlL5UtYTioRBhS_iQs7sHZOvK3OjHxeqDBer93Qhqk9f4Z uuRonY8DFXJJe_w0thbdKkxqPkACe3ZkP-RRdp0Hp-fHhGttcpCMMUJhA5mjn8qwAzuY0J-57E8ZqI_yXlgn666mYSoncRD2m9uQAqj6c8a21KjUF4FE2rZ4B JnEWSFTkgAChit0=w1165-h694-no

[steve_g]

That did it, for me anyway. Thanks!
SG

[dmidkiff]

Worked for me too. Very impressive!! Thanks.

[Bobtail Farms]

And now I see (too). Thanks.