Are complex 3D forms possible using an indexer?

[rley]

A lot of the posts regarding indexers involve wrapping a 3D texture file or text onto a cylinder of sorts and I'm curious if it is also possible to do complex 3D forms with an indexer?

Currently, we are doing 2 sided flip mills of 3D shapes and finding it to be tricky at best. On the software side, we use Rhino 3D and Rhinocam (which is actually Visualmill) so creating 3D toolpaths would seem to be possible. Attached is a few photos of a recent flip mill that would be great to be able to create on an indexer instead. Would this work?


Thanks.

Rob

[markevans]

Rob,
I'm not sure if you are asking about Rhino or if indexing will do the trick? I know nothing about Rhino but yes an indexer / fourth axis will do what you want with the right sw.
Take a look at the handibot blog as they have been working on this and it will work the same on any size sb.

[rley]

Thank, Mark. The Rhino and toolpath part, I feel comfortable about. I'm asking more about the capability of the indexer itself on a shopbot. I've seen some videos where the indexer appears to rotate a fraction of a degree and then the Y axis runs, and then it repeats. Shapes like I'm showing above would seem to work better if the index axis was constantly turning and the Z axis were going up and down to shape the contour. If you've ever seen a potato peeling machine, that is the kind of action I'm imagining.

[gc3]

http://legacycncforum.com/viewtopic.php?f=28&t=3362

[Brady Watson]

There is a relationship between the main body diameter of the part & any 'appendages' hanging out in mid air that will result in loss of resolution and detail at those portions. It is possible to program it to 'potato peel' but the Z will need a very long stroke to do this on your part and it won't work quite as nicely as you think it should. Feed rate would have to be slow enough to not exert too much force when the tool is way out on one of those features and to keep the tool on the surface of the material without bouncing/gouging. Since the part is only held between centers, care needs to be taken not to push it too hard - especially in HDU, or it will loosen and get wonky.

The most efficient way to produce that part would be to slice off the appendages in Rhino & save them out as their own entities. Then machine all 3 parts on the indexer, individually or ganged up - and then glue them together.

-B

[rley]

Brady, good points. I should have mentioned that we have a 12" Z axis and that the material is lightweight 10lb polyurethane foam, so shouldn't be much force involved. I found a video that shows what I am hoping to do. This video shows a vertical mill and it supports the foam stock on only one side, but it does show the behavior of the rotating index axis and the spindle motion that I was describing:

Youtube How Its Made Video (https://youtu.be/Yi8zTeav1SU?t=65)

Aside from the vertical orientation and one sided stock mounting difference, would the Indexer work in a similar manner on a shopbot? Again, the software side I can figure out using Rhino, Aspire, etc., so not worried about that, more concerned that the hardware and controller will work in this manner?

Thanks again, guys

[Brady Watson]

You still may have problems with the foam if you push it too hard. Been there, done it, got the feather...Even with really good steb drive/tail centers it can walk out and get sloppy in 18# foam. 10# will be worse.

The indexer will work in a similar manner, however this is completely CAM dependent. At some point the SB controller was upgraded to allow it to exceed 360 degrees during it's A/B rotation, however few post processors will write code this way. It will either raster along the long axis or raster around the circumference - 'turning around' and going the other way when the degree mark hits 360/0 deg. Taking a look at the SB Indexer tools in SB3 may help you regarding this & some custom programming. CAM is just an offering...sometimes you need to hack it to make the tool do what you want.

The best advice I could give you is to just start cutting and trying things out. That's all I ever did because there was nobody else to ask... :cool:

-B

[bob_dodd]

Rob I second what Brady posted above, You don't say what size this part is that you are trying to make , or what machine you have , any slack Play) in any of the axis is going to affect the outer diameter of your part , I watched the video , that is a machine built to do that part ,( just the length of the cutter alone) ,
Yes a indexer will do this (my opinion belt drive to minimize play) You may have to machine at very slow speed to get good results , as Brady suggested you may need to disassemble your part into 3 pieceshttp://www.talkshopbot.com/forum/attachment.php?attachmentid=24801&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=24802&stc=1 These small part pictured have over 2 hours machine time , as the many Z axis moves , as your part also has , I would have a indexer built to do the job , send me a PM and I could suggest a couple of people good luck

[rley]

Gentleman, thanks for all your input. It helps a lot. Going to jump in and give it a go. Just wanted to test the water a bit before spending next week building the indexer. Take care.

Rob

[rley]

Brady, do you know if its possible to drive say a gecko driver for an 4th axis/Indexer, using a PRS Alpha controller from around 2011? I know that there are higher end Oriental Motors closed loop stepper drivers used for the 3 main axis in our PRS Alpha, though given the low frequency I would be using the indexer and the low force exerted on that axis, I wouldn't mind using a less expensive Gecko driver and stepper (which I already have from another cnc project) for this if its possible to interface the Gecko into the controller. What are your thoughts?

Thanks.
Rob

[Brady Watson]

Yes, it is possible, but involves a Gecko with the same common polarity as the Alpha, and it's own power supply. You'd need to make up a few cables to interface the drive to the board as well.

-B

[rley]

Thanks, much. Going to look into it further.

Rob