Z axis capabilities

[nickem@geowood.com]

I am a sculptor. I use mostly wood. I am a machine designer by trade and am familiar with 3D design software such as SolidWorks and Autodesk Mechanical Desktop.

My questions regarding the capabilities of a ShopBot are as follows:
Many of my sculptures begin as a cube. 4" up to 10". I would like to know what is the maximum height that I can consider when designing a piece which requires boring (milling) down to atleast half way down in such a cube.

Also, what processes can I consider for fabricating a (close to perfect) cube.
Thanks in advance,
Nick

[richards]

Although Shopbot can build a machine with a Z-axis length to match your specifications, to me, the greater question is what kind of bit/cutter are you planning to use to make that deep of a cut? A 'standard' cutter might have a cutting length of less than 2-inches. If you went much deeper than that, with that particular cutter, the router/spindle would get in the way. Using a cutter with a 5-inch cutting length would be 'interesting' to use, with the flexing/breakage possible with a long cutter running at router speeds.

As to your second question about fabricating a perfect cube, I'm still looking for that solution myself.

-Mike

[paco]

Hi Nick!

4 first sides are not a problem; within 0.010" - 0.020"... it's the 5th and 6th side that need some gig/indexing/thinking... miter saw is good for this purposes; at least for the 5th side...

As for larger than 5-6" (depends on your Z installation/setup), one need a custom Z rail(s).

[chris_booth]

Hi Nick!

Everything you would like to do is possible, and presumably more easily for a machine designer than by an only-hands-on sculptor! Most creative people who aren't repeating and repeating and repeating the same jobs want a very general purpose tool that can deal with what's most likely to come along. But if in fact you are quite clear you want to basically work with cubes then in a way you're at an advantage.

Mike's comments about cutter length are very important if your sculptures will at any point have a wall steepness and depth that is more than "normal" - it's about making sure you can get that cutter down enough to the lowest part of any sculpting without the "first-parts-above-the-cutter-that-get-wider" ever getting unacceptably close to the work(e.g. spindle collet, router body, even a cutter's shank above a small diameter cutter could be a problem in some steep-walled circumstances, although on ballnose cutters the shank is the diameter of the cutter). But there are very long ballnose cutters available for e.g. prototyping - for example (at http://www.pacersys.co.uk/acatalog/Ball_Nose_Cutters.html) you can get a long series 3mm ballnose cutter with Cut Length: 25mm Shank: 3mm and Overall Length: 75mm, or a 6mm extra long series with Cut Length: 25mm Shank: 6mm and Overall Length: 150mm - that'll get you "at least halfway down in such a cube" (but won't let you leave anything "sharp" or "detailed" down there!). And I'd be careful about the forces you put on a cutter working that far from the spindle/router - move slowly, I guess!

I reckon you need 12" of Z, because the daft thing about using cutters like those mentioned is that not only does it have to go down that far into the part, but it also (typically - but maybe not for you) has to be able to move above the top of the uncut material before any initial cutting - so the body of your spindle/router needs to be abnormally high over the cube before you start going down (if you'll forgive the expression!).

The same applies to your table, you'll need to modify the standard ShopBot design by extending the legs or lowering where the bed is or a bit of both.

And if want to machine all six sides of a cube without re-positioning-from-scratch, then it could be done by using a special double-hinged jig on an indexer. The indexer will deal with sides 1 to 4, and then the jig can hinge one way 90 degrees to let side 5 be machined, and then that hinge be closed again and the part-holding modified without moving it before unfolding the other hinge (and rotating the indexer 180 degrees) to access side 6.

You don't need a perfect cube for sculpture - as an artist you can remind the admirers of your work of "the perfection of imperfection".

And are those cubes to be hollow? And is any of your sculpture modelled in Solidworks? - If so I'd like to see it - in fact I may be able to make it for you!

[beacon14]

If your maximum size is 10" and you only need to get halfway down, then the standard 6" Z-axis travel should be sufficient as long as the rails/table are modified to allow that travel to range from 5" to 11" from the table (actually the tip of the longest bit you will use needs to travel in that range) Then you could use risers to machine the smaller cubes.

[mikejohn]

To make a cube (assuming your shopbot is square)
Hold your wood on the table and even off the top surface.
Flip over and level off the under surface to the cube thickness.
Machine along one edge to the depth of the bit.
turn the wood over 180 degrees, use your machined edge against a strip of wood on the table and machine along the opposite edge, so both edge machined parts are level.
using two equally thick strips of wood on the table, turn your block over, position your machined edges on these strips.
Now level off the 3rd face.
Flip it over and machine the fourth side to the thickness of the cube
Assuming you have been machining everything in the x direction, Now machine the edge in the y direction.
Flip 180 degrees and do as before along the opposite edge
Sit again on the two strips, Machine surface 5.
Flip 180 and machine the final surface.
This works with any old lump of wood, providing you can hold it to make the first surface.
..............Mike

[ted johnson (Unregistered Guest)]

whoa i <333 this site!!! its the best anyways this is all about machines and wood making correct? wow i love u guys u guys keep doing what your doing

[srwtlc]

2557

[gene_marshall]

CHRIS!!!

holy cow what a great idea for a jig.
I have never seen anything like that... do you have any pix you could post.
Thanks

[chris_booth]

Pix - I'm afraid not! But I've posted a series of images from a concept model in a new thread in the "Variations & Modifications of ShopBots" section.