Re: [CAD_CAM_EDM_DRO] Re: Steel plate for hexapod bed

Simon Arthur <chroma@...> wrote:

If I welded everything, I'd never be able to get it into my workshop. I
like your thinking, though. I have yet to cut anything, so I don't
really have a good grasp of how strong the frame needs to be.

Some improvements I've made since the photo was taken:
1. Legs are now 1.25 OD x 0.125 wall steel tubing instead of EMT.
2. I now have 2 0.25" plates holding each endpoint at the top.
3. You're absolutely right about the torsional stresses. I've added
several long pieces of threaded rod and can tighten down the whole frame
using turnbuckles.
4. I've attached a plywood bed
5. Adjustible feet for leveling

I may yet add some large weights to keep the whole thing from being
bumped around.

My current bed is, in fact, plywood. But it's not very flat, hence I
decided to put a flat piece of steel on top of it. I need it to be as
flat as possible in order to calibrate the machine.

You say that I won't be able to apply much force to the workpiece. I've
got six stepper motors which move my cutting head. How many motors does
the typical 3 axis mill use to exert force on the workpiece?

//// Apples and oranges, no comparison. What was meant by not being able to apply alot of force is again the design: long segments/moments virtually impossible to support adequately to eliminate deflection of materials. A 3-axis mill has only three actuators and deflects considerably more than one would think. Even with the large amounts of cast iron and mass. A hexapod may have the power available from six separate actuators but the design prohibits ever using it with any degree of accuracy. Limiting it to soft materials. If one thinks they will throw a 1/2" rougher in the spindle of a hexapod and destroy a piece of steel, they have miscalculated. The chatter alone would be ridiculous.

Ron

////

Website for RoboFac (mostly about the software):

Simon


R Rogers wrote:

>If I were going to build a Hexapod, I'd use a welded frame construction due to its "lanky" design. Use some 3X3X1/4 w/t or 2X2X1/4 w.t square tubing and build a hexagon and at the intersections of this base weld an upright riser to attach the 6 actuators atop of each. Then tie all risers together at their tops with anything i.e. water pipe, conduit, etc. Torsional stresses are going to be the biggest issue and its inherent inability to apply much force to the workpiece, the table/ work surface could be pratically any type of sheet material (plywood even) inset and bolted into the tubular hexagon base. That would be the cheapest route, just some tubing and a welder. Use gussets at the joints and it would be light, strong and rigid. Just another alternative. Granite surface plates are very heavy and not very durable, they break easily. 1"thick plate base is redundant because the machine will never exert those types of forces, 1/4" plate is too flexible.
>
>Ron
>
>
>

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