portable and lightweight fixed-gantry router - water filled tubes?

[dmorton]

I'm looking to built a small, portable fixed-gantry router.

The lightest weight ones I have found are around 30kg, with an A4 or A3 sized working area. This is pretty light, but perhaps not quite light enough.

From what I read, most people advise going for the heaviest machine possible, using thick aluminium or steel for construction, so as to avoid vibrations.

Since the machine needs to be portable, it needs to be as light weight as possible, which rules out using very heavy aluminum or steel sections.

I read about people using epoxy-granite, or filling their sections with sand, and wondered if a machine made from welded, connected, hollow sections could have those hollows filled with water, thus doubling or tripling the weight of the machines on-site.

Drain the water for transport, refill at the destination.

Thoughts anyone?

[Geof]

All the water would do is increase the weight it would not significantly reduce any vibration. Epoxy-granite and sand are solids which dampen the vibrations water is not solid and doesn't dampen vibrations as effectively.

[dmorton]

I wonder if filling the interior space with an open-cell or reticulated foam of some kind, much like the anti-slosh foams found in fuel tanks, would increase the damping effect.

EvoMx Inc. » Fuel Tank Foam Information
Safety Racing Fuel Cell Safety Foam - Speedway Motors, America's Oldest Speed Shop

There's an paper here on fluid filled foam damping, but I dont have access to it
Mechanical Damping in Liquid-Filled Foams | DeepDyve

Here's another paper on gas-filled open cell foams
Cellular plastics: proceedings of a ... - National Research Council (U.S.). Committee on Foamed Plastics, U.S. Army Natick Laboratories - Google Books

Heres another approach which gels the water with a superabsorbent polymer, effectively creating something like a reticulated foam but at a molecular scale. Question is - how do you drain the water out of the polymer for transport?
http://www.google.com/patents/about?...BAJ&dq=5472761

[RomanLini]

In machine design I like to think a while about the problem before designing the solution...

Why does it need to be portable? Do you need to take it to work or college or to a friends house etc? So that means it also needs to fit on a car seat or in the trunk?

It might be better to build it in two pieces, like the base piece and then a removable gantry piece that also has the spindle etc. The PSU box might be a third piece.

Then that would be easy to carry and transport but might require 3 trips to the car to carry each of the 3 pieces. Which is why it's a good idea to really think through the problem (the requirements) first...

[dmorton]

Originally Posted by RomanLini In machine design I like to think a while about the problem before designing the solution... Why does it need to be portable? Do you need to take it to work or college or to a friends house etc? So that means it also needs to fit on a car seat or in the trunk?

Portable, to me, means shipping it internationally, several times a year. This means that shipping weight and volume are important.

Ideally it should be able to be packed into something that can fly as checked luggage.

If it can be cut down from 30kg to 15kg - that means 1000s of dollars saved over the life of the machine.

[RomanLini]

Well that's handy information!

But what does it need to cut? If you can reduce the cutting area that makes the machine smaller and lighter, and if you can reduce the tool size and cutting power that allows a small lightweight spindle and smaller stepper motors and smaller PSU/drivers etc.

And small tool size and reduced cutting power mean you can use a less rigid machine so that opens up options of a lightweight plastic frame build. Maybe fibreglass or carbon fibre tubing? I think you can buy both types in rectangular tubing.

A really neat solution would be to design the machine to fit in a single suitcase or travel case, all custom fit so you just get to your location and open the case and plug it in.

[dmorton]

Originally Posted by RomanLini But what does it need to cut? If you can reduce the cutting area that makes the machine smaller and lighter, and if you can reduce the tool size and cutting power that allows a small lightweight spindle and smaller stepper motors and smaller PSU/drivers etc.

Needs an A3 cutting area (about 12x16 inches), and needs to cut aluminium and plastic. In general, if the parts are large, they will tend to be from thinner/lighter material.

It doesn't need to be very fast, but it should be as precise as possible, given the weight constraints

My impression is that a fixed-gantry, moving table design might be the right way to go.

I thought about laying up carbon fibre over open-cell rigid foam, which can then be water-filled.

[PaulRowntree]

Hey, I just had an idea on this, and I want to write it down before it flies away.

I agree that water does not damp the vibrations, it is too fluid. I agree that sand does, because it offers resistance to displacement, but it may be tough to fill a tube evenly.

What about the non-Newtonian fluids that you see in YT videos, mostly made of corn starch and water. Under low accelerations and forces it behaves as a liquid : no problem because at gentle changes of speed and direction you don't need damping. But if the machine tries to buck or vibrations want to set in, the fluid turns viscous and damps motion quite effectively. If you stand in this stuff you go down to the bottom, but if you jump onto it it will firm up under your feet and you can walk-on-water. Until you stop walking, then you sink.

Viable?

[Walky]

What about MDF with a torsion box-based design? that can save a lot of weight while mantaining rigidity.

[keebler303]

I think a Widgitmaster Wide might be just what you are looking for. Its not really built for machining aluminum, but if you are only working with thin sheets it might be ok. It would break down to fit in a suitcase quite easily.

Widgitmaster, Inc.

Matt

[zeed]

check this out:

[dmorton]

Originally Posted by PaulRowntree What about the non-Newtonian fluids that you see in YT videos, mostly made of corn starch and water. Under low accelerations and forces it behaves as a liquid : no problem because at gentle changes of speed and direction you don't need damping. But if the machine tries to buck or vibrations want to set in, the fluid turns viscous and damps motion quite effectively.

I think I came across some articles about using non-newtonian fluids as dampers.

I think that there is an equivalence between a gel, a water-filled foam, and a non-newtonian fluid, in that all of them present impediments to clean fluid flow.