Filling the voids

[Drools]

I'm wondering if filling the void area inside a frame would help the router in any way or maybe hurt the overall performance?
I'm building a frame from 80/20 and I notice there are large void areas inside the frame totaling 1.736 cubic feet (not including brackets).

Thanks for the help.

[aarggh]

If it's a non-moving part such as the base, then filling it with something suitable would add mass (always good!) and add to the damping of vibration and noise.

If it's a moving part adding mass to fill voids may throw your balance, inertia, and reliability out to an extent, or certainly make it harder for the steppers. But filling voids with a light but material such as expanding foam, or similar, could add quite well to the damping of virbation and noise.

cheers,
Ian

[Drools]

It is the non-moving section between the 3030 rails. I have a few 1530 cross braces but there are large areas that are wide open. I could make some sandbags to fit in the compartments what else should I use? Now is the time to think about this before I get the top on it.

[aarggh]

Some polyester/fibreglass resin might be just perfect for that then? Others will correct me if i'm wrong i'm sure, but resin also has very good to excellent damping properties I believe?

A few support rods or bolts to give a grab would add significant strength to your frame, but you would need to allow for some minute shrinkage possibly while its drying.

cheers,
Ian

[CNC Lurker]

Originally Posted by Drools I'm wondering if filling the void area inside a frame would help the router in any way or maybe hurt the overall performance? I'm building a frame from 80/20 and I notice there are large void areas inside the frame totaling 1.736 cubic feet (not including brackets). Thanks for the help.

I'd say you are probably looking for a solution without a problem. There are many on here who have built there machines using 80/20 with great success and without filling the voids. Some of those builds can be found here: CNCRouterparts build logs and links

Just make sure you not using the "Lite" version of 80/20 extrusion (see screenshots).

[Drools]

nope not using the lite versions. You are correct, I have not seen any of the other builds fill the open areas but I thinking about it so I thought I would ask.

[aarggh]

To my mind anything that increases the mass ratio between the table and gantry is generally good for stability, vibration, and noise.

For the new 8 x 4 machine I'll be starting next year, I'll be filling the base frame in with a resin'ish type material, and for the gantry I'll be using an expnding foam most likely.

For the current machine, when I replace the top on it I'll also be filling the table base as well.

Some peope don't, some people do, at the end of the day it's just a personal choice, but for me it means a better end result.

cheers,
Ian

[RicknBeachcrest]

I am in the process of building an 8020 machine. I have seen a build (Senna) who used 1/2" foam backer rod to fill the voids for the purpose of preventing the slots from accumulating debris.

http://www.cnczone.com/forums/diy-cn...router-12.html
or this one depending if you are logged in or not (seems like a bug in the forum to me) Anyway it is post 136

http://www.cnczone.com/forums/diy-cn..._router-6.html

[CNC Lurker]

Originally Posted by aarggh Some peope don't, some people do, at the end of the day it's just a personal choice, but for me it means a better end result. cheers, Ian

No, nobody does, at least not that I recall. Maybe it would be more honest to say that the overwhelming majority do not fill the voids in the manner that the OP is talking about.

Could you link to a build that filled the voids to increase structural integrity?

[dave22]

WOW
Paul: What is it about this subject that causes you to be so confrontational

I don't recollect, you ever responding like this.

1) "No, nobody does, at least not that I recall."
This would imply that you know everyone and that you have eidetic memory.

2)"Maybe it would be more honest to say that the overwhelming majority do not fill the voids in the manner that the OP is talking about."
I just don't see any dishonesty in any of suggestions put forward by aarggh

3)"Could you link to a build that filled the voids to increase structural integrity?"
I do not see where the OP asked this question.

As to whether there is any benefit to filling the voids, I would respond, yes most certainly.
There are literally dozens of scientific papers that document the enhanced damping of vibration that results from filling hollow machine sections with a damping material (sand, epoxy/polymer granite, concrete, foam, etc.)

"Richards and Lenzi4 carried out several experiments on sand-filled tubes and have studied the influence of the quantity of sand, grain size, cavity shape and size, and the direction and amplitude of excitation. They report that damping attains a maximum at frequencies where resonances can be set up in the granular medium. Bourinet and Le Houedec5 expanded on the ideas of Cremer and Heckl and developed a quantitative model for the vibration of beams filled with granular materials. They model compressive waves in the granular material in the direction transverse to the vibration to develop an "apparent mass", which they couple to a Timoshenko beam. However, the high-density fills add a great deal of mass to a structure and hence are rarely used where weight is a concern. But recent experiments (e.g., Fricke6; Nayfeh et.al.7) indicate that a low-density granular fill can provide high damping of structural vibration if the speed of sound in the fill is sufficiently low."

As far as a build that has used this technique see here; CNCCookbook: Epoxy Granite Fill
Although not an 80/20 build, it still uses the same method to achieve vibration damping, which should produce superior cuts.

I, seem to recall Helmsworthlad advocating that builders fill the voids in 80/20 for damping benefits like he did. Although I may in all likelihood be wrong on this one as I most definitely do not have eidetic memory.

Please don't take this as a personal attack, I just want to emphasize that we all remain civil in pursuit of our hobby/business.



If anyone is interested in some reading, check out these two MIT papers and their respective bibliographies.
http://web.mit.edu/people/kripa/publ...wsm_spie03.pdf

http://web.mit.edu/kripa/www/publica...dia_spie02.pdf

[Drools]

First I just want to thank everyone that has taken the time to respond. There are quite a few of these 80/20 builds now and I have always wondered why none of them have filled this inert space with something.
I certainly will fill the voids inside the 80/20 3030 and 3060 extrusion with sand now that I have seen the link you provided Dave!
I would guess the voids in the frame itself would benefit as well. I'm talking about 2 different areas, first the voids inside the 80/20 itself and second the voids inside the frame. The 80/20 frame has large areas between the rails that do not contain any moving parts.
The attached picture shows the top view of an 80/20 frame, the black areas is the extrusion itself and the red areas is the voids that I'm wondering about filling.

Thanks

[PaulRowntree]

I have built instrumentation frames out of welded Al rectangular tubes, and can attest that filling with fine sand is an amazing dampener; the bright sound when you strike normal Al is replaced by a dull thud. It was a pain to do (filling ports etc) but for that application, it was definitely worth it. This was for a surface analysis instrument that was able to image the individual atoms, so stability was measured in nanometers.

On a CNC? Are the small scale vibrations a limiting factor? Since the filling does not improve the rigidity of the beams, I don't see how dampening would materially affect the stability. I would have thought that improving the stiffness would yield greater returns than increasing the dampening. Dampening can only help once the frame has flexed to some degree, and you want to dissipate that flex energy. Why not just prevent the flex?

Free advice is worth every penny.