Harmonics of the Table.

[spektr]

Hi Guys.... The neat table drawings got me thinking about the freq response of the table. It seems that our accuracy in constructing things is not helping us. WHAT IF we make all the angles and gussets a bit different in length. What we end up with is a table with very few resonant freq's because something will always be the wrong size to be excited. So on the cross braces, not meeting in the middle would be a good thing. Also, the channels supporting the spoil board/platen don't need to be paralell to each other as long as their tops are coplanar. MAYBE thats why some really crude looking junk works so well and the anally assembled perfectly dimensioned tables vibrate. Just thinking out loud.... Scott.

[gerald_d]

Your points are completely valid.

[erik_f]

I think more legs and then bracing the legs together would go a long way to raise resonance of the table...also...I would have to imagine that the table top itself is a large part of the problem...if it is a problem...I would guess than if you made a sacrifice board of two layers of MDF with a thin layer of sheet metal laminated inbetween using some liquid latex.

Erik F.

[dvanr]

Erik,

Is liquid latex glue elastic?

DvanR

[erik_f]

The stuff I've used remains gummy...not sticky...but doesn't turn rock hard...I bought some in a gallon bucket at the home depot, made by liquid nails...

[dvanr]

Hi Erik,

I wouldn't use the glue. The clamped work should not move laterally or up and down. Mounting your work to a surface that is gummy will probably result in different problems like varying cut tolerances depending on the force of the cut.

DvanR

[erik_f]

The surface wouldn't be gummy...the idea is that the table itself be made out of multiple materials...this way it will be self damping. The layer of latex is used as a dual purpose material...one, to bond the sandwich of materials, and as a third material...the more materials you bond together, the better your dampening will be. You wouldn't want the layer of latex to be very thick...just enough to bond the materials together. Bottom layer MDF, latex glue, sheet metal, latex glue, top layer MDF.

Erik

[gerald_d]

1 to 1.5" of wood table does not need any more "deadening" - it is pretty "dead" already.

[dvanr]

I did say "surface that is gummy" should have read " that is resilient"

Be interesting to see what the comparitive results are between your original spoil board and the new one.

DvanR

[erik_f]

what if you took sono tube and capped off the bottom put it around the legs of the table and filled the tubes with sand or lead shot? I don't think the spoil board would be resilient with such a thin layer of latex...I don't plan on doing anything like this...I'm only applying knowledge of dampening materials and resonance from speaker design.

Erik

[gerald_d]

Erik, you already have a working table. Can you tell us what design you used, and can you describe the problems that you may be having?

[erik_f]

I'm only using 3 layers of 19mm or 3/4" MDF for my table top. I'm not having any problems...only offering ideas. Mostly I'm using a stock Shopbot table. These are only ideas that would help in damping table vibrations...

Erik

[gerald_d]

That's what I thought Erik - most of us don't have problems. Newbies may be intimidated by all this talk of table problems, when they actually are rare.

[erik_f]

Yeah...I was only offering ideas...but in reality...I find in a waste of time...at least for my application. I did order a second Y axis motor...even though I had no real problems running a single Y-motor...I did notice that my x-axis has seemed to be more accurate on a continual basis than my Y axis...now I'm sure this has some to do with set up and I plan on trying a few things this weekend to bring her most of the way in before I apply the second Y-motor...but I really feel that the second Y-motor will give me all the shopbot can deliver. Vibration and table harmonics are the last of my worries...Maybe I should have read better, I didn't know it was a newbie asking the question...standard table once dialed in has worked fine for me.

Erik

[gerald_d]

Erik, there are lots of silent readers on this Forum - that table drawing over in the other thread was downloaded 73 times so far.