T-slot stand, how much deflection

[vhuang168]

I'm trying to design and stand using 80/20 T-slot extrusions. The tank is 48/30/20 + 48/18/16 sump on the bottom. I estimate 2000lbs on the top end (I'd rather go way over than slightly under).

I plan on using 1515 all the way around but want to span the whole 48" in the front top piece. I using the deflection calculator and have some figures but I don't know the limits I should be looking for. I've looked on their website but can't find any numbers I should be comparing to.

Also, how much weight should I be using in the calculator? I'm sure the single beam I'm calculating doesn't see the whole 2000lbs but what figure should I use?

As for deflection, what is a good number to stay under?

TIA
Vincent

[rjallen]

These are good questions. You should use the fixed load figures and each long side would support no more than 1000 lb. on a level surface [actually far less as the short sides will support weight as well.

One design issue...do you plane running the long side 1.5 x 1.5 beams on TOP of your upright supports or use a connector off the side? The former will support more weight. The latter is limited by the weight the various connector can support. The down side of using the top of the support is each support must be absolutely the same height.

RJ

[vhuang168]

So I'll use 1000lb loading but what should I aim for in deflection?

I plan on having all the corners of the upper pieces mitered and having the vertical members sitting underneath the joints.

I will have leveling feet under 1" risers below the bottom horizontal members putting about 1 every 2 feet.

Would love to know what max deflection I should keep under though.

[rjallen]

Using the 80/20 deflection guide and using the option of beam supported on each end, an extruded aluminum T Slot beam 1.5" x 1.5" [part" 1515] the results for x axis [downward force] = 0.0006". I read this a 6/ten thousandths of an inch]

I did note metric 45mm x 45mm extrusion on same length had a deflection slightly over 0.0017 or almost 3x greater deflection although 45mm = about 1.7"- slightly larger size. I do know Canadian and German stand builders use 45mm x 45mm on stands with around 48" span w/o a center support.
A sheet of typing paper is about 0.0022 ten thousandths of an inch I believe. This is the unladen deflection of a span of 48"

With your projected load of 1000lbs the deflection is 0.1117. Quite a bite more slightly over a 10th of an inch. I got to thinking about your load estimates and I think you are way over.

I will base this on my tank your will be different

120 gallon tank standard 48" x 24" x 24" weight under 200lbs but we will use this
120 gallons sea water= 8.556 lbs. per gallon x 120 = 1026.72 lbs. You can't get 120g into a 120g tank plus the below will displace water
100 lbs rock
100 lbs sand
30 lbs misc equipment
10 lbs. livestock
30 lbs. lights, hoods etc.
me leaning on the edge looking at stuff 100 lbs.

1396 lbs....okay we should say 1400 lbs. See above there is a great deal of safety margin built in.

A level/ plumb tank will equally divide this load into 350 lbs per corner leg. Of course a sump, water and equipment would take up the lower level and would add to each leg but you were talking about the upper level.

This next number will assume a perimeter on the upper level of a tank that is level and plumb. I take the total length of the perimeter of othe upper level in inches and divide the total weight of the upper level = weight per linear inch = 144 total inches = 9.72222 lbs per inch Lets up this to 10 lbs per inch.

This means a 48" span would carry a load of 480 lbs. If you carry the beam on top of the 1.5" x 1.5" uprights, this reduces the load to 450 lbs.

This gives you a deflection using the above structure as 0.0506" less than 1/16th of an inch. The bottom line though is you should check with your aquarium manfacturer. They can supply a real number I hope. If they tell you zero deflection, every structure ever built sags between spans. As I mentioned many manufacturers are building tanks with the weaker 45mm extrusions and without a center brace and are doing just fine. If it is a worry, go ahead and put a center post front and rear and you never worry again.


RJ

[vhuang168]

Thanks for the estimates.

Unfortunately the tank manufacturer has gone out of business but I think I can call a few other custom tank makers and ask a quick question.

Although I think if I went 1530, I can span the whole 48" with no issues. The rear horizontal piece will have 2 vertical supports and there will be 2 more spanning the front and rear cross pieces to tie them all together.

[rjallen]

Just about to hit the rack. 1530 is another way to not have to worry. Just costs. One thing, if you need to pay to have those miter cuts, hang the ends off the long parallels. Good luck and be sure to post photos.

RJ