Long table, how to support

[Rick Herrick]

I am trying to put together another sewing table for my wife.  She wants it open enough in the center to put and use 2 machines at the same time.  The end supports will be a couple of small cabinets for drawers.  I am mocking up a demo now and I am looking for some suggestions on some 'under table' support.  The boxes are ~ 425mm wide and I have ~ 1400mm of an opening.  I will be adding an ~ 150mm rear vanity skirt which should help.  Also thought about another, 50mm or so, stringer (on edge) in the middle to give more support.  She just doesn't want anything in front.  If I put something on the front, it doesn't give her the right height and clearance.  Some of these machines have a knee controller so overall height and overall clearance is tight.  The middle support won't be in the way.

 

[AlexThePalex]

Over here we can get these in serious sizes like 50 x 50 cm long, about 1,5 foot.

2 or 3 of these under your table and you have all the support you need in the middle.

If your supplier doesn't have them, any metal company can easily make them.
 
[attachimg=1]

 

[DynaGlide]

You could probably rout in some metal supports the length of the unsupported section. That's what my friend did with an overhanging countertop.

 

[Mike35x95x1]

Hi,

I finished similar table week ago and used silicon antislip stoppers:
https://r.tapatalk.com/shareLink/topic?share_fid=11638&share_tid=66027

you can also place one extra vertical wooden board at the back to support the table top. Something like this:

Mike

Sent from my iPhone using Tapatalk

 

[guybo]

Hi, maybe if you have left over ply,make a couple of wooden I beams front and back to the size you need,attach with the flange and fill the webs to attach the end cabs.looks nice,guy

 

[Peter_C]

For my industrial sewing machine the supports are all steel underneath the 2" thick top. The machine is very heavy and since it is flush mounted the top has a BIG hole cut out of it.

Knee lifts are awesome! So is auto-cut.

 

[mike_aa]

They make "L" supports for granite and stone countertops.  Maybe something like this would be sturdy enough for you.
https://www.bbindustriesllc.com/i-brace-countertop-supports.html

Mike A.

 

[Sparktrician]

You could also use some low-profile strut channel end-to-end.  [smile]

 

[Crazyraceguy]

You mentioned the height in the knee space being important, but what about overall height? If you could build the countertop as a torsion box, it will be much stiffer. This will span the gap with much less potential for sagging between the cabinets. The top will have to be thinker to accommodate it. It can be made with thinner material because the strength/stiffness comes from the glue line of the outer skins.
Even if it could only be two layers of 1/2" material glued together, it would be stiffer than a single sheet of 3/4" and only gain 1/4" overall.

 

[Bob D.]

What is the maximum allowable thickness for the top?

 

[Rick Herrick]

What is the maximum allowable thickness for the top?

I think 1-1/2" total.  I built her 2 smaller tables about 30 years ago, with only the 3/4" top, and she says they are perfect.  But those only had about 28" left to right opening where this one needs 5'.  The issue is having the knee clearance just right, so that the operating height doesn't put her arms at a weird position.

I like Alex's idea of the L brackets but I haven't been able to find (easily) bigger ones, still looking.  Willy's suggestion of that strut channel looks very interesting and simple to use. 

 

[Svar]

Looking at your constraints square or rectangular steel tube will be the most rigid (since they don't make I-beams this small).
For example, 1" x 3" x 0.125" wall steel tube placed flat, over a span of 5 ft will deflect less than 1/8" under 100 lb load.
U-channel/strut would be my second choice, angle - third. Although angle is most easily available.
Whichever beam you choose, securely attaching it to the top along entire length will further increase stiffness.

 

[Bob D.]

Easy to find.
https://www.homedepot.com/p/THE-ORI...et-Countertop-Support-Bracket-LB-26/311400497

Do a Google search and you will find many choices in multiple sizes.

Now that we have a depth you could embed a couple of 1-1/4 x 1/8 steel angle (or 1-1/4 x 1-1/4 x 1/8 T bar) front and back using epoxy and screws. To hide the front angle cut a slot just wide enough for the vertical leg and epoxy it in. Doing this will not increase the thickness of the top more than the 1/8" of the steel. I don't know if aluminum would be strong enough but it might work.

If you wanted to go crazy drill some 1/4 or 5/16 holes in from the front edge through the angle and insert a rod to cross pin the angle and lock it in place. Cap the edges with a veneer to hide the holes.

 

[Steve1]

When you need high stiffness with short height, the answer is steel.
I would use angle iron, probably something like 2 x 2 x 3/16.  Ideally, running the entire length - if its fully supported on the end boxes, mounting screws are seeing very little load.
But I rather like Spartrician's idea of using Unistrut - looks a little better than steel angle and has nice rounded edges at the bottom. (but not the low profile aluminum stuff, you need the standard full height steel stuff to get good stiffness)

 

[morts10n]

A 2" thick plywood top made from two 1" sheets glued together is a "solid" choice

 

[Bob D.]

This is what I was thinking of.

Adds nothing to your desired depth of 1.5 inches.

Cut a slot on the underside of the top then slide the angle in which has been buttered up with epoxy.
You can either recess the horizontal leg as shown in a groove or leave it below the underside of the tabletop.

If you don't think that is strong enough drill some 1/4 inch holes in from the front edge and insert some pins. Then cover the front edge with veneer or a cap of hardwood.

 

[Peter_C]

No one has asked so...Do these sewing machines mount down in the table requiring a large hole cut into the top surface for flush mounting? Are the motors mounted under the table? What is the weight of the machines? Pictures of said machines?

 

[MikeGE]

A 2" thick plywood top made from two 1" sheets glued together is a "solid" choice

Along that theme, here's a video of a guy making a wide bookshelf that doesn't sag under the load of books.  He used two layers of plywood with steel strips sandwiched between the layers in a dado along the length of each shelf.

 

[Sparktrician]

A 2" thick plywood top made from two 1" sheets glued together is a "solid" choice

And ridiculously heavy to move!  [eek]

 

[Sparktrician]

No one has asked so...Do these sewing machines mount down in the table requiring a large hole cut into the top surface for flush mounting? Are the motors mounted under the table? What is the weight of the machines? Pictures of said machines?

Although unstated, this is what I was considering when I suggested Unistrut.  That stuff is quite rigid and can withstand considerable weight without bowing.  If concealment is desired, set the Unistrut into a 1/2" deep dado with epoxy.  If the appearance of thickness is desired, double up the front and back 3" (as we often do with solid surface material) or so and band it with solid wood to cover the plies.