Darryl Keil Last Activity 2025-09-09 11:09 AM
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Dave Shaw

Posts: 37

Joined: 2005-11-06
Location: Arizona

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Subject : Substrate ll
Posted : 2006-01-30 11:06 AM
Post #32764
Hi all,

I didn't want to change the direction of Wade's post on "Substrates", so here is another post on substrates.

I'm about to start on another round, expandable pedestal dining table with 1 leaf. I want to keep the 1 1/4" thick top relatively stiff and lighter than all MDF so here is the plan for it. The substrate would be 3/4" Baltic Birch plywood with a 1/4" MDF skin on both sides. That would be shaped and then veneered with a figured cherry starburst with a walnut burl banding.

The base is 2" thick and is planned to be 2 layers of 3/4" Baltic Birch ply at 90 degrees to each other and again, 1/4" MDF on each side. Also veneered with figured cherry.

Both top and base will be veneered and they the edging put on, which will be end grain (grain running vertically) and about 3/16" thick.

The main reason for the ply is 1) lighten up the top, and 2) to give the mounting screws something to bite into. I just get nervous with holding the top on with just screws into MDF. The upright (solid cherry) will be attached to the base with hanger bolts and I want the base to be less compressible than MDF so added the plywood. Weight is not an issue on the base so maybe I could do it with 2, 1" pieces of MDF and do a big counter bore in the bottom to accommodate large washers on the hanger bolts to prevent compression.

Does this sound like a plan? Is there a better way to do this? I would like some options and any comments anybody may have.

Thanks,
Dave




 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: Substrate ll
Posted : 2006-01-30 10:32 PM
Post #32768 - In reply to #32764
I am also not a big fan of standard screws in MDF.

When in comes to shop jigs, shop fixtures, and general construction, standard screws are usually OK in MDF.

But with fine furniture, and in your application where you probably don't want to use glue, I would turn to confirmat screws if your substrate is all MDF.

If you've never tried them, they realy work well in MDF and particleboard where normal screws don't do so well.

I haven't seen them shorter than 2", but it sounds like this would be alright for your project.

That being said, if you elect to go with your plywood solution, I think that your application would work just fine if you want to use standard screws.


 
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Larry Root

 
Subject : RE: Substrate ll
Posted : 2006-01-31 6:46 AM
Post #32769 - In reply to #32764
Dave,

I'm assuming 64#/5x5 sheet for baltic birch and 100#/4x8 sheet for MDF. If your round table is 4 foot in diameter, the BB cored top would only weigh about 7 pounds less than the MDF. You might want to weigh (pun intended) strength and screwholding ability more than weight in your selection unless weight is somehow critical. How much strength does your design require?

Baltic Birch is pretty stable. But, if I were to laminate two sheets, I'd align the surface plys rather than placing them at 90 degrees. That way, the glued (inside) surfaces would form a parallel core and you'd have a panel with the effect of an odd number of plys with the two (final) surface veneers parallel. (Look at 4 ply fir plywood.) Laying the panels at 90 degrees would yield a panel with an even number of plys with the surface plys at 90 degrees. For a 1 1/2 BB panel, I *doubt* it would ever make a difference, but with other sheet goods or with thinner panels it might. Why take the chance?

Very respectfully,
Larry




 
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Jeff Patrick


Joined: 2004-04-15
Location: Bainbridge Island, WA

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Subject : RE: Substrate ll
Posted : 2006-01-31 1:36 PM
Post #32771 - In reply to #32764
As Larry explained, I too would align the two layers of baltic birch to give an odd number of plys. We have done this in my shop a number of times for stair treads. And although these projects are not too old, there has been no problem with warpage or de-lamination. Personally, the primary advantage of using the ply core is I just hate (!!!) working with mdf and will avoid it whenever possible. This would be one of those times for me. Baltic birch is great to work with, and tho it sometimes comes with a bit of a bow to it, that is completely gone after laminating to another sheet.


 
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Dave Shaw

Posts: 37

Joined: 2005-11-06
Location: Arizona

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Subject : RE: Substrate ll
Posted : 2006-02-01 10:31 AM
Post #32776 - In reply to #32771
Thank you all for your valuable inputs.

The screws going into the top attach the top to the pedestal opening mechanisim which is attached by 8 screws on each half of the top. My concern is that when people move the table they will pick it up by the top edges and the screws will have to support the weight of the bottom. I don't want them to pull out. The bottom probably doesn't weigh more than 30 pounds so maybe I'm worrying about nothing.

I'll need to take some measurements on the top and top support to see if the confirmat screws will work. They look like they would work fine. Thanks for putting me onto them, Brian.

I agree with aligning the BB surface layers parallel. That is what I will do.
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