4mm or 5mm for 1/2 ply?

[Kevin Johnson]

Hi,

I have a 2 part question.

1.  I just got a contract to build some storage units for a warehouse .  As part  of the design, I want to route a groove down the middle of a two vertical 2x4's and slip a 2x2 1/2" plywood panel in between them.  However to conserve material I want put dominoes on the edge of the ply and slip the dominoes into the groove.  So my question is, would you use 4mm or 5mm dominoes for this application?  I am inclined to use 5mm because I have a million of them, but I don't want to compromise the integrity of the panel.

2.  What type of bit would you use.  I see that Festool makes a 4mm and 5mm straight bit, but I am nervous about using a straight bit because I would probably have to take at least 2 passes to prevent breakage of the bit.  The other alternative is to find a slot cutter that is slightly larger than the domino. The problem I see with that is that the depth of cut might be to great to get to the middle of a 2x4. 

Any comments?

Thanks

 

[srzsrz]

I was having a little trouble understanding why you would go to all this trouble to save such a small amount of presumably construction grade plywood. In my experience (mostly derived from doing software work, not woodworking, but bear with me), it is usually good when giving advice to know the actual underlying problem a person has, not just the way in which they have so far been trying to fix it, so it might be good to spill a little bit of digital ink over this.

The only reason I could think of you'd be concerned about using up some extra plywood that would end up hidden inside your grooves is if the spacing between your 2x4s must for some reason be exactly 2' inside-to-inside (not on center!), and you are cutting the panels out of 4'x8' sheets, meaning that if you were to make them 25"x24" instead of 24"x24" you would get only 6 out of a sheet instead of 8. That way, even though initially it seems like you're only wasting a little, because of the size of the stock you're using, you're wasting more than that. Is that indeed the case, or am I just making stuff up?

 

[ccarrolladams]

Only use 4mm Dominoes with 1/2" (12mm) plywood. In theory it is possible to make a 5mm mortice in 1/2" plywood end=grain with a Domino, but the minimum depth of mortice in the face of the plywood with a 5mm bit blows though the plywood.

Dominoes have an infinite shelf life. In my experience the cost of the Dominoes plus labor for the project you describe makes no sense, but do what you want.

 

[semenza]

While I think it would be better, far faster, and easier to just slip the plywood into the groove, I am guessing that you will end up with a stack of partial sheets that will not be wide enough to use.  So you'd be looking at buying twice as much plywood as you need for the job?

Any way you could alter the sizing of some part to make it work?  Shallower groove? 

Thicker 2 x 4  ;D    Although  .... maybe a layer of plywood attached to the 2 x 4 to  in fact make it thicker would do it?

And , especially on construction grade plywood , go with the 4mm dominos. Most of that has very few plies.

Seth

 

[Kev]

I'm inclined to ask what these shelves are going to support ?? My first concern would be use and when you say "warehouse" I'm guessing probably not a few cushions!

With a better idea of the application you're likely to get better informed responses.

If what I'm visualising from your description is accurate, the result will be very fragile regardless of 4 or 5 mm dominoes ... and to points made, you should generally observe the 1/3 ratio rule with tenons.

I personally like shelves to sit on pins or some form of rail, with the weight bearing shelf edges retaining all of the material's integrity.

Sorry if I'm misunderstanding the design.

 

[semenza]

From what I gather the 1/2  ply and  2x4  portion is for uprights.

Seth

 

[Kevin Johnson]

I tried to get a reply in here last night, but was too sleepy. :-\

I am to get 2 sheets out of a 4x8 sheet, but maximize the width of the shelves.  That is why I did not want to house the sheet in the groove.    The company does interior staging to sell houses.  The shelves will store their artwork.  They wanted the shelves to be open on both sides and 24" deep.  I am having trouble attaching the drawing, but will try to get it attached later.

 

[Julian Tracy]

I wouldn't go to any trouble just to save 1/2"-1" of space for a general storage requirement.  Plus, placing the plywood directly in the groove is stronger, faster and easier.  They'll adjust to whatever end width you come up with.

JT