[scrimshaw]

I am building a bench seat for a custom application. I would like the seat to have a plywood base and, to keep things simple, have the cushioning part to be made from foam only, no springs.

What kind of foam (or combination of different foam) should I use for comfort, and how many inches thick should it be?

Also from an ergonomic point of view, how deep should the seat be and what angle is best?

Thanks for any suggestions/replies.

[DanTwoLakes]

Don't just use a piece of 3/4" plywood alone, it will make the seat very heavy and stiff. Cut two squares out of the plywood blank, leaving a 4" wide strip down the middle and around the perimeter. Then stretch and staple some 2 1/2 to 3" wide elastic webbing criss-crossed over the openings you cut. That will keep the seat from sitting like a brick. You will need to support the base in the middle. The seat back can be made the same way, only you can get by with 1/2" plywood.

I would use a minimum of 4" foam, and use stiffer foam like 65 to 80 compression which will hold your seat cover better and not break down as quickly. I would also use a higher quality foam, at least 25 or 27. If you want shape to the seats, you will need to build up the foam using pieces of different heights.

A seating area, to be comfortable for adults, should be about 18" deep. The seat should be about 1" higher in front than the back.

[scrimshaw]

Thanks Dan. Can you recommend a good online supplier. We don't have a local store that I know of in the area.

[DanTwoLakes]

This place has the elastic webbing and foam. The webbing is called Elasbelt, and you want the 2" wide stuff that is black with a red stripe down the middle. CLICK HERE

Foam is sold by a 4 digit number. The first two numbers indicate quality. 12 is poor quality and 36 is very good quality.
The second two numbers indicate density, or firmness. 20 is very soft and 80 is very firm. So what you are looking for is something like 4" 2565 or 2580 for the seat. The back foam doesn't need to be as good or as firm, so it can be 2045. It won't be cheap, so be prepared for some sticker shock.

If you have trouble finding foam, PM me.

[OneMoreTime]

Dan is the expert here on the construction but i will suggest a 15 degree layback to the seat for the backrest and I think a fellow could use say a 2" foam on the backrest..seems to me that should work fine..

Sam

[DanTwoLakes]

Sam is right, the seat back should also have a slight pitch to it. I neglected to mention that.
The 2" foam idea is a good suggestion also. The top of the seat will look too narrow and out of proportion to the seat bottom, but the way to get around that would be to build up the perimeter edges of the plywood by attaching a 1 1/2" to 2" piece of wood to act as a shelf both on the top and bottom. The two ends of the seat back should probably have that also to give the entire seat back some depth. An extra piece down the center from top to bottom would also be a good idea from a stability standpoint.

[scrimshaw]

Thanks again for the help Dan. I am concentrating on building the seat for now so will continue to look for foam online as I have plenty of time before I start the upholstery. I guess the foam is going to cost about 3 to 4 hundred does that sound right?

Originally Posted by OneMoreTime

Dan is the expert here on the construction but i will suggest a 15 degree layback to the seat for the backrest and I think a fellow could use say a 2" foam on the backrest..seems to me that should work fine..

Sam

I am assuming that you mean a 15 degree layback from a perpindicular up from the seat which will mean a 105 degree total angle with the seat. I haven't got room for that and will just manage a 7 or 8 degree layback. I hope this is going to suffice, although I have a few more details to work out as the back of the seat needs to be easily removable as it is my only way to get into the trunk. Thanks and will put some pictures up when I have time.

[DanTwoLakes]

No, your foam should not be more than $200.00. Any layback will be better than none.

[scrimshaw]

One thing I am having a problem with is estimating the final ride height. I know what height I want to be at but without having the foam I don't know at what height to place the plywood base. How much lower do I need to adjust the base to allow for the thickness of foam?

Once again thanks for taking the time to answer my questions.

[DanTwoLakes]

It only needs to be 4" lower.

[scrimshaw]

OK I have lots more questions and now I am finding out just how little I know about this subject and how much there is to find out.

First how should the two main parts of the seat, i.e. the seat cushion and the back cushion come together. I am thinking the seat cushion should go all the way back to the bulkhead then the back cushion sits on top is this correct, or should the seat back come all the way down to the seat base and the seat cushion butt up against it? (Hope this is making sense)

Also how is the foam fixed to the plywood base is it simply glued on with a contact adhesive?

I would like to have some shape to the foam, e.g. an overhang at the front with a little thickness at the very front of the seat and a simple lumbar support on the seat back. Should I be thinking of this now or can I just add that in later when I upholster the seat?

Thanks again for all the help, I have looked through the tutorials and previous threads but can't seem to find anything on this.

[DanTwoLakes]

Generally, the seat back is attached in place and then the seat bottom is put in and butts up to it. You will have to figure out right now how the seat bottom will be attached. Generally, you make a framework the correct height, leave the framework open in the front, reach in and screw the seat bottom in place, and then attach a panel across the front of the framework. I would make the framework out of angle iron. Then all you have to do is drill holes for whatever screws you will be attaching the seat with, and for whatever clips will hold the panel in place.

How are you going to make the seat? Normally, you can add extra foam for shape as you go along.

The foam is glued onto the frame with contact adhesive or foam to foam glue, and the extra foam is added the same way. Make sure you do all your gluing ahead of time so you don't get anything on the seat covers while you're assembling them.

[OneMoreTime]

I can see letting the foam overhang the edge of the seat portion but if one wants some edge thickness would it not be easier to place some foam in the edge of the seat cover and sew it in?? Also do that for the lumbar support..?? Just asking as I may need to do this before I am done with my project..

Sam

[DanTwoLakes]

It depends on how he wants to do the seat cover. If he wants to have separations with different levels, he may need to add wires and sew in listings. If it's going to be a simple pull over cover, it wouldn't need anything else if the raised areas are not too dramatic. I would use sew foam under the top of the seat one way or another. These pics are of seats that are simple pull over types, but they are sewed to sew foam.

[DanTwoLakes]

No, DO NOT use the clips. Those clips are intended to be closed on the ends of sections of the webbing and then stretched and inserted into grooves in finished hardwood furniture frames. ( a lot of Scandinavian furniture uses this method, only the Pirelli webbing used is rubber ) If you try to do that with a piece of plywood, it will fail. All you have to do is staple the webbing at one end, stretch the webbing across the openings in the plywood and staple it down at the other end. Attach it in a criss-cross pattern, weaving the webbing under and over to interlock it. It only has to be stapled on the top of the plywood, it doesn't have to be pulled underneath. For your openings, you only need 3 pieces of webbing top to bottom and three pieces side to side for each opening. Find a pneumatic stapler to staple it down, and use at least 1/2" staples.