Project design assistance please

[Sandking]

Hi all. It's been awhile since I've posted. All my projects the last three years have been geared to rebuilding our home. I'm finally starting to get into more finish work so I can use my woodworking tools again

My wife and I are tired of all the toys in the playroom so I'm designing a built-in cubby storage system. The thought is for now we can slide in canvas storage bins and when it becomes an office I can add doors to the bottoms and have storage/library shelves.

The wall is approx 95' wide with 8' ceilings. I first though to purchase some IKEA bookshelves, mount them to a base and trim everything out with baseboard and crown. The issue is the color won't match what we are painting all our trim with. So I decided I should build something. The last bookcase I made was out of 3/4" birch ply and came out great. For this project I'm trying to keep costs to a minimum so I was thinking of using 3/4" MDF.

My plan will look similar to the picture below. I will construct 5 x 36" wide by 36" high shelving units (two will be stacked on each other). Each unit will contain 2 horizontal shelves and two removable dividers (creating a total of 9 cubbies each unit). The 1/2" vertical cubby dividers should remove all the threat of sag over the 36" span, but when we are ready to use this as a library bookcase we will not use the dividers so the horizontal shelves will have a poplar face frame to make sure there isn't much sag. I think that should future proof the use of the built-in for our needs.

So 2 questions:

1. Does my design thoughts regarding material, support (the dividers and poplar face frames) sound valid. Should I suck it up and build out of plywood instead?

2. How would you go about building the units themselves. I was considering glue and pocketscrews for the 36"x36" frame and then glue the horizontal shelves into a dado.

Am I on the right track here?

[JGrout]

MDF is the correct choice as you are painting the units.

I dislike the very permanent shelf placement. build in adjustable shelving and you can gain more useable space for storage

As for construction rabbets and dadoes and glue would be my first choice my second would be biscuits.

Pocket screws will cause more time covering holes than they are worth...

Joe

[Cooler]

MDF glues well, but I always paint on two coats of glue because so much of it gets soaked up by the MDF.

MDF is HEAVY. So be aware that the sheets and the sections will be HEAVY.

MDF takes paint beautifully. But fill and dress the edges with a shellac based primer. A water based primer will raise the "grain" and look terrible.

If it is properly filled and primed the joints will completely disappear under paint. Any cut or machined surface needs to be coated with a shellac based primer. Don't sand the smooth surfaces. They will take the primer and paint fine.

But depend upon the glue. Fasteners are not very good in MDF. They are good as a replacement for clamps however.

You can use pocket screws. But if you are cutting dados ("grooves" I guess in MDF) and gluing only brads will be required. It should be plenty strong enough.

If you plan on adding doors, then face frames are a good idea. It will be a pain to attach doors directly to the MDF. It also eliminates almost all of the machined surfaces.

I have mounted hardware to the edges of MDF. The only satisfactory method I found was to drill oversized holes for the screws. Leave just enough material that you can drive the screw in with your fingertips. Then fill the hole with SLOW CURING epoxy and screw in the screw. The slow curing epoxy will soak into the pores far better than fast cure. I used this for cafe door hardware and it remained solid for the life of the door.

So:

MDF is cheap
It machines beautifully
It takes paint well
It glues well if you give it enough glue

It is very heavy
Not particularly strong, but your short shelves should do fine
Does not take screws or hardware well--depend on the glue
The later doors will do better when attached to face frames.


Finally mitered edge construction is going to be much faster and stronger than butt edge assembly. When you glue up butt edges you have a .75" glue area. But when you glue up mitered edges the glue area is 1.06" about 30% more glue area.

Here is the process:

1. Cut the board to width (depth of the cube).
2. Cut a groove along the length of the board to accept a rear panel.
3. Cut the board into squares.
4. Miter the edges to be joined.
5. Use packing tape to place the four sides in one long length.
6. Apply glue to all surfaces
7. Insert the back panel in one of the grooves
8. Fold up the cube into its final shape.
9. Tape the final side together and allow the glue to dry.


Cutting the miters is very easy if you follow this process.

1. Make a sacrificial fence.
2. Cut a 1/8" off the edge of the fence 5/8" high
3. Set your blade on a 45 degree angle slightly burying it in the fence.
4. Trim the edges to be joined.

By relieving the fence below the cut you provide plenty of room for the scrap from the 45 degree cut to fall clear. I've made plenty of pieces like this in both MDF and plywood and I have never seen a kickback of any sort. With the 1/8" relief you have plenty of space for the scrap not to bind with the blade. If you are nervous make a pusher board for the final bit of the cut.

This method is faster, stronger and makes a neater looking piece. It requires no fasteners at all. But it is still VERY HEAVY.

[Sandking]

Ok thank both. Looks like MDF will be the material. Great point about adjustable shelving options. The first bookcase I made I installed these I think I should add these instead of a dado and fixed shelf.

[Cooler]

Sandking said:

---

Ok thank both. Looks like MDF will be the material. Great point about adjustable shelving options. The first bookcase I made I installed these I think I should add these instead of a dado and fixed shelf.

---

I've used those. The installation is easier and much neater if you use your dado head to make the grooves in advance. The hardware will then be flush and you don't have to measure to make sure it is perfectly vertical. The shelves end up a bit wider too.

[Sandking]

Cooler said:

---

I've used those. The installation is easier and much neater if you use your dado head to make the grooves in advance. The hardware will then be flush and you don't have to measure to make sure it is perfectly vertical. The shelves end up a bit wider too.

---

Yes that is how I installed them as well.

[Sandking]

Cooler said:

---

MDF glues well, but I always paint on two coats of glue because so much of it gets soaked up by the MDF.

MDF is HEAVY. So be aware that the sheets and the sections will be HEAVY.

MDF takes paint beautifully. But fill and dress the edges with a shellac based primer. A water based primer will raise the "grain" and look terrible.

If it is properly filled and primed the joints will completely disappear under paint. Any cut or machined surface needs to be coated with a shellac based primer. Don't sand the smooth surfaces. They will take the primer and paint fine.

But depend upon the glue. Fasteners are not very good in MDF. They are good as a replacement for clamps however.

You can use pocket screws. But if you are cutting dados ("grooves" I guess in MDF) and gluing only brads will be required. It should be plenty strong enough.

If you plan on adding doors, then face frames are a good idea. It will be a pain to attach doors directly to the MDF. It also eliminates almost all of the machined surfaces.

I have mounted hardware to the edges of MDF. The only satisfactory method I found was to drill oversized holes for the screws. Leave just enough material that you can drive the screw in with your fingertips. Then fill the hole with SLOW CURING epoxy and screw in the screw. The slow curing epoxy will soak into the pores far better than fast cure. I used this for cafe door hardware and it remained solid for the life of the door.

So:

MDF is cheap
It machines beautifully
It takes paint well
It glues well if you give it enough glue

It is very heavy
Not particularly strong, but your short shelves should do fine
Does not take screws or hardware well--depend on the glue
The later doors will do better when attached to face frames.


Finally mitered edge construction is going to be much faster and stronger than butt edge assembly. When you glue up butt edges you have a .75" glue area. But when you glue up mitered edges the glue area is 1.06" about 30% more glue area.

Here is the process:

1. Cut the board to width (depth of the cube).
2. Cut a groove along the length of the board to accept a rear panel.
3. Cut the board into squares.
4. Miter the edges to be joined.
5. Use packing tape to place the four sides in one long length.
6. Apply glue to all surfaces
7. Insert the back panel in one of the grooves
8. Fold up the cube into its final shape.
9. Tape the final side together and allow the glue to dry.


Cutting the miters is very easy if you follow this process.

1. Make a sacrificial fence.
2. Cut a 1/8" off the edge of the fence 5/8" high
3. Set your blade on a 45 degree angle slightly burying it in the fence.
4. Trim the edges to be joined.

By relieving the fence below the cut you provide plenty of room for the scrap from the 45 degree cut to fall clear. I've made plenty of pieces like this in both MDF and plywood and I have never seen a kickback of any sort. With the 1/8" relief you have plenty of space for the scrap not to bind with the blade. If you are nervous make a pusher board for the final bit of the cut.

This method is faster, stronger and makes a neater looking piece. It requires no fasteners at all. But it is still VERY HEAVY.

---

Ok thank you for the detailed assistance. Just a quick question I agree that mitered Assembly would be great if I was making individual cubes but since I'm making a 36" wide case with two horizontal shelves and two removable vertical dividers I'm not sure mitered would carry the weight of the second 36"x36" case on top of it? Just thinking of downward force wouldn't that put pressure in a manner that would want to push the miters apart? I would think a butt joint with the top glued and pocket screwed to the sides would be stronger. Am I not thinking this through correctly? I'm thinking in terms of how you disperse load in construction.

[Cooler]

Sandking said:

---

[blockquote]Cooler said:

---

MDF glues well, but I always paint on two coats of glue because so much of it gets soaked up by the MDF.

MDF is HEAVY. So be aware that the sheets and the sections will be HEAVY.

MDF takes paint beautifully. But fill and dress the edges with a shellac based primer. A water based primer will raise the "grain" and look terrible.

If it is properly filled and primed the joints will completely disappear under paint. Any cut or machined surface needs to be coated with a shellac based primer. Don't sand the smooth surfaces. They will take the primer and paint fine.

But depend upon the glue. Fasteners are not very good in MDF. They are good as a replacement for clamps however.

You can use pocket screws. But if you are cutting dados ("grooves" I guess in MDF) and gluing only brads will be required. It should be plenty strong enough.

If you plan on adding doors, then face frames are a good idea. It will be a pain to attach doors directly to the MDF. It also eliminates almost all of the machined surfaces.

I have mounted hardware to the edges of MDF. The only satisfactory method I found was to drill oversized holes for the screws. Leave just enough material that you can drive the screw in with your fingertips. Then fill the hole with SLOW CURING epoxy and screw in the screw. The slow curing epoxy will soak into the pores far better than fast cure. I used this for cafe door hardware and it remained solid for the life of the door.

So:

MDF is cheap
It machines beautifully
It takes paint well
It glues well if you give it enough glue

It is very heavy
Not particularly strong, but your short shelves should do fine
Does not take screws or hardware well--depend on the glue
The later doors will do better when attached to face frames.


Finally mitered edge construction is going to be much faster and stronger than butt edge assembly. When you glue up butt edges you have a .75" glue area. But when you glue up mitered edges the glue area is 1.06" about 30% more glue area.

Here is the process:

1. Cut the board to width (depth of the cube).
2. Cut a groove along the length of the board to accept a rear panel.
3. Cut the board into squares.
4. Miter the edges to be joined.
5. Use packing tape to place the four sides in one long length.
6. Apply glue to all surfaces
7. Insert the back panel in one of the grooves
8. Fold up the cube into its final shape.
9. Tape the final side together and allow the glue to dry.


Cutting the miters is very easy if you follow this process.

1. Make a sacrificial fence.
2. Cut a 1/8" off the edge of the fence 5/8" high
3. Set your blade on a 45 degree angle slightly burying it in the fence.
4. Trim the edges to be joined.

By relieving the fence below the cut you provide plenty of room for the scrap from the 45 degree cut to fall clear. I've made plenty of pieces like this in both MDF and plywood and I have never seen a kickback of any sort. With the 1/8" relief you have plenty of space for the scrap not to bind with the blade. If you are nervous make a pusher board for the final bit of the cut.

This method is faster, stronger and makes a neater looking piece. It requires no fasteners at all. But it is still VERY HEAVY.

---

Ok thank you for the detailed assistance. Just a quick question I agree that mitered Assembly would be great if I was making individual cubes but since I'm making a 36" wide case with two horizontal shelves and two removable vertical dividers I'm not sure mitered would carry the weight of the second 36"x36" case on top of it? Just thinking of downward force wouldn't that put pressure in a manner that would want to push the miters apart? I would think a butt joint with the top glued and pocket screwed to the sides would be stronger. Am I not thinking this through correctly? I'm thinking in terms of how you disperse load in construction.

---

[/blockquote]

If you use a 3/8" back panel set in grooves and you add a face frame to the bottom shelf I think it is OK. I looked up on the SAGULATOR a 3/4" x 16" MDF shelf with a front strip of 3/4 x 1.5" and a 36" span and with 100 pounds of load it shows a sag of 0.07". That does not take into account the added strength the 3/8" thick back panel will lend.

I think face frames for the bottom cabinets are a good idea. The will allow easier attachment of doors later on as well as adding strength.

That said maybe you should build one carcass and see if it can carry sufficient load.

I am not an engineer so you will have to decide on your own.

But I suspect that properly glued the joint will structurally "disappear" and the joint will be homogeneous, that is as though formed from one piece.

Keep in mind that machined edges of MDF absorb lots of glue. I first paint both surfaces with glue and then go back and paint them with a second coat before it dries and then join the pieces. That way I know that the joint will not be glue-starved.

But test with one bottom cabinet to see if it is strong enough. And wear a dust mask when sawing the stuff.

[bennybmn]

I've become a real fan of cubbie/basket storage over the years, so I like your approach. I've also used those shelving brackets before, and I wish I inset them! I'm sure I've asked you before where on the Island you are, but I'm in Holbrook if you ever need a hand.

[Cooler]

bennybmn said:

---

I've become a real fan of cubbie/basket storage over the years, so I like your approach. I've also used those shelving brackets before, and I wish I inset them! I'm sure I've asked you before where on the Island you are, but I'm in Holbrook if you ever need a hand.

---

The other advantage of the mitered joint approach is that you can cut the grooves in the MDF (are they dados if you are doing them in MDF?) and they will not show as gaps on the edges like it could on a butt joint.