I recently moved into a smaller apartment, downgrading from a 2 bedroom to a 1 bedroom. In order to make the most of the space, I decided to build a loft bed with a trundle for nights when my son stays with me. I went through some design options in sketchup before settling on a final design.
Step 1: Preplanning
First step was to look up standard bed sizes for a twin and full mattress as a basis, then confirm the sizes of the mattresses I'm working with. A standard twin is 38" x 75" and a standard full is 53" x 75". I verified this on my mattresses (though getting the length and width of a mattress with a tape measure is a best guess scenario), then took a measurement on the heights. I found my mattresses to be thicker than average, but decided that 9.5" would give me sufficient clearance. I picked out casters that I wanted to use and took actual measurements from those and determined that the are 4 1/16" tall (Here are the casters I used, but pick out ones that will suit you). I wanted the bottom of the trundle to have at least 1/2" ground clearance and the top of the bed a generous inch to account for bedding, at least. I used sketchup to first construct the trundle based on a simple box design. 4 sides, 2 cleats attached to the sides, slats going across the cleats to support the mattress, and six casters attached to the slats to allow the trundle to slide out as needed. I determined the position of the cleats by starting with a standard board for the side, lifting it 1/2" off the ground, then positioning my casters at floor level and working backward to slat and finally cleat. Once the trundle was constructed, I determined my leg positioning. I wanted wider legs, but didn't want the bed to be substantially longer than the mattress so I compromised with narrower legs on the trundle side and wider legs in back. I made the measurements tight, only about 1/2" of space to either side for the trundle to clear the legs.
My long rails will butt up to the legs and be secured with bed bolts from Lee Valley, so they only have to be exactly as long as the space in between the legs. The cross bars on each end, however, I am going to join using a drawbore technique, so those boards will get a tenon that will go into a mortise in each leg.
The legs will be 1 1/2" square on the front, and 1 1/2" x 3" on the back, so I decided a 1" tenon would give me sufficient tenon to drawbore and I'd be able to locate the pins at the halfway point of the leg, for a nice symmetric feel. Therefore I added 2 inches to each span between the legs for a total length of 56" for each end board (EDIT: While this is what I did, my bed came out slightly too wide. I thought I'd be able to put a box spring directly on the cleats, but it fell through, and I'm thinking I could have made it narrower and been fine. I'd probably go with a tighter tolerance if I had to do it again, maybe 54.5" or something closer to the actual width of the bed). The rails are 2 different lengths because of the different legs. The front is 77", the rear is 74". The cleats stretch from end board to end board and so are of equal length, 77". I decided to add a center support for added security, and it will also be 77" long. I want to position my slats no more than 1 1/2" apart. Because of what is available at my local big box homestore, I'm going to use 1" x 6" boards of 8' length, so one board will give me 1 upper bed slat and 1 lower bed slat. The upper bed slats will be 54" and the lower bed will be 38". A little math on the 75" of space (remembering that 6" boards are really 5.5" wide), gives me 11 boards spaced 1.45" apart. I probably won't be precise with that, but just eye ball it in the build.
See the sketchup file for full details. You can see I wasn't precise with the slat placement for the design.
Also, I made a cut list and a purchase list, based on materials and prices in my area, ymmv. Lengths and thicknesses are nominal.
Normally, I work in hardwoods and primarily use hand tools. For this project, I decided to go with construction timber and power tools. Overall, the joints are going to be simple, with the exception of the drawbore technique I will use to make the ends, but you'll see drawbore isn't so hard. This is the same construction I used on my traditional workbench, so I think it will turn out well.
Step 2: Wood Prep
I start all woodworking projects by getting all my lumber ready for joinery. Since I'm using construction lumber on this, I won't have to worry about surfacing and that sort of thing, so this is just an exercise is sawing. The whitewood they sell at the big box stores is very brittle, and my handsaws turn it into splinters, so I'm using a fine cut circular saw blade to cut the wood to length. I basically just go down the cut list and measure boards with a tape measure, then draw a line with my square, then use the square to guide the circ saw. Easy peasy. Before I cut, I like to go back through my plans and make sure I didn't change anything that would affect lengths. I already did this in my attached cut list, so you should be golden. Leaving pieces slightly long is better than slightly short, because you can remove wood a lot easier than you can add it back on.
I like to take my time with the circ saw and ensure as clean a cut as I can get. Also, take time to inspect the boards after you measure to look for potentially trumblesome knots. Try to cut in such a way that there are on knots on the ends of any board, as this can make joinery troublesome and can seriously weaken the joints.
Once the boards are cut, double check the lengths to make sure everything is correct and that board ends, especially on the long rails, are square. If not, touch them up with a block or jack plane to get them just right.
Step 3: The Trundle Frame
Start the trundle choosing inner faces for each board. You want the nicest faces showing, and a little inward bow will be better than a little outward bow, though the slats should correct both. The ends of the trundle will be screwed onto the sides, so you can attach the cleats to the inside faces of the sides along the entire length. If the cleats are slightly too long, trim them flush with the ends using a block plane. The placement is 1 3/16" up from the bottom for the bottom edge of the cleat. You can use one of your casters to verify the placement. The top edge of the caster should align with the top edge of the cleat. Remember to leave yourself 1/2" or so of clearance for the wheel below the bottom edge of the side. It's less important that the measurement be exact than that you have sufficient clearance for your wheel and that the cleats are a uniform distance from the bottom. Set an adjustable square the desired distance.
I drilled clearance holes for your screws about every 6 inches down the length of the cleat (you don't have to countersink these holes, as screws will easily drive into the pine and countersink themselves). Apply some wood glue. You want to use 2" screws if you are following my plan. Any longer and you risk breaking through the side board. On one end of the the cleat, but the board up to your adjustable square blade and screw it into place. Repeat on the other end, then down the length using the same procedure. You should have a cleat perfectly spaced from the bottom edge. Repeat with the other side. Now you want to predrill holes for the end boards. I used long screws, since glue won't hold well on the endgrain of the sides. You could also do pocket screws in this application. You might want to predrill your ends with small pilot holes to keep the screws from straying, but the screws should bore fine into the endgrain without them.
The final step is to drill 2 holes about 3/4" in from each end of the slats to secure them to the cleat. I am lucky enough to have a drill press to speed this up. I clamped a board to my table as a fence to make the distance from the end equal then just eyeballed the placement. I went ahead and did the main bed slats too, while I was at it.
I assembled the trundle in my room so that I could transport everything. I cleared a space, attached the ends to the sides with 3 1/2" screws, then attached the casters to 4 different support boards, as shown in the plans, and screwed the first two of those to the cleats (the ones one the ends) to lift the bed up. Then I laid out the other boards. I knew approximately where I wanted the other two castered boards to go, so then I just filled in the space with the other boards. I didn't bother measuring, because exactness is not required. Then I just attached all the support boards with 1 1/4" screws. I did test the mattress fit and laid on it to make sure it would support my body weight. Everything was perfect. If yours is a little warped, the weight of tho mattress should fix that. If not, you may need to redrill your holes or you may have a board that was very warped to start with and may just need to replace it.
Step 4: Finishing the Trundle
I showed the trundle assembled in the last step, but I finished it before assembly.
Thing is, once you get everything assembled, finishing the bed will actually be a lot harder to finish. If you plan to stain the wood, you will be better off doing so before everything goes together. Bear in mind that you only really need to stain wood that will show, but with pine it's a good idea to finish both sides the same so that you don't get wood movement problems (Note, despite my best efforts, I did get a twist on one of the rails, so it goes). The parts that need to be stained are: the trundle sides and ends, the bed end boards and rails, and the legs. The slats and other support wood doesn't need to be stained since no one will see it.
I used a dye that comes in a powered form and you add water. I've found this dye is very strong and I think I have it at about half the recommended strength. Of course, once I finished the trundle, I realized I wasn't going to have enough dye for the bed, so I opted for a water-based stain from the hardware store. The colors don't match at all, so I should have just bought more dye, but I wanted to try a product I'd never tried before. That said, I doubt I will do the water-based stain again. I didn't like it much.
Step 5: Bed Ends
I put together the ends of the main bed first, because joining the rails is the easy part. For the legs, I ripped them out of some 2 by material and planed them square, then added a simple chamfer with my block plane on the tops to both eliminate painful corners and to add just a touch of decoration. To do this, I set a marking gauge to 1/2" and mark the two inner faces of the front and rear legs, then chamfer down about half that or so and carry that around. Precision isn't necessary, just don't plane all the way down to the 1/2" mark and certainly no lower.
For the crossbeams, I set a marking gauge to 1" and mark in 1" from the end of each beam, since this is the length of the tenon. I decided on a sturdy tenon, so I beefed it up to 3/4" instead of the 1/2" shown in the sketchup. This also made it easy to find scrap to fill the mortise when I was drilling. To do this, I set my marking gauge to 3/8" and marked from the face to the end grain. The top and bottom shoulders I made the same for convenience. That gives you 4 cuts on the each end, defining your tenon. Then I used my gauge as a guide set the depth on my crosscut saw and put a piece of tape on the saw as a visual fence. I cut down the front and back face to that depth, then top and bottom, then chiseled from the front back to my mark (start no more than halfway to make sure your grain isn't running in, if it is you'll want to pare across the grain to keep your tenon in tact). Once the faces of the tenon are revealed, it's a simple tap on each end with the chisel to get the top and bottom shoulders free.
Now I set the boards with the shoulders butting up to the leg and the tenon laying on the face that will get mortised. I mark the top and bottom of the tenon, then, using a mortising gauge, measure my acutal tenon and mark that on the leg. Then I number the tenon and just above where the mortise will be. This ensures that each mortise is custom fit to the tenon, and that I don't end up having to make any last minute adjustments.
For the mortises, I chopped into the mortise about 1/4" or so with the 3/4" chisel to guide my drill and eye, then drilled down a little deeper than 1" and cleaned them up with a chisel. Then I test fit the corresponding tenon until I get a good fit (a little loose is okay)
Before final joining, I did one last check on my crossbeams, checking that the distance between tenons perfectly matches for the two pieces on each end (ideally all four should be the same or very close). The total length is less important than the distance shoulder to shoulder. Also double check for shoulder squareness of the shoulder to prevent wracking. Clean up with a sharp chisel or a shoulder plane to get those as precise as possible.
The final part is and old technique called drawboring. I used some scrap to fill the mortise, then drilled two holes, high and low, about halfway back, through each mortise. The narrow front legs got through-holes, but the wider back legs I only drilled about three-quarters of the way through You can drill those through as well, it makes no real difference. I didn't measure or exactly place the holes, just eyeballed it, but you can do whatever you like.
Insert the corresponding tenon into the hole and push the drill bit in to mark the tenon, for each mortise and tenon. When you pull the tenon out, it will have two dimples corresponding to the holes. You want to drill through the tenon, but here's the trick: you want to offset the holes in the tenon toward the shoulder just a bit. When you drive the peg through, this will draw the tenon tightly into the mortise. So using that same drill bit, bore through about 1/16" of an inch back from the dimple.
Before joining I went ahead and finished the cross beams and legs. I decided on a reddish color for the legs for contrast with the brown beams and rails. I left the bottoms of the legs unfinished because I didn't want to rub a bunch of stain on my floor while moving this thing around, plus, endgrain has a lot of friction and you want to keep that so your bed doesn't slide around.
Now for joining. For the pegs, I used a 1/4" oak dowel cut longer than I needed, but not too long or you risk snapping them off when driving them. I sharpen one end of each like a pencil to guide the peg through the holes. I happen to have a drawbore pin, which makes this whole operation easier (you can get them online), so I use that to pull the tenon in, then drive the peg into the hole (for the stopped holes, the sound changes distinctly when you bottom out, for the others, I drive them until they come through the other side. Try no to whack these too hard, as it is easy to snap one off.
Once the pegs are in, I used a flush cut saw to saw them off and a block plane to make them flush, then touched up the finish.
Step 6: Attaching Rails
To attach the rails, I used bed bolts, basically a barrel that is tapped to receive a bolt (Here is the link to the bolts I used, though googling "bed bolts" should give you a wide variety of options). I didn't really get any pictures of this step, but basically I set a sliding ruler to the halfway point of each rail, lengthwise, then set a smaller sliding ruler to the halfway point widthwise. I marked the ends of each rail with these two rulers to get the halfway point. Then I marked the ends down from top crossbeam to this point. The idea here is to get the bolt through the midway part of the tenon, not through one of the pegs.
Once the marks are done, I set my legs up and made double sure I was drilling the right face. You want a counterbore on the outside of each leg where the rail attachs to accommodate the head of the bolt. I measured the diameter of the socket I'd use to secure the rails and selected a forstner bit a little bigger than that diameter. Then I counterbored the hole in the leg down to about where the tenon is. The forstner bit leaves a dimple you can use to guide the smaller drill bit. I drilled through the rest of the way with a bit a little bigger than the diameter of my bolts. One hole in each leg (making extra sure you counter bore the correct side), and that's done.
For the rails, first I put the bolt through the leg and measured a distance from where it stuck out to halfway down the threads. I just marked this distance on a scrap stick for convenience. You'll need two of these, one for the wider legs and one for the narrower legs. Then, on the inside face of the rail, I marked about halfway from the end with this stick, then used my sliding ruler to mark the halfway point from the side. Where those two marks crossed, I used a forstner bit marked with tape to drill into the inside face to receive the barrel nuts of my bed bolts, to just the right depth (not all the way through). Then I drilled into the end of the rail to receive the bolt with a brad point bit, making sure that it came through the nut hole right at around the midpoint. It may help to attach the cleats first to ensure that you are drilling into the same face (I didn't do that and ended up with one rail that had nut holes on each face, so I had to drill one through. I also accidentally attached cleat on the back to the wrong face and ended up with the bolt holes showing (but it's the back so you can't really see them anyway. Oh well).
Once the holes were drilled, I tested each to see if my bolts and nuts lined up and would thread in sufficiently. If not, drill some more or use a rasp to get everything aligned. It's also worth checking the fit with the end to make sure that those all line up well.
Step 7: Step 7: Slat Assembly
Again, I had to assemble in my bedroom. So I just assembled the sides to the ends there. You'll have to problem solve for that part depending on your space etc. What I did was lift one end of the rail and tip the end down, then bolted one rail on, then bolted the other end of the rail to the other bed end. Then I used a bolt to prop up the other rail while I bolted the opposite end on, then finally I did the last bolt and went around and tightened them all again.
At this point, I should have added the center rail in my plans, but I totally forgot. So, I screwed in all the slats, just making them roughly equal, with two screws on each end. My plan was to just use my mattress, but haven't been able to offload my box spring yet, so I kept it for now. Somehow I ended up with the space being about 1 1/2" too wide, I had thought I could put the box directly on the cleats, but it didn't work because of this (so double check those plans, maybe, eh?). It's way too tall, but I have someone coming to buy the box soon.
Anyway, a day later I suddenly rememberd the center support beam. I used a kreg pocket screw system to put two screws on each end of the support beam, then took the mattress off and butted the beam up to the slats.The purpose of this beam is to keep the slats from sagging. I screwed it in with two screws. It wasn' flush exactly, but It will be fine.
And that's it! The trundle fits under the bed well with a blanket, even, though there isn't room for the pillow, so making it a little taller would probably work. I've slept on it and it holds up fine. Since the last pic I actually swung it around so that it's back is by the window because that gave me more room in the bedroom, but otherwise I'm happy with how it turned out.
Step 8: Step 8: Mattress Fit and Adjustments
Test fit your mattresses. If you made the beds too narrow, you will have to redo the ends, so hopefully you were careful with your measurements. If the frame is too big, you can pad out the gaps with some foam to keep your mattress in place, but better slightly too big than too small. If the bed rocks you want to trim the two legs that don't knock, or shim one or both of the legs that do. Be careful to ensure you don't trim too much and lose the ability to fit the trundle under the main bed.
Make up the lower bed and check that the clearance is sufficient. If there isn't quite enough space, add some feet to the bottom of each leg of the loft bed. There are lots of choices in the hardware store for feet that slide or don't slide as you see fit, so choose appropriately. These can give you a quarter inch or so more clearance. If that isn't enough, then cut equal thickness pieces of wood from your scraps and attach them to the bottom of the legs with countersunk nails or screws to shim the bed up further.
Step 9: Step 9: Finish?
If you prefinished, you might be done. Perhaps you prefer to spray it down with a coat of lacquer. Mabye you'd like to rag on a coat of danish oil. The finish is entirely up to you. I don't like lacquers and heavy plasticy finishes, but that's just my preference.
Step 10: Step 10: Improvements
One easy way to improve on this design would be to make one end taller and add a headboard. This could be a simple plywood headboard, or a whole bookshelf if you wanted. Another improvement might be to add a third leg right where the trundle ends to give you access to the empty space that is formed behind the trudle. You could add a sliding drawer there or just put plastic tubs in the space or spare bedding. If you try this, post some pictures so we can all see what you did!