Step 4: Loft Bed: cross members and rail

Picture of Loft Bed: cross members and rail
by now your frame and legs are attached - you can turn it upright and start cross member placement.

cut four 41 inch boards and notch them as done previously for the frame. (there is some overlap in this instructable - hopefully you'll read the whole thing through and realize you can compress some steps). these will hold the legs together and the notches are for the long cross members.

cut two 74 inch boards and notch them as well. these long cross members will be attached using bolts.

cross member placement:
using a jig is important in this step. grab some scrap lumber and cut it to about 18 to 20 inches or so. mine ended up being 19 inches, and upon reflection i would have been happier if i had put more thought into the spacing, but at least with a jig it is consistent. 

start with the 41 inch cross members that are notched. hold the jig in place along the inside of one of the head legs pressed upwards against the bottom of the frame and press the cross member against the other end of the jig and clamp the cross member in place. do this for the other end and repeat your measurements with the jig to be sure it is precise. with the 41inch cross member clamped in place, screw it to the legs - see pic - i used 4 screws as shown. remember to use a pilot hole - it reduces splitting. repeat on the two foot legs. now use the jig to repeat for the lower cross members - pressing the jig against the bottom edge of the mid-cross members. make sure the cross members are all the same orientation - that is, the notches should all be facing the same way. i choose "notch down".

a note on jigs: a jig is just a measuring device, and in the case above, it's simply a stick cut to the exact length i want to measure. jigs are useful because they produce consistent results, and your work won't look crooked and rickety.

now that the 41 inch cross members are in place, get out the long 74 inch cross members, turn these over so the notches fit (in my case, the long cross members need to be "notch up") and wedge them into the notches on the small cross members and clamp them. use a wood chisel to shape the notches if they don't fit. after they're clamped in place, then drill 1/4 inch holes for the bolts. i put 2 bolts on each end of the long board - for a total of 8 bolts. why bolts? because they're removable and i can't shove a completely put together loft bed through the doorway, so i need it to be modular.

why are the long ones "notch up"? my logic is this: due to leverage it would take less force to crack a long board than a short one, so i wanted to put the notches on the long boards "inside" the force - this is the same concept used when they make old fashioned long bows (you know: bow & arrow) - they shave & work the wood on the inside of the bow, leaving the wood uncut along the outside - it keeps the bow from splitting.

i could have put a ladder at both ends to make the bed more symmetrical and reversible but i was running out of wood and, frankly, feeling kinda lazy... cut 2 rungs to a length of 41 inches - no notches needed. and measure the gap to put the rungs in the middle of the space. i made a jig for this too. screw them on - bolts not needed, since the ladder is permanent.

i chose a 4 foot length for the rail - it's a round number and during mock up, it seemed to be the right size. i wanted the rail to be removable so the bed can be made easily and etc. so here is how i did it:
the width of the cross board of the rail is 5.5 inches (a 2x6) and based on the height of the mattress i needed it 6.75 inches above the frame, so i cut two 2x6's to a length of 6.75 inches and set them aside. i cut 4 2x6's to a length of 16 inches and sanded them and beveled them. i laid the 4ft cross rail sitting upright along one edge and clamped it to the table and made a 3-board sandwich as noted in the pic and screwed everything together - leaving a gap where the rail will be wedged onto the frame.

there you have it!
please leave a comment, and be sure to rate this instructable (on the right side of the screen) so i can improve it if necessary.