I would like to start this post by thanking instructables for featuring my previous post. Hence I am still here and I am writing another instructable.
In this instructable, I will be teaching you how, incredibly cheaply, you can make a leg for a wooden table that is incredibly sturdy, without the use of any wooden support features and/or metal brackets. The wood needed is only that for the leg and that for the table top, but nothing else!
The concept demonstrated in this instructable is inspired by a type of a fastener called a "barrel nut", which is often used by furniture makers (such as the furniture made by IKEA). This concept is taken to its limits in this instructable.
Assuming you got your 4 in x 4 in posts for the legs, and any wood of your choice for the table top, then this instructable requires merely the following:
(a) A 1/2'' GI pipe nipple for each leg you intend to attach to the table top
(b) An M12 bolt of your choice for each leg you intend to attach to the table top
(c) Only two 1/2'' GI pipe caps, which you will use during the making of each leg but do not need to remain attached to the leg
The cost of all the above combined in Dubai (where I currently live) is 30AED (for a table with four legs!) which is equivalent to $8 US.
Beside the enormous savings and the rigidity, this construction method works very well even with low-quality wooden posts with cracks running along them. The only disadvantage I can think of is the fact that the table top strength becomes the weakest link in the design (more on that in the last step of the instructable, when we stress test the leg made).
So let's begin!
Step 1: Clamp and Mark
The first step is clamping your choice of table top onto the leg's wooden post and following your choice of the M12 bolt, mark the end of the usable thread. Let's call this "the first line".
Now grab your caliper and measure the outer diameter of the GI nipple you purchased for this build, doing so, tighten the locking screw on top of the caliper to prevent the measurement from drifting as you remove the nipple.
The reason for doing so is that we are going to use the caliper's internal jaws to offset "the first line" in the direction pointing towards the table top, resulting in what we choose to call "the second line".
The two lines are parallel, and they represent the deeper and the shallower side of the GI nipple as it passes through the leg's wooden post. From the two lines, it is easy to discern the center for drilling. (in the next step)
Step 2: Drill the GI Nipple's Support Hole
Before drilling, it is also advisable to use a center punch to mark the exact position where the hole is to be drilled.
Once punched, use a 22mm spade drill bit, drilling from below (very important!) and penetrating the wooden post throughout.
Take it easy as you drill, try to go up as straightly as possible.
Once finished drilling, it is the time to drill the bolt's mounting hole. (in the next step)
Step 3: Drill the Bolt's Mounting Hole
Perpendicular to the previous hole, and centered within the leg's face meeting with the table top, we drill a 12mm hole to pass the mounting bolt.
Doing so, it is incredibly important to drill past the cavity created by the previous drilling operation (check the last photo attached to this step).
Now that both of the perpendicular mounting and support holes are created, it is the time to insert the GI nipple which would act as a giant barrel nut. (in the next step)
Step 4: Insert the GI Nipple
Doing so, you need to distribute the thread equally between the right and the left side, by skillfully loosening and tightening the right and left GI caps.
Now that the GI nipple is in place, it is the time to drill it, which is by far the most time consuming part of this build (takes 5-10 minutes, and is the subject of the next step).
[Note that in the video attached to this step, the hole for the bolt is not made, in your case you should have that hole already made so do not doubt yourself]
Step 5: Drill and Tap the GI Nipple
Congratulations! You're not very far from finishing this build, however, this is the time where you need to take a break as it is the most critical, and arguably the step that requires the maximum amount of attention and care.
Before we start, you need to mount your leg post in an upright position, preferably in a vice. It needs to be mounted pretty sturdily as both the drilling and the tapping will happen in this position. Take your time and make sure it is mounted well.
Before you drill, and since the drilling will occur on the round surface of the GI pipe, it is essential to center punch the drilling center using a center punch, or using a center drill first.
Once that is done, get your 10mm drilling bit and tighten it in the chuck of your corded drill.
For the drilling, the best practice is to lubricate the drill bit (not the hole), applying pressure straight down for a maximum of 20 seconds at a time. After each 20-second round of drilling, wipe the drill bit with a cloth and apply a fresh dash of oil (very important!).
As you repeat the above, please be conscious of the progress of your drilling by looking through the mounting hole.
Once both of the upper wall and the lower wall of the GI nipple have been penetrating with the 10mm drill bit, it is the time to thread both holes using an M12 hand tap. The good thing is, all this can be done with the GI nipple in place, in the upright mounted position of the post.
Beware that as you tap, the tap will show a lot of resistance (a sign of tapping the upper wall), then no resistance, then a lot of resistance again (a sign of reaching and tapping the lower wall). Work your way carefully until you have threaded both the upper and the lower wall of the GI pipe, and the tap is showing no resistance for the second time (this happens as the manual tap's handle get's closer and closer to the post).
Once that is accomplished, you have successfully passed the hardest part of this build. All is left is to attach the leg's post to the table top, in the next step.
Step 6: Drill the Table Top and Attach the Leg
Wow, you've been a long way! The good news is that you are 3 minutes away from seeing your post attached to the table top, all is needed is to drill the table top at the point where you want to attach the leg, then using your M12 bolt to join the table top with the fabricated leg's post.
Doing so, and in case you wanted the M12 bolt to be flushed with the surface of the table, then bare in mind that tightening the bolt will compress the wood, hence bore the hole but while leaving at least 1mm of the bolt protruding. This way, when you tighten the bolt to full strength, it will be flushed with the table's surface.
Immediately after assembly, the strength of this joint should be evident. However, if you need a proof of how strong it is, please feel free to move to the next (and the final) step of this instructable, where we would be trying our best to destroy it.
Step 7: Test It!
It is important to note that if it wasn't for the countersunk feature of the socket cap bolt, this leg would have been much stronger. In fact, letting the bolt sit on the table top, with a thick washer would have made it indestructible, but while compromising looks.
As we reach the end of this instructable, please feel free to improve on our work and/or to throw in your ideas and suggestions. We believe this is an excellent and a truly viable build technique which we wanted to share with the community. Thank you!