Edgejoining pine 1 x 7

[Kevin Tunis]

I started a new project a wall mount bookcase. Using 1 x 8 pine - actual size ¾ x 7 ¼. I am edgejoining these together. Making sure the pieces are flat across the edge I used the 1 ¼  inch coarse screw. With the 1 ¼ screws they seem to not get into the other board deep enough and the boards were not tight. Also they were striping very easily. I then tried the 1 ½ screws and some of these came through the board and protruded on the surface. I have had this problem before, so I thought I would bring it up here to get some ideas as to why this happens and how can I make this work

[Jay Boutwell]

Hi Kevin,  Happy 4th.  In answer to your post the 1 1/2 inch screws are actually too long to use if you are boring the pocket hole according to the specifications on the drilling guidelines.  Since pine is one of the softest woods common in woodworking it has little resistance to screw tear out.  Some of the pines are better quality than others and will therefore allow you to be more aggressive on the tightening of the screws.

Providing that you have bored your pocket holes correctly the 3/4 inch pine should require the 1 1/4 inch screw.

There are two reasons screws protrude out the back and that is either being too long for the material thickness or the pocket hole is being drilled to deep.  Since we know that the 1 1/4 inch screw is correct for the 3/4 inch material this is what we should use.  To verify that you are drilling correctly the screw should protrude out the bottom of the bored piece at or near dead center. 

If I was to start the project that your are indicating I would first edge joint the material by running it across a jointer or a highly accurate table saw.  I would then check the edges to be sure that they are flat and true both in the "long" direction and also across the edge.  Some times when we edge joint we do not get the edge at a perfect 90 degree.  Also some times when we cut an edge on a piece of lumber it will immediately begin to change and bow.  This is often the case in new lumber that has not been properly dried and it has what is called a "case hardened"  just like in metal where the outer surface is tempered to be hard on the outer surface.

In the case hardening of wood, it is due to the rapid drying of the outer surface at a faster rate than the inside.  As it dries it forms a hardened surface of which now has locked in the moisture remaining in the inter core of the wood along with all the stress factors that it has.  The drying will induce even more stress factors into the wood.  Now when we cut it, we cut through that case hardened surface and the moisture again begins to attempt to leave the material as well as it releases its stress.  The stress being released now causes the wood to move in unpredictable directions and the results is things like twists, bows, cupped lumber and even cracks.  How rapidly this occurs depends on the humidity of the surrounding environment (moisture content of the air) and the amount of  moisture and stress factors that were trapped inside the wood when it was dried.  

The method of how it was dried makes a big difference in the quality of material we ultimately use in our projects.  If it was air dried, the speed of how fast it will dry will depend on the climate it was in while drying, therefore  will depend on how much moisture was trapped inside, and the amount of stress that is inside.  If it was stickered (stacked where equal air circulation was allowed) and how much heat, cold and humidity was it exposed to and the length of time since it was allowed to dry effects the final lumber quality.  The same with kiln dried lumber, how fast the drying was done and how much heat it was exposed to.

Have you ever seen or cut a piece of lumber on a table saw and have one end or side try to go into the next county?  This is the stress that is in the lumber.  It may release quickly or the release may be slow.  This is why I always cut my lumber for a project and allow it to set for awhile before I begin using it.  This is my rule of thumb especially critical when I go to make cabinet doors or furniture.  Build it too quickly and it will become something that you may have a hard time believing that you built it.  This is another reason my preference if to buy rough cut lumber and mill the final size myself.  I get a better quality and I can control the lumbers reaction to being milled much better that if I buy dimensional lumber already milled.

When lumber is cut through the saw mill it is cut oversized so that it can be surfaced to a final size.  This is know as rough cut.  Depending upon how long the wood sits between the rough cutting and the final milling and the final milling of the wood will have an effect on how much it will change before we purchase it to use on a project.

If it is introduced to a kiln to dry then the wood will react to how much heat and air is applied and the speed in which it is introduced will determine if it gets a case hardened effect and how severe it is.  The fast heat or poor air circulation will induce a higher degree of case hardened wood than a slow even heat and air circulation.

The other thing I have not yet mentioned is the wood cell structure and how big and or how small the cells are will determine how fast wood will release moisture and also how fast it will take in moisture.  This is the reason for the painted ends you will see in most hardwoods.  It is an attempt to seal the wood grain cells from taking in moisture.  As a rule oak lumber will air dry at the rate of about one inch per year if kept stickered and covered from the elements.

Since pine is a soft and open celled wood it is not often kiln dried due to the expense it takes to operate the kiln.  Pine will air dry much faster that the wood having a smaller and denser cell structure.

After I have determined that the material is dry and will not change its shape I will then bore my pocket holes and apply my glue, if using, and then screw the joint together.  Since you are using the course thread screw it is important that you apply enough pressure to the joint to insure that the screw  will not rise up off the joint.  I suggest a light clamping pressure on most applications. The entrance of a screw between two pieces of lumber will usually attempt to push each other apart.

If using glue, a trick to keep your joints tight and in alignment is to dry fit and bore a couple screws then remove and apply glue and then put the screw(s) back in.  It will seek the hole and keep your material in position preventing it from slipping around due to the slippery glue. 

If in doubt about the correct depth of the drill bore in the kreg jig, I would set the jig to the 3/4 markings and then set the drill bit in the jig.    Take a nickel coin and lay in on the base of the jig and lower the drill bit and allow the bit point to rest on the nickel.  The stop collar should be resting on top of the jigs drill insert.    This has been the best method of setting up the kreg jig since it was first introduced.    When I started there were no markings or gauges to set the stop collar and after much trial and error,  I found the nickel was the best aid in setting the jig.  It is a quick and accurate check as stop collars often move on the bit usually pushing it up the shank towards the drill.  The results of this then will be too deep of a pocket hole.

Contrary to some the bit is not supposed to exit the bottom of the hole being bored.  It is best to leave it closed and allow the screw to make the exit point when it drills itself into the adjoining wood.   The reason is that the dimple that is often left on the end of the wood will not allow a tight seal and in order to get the tight seal, it requires more screw pressure.  The results of this is often loose joints, cracked wood, broken screws in hard wood, and the over tightening causes the screw end to exit the material it is driven into.  The exiting of a screw is particular  the case when the pocket hole is drilled too deep in the first place. 

What causes the screw to exit the piece your are screwing into:  1. pocket hole drilled too deep.  2. too long os screw.  3. improper wood thickness. 4. over driving the screw causing the screw head to act as a drill and pulls itself further into the pocket hole's drilled depth.  This is particular true when the wood is soft like pine.

What causes a screw to not hold the joint tight:  1. too shallow of a pocket hole drill depth. 2. poor quality of material. 3. screw not long enough for the material used.

One more thing:  Trick to make your screw hold better in soft wood, apply some wood glue to the screw thread.  It acts like an lubricant when being driven in and acts like a thread lock when it dries.  It will also seal up some small unseen cracks in the wood pocket hole.

[James Waller]

Jay, have you ever thought about writing a book? A lot of the answers and help you provide would make for a great woodworking book and it would benefit newbies as well as seasoned pros. I certainly would buy one for it will not only be of great help but would be an excellent read.

[Kevin Tunis]

Jay, very well thought out answer and such depth. I agree with James "thought about writing a book?". Thank you, this answers my question and more

.

[Ken Darga]

Kevin,

I've experienced board warpage (cupping), when edge joining 1x8.

I generally rip to 1x 3 or 1x4, and then edge join the narrower strips, to minimize warpage---and in most cases, no warpage (cupping)

When edge joining, I alternate the boards grain direction, so that one board has the ''grain up'' and the adjacent boards with ''grain down''.

Works for me.

[Jay Boutwell]

Well James If I was to write a book, I would have to get someone who likes to type,  I still have the habit I got from working my prior job of writing long and detailed dialogs  from the days when I worked on "who done it ?" cases and a short synopsis would not do the job.  I don't think I could type fast enough and I do misspell often. 
 
James Waller said:

Jay, have you ever thought about writing a book? A lot of the answers and help you provide would make for a great woodworking book and it would benefit newbies as well as seasoned pros. I certainly would buy one for it will not only be of great help but would be an excellent read.

[Jay Boutwell]

You are welcome Kevin, glad I could be of some help to you.  Hope you get the project finished and when you do don't forget to post it. 
 
Kevin Tunis said:

Jay, very well thought out answer and such depth. I agree with James "thought about writing a book?". Thank you, this answers my question and more

.

[John A]

Damn Jay, I went got lunch, took a nap, and then finished your post, great work, thanks for taking the time to post a great explanation!

[Jay Boutwell]

Thanks John, I always try to explain my point of view in hopes that it helps someone with their work.  Have a great day.
 
John A said:

Damn Jay, I went got lunch, took a nap, and then finished your post, great work, thanks for taking the time to post a great explanation!

[KregCS]

Kevin,

It sounds as if the depth collar setting on your bit is not set correctly.  You will want to make sure that you are setting the depth collar based on the step of the bit and not the tip.  If based off the tip the drill bit will not drill deep enough to allow you a solid joint.  The next thing to check is to make sure your clutch setting on your drill is not set to high.  With pine being so soft and our coarse threaded screws being so aggressive, if the clutch setting is set to high it can strip out the holes instead of pulling the joint tight.  Hopefully with these tips the system will work for you like it is supposed to.