Kreg Owners' Community

I recently used 2x6 pine to build a table top for a buffet.  I used pocket screws on the middle of 3 boards going outwards to the two boards on the outside.  I clamped the boards together and had them on a flat surface, but after mounting the top to the buffet, one of the boards had cupped upward.  How do you or can you prevent the cupping?  I guess I'm being clear, no other way to describe it.

Wayne

Views: 3771

Reply to This

Replies to This Discussion

Several possible explanations:

(1)  The board is cupped.  Home center pine is very susceptible to movement.  If you look at the curved growth rings on the end grain of the board, expect for it to cup in the direction of the curves.

(2)  The edges of the boards are not flat or square.  Home center lumber is not very accurate when it comes to the cuts, meaning they are often not consistent or square, especially if the wood moves after it goes into the kiln.  The rough lumber may have started with an edge square to the face, but if the board cups during the drying, storage, or transportation of it, then the edge is no longer square to the face.  If you clamp up two boards into a panel and the mating edges are perfectly square to the face, then you will wind up with a bow in the panel equal to the difference in angle between the joined edges.

(3)  The pocket screws themselves have caused the panel to cup because their force is not distributed evenly between the mating pieces.  In other words, all of your pockets on are one side of the joint, which is going to pull the joint in the direction of the screws.  Try loosening the pocket screws a bit and see if the panel goes back to flat.

When you do a panel like this, it's very important to choose boards based on end grain that are unlikely to move very much.  Dealing with dimensional home center lumber is tough, but look for grain that is as vertical as possible, i.e. it looks like this when you look at the end of the board ||||||||||.  You should also rip the boards where they will be joined to ensure a good, straight, square glue seam.  Table saw is good, track saw is fine.  Or, you can clamp the two edges to be joined together and plane them down together, which will ensure a complimentary set of angles when you go to glue them up.  And last, consider skipping the pocket screws.  I love them, they're awesome, and I credit them with opening the door to the wonderful world of woodworking for me, but for making a panel, I'm not convinced they are the best method to use if you have alternatives.  Good ones to consider are biscuits or dowels and glue.  You don't need a mechanical fastener to make a panel if your glue seam is straight, square, and tight.  Put in a few dowels to help you align the pieces, then glue them up and let the panel sit in the clamps for a few hours.  If it ever comes apart, then let me know and I owe you $5.  Modern wood glue is stronger than the wood itself.  Get a good glue seam and it's never coming apart.

The last trick is to make sure the panel stays flat when you exert clamping pressure on it, whether from clamps or pocket screws.  Best way to do that is by (1) using cauls, and (2) alternating your pipe or bar clamps.  

I hope this helps.  You can still save your panel by taking it apart, truing up the edges, then reassembling it as discussed above.  Let us know if it works and how the project turns out!

Thanks for the info, I think I need to spend more time looking at the lumber before putting it on the cart.

Reply to Discussion

RSS

Need Help?

For Technical Support, please call 800-447-8638 or send a message. Reps are available Monday through Friday from 8am to 5pm CST. 

Videos

  • Add Videos
  • View All

Forum

Jig settings for 2 ¾ x 1 ½ boards with 30 degree miters?

I making a hex ring out of 2x4s ripped to 2 ¾ inches wide with 30 degree miters.  What setting on the Jig should I used? 1 ½ is too much.  Thanks.Continue

Started by Patrick Halinski in Kreg Jig® Operation Dec 30, 2023.

40mm Cup Hinge Jig Question

Hi All.....I have the 35mm Kreg Jig hinge drill guide. The guide is great for 35mm Hinge Cups, but I have a speciality 40MM hinge cup to drill.Has anyone adapted the Kreg guide to work with 40mm Forsner drill bits? Or have a guide that works…Continue

Started by Ed Anderson in Beginners' Zone Oct 3, 2023.

Product Reviews

New Kreg 720Pro

I saw the video Kreg put out for this new jig and had high hopes for it.

I purchased one today and am very disappointed with it.

First the docking station is extremely cheap. The plastic is pathetic. A Lego has more…

Continue

Posted by Duke Leon on February 15, 2021 at 9:00pm

Not Pleased With Pocket Hole Construction

Several months ago, I purchased the Kreg K4MS so that I could build the Lego Table as outlined on the companion "buildsomething" web site which exclusively uses pocket hole construction.  I have considerable experience with conventional…

Continue

Posted by Robert Ringel on September 17, 2020 at 1:48pm — 9 Comments

© 2024   Created by KregRep.   Powered by

Badges  |  Report an Issue  |  Privacy Policy  |  Terms of Service

_