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Deck construction how to straighten bowed boards

I recently needed to know how to straighten bowed boards. I was rebuilding my deck and of course, I wanted to rebuild it with as much of the old deck materials as possible. The largest problem was that most of the deck boards were bowed. The boards that were straight when new were now bowed and not by a little.

I thought I’d check in on youtube and get some pointers. Good news there are tools out there that are used to straighten bowed boards. The bad news it that the tool costs almost as much as all new boards on my little deck. I live in the San Joaquin Valley in California so douglas fir has a tendency to last a very long time even exposed to weather. Douglas fir is my choice of decking material because it is cheap to use and in my area, if properly treated will last a very long time.

Back to the bowed boards

I counted out buying tools because I could spend the same amount on all new boards rather than tools that would not see use again for another twenty years. One of the videos on Youtube suggested using clamps to bend the boards back into a straight condition. I liked that method it seemed very easy.

My local national tool store had clamps that could be used to clamp or push and were cheap enough that I could accept the risk for a chance at success straightening out my old boards. I tried that method. Well, that method while looking very easy on the video proved not to work with my old boards. Both clamping and pushing methods failing miserably. The failure was due to the amount of pressure needed to straighten the boards was beyond the ability of the clamps.

I have steel digging bars six feet long that are used for all sorts of things. Using this bar’s length to the most advantage to pry on the warped board took all my effort to get one board straight. It was clear that I was going to need a device to straighten out my bowed boards.

Board Straightener tools

One of the board straighteners that I found really looked promising. It used a threaded turnbuckle to slowly get the boards to straighten. Again the cost of the device is prohibitive for my purposes. But I thought that it is not that difficult to reproduce the principal moving force using simple hardware and some scrap lumber. It seemed that this device could easily exert the pressure needed to straighten the boards. Its drawback is that it would be slow(the turnbuckle moves at twice the speed) but I have a lot of time on my hands and as a homeowner, I could deal with the added time needed to get the tool to work. In the video, the bow looks to be less than an inch over a very long board. I was dealing with boards less than ten feet in length and bows exceeding an inch.

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The tool

The tool I came up with doesn’t use a turnbuckle. It uses a carriage bolt.

Carriage bolt
A threaded bolt with a round, smooth head. The bolt is prevented from rotating in its hole by a square neck directly under the head.
DICTIONARY of CONSTRUCTION.com
http://www.dictionaryofconstruction.com/definition/carriage-bolt.htm

A nut and large fender washers round out the other parts required. Large washers spread the load across a larger part of the board. It will take twice as long as the turnbuckle to extend out and straighten the board. It is a simple device nothing fancy. The metal parts can be purchased at any local hardware store. I like the use of a carriage bolt for two reasons. The head is round and domed. It presents a larger surface area over a hex head bolt. The second reason is the square neck under the head allows me to put a second tool on the bolt to keep it from turning when applying pressure for straightening. The only criteria I had for this bolt was that it be all thread so I could use it’s entire length if needed.

Due to the pressure applied on the threads during its operation, they will need to be lubricated. If your project can not accept an accidental oil spot you can use a silicone spray. Carriage bolts are not super hardened. So it is best to start the bolt at its shortest length. Do not have it extended out of the wood block by a large amount when starting to straighten your board. By controlling the start position, it should limit any possibility of bending under pressure.

The wood parts

The wooden parts are scrap pieces from installing the framing for the deck. Any modifications to the wood required a hand drill(electric preferred) and a stepped down drill bit larger than the 1/2″ bolt to fit into my 3/8″ drill. I had a 9/16″ drill bit that worked for my board straightener.

I made two of them so as to spread the tension load across a larger area over using a single tool. The major cost is the bolt at less than three dollars each and the two washers with a nut at approximately a dollar. So for less than ten dollars, you can get two tools for board straightening provided you can live with the amount of time it takes to extend out the tools for board straightening.

I fabricated my board straightener tools and installed them on a board with a bow greater than one inch. They performed beautifully. I could hear the boards being coaxed into position. A little adjustment on one of the tools and then an adjustment on the other and in two minutes that old bowed board was as straight as it should be.

Parts needed for 2 board straighteners

two 6″ by 1/2″ by 13 threads per inch all thread bolts(it means that there are threads the entire length of the bolt not just part of it)
two 1/2″ washers
two 5/8″ washers
two 1/2″ by 13 threads per inch nuts
Scrap lumber for the body

Tools needed

Drill motor
A drill bit that is larger than 1/2″

Making the main body of the tool

Gather a scrap piece of wood that will become the main body of the pusher tool. It must be appropriate(length/width) to your deck framing. The piece must be at least 1 1/2″ thick so that the bolt head will be centered on the decking material when pushing.
Measure to the center of the thickness and the center of the width, mark the location
Use a drill bit larger than a half inch to drill a hole into the wood as deep as the drill bit will go at your mark. (mine was a 9/16″ drill bit and at least 4″ deep into the wood.
Place the bolt into the hole and make sure that the hole is larger than the bolt and that the bolt can move freely into the wood.

Making the protective end (bolt head end)

The protective end is a right angle bracket with a dimple for the carriage bolt head. It is meant to rest on the board to be straightened and protect it while it is being straightened out.

Measure out the width you will need for the vertical pieces. I made mine a little too wide and when I tried to use them I had to cut off part of the wood block so it would fit where it was needed.
Determine how much width you will need for the horizontal pieces
From scrap wood cut four pieces to make up the two right angle pieces
Join the vertical and horizontal pieces using screws/nails(whatever you have on hand)
Place a scrap piece of decking into the right angle and visually locate the center of the bolt head where it will be pushing on this right angle piece. Mark the location
Using the drill bit create a dimple(not a hole) for the bolt head to push into.

Your pusher tool is now complete except where the holding screws will be located. That will be determined by your deck framing. Use a combination wrench to turn the nut and a pair of locking pliers to hold onto the square part of the bolt head for tightening. You’re all set you now can answer the question on how to straighten bowed boards.

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Author
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RayC.

Editor at Mybusyretiredlife.com

Trained in the mechanical arts. I have worked on anything dealing with a home from changing a light bulb to moving a load bearing wall. As for the recipes, they came about after I could not find what I was looking for and recipes that over a lifetime I have come to love and want to share with the world.

2 responses

Nick v.
August 14, 2019
I respect your ingineuity. Because I have been trying my own methods of dealing with all of this. I live in Michigan. I am wondering what the cost of these tools are for you? Here I can get them on Amazon or home depot for 35.00 or less. However…I prefer to work the problem. I found that sticking the claw of a prybar in the gap of an installed board and using a pipe clamp to draw in the new board is perfect.
- RayC.
  August 14, 2019
  Hello Nick,
  First thing thank you for your comment. If your going to use Amazon for the board straightener the hardware should run less than 30.00. That would give you enough hardware materials to build my board straightener eight times over. Of course you will need some scrap wood material and a little time to construct them. Also it will be slower than the commercial straightener but so much cheaper and no expensive tools in the toolbox turning to rust before they are needed again. As for using the pipe clamp and the prybar that sounds like you have a system that works for you. I don’t have pipe clamps so I developed this straighten with the idea of something simple using ordinary off the shelf cheap parts that can be easily found online or at the local hardware store.
  Again thank you for the comment its always nice to hear from someone who is dealing with the same type of problem as I have faced.
  RayC