How to Cut a Straight Edge

Working with rough lumber can be a little rough, and learning how to cut a straight edge is just the tip of the iceberg. It’s not for the faint of heart, but it can be fun and rewarding when it’s all said and done. In this post, I am going to show you what I consider one of the best ways to get a straight edge, especially if you are doing several boards.

How to NOT cut a straight edge

When you get started woodworking, you will try anything to find a solution, but I want to quickly layout a few tips of solutions that do not work.

Do not hand cut a board with a circular saw without a guide!

We are good, in fact, many woodworkers will say they are the best. They are wrong, and we are all learning every day. If you aren’t learning then you are going to get hurt or going to lose your edge, and don’t make me tell you about tools that aren’t sharp being used in your workshop. Drawing a line and hoping you can cut a straight line with a circular saw is madness. You may get lucky, but it will not be repeatable.

That said, you can get a straight edge and use that as a guide. I still don’t like that route unless absolutely necessary because it is too easy to human error (twisting the saw slightly, coming off the guide, the guide coming loose, etc..) The best way to get a straight edge is by taking out as much human error possibilities as you can.

Don’t expect to run a rough edge along the table saw fence and get good results!

I remember when I first starting trying to figure out the best way to get a good straight edge, and I tried EVERYTHING. My issue was I needed to repeat it, and repeat it as fast as possible for profit. Unless you have an absolute (or incredibly close) straight edge on one side, you can not expect to get good results. The fence doesn’t make straight boards, it just guides. If your board has a bend in it, that will be represented in the cut on the other side. Unless you have a fence longer than your board, you just aren’t going to get good results.

DON’T GET DISCOURAGED WHEN LEARNING HOW TO CUT A STRAIGHT EDGE!

This is my most important piece of advice. Woodworking is a skill learned, not handed down or given away. It will take trial and error, you will need to practice, and you will mess up, I promise. When I owned the furniture company we would push out 5-10 tables a week. That means we had to take 30-60 rough-cut boards, plane them to thickness, get good edges on both sides, and get end caps in place. After many years of doing this I still messed up, I made many human errors that cost me on lumber. It happens, but it is part of learning. Every time I build with my son Corbin (If you haven’t seen his series, make sure to check it out here) and he makes a mistake, we talk about what we learned from that. We can’t get better unless we are open to learning.

Prepping to cut a straight edge

For this technique, you are going to need a couple of things. The wood you are working with, a table saw, a couple of screws, and a piece of 3/4″ MDF. If you don’t know what MDF is, it is a sheet you can find at most big box stores (check it out on Lowes.com). IMPORTANT NOTE: This method only works if you are ok with having a couple of screw holes on one side of your board. If you are doing a tabletop you can wood fill and put that side on the bottom and no one will ever know.

Step 1

The first thing we want to do is prep the board that we want to cut a straight edge on. Before we run anything down the table saw we want to make sure you have a flat top or bottom of the board. You can obtain this with a planer, jointer, or even some elbow grease and a sander. Either way, if the board is wavy or uneven then it will cause issues on the table saw, I can promise.

Step 2

With our main board ready to go, let’s get our MDF ready to go. We need to first cut a long piece of MDF. I would suggest 6″ wide or so, not a huge deal. You can either run it through a table saw or hand-cut it, it doesn’t have to be a perfectly straight edge, however, if you can keep a perfectly straight edge you can get more out of the board. I have a few of these in my shop, all different lengths. If I am trying to get a straight edge on a board that is 6′-8′ long, then I obviously want an 8′ piece of MDF. However, if my main board is only 2′ long, I want to use a shorter piece of MDF that can be handled easily.

Step 3

Now it’s time to attach out MDF to the board we want a straight edge on. The way this works is by attaching the piece of MDF to the board, with the straight edge of the MDF overhanging the board. We are then going to use that edge against our fence on the table saw in order to get a good straight edge on the other side of our board that is exposed. When attaching the MDF I want to make sure that it is aligned with the board as best as I can. I also want to make sure I use screws that won’t go all the way through my main board, as that will not slide on the table saw.

Once you have a few screws in it you can measure from the straight edge of your MDF to the exposed board, and then subtract however much you want to cut off in order to get your measurement for your fence. If you are having a hard time following make sure to check out the video below for full instructions and a demo

Time to cut the straight edge

You now have a flat top or bottom, you can cut a strip of MDF, and attached it to your board. You also have your measurements setup, and you are ready to show this board who its master is. Remember a couple of things though:

  • Do not get rushed
  • Keep the MDF flat against your fence
  • If the board is too big for you to control, get help
  • Protect those fingers!

Once you have successfully cut your first straight edge, take your MDF off, and then you can use the straight edge you just made to get your straight edge on the other side of the board (if needed).

YOU DID IT, YOU MADE A STRAIGHT EDGE!

Just like anything in life, there are lots of ways to obtain straight edges in woodworking. Make sure you look around, watch videos, ask friends, and practice, see what is best for you. What works for me might not be for you, however, I can say this technique was used to create many thousands of tables across the southeast, and with some practice, it can prove quick and efficient.

Do you have some other tips for getting a straight edge, or questions about this process? Drop those in the comments below so we can all learn and grow together!

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