Ultra-Precise Circular Saw/ Router/ Jigsaw/ Sawzall Cutting Guide





Introduction: Ultra-Precise Circular Saw/ Router/ Jigsaw/ Sawzall Cutting Guide

 I didn't find a guide to making a circular saw guide that was made this way, and it was shared with me years ago.  Before I bought a small table saw, and even after because it is often easier than dealing with sheetgoods on a small saw, this is how I cut plywood.  This guide will be as precise as you can mark a board and clamp.  To aid with precision, I use a mechanical pencil- I have never understood the use of a carpenter's pencil, but as a cabinetmaker it shouldn't make a lot of sense.  Another option is to use a metal scribe.

But, let's get on to the saw guide.

Step 1: Base and Guide

First you need a board with a very straight edge on it.  If you have the tools to do this yourself there is a chance this saw guide is not for you anyway, but it could be done with a jointer, or taken to a lumberyard and ask the to straightline the board for you.  It shouldn't cost much at all, and the dollar or two is worth the investment to insure that the rest of your cuts from here on out using the guide are straight and true.

For example's sake, let's say the board that you straightlined is about 4 inches wide, and your saw's base is about 8 inches wide.  The board you choose for your base needs to be the width of your guide board, plus the width of your circular saw footplate x 2.  [Guide board width + (saw base width x 2), so in this example 4" + (8"x2)= 20" wide].   The length of these two boards depends on how wide a board you want to be able to cut.

Ok.  Mount the guide board to the base, centering it as close as you can.  this does not have to be uber-precise, but does require that on one side when you put your saw on the base up against the guide it will cut the entire edge off.

The cutting of the edge is very important- this is how this guide is so much more precise than other guides that require you to measure the offset and yada yada yada to get the guide to put the saw where it will hopefully cut..

The first picture shows the assembly uncut.  With the saw that you plan to use the guide for snugly up against the guide, cut the excess wood off of the base keeping the saw along the guide.  The second picture shows the saw part of the way through the cut.

Step 2: Using the Guide

Now that the base has been trimmed by the saw that will be used with the guide, the edge of the guide should exactly match where the edge of the saw blade will cut.

When you have a board you wish to cut, measure from an edge and make two marks on it to line up the guide.  The nice thing about this is that since the saw cuts where the guide actually is, you don't have to do any further math.  If you need to cut at 36" from an edge, make two marks 36" from that edge and clamp your guide exactly on those marks- this is where your saw will cut.

I didn't model in the clamps, but the reason that you need material on the other side of the base is so that you can clamp the guide down more easily.

You can see in the pictures where the guide should be attached in relation to your marks.

Step 3: Using a Router

This guide will work equally well with a router- the only problem is that you need to have an edge for each different diameter router bit for it to work precisely.  You could use each side of the base for a different router bit, so if you have a couple that you typically use for straight runs you can size each side for one of those bits.  

Otherwise you need more than one guide for multiple bits, but it will work just as well with a router.



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    15 Discussions

    I use this technique all the time when I need to rip down large sheets of plywood. Once they're a manageable size, I sweeten the edges on the table saw

    Make both a left handed and right handed version of this. There are times you have to cut differently.

    2 replies

    I like this idea - I may add the "other handed" version to the opposite side of the item shown in my sketch...

    I would be careful with the other handed version, simply because the other side of the saw usually doesn't have a lot of surface area to keep the saw level. I currently use a worm drive saw and it is particularly not fond of cutting on the other side because of its heft. Something else to keep in mind for the tube idea (I like the built in clamps if possible) is that the body of the saw will need to most likely ride over the straight edge part of it and it can limit the height of the straight edge unless you are pretty regularly cutting only thinner materials. The straight edge portion can be as short as the top of the plate on the saw, or as tall as the saw in the uppermost position that you will need to be cutting in.

    If you try the built in clamps in the tubes please post a picture.

    The other thing I would suggest if you have the space is that you may want to make a couple of lengths of the guides, one maybe four and a half feet and one eight feet long- that way you can use a less unwieldy guide for plywood crosscuts and use the longer one more solely for ripping.

    Thanks for sharing this saw/router guide. Looks really useful! I plan on using it soon. I've been thinking of using square tube for the upper "straight edge" piece. And also trying to dream up a way of insering a quick adjust flush clamp. (an integrated clamp might allow you to avoid dealing with C Clamps)

    2 replies

    I got inspired and have a sketch of a suggestion for improvement. If you have any additional thoughts - please share!

    Improved Saw-Router Guide.jpg

    Very good tip.  I think I saw this same idea on "Ask This Old House" several years back.

    1 reply

     It is an old idea and was surprised to not see it on here.  I first used it working at home on the weekends for personal stuff when working for a cabinet shop by day.  They had all the cool toys and I had the job sweeping up and spraying glue for a while (so no money for cool toys).

    I have been rebuilding my "cool tool" collection after a couple of hard-hitting thefts, but old school still works best in some situations.

    Thank you for a good Instructable.  The user of this guide would also want to use the same saw blade always, or a difference in blade thickness would introduce error.  Fortunately, carbide tipped blades are not too expensive, do a good job even on plywood, and last decades for most home users.

    1 reply

     That and the width of carbide tipped blades (does anyone use anything else?!?!?  If so, why?!?!?!?!) is pretty standard at 1/8".  The width may vary as much as a 1/32nd of an inch, which translates to 1/64th inch error in the fence, which is often an acceptable error, and should be about worst case.

    I built a couple of these as a part of my workbench project.  Make sure that the you have enough width to clamp beyond the back end of the saw - my first attempt was too narrow, and as a result the clamps would get in the way of the body of the saw, when the saw was cutting at full depth.


    The "factory" edge of a sheet of plywood is usually about as straight as you can get.

    1 reply

     When I worked at a cabinet shop and we had a sliding table we would always use it to remove the factory edge because it was more precise to use the sliding carriage saw.  Since I no longer have access to a $20,000 table saw ( : P ) I would have a lumber supply do the edge for me.

    (If you aren't familiar with sliding carriage saws check out Altendorf saws online- that is the brand that I am familiar with)

    This seems like a really good idea. I've used a straight edge for years, but I always have to offset my straight edge from my marks by the distance from the blade to the edge of the saw foot. This does it all automatically, but with a slight loss in cutting depth.