Mitre sled question???

[Dan McGuire]

I am in the process of building a mitre sled for the table saw. I have searched previous threads and have a general idea of what I want (need) to do, however I did not see anything on how to establish the 45 degree angle and it has been years since my last geometry lesson.

I am using 3/4" oak plywood for the base and poplar for the runners. If I were to take the framing square and place each leg at say 10" and trace intersecting lines to use as a guide for the fence I am thinking that would get me close. Is there a better way?

Dan

[Frank Hagan]

The best way is to make a test cut on something like a 1 x 4 at your best guess of a 45° setting and then flip one piece over to make an "L" with the two pieces. If the "L" is square, you have a true 45° cut.

[Bob Johnson2]

I believe you use a compass. Make an arc from your 0 point (where the blade will intersect the 90 square), then make another set of arcs, from where your first arc touched the 90 degree board and the 0 line (saw blade slot if you've already cut it). Draw a line from the intersection of these 2 lines to the 0 point, it should be 45 if your 90 is right. I think.

[Paul Prescott]

Try a plastic drawing traingle. Worked for me!

[Tom Donalek]

One of the recent magazines had a bit about making a sled. I think that they used a plastic drafting triangle for the initial setup. I know from my experience drafting that they are pretty darn accurate - I'm talking about 'good' ones from the drafting department of a good art supply store. I have no idea about the 'school supplies' ones from WalMart or wherever.

One trick they suggested was to screw the fence down to the table from the top using 2-3 screws in oversized holes, so that you could do test cuts and tweak the fence as you go. Once you've got it perfectly aligned, you would then screw in into final location from the bottom of the sled. Also for the final test cuts, you may want to try cutting a full 4 sided square and assembling it. You'll 'magnify' any error that way.

While we're on the topic - does anyone have a strong preference for the 'base' material for sleds: like plywood vs. MDF?

[Alan Turner]

MDF is my choice, only becaue of its flatness.

[Fred Voorhees]

MDF is my choice, only becaue of its flatness.
I agree. MDF is the only answer. I have used plywood in the past, only to have it eventually warp. MDF is not going to warp. I have both a 90 degree miter sled and a 45 degree sled and both are of MDF and neither have done anything but stayed flat for years on end. I would also upgrade the runners from poplar to a harder wood for longevity and strength.