How to Use a Speed Square to Mark Angles, Rafters, Slope

hey jonathan here at colfax math this is a practical math channel i teach high school math in woodshop and today i'm going to go over a harbor freight speed square all of its uses it is kind of the essential tool on the job site for construction woodworking layout metal this is really an incredible tool once you understand a little bit of the math behind it it is an invaluable tool it usually just sits on your bags right there and you pull it out for drawing inscribing perpendicular it's also a saw guide protractor scribe angle finder you can set out your joists i'm going to go over all of that today so let's get started probably the main way people use these on the job site and building homes is just you have it in your bag you pull it out of your bag and you have a perpendicular line the other thing you could use it for is the saw guide and how that works is you put your mark on there you hold it on there with your left hand and then you bring your saw right up to it and then you run it down the board using that to stay perpendicular we'll put the camera over my shoulder on my desk and i'll explain some of the math on the speed square this is a professional laser etched aluminum rafting square seven inches it is made by doyle and i got this at harbor freight you need to have this in your bags on the job site wherever you go in the wood industry and you need to know how to use it so possibly the first feature is drawing perpendicular lines and the next use for this tool is as a scribe here's my ruler here one two three four so there are eight lines so each line is an eighth of an inch and then for one here's my little notch if i want to scribe a one inch line i could scribe it right there at one this little arrow right here is for layout reference it's one and a half so that's where stead would lay out so you could lay out a one and a half the next line that might be used for layout is over here at three and a half a two by four is actually one and a half by three and a half so if you want to describe a line for a floor plate you could do that right at three and a half there this is alder here so let me scribe my 90 degree angle 90's perpendicular and math classical little box in there and carpentry you assume it's square unless it's marked otherwise and then the next thing you do with this is measure angles with it so here your angle measures down here and it's telling you it's in degrees it goes all the way up to 90 down here you count them out one two three four five lines so each little line is one degree so 5 10 15. and that's telling you right here this is my pivot point so the way i set these angles is i pivot on that and i move it to let angle measure there is on the edge of the board so that's 5 degrees i draw that line from my pivot and then kind of the key on understanding this is knowing a little bit of math and geometry so this is a 90 degree angle i pivoted 5 off this little angle here is 5 degrees so this angle from the edge of my board to here i need to know is 90 minus 5 or 85 degrees so two angles that add up to 90 are called complementary and this is the complement of that 5 degree angle so if i wanted to draw a 30 degree angle off of perpendicular i would set this right here at 30 right there at 30 and draw that angle and i know this angle is 30 degrees off perpendicular therefore this angle right here would be 60 degrees so that's how you're able to draw whatever angle you want by knowing the complements of the different angles i'll just do one last one right here so and i can flip it either way let's say i want a 70 degree angle off of here i would take this and i go 90 minus 70 is 20. i would set this right there at 20. draw that 20 degree angle and then i would know that 90 minus 20 would give me a 70 degree angle here that's really a useful feature not only can you do it that way but if you have a board that's already cut and you want to use it as an angle finder you could do it the same way let's say i have a cut board already no matter what it is whether it's a rafter or sheeting or anything and i want to figure out what angle measure this right here is i could use this as an angle finder the way i do this just hold it right to that pivot point onto the vertex vertex is a math class term where two lines come together then i'm going to bring it off of that pivot till it's flush on here and then i'm going to read it right off of there and i know it's 15 degrees so that's 15 knowing that i traveled from perpendicular to there's 15. so this angle right here is a complement of 15 so 90 minus 15 is 75 degrees so that's how i can find the measure of an angle on a board let's take a look at this common rafter marking here so before i go over what the common rafters are let me just talk about pitching a roof in the u.s so the way you do roof pits in the u.s is rise over run so if you have a roof that's called six and 12 has a pitch of 6 and 12 that means you rise 6 you run 12. that's a ratio what that means is for every unit you rise you re you run twice as long so you could rise 6 inches run 12 inches you could rise six feet run 12 feet or any similar to that if i cut that in half i cut that in half so you could rise three inches run six inches so it's a fraction or a ratio or a pitch or a slope in math it's also tangent that means rise over run is greek word but you could just find that angle with your calculator using tangent so i've just shown you all the connections so let's see how that works on my speed square so first thing i'll do here is i'll draw my perpendicular and let's say i have that six and twelve pitch so i bring this thing over to six right there so i'm right on six my pivot's in the correct place so i'm right on six there i mark this now the ratio of this triangle should be that 6 and 12. so i marked it on a 6 and 12 common rafter so if i measure this length i can see this is 3 inches so this this length right here should be six inches so even though this triangle opposite leg right here is three adjacent leg here is six the overall pitch or the slope is three and six which is six and twelve okay let me do another one i'll draw my perpendicular first using a sharpie just so it's easier to see let's go over to 3 and 12. i'll line that up to 3 and 12. by drawing that line and then 3 and 12. so rising 3 and 12. well i know this length right here my run is actually 6. so my run is 6. i cut that in half so this top number should be cut in half as well should be one and a half over 12 and let's see if it is so i measure right here and i could see that my rise is one and a half okay so that's how that common rafter markings work pitches slopes of roofs rise and runs if you take the speed square and flip it over there's a conversion table here but this conversion table is really the same thing is lining up these numbers you could look at this conversion table and see that you know a slope of 12 and 12 and 12 it says enter rise over foot so 12 and 12 is 45. so you could use that conversion table or you could just line it up at the edge of the board and see that a pitch of 12 and 12 lines up to 45. a pitch of 8 and 12 lines up to 31 to 33 degrees a pizza 6 and 12 is about 26 27 degrees right there this is a fantastic speed square that i got at harbor freight i really like the white riding on the black background i could see it well i like the aluminum i don't really like the plastic ones because i can't read them as well on the job site if you understand a little bit of math on this tool this thing could take you far you could build a whole house really with a speed square and a good level well i hope you enjoyed that video like to hear your comments below if you have any questions or thoughts on this video and if you like what you hear here think about subscribing thank you

Channel: ColfaxMath

Views: 121,378

Keywords: Colfax, help, math help, topsaw, Jonathan Schwartz, teacher, exponents, Integrated 1, math, CPM, college prep, mathematics, IQR, how to, Integrated 3, Integrated, applied math, tree, transformation, treetransformation.com, web store, web, online store, transformations, tree service, tradesman, trade exam, Plumber’s exam, IBEW, electrician exam, speed, square, speed square, diy, how to use a speed square, rafters, angles, slope, pitch, angle finder, how to use, carpentry tool, harbor freight

Id: MJhdFKDOEb0

Length: 9min 52sec (592 seconds)

Published: Fri Oct 16 2020