you know squaring wood is one of the most basic fundamentals and we're working and your slab plays a huge part of that today I'm going to show you a very simple method that you can use to check the accuracy of your sled I'll show you how to calculate the error ratios needed to correct any errors you might have now I've been sharing this method at the woodworking shows for the past five six years and I still get emails when people asking me how do I calculate the error ratio now I teach and share this method in the beginning of all my classes here at the school because I believe the sled is the most important jig in your shop it will help you with accuracy repeatability and most of all safety now I've made some pretty hairy cuts that I would never have done without my sled if you don't have a sled new shop you might want to reconsider when I started with working the way I was taught to square a sled was to get a board cut it in half flip one board over and see if there's a gap if there's a gap it means that your fence is off and by flipping one board over you've double your ear now that was very frustrating for me because it was a guessing game if there's a gap I would take the screw out put the square back on and readjust my fence sometimes I would overcompensate and I end up adjusting my sins back and forth that drove me crazy so I thought there's got to be a way that I can measure this so what I did was after I made my cut in half I flipped one board over and I move it out and I cut it again now I can physically measure exactly where I'm on I take the top measurement subtract it from my bottom measurement now I have a real number that lets me know exactly how much I'm off so I took this a little further and I thought if I cut this four times it will quadruple my problem now you don't have to be an engineer to understand this is simple geometry now I know a four-sided board has one thing in common it has four angles that equals 360 degrees it can look like this or it can look like this or even look like this it doesn't matter they all have four angles that equals 360 degrees so by cutting a four times I'm trying to divide angles into four equal parts which hopefully equals 90 degrees let me show you how it works first you're going to need the board that the board doesn't have to be square because when you make your first cut it will set us or an angle now if your fancy square to the blade this hopefully will become 90 so now I'm going to put a little breakfast mark here this is tell me that this is where I started with so after my first cut I take the side that I just cut I put it against the fence and I cut it again that's my second cut and hopefully it will become 90 of your fancy square and I go for my third cut I do the same thing I take the side that I just cut I put it against the fence and I cut it again and we're hoping that this would be also 90 degrees and then my fourth cut I'd do the same thing this will become 90 so when I get back to my original my first cut if everything is 90 degrees these two sides should be parallel the distance between here and here should be the same now since I don't have a caliper that that's big that I'd measure that what I can do is I can move it over about an inch I can cut this part off and I should be able to measure the distance between the cut off here on the top now we're here the bottom and it should be identical now I'm going to show you how to fix and calculate the error ratio if your fence is not square so let's just say your first cut instead of being on 90 let's just say we're five degrees off okay so I'm just going to exaggerate angle a little bit here so this is my first cut I always draw a little reference mark so it tells me that this is my first cut so out there for me my first cut let's just say this is 85 degrees for a time being so my second cut am i rotated and I'm going to make my second cut so here's my second cut so visually you can see that the distance here has doubled so I doubled my ear so now this becomes 85 degrees now I rotate it for my third cut again I take the side that I cut put it against my fence and I'm going to cut it so now the angle would look like this this is my 85° and as you can see it doubled now it tripled you can see that again I'm gonna go to my fourth cut put this against my fence make my fourth cut too so this will be my friends lined up here and so when I cut this again this will become 85 degrees now this angle has changed because I put a new angle here so this angle have to be 105 degrees because a total of these four angles equals 360 degrees so this has to be 105 degrees so all I have to do now is take 105 minus 85 that will give me 20 degrees divided by the four angles and as you can see I'm five degrees off now we can measure this in two ways one is by a protractor and the other way which I prefer is by distance how far am i off from 90 so again on my fifth cut I'm trying to measure the distance that I'm off from 90 so on my fifth cut I just move it out a little bit and I cut this part off now I can actually measure the ear all I have to do is take the difference between the top cut which I call the a cut – the bottom cut which the be cut divided by four which represents the four angles now I have an error per cut over the length of the fifth cut only so let's just say your fence is off like this and so as you can see you have a bit lot bigger error up here then down here so the larger the board the larger the error ratio which makes it a little easier to work with now I advise all my students to use a large board when doing this so if you have a rectangular board like this I always advise to use the longer side as your first and fifth cut it gives you a bigger error ratio reading which might help in your slates accuracy remember we're measuring the four angles not the size of the board so your board could be like this is 16 by 24 or even a smaller board like this a 524 it really doesn't matter the only side that matters is the fifth cut so let's just say we made our fifth cut and our measurement on top is 20 thousands of an inch and the measurement on the bottom is 60 thousandths of an inch so 20 minus 60 equals a minus 40 divided by four that will give you a negative 10 that means our fence is too low so look at it this way our blade is at 90 our fences that's zero so plus one two three and a minus one two three so if it is a negative number that means our fence is too low so to adjust my fence by ten thousandths of an inch I use a feeler gauge that you can pick up at any auto parts store now there's a couple of problems that we have to deal with here first the error ratio is ten thousandths of an inch over my fifth cut which is 24 inches so the error from here to here is the same as my error from here to here so that means that I have to move my fence up ten thousands of an inch over here not here so my first problem is my fence is too short my second problem is even if my fence is long enough when I make my adjustments here right here where my blade is the fence also moves up which throws all my adjustments off now because my screw or my pivot point is down here how do I calculate the distance I need to adjust here at the end of my fence so that the distance here is still ten thousand seven is greater than here well you have to calculate the error ratio you take the ten thousands that you're off divided by the length of your fifth cup which is 24 inches that will give you the error per inch you multiply that between the distance between your pivot point which is the screw underneath here to the distance where you want to make your adjustment that will give you the exact error ratio that this is you need to make the adjustments right here at the end of your fence remember the ratio is constants which means that if you are off by ten thousandths of an inch here as you can see it gets bigger and bigger when you close out further so by multiplying the distance between here here you will get the exact distance you need to make your adjustment now I'm not going to torture you guys by showing you the whole process of how I came up with the calculations that is a bit cruel so I'm just going to give you the resulting formula so after your fifth cut it's a which is the top measurement minus B which is the bottom measurement divided by four which represents the four angles divided by the length of your fifth cut times the distance between your pivot point and that point of adjustment on your fence that will equal to e which is the actual error ratio needed to be adjusted at this particular point if E is a positive number that means your fence is too high if it is a negative number that means your fence is too low so if you want to double-check my calculations to make sure that the distance here will be ten thousands range greater than here all you have to do is multiply the distance between the pivot point to here and then multiply the distance between the pivot point to our here and you will see that the difference is exactly ten thousands to make my adjustment I made this block which has a point in it because right here is where I want to make my adjustment not here or not here so if I want to adjust my fence up I put my block right here with my fila gauge like this now you want to make sure that you're not squeezing these things so hard so tight that you're compressing the wood where I have it too loose where the feeler gauge is not really there you want to allow for its true dimension where there's ten thousands or 12 thousandths so after I put my feeler gauge right here what I do is I pull my sled out I clamp it remove my feeler gauge take the screw out underneath and move my fence up Irie clamp it and I put another screw in using a different hole don't use the same hole because you'll try to pull the fence back to where it was if you use my calculations I'll guarantee you that your slip will be dead-on on your first adjustment now there are a couple of pitfalls that might come into play if you calculate your error and it's ten and a half thousands well I don't have half a thousand on my field gauge so we use ten thousands for eleven thousands you're going to be off by half a thousands per cut so you can adjust your calculations instead of multiplying it by say twenty eighteen just from here to here try 27 or 26 now don't get crazy with this if you're inside a thousandth of an inch after your fifth cut it's good enough now another thing you have to be careful about is when you're using your calipers make sure that is sitting flat use two fingers and squeeze it wiggle a little bit to make sure that the arms are parallel to your piece it will give you a better reading if you're trying to hold it like this what's going to happen is that it will tend to dip on one side you want to make sure that is parallel that will give you better reading because if it dips on you you're actually reading diagonally now obviously that is wrong and your reading will be bigger than what it actually is as you will see later on in the video I did exactly the same thing I realized it later and I remesh and it was dead-on now it's important I just led is accurate to within a thousandth of an inch because from here I use this to make my 45-degree sled as you know a three sided board has 180 degrees so if my sled is dead-on ninety this angle is taken care of and all I have to do is calculate my 245 you can do it with a to cut or four cut and you can measure the ears now I'll show you how to do that in another video now some of you might notice that my sled is off centered now I do this to avoid what I call get spots if my slave is dead on center well if I want to cut something that's 13 inches I can know where to climb my stop so because it's off center I can go from 13 all the way up to about 15 about 15 inches and then from there I used my fence as a stop and I can cut all the way up to about 52 inches now if you're going to use your fence as your stop make sure that you use a relief block what a relief block does is that if your cutting a piece and you're not using a relief block what's going to happen is that if this thing drags on you or a little bit sticky it's going to pull the piece off of the fence and it's going to go right into the blade the blade will pick it up and that's what kickbacks happen it's going to throw this piece right back into your face and as you can see I can't afford to take another hit so if you're going to be using your fence at your stop what a relief block does is that when you're cutting now your piece is actually free in that chapel against the fence so make life a little easier and avoid doing any math make sure that your block that you're using is one inch thick so the only thing you have to worry about is if you want to make a cut that's 27 inches sets your fence to 28 inches to compensate for your 1 inch block now I've been asked why do I make my fence shorter than my sled well there's a few of jigs and fixtures that I attach to my sled that requires a shorter fence and also when I'm doing angle cuts if my fence is too long I have to move my pieces up a little bit too high which makes a little bit difficult to use so hopefully I've convinced you the importance of the sled stick around because I'm going to show you how to build this step-by-step so to construct our sled I'm going to begin with the runners now there are a couple of things you have to consider the type of wood and also the grain pattern you want to choose a width that's hard enough that can stand up to the wear and tear you also want the grain to be running as vertical as possible because the wood movement remember would always expands and contracts along the grain if the grain is running horizontally and there's a little bit of humidity in the air well the runner is going to expand so tight you're going to have a hard time moving it which makes it very dangerous to use so here I have a piece of hard maple which I chose for my runners and as you can see I have some very nice vertical grain right here which I'm going to use and right about here the grain changes to about 30 45 degree which I'm going to pass on that because this do some horizontal movement remember wood moves along the grain so as you can see there's still some side movement so this is the only part that I'm going to use now before I start cutting I want to measure my miter slots with the caliper is very important to cut your runners to fit exactly the width of your slot not a thousands bigger not a thousands less it's got to be perfect it cannot be any play now I also want to cut my runners 1/16 of an inch thinner than the depth of my slot in most table saws the depth is 3/8 so I want to cut my runners 5/16 the reason is I don't want my runner to bottom out if there's any kind of sawdust underneath here what's going to happen is that it will lift the sled actually off the table which results in inaccurate cuts now this piece of maple is mailed to about thirteen sixteenths of an inch thick just a bit bigger than my miter slot so let me cut the first part I'll first my waste and I'll set my fence to 5/16 and see how many runners I can get out of this piece well it looks like I got six good pieces out of this I got two that's marginal so I'm just going to use these as my test pieces now I'm going to cut the width to fit into my miter slot now this is your money cut I need to know the exact size I have to cut it too to get that perfect fit so I'm going to use my caliper take a few readings in different spots to make sure that my miter slot is consistent in width so here I have about 0.75 to 0.75 two and a hairline 0.75 to measure this I point seven five two this is a point seven five two plus a smidgen this one here is point seven five two so my target is going to be point seven five two which is two thousandths of an inch bigger than 3/4 now I set my fence to a little bit bigger than 3/4 of an inch I'm going to make my first cut I'm going to check out what my caliper and see how much I'm off then I'm going to sneak it in now I tell my students that the most important tool in your shop is really your hands and eyes you have to trust it and develop it so if you take up a piece of paper like this you can actually see the edge of the paper now that's three thousandths of an inch so yeah I is actually better than what you think they are so if I need to make an adjustment it's just a few thousands of an inch I can just loosen up my fence and I keep my eye on my line and we'll just tap it over keep in mind what 3,000 dimension looks like now if you're not comfortable with this technique I'll just show you how to do it using the caliper so my reading it looks like it's a 0.76 – so I'm about ten thousands of an inch off normally what I do is I would just loosen up the handle keep my eye on my line and just tap it over make my cut and just kind of sneak it in I've been doing this for a while now so I feel real comfortable with it because this is such a critical cut I'm going to show you another way that you can nail this cut using a caliper so to use the caliper to measure the fins basically what I'm doing is I'm placing the caliper right up against our friends see what my reading is and just tap it over ten thousands of an inch now you can get really fancy I make a holder for this one magnets or something like that like I said I don't use this method I just tap it over just as fast as using the caliper so I'm just going to do it very crudely I'm just going to use magnetic feather board just laid it down kind of square it off a little bit put my caliper right up against here okay whatever my reading is there I'm just going to bring it over ten thousands of an inch well my caliper is reading at thirty four thousands of an inch now I need to go ten thousands less which is twenty four thousand so I'm a losing the fence and I'm going to move the fence over ten thousands of an inch so here we go so let's take this out and just make our cut and see how it fits okay Oh baby now I want to stress the importance of this cut see this is my reading I cut it exactly at 0.75 to now look at a fit look at this fit here and this is basically what you want you just want to be barely having fiber just barely touching each other not too tight not too loose it's perfect next I'm going to attach the runners to my base here I have some spacers that goes underneath the runners to raise it just above the table remember we cut our runners 1/16 of an inch thinner than the death of our slot so my runners right now is sitting below my table so I cut my spacers to three thirty-seconds I'm going to put underneath here put my runners back in and I want my runners to be about 1/32 of an inch proud so when I have my base on here when I screw it in you'll be nice and tight there's no gap between my base and my runner so to position the base I need to know where my saw kerf is because I want to offset my sled to avoid any dead spots as I have mentioned earlier now your saw should have a notch on your fence to indicate where the blade is if it doesn't all you have to do is just raise the blade difference against here use a sharpie and just mark your spot so here I'm going to find Center and I want to offset my sled to a minimum of one and a half inches to a maximum of two inches now it's not that critical where you put it as long as it falls within those boundaries so just to mess with you I'm going to offset my slit one and twenty three thirty Seconds so here I have my base position to where I want it so now I'm going to eyeball the center of my runners this way I can draw a line to kind of help me see where I'm going to be putting my screws now I'd like to overbuilt everything so I want to mark for my screws every three inches so to insult these screws I'm going to be using a taper bit because I want to make sure that when I install these screws that the heads are below the surface now I'm going to be using a number 6 by 5/8 inch screw now you want to make sure you have enough screws because you don't want to run out now I'm ready to add my fence to make my fence I'm going to be gluing up three pieces of half-inch Baltic birch now you can use two 3/4 inch if you want to that will work that by experience I've found that using three pieces seems to be a bit more stable now the trick is to do your glue up on a surface that is absolutely flat now here people suggesting using a jointer or a table saw top well the problem I find is how do you clamp it so I decided to make my own clamping table where I can have clamps on all four sides I got myself a big 12 quarter piece of maple I joined it it planed it now I have a flat surface I can clamp too and it's gluten up so here are my fences I took a steroid straightedge and I check off a flat and I got pretty lucky it's pretty darn flat now I'm just going to true it up on my table saw I'm going to trace and cut my pattern so here I have a pattern bit that I'm going to use to route up my pattern now you can also take other sander and just send it to a shape it's not that critical if you want to use a pattern bit I would highly recommend you dedicate a certain bit especially for routing plywood plywood is horrible on tools you would just eat it up now those of you who have bought my Big Daddy pattern bit I would not use this thing I would refrain from using it because plywood will eat up any kind of tool so I'm going to start by installing my back fence first since I'm not using it for squaring my cuts I'm just going to position it flush to the back edge okay now I'm ready for my first cut I need to solve so this way I can use that as a reference to screw off my sled so before I do that I want to use a backing board this way when the Salt Lake comes through would be a nice clean cut so I want you to take notice that my saw curve didn't cut all the way through a stops I of the fence if I cut all the way through I would have more support here so I want to make sure that my fence is properly adjusted and securely fastened before I make my final cut now before I install my fence I want to cut a athens by Athens rabbet on the inside bottom of my fence for dust relief so to install my fence I'm going to screw down one side first leaving the other side free to pivot so that this way I can get myself close to square so the help square off my fence I'm going to put an eighth inch Jim right in my saw curve my square right up against it give it my fans until I right about there I'm going to clamp it down and I'll put a screw on this side now I'm ready to do my five cuts now as you can see I have a rectangular piece here I always like to use the longer side as my first and fifth cut it gives me a better reading so remember let's mark our first side and let's make our cuts okay so let's take our reading and see what we have for the top here or a reading we have 0.896 let's see what we have in the bottom meeting our be reading he is 0.842 so now I'm ready to calculate to see how much we're off the top measurement which is a measurement is point eight nine six – the bottom measurement which is B which is point eight four two divided by four which is the four angles divided by the length of the fifth cut which is twenty four times the length between my pivot point on my fence in this case my screw right down here is about here and it's about twenty eight and a half so twenty-eight point five and my error is actually sixteen thousand over twenty eight and a half inches so to make my adjustment I put my fence back out not because it is a positive number that means my fence is too high I have to bring it back down I first find sixteen thousand here's my feeler gauge here sixteen thousands of an inch right here because the fence is going down we'll put my clamp right at this point where I'm going to be putting my feeler gauge up I'm going to clamp it down bring out this a bit I usually like to put two clamps on here unscrew the screw screw here defense back put the feeler gauge right here and then I'm going to clamp it down now I want to double check make sure it wasn't too tight perfect okay so I'm going to put a different hole in here now I'm ready for my second five cut and just remind myself I might draw a little line here so here we go okay so here it is our fifth cut the moment of truth remember just bring about about an inch or so like this okay so here we go get my caliper and let's see what we got a cut is the top you'd read seven nine zero let's do our bottom cut let's see what he reads seven nine one some only a thousandth of an inch off I can live with that woohoo now that the sled is all squared up I'm going to install the rest of the screws to secure my fence so for the most important part about the sled is your safety guards you want to make sure that you have a top guard and also a rear guard so to make the top guard I'm going to start by routing the slots so now I'm going to mark out for my slots I'm just going to go two inches on each side so I've 10 inches right in the center I'm just going 8 and then also want to go 5/16 over because that's the size of bit that I'll be using because my stock is the quarter of an inch so now that I have that marked for the square in here so here I have my router bit position right between the two lines where my cuts going to be I set my stop I also did the same thing on this side I have my stop set over here so the depth of because it can be 1/2 inch I'm going to be done two passes so to cut the rabbit all i have to do is just put a stop against my fence and that will right against that so this is a glue that I'll be using I picked this up at my local plastic store where I bought my material you also want to make sure you get yourself a little applicator we've got almond you can see this but this tiny little needle this will help you get your glue right in the corner very easily I don't know if you can see the glue but just fill this up right into the gap so here it is the glue dries almost instantly so what I'm going to do now is I'm going to use one of these figure 8 top fasteners to kind of secure it in place I'll just put one here and if I needed to get I just pivot it out so for my rearguard I just use some scrap wood and I make myself basically an open box like this and I just glued on right to the back now I don't use any screws or dowels and this lads have been around for like 2 3 years a lot of students come through here and use it I never have one break off or failed on me yet so before I glue my guard on I want to do a little bit of a relief cut right here on the edge here because my base is actually sticking out a little bit and it's not really quite flush with my fence make sure you put enough glue in here use a real thin little for a spacer okay I'm going to clean up my glue let that sit for 24 hours there you have it so I hope you made a stand along with me I know you're gonna love it it's going to serve you well we've got a lot of videos in the work subscribe to my channel and we'll get it out to you again thanks for watching and we'll see you next time you