Table saw sleds, How 5 cut do you need to be?

good forum to add george. this made me think about my sleds and if there still accurate so i went and made some cuts. using a good quality square both are still dead on. my big one is made from melamine and oak, the smaller one used for dados is made from baltic birch and oak.

I made my big sled using the 5 cut method and find it’s still very accurate. The problem is that I have an Incra HD miter gauge which is so accurate it makes anything else seem poorly done. I use the Incra far more than the sled, unless it’s a weird shaped piece that I can’t hold true on the miter gauge. 

I also tend to use manufactured miter runners for jigs now. They’re adjustable and don’t swell or shrink.

for the sled on my delta TS i used the ones from rockler.

If it's a sled that I plan to use a lot I used to use the MicroJig Zero Play bars.

On a 45* sled I made on the cheap for my Right tilting General 350 I bought a pair on Amazon, Chinese made, Aluminum, fully adjustable, ball bearing, and measured at 300 MM. They were cheeep, and actually worked quite well. I loved the name, Estink. I laughed about that for a while. The Zon must have been selling a bunch of them, they got to me next day, even though they said 2, 3 days. I would seriously buy them again. Beside price I don't see anything between them and the MicroJig sliders. Actually the MicroJig are flimsy until they are mounted, these were rigid, and quite easy to use.

The last quick jig I did was my 1/4" finger joint jig, and I cut out some QS WO and fit them using a shooting board, they remained stable and slick through all 4 seasons. Just only over a year old, so long term hasn't been decided.

Estink 🤣🤣🤣

Those look exactly like the Incra bars except in aluminum, though the zoo says aluminum alloy and then says stainless steel). Don't see any form of ball bearings, just the expanding nylon washers.

I haven't looked for slides in eons, surprised at the variety now available.
My wider-than-standard Unisaw is unable to best use the design as the adjustment range (of the Incra) is not enough, but these appear to be a decent and inexpensive way to make some jigs that fit a slot without the usual headaches and expense of other aftermarket stuff.

The ones I have gotten are Aluminum. I saw the discrepancy when I first ordered, and after thinking about it figured if the MicroJig product was plastic, any metal would be ok. I guess my word use of ball bearing was trying to eggsplain the adjustable effect that widens them in the slot. It's full travel, to the point you can actually lock them in place, or make them sloppy. I kinda prefer the just right option though. 

Yean, they really aren't stinky at all.... :-)

Both my General, and my contractor Delta have a standard 3/8 x 3/4 slot, but both are a sloppy 3/4" so the adjustable feature is a good thing.

Good thread George.  As a machinist-turned-engineer, I have some thoughts on using wood for fixtures/jigs that I generally try to keep to minimum.  But since you opened the door...😆 

How precise should you dial it in when you make it?  Well, as you said, over time it's only going to get worse.  So I say as precise as you possibly can.  Regarding sleds specifically, the 5-cut method is a sound one IMO and a method that most woodworkers can use with measuring tools they already have.  I'll go with the supposition that (a) the blade is set dead parallel to the miter slots and remains that way and (b) the sled fence is dead flat and can't move and (c) the miter runner is locked in solid and can't move and is consistently tight through the entire cut in the slot.

Let me back up a bit...  In mechanical design, we use a principle called exact constraints.  What this basically means is that you control a design by making sure that no components are over or under constrained.  Applying this to a table saw sled, you have 6 degrees of freedom to consider:

Exact constraints tell us that we must constrain (prevent) motion in any of these that we don't want the sled to be able to move in.  So for each DOF (degree of freedom) we need a design control to either (a) restrict it to a desired range (b) allow unrestricted motion or (c) eliminate the possibility of motion.

So, for our sled, we want the only motion to be unrestricted freedom to move front-back through the cut.  We want all other degrees of freedom eliminated.

Let's assume our sled is heavy enough that it's unable to lift off the table.  So the weight of our sled constrains #1.  

#2 is a little trickier.  Our miter slider has to stay engaged with the slot through the full cut for us to get the results we want.  No problem keeping the bar IN the slot right?  As long as the bar is at least as long as the sled, we're good.  BUT, from experience I can say that it may not be that simple.  My miter slot on the right side of my table is pretty worn and measures several thousandths of an inch wider in the center than it does at the front and back of the table.  So in order for my slider to constrain the sled against motion, it not only has to be IN the slot but it has to engage the slot fully through the full range of motion.  So on my saw, that can't be done with a simple bar (I'm not even going to get into sliding fit tolerances in this particular diatribe) because if I use a bar that can slide freely through the infeed and outfeed sides at the front and back of the table, it will be "sloppy" in the center of the slot and the sled could shift while the work is in the cut.  So what's a girl to do?  There are some options:

#3, as we said, is a DOF we want to retain.  We want our sled to slide front to back freely and unconstrained.

#4 is in most cases constrained by the table and gravity like #1.  Special cases may exist for very large sleds that aren't fully supported by the table during the full cut and can "tip" off the table either at the infeed or outfeed of the cut.  Most of us would solve that by using either temporary or permanent infeed/outfeed additions to the saw.  As far as the sled itself goes, most of us have "T" miter slots with wider sections at the bottom.  Adding washers to the bottom of the slider that will engage the bottom portion of the slot can prevent rotation in this direction.  But they should only engage the top/bottom of the wider part of the miter slot.  If they engage the sides as well, we have committed a faux pas and over constrained #2 again!

#5 is again not a big issue in most cases unless you have a really big sled and a really small table.  If your sled is fully supported by the table, gravity takes care of this.

#6 ties in with #2.  Same basic resolution of the latter will prevent the former assuming your slider(s) are rigidly attached to the sled.

So there is a birdseye view of the Principle of Exact Constraints and how it can be applied to something like a table saw sled.  We could dive much deeper of course and go into material selections, thermal considerations, sliding fit tolerances and if we really wanted to dig in, we would need to consider the design and tolerance of the flatness of the saw table, how the arbor is constrained to run true and stuff like surface finishes and hardness of the table and miter slots.  So feel free to expound if you wish 😁

Now for a little practical experience instead of theory...

I started out using a sled when I first got my saw.  I didn't have a miter gauge and it was the best way for me to get accurate cuts.  Then, like Ryan, I got my Incra miter gauge and shortly after decided I was tired of storing my sled and to the dump it went.  So my general methods have changed and there are times I have wished I still had the sled like for really small or really large pieces.  But I haven't ever wished hard enough I wanted to store another one.  I will say that the sled stayed really accurate for several years.  I built adjustability into my fence when I made it because that's what always seems to go bad for me with wood jigs, the squareness.  

lot of good info kenny. i know you say, dont do two sliders but i always have and never had an issue. after seeing this thread it made go and check how accurate mine were. after several years they were both still dead on. maybe i got lucky ?

Wood runners like you have are a different animal pottz.  When you factor in wear and movement of the wood, two is probably the better solution.  If I were designing a sled to sell, or for someone else, I wouldn't use wood because of the variability with humidity and the fact that it wears pretty easily.  On the other hand, if I was making a sled for me and I didn't want to buy metal runners, I could find some wood that was stable enough for the task and do like you did.  And like I said, my long post was just about theory.  Practice is what really matters in the end and if you have 2 wood runners and sleds that stay accurate, there's no point in fixin' what ain't broke!

Awesome info Kenny. I don't have the first bit of engineer in me. :-)  Other BIL, and his ultra wierd Son are both Engineers, and they drive me kinda goofy. :-))))) The BIL is always looking to re-invent the wheel, just to open the cars door. Me, I'm like, just grab the doors handle, and open the thing dood. It's good to get the idea though. As a whole we are much better for having Engineers 

I'm like Larry and for a "sled" I prefer the use of both slots. I suppose it makes things a little harder to get right, but in my mind a Miter gauge is just one slot, but it's principle problem is probably the rotation, or potential to lift and move that way. With a sled and using both slots I feel it is much more grounded, and once you do get it moving freely, but not sloppily you have a sled that can bring greater accuracy, plus carry larger pieces. My poor mans sliding table.... :-) 

Saying this, my way of checking results is to use my trusty Starrett and placing it on each corner check to make sure I'm not seeing any daylight. I guarantee you use a much more thorough checking which is more like the 5 cut result.

Because at the end of the day, you have that "Wood moves" thing I referred to earlier, I find that my way is fine, and after you put all the pieces together if it sits flat, and doesn't have gaps all over I'm good with the result.

Plus my average time spent on any jig or sled is less than 30 minutes if I am able to do it that quickly. I guess I'm not looking for pretty, just helpful. My principle operating theory (when it pertains to shop fixtures, cabinets, whatever) is Life is too short....

Too short to worry about...

Too short to spend time on....

on and on.

I see a lot of makers that have Walnut cabinets, beautiful, but I'd rather spend the resource, and time for something that will live inside the house, not out in the shop where there is always a fine layer of dust, and everything gets beat to he!! and back. Different strokes for different folks kinda thing. But shop stuff s not something I will use expensive resources, or time to make. It's as if the shop stuff is the goal. My brain doesn't work that way. I don't think either way is wrong, it's just what floats a persons boat, ya got to be happy with what you are doing.

Now with your view that you want to make it as accurate as you can. I have always said if the machine is set up to 0.001 kinda standards than you can only blames yourself if the cuts are dodgy, and I still try to do just that. but just on metal machines. I feel the differences between wood, and metal are metal set up's will stay put a lot better than wooden ones. Thoughts like screws wallowing out, and becoming loose, things like that. Screws and bolts on metal could potentially loosen too, but a dab of reversible locktite can go a long way toward holding them tight.

I guess I mirror my Dad, and Uncle's thoughts about same, probably most of us pick that kind of stuff up as we grow up.

Probably a Pschy person would say, these are some troubled doods. LMAO..

After watching those videos I went out and checked my seldom-used big sled and found it had some considerable slop (from a precision standpoint anyway). I used the blue tape trick and tightened it right up. 👍🏼

I know my two miter slots are different from each other owing to wear on an old saw. That said, my trunion is true and the blade runs parallel, so my jigs and setups seem to work pretty well from a precision standpoint.

Having a little (and just a little) metal working experience, I concur with Kenny. I spend a lot of time dialing in my chineseum mill and lathe, down to the thou. They do fine for the work I do, but it becomes obvious how much more pressure is being forced on the metal working tools trying to engage the project.

‘Flex’ is a real thing and it’ll show up in (my) finished projects if I’m not careful. That’s why real metalworking tools are super beefy. But it also brings an interesting ‘workshop premise’ to light that I think any woodworker needs to think about: understand not only the design limits, but also the practical functional limits of your wood working tools.

That doesn’t mean you have to have all the numbers at hand, but understanding how hard you can (vs should) push a machine will certainly affect your outcome. I was just reading something about bandsaw drift, which I think is a perfect example of this. A properly set up and used bandsaw of reasonable quality does not drift! Improperly set up wheels and tires, improperly tensioned blades, dull (improper) blades, improper tooth count, or improper feed rate will cause drift. 

I certainly needed a lesson on feed rate early on, and I think a lot of guys do. You wanna make your head spin, read a good article on chip load and feed rate for end mills. 😳 But, once you start to understand the limits and range of your tools, you can turn out great stuff. 

It’s arguable (I’d say I agree with it) that larger, heavier, more ‘professional’ tools will make all this a little easier. Specifically because of their build quality and (usually) mass, they’re less likely to lose their settings once dialed in, and they’re less likely to suffer from being under powered (which leads a novice to over-feed). That’s not to say a professional machine makes a novice’s work turn out like a pro’s, but it does take some of the variables out of the equation. And I need as few variables to contend with as I can get!!

What’s the saying about a professional is just better at knowing how to correct their mistakes? I’d also argue a professional has a better understanding of his machines and how to get the best out of them. 

All this to say that building on simple, accurate benchmarks when making a jig is probably the best way to get an accurate jig. Aim small, miss small. 

On Wooden runners, you are asking for movement and trouble ahead if you don't use QS wood with the grain presented with it running up and down as it sits in the slot. That way the wood movement will possibly make your sled taller or shorter, but won't make the wood bind in the slot due to seasonal changes. I'd suggest never to use flat sawn wood, as it will definitely bind up if it moves, or at least gets overly snug.

Pics below to show what I mean here, in case the words didn't do it.

Any of the above runners could work. The plywood slice is "Dimensionally stable" so it shouldn't move. I don't suggest it's use on a runner though as my experience shows a much higher likelihood of delamination on very small slices of plywood, so while it may seem stable, it, with the addition of screws will likely delaminate. Both of the other pieces are heavily rift sawn pieces, and likely won't have much movement side to side. So again the taller, or shorter sled won't effect operation, except for needing more blade height. True QS would be better IMHO though.

Probably will work fine

IF you have a slotted miter slot, that is used as a safety feature to prevent tipping of the gauge, or a sled. I wouldn't ever suggest trying to fill the lower slotted portion with wood, even QS. Instead make the QS runner just to fit the upper portion of the slot, and if you wanted the safety feature of using the lower slot, then screw a washer to the bottom of the runner, so it engages the wider slot. You will have an easier time of it that way.

My thoughts on this and 75 cents may get you a weak cup of coffee at a diner. 

i dot see any need for a t type runner though, very little chance the sled will ever lift up during a cut. mine will get ya that coffee and one sugar cube !

Wood still moves radially.  It's less than tangential movement, but it is a factor.

You da man Kenny!

I almost always use my sled for 90° cuts.  I followed William Ng's design fairly closely.  I have not checked it in a while to see if it is still square but I have not noticed any problems with non square cuts either.   I make a lot of cuts with my sled that I would not even attempt on my table saw without it.  I have an Incra miter gauge but only use it for cuts other than 90°.  For fairly long pieces, I find the miter gauge cumbersome and for relatively small pieces, unsafe unless I attach an extra long fence to it that extends  past the blade.  A long fence on the miter gauge adds more variables.  It can flex and add error to the cut, for example.  Also, especially with small pieces sitting on the table, the friction with the table adds another thing that can cause pieces to shift.  The fence on the sled also ensures that the cuttoff piece, which would be unsupported with a miter gauge, is pushed through the cut reducing issues with the cut off pivoting at the end of the cut and being damaged or even splinter off at the end of the cut.  

EDIT to add: It seems to me that there may be 2 more constraints to consider which may be special cases or use cases perhaps.    
First, when cross cutting really long pieces, the weight of the unsupported end can make a cross cut difficult because the supported end with tend to pivot upwards.  With a miter gauge, this can be difficult to achieve but with my sled, I can use a clamp on the fence  to help hold down the short end.  
The second thing is eliminating issues that friction between the piece and the table can cause, like the unsupported cut off mentioned above.  A sled eliminates this by pushing both sides of the cut completely past the leading edge of the blade.

Larry, especially with a heavier sled the T slots with an engaged washer will really help at the start of a wider cut. Something where you really need the sled pulled back to lay the stock on it in front of the blade. Say a panel cut on 12" or wider stock. Most cabinet TS's only allow about 14" of running space in front of the blade. Benchtop, and other smaller saws less.

If your runners do extend out front as Kenny suggested, they would engage the T slot and while not being hands free kind of stable, will let the T help hold the sled when pretty much fully withdrawn.

Internet maker Izzy Swan has 2 different items he markets that will help with sled or wide stock support even if you lack a T slot.

Saw mounted support leg. He calls it the "Large material folding table saw infeed"  The page has a video showing it being set up, and in use. You could opt to get his plan, or look at it and roll your own.

Also saw mounted is a small extension support he calls the Table Saw infeed saddle Here he offers to sell you the saddle, but again watching the video you could suss out enough knowledge to pretty easily roll your own.

I never know with Izzy if he has the original thought, or if he is a great copier of ideas?

Wood still moves radially.  It's less than tangential movement, but it is a factor.

Hi Rich. this is why I will always use QS WO, or Hard Maple, both will move very little, if at all. You will see that tangential movement a lot more with softer woods of the hardwoods, and almost all of the softwoods.

Good to point out though, as wood choice here will effect result greatly

I think those forefather guys heading West all those years ago, and their predecessors who in Europe, and elsewhere used and tried all manner of trees for different jobs to figure out which were the best performers. I imagine a lot of trial and error went into that knowledge base.

Maybe the biggest reason I like the Wood Database so much. Each listing for every species/variant has a section showing what it is good for as far as uses. Strengths, and weaknesses so to speak.

WO

Likely you won't find a wood listing saying makes killer table saw sled runners, but if a wood is listed as being strong in the flooring market, then it will be stable as a runner. Especially if a QS section is used, and correctly positioned. 
 

Good ideas for infeed supports George.  I have 3 of these guys I use when needed for infeed/outfeed helpers.  They suit my needs but can be a little of a pain on uneven floors like my shop/driveway.

Nathan, you're right about the downsides of a miter gauge.  I have trouble with longer pieces using mine which is precisely what prompted me to finally make a shooting board.  I'd disagree about the friction issue being a problem for miter gauges though.  More surface area=more drag from friction.  And unless your Dr. Who, your work has to be smaller than your sled 😉  But I agree that friction is a concern in general.  I think in both cases, sled and miter gauge, the greatest source of friction is in the miter slot/runner.  At least on my table saw.  I wish all saw makers would standardize miter slots as dovetails.  When I had my sled, I put formica on the bottom side and that worked great.  

If you go to my project on the bad place, you'll see I built it with two hardwood runners.  I eventually replaced them with a single adjustable runner.