How do I make a table saw sled square, and will that make a not so great saw better?

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  • FuryRoad
    Forum Newbie
    • May 2016
    • 19
    • Atlanta, ga

    How do I make a table saw sled square, and will that make a not so great saw better?

    I hope "square" is the right turn. How do you know if a sled is square, lined up right and all on the table saw? I saw plans to put a piece of wood in the miter slot and glue the sled on top. And let's say I can get it square, does that make things better than using the fence? I mean this for cross-cutting, no fence, just the sled. I was hoping I could turn a not so good saw into a much better or consistently cutting saw. Am I fooling myself?
  • mpc
    Senior Member
    • Feb 2005
    • 979
    • Cypress, CA, USA.
    • BT3000 orig 13amp model

    #2
    If the saw doesn't cut consistently you'll need to figure out why... some problems can be fixed by a good sled, some won't be fixed.
    With the saw unplugged:
    * raise the blade all the way. Kneel down in front of the saw and spin the blade by hand as you view it edge-on. Look for any wobble. If you see any, the blade is either bent or the arbor shaft is bent. Whichever is bent must be replaced. Otherwise you'll get an extra-wide and sloppy cut... If the blade is bent, install another one before proceeding with the rest of the tests because we're going to use the face of the blade as a reference for a lot of tests.

    * raise the blade about half way. Grab it just below the teeth and try wiggling it side-to-side (left-right as you face the saw). Is there ANY play, looseness, etc? If so, the arbor bearings or the structure that supports the arbor are worn, loose, etc. No sled or other gizmo is going to fix this... basically the arbor isn't holding the blade consistently so there is no possibility of consistent cuts.

    * With the blade still half-raised, get a small block of wood (about 4 inches by 4 inches) and put it next to the body (not teeth) of the blade. Bring the rip fence just to the edge of the wood block. We're setting up a reference distance... move the block fore/aft (along the side of the blade but not into the teeth) and get a feel for how much friction there is.

    * Now raise the blade all the way and repeat the wiggle test test without moving the fence. Any difference? Some badly aligned saws, or saws with bent internal parts, may show varying amounts of slop/play depending on blade height.

    * See if that test block of wood still fits between the blade and rip fence - and move it fore/aft again and see if it feels about the same. No? Then the blade might be moving left/right or angling a bit when the blade height is adjusted. That's a sign of really messed up saw guts. That also means any inch scale on the fence assembly can't be trusted because the blade moves left/right as height is varied.

    * Get a small machinists square, a woodworker's combination square, or even a plastic drafting triangle from an art store or office supply store (they're amazingly accurate... buy a "30-60-90 triangle" with the short side about 3 to 4 inches long if possible). Set it on the table next to a fully-raised blade. Is the blade really 90 degrees to the table? If not, use the saw's bevel adjust wheel to get 90 degrees. Most saws have a screw+locknut inside somewhere to make a positive 90 degree stop; you may need to adjust this. While the square is still next to the blade: rotate the blade half a turn and see if the blade moves towards or away from the blade... it shouldn't. If it does, then the blade or arbor are warped/bent.

    Check the main rip fence:
    * use a Sharpie or other pen to mark one tooth on your saw blade. Rotate that tooth towards the front of the saw, close to the top surface. Use that little block of wood again to set the fence with the wood block against that tooth this time. Now rotate the blade so that tooth is at the back of the saw. Use the block to check the fence-to-blade distance. Is it the same as the front? If so, great. If not, the fence needs to be aligned to the blade. Lots of methods to do that... usually a few screws have to be loosened. If the back (outfeed) end of the fence is SLIGHTLY further away from the blade it's not a big deal; some folks purposely miss-align fences this way to reduce the chance of kick-back. If your fence is this way though you must remember to never move it to the other side of the blade. If the distance at the back of the fence to the blade though is closer than it was at the front of the blade that's dangerous (and it's the same as moving the fence to the other side of the blade): the infeed side of the blade will cut the work... but as that cut piece now moves to the rear of the blade it will be pinched by the incorrectly adjusted rip fence into the up-moving blade teeth. That leads to kick-back and the workpiece being thrown back towards your face. Especially if you don't have the blade guard and outfeed hold-down palls in place.

    * next, use your square to test the fence: put the square on the tabletop against the rip fence. Is the face of the rip fence exactly 90 degrees to the table top? If not, you'll get different cut sizes depending on the thickness of your workpiece. Imagine the fence "leans in" towards the blade at the top. A thin panel will run against the bottom of the fence... a thicker board will ride against the top of the fence so you'll end up with a slightly narrower cut than you planned. It's really annoying when cutting tenons since you'll be turning the workpiece edge-for-edge several times. Two cuts will be close to the bottom of the fence, two will be guided by the top of the fence (if the fence is leaning in) resulting in slightly different shoulder cuts on the tenon. Yuck.

    * how snug/tight is the fence? With it locked down normally, push side-to-side at the far (outfeed) end of the fence. Any deflection? Hopefully not but many fences will flex slightly if you push hard enough. If it moves with little force then you'll have inconsistent cuts as the fence flexes in response to whatever force you use to hold the work against the fence. Not good. And not safe either. If it takes a good shove to flex then it's okay.

    miter gauge checks (this is what is most likely bad on your saw based on your desire for a sled):
    * First, put it in a slot so the bar is completely in the slot - no part of the gauge is hanging off the front or back of the saw. Wiggle the gauge side-to-side. There is probably a little motion - very common in inexpensive saws or older (worn) saws. Aftermarket miter gauges come with adjustable width bars, screws poking sideways, or squishable plastic washers, to remove this slop. Thin metal foil tape (duct work tape) applied to the one side of the bar is a simple way to adjust your existing miter gauge to remove this slop. Re-test with the bar half-way hanging off the front of the saw and half-way hanging off the back of the saw. If the "feel" changes depending on where the bar is in the slot then the slot may not be straight or a consistent width. That's not easy to deal with. A sled - with extra long slot runners - is about the only realistic option.

    * lay your square flat to the table top, against the face of the miter gauge and against the body of the blade. Verify 90 degrees. If not, adjust the miter gauge.

    * if the miter slots in the saw table are not parallel to the saw blade the miter gauge (and sleds) will never work correctly. On most saws, you adjust the assembly holding the saw blade to the table to get the blade parallel to the slots. The BT3 saws are unique in that the blade is fixed and everything else adjusts to match. Use that Sharpie-marked tooth to measure the distance between the slot and the tooth with that tooth at the front of the saw... then again with the blade turned so the tooth is at the back. The measurements need to be identical. If not, find out how to adjust them on your saw. You'll then have to re-align the rip fence and miter gauge.

    Those are basic tests for any table saw. You are looking for 90 degrees wherever things are supposed to be perpendicular, you are looking for any slop/freeplay, and looking for things that move off-axis such as blade height altering 90 degree angles.

    A good sled helps make accurate crosscuts since most miter gauges are rather small (in width) to fully support a workpiece. And you have to double-check that it actually IS set to 90 degrees whenever you reset it... a sled doesn't change its angle so it's always whatever angle it was when built. Another thing that helps a sled is most folks make the "runners" for the miter slots fairly long - much longer than the factory miter gauge. So the sled will have better guidance especially when half of it is hanging off the front of the saw for larger workpieces. Trying to cut a too-large workpiece with typical miter gauges is difficult... it's just too hard to hold that unbalanced board hanging off the left side of the saw and to keep it consistently in contact with a small factory style miter gauge fence.

    To make a sled... make a flat base that straddles the saw blade and both miter slots. Attach the miter slots (sticking them into the slots with double-sided tape on top of them, then setting the base onto them is a quick way to get those parts aligned. Don't worry about the base of the sled being square to the miter slots... it's the back fence that matters. Add something along the outfeed end of the sled to hold the base together when you make the first cut - that cut wants to cut your sled in half, right? A 1x4 or 1x6 on edge for example. For the back side of the sled - where you'll be attaching a fence, use your 30-60-90 triangle or your combination square: attach the fence to the sled base with a screw about an inch to the right of where the blade will cut through but don't fully tighten it just yet. Run the sled through the spinning blade until it just cuts the fence. Shut the saw off. Pull the sled back a little and then raise the blade so you can put your square against the blade body (not the teeth) again. Pivot the fence into the other side of the square to align it and then install a second screw to hold it there. Tighten everything. Then sand or cut off any bit of the base sticking past the fence if you want to pretty it up.

    mpc
    Last edited by mpc; 05-23-2016, 05:05 AM.

    Comment

    • poolhound
      Veteran Member
      • Mar 2006
      • 3195
      • Phoenix, AZ
      • BT3100

      #3
      You are not fooling yourself. x-cut sleds properly built and setup and very accurate. I have a x-cut and panel sled I built years ago for my byt and they cut dead one 90 degrees or "square: every time. As mpc said you do need to start with your saw and make sure its tuned appropriately as that is always your baseline.

      Check out this wood whisperer video. as well as showing options for construction he shows the "4 cut" method of measuring and adjusting a sleds fence.

      Jon

      Phoenix AZ - It's a dry heat
      ________________________________

      We all make mistakes and I should know I've made enough of them
      techzibits.com

      Comment

      • Bill in Buena Park
        Veteran Member
        • Nov 2007
        • 1865
        • Buena Park, CA
        • CM 21829

        #4
        Originally posted by mpc
        * if the miter slots in the saw table are not parallel to the saw blade the miter gauge (and sleds) will never work correctly. On most saws, you adjust the assembly holding the saw blade to the table to get the blade parallel to the slots. The BT3 saws are unique in that the blade is fixed and everything else adjusts to match. Use that Sharpie-marked tooth to measure the distance between the slot and the tooth with that tooth at the front of the saw... then again with the blade turned so the tooth is at the back. The measurements need to be identical. If not, find out how to adjust them on your saw. You'll then have to re-align the rip fence and miter gauge.
        After all the other checks, this is the last and most critical check for using any sled with a runner that rides in the miter slot. Depending on the size of the workpiece you are crosscutting, you could have a sled that rides the rip fence, but the fence also needs to be correctly aligned and the workpiece should never contact the rip fence during the cut.
        Bill in Buena Park

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