Making accurate angle cuts on short pieces on a miter saw
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  1. #1
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    Default Making accurate angle cuts on short pieces on a miter saw

    I'm trying to make an angle template for cutting small angle adjustments (5-9 degrees off of center to the left or right on the rotating base) on a miter saw. The problem is that the fences on all miter saws are not a continuous straight fence (they start moving forwards slightly as you go off-center). If the piece is long enough to cover the entire fence length (on both sides of the blade), then you're good. But if you're just trimming the end or cutting only a bit off the end, then the angle you set the blade to doesn't match the angle of cut you'll get. I was going to make some laser-cut templates that would work "better than the current method" (especially when just trimming the end) but it when you're shortening the length and cutting at an angle (or even just wanting to cut at 90 degrees) that the main problem is.

    I attached two diagrams that hopefully show the problem. Tried a Google search and couldn't find anything. The angles they need to cut are 5, 7, 7.5, 8 and 9 degrees (off of center). The "gauge" I show is triangular but, if I go with this method, I would make them more like a parallelogram (one and on one end, a different angle on the other). They could be flipped depending on which side your cutting on.

    Just trying to find out if there's a better way. The main benefit of the templates is that they would be "fixed" for these angles (avoids adjustments).

    Thanks,
    The Dude

    miter-gauge-2.jpg
    miter-gauge.jpg

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    If you are going to cut small pieces at an angle on a miter saw the first thing is to make sure you have a zero clearance base. The easiest way to do that and cure the fence issue is to make a piece of "angle iron" out of thin plywood. In use you clamp it to the fence with small clamps. The angle piece also makes a good place to mount the wedge that positions the work piece at an angle to the 90° blade.

    With small pieces you NEVER want to hand hold as it is too easy to get pulled into the saw. Also, with small pieces you must cut through and then stop the saw before raising the blade.

    I've cut many small pieces at odd angles on a miter saw and I always improvise some sort of jig unless it's a one-off and then I just tape it to a piece of scrap with double face tape and turn the blade to the appropriate angle.

    PS: What brand of saw has a non-linear fence like that? Usually the height gets shorter as you get closer to the center to allow clearance for the saw motor, etc. on compound angle cuts but I've never seen a fence that wasn't straight across.

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    I often use a pencil or nail to make small angle adjustments. Put it between the work and the fence. Make a mark to repeat. Its like a sine bar.

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    Thanks for replying. The pieces aren't "small", the angles are (just off zero). I thought about making some kind of shim, sounds like it would work like the pencil/nail thing.

    The Dude

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    You’ve probably already thought of this, but I have to ask — are the fences adjustable?

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    I just checked my three miter saws with a straight edge. All are straight. What brand saw do you have? I will want to avoid it. From what you are saying, a long piece of material would only touch the fence on the outer ends of the fence. I have never experienced this on any miter saw.

    Remove the fence and use some shim stock to fix or have the face of the bed machined true. No need to make fancy gadgets to bandaid a defective saw.

    If they are not straight you can not even make a true 90 degree crosscut in long material as the material would pull in (and pinch the blade) as the blade nears completion of the cut.

    And if what you say is true, for end trims, just offset the angle by the amount of error. This will be a constant offset for any desired angle.

    Bill

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    Quote Originally Posted by medsar View Post
    You’ve probably already thought of this, but I have to ask — are the fences adjustable?
    No, they are not.

    Quote Originally Posted by Bill Simmons View Post
    I just checked my three miter saws with a straight edge. All are straight. What brand saw do you have? I will want to avoid it. From what you are saying, a long piece of material would only touch the fence on the outer ends of the fence. I have never experienced this on any miter saw.

    Remove the fence and use some shim stock to fix or have the face of the bed machined true. No need to make fancy gadgets to bandaid a defective saw.

    If they are not straight you can not even make a true 90 degree crosscut in long material as the material would pull in (and pinch the blade) as the blade nears completion of the cut.

    And if what you say is true, for end trims, just offset the angle by the amount of error. This will be a constant offset for any desired angle.

    Bill
    I have two miter saws at home and both have a slightly convex back gauge, just like the one at my clients. Also, the angle will change depending on how far you move the piece along the back gauge, unless you reach at least the outward point on each side. This is a real pain when you're trying to make 90 or 45 cuts as the detents are right at the edge of where you need to adjust, making it difficult.

    I'm starting to think that they best option is to just modify the back gauge.

    Thanks,
    The Dude

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    Dude, as Bill mentions the back gauge as you call it should be straight across. It's incredibly unlucky that you've come across three saws with the same issue, which is clearly a design/manufacturing flaw.

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    I wondered about that, was thinking maybe it was a safety thing to avoid jam-ups or something like that but, if anything, seems like it would have a slightly convex angle to accomodate that. Mine aren't high-grade but the customer's is. I would urge you to check yours as it's a very slight angle although, if you're needing to make accurate cuts it's likely that you would have discovered this by now.

    The Dude

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    I would straighten the fences or fence depending on the design. If the fences are two separate pieces manually sand them flat and then adjust them true.

    You can sand them flat by using the cast surface of your table saw or shaper table (check flatness first) and sticking down some sand paper. Move part in circles and figure eights and reverse part occasionally to provide even sanding. If the part is not flat it will show immediately on the sanded surface.

    If your fence is a continuous piece with a horseshoe connector then you will need two sheets of sandpaper on the cast surface for the increased length. The grit to use will depend on the amount of material to remove. The horseshoe may flex so a more gentle sanding may be required for this design.

    With some patience and periodic checking you should be able to get it flat within a few minutes.

    I have corrected everything from aluminum intake manifolds, heads to bearing retainers using this method.

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    Quote Originally Posted by Bill Simmons View Post
    I would straighten the fences or fence depending on the design. If the fences are two separate pieces manually sand them flat and then adjust them true.

    You can sand them flat by using the cast surface of your table saw or shaper table (check flatness first) and sticking down some sand paper. Move part in circles and figure eights and reverse part occasionally to provide even sanding. If the part is not flat it will show immediately on the sanded surface.

    If your fence is a continuous piece with a horseshoe connector then you will need two sheets of sandpaper on the cast surface for the increased length. The grit to use will depend on the amount of material to remove. The horseshoe may flex so a more gentle sanding may be required for this design.

    With some patience and periodic checking you should be able to get it flat within a few minutes.

    I have corrected everything from aluminum intake manifolds, heads to bearing retainers using this method.
    Thanks, that was part of a plan (to try and modify it). The main fence bracket is rather long, I was originally thinking I might have it machined but your suggestion is worth trying. I looked at it again yesterday tyring to figure our a way to shim the fence extenders that mount to it but there's just no easy way.

    The Dude

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    Cut it slightly long, measure the angle, then adjust and make your final cut?

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    Unless you are maxed out in capacity of the saw, just shim a sacrificial fence so that it’s square to the blade(and travel if it’s a slide miter)
    All the compound miter saws I have seen have the stock fence relieved to accommodate the left/right tilt and even a non compound saw usually has a wide blade slot, a sacrificial fence will help in both cases by making a tight fit to the blade.



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