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Thread: advice on cuting a straight line cut using a jigsaw

  1. #1

    advice on cuting a straight line cut using a jigsaw

    I am making a bookshelf with 3 degree angled sides bottom to top. Bottom and top shelves have through tenons. I cut the tenons and now need to remove the piece of waste between each tenon. I made a 3 degree tapered base for the jigsaw to sit on during the cut so the angle will match the sides, but my first cut was terrible. Not even close to straight. I set up the tapered base as a guide for the saw blade while the jigsaw rested on it at the proper angle, but my technique was crap. I think I can salvage it using a rasp and cleaning it up, but hard to maintain that line across the end of the shelf where it meets the side doing it this way and I am concerned it is now short of the other cuts...

    Should I cut proud of the line with the jigsaw and do my best with the rasp to bring it to down to the line?

    Thanks.

    Brian

  2. #2
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    I use a 1x4 straightedge to make long rip cuts with a skilsaw. It should work with a jig saw.

    Home Depot has 72" straight edges.
    https://www.homedepot.com/s/72%2522%...520edge?NCNI-5

  3. #3
    There are at least two potential pitfalls. You need to use a guide for the saw, as Lowell suggested so the saw base is moving in a straight line. The second potential pitfall is that jigsaw blades deflect very easily, especially when cutting thick material. When the blade deflects you will get a wavy cut that is not 90 degrees to the saw base. To minimize this, use a new, sharp blade that has fairly coarse teeth (3-4 teeth per inch) and cut very slowly so the blade has time to remove the waste without deflecting. Also, start the saw with the blade not touching the wood and slowly bring the moving blade up to contact the material. That may mean drilling a starting hole in the waste for clearance. If your jigsaw has an orbital action setting, it usually helps to have it turned on to maximum orbital action, although that may result in a little tearout or splintering on the top edge, so you may have to compromise. Scoring the cut line with a knife can help avoid splintering on the top surface. Some jigsaws come with a zero clearance insert that helps with this too.
    --Certainty is the refuge of a small mind--

  4. #4
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    Brian, Please forgive me but I am having a hard time visualizing what you are trying to do. Maybe a sketch or a photo might help clear it up. I suspect you may be asking about how to cut a mortise with walls that are not perpendicular to the face of the board you are working on.

    Not knowing exactly what it is your trying to do, I only have a question that may (or may not) guide you to a solution. Instead of using a rasp, would a sharp chisel work better? Often times you can cut a thick guide block to act as a straight straight-edge to register the back of the chisel against. If you need to have the wall of the hole angled relative to the surface you clamp the block to, you just angle (bevel or taper etc.) the registration face of your guide block accordingly.
    Last edited by Andrew Nemeth; 02-05-2020 at 12:18 PM.

  5. #5
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    I can't "see" what you're doing either, but perhaps a flush cut pull saw to cut as Andrew above has envisioned. That's what I would use. Not a jigsaw.

  6. #6
    I've made some pretty straight cuts using my Bosch jig saw and a T-234X blade and a straight edge guide. The blade leaves a very smooth finish and it does not like to turn corners.
    t234x.jpg
    Lee Schierer
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  7. #7
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    Why do you make a tapered base for jig saw? doesn't the base of your jigsaw rotate to cut at an angle? sliding the jigsaw on a tapered base means it will have tendency to slide off the taper and not cutting straight. You need a level base to work with. Also as suggested use a straight edge and go slow, use a good blade as well.

  8. #8
    Quote Originally Posted by Andrew Nemeth View Post
    Brian, Please forgive me but I am having a hard time visualizing what you are trying to do. Maybe a sketch or a photo might help clear it up. I suspect you may be asking about how to cut a mortise with walls that are not perpendicular to the face of the board you are working on.

    Not knowing exactly what it is your trying to do, I only have a question that may (or may not) guide you to a solution. Instead of using a rasp, would a sharp chisel work better? Often times you can cut a thick guide block to act as a straight straight-edge to register the back of the chisel against. If you need to have the wall of the hole angled relative to the surface you clamp the block to, you just angle (bevel or taper etc.) the registration face of your guide block accordingly.
    One end has waste removed one end does notShelf tenon.jpg

  9. #9
    Quote Originally Posted by Paul F Franklin View Post
    There are at least two potential pitfalls. You need to use a guide for the saw, as Lowell suggested so the saw base is moving in a straight line. The second potential pitfall is that jigsaw blades deflect very easily, especially when cutting thick material. When the blade deflects you will get a wavy cut that is not 90 degrees to the saw base. To minimize this, use a new, sharp blade that has fairly coarse teeth (3-4 teeth per inch) and cut very slowly so the blade has time to remove the waste without deflecting. Also, start the saw with the blade not touching the wood and slowly bring the moving blade up to contact the material. That may mean drilling a starting hole in the waste for clearance. If your jigsaw has an orbital action setting, it usually helps to have it turned on to maximum orbital action, although that may result in a little tearout or splintering on the top edge, so you may have to compromise. Scoring the cut line with a knife can help avoid splintering on the top surface. Some jigsaws come with a zero clearance insert that helps with this too.

    Paul: thanks. I did drill a relief hole for starting the saw and did cut slowly, but a guide for the side of the jigsaw would make a straighter cut. thanks. brian

  10. #10
    As much as I love my jigsaw, I would only use it to remove the bulk of the waste, keeping about 1/8" or 1/16" off the line. Then make a chisel guide by sawing a 3 degree angle on the long edge of a scrap board. Clamp this board right on your line, and use a sharp chisel to clean up your jigsaw cut precisely. The back of the chisel is registering against your scrap guide board. Make sure there is another piece of scrap under your workpiece so your workbench will be protected. Tap, tap, tap and in short order you'll have a clean 3 degree edge. I hope this makes sense.
    Edwin

  11. #11
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    Machine an angled board to attach to a router base. Then use a straightedge for a clean line. I'd waste out the bulk of the material with a saw and just use the router to cut to the line.

  12. #12
    thanks for the input brian

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    Part of the problem could be your jigsaw. I have on old cheap Skil jigsaw that is hardly worth using it cuts so inconsistently. I have a new PC cordless that is a world of difference. The PC, and most better, newer saws, have a fixed roller blade guide as close to the bottom plate as possible. It helps keep the blade from flexing from side to side. Still it is not uncommon, like a band saw, for the blade to want to cut in a direction that is not perfectly parallel to the base, making using a guide problematic.
    Last edited by Ole Anderson; 02-06-2020 at 12:38 PM.
    NOW you tell me...

  14. #14
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    Ole is correct. There are a few jig saws that cut pretty accurately including in thick stock. Festool and Bosch (higher end) are like that. These tend to have better blade guide/support. The blade you use also comes into play...a stiffer blade with a little more aggressive tooth pattern will deflect less in these conditions, albeit at the cost of a slightly rougher cut that will require more cleanup.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
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    Blade, Blade, Blade! A jigsaw is only as good as the blade being used.
    I have a Festool Carvex and you can do some really crappy work with it, if the blade is junky, or is the wrong blade to begin with.
    Straight edge guide, something to control the angle and the right, sharp, non distorted, blade.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

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