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consistent accurate crosscuts

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  • consistent accurate crosscuts

    This may be a real simple question, and it may just be that accuracy will come with practice, but what is the best way to crosscut several pieces to exactly the same length? I've tried putting a block on the rip fence and using that as a guide, but sometimes they still are not right. Is it possible that my saw is out of alingment. When I see that some of you measure to the nearest .0001 it makes me wonder. I am not talking major differences hear, but maybe 1/16 of an inch. What do you do when the piece to crosscut is longer than your rip fence will go out?
    Any help would be nice, Thanks

  • #2
    Re: consistent accurate crosscuts

    Artho,

    I use a Radial Arm Saw! That's never a problem doing cross cuts on any length... But I know that's NOT the answer you want to hear.

    I'm relatively new to the table saw and mine is a Ryobi BT3100 which has a sliding miter table. For me, that's much easier to do cross cuts on... but again, most saws don't have that.

    I think the biggest challenge to doing crosscuts on a table saw, is of course making sure the piece doesn't slip while you're manuevering it into the blade.

    As you mention doing, setting up a block on the fence is the proper method, as I understand it... hence, there should be no binding with the fence as you advance the miter guage. But, the miter gauge, IMHO, has so little surface to it, that the stock undoubtedly slips enough as to be inconsistant.

    You could try to screw some piece to the miter gauge to increase it's support surface and glue some sandpaper to the edge so provide more friction and thus increase the friction on the face where you place your stock.

    They also make a miter gauge that has a hand-levered clap to hold you stop firm, as you advance.

    Lastly, you could build yourself a cross-cut sled, that uses both miter gauge tracks and has a much wider supporting area for stock to be cross-cut.

    I hope this helps,

    CWS
    Last edited by CWSmith; 12-29-2009, 08:43 PM.

    Comment


    • #3
      Re: consistent accurate crosscuts

      CW gave good advice. How wide is the cross-cut, and what are you using to push it? If it is the stock miter gauge, you may notice that it is somewhat loose in the slot. Technique will minimize this problem (an after-market like an Osborne or Incra is a better fix):

      Get into the habit of putting a little side pressure on the miter gauge. I prefer to press it away from the blade for safety purposes, but do what is comfortable. Just don't go to extremes with the pressure. The trick is to push it to the same side every time.

      When setting up the cut with the stop block, make sure the miter guage is pushed all the way left (or right) in the slot. Continue to keep pressure to that side when making the cut. A piece of sandpaper on the face of the fence will greatly help keeping the piece from sliding sideways, but you also need to keep it pulled back tight against the fence. I am assuming you have screwed a fence (a straight rigid piece of wood or plastic) to the miter gauge. If you haven't, that should be the first thing you do to correct it. A 3/4" thick piece of cabinet-grade ply or MDF will usually work well. I always make mine long enough to go past the blade, so the cut the blade makes gives me a reference for positioning the next piece for cutting.

      Hope this helps

      Go
      Practicing at practical wood working

      Comment


      • #4
        Re: consistent accurate crosscuts

        Originally posted by artho View Post
        This may be a real simple question, and it may just be that accuracy will come with practice, but what is the best way to crosscut several pieces to exactly the same length? I've tried putting a block on the rip fence and using that as a guide, but sometimes they still are not right. Is it possible that my saw is out of alingment. When I see that some of you measure to the nearest .0001 it makes me wonder. I am not talking major differences hear, but maybe 1/16 of an inch. What do you do when the piece to crosscut is longer than your rip fence will go out?
        Any help would be nice, Thanks
        You can't get .0001 with wood, it moves more than that (up to 7-12% across the grain, about 1-2% with the grain).

        If you are using a stop block, and the miter gauge you should be able to get repeatable cuts (not necessarily any measurement you want), but the same as each other). One way to do this is to cut things "almost" to length on something like a CMS, but leave a bit extra. Then cut the last part off using your table saw and the stop block/miter guage. The bigger the piece you are working with the more likely you'll get it twisted or something.

        Comment


        • #5
          Re: consistent accurate crosscuts

          1/16" is a fairly significant variation. I agree that something is not quite right.

          If you are getting burn marks on your stock, your blade is likely not parallel.

          If you are using a miter gauge, consider adding a fence to the gauge the is long enough to accommodate your stock. Add a stop block to the fence, place your stock against the fence and stop block and firmly hold the stock in this position as you make the cross cut.

          Another item that would increase accuracy is a cross cut sled.

          Comment


          • #6
            Re: consistent accurate crosscuts

            when using a stop, if one can put a small bevel or dado on the bottom edge of the stop block so "dust" and chips do not get trapped causing a difference,

            depending on the size of material being careful on sliding it up to the stop can be significant, just a small tap over and over can drive the stop to a different position,

            If you mark the piece as well with a Knife cut as to where to cut one can eye ball the cut and double check the start of the cut before the actual cut is made,

            Also are you cutting clear through the stock, some times when a cross cut is made one can cut it into but on the main stock there may be a small protrusion of uncut material left if it is not passed clear past the blade,
            and that protrusion my catch the stop, and push the stock out and making the cut short,
            Push sticks/blocks Save Fingers
            ~~~~~~~~~~~~~~~~~~~
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            • #7
              Re: consistent accurate crosscuts

              A number of good comments here already.

              Machining metal on precision machinery in a temperature controlled environment generally doesn't achieve 0.0001 tolerances. That's a precition grinding tolerance. But your 1/16 errors are not adequate for any type of woodworking other than construction framing. In woodworking, you should be able to get by with +/-1/64 (+/- 0.015) for most cuts. For cuts on joint surfaces where things need to fit together you need better. For these, 0.003-0.005 is about the best anyone is going to do. And it's fine. Woodworker's glue requires a bond line thickness of 0.002 to 0.003 so tighter tolerances are just for bragging. Plus trying to get that wastes time. Anyone claiming 0.0001 is full of something unmentionable.

              BHD mentioned knife cuts. This is a great old-school method and the way to mark precision surfaces, IMO. A knife scribe is only a few thousandths wide, compared to a pencil line that is about 0.020 wide. They actually make knives for this purpose, that are flat on one side and beveled on the other. This lets you hold the flat of the knife right against your square for the best precision. But you can achieve the same thing and get excellent results with a regular utility knife if you hold the blade at an angle so that the scribe line is right on the edge of your square. I don't use a fancy marking knife... just one more thing to buy that you really don't need.

              For precision cuts without a stop block, I bring the wood up to the blade (power OFF!) and manually put the sharp bevel point of the tooth right in the knife score. Note that most blades are alternate top bevel, so you have to use the POINT of the tooth in your cut. The tooth that's bevelled the "other" way will not work. This method also only works well if your blade has negligible runout - blade + arbor. If you have too much runout, you have to fix that before you worry about precision. Once set, grab a pistol grip clamp and clamp your wood to the miter gage. You can use your hands to hold it, but the clamp is less likely to let the wood move.

              Many saws come with a super cheapo miter gage that has a lot of play in the table slot. You will want to upgrade sooner or later, but in the meantime you can impove accuracy if you make sure that you always lightly push your miter gage to one side of the slot or the other. Set up with the same light pressure in the same direction!

              A radial arm saw is a great tool, as is a compound miter saw. I have both, and you can get comparable accuracy with either as long as they're good quality tools. The radial excels at getting accurate cuts on wide boards. For most work these days I use a 12" miter saw for cross cutting.

              A big source of errors when using stop blocks is squareness - both of the block and also of the surface of the wood that's up against the stop. If both these aren't square - in BOTH directions - you can't get a precision cut. If you see any daylight at all ("no daylight" is the only acceptable level) between your square and the wood, you need to adjust your tool. If using a table saw, you might need to validate your blade perpendicularity to the table. Like many others, I use an electronic tilt box to speed this up. But you don't need to spend $35 on one (they're a good investment for general use, though). You can always tweak your blade setting with repeated test cuts until you're getting a square result.

              Now, the fence should also be perpendicular to the table if you're clamping the stop block to it. This is a problem if you're cutting boards of various thicknesses with the same setup. Some fences are adjustable, but on some you have to install an auxilliary fence and shim it to perpendicular.

              If you have a sled that fits the miter slots on the table well, you should be good to go.

              Machining tolerances are most often the result of several small effects that combine to make the cuts inaccurate. This is true in woodworking OR machining of metals.

              Personally I almost never cross cut boards on the table saw. The radial arm and miter saw are much better suited. I also try to strategically arrange my cuts so that I move the tablesaw fence a minimum number of times, so it's nice to go to a different machine for the crosscuts so as not have to move the fence.

              Good luck, be safe.
              Last edited by Andy_M; 12-30-2009, 03:27 PM.

              Comment


              • #8
                Re: consistent accurate crosscuts

                Originally posted by artho View Post
                What do you do when the piece to crosscut is longer than your rip fence will go out?
                I didn't notice this the first time I read the post, but when that is the case, I would strongly consider using another tool. One thing that can help is if you gang cut the pieces (e.g., stick them together with double sided tape). That way there is only one cut instead of many to keep the same.

                Comment


                • #9
                  Re: consistent accurate crosscuts

                  Use a crosscut sled. I can crosscut identical pieces all day with minimal effort by using a sled and a stop block. Slide to block, make cut, remove piece, rinse, lather, repeat.

                  Comment


                  • #10
                    Re: consistent accurate crosscuts



                    http://www.ridgidforum.com/forum/sho...ighlight=incra

                    I made this and turn to it for every crosscut. I use my Miter saw too but only to get close, or on rough cuts that don't need accuracy!
                    Love it and very accurate!

                    Comment


                    • #11
                      Re: consistent accurate crosscuts

                      Thaks for all the advice. I was gone for several days, and just got back to read these. I am using the miter gauge that came with the saw. Rigid 3650. I am thinking I will get anew miter gauge, or make a crosscut sled. Thanks for all the help.

                      artho

                      Comment


                      • #12
                        Re: consistent accurate crosscuts

                        Here is a Miter gauge you will not regret getting, Incra 1000SE. I have this miter gauge on my 4511 and I use it for cutting duplicate lengths or angles. You can calibrate it to your miter slot width. You can set the length of cut repeatedly to 1/32" length and angles presicisly.

                        http://www.amazon.com/Incra-MITER100...3621879&sr=8-1

                        Comment


                        • #13
                          Re: consistent accurate crosscuts

                          And if you are willing to spend a about $100 more than the Incra 1000SE, the fence on the Incra 3000SE telescopes out to 49" I think you can get in the 3000SE in sled configuration with an even longer fence for another $25 or so.

                          Comment


                          • #14
                            Re: consistent accurate crosscuts

                            ... Or you can make a Sled in a few hours with material you have around the shop that will be 100% as accurate as you abilities and tailored to your saw. I have used a sled for years. You can add stop block directly to the cross-cut fence, or even to your regular fence for longer cuts.

                            SAFTY NOTE: I didn't see it mentioned earlier, but the work piece should not be trapped between the stationary stop-block and the blade when making the cut!!! Add a removable spacer between the static block and work piece.
                            e.g. Sandwich a removable 3/4" scrap between the stationary stop block and the work piece, hold work piece in place, remove 3/4" scrap, make the cut. Remove finished piece, repeat

                            The most important piece is the fence. It needs to be 100% flat and 100% perpendicular to your blade. I glue up 3 pieces of veneered MDF and used a router to round over the top edges for comfort.

                            The other most important pieces are the runners. I run maple through the planner to be the exact thickness as the width of my table saw guides, then rip them to a thickness shallower then the depth of the glides.

                            There are 2 different thoughts of how best to square up the cross cut fence. 1) mount the rails first and square up the fence to the blade, or 2) Mount the fence and square up with the runners. I prefer #1. Mount the runners on the sled surface (3/8" or thinner) so there's no play when sliding on the table. then attach 1 end of the cross-cut fence, square to the blade, and attach the other side. Verify for accuracy and add more screws. Ad a back brace that spans both runners and is deeper that your blade will cut (2x4).

                            Comment


                            • #15
                              Re: consistent accurate crosscuts

                              When the piece is significantly longer than the rip fence, I install an auxiliary fence that is longer. It sounds to me that your are ripping sheets of ply wood, or other wide stock. Ripping usually is not a problem with the stock fence. However, if you are cross cutting it, the long length causes a major problem trying to hold it flat to the fence due to drag and the saw blades resistance.

                              I put a saw horse out to the side to help hold up a long board. For a wide one, I clamp an old bed rail angle iron to the outer edge of the table. I then put a piece of cellophane packing tape on top of it and wax it. That supports the board and makes it easy to push. Either way, the key is to have full support of the board across its width and length to keep it flat with the table during the entire cut, and that support has to be slick. A 2 x 4 on edge that is level with the table will work, but again, needs to be slick. The cellophane packing tape will work on wood as well as metal. If the outfeed support is slanted , etc, it will pull the board off straight line, curving your cut.

                              Sounds like your problem may be outfeed support, not miter gauge which should not be a player in crosscuts wider than the distance from the table front to the blade. The outfeed support has to be level with and in the same plane as the saw's table.

                              Although I have successfully cut 12" off the end of a 4 x 8 sheet of plywood with the TS, I normally will use a circular saw and a cut guide first to get the pieces close to finish size before using the table saw.

                              Sorry I missed that question when I first read your post.

                              HTH

                              Go
                              Last edited by Gofor; 01-20-2010, 12:23 AM.
                              Practicing at practical wood working

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