Timbo Posted October 25, 2017 Share Posted October 25, 2017 I need a spot of help with a math problem. My brain does not do measurements, I just cannot get the bits that stroked out to work properly. I'm currently building a couple of table saw sleds. One is a crosscut sled, and the other is a mitre cut sled (for making boxes). I'm trying to align the fence that the lumber to be cut will register against. To do this I'm using the FIVE CUT METHOD. I've used the result to adjust my fence and retested using the five cuts again. So far so good and I have my results but cannot understand them and I'm hoping someone with more technical ability can help? I've managed to discern that my fence is -0.04mm out of square or 0.001574803 inch over the length of my table saw top. Is this square enough? Quote Link to comment Share on other sites More sharing options...
TheQ Posted October 25, 2017 Share Posted October 25, 2017 I don't think so, I only work in decimal points per parts per million... I've just Typed in, 0.000 000 03 -0.000 000 06 0.999 911 73 1.000 088 28 0.499 977 89 0.50002189 Quote Link to comment Share on other sites More sharing options...
Daddy Mouse Posted October 25, 2017 Share Posted October 25, 2017 It depends on how square you want it and how long your bench is Quote Link to comment Share on other sites More sharing options...
Vaughan Posted October 25, 2017 Share Posted October 25, 2017 I do it by eye. If the "work" starts to pinch between the blade and the fence, then the fence is turned towards the blade but if you have to maintain the work against the fence, by hand pressure, when running it through, it is turned away from the blade. I have often found that this is more a matter of making sure that the blade is running square to the table, than the actual alignment of the fence to the table. Quote Link to comment Share on other sites More sharing options...
grendel Posted October 25, 2017 Share Posted October 25, 2017 I think we might let you get away with one thou out of square, you will go further out of square if you sand it anyhow. you could always square it up when you varnish it, by adding an extra layer of varnish down that edge. 1 Quote Link to comment Share on other sites More sharing options...
grendel Posted October 25, 2017 Share Posted October 25, 2017 take your glasses off, now hit yourself over the head with the piece of timber - does it feel square? 2 Quote Link to comment Share on other sites More sharing options...
grendel Posted October 25, 2017 Share Posted October 25, 2017 is that the total error after 5 cuts, or the total error divided by 5 to get the actual error? 1 Quote Link to comment Share on other sites More sharing options...
Timbo Posted October 25, 2017 Author Share Posted October 25, 2017 Err....so I have to divide by 5? I'm struggling here, to give you a clue, Ellie has to check my change at the shop because I can't add it up...right, let's see... I've made five cuts on a board that is 219mm long. On the fifth cut I've taken a wider strip that at the front measures 11.65mm wide and at the back (closest to the fence) measures 11.60 mm wide. So I subtract one from the other which gives me 0.05 mm difference. Divide this by 5, and I now have 0.01 mm If my 'summing' is right Quote Link to comment Share on other sites More sharing options...
grendel Posted October 25, 2017 Share Posted October 25, 2017 yep, so the answer to that is pretty OK, the guy on the page I looked at said his runout was 2 thou total, at 0.05mm yours is 1 1/4 thou, he was perfectly happy with his runout, so as yours is about half of his I guess yours is fine. 1 Quote Link to comment Share on other sites More sharing options...
Timbo Posted October 25, 2017 Author Share Posted October 25, 2017 Thanks guys. That's another dream of mine come true...the ability to drop in the phrase 'true to 1 and 1/4 thou' into a conversation with my father in law Ben Gun...and know what it means! 1 Quote Link to comment Share on other sites More sharing options...
grendel Posted October 25, 2017 Share Posted October 25, 2017 you are actually true to 1/4 thou (1/5 of the total - remember) so even better to impress with. 1 Quote Link to comment Share on other sites More sharing options...
BrundallNavy Posted October 25, 2017 Share Posted October 25, 2017 Tim, is this square enough..... 1 Quote Link to comment Share on other sites More sharing options...
Wussername Posted October 25, 2017 Share Posted October 25, 2017 Bit confusing all of this. Are you on the square or not? 2 Quote Link to comment Share on other sites More sharing options...
Timbo Posted October 25, 2017 Author Share Posted October 25, 2017 Weeeeelllll, I'm on the level... Let's put it this way I just cross cut and put a square up against it and it was square, but how square is my square? I couldn't see daylight...but then I was blinded by that shining from my ear holes! Quote Link to comment Share on other sites More sharing options...
CambridgeCabby Posted October 25, 2017 Share Posted October 25, 2017 Reminds me of a joke I was told years ago concerning two engineers watching a blacksmith at work and commenting to him that in their work they have to be accurate to within a thousandth of an inch , prompting the old blacksmith to state that he prefers his work to be exact 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted October 25, 2017 Share Posted October 25, 2017 34 minutes ago, CambridgeCabby said: Reminds me of a joke I was told years ago concerning two engineers watching a blacksmith at work and commenting to him that in their work they have to be accurate to within a thousandth of an inch , prompting the old blacksmith to state that he prefers his work to be exact How does another story go: measured with a micrometer marked with a pencil and cut with an axe Quote Link to comment Share on other sites More sharing options...
ranworthbreeze Posted October 25, 2017 Share Posted October 25, 2017 I always liked the story of the American company that sent the worlds smallest drill to Sheffield, the story goes that the Sheffield company drilled and tapped it, made a nut and bolt and sent it back. Regards Alan 1 1 Quote Link to comment Share on other sites More sharing options...
KaptinKev Posted October 25, 2017 Share Posted October 25, 2017 If the measurement had to be close, it was always referred to as "being within a gnat's cock". Hopefully I haven't broken any rules with this comment. Quote Link to comment Share on other sites More sharing options...
TheQ Posted October 25, 2017 Share Posted October 25, 2017 Just now, KaptinKev said: If the measurement had to be close, it was always referred to as "being within a gnat's cock". Hopefully I haven't broken any rules with this comment. on a model railway forum I belong to, the automatic net nanny would have changed that to "being within a gnat's large chicken". This is awkward when describing a locomotive on the LNER with it's official name being Large Chicken O' the North https://en.wikipedia.org/wiki/LNER_Class_P2 2 Quote Link to comment Share on other sites More sharing options...
SteveO Posted October 26, 2017 Share Posted October 26, 2017 A gnat's whisker is what we used to call it in polite circles. Quote Link to comment Share on other sites More sharing options...
Poppy Posted October 26, 2017 Share Posted October 26, 2017 5 minutes ago, SteveO said: A gnat's whisker is what we used to call it in polite circles. Is that thicker or thanner than a **** **** ? Quote Link to comment Share on other sites More sharing options...
Viking23 Posted October 26, 2017 Share Posted October 26, 2017 Just remember, it is easier to take material off than to put it back. Buy a decent vernier and measure as you go. What material are the tolerances being measured on? Richard Quote Link to comment Share on other sites More sharing options...
SteveO Posted October 26, 2017 Share Posted October 26, 2017 4 minutes ago, Poppy said: Is that thicker or thanner than a **** **** ? Hopefully, for Mrs gnat's sake, quite a lot thinner. 3 Quote Link to comment Share on other sites More sharing options...
HakunaMatata Posted October 26, 2017 Share Posted October 26, 2017 Hi, so far I know, after having done the five cuts and did your calculation, it has to be devided by 4, the 5th cut is just to get your peace to measure the alignmend. Than it depends how long your cut is actual to get the missalignment for 1 meter ( approx 3 feet ). that means 0.0125 * 1000/219 = 0.058 mm per meter. If you cut a peace which is 33 feet in lenght you will be missaligned 0,0023 inches. For a space station may be not ok but i think its harder to get it better. I think think you are really square 2 Quote Link to comment Share on other sites More sharing options...
Timbo Posted October 26, 2017 Author Share Posted October 26, 2017 So here is the first finished sled...I used a design by a chap from Germany (as his English is much better than, well, most peoples) as he seems to have an almost identical inventory of tools and manufacturers to mine. The test cuts I've made on projects so far seem to indicate I'm getting much better results using the sledge than the mitre gauge. It also feels much safer to use. My test cuts were made on plywood and MDF as I assumed a man-made board would be much flatter and uniform but perhaps not. This week is turning out to be a 'jig building' week as I have the mitre sledge to build next (with the blade at 45 degrees). A separate sledge for mitres means I have a 'zero clearance' slot for the blade in the bed. Makes a better job of cutting those mitres. I also have to build a planer sledge as my jointer is not wide enough to take some of the boards I want to flatten. I do have hand planes but...I still have problems getting them flat. It must be the 'one-handed' thing! Quote Link to comment Share on other sites More sharing options...
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