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Hi,
I’m trying to put together an octagon that will end up becoming the perimeter of a table. I have a hard time getting the correct angle with my miter gauge.
Please tell me where I’m going wrong and what to do to get it right. What I do is as follows:
I mark out the 22.5 angle with my protractor on my bench.
I set my bevel gauge to that line.
I set my miter gauge after the bevel gauge.
I have an extension on my miter gauge as I try to cut the sides.
When I lay out the cut parts they do not come together but rather I get a gap that is to big to accept.
The parts are 6″ wide so I can’t cut it on my miter saw. I also tried to set the bevel gauge after the miter saw and then cut the parts but I get the same result.
Am I getting come creep when I cut on ST? How should I do this?
Than, labor.
Replies
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6" wide mitered boards may have a true angle on them one minute and a different angle the next. As wood expands and contracts the angle across an end cut at anything other then 90 degrees will change. Knowing this, I avoid making anything mitered with wide boards.
That said, try this trick: Put 4 of your pieces together. Run a straight edge across the two ends and see if they line up perfectly. If they don't, measure how much from that straight corner-to-corner line one end is off. Let's say it's 2 degrees. Change your miter box by 1 degree (1/2 of the error at one end). Recut the ends. Try the straightedge trick again.
If you get within a whisker of straight with four pieces, don't try recutting them. Clamp a straightedge across the two corners and use a long and bearinged straight bit (pattern bit) on a router to trim them to a straight line. Do the same with the other half (4 pieces). Glue the two flat edged octagon halves together.
Then wait a day to see the joints open up, either on the inside or the outside of the miter joints.
The only similar table top I've helped a student engineer that stayed together was held at each miter joint by a double dovetail sliding spline thru the endgrain. Hard to make, but locked the corner securely. It also made a nice detail at the corners of the table when trimmed flush and sanded.
Dave
*Your only hope is to use stable, quartersawn stock of some sort. Everything else is just a wait for the mitres to open up and then they will anyway.
*Hi David,Thanx for the response. I am planning on putting a simple spline at each joint. I hope this will hold it together. I made a smaller version of this table a couple of years ago and it's still good. I think I must have been lucky with my miter cuts. The parts at that time were 4" wide, so I could cut them on the miter box. Maybe that accounts for why the angels were OK. Thanx,/Gabor.
*Did a similar edging some years ago. Found a couple of tricks that really helped out:1. left the miter a bit long, and finish the miter with a 2-degree sanding disc on the RA saw. This disc, when canted 2-degrees, sands in a straight line, like the edge of a very large sanding drum, resulting in a very straight sanding line. Set the RA for the correct angle, and work up to the line. Its easy to fine-adjust the final angle by shimming the appropriate end of the part away from the fence.2. If you make the part slightly wider than final dimension, then (following getting the angle just right as above) you can also adjust for a part that's too short. Jointing the inside edge has the effect of lenghtening the part (as fitted to the table edge).3. If only the face of the joint shows, ever-so-slightly undercutting the miter helps final fitting.
*Hi Gabor,I recently made up large (6 " diameter) table legs by gluing up 8 oak wedges, each cut at 22.5 degrees. I did this on my cabinet saw by using an angle gauge to accurately set the blade. It worked great, with "invisible" joints. I glued the 8 wedges (each ~ 36 inches long) together by loosely assembling the leg, then using duct tape around each leg. Cutting the duct tape at one spot, then rolling out the stakes, I could apply glue (Titebond II) with a brush rather quickly. Rooling the assembly back up and using 8 large (6 ") hose clamps to really squeeze the stakes together made a great seemless leg for turning. Hope some of this helps. Good luck!Charles
*you could try cutting 7 of them the way you have been and cut the eighth piece to fit what ever slight angle change your left with. the less you measure the better.
*I have my students cut and assemble two halves of octagon or hexagon or any even numbered whateveragon sides. If when assembled the ends do not make or exist in a straight line, I have them joint them or trim them straight across with a guide and a router with a straight bit. Then assembling the two flat halves is easy. Works every time. It's only about 10% of the time a student cut multigon works out perfectly the first time, in my experience.Dave
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