ross

Hi, my name is Ross, and I am fairly new to woodworking. I am trying to make an octagon picnic table top. Here is my problem:

I cut the 8 pieces each at 5.5 inches (on longest side) using an angle of 22.5 degress (stock is dressed 2 X 6 ), but when I try and join all the pieces together, I am left with a gap of 1 5/8 inches.

I am using a laser guided miter saw and have checked the angles it is cutting against a radial arm saw and the angles are accurate. This is driving me crazy as all of the pieces I have cut have the same problem. I have a total of 8 sections (each a larger octagon) for the top and need to complete this project this weekend.

Any help provided would be greatly appreciated.
Thank you, Ross

Roy Harding

Have you got a picture or a rough drawing of what you're trying to accomplish?

I have an idea that I know what your problem is, but without a concept of exactly what you're trying to accomplish, it's not worth putting out there.

ross

thanks, here is a link to what I am trying to build:

http://www.buildeazy.com/picnic-table_callum_big.gif

This will show what I want the finished product to look like.

ross

I am on googletalk as rossco.mh if you have that program
my email is con-op@hotmail.com

skymaster

Ross; your pcs are 7/32 too short. The eziest way is to lay out one section full size on a pc of plywood ,cardboard etc. Take outside diameter of a circle the size of the table layout your angled lines to that circular line then measure point to point

ross

skymaster, I don't understand what you mean. All the pcs are 5.5 inches long and all angles are 22.5 degrees. I don't know where I went wrong, I thought that as long as all pcs were equal length and used the correct angle then you would get a perfect octagon shape.

Roy Harding

Two things immediately spring to mind.

Are you SURE all the pieces are the same length? (Measure them all - it's possible you cut one or two on the wrong side of the line).

Are you SURE all the pieces are cut at 22.5 degrees? Don't trust the markings on your mitre saw, unless you dialed it in precisely. Use a protractor and a bevel finder to make sure.

When you say that the finished product is 7/32" short - is that the size of a gap between mating pieces, or are the mating pieces 7/32" offset from each other (no gap)?

PS - Skymaster is right - what he describes is the easiest way to do it.

Rob

Ross,
I just drew this out in CAD and using 2x6 lumber (5.5" wide), the short end of the piece should end up at 15/16" wide after the cut. Is the gap of 1 5/8" uniform after fitting the last section or do you have a closed heel and open toe or vice versa?
If one of the corners (inside or outside) is closing but the opposite one is not, your miter setting is off. 1 5/8" = 13/8" or 26/16". Since there are 16 cuts, it's only going to take less than 1/8" over a 5.5" span to magnify into that kind of gap...meaning your settiing doesn't have to be off my much. Blade deflection, a slightly twisted board, miter setting or a not so straight piece of stock can help to frustrate things
It can be difficult to get 4 miters to fit perfectly, let alone 8.
Sorry I can't give you the magic answer.

__________________
Never lick a steak knife.

ross

I checked all the outside measurements and they are exact, but not one of the inside measurements is 15/16. They range between 29/32 and 1 inch. The gap is (or seems to be) uniform. When I mate up the miters they all match up until I fit in the last piece and then I have the gap
This is for a picnic table top to they don't have to fit perfectly, but they do have to at least meet. (I can't have a gap of 1 5/8" inches where the octagon does not even meet)

Roy Harding

Ross:

Rob is right - there are many factors to be considered, and he listed most of them.

I would suggest that you forget the mitre gauge on your mitre saw, and use a trusted bevel gauge to mark your angle - line up the saw (precisely) on the line, and lock it in. Set up a stop block to ensure that all your cuts are the same length, then try again.

As Rob said, there are sixteen cuts involved - if you're off even a smidge on either the angle or the length, it's not going to work.

Best of luck - post pictures when you're done.

Rob

That seems to be your problem.
3/32" multiplied by 16 will give you about 1 1/2"

__________________
Never lick a steak knife.

ross

Thanks to everyone who took the time to answer my questions and hep me out. I will be getting a bevel guage as suggested and cutting all pcs again, and trying this one more time.

If I get this to work I will post some pics of the finished product. Will not be working on this again until next weekend (got an extension on the deadline)

If anyone would like to suggest a good bevel gauge that would be great, thanks
Ross

cabinetman

One method that works pretty good is to size all the pieces to width, and leave them long, before any angles are cut.

Then cut a 22.5 on the left end (or right end) of each piece (one end).

Then determine the length of the finished cut (could be the short or long end of the other end).

Then set the piece with the one angle on the saw (like a CMS) and set the line of cut to the dimension. Then put a stop against the already cut angle end. Then place each piece, and cut them all to the same exact length.

Note: If you use a cut off angle for a stop, make sure sawdust doesn't gather at the base of the stop or the fence...that would change the size/angle.

Rob

Even after quite a few years of doing this, I will still do a practice run on some scrap before I cut my "good" wood. It really is worth the time and effort to take some scrap and do a test run to make sure everything comes out as you were expecting. Often, you'll see the angle needs to be tweaked just a hair to get perfection. Sometimes using something like a playing card for a shim, taped to the fence will get you where you need to be.
Good luck with your project.

__________________
Never lick a steak knife.