How can I cut this?

[scrollski]

I have a 36” diameter pine table top I want to cut into quarters. What this the best way to correctly measure and cut this exactly into 4 equal parts?

[McRabbet]

Assuming the table top is flat, I would make a fixture from MDF about 18" by 30". Leave one long side straight and cut an 18" radius arc to within a few inches of that edge, creating a "socket" for the top to fit against. I'd probably add a few glue blocks to the underside of the top and the fixture and use clamps to hold the top snug against this socket. Set your tablesaw fence to have the blade cut through the center of the top, using the straight side of the fixture to ride against the fence. I'd then cut the two resulting halves on crosscut sled that straddles the blade, with the cut edge of the workpiece centered on the cut line against the fence.

Hope this is clear.

[DaveD]

There's probably a lot of ways to do this...one way.....

Make a homemade compass and set it to the radius of the circle. Put one edge of compass on edge of circle and mark a radius in the center. Move the compass about 1/3 around the outer edge of the circle and mark the center again. Do it a 3rd time. You will either have the center at the crossing of the 3 marks or, if a little off it will be in the center of the 3 marks (assuming the radius was a little long).

Draw a 'diameter line' through this point. Measure circumference of each 180 degree part. They should be equal. Clamp a straightedge on the circle and cut in middle of line.

Now take flat edge of the 1/2 circle you just cut and bisect it with a framing square and mark you next cut on the other edge of the framing square. Clamp/cut as before.

The 4 pieces should end up as accurate as you do the measuring/cutting. Don't be surprised though if they are off a hair or so.

[JimmyC]

As long as one side of table can have screhles in it, this is what I'd do.

Take a pice of scrap (ply., mdf, masonite, etc.) that is at least 36" long and 18" wide and screw it down onto the bottom of the table, making sure that the edge of the table is on the edge of the scrap and centered. Then set your tablesaw up for an 18" cut and use the scrap as a straight edge. this will give you two halves, now put the flat side on a miter attachment and cut to 18' on your tablesaw. Remember to take the sawblade thickness (1/8" ?) into consideration when cutting.

Good Luck.

[DaveO]

Great advice already given, but as JimmyC mentioned if you take a 36" dia. circle and cut off a 18" wide section the off cut won't be 18" wide. You have to take your blade kerf lose into consideration. Generally a full kerf blade is 1/8" thick at the teeth, and a thin kerf blade is 3/32", and they can vary more the FK blades.
Measure your blade tooth thickness and take half of that off of the 18" tablesaw setting and you should end up with two identical width halves.
MTCW,
Dave

[scrollski]

Thanks for the suggestions..