Thread: How to test 45 deg mitre cut accuracy?

Yes,
If you place the offcut piece face against the just cut face, it should form an exact 90degree right angle, that you can check with your square.
Simple & easy!.

...easy peasy... get one of these
I use mine all the time, nearly as much as my digital calipers.
For instance, you setup your table saw to cut perfect mitres, great. move it back to 90º and carry on cutting.
Next day you want to do repeatable mitres again, that guage will let you set it up in seconds.

Thanks everyone. I thought that there might have been an equivalent 5 cut method.

Thinking about it, I will actually do 4 cuts, form a box with the first three corner angles tightly fitted together, and any gap on the 4th corner will be 4 times the error of a single cut - is this correct logic?

Originally Posted by Dengue

Thanks everyone. I thought that there might have been an equivalent 5 cut method.

Thinking about it, I will actually do 4 cuts, form a box with the first three corner angles tightly fitted together, and any gap on the 4th corner will be 4 times the error of a single cut - is this correct logic?

You logic is almost perfect, the gap left will actually be 8 times the error because you have to make 8 cuts to mitre 4 corners.
That is also the best way to check it because, like the 5-cut method for checking squareness, you are not relying on the accuracy of anything else, such as a square or angle gauge - it is self-proving

I have done the 5 cut method numerous times to check drop saws and it's the best way.
But... when I can get into my shop I want to build things, make jigs repair bits and pieces etc...
I don't want to frigg around checking my saw is cutting perfect like it did a month ago when I made that other box.

With that Digital Angle Gauge I know when it reads 45º it is 45º cos I did the setup last time and was perfect.

Saves a heck of a lot of time and scrap pieces.

He did say easy way...



That's another way if you can afford it and wait a few months while it's hand made.

TS-Aligner Home Page

Reckon my way is easier.

Cheers

Thanks for your helpful comments, everyone. I did this thread because I wanted to be able to test the mitre cuts of the mitre crosscut sled I was making for my tablesaw, and have just finished it. I do use the Wixy digital angle gauge to get the 45 degree angle spot on, but I still need to test my first cuts to make sure the rear ( nearest) fence is at 90 degrees to the blade kerf, and that the resulting cut angle is 45 degrees, in case the base of the sled or the workpiece moved during cutting.

I have attached pictures of the sled I have made. It is made of 18mm ply and kwila for the front and rear fences, and the runners are made from ripping 3/4" square section Tasmanian Oak timber in half. This size is available at one of our local timber yards that the tradesmen use.

The construction is based on having a dead straight edge on the plywood base nearest the operator as the reference line, screwing the first of the runners at exactly 90 degrees to this. I then put some $2 coins in both mitre slots and lowered the remaining runner on to them, fitted thin double sided tape to the top of the runner, and lowered the base and the first runner into position in the other mitre slot. The 2nd runner held on to the base nicely via the tape. I then removed the coins, and lowered the base and the two runners into position, check the freedom of movement of the whole assembly, and then screwed the 2nd taped runner to the base from underneath.

I then set a 50 x 25 aluminum box section as a straight edge along the base parallel to the reference edge, clamped the rear fence to it and to the base, then screwed the rear fence to the base. The front fence was done the same, but it is not as critical as the rear fence.

I then set the blade to 45 degrees using the Wixy digital angle gauge and did a few passes, and finally screwed a safety block over the rear fence where the blade comes through after the cut.

After doing a few cuts, I found I needed to be able to hold the workpiece firmly down near the blade, and was not comfortable with having fingers so close to the blade. It is not normally a problem, but when something goes wrong, and things start flying or moving, you don't want the digits anywhere near anything sharp. So I added a hold down, and that works well.

Did some more test cuts on four identically shaped boards, and formed a square very nicely. No obvious gaps in the 4th corner angle when the first three were firmly bound together.

So, overall, I am happy with my first crosscut sled. The only problem is that the blade shoots out a steady stream of sawdust from the cut in the safety block, even though the 2hp dust extractor is connected. Perhaps I might need to take the zero clearance plate off the tablesaw, because the sawdust has to be dragged down through a 40mm deep kerf 3.2mm wide when cutting at 45 degrees through an 18mm base and a 10mm zero clearance plate. Lots easier for the blade to shoot it out the end, as it does in large quantities.