Thread: Sliding extension table - out-of-square cuts

Not sure if anyone else has experienced this problem, but here is what I found and how I fixed it.

Ever since attaching the (maxi) sliding extensiontable I had been disappointed with the accuracy of cuts performed in sliding mode. Ripping cuts with the table locked and running the timber against the long extension table fence have always been spot on. However cross cuts performed with the table unlocked, particularly when cutting sheet material (ie using it as a panel saw) were never quite square if the fence was located firmly fully back or fully forward in either of the two cross tracks of the table. Cuts were about 1.5mm out over a distance of 600mm - not a problem when crosscutting or docking timber that was less than say 200 mm wide, but the larger the sheet width (front to back) the more noticeable it became. (I compensated by trial and error and found that adjusting the right-hand end of the fence forward or the left-hand end of the fence backwards about 1mm before clamping gave me an accurate 90 degree cut - but things like that annoy me!).

Anyway, after much thought (sitting on the loo actually I came to the conclusion that the problem had to be in the sliding table somewhere. First step, check the diagonal measurements of the table - perfectly square. Second check, lock the fence firmly back in the cross (longer) track and check squareness with the two shorter tracks - perfectly square (and the fence was perfectly parallel with the cross track. So it was not the table itself, nor the positioning of the fence in the table channel giving me that 1.5/600mm error.

The ONLY thing left was that table wasn't plumb with the inner track (the tube attached to the workcentre which gives the sliding table all it's accuracy). Well this is a DIFFICULT measurement to make accurately because of the difference in height between top of the sliding table and the cylindrical inner track, but it DID seem to be out by a bee's dick. Could that account for the error...and why was the error there in the first place? Well I found it on my next check. When I took off the two inner bearings from the sliding table, I noticed a tiny dag of plastic (see pics) jammed between the front bearing and the corner block. And it WAS tiny! It had presumably occurred originally when I assembled the table at the time I was tapping the corner block into the aluminium extrusion.

So I cleaned it off, reinstalled the two bearings and did a test cut. Perfectly square for the first time!

My explanation of what was happening is that the little plastic peeling (no thicker than a bit of alfoil!) was tilting the bearing slightly anticlockwise in relation to table. Quite tiny problems here are naturally magnified, and translated to an error of 1.5mm in 600mm of sawcut.

All up, about an hour's work measuring and testing (but the thinking that led me to find the problem took quite a bit longer!)

Jeff.