Tracksaw accuracy

[Mrs C]

I came across this by accident yesterday and it’s now annoying me, but I don’t know if I am expecting too much!

Squaring up a bit of ply to try to get 350mm square by rotating round 4 cuts using mft type top and ts55. By the 4th cut, the error had multiplied, so It ended up about 1mm out across the diagonals and noticeably not square if held up to the light.

Track and wood were both clamped down, dogs are identical and screwed into the table from underneath, the table is clean. Cut is wider at the start of the cut and the problem is repeatable. The Saw is snug in the rail.

Track, Saw and top are all about 4 years old so something could have worn but I am not sure where to look next to find out what is out.

Any ideas what to try next?

 

[Nelsun]

Has the top sagged? If it's MDF it will have most likely sagged over 4 years and this will introduce alignment issues even with a CNC cutting the hole pattern.

 

[Eric The Viking]

Good answer from Nelsun.

A couple of extra thoughts:

1. Over-tightening the rail clamps causes issues for me, as I think it compresses one of the two strips underneath too much and tilts the saw. So not just not straight, but not perpendicular to the surface either. I was a bit put out when I got some more Makita splinter strip recently - it's a different thickness to that on my oldest rails!

2. On a practical note, by cutting two parallel sides (rather than rotating), you will halve the error. It's not ideal but might help.

3. For diagnosis, You could do worse than a known good straightedge and large compasses. I made my large compasses from beech, with a sharpened masonry nail as the point (because it's hardened). Because you're deriving the squareness from first principles, it should be better than any bought tool, as long as you are careful that the distances are as exact as you can get them. Obviously a rod with pinholes would do as an alternative to compasses, but I'd guess the accuracy might not be as good.

4. Is there any way that either stock or rail could move in use? I found it's harder than it looks to keep everything in the right place - I tend to concentrate on the cut and miss the fact that the rail has slightly moved, for example...

Just wondering. E.

 

[Quickben]

Does your saw have plastic adjustable track runners like the Makita ?


Mine have worn to the point where there is a very slight (maybe 0.2mm) amount of play when the saw is seated in the track. I have to gently force the saw in towards the splinter strip as I cut, else it wanders within groove.


I imagine if I was using the same method as you described, that 0.2mm would compound to a greater deflection.


Gary

 

[Mrs C]

Thank you folks, time for a new top. Moved to a different area and it is fine.