Weird issue squaring mitre saw

[solexious]

I'm trying to square the bevel on my mitre saw, but rather than any slant being mirrored on both sides of the cut like \\ or //, when I get as close to 90 as I can, I end up with a slight /\ cut. I've marked an exaggerated version of what I'm seeing on the cut:

So far I've checked the blade is tight and not wobbling, that my square is square I'm checking with, tried with different wood to check its not some oddness with that.

Any idea whats going on?

Cheers

Sol

 

[Kayen]

It sounds like the bed of the saw isn't flat - it's probably angling down from the middle. Put a straight edge across it to check. You should be able to fix it using a packed, flat over-base.

 

[solexious]

It sounds like the bed of the saw isn't flat - it's probably angling down from the middle. Put a straight edge across it to check. You should be able to fix it using a packed, flat over-base.

I've checked the metal bed and it seems to be flat, I can't see any light coming through, but the plastic insert in the center does sit slightly lower than the metal, could that be it? If so should I pack up the insert from below with washers or something?

 

[johnnyb]

You find with these saws occasionally the head travel and the blade aren't properly aligned. When a blade is forced into a piece of wood slightly skewed it can still cut ok but it does lead to odd cut effects. To check take a widish plank and plunge in like a non slider. Then without moving cut the outside to 5 or 10mm of the first cut. These should be perfectly in line.

 

[johnnyb]

And just to say when there perfect everything seems to cut easier and safer. Even with non sliders. Of course some saws just won't align...

 

[squib]

Quite often it is the sharpness or quality of the blade.
A blunt blade will deviate as it cuts especially on a blind cut, the squarest cuts can be achieved by leaving a mm of waste and then cutting to the mark again.

 

[solexious]

Thanks all.

I should have mentioned that while its a slider, i've got it locked to not slide at the moment. Haven't seen if it works differently with a slide cut,

Will try a new blade to see if that makes a difference, £90 is a bit too much to spend at the moment and I need to get this project done today. So will need to live with with almost there it is now with the kerf plate raised and get in a new blade to try when a freelance invoice gets paid!

 

[deema]

There are three things that can be the cause that I can think of, one has been mentioned, blade condition. The other two are stiffness of the saw frame. A lot of the chop saws / CMS are built to a price and arn’t that stiff. If you can move the saw head with your hand pressure, it’s not very stiff! You’re not going to improve the cut.
The last is the saw shaft is moving, bearings, or bearing seats are worn / poorly made / designed. With the power plug out, grab hold of the blade and give it a tug, if you can move it, it’s a shaft issue.

Saws were always the method used to get stock to rough dimensions, they were and are a roughing tool. Precision is achieved with planes and simple jigs or a guillotine.

That said there are some saws that can achieve virtually the same finish and accuracy. I used to have a Wadkin BRA Radial Arm Saw that had awesome accuracy. Mind you, I could stand on the arm with worrying about damaging it or changing its precision. It was built to be stiff and accurate and last forever. If I thought I would be doing a lot more woodwork going forward I would have kept it! It now lives at a friends so I still have use of it when needed!

 

[deema]

Just looked at the photo of your bed, where the blade / turn part is lower than the main bed which is common: if your cutting thin stuff, it will flex downwards as it’s cut creating the V you describe.