Thread: Cut depth accuracy for mitre saws

SCMS will always be rather dodgy when attempting flat bottomed trenches, tenoning & the like. They were never designed for such tasks & whilst capable, will never, ever be accurate. There's just way too much inherent flex from such lightweight components.

If you wish to accurately create trenches, tenons & dadoes, then you'll need a sturdier machine like a quality Radial Arm Saw. Even these will require packing the workpiece out away from the fence to allow for the blade's curvature.

There is probably only one mitre saw that does not flex at all - Omga.

This is my 3rd Omga mitre saw, the unit itself weighs 47kg.

Heavy. rigid. Cast Iron everything. only plastic is the belt cover, and switch on/off.

my current Omga

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my second saw. pneumatic controlled Omga AL29
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Chop saws and SCMS’ are carpentry tools; accurate to around +/- half a stud’s width. The more money you spend the the larger the saw and the less flex is experienced but you’ll never eliminate it.

Try defining your edges using a knife cut and trim by hand using a sharp chisel; you can clamp a guide block to your workpiece and run the chisel along it.

Unfortunately Miter Saws can't trench, dado or tenon either, as the head is fixed & pivots only without sliding. To provide a straight cut parallel to the bed the entire saw head assembly also needs to slide along the axis of the cut. But you know this already, of course.

Look, you're going to get an approximation of what you require from just about any "quality" SCMS. Its just that, once packed out away from the fence, multiple cuts will tend to be a bit "ripply" & uneven. Worst of all is if your cuts are occasionally too deep, which adversely affects the integrity & strength of joints.

Some may be better than others. My Bosch glide saw, using pivoting castings in a similar manner to the old NZ Spida Saw instead of tubular slide arms, is perhaps slightly less prone to flex. Saws fitted with horizontal handles rather than vertical (such as the execrable Fes-fool Kapex does) will fall more naturally "to hand" & possibly be less prone to flex either.

An old fashioned Stanley or Record Router Plane fitted with a nicely sharpened "Hag's Tooth" blade, or even a Record, Preston or Clifton Shoulder Plane (basically all clones) of appropriate width will likewise be able to rapidly smooth & even up the bottom of multi-cut dadoes. The advantage of a Hag Tooth plane is that the depth is preset to provide accurate smooth-bottomed housings of uniform depth. This could provide a remedy for any issues of unevenness from multi-cut SCMS trenches. Just set your DOC slightly less than required (to prevent flex-induced overcutting) & clean up with the Router Plane.

Cheers for the help lads. I have to build my partners grandmother a bench for her pot plants in the next few days so when i do that i'll work on defining my cuts before hand. Router plane looks like a goer as well so i'll be sniffing out one of those now. The saw itself has to go anyway because the flex isnt my only gripe with the thing. I lose my mind having it drift off square every 4 cuts and the factory preset angles are woefully inaccurate but ive learnt my lesson now about buying quality!!

Originally Posted by Ratbag

An old fashioned Stanley or Record Router Plane fitted with a nicely sharpened "Hag's Tooth" blade,
will be able to rapidly smooth & even up the bottom of multi-cut dadoes. The advantage of a Hag Tooth plane is that the depth is preset to provide accurate smooth-bottomed housings of uniform depth. This could provide a remedy for any issues of unevenness from multi-cut SCMS trenches. Just set your DOC slightly less than required (to prevent flex-induced overcutting) & clean up with the Router Plane.

I've found a router to be as accurate as I've needed. Miter saw cuts precisely to length only.
Steam-bent wood box joints need to be precise or the undercuts simply will not fold at the corners.

I did a lot of half lap joints with the drop saw and it is best to use it to remove the bulk only and finish it up with a router