Thread: Sliding compound mitre saw cuts bowed

Hi S26. Bummer!! I dont think that the boards are the problem. And I think you deserve that beer . I assume that you purchased this saw from a tool shop, Metabo is a brand with a good rep but not what you will find in Bunnings. I would be taking it back to get it looked at. Re reading all the posts it appears that as the load on the motor increases, the quality of the cut drops. The blade supplied should be suitable to most tasks the machine could be expected to perform. A replacement blade should be even better. But if 2 blades gave the same problem it's probably the machine.

I assume that you have a bolt that is threaded into the arbour and clamps the collars to the blade. I have not seen the keyed system before on these saws. Are you able to make sure that it is tight?

Another train of thought. I must admit I have never used the clamps that come with these saws, prefering to rely on me holding it hard to the fence. If you were clamping the timber only and not holding as well, the timber could move enough to leave those saw marks, pivoting back and forth ever so slightly under the clamp. Holding the timber helps you feel how the saw is cutting, as well as listening (even with ear muffs on). Does this help at all?

Try another blade, a correct thickness one.

Originally Posted by riverbuilder

Try another blade, a correct thickness one.

That's definitely worth doing.
The other thing would be to check the blade run out.

He's already changed from the supplied blade. He previously had a Makita saw that had sufficient use to die so we can safely assume that he knows how to use the thing. Take the saw back.

Looking at your two cuts makes me wonder if the saw is describing the same arc on the cutting and the return stroke. Does the blade contact the timber on the return stroke and cause the cut to be chewed out as it rises. The red witness mark and movement of the cut to the left as the blade exits the cut would seem to indicate that this is a possibility.

Are you satisfied with the results you get on softwood and MDF? I have had a similar issue with mitres on Ironbark but don’t experience the same issue with say pine.
I suspect that because the cut is going on a diagonal across the very hard grain it is pulling/ distorting the blade in the process.

I have had no joy with thin blades on hardwood mitres. I agree with RB. Try a standard thickness blade.

Originally Posted by rustynail

I have had no joy with thin blades on hardwood mitres. I agree with RB. Try a standard thickness blade.

Yes my issue was with a thin kerf Diablo blade as well

Again, thanks for the replies.

Mountain ash, the arbor bolt is an allen headed bolt and the supplied key is less than 100mm long and there is plenty of space where it is mounted on the saw for a bigger one so I assume it's to prevent you from overtightening the bolt and breaking the bolt / stripping the thread. So even though I was cautious, it is tight.
I do normally use my hand to hold the board on 90 degree cuts but found even with my old Makita, when cutting 45's at times there was a tendency for the board to try to move slightly during the cut so I began to use the clamp and continued to with the new saw so haven't done any "freehand" mitres, otherwise I mainly only use the clamp to prevent the overhanging waste piece falling onto the floor.

aldav, I don't get any of those marks on sliding cuts, only when I drop it and when they do happen, they seem to indicate the cut heading toward the motor the lower the blade gets.
I haven't noticed the blade contacting the board when I lift it and have tried holding the blade down until the motor has stopped and the cut doesn't change.
The thing that is most noticeable, as I mentioned previously, is if I make a sliding cut, raise the blade, then drop it back over the cut (with the board clamped so it hasn't moved), it takes a definite extra 0.5 - 1 mm out of the centre of the board, yet if I repeat the slide cut it only slightly touches the board and doesn't remove any extra material, as you would expect it to do.

Beardy, it's worth mentioning this also happens with straight cuts as well as mitres.
Yes, I am happy with the results I've seen so far on mdf and pine, but as I said, I bought this saw for this job and haven't done a lot of other cutting.

BobL, I have a dial indicator, so testing blade runout should be easy.
Thanks, I'll certainly give that a go as it should show if the collars are flat and true too.

riverbuilder, I'm not disregarding the thoughts about the suitability of the blade but for the time being I'm probably going to put ANOTHER blade change on the backburner until either the job is done and I can do some serious test cutting or I get p****d off to the point of total madness (probably not that far off).
If / when that happens, can you recommend a particular blade I should look for ???

For what it's worth, I'm leaning toward agreeing with Mountain Ash that as the load on the saw increases the quality of the cut suffers as it seems to me that the blade is moving toward the motor under load in the middle of a sliding cut, giving me the bow in the middle and is also moving toward the motor as the blade lowers on drop cuts.

Thanks again for taking the time to reply and please share any other ideas you have.

I'll let you know if I come across anything else noteworthy, cheers.

Having a look at the photo where you are using the saw's hold down clamp, it is positioned over the centre of the board and any pressure will force the face of the board into a concave position and when you release it, it springs back.
Try an experiment of cutting the boards with the face of the boards against the fence or face down on the deck of the saw.
from my experience, those old skirtings and architraves tend to "cup"with age and has always been an issue when re-cutting.

could be a combination of saw/blade/use

I have a 12" dewalt saw and use a 120 tooth thin kerf blade for fixouts.
Most of the fixout material is pine and mdf skirting/arcs and cuts this perfect.

But when I need to cut 140x19mm merbau for post trims, if i go too quick or too much pressure i definitely see a "curve" in the cut as the blade flexes - To minimise the curve, i need to do multiple, light passes..

Any heavy hardwood would too much pressure on a thin kerf blade...


If you are doing a drop cut, raising the blade and repeating and its taking any material off on the 2nd drop cut, to me, this is an issue with the saw..

Originally Posted by rwbuild

Having a look at the photo where you are using the saw's hold down clamp, it is positioned over the centre of the board and any pressure will force the face of the board into a concave position and when you release it, it springs back.
Try an experiment of cutting the boards with the face of the boards against the fence or face down on the deck of the saw.
from my experience, those old skirtings and architraves tend to "cup"with age and has always been an issue when re-cutting.

While reading through this , I kept thinking are you over tightening the clamp an putting a little cup in the Board ?
But Ray was right on the money too.

Cheers Matt.

Yes RW, when this initially happened, I thought excess clamp pressure may be causing cupping too, particularly as the back of the boards aren't completely flat having a 2mm trench through the centre.
I flipped a board over and did several straight and mitre test cuts and got the same result. Also while doing this I checked to make sure the board was lying perfectly flat and not rocking at all due to cupping.
Also, while sanding the cuts flat on my disc sander I've flipped several boards over and I haven't seen any rocking there either.
The test cut in the photo with the ruler was done by standing a board up and clamping it against the fence and doing a drop cut and that was one of the worst cuts it's made yet.

Tomorrow I'm going to check the blade run out and I'm thinking of (maybe using my angle finder) trying to somehow check if the saw actually drops and slides perfectly straight.
After changing the blade I've carried on with the job even though it's a pain to sand the cuts flat because if indeed the boards are cupped slightly causing the issue there's nothing I'll be able to do to get it to cut perfect mitres anyway.

What's annoying me and making me doubt the saw though is the board with the saw marks in the photo is one of the smaller boards for the window frames in the living room so it was drop cut.
Surely a 12" saw with a brand new quality blade (even a thin kerf one) should be able to make a straight even drop cut on a 65 x 19mm tassie oak board ???

Originally Posted by sneem26

65 x 19mm tassie oak board ???

I have some 120x22mm Tas oak in the garage - If i get a chance during the week, ill grab some out and give it a few cuts with my 12" SCMS saw - just to see if i get same deflection in the cut

Fully check the saw for tilting limiting stops using nuts and bolts as seen in my photo. Saw designs vary and what
each manufacturer uses is possibly different.
When the 90 degree vertical adjustment is off the incremental error will increase as the lumber thickness increases. This can result in a slight bevel instead of a square cut. I also prefer a thicker 80 -100 TPI blade preferably without slots as others mentioned later on.