Thread: Mitre saw clamping question

There are 2 main issues:

1. Never clamp 'both' sides - it risks the wedged/thrown issue... As an aside, one of my scariest near misses in the shop was hand holding a small piece on a mitre saw. I angled it the wrong way for a cut, and it wedged and 'exploded' out of the mechanism, hitting my thumb so hard that I thought I'd lost it... Lesson learned!
2. Then, think about it - why would you wish to ever clamp the cut off side? You will clamp the 'keep' piece to keep it square and true, and you'll be setting length stops on the keep piece, because that's how you use the thing.

It's not that it 'can't' be clamped, it's that you wouldn't want to.

Originally Posted by jpdv

There are 2 main issues:

1. Never clamp 'both' sides - it risks the wedged/thrown issue... As an aside, one of my scariest near misses in the shop was hand holding a small piece on a mitre saw. I angled it the wrong way for a cut, and it wedged and 'exploded' out of the mechanism, hitting my thumb so hard that I thought I'd lost it... Lesson learned!
2. Then, think about it - why would you wish to ever clamp the cut off side? You will clamp the 'keep' piece to keep it square and true, and you'll be setting length stops on the keep piece, because that's how you use the thing.

It's the second time i've seen this question on a forum in the last week

I whole heartedly agree with 1. never ever have the cut off loose side between the blade and a stop block, it gets even scarier when your cutting Alu, i cut a lot of 6mm rod and even without stop blocks etc the un restrained side can become a missile real fast if your not careful. same with timber if you don't wait for the blade to stop spinning at the bottom of the cut.

However there is at least one reason I have to clamp both sides and that is when the offcut side is longer than can be supported without resorting to four hands, it is far more dangerous to have that piece flip up than cut through a securely clamped long piece. Don't do it often but when needed it can be done.

Best practice would be to rough cut just over length and trim, clamping the keep piece in place if needed

Good points Phil. Your best practice point is how I normally use it if I'm after zero excitement and best possible precision: inspect the raw stuff, cut off an end to give a square/true reference, rough cut excess at other end if unwieldy, then cut to length. That said, there are those occasions when the off-cut is unwieldy and/or you're in a hurry/a bit lazy and you leave it sticking out... If it's too long, my response is to adjust the workspace and prop/support it somehow - tablesaw, assembly table, roller stand. I'd rather do that than double clamp.

And let's be honest, when repeat cutting a load of bits, I don't clamp the keep side: slide to length stop, hold down firmly with left hand, cut, repeat... That's when support along the whole length is really important.

Thanks for the responses.
So, double clamping is in itself dangerous?
I can understand why a stop block alone would be a problem - if the piece bounces off it into the blade for example - but I wouldn't imagine there'd be the same issue if the piece is clamped on both sides.

I was half wondering because setting up a zero clearance fence seemed to be equivalent to double clamping.

Originally Posted by Stopblock

Thanks for the responses.
So, double clamping is in itself dangerous?
I can understand why a stop block alone would be a problem - if the piece bounces off it into the blade for example - but I wouldn't imagine there'd be the same issue if the piece is clamped on both sides.

I was half wondering because setting up a zero clearance fence seemed to be equivalent to double clamping.

Double clamping - is it dangerous - a highly qualified yes and no and highly dependent on what your doing, all cuts should be considered dangerous in some way and i'm not trying to scare you just get you thinking.
Lets do a couple of scenarios to give you some things to consider
ALL of these assume a FLAT and STRAIGHT fence and a initial length 1000mm or greater

* A length of flat stable MDF
This would be fine to clamp both sides held tight against the fence, do not lift the blade back up till it stops spinning after the cut.
Why: the teeth of the blade will be under the wood after the cut and cannot engage/lift/kickback, clamping stops the unsupported length lifting up and hitting spinning teeth

* a length of timber with TWO flat edges that can be held against the fence AND the table.
Same as for MDF

* any length of anything that is not flat against the fence AND table
NEVER clamp both sides.
Why: they will move after the cut and potentially hit spinning teeth causing kickback

* any bowed, bent, twisted item
NEVER clamp both sides and likely NEVER cut it in the first place.... it just an accident waiting to happen.

A zero clearance setup sort of but not the same even though it requires it to be fixed or clamped on both sides, zero clearance setups fall into my first scenario above with flat stable surfaces that once the kerf is cut should generally be safe to use.
For my ALU work i'll generally setup two independent mdf sections left and right of the blade nearly full kerf width spacing, clamp securely and then trim them to zero clearance, i've done the same with 50mm AL tube to do a zero clearance fence for some timber.

You will notice that in both cases i'm completely avoiding cutting a single piece clamped on both sides. Oh and apart from adhoc bad practice zero clearance fences SHOULD be bolted or screwed to the existing fence making them secure.

Try it and see what happens, then make up your mind.

Watch this video for cutting small parts

Originally Posted by Aussiephil

Double clamping - is it dangerous - a highly qualified yes and no and highly dependent on what your doing, all cuts should be considered dangerous in some way and i'm not trying to scare you just get you thinking.
...

I really appreciate the explanation. I'm currently setting up a mitre station so my pieces are supported on both sides. In the meantime I'm trying to make sure I've got the safety down pat before using the saw.

Is the issue that the clamp can force the wood into the blade if the cut releases tension in the wood? I guess that can throw the wood, or throw the saw if the wood is clamped too strongly.

If that's the case, then my next question is - why isn't this an issue for clamping on the keep side?

If you clamp both sides you are potentially creating a wedge foe the blade to get jammed in whereas if you clamp only one and that can be either side doesn’t matter the blade has some deflection room
99% of the time I don’t clamp at all which is how these saws are mostly used in the majority of cases but by all means use a clamp if you feel more comfortable that way

Originally Posted by Beardy

If you clamp both sides you are potentially creating a wedge foe the blade to get jammed in whereas if you clamp only one and that can be either side doesn’t matter the blade has some deflection room
99% of the time I don’t clamp at all which is how these saws are mostly used in the majority of cases but by all means use a clamp if you feel more comfortable that way

Ah. That makes sense. Thanks.

I dont think it has been mentioned here, but the major cause of kick back is bowed timber. be it cross cutting on a drop saw or ripping on a table saw the potential for a log jam is high.

Originally Posted by rustynail

I dont think it has been mentioned here, but the major cause of kick back is bowed timber. be it cross cutting on a drop saw or ripping on a table saw the potential for a log jam is high.

Post 6 above, it was part of my never ever cut scenario... if you clamp it both sides