kickback on circular saw

[sean_in_limerick]

Hi Guys
- when i am crosscutting 1" thick oak planks - maybe 7 or 8 inches wide, when i get nearly through the plank, maybe only the last quarter of an inch, the saw nearly always stalls and won't go any further, usually adding a bit of kickback in for effect. The saw is new and has a new blade which is fine. Despite my best efforts i cannot see what is causing the stall. The riving knife looks fine and level with the blade and there is nothing obvious wrong. Is there some special technique to this?

Cheers,

Sean

 

[DaveL]

Sean,

How long is the plank? How well supported are the ends? It sounds to me that the ends are dropping as the cut nears completion and pinching the blade.

 

[scooby]

Just to add to what davel said, are the planks supported near when you are making the cut? If not, the 2 sawn edges could be drooping, which would cause the blade to bind.

 

[engineer one]

sean, you really need to be cutting between two close supports on
either side of the cut, or after a little distance put a wedge in to keep
the slot open.

we often tend to think that only really long cuts need supporting,
but any piece should be properly supported, in particular as near
the sides of the cut as possible.

if you use a 2x1 frame which many suggest then try to cut as near an
intersection as possible.

paul :wink:

 

[jasonB]

I assume we are talking table saws?

How are you guiding the wood through the cut with a mitre guide, sliding table or cross cut sledge, if any one of these is not running parallel to the blade one side of the cut will be getting pushed into the side of the blade - may show scortch marks.

Have you checked the riving knife is just narrower than the kerf of the blade and is central to the blade, hold a straight edge against the teeth of the blade front & back and make sure the Riving knife is not touching the blade.

Is the crown guard too low and pinching the wood under where it pivots on the riving knife.

Jason

 

[devonwoody]

Sean, what method or saw accessory are you using when you make the cross cut?

 

[Anonymous]

Sean

Sounds like you just need to support the off-cut a bit better to stop it twisting against the blade under its own weight

 

[Scrit]

Hi Sean

How long is the piece, how long is the offcut and is this timber rough sawn?

Scrit

 

[sean_in_limerick]

ok guys - just to clear up any misconception from my description of the saw it is a makita hand held circular saw similar to http://www.toolbarn.com/product/makita/4200NH/. (but bigger). I am crosscuttting the boards which maybe as wide as 7", and the boards are well supported on both ends - to say within 3 or 4" of the cut - the timber is rough sawn, i am crosscutting it to make it easier to handle on my planer. It doesn't feel like the wood is pinching the blade, it is like something on the back of the saw base is catching the board, but i can't see a thing. This happens on 90% of boards but not all, and i cut them all the same way - it can scare the life out of you when the saw kicks back, but i now stop the saw when i feel it stall and back out, before finishing the cut with a handsaw. This only takes a few seconds because the saw gets most of the way through. It also happens on narrower boards, say 5" wide. I have to admit to being perplexed by it

 

[Scrit]

Hi Sean

I'd suspect one or more of the following:

1. Work not adequately supported either side of cut (i.e. material moving at end of cut)

2. Riving knife bent/damaged. If saw has no riving knife it may be necessary to knock a wedge into the start of the cut before finishing

3. Saw underpowered, leading to stalling (can feel similar to kickback)

4. Blade not sharp, leading to stalling

5. Blade too fine for cut - use a coarser blade than one you'd have for sawing-up MFC or plywood

6. Wrong type of blade - needs a crosscut or combination cut blade, not a flat-top grind rip blade

7. Timber wet - leads to binding in cut

Scrit

 

[sean_in_limerick]

thanks scrit - i will check the blade this evening, i have a fine tooth blade but i only use that for cutting MFC, i am using blade that came with the saw, which is a carbide tipped combination blade (i think), but i suppose they might have supplied a rip-tooth blade. The riving knife looks good, this is what i initially thought it was as well. I will get the specs of the saw, but i doubt it's underpowered. The blade is brand new, so it should be sharp, but i will check. The timber isn't wet.

Sean

 

[devonwoody]

No. 8= The saw blade guard is not lifting up high enough as the blade goes through used to give me a problem.

 

[sean_in_limerick]

now the saw-guard has potential!

Thanks all

 

[engineer one]

sean, can't see how it can be the blade guard due to the sizes. the blade
is what 7 in dia, so if it is going to be the guard, it would cause the problem
within 4 inches of the saw moving across the wood. unless it is binding
as it lifts, but that seems illogical.

paul :wink:

 

[Scrit]

A further thought on this:

9. If the saw is not being run on a rail system or against a batten is the saw being twisted slightly towards the end of the cut?

10. If the timber is rough sawn and is slightly cupped or in wind AND the saw is being run directly on the face of the timber as opposed to being on a rail or the like it could just be that the base plate is following the contours of the timber. See 9. above

Scrit

 

[sean_in_limerick]

i have tried vary carefully to cut square, but i am doing it by hand. i will try an d cut against a square that i have to see if this helps.

Sean

 

[jasonB]

I think the foward pressure of the saw is pushing the board forwards and the last bit of wood is acting like a hinge and closing the gap at the start of the cut.

Are the boards clamped down or just loose?

jASON

 

[9fingers]

Dare I suggest no 11?

Is the kerf of the cut too narrow for the riving knife? I sometime get his problem when using US sourced 'Oldham' contractor saw blades in my Bosch circular saw.

Regards

Bob

 

[mel]

had a simular problem a few years back with a hand held circular
it turned out that the sole plate on the saw was slightly twisted , probably
due to not keeping it in the case and storing it in the back of the van
it was more noticable when you finished the cut leaning forword , pushing the saw away from you .
hope this helps
mel

 

[sean_in_limerick]

thanks everyone for the replys, the timber is not clamped to anything when i cut. I don't think the base plate is bent, but i will check this - the kerf of the blade is wide enough, i had considered this - i need a few days to go through points 1 through 11!! Probably over the weekend at this stage. Does anyone know how to get an extra 4 or 5 hours in the day so i can do some real work in my workshop?

Sean