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Mark J

SCM Saw Technique

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So the question is how best to cut 12 inch wide 16/4 boards on the sliding compound miter saw. 

This is a big board and the largest I can cut on my SCM, but I regularly do cut down or trim up 16/4 hard maple and in widths up to 12".  The saw can handle the cut, but the problem is that at this thickness even a little reaction in the wood can bind the blade.  In fact on one occasion it took me 45 minutes to get the blade extricated from the board.  

What I find myself doing, and questioning, is cutting through an inch or so of thickness in one pass then repeating 4 or 5 times to cut through the whole board.  I can still encounter some reaction, but it can be more easily managed.  Although I have seen Tom Silva start an SCM cut by first scoring the top surface of the board with a pull back stroke (saw pulled toward the operator), the manual, Marc and common sense all say this is a risky proposition (i.e. kick back); https://www.thewoodwhisperer.com/videos/miter-saw-safety/

My technique is still a push forward stroke (saw pushed toward the fence) and there is such as thing as cutting dadoes with an SCM (see "proper use" https://www.thisoldhouse.com/ideas/toh-tested-sliding-compound-miter-saws).  But I'm interested in your views on this technique.  

Let me also mention a few words on my standard safety approach.  Eye and ear protection, saw is unplugged until I am ready to make the cut.  Generally the larger piece is to my left and the smaller to my right.  If possible both pieces are clamped in place, but if the right is too small then at least the left must be clamped down (or this is the wrong saw for that cut).  I usually stand to the left of the blade and operate with the saw with my right hand.  Operation of the saw is one handed and my left hand must be behind my back not on the work.  

Alternative saws.  This is 4 inches thick; my jig saw is not going to cut it.  I do use the my band saw for rough dimensioning when the board is short enough, but this does not yield a sufficiently smooth cut for my purposes, so there is frequently an inch to trim at the SCM and that is sufficient to have internal stress.  Also I may buy a 6 foot long board and cutting 10 or 12 inches of that off on the band saw is not practical, so in that instance I am back on the SCM.  

 

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If it was me, in the situation that you present,  I would make multiple passes, five or six if needed and I would do them all from the front and push toward the fence.  This is what I have done with thick stock, though nothing as thick as you have.  I do the depth based on eh sound of the motor, I don't want to hear it bog down in the slightest.

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My two cents:

I only clamp the left side of the board and cut with my right hand, so my body is in front of the left side of the board, my left hand plays no role.

I wear full face protection.

I've been using my SCMS (12" Bosch glider with depth stop) to cut dadoes lately. I did not feel unsafe doing it.

I never do the pull back stroke thingy. Honestly it doesn't feel right when I see it on video.

About cutting thick hardwood stock on the SCMS, I've never done it so I have nothing to contribute.

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10 minutes ago, Immortan D said:

My two cents:

I only clamp the left side of the board and cut with my right hand, so my body is in front of the left side of the board, my left hand plays no role.

I wear full face protection.

I've been using my SCMS (12" Bosch glider with depth stop) to cut dadoes lately. I did not feel unsafe doing it.

I never do the pull back stroke thingy. Honestly it doesn't feel right when I see it on video.

About cutting thick hardwood stock on the SCMS, I've never done it so I have nothing to contribute.

Yeah, that's why my left hand is behind my back, actually clenching my belt.  I want it to take at least 1/2 a second for me to let go and reach forward with it, in which time hopefully some part of my brain will have thought better of that gesture.  

I've started wearing a face shield more often, too.  I have it for the lathe and its sitting there in reach, and while mine is not a very handsome face I certainly don't want it altered.  I mean just the thought of having to get a new driver's lic photo should put the fear in you.  

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Best would be to break down with a jigsaw. Especially if it's not flat/square... 

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1 hour ago, Llama said:

Best would be to break down with a jigsaw. Especially if it's not flat/square... 

This. Or if the board is too thick, then use a reciprocating saw. Use that for a rough cut, just a little oversize & then finish up on the SCMS to get a smooth, accurate cut. Then there are no worries about binding or kickback.

I've never used an SCMS for cutting dados. All the ones I've used (around 10, of various brands) have too much up/down flex, even with the depth stop secure, to yield a dado with consistent, accurate depth. If the board's too long to cut the dado on the table saw, then it's a job for a router.

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I almost never do a push stroke with a sliding miter saw, unless I'm doing multiple passes, and then back, and forth.   Also, I don't ever remember clamping anything to a miter saw.

If I need to rough shorten something like that, I'll use a circular saw while it's on the back of the pickup.  Even though I have circular saws that would cut it in one pass, for rough shortening I'll make one pass not quite half way through from both sides, and then adjust the saw to finish.  That way, if there is stress in the piece, the reaction won't be so violent.  Finish length is cut after flattening, and to final size.

For dadoes, I use a Radial Arm Saw, and keep one with a dado set on it, set to 3/4, but will of course change the size if smaller is needed.   I have never considered, and won't, cutting dadoes on an SCMS.

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I kind of agree with Tom, even though it’s frowned upon here and probably not the safest way to do things so, don’t follow my lead. I take the plank to the yard and prop up the longest side slightly with it being to my left and make several passes with my circ saw. If there is a bind, I can feel it way before the kickback and release the trigger. It seems to me, that if you clamp a wompy board down, to a miter station, you’re asking for a bind. But then again, I don’t have a dedicated miter table. 

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(Hi, folks; long time no see!)

I assumed that Mark's comment about dado's meant cutting dados with multiple passes using a cross cut blade (not a dado stack.)  I'm surprised (and informed) if a SCM handles a dado stack.

Now and again (yesterday, in fact) I have the need to cut a beam or square a previously cut beam, so I read this thread with hope that a 12 inch SCM is the/an answer.

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Hey Pondhockey,  you are correct regarding cutting dados, it's multiple passes with a standard blade.  That technique is described in the "This Old House" web page I referenced giving it some legitimacy.  My point was that if it is acceptable to make a partial thickness cut accross a 1 or 2 inch board then it should be acceptable to make multiple partial thickness passes accross a 4 inch board.  I wanted to check that thinking with others.  

The value of breaking down stock with a jig saw or (good idea) a sawzall is not lost on me.  However, if I'm cutting out a 7 inch turning block I still might need to crosscut or rip an inch or two off the rough sized piece and at 16/4 I have been impressed with the tension that might be stored in the piece.  

@Pondhockey what size beams are you going to be working with?

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If you're cutting this for turning and aren't looking for a nice smooth surface, wouldn't a chainsaw be quicker and accurate enough?

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Although I am preparing a turning block I do need a nice smooth surface, indeed 6 flat, square and smooth sides.  

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If you do multiple passes with your SCMS chances are you'll get a nice burn. I saw that happening on my dado walls,  mainly because I was being extra cautious, pushing the blade too slowly.

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You mean brown stains like these:

20190529_122910.thumb.jpg.03f994c85fea892bdd08014514806d47.jpg

I think better these brown stains than the ones in my underwear:D, which are more likely if I take the whole cut in one pass.  But, you're right about the burn marks.

That's the square blank in the middle with some of the trimed pieces.  The big piece is what's left of the "mother board", that was originally 5 feet long.

20190529_130731.thumb.jpg.645e404ff5d6146ddeed9cf93e37ce12.jpg

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6 hours ago, Mark J said:

@Pondhockey what size beams are you going to be working with?

Last one was 5 1/4" by 6 3/4".  I cut most of the end off with a 12 inch (non sliding) mitre saw and used a flush trim handsaw to finish up.  It's not perfect but it will do; especially because it will be part of a live edge book shelf.

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