SCMS dust collection revelation

[Tom King]

Today, I had a friend "helping" me.  He was using the SCMS and spraying sawdust Everywhere.  I have a collection box on that saw, that's been used for 7 years now, and when I use it, we don't even get fine dust inside finished houses.

I told him that I wanted to watch him make a cut.  He pulled the saw all the way out, then lowered it into the board, and pushed.  That board also jambed on him.  I've never had a board to jamb using the same saw.

Having used a RAS since I was probably 15 years old, I never even thought about starting a cut like that.  Normally, no one but me ever uses that saw.  I always lower the blade on the inside edge, and then pull it through.  The saw kerf helps to direct the sawdust into the box from the bottom edge of the blade, but I never even thought about that.  By lowering the saw on the outside edge, the sawdust is not directed by any kerf, so it just goes all up in the air.

Anyway, I thought I'd pass it along.  I still don't understand why anyone would use one like he did, but think this might be why so many have trouble with dust collection.

[JohnG]

Because that’s how SCMSs are “supposed” to be used. 

From festool kapex manual, but all others say almost the exact same thing-

“For slide action cutting, first PULL sawhead assembly away from the fence, until blade clears the workpiece or to its maximum extension if blade cannot clear the workpiece. Make certain the clamp does not interfere with the guard and head assembly. Second, turn saw “ON” and lower the saw to the table. Then PUSH saw through the workpiece. Release the switch and wait for the blade to completely stop before raising the head assembly and removing the workpiece. Never “pullcut” since blade may climb the workpiece causing KICKBACK.”

Regardless of personal views on safety and kickback probability, this is how SCMS operation is taught, and is also why some believe RASs are inherently too dangerous.

Interesting though, with so many people complaining about dust collection on miter saws and the surge in popularity of old DeWalt RASs, you’d think more people would be talking about this. 

[Tom King]

I see absolutely no reason why that way would be recommended.  I expect the method was invented by a theorist, and not someone with experience.

I have never clamped a board to the SCMS, and never experienced a blade lockup.  I can see where pushing into the board can easily lockup if the board is not perfectly straight, and against the fence.

When I was 15 years old, the only saw my family had was a 9" Craftsman RAS.  That was in 1965, so gives me whatever that number of years is using one.  I prefer to do crosscuts with either a RAS, or SCMS, and don't even own a sled for crosscutting on the table saw.  I do still have all my fingers.  Also, I have never used a negative tooth rake blade on one.  I've made my living building stuff for 45 years now, and probably have made over a million cuts with a RAS, and SCMS.

My accurate cutting RAS has not been touched for tuning since 1991, still cuts dead true, and since it does still cut dead true, the blade has never been locked up in a cut.

I don't care who says that's the proper way to use one, or who has been seen doing it.   My belief is that these people just don't know that there is a better way.  I'll continue to do it the way that works best.  I do admit that I have never watched any kind of how-to video, and have figured out this kind of thing on my own, for a good living.

Why would anyone prefer to spray sawdust all in the air, and have a high risk of the blade locking up?  Using a clamp- come on man.

edited to add:  After thinking about it for a minute, I expect the reason pushing is the recommended method is because they have to take into consideration that a fair number of people will be uncoordinated, and stupid, so there is probably less chance of someone hurting themself (as badly) by pushing.

[Chestnut]

Your way probably is better after all it's how RAS were designed.

That said any time you make a climb cut there is slightly more danger than the alternative. The climb cut is going to give a lot better cut quality and with experience is a non-issue. I use the "recommended" method above and get OK dust collection and don't have issues with the blade binding even with twisted wood. A lot of this boils down to experience.

Negative hook blades are silly.... had one and it was terrible. Felt like trying to cut a board with a butter knife.

[G Ragatz]

Instructions that came with my DeWalt SCMS are to push the saw, also.

But I looked at a copy of "Mastering Woodworking Machines," by Mark Duginske, and he discusses the SCMS, briefly, as an "alternative to the radial-arm saw."  (The book has a 1992 copyright, which I guess is about the time the RAS was starting to fall out of favor.)  There, he says:

"The beauty of the sliding compound miter saw is that it offers the option of three different sawing techniques.  Like the miter saw, the blade can be lowered through the work.  As with the radial-arm saw, the blade can be pulled through the work.  It also allows the third option of pushing the saw through the work, which is a European concept."

He goes on to say:

"It may take some time to get used to the push technique, but once you do it will seem very natural.  When you think about it, pushing is the logical way to cut.  No one would ever consider pulling a portable circular saw backward when cutting a sheet of plywood, yet that is exactly what you are doing when you pull a radial-arm saw through a piece of wood.  Pushing allows you the option of feeding the blade a manageable amount of material.  When the blade is pulled into the wood, it has a tendency to feed itself and can take too much material at once.  This creates the familiar radial-arm saw phenomenon of the saw bogging down, which in turn causes a rough cut."

So that sounds to me like the issue with the pull cut is one of control and the impact of lack of control on cut quality - but not an issue of safety.  If that method is the one Tom is familiar with, and he gets good results, then I don't see anything wrong with it.  I'm going to give it a try - if it improves dust collection and I can control it okay, I might be a convert.

Edited July 22, 2019 by G Ragatz
Typo

[Tpt life]

This is a context issue. If you are on site with janky setup and holding...it’s a dumb cut. I have seen the climb bind, kick, steal fingers, and throw work. SCMS was designed to throw from job to job. Tom, your material selection and controls—along with your ability to walk away with no boss over you, gives you advantages most young 19 yr old site workers don’t have. Please be careful to instruct the issues surrounding climb cuts before teaching anyone to use the saw this way. 

My .02

[curlyoak]

Tom, I have had a ras for decades and I agree with you. I have one exception. When building doors or panels with a bread board end I push. That is my one percent. With practice I have been able to cleanly cut off the "ears" for a finish cut. Otherwise no push. I have a 12" delta. Not a bad saw. I never used an RAS that I liked better than a Dewalt. I learned on a 9". Reliable, dependable and accurate.

[Tom King]

Somewhere in this thread I remember someone saying that no one would climb cut with a circular saw.   I remembered a set of housed stringers I made sometime in the 1970's, and that I had some pictures in a stack of 35mm pictures. 

Here is a picture of one of the stringers.  Both stringers, and two beams were saw out of a 12 x 12 Heart Pine beam with a 16-5/16" Makita circular saw.  The stringers were planed in a 16" green with white racing stripes Powermatic planer.  This picture shows how I had to space the housings so a bad place in the beam would be hidden.   I don't have any other pictures of these stringers, or stairs.  The ledger is to hold the treads, which were hinged to offer extra storage (reason the treads weren't housed).  The treads seen in the picture were just temporary.  The bottom of that staircase was closed in with tongue and groove Pine boards.

It was in a house I built, and sold sometime back then.  The house was a really nice little house, sitting on a really nice lake lot.   Sometime in the early 2000's, the third or fourth owner burned it down to build a giant McMansion on the nice lot.

I used a Rockwell 8-1/4" Speedmatic circular saw.   That particular saw didn't have any shoe on the right side of the blade, so there was a clear view of that whole side of the blade.  That was during the time when Rockwell had bought out Porter Cable, and what would be a Porter Cable saw had the Rockwell name on them.

I wanted to get those stringers up that day, didn't have a shop then, and the only blade I had for that saw did not leave a clean cut edge with a push cut.   Long story short, every edge of every riser housing was cut by climb cutting with that saw.  The housings needed to stop barely short of coming out the top of the stringer, because those surfaces would show.

Anyone who says that pull cutting is uncontrollable, and leaves a rough cut because of it, doesn't know what the hell they're talking about.   I'm not saying that it doesn't require skill, but it's not an absolute statement.

That was the only time I remember using a circular saw for a climb cut, but it was the right way that day.

[RichardA]

23 hours ago, Tom King said:

Today, I had a friend "helping" me.  He was using the SCMS and spraying sawdust Everywhere.  I have a collection box on that saw, that's been used for 7 years now, and when I use it, we don't even get fine dust inside finished houses.

I told him that I wanted to watch him make a cut.  He pulled the saw all the way out, then lowered it into the board, and pushed.  That board also jambed on him.  I've never had a board to jamb using the same saw.

Having used a RAS since I was probably 15 years old, I never even thought about starting a cut like that.  Normally, no one but me ever uses that saw.  I always lower the blade on the inside edge, and then pull it through.  The saw kerf helps to direct the sawdust into the box from the bottom edge of the blade, but I never even thought about that.  By lowering the saw on the outside edge, the sawdust is not directed by any kerf, so it just goes all up in the air.

Anyway, I thought I'd pass it along.  I still don't understand why anyone would use one like he did, but think this might be why so many have trouble with dust collection.

I'm 76 years old, and I always pulled a RAS, I never had a problem, Pushing seems like a mistake.