Shopsmith Forums

I don't know that there's a definitive answer for all circumstances, but Mr. Sawdust did allude to the workpiece being launched off of the table if you pushed rather than pulled the saw through the cut. However, he also spends a lot of time explaining how to rip safely on a RAS, which has the same lifting problem, in spades. To rip safely, one of the requirements is to constrain the workpiece such that it can't lift significantly. For typical rip cuts, the nose of the saw guard can easily be positioned to do this. But in special circumstances, workpiece hold-down guides or jigs may be needed.

Here's a couple of other considerations:

1) If a radial arm saw is sufficiently rigid, the blade simply can't climb up on top of the workpiece, and the motor must stall instead. A vintage cast-iron DeWalt approaches that level of rigidity.

2) By pulling the saw through the workpiece, the fibers on both the top and the bottom of the workpiece are severed while the saw teeth are on the downstroke. This inherently gives a clean cut on the top side. On the bottom side, assuming that there is a crisp kerf in the sacrificial table, the table acts like a ZCI and also provides a clean cut. But if you push the cut, you'll tend to get tearout on the top side of the workpiece.

So JPG, that last consideration is one difference between a RAS and a sliding CMS. With the latter, it's easy to do a scoring cut first, followed by a through cut. Doing the same on a RAS would be a royal PITA.

Similiarly, if cutting thick lumber on a SCMS, the cut could be done in several passes, so that the blade's lifting angle of attack is never very high. And if you're bound and determined to cut push-cut thick lumber in a single pass, that could still be done safely if using hold-down clamps.

Check your blade if you are getting too much tear out ? . if you look at a plain miter saw that is made for 2x4 or trim and pushed straight down the saw dust is all ways lifted out of the cut and blade channel .

I agree with Hobbyman2. I was taught in high school woodshop to push the blade thru. I feel it's safer. What if trying to cut thru a 4x4 or you hit a really hard knot or there is a 16 penny nail that you didn't notice and the blade grabs it when pulling thru. I try to push thru when possible. Obviously I need to pull thru if I'm crosscutting a 16" wide piece of plywood. Then I watch a little more closely.

I do not see where the nail encounter is improved when pushing rather than pulling. Nor do I see how the out the top is better than out the back as an exit path for the swarf.

Maybe I'm wrong, but when pushing the blade through a nail or very hard knot the should try to flip the board up, while pulling the blade it would try to climb I guess. Overall, I'm not seeing big advantages one way or the other. And these issues highlight the advantages to a table saw. I do admit I'm not making a fair comparison since my table saw experience far exceeds my experience with an RAS.

And I will note my father-in-law built a lot of household furniture with an RAS as his only large power tool. At some point the skill of the user is much more important than the tool.

"And these issues highlight the advantages to a table saw."

Advantage?

Oh there are ways to misuse then also.

However it requires a simple advancement of the work piece towards the blade. Only one set of geometry/vectors likely possible.

What I was referring to was binding or jamming the blade. When pushing you will "feel" the resistance to the cut (or hear it in the nail case) and give you time to react. When pulling with the blade going 3400rpm, it could it could bind, catch the nail and if conditions were right could send the blade towards you before you even think. Same with the 4x4.

maybe we can compare saws ? take a look at the saw its self, a RAS is a power saw on a arm ? , a sliding miter saw is also a power saw on a arm?, now compare the track saw , it is a power saw on a track , would you pull the track saw backwards to make a cut because it is on a track ? all of the the saws "cut" are exactly the same only there is a arm involved that allows the saw to slide on with a RAS and a SMB . look at the saw cut its self , when cutting a wide board pulling the saw allows the cut in front of the blade to fill with saw dust ? it can also get under the wood throwing the cut out of 90deg vertical ,maybe even cause pinching , if you have a dust collector in use you may not be getting the full use of its potential ? pushing the saw keeps the cut clean and the dust moving . I can not comment on cutting old boards with nails with my saw, It is not something I would do . when using rough cut lumber if the tree has nails it usually will show a bluish to black stain . JMO

Let me see here:

Pushing(saw contacts the board from the bottom and cuts upward) imparts an upward force on the board and the saw dust exits the kerf at the top of the board at it's yet to be cut edge.

Pulling(saw contacts the board from the top and cuts downward) imparts a downward force on the board and the saw dust exits the keff at the bottom where the board has already been cut.

As for saw dust obscuring the cut line, we are not guiding either the board or the saw, so that is irrelevant.

I think pulling is preferred considering the physics above.

Yes I am ignoring sawdust that travels in the blade gullets and exits Lord only knows where.

JPG wrote: ↑Mon Jul 26, 2021 3:58 pm Pushing(saw contacts the board from the bottom and cuts upward) imparts an upward force on the board and the saw dust exits the kerf at the top of the board at it's yet to be cut edge.

Pulling(saw contacts the board from the top and cuts downward) imparts a downward force on the board and the saw dust exits the keff at the bottom where the board has already been cut.

When pushing, the upward force as the cut starts is at the point on the board furthest from the back fence and that minimizes the force needed to lift the front edge of the board. Pulling applies downward force right at the back fence so it is impossible to move the wood at all. However that is what could lead to 'climbing' if the arm isn't stiff enough to stop it since the wood can't move down through the table or backward through the fence the blade will try to move upward if it can't cut through the wood.