Is a climbing cut on a table-saw ever justified?

Question

Having seen the expression "climbing-cut" used in several questions on routers and once in comments about table-saws, it finally registered on me that I didn't know what the heck a climbing cut is.

As far as I can tell, with a router, a climbing cut occurs when the cut occurs as the cutting edge of the bit enters the cutting path, whereas the normal way to rout is with the bit doing its work as it leaves the cutting path.

On a table-saw, a climbing cut is when the wood is introduced to the blade as the teeth are coming upward rather than downward as we normally would cut wood. That is, the wood is introduced from the rear of the saw instead of the front. Here I am calling the position where the operator normally stands (probably near the on/off switch) the front.

So, basically, it seems that a climbing cut is one that's made backwards.

Does it ever make sense to use a climbing cut on a table-saw? If so what are the safety precautions that should be followed?

Answer 1

Despite all the no, No, NO, NO!!! I have just done it. I needed to cut a slot/dado in piece of wood and the only way to properly align the cut was to lower the piece onto the blade and then do a climbing cut for a cm or two before sawing the normal way. Since it is a dangerous cut I stood to the side of the table.

It worked just as planned.
Dangerous? no.

To experiment, I put sideways pressure on the piece and it flew away, just as suspected/planned. I still not consider this dangerous since I was to the side of the table and the piece would have to fly 2 meters before bouncing of the ground, 2 meters back and then manage to hit me.

So the answer the the question is It depends.

Answer 2

A "climb cut" is called such because the workpiece wants to "climb" over the blade--or, if the workpiece is fixed, the blade wants to "climb" over the workpiece. Where do you think Galoob got the idea for THE ANIMAL monster truck? Some guy trying to make a deep climb cut with a rip blade on a circular saw, no doubt.

Some people use a very shallow climb cut with a tracksaw or circular saw as a scoring cut to prevent chipout on the subsequent cut, so I suppose there may also be people who use the same technique on a table saw. But does that mean it's justified? No, not when there are safer ways to achieve the same result.

But what if I find a case in which I need to make a climb cut on the table saw?

On a normal table saw, don't do it. But assuming there was some legitimate reason to make a climb cut on a table saw and it could be done safely, I would use a blade with a negative hook angle and would insist on using a saw with an active safety system like SawStop or REAXX. I wouldn't even begin to consider taking anything more than a scoring cut (1/32" or less, depending on the material), and even then I would want to use a big heavy sled and would want want the workpiece strongly secured to the sled. That said, I would still highly recommend against making the climb cut in the first place.

That said, it's worth noting that some high-end panel saws/sliding table saws have a scoring blade that makes a very shallow scoring cut (using a reverse-spinning blade; i.e., a climb cut) before the wood reaches the main blade. On these high-end saws, the scoring cut is very shallow and the wood is securely clamped to the sliding table, so the cut is reasonably safe. It's significantly more dangerous to attempt the same cut on a normal jobsite, contractor, or cabinet table saw, even if you follow the extra precautions that I outlined above.

Why is it so dangerous?

There are many serious problems with making a climb cut on a table saw, but here are a few that I hope scare you enough not to try it:

1. You can't use a riving knife to prevent kickback in the event of the material pinching the blade or binding between the blade and fence (or is it kickforward in this case?)...more specifically, you have to remove the riving knife to feed the material into the back of the blade, and you cannot install the riving knife at the front of the blade.
2. If the workpiece gets pulled away from you, you may be pulled with it, right into the blade.
3. The higher the blade is, the harder you will have to fight to keep the workpiece from being lifted off the table and rolling over the blade. And harder you're fighting to keep the workpiece down, the more you'll slip when you lose control.
4. If you're feeding material from the back of the saw, the OFF switch is on the other side, far out of your reach...so you can't turn off the saw partway into your cut when you begin to realize what a stupid idea this was!

Answer 3

Been doing this work for 20+ years professionally. I've never run material into a table saw from the back of the blade. Seems like absolute lunacy to do such a thing. The table saw will want to rip that wood from your hand and if you don't let go immediately it will eat your hand and laugh while it does it. I have run an all metal (ie, not carbide tipped) plywood blade backwards on a SKIL saw on purpose for thin plastics, but the forces at work are quite a bit different than on the table saw. I can't imagine why such a cut would be needed nor how to do it safely.

As far as the router...I just can't imagine what you are describing. My brain says there are only two ways to route: either you are pushing the router bit into the wood against the rotation of the bit or you are going with the rotation of the bit. The latter can get you in trouble for the same general reasons it can on the table saw: the router can more easily run down the wood uncontrollably and paint the room with the insides of your nearest digit.

Answer 4

From looking around the interblag there are people who admit to doing it. Some do it to cut aluminum or they install the blade backward to get a similar effect. A weak point to make would be I'm sure the manual for the saw says don't do it.

Feeding the work piece backwards should be considered is a bad idea. The blade will be trying to both pull the piece away from you and push it away from the table. With normal function these forces are opposite and are less likely to harm you if something goes awry (with the aid of other safety equipment and features). You can use something like fence mounted rollers to help keep the piece down but there is still that force from the blade that will be there pushing. This also leads to tear out.

Sure you can try to be safe and with controlled movements make your cut but all it takes is a surprise in the wood like a knot or a nail to move the piece erratically.

Many admit to doing it. None seem to advocate it or are willing to go on video showing themselves. Even if they do it still does not make it right, like making a video of cutting glass on a table saw. The table saw is already one of the most dangerous power tools. Use it as intended.

I was reading a post in regards to this topic over at WoodWorkingTalk and they were advocated to both sides of this. Safety should always be the first concern and sometimes experience breeds complacency.

Answer 5

I've never seen mention of any cut made starting from the back of the blade.

Cove cuts use the full exposed arc of the blade, but approach it from the front so there's no risk of the wood being pulled into and thru the blade -- and are done with serious hold-downs/featherboards/guides to control the process.

There are some tenoning techniques which approach the blade from the side, but those generally act at the top of the blade's arc -- again, avoiding the back -- and even those are tremendously safer if guided/anchored by a jig.

You shouldn't walk around the back of a horse without extreme care, and the back of the blade is at least as dangerous. Probably more so. Best to avoid the situation.

Answer 6

Avoid using a climbing cut for any normal cuts. However, with the help of a sled, Matthias Wandel has shown you can use an extremely shallow reverse cut on the lower face to avoid tear out on the following normal-direction cut. I'm not completely sold on his analogy to the reverse-spinning blade on some high end saws, but as he writes:

This should only be done if the stock can be securely held, such as on a crosscut sled. The scoring cut should only be about a millimeter deep, so that there is not enough for the blade to grab hold of, as cutting backwards across a sawblade is generally not the safest thing to do.

^{From Matthias Wandel's Avoiding tearout when cutting veneered sheets.}

Note as well that his phrase "is generally not the safest thing to do," should be interpreted as if he had said "is not safe."

Answer 7

I made an expanding plate that was parallel strips dovetailed into each other, so it would not fall through like a pot-rest I had. It was tricky to cut the shapes, and I don't remember why but I made one set of cuts backwards on the blade. I think it was because of the curved shape of the curf-end of the cut that doesn't go all the way to the end of the board, and it curved the wrong way.

So the reason is lack of a different tool such as a band saw, and cutting things out of a large shape rather than a flat board (so you can't just turn it over).

I used a clamped board with a spacer the same thickness as the cut board, to prevent the piece from moving up off the table, and provide a stop point as well.

Answer 8

Climb cutting with a table saw can cause the wood to grab, throwing the piece at high velocity. One word, don't. Two words, don't, ever.

Answer 9

Does it ever make sense to use a climbing cut on a table-saw?

NO. It never makes sense to feed lumber from the back of a table saw.

Don't do it. If you're thinking of doing it, stop, and then don't start again. There are many reasons not to do it, and zero reasons to do it.

_{We make climb cuts with a router mainly to avoid tear out in situations where the grain makes that likely. Climb cutting in such situations lets the remaining wood support the area where the cut is occurring. Tear out usually isn't as great a problem on a table saw, and when it is a concern you have several options (none of which involve feeding from the back!): 1) use a zero-clearance insert, so that the wood is supported right up to the cut line; 2) flip the work over and cut with the good side up; 3) use a sharper blade; 4) protect the cut edge with additional material such as tape or a thin piece of sacrificial stock.}

Answer 10

Anyone advocating climb feeding needs to meet two local craftsmen who tried it.The fortunate one got patched up in a doctor's office. The less fortunate one went to the hospital and had his hand sewn to his chest for skin grafting.. I expect that they could tell you jus how "safe" this is.

Answer 11

Trapping the cut off between the blade and fence is another way to get a climbing cut. Wanted a width that matched another piece, took the original and set it against the blade, move the fence against that, locked it down and put new stock in and proceeded to cut away.

As soon as I pushed the wood past the cutting surface, the back part of the blade catches the piece - which is now a climbing cut - and promptly turned the stock into a missile. Had a bruised chest for a couple of weeks and I've never trapped another piece of wood since.

Climbing cuts are bad and I don't think there is ever a reason to use one.