Methods of Work
Table Saw Inserts
Believe it or not, after all my many years of woodworking I have never had a zero-clearance insert for my table saw. I always intended to make one but somehow never got around to it. With the replacement of my old Craftsman table saw with the Ridgid R4511 table saw I decided it was time to tackle this little job. Actually, real life convinced me to make an insert. I was cutting a small piece off the side of a larger piece of wood and the small piece was just thin enough to fall down into the opening of the stock insert next to the blade, which promptly grabbed the cutoff and winged it at the wall. Gratefully I was aware of what was happening and had gotten out of the way. If I had a proper zero-clearance insert installed it would never have been a problem.
Here is the stock table saw insert. As you can see, there is plenty of room on either side of the blade for something to slip down in there. Of course, safety isn't the only reason for using a zero-clearance insert. The idea is that if you have zero-clearance between the side of the blade and the insert, you are much less likely to have tearout in the wood, particularly when crosscutting. This is because the wood is supported right up to the edge of the blade and so is more cleanly cut. Both of these shots, by the way, are looking at the insert from the back of the table saw, not from the sawing position. The black area is where the splitter/blade guard assembly goes through the insert.
With the insert removed, you can see the cut out that the insert sets into. There is next to nothing on the sides of the opening to support the insert. So little, in fact, that I'm not sure that it even comes into play. The cut into the granite leaves a good sized shelf at the front of the insert cut out (away from you in this view) and a couple of areas on each side of the back. There is also a metal bracket at the near end that you can barely see that provides some support and which the stock insert screws into.
I decided to make my inserts out of MDF (medium density fiberboard). The depth of the opening is a tickle over one-half an inch. It is much easier to get half-inch thick MDF than hardwood, but if I make more inserts I might pick up some half-inch oak for the insert. The MDF is not the stiffest stuff in the world and with little to no support on the sides of the opening I think that oak might be stiffer and able to do without the side support better than the MDF. MDF is also tough on blades and bits and dusty as hell to work with, but it is dead flat and I don't have to worry about warping.
I have a blank cut out here just a little bit wider than the opening. I'm going to use a router to trim the insert blank down to actual size and I want the blank to be as close to actual size as I can get so that I don't have to try to trim a lot of stock off. The blank is too long, but I'll be cutting the length down on the bandsaw. I made up six blanks in all, just to have some on hand when I need them.
I have applied double-sided carpet tape to the insert blank. On top of that I have put a piece of chipboard from some packaging I had laying around. The idea is that the chipboard will give me a little gap between the insert blank and the stock insert, which is metal. When I pattern route this (coming up soon) I don't want the bit to come close to the metal.
Here I have applied double-sided carpet tape to the stock insert. At first I only put it down one side, but then I decided to put some on the other side of the insert as well to make sure it adhered evenly so that the gap caused by the chipboard would be equal all the way around.
Rather self-evident, this is my "insert sandwich" sitting on edge. You can see that I have trimmed down the end to remove the excess stock.
Is this the right bit to use? Um, no - that's a rabbeting bit. Interesting posibilities here, though. If I ever wanted to reduce a pattern by the amount of the rabbet depth, this might do it, but I would have to be careful of the bit to pattern clearance and where I placed my tape. Want the truth? I'm embarassed to admit that I started using this bit. I wish I could come up with a reason for doing something so stupid, but I can't. That bonehead move cut my six blanks down to five.
Is this the right bit? Well, it could be. It is a pattern bit, but even with my router cranked up as high as it would go in the router table, I could not get the cutter to clear the metal insert. Would this have been a real problem? Theoretically the cutter does not extend any further out than the bearing, so theoretically if I were to cut my blank like this the cutter wouldn't touch the stock metal insert. Anyone who wants to rely on that theory is an idiot (unlike someone who would use a rabbeting bit by accident). I have no desire to ruin a carbide pattern bit, so I think I'll pass. If I were to put the bit into my handheld router, I might be able to get the cutter below the stock metal insert, but then I have to figure out how I'm going to hold the work because the bit is longer than the insert blank. That's not going to work.
What to do? A simple trimming bit with a bearing on the end is required, but I don't have one. Hard to believe, but true. Checking prices on-line and then in the big orange store, I find that the online price is about seven dollars cheaper. I can wait, so I ordered it and waited for four days for it to arrive.
There's the right bit! Bearing on the end and not too long. There are different length trimming bits and if I had bought a longer one I would have had the same trouble I had with the pattern bit, only in reverse - I would not have been able to lower the router enough to make it work. Ok, you got me - yes, I could have used it even then by stacking a couple of blanks and doing them both at one time. At least that problem would have an easy solution.
I want to set the height of the bit so the cutting edge just catches the very top of the insert blank and but not high enough to touch the metal insert pattern. I may be overly concerned, but I set it so that just the very smallest bit of stock remained at the top of the insert blank. It was a very simple matter to just swipe the edge of the insert with a piece of sandpaper after routing. Setting it up this way eased my mind.
Here are the four blanks after routing. Four? Yeah, one more little screw-up, though kind of not my fault. I had let my insert sandwich sit taped together while I waited the four days for my router bit to arrive. When I finally got to routing, I suddenly found the router bit pushing the stock insert (my pattern) out of alignment and I was routing into the body of my insert blank. Apparently double-sided carpet tape does not retain its adhesion when stuck to MDF for four days. The MDF seemed to suck the life out of the tape. Who knew? So then there were four.
You will note that one of the blanks is marked "pattern." That is the first blank that I produced with the stock metal insert. After making that blank, I used it as the pattern to produce the other three. Why? Because then I didn't have to worry about hitting the metal insert with the router bit. Even if I routed into the new pattern a tiny bit it would not hurt its function. However, note that I used the one marked "pattern" to produce each of the other three. I did not use it to make one, and then use that one to make the third, and that one to make the fourth. That can result in "pattern creep." What's that, you ask? Well, you should have asked!
It's kind of like the old "telephone" game, where you get a bunch of people in a line and tell the first person a short story. That person then tells the next person in line, and that person the next, until it gets to the other end of the line. Comparing the story that went into the front of the line with the one that comes out at the end is always revealing; it usually is totally different. This happens to patterns, too, as slight differences in processing technique and/or tools modifies each generation of pattern until there can ge a significant difference between the first and the last, rendering the last potentially useless.
Making the first insert blank produced the new pattern and I marked so I don't forget which one it is. Even if I use it for an insert (preferably a dado insert), I can still use it for a pattern.
If you drop one of these blanks into the table saw insert opening, you'll have a little trouble getting it out again. They need a finger hole! An appropriately sized Forstner bit is the answer. (BTW, ever wonder why "Forstner" is capitalized? Because it was invented by Benjamin Forstner, way back in 1874.)
There, all done. Now I won't have to crawl under the table saw to pop out the insert.
Oh-oh. Even with my blade lowered as far as it will go, my new insert won't go down all the way. How do I deal with this? Well, there are a few ways, not all of which are safe. I'll stick with the safe ones, thanks.
First, an explanation of how one cuts the opening for an insert. The usual method is to put the insert into the opening with the blade lowered below the insert, hold the insert down in some manner, and then slowly raise the blade until it cuts through the insert, thus forming a zero-clearance slot. If I can't get the blade lower than the insert, I'll have a little trouble with that method.
One easy solution is to mount a smaller diameter blade in the table saw and use it to cut the slot. However, if the smaller diameter blade is wider than the full-sized blade the insert will not have zero-clearance. If the smaller blade is narrower, then the full-sized blade would not fit into the slot and will bind. That would not be acceptable. There's another solution.
Here's the solution I used. I very carefully lined the table saw fence up with the edge of the existing insert. Actually, what I really did was take the insert out, hold a block of wood up against the side of the insert cut out, push the fence against the block of wood and lock it down. That seemed like a better idea than doing it by eye. With the fence in position, I raised the blade just high enough to cut through the top of the insert blank and started cutting a slot in the blank.
Here's where I stopped cutting. Once I reached the point where I was in the same position as the existing insert I shut the table saw off and let it come to a stop. Then I moved the fence out of the way and backed the cut insert off the blade. I'm not done cutting the slot in the insert yet, though. I'll do that after I take the stock insert out and replace it with the zero-clearance insert.
Looks good, doesn't it? However, it is sitting just slightly below the surface of the table saw. If you are cutting all the way through a piece of wood it can get hung up as it hits the back of the insert cut out, and when cutting a rabbet or dado it can create a varying depth, which is something you really don't want. One more thing to do before I'm finished.
The stock insert has set-screws (see arrow) to adjust its elevation. Heck, if it's good enough for the original, it should work for my replacement inserts. I found a package of one hundred
10-24 set screws, 7/16" long (cup end), for less than $4.00 on Amazon.com. Perfect! That should last me a lifetime. While I can think of several other ways to make this adjustment, the set screws make the most sense.
I placed the stock insert on the top side of my new insert, lined them up, and tapped on each of the four set screw positions with a deadblow hammer to transfer their location.
That worked pretty slick! I marked the impression the set screws made with pencil here so you could see them better. Looking at the location of these two holes, I realized what works well in metal doesn't necessarily work well in MDF. Those set screws would be too close to the edge and would likely blow out the side. I checked the support areas in the cut out in the table saw and found that I could move them in a bit, which I did.
I stacked three inserts and clamped them together. I used a 9/64" bit to drill the holes. Clear the chips a couple of times for each hole while drilling. That MDF tends to clog things up if you don't.
I got some chip-out on the bottom insert. I should have put a waste piece of stock under it to help keep it from chipping like that, but the truth is that it doesn't really matter much. That's the underside of the insert and I'll be creating more "chips" in the area in a moment.
All set - four set screws and an Allen wrench. Why is "Allen" capitalized? Actually, the tool is a "hex wrench," but according to Wikipedia, the Allen Manufacturing Company took out the tradename of "Allen" for their hex wrenches in 1943 and it stuck. It's kind of like "Kleenex" being used as a generic name for a tissue.
It was pretty easy to drive the set screws in. It took a couple of careful, forceful turns to get them started but it worked pretty well. I did not use any lubricant because I want them to stay in place once I set them. I experimented with putting a slight chamfer on the hole with a large drill bit before starting the set screw but it didn't seem to make a difference. They did creak a bit as they went fully into the MDF.
As I drove the set screws in a "bump" arose on the top of the insert at the screw hole and when the screw came out of the bottom they pushed material out with them. After screwing them just until they came through the bottom, I backed them off until they were just shy of the surface. I then took a file and flattened the bumps around the screw holes on the top and bottom of the inserts.
Oops. Well, not so bad. Only one out of all the screws I put in had a problem. Not too unexpected in MDF, I guess. This split in the MDF made this insert sit too high in its corner of the table saw cut out. Since the real bearing surface of the insert is the set screw and not the MDF I simply cut the split section of insert out with a utility knife. Worked like a champ.
With the insert in place in the cut out, it's a simple matter to adjust its elevation. I found that the easiest way to do it was to take a short piece of wood with a straight edge (a metal rule or small square would work, too) and run it across the end of the insert. I would screw the set screw in until the insert was just proud of the surface of the table saw and then back the screw off until the piece of wood slid over that location without hanging up on the insert.
I played with the idea of dropping a bit of super glue into each threaded hole once I had the height set, just to make sure it stayed that way. I decided that it didn't really need it. Besides, if I ever needed to readjust the height for some reason I wouldn't be able to do it.
Here we go - the job's all done. I have even finished cutting the slot by raising the blade higher while it was running. You can compare the stock insert with the zero-clearance insert. What a difference! It will be pretty tough getting anything to fall into the slot where the blade is.
The stock insert has three screws to attach it to the table saw. I have not added that to my new inserts. Almost everything that I have read about making table saw inserts either disregards the need for screwing them down or actually says it is not necessary. I'll go with that until I find some reason to change.
You might think that the new insert would be better off if the slot didn't go all the way through to the back of the insert. After all, that has some potential for pinching the blade, which surely would not be a good thing. Well, there's a reason for that slot going all the way back, and a good one, too!
Let's pretend that you are one of those people who actually uses the blade guard (you should, you know). How the heck are you going to install the zero-clearance insert with the blade guard on? Can't be done. Also, you can't install the blade guard with the insert installed.
You see, this table saw has a true splitter or riving blade. It rises and falls with the blade because it actually mounts in the same casting that holds the blade arbor. Without that slot cut all the way to the end of the insert you wouldn't be able to slide it past the blade guard and under the anti-kickback pawls (the toothy things on the blade guard).
If I install just the riving blade (not the the blade guard with the splitter) I don't need to have the slot cut all the way to the end, but the riving knife keeps the kerf on the insert open anyways so there is no real problem with the slot going to the end. With the slot cut this way I have the option of using the blade guard or just the riving knife with the same insert.
So the story is told and we all lived happily ever after, right? Ha! Not yet, my friend. Let's look at one more option - the dado blade. This dado stack, which is a smaller diameter (6") than my 10" saw blade, is easily lowered beneath the cut out area on the table saw.
Here's an insert blank seated in the cut out with the dado blade lowered. No problem! Now to cut a zero-clearance opening for the dado blade.
I noted how far over the right side of the dado stack came. I then moved my fence over the top of the insert to hold it down while I raised the spinning dado blade, making sure that I was not going to hit the fence with the blade. Unfortunately, the fence on this saw is not the best and there is a fairly large gap under the bottom of the fence (I need to make a face for this fence). However, the far end of the fence is tied to a rail at the back of the saw, so I was able to slide a couple of shims under the fence and over the insert to hold it down while I raised the blade.
I got a little over-enthusiastic, though. As I was raising the blade I suddenly realised that it was doubtful that I was ever going to cut a dado more than inch deep, or even three-quarters of an inch deep. However, I had already raised the blade higher than that, so I have a slot that is a little longer front-to-back than I probably will ever need. That's certainly not the end of the world and I can't really think of how that could possibly be detrimental to the function of the insert. It was just one of those "hmmm, why are you doing that?" moments.
The half-inch wide dado insert is done. Doesn't it look pretty? I need to mark it so I don't forget what size it is. I made this one now because I am cutting some half-inch wide box joints for another project. I have two insert blanks left that I can use for different width dadoes. Also, my main 10" table saw blade is a thin kerf blade. If I were to switch to a full-kerf blade I would need to make an insert just for it.
Now I'm done. That's the way I make table saw inserts. It almost took longer to explain how to make them than to actually do it. There's no excuse now for not having the right zero-clearance insert available for the job at hand. Not only does it give a better cut, it is much safer, too.