BT3000 tall rip fence

mpc · 09-15-2021, 05:10 PM

Okay, got a bunch of pics today. I'd already posted the low rip fence add-on; today's pics show why/how I use it. First up: what you get when trying to make a rip cut narrower than 1/2 inch on the stock BT3000 guard assembly with the stock rip fence:

The fence holds the guard off the table by the height of the rip fence. Not exactly optimal. And there is no way to get a push stick to the right of the blade. With the guard and stock riving knife, the Grr-Ripper is not an option either as it needs to be able to pass over the guard and knife assembly.

So install the low rip fence add-on:

Now the guard is lower but there is still no way to use a push stick nor the Grr-Ripper properly.

So remove the stock guard and stock riving knife and replace them with a shop made riving knife that is just a tick lower than the blade:

Now I can access both sides of the walnut workpiece to push them past the blade. But how to push? I'm mostly concerned with the right side - the part that is between the fence and the blade. It must be pushed past the blade or else vibrations might cause it to kickback. The left side is likely to drift to the left after the cut is made so there is less chance of kickback but it really should be push beyond the blade as well for proper safety. My push stick just barely fits between the blade and the low rip fence so, in theory, could be used to push the right side of the workpiece:

There's little room for error and this would not be pushing the left part of the workpiece either. So it's not what I'd do. Instead I'd reach for the Grr-Ripper and use the add-on "L" shaped support foot:

The black foot is lowered to match the workpiece thickness (the walnut sample board) so the Grr-Ripper sits flat. The fat middle leg of the Grr-Ripper will pass to the left of the blade, the right leg will pass to the right of the blade. It slightly overhangs the low rip fence which gives me a tad more clearance to the blade while still making firm contact with the workpiece; both sides of the workpiece will be pushed by the Grr-Ripper past the blade.

A view of how the Grr-Ripper and blade line up to each other:

You can just make out the thin head-on view of the blade. It passes between the Grr-Ripper legs and below the Grr-Ripper top so my hands are shielded from the blade and from any splinters or shrapnel that gets produced during the cut - even if the workpiece shatters for whatever reason.

again.

No Grr-Ripper? Then use a sacrificial square/rectangular push board. I grabbed a piece of MDF and a smaller walnut scraps to demo how this is done... the walnut workpiece is different from the one in the prior pictures. The push board needs to have at least one 90 degree corner: one side riding against the rip fence the other leg pushing on the workpieces. The push board side needs to be long enough that it is easy to keep against the fence and keep straight and long enough to reach to the back end of the blade: you don't want to cut through the push board. You'll push the workpiece past the blade and have cut 80-90% through the push board... hold it still and turn off the saw. After the blade stops, retract the push board. If you cut all the way through the push board, the section between the blade and fence might kickback. This picture shows my riving knife installed; this same technique though would work with the stock blade guard and stock knife installed. If the stock blade guard were used, adding the low fence would be required... having the guard sitting on the rip fence renders it nearly useless.

This scrap of MDF is just barely big enough to satisfy the "don't cut all the way through" goal. Turned 90 degrees would have been smarter.

My shop made riving knife:

Made from Lee Styron's pattern. I used 0.075 inch thick low carbon steel blank (McMaster-Carr 6544K54 which is a 12 inch by 12 inch panel - way more than necessary but it gave me extra in case I screwed up) and then used powder coating, not paint, for durability. A thin-kerf saw blade is 3/32nds of an inch thick (at the teeth) which is 0.09375 inches. My riving knife is about 0.08 inches thick; another 0.01 inches thicker would not hurt.

mpc

edit: by the way, the black foot of the Grr-Ripper can be mounted to either side or left off entirely. Two small thumbscrews hold it to either side of the Grr-Ripper main body.
And the white thing on my stock blade guard is a glued-on bit of PVC pipe to hook up to my dust collector. I added a "Y" fitting at the stock BT3's dust port so I could run a smaller hose to the blade guard... I didn't bother hooking that up for these pictures.

edit #2: in one of your recent posts Nicer20, you showed crosscut fence extensions. To use those, you have to remove the stock blade guard and riving knife assembly, right? The stock knife is rather tall. Using a riving knife lower than the blade top would let your crosscut fence work while maintaining the safety of having a riving knife. Which is why I made my riving knife in the first place.

LCHIEN · 09-14-2021, 11:07 AM

Documented a similar DIY low bandsaw "L" fence here in post#19 of this thread:
https://www.sawdustzone.org/forum/di...ade#post826884

nicer20 · 09-14-2021, 09:37 AM

Awesome - awesome - awesome.

I got the idea. Especially having encountered exactly the problem with the stock blade guard assembly when doing narrow cuts. I am guilty of removing the guard assembly all together due to this.

And yes, I have seen the Grr-Ripper in some adds and YouTube videos. Looks like you use right side outer leg (of the M structure) to ride on top of your L fence. And use the left side outer leg and the middle piece to move the board being cut. That is nice.

I have read about the Lee's plans here on the forum. I should definitely look into making one for myself. And I think I understand the thickness science for the riving knife stock. Where do you get your stock for the metal plate required to carve out your own riving knife?

Thanks a million for all your patience and time to educate a newbie like me.

mpc · 09-14-2021, 02:10 AM

I'll try to take pics in the next couple of days... when it's not bloody hot in the shop. But imagine trying to cut a narrow workpiece - something small enough that the stock blade guard is wider than the workpiece. You'd have the rip fence under the blade guard... a low rip fence extension lets the guard sit lower down. You still cannot get a push stick in there as it would have to pass through the blade guard, right? So what I do is use a scrap piece of plywood, laying flat on the table behind the workpiece, to push both parts of the workpiece past the blade. Once the workpiece is actually cut, I stop pushing and turn the saw off, letting the blade coast to a stop inside my scrap plywood. That's one option.

The other option is to remove the guard assembly and instead use the riving knife. Now the blade is exposed... The Grr-ripper tool is a square "M" shape pushblock gizmo that straddles the blade. Each arm of the "M" pushes on the workpiece: one arm on the "keep" part and one arm on the "cutoff" part, and a movable center arm that can push on either side of the workpiece. Having the low fence lets the Grr-Rripper work for really skinny cuts: one arm rides above the low part of my add-on low fence.

Are you familiar with riving knives? If not: look at the stock BT3 blade guard assembly. The thin black metal piece that the guard mounts to is basically a riving knife. It has a curved leading edge so it can closely hug the blade; it also mounts to the same saw structure as the blade itself so it moves up/down with the blade and tilts with the blade. Older table saws had "splitters" mounted well behind the blade; they were close to the blade only when the blade was raised to its maximum height. Often these splitters mounted to a metal dowel rod sticking out from the back of the saw chassis; you could pivot the splitter to match blade tilt... but it was never close to the blade at normal blade heights. The whole safety intent of splitters and riving knives is to hold the kerf open as you make a cut; sometimes the internal stresses in workpieces (crazy grain or stresses from areas of the tree where branches separated from the trunk - gravity made the wood have internal stresses) would try to close the kerf, making the kerf pinch shut and grab the back of the blade. Grabbing the back of the blade is BAD! That's where the blade teeth are coming UP so pinching and grabbing the upwards-moving teeth makes the workpiece want to lift off the table and follow the rotation of the blade. A split second later the kerf will be at the 12 o'clock position of the blade - where the blade motion now tries to throw the workpiece directly forwards from the saw... likely into you. That's classic kickback. Splitters and riving knives prevent the kerf from pinching the blade; the workpiece and kerf pinch the splitter/knife instead so the blade does not cause kickback. Old style splitters sat pretty far behind the blade (when the blade was adjusted to normal cutting heights) so there was opportunity for the kerf to close before reaching the splitter. Riving knives are as close as possible, reducing the exposure window. Ideally though the safety item would be right behind the forward teeth of the saw blade - but obviously the body of the blade prevents that. This page has pictures that show the "danger zone" differences: Comparison of riving knives to splitters

My shop made riving knife: thin metal stock powder coated red to make it quite visible - similar to the "paint the red line" on the top of the BT3 saw right in front of the blade. Red is a color I try to use for safety items. The thickness of the riving knife should be the same as the kerf cut by the blade... so basically as wide as the carbide teeth. A fraction smaller is okay; significantly smaller is no good as the kerf will be able to pinch the blade tightly; thicker than the blade is bad as it would be a stop (think running into a curb) that the workpiece would smack into. Tapering the leading edge of a too-thick riving knife doesn't really help; it eliminates the curb/stop but a fat knife reduces the spacing between the knife and the rip fence causing excess friction.

The little hooks at the top would fit Lee's Shark Guard; they were part of the plans he graciously donated to this website long ago. I cut them into my riving knife, even though I don't actually have the Shark Guard blade guard itself, for future expansion if/when I bought a Shark Guard and to be faithful to the plans he gave us. Riving knives are often just a tad lower than the top of the blade... that way you can leave them installed when making "non through cuts" such as rabbet or dado/groove cuts. A normal splitter sticks up well above the blade and would get in the way of non-through cuts.

Woodcraft's description of the Grr-Ripper: Grr-Ripper pitch
It looks like a complex gizmo, especially in the first picture... that's a Grr-Ripper with a whole lot of add-ons. The yellow part is the main Grr-Ripper and that's what I use. The thin green stuff at the base of the yellow body is a grippy rubber material.

Low fences are quite common on bandsaws these days too: they let the blade guide and guard assembly get close to the workpiece; the regular fence height is much taller.

This is my Rikon bandsaw fence which has "normal" and "low but wide" positions. You can see how the "low but wide" position lets the blade guide and guard assembly sit closer to the workpiece and provides more room for push sticks. The table saw version does a similar job. I happened to already have these pics for a bandsaw how-to guide I'm making for a couple friends new to woodworking.

mpc

nicer20 · 09-13-2021, 11:21 PM

Originally posted by mpc

................

I also made a low fence for making narrow cuts. This lets me use a Grr-Ripper gizmo (I highly recommend this thing!) to push the work past the blade without the main rip fence getting in the way. I have a shop-made riving knife (using the PDF template Lee Styron gave us years ago) to go along with the low fence.

.......................

mpc

Is it possible to get some pictures to understand how the "Low Fence" works and helps. Also, interested to see how shop made riving knife works in conjunction. Hope this is not a lot of ask.

Thanks in advance.

mpc · 09-13-2021, 06:56 PM

I too use the Rockler clamps for quite a few jigs and fence add-ons. My tall fence is two plywood bits glued together: a tall section glued to a low plywood strip drilled for the Rockler clamps. A little shimming or hand planing of the low strip can correct the assembly if it isn't exactly 90 degrees... or the thin piece can be intentionally beveled to make the tall fence tipped a few degrees if you want to cut bevels on cabinet door raised panel inserts for example.

I also made a low fence for making narrow cuts. This lets me use a Grr-Ripper gizmo (I highly recommend this thing!) to push the work past the blade without the main rip fence getting in the way. I have a shop-made riving knife (using the PDF template Lee Styron gave us years ago) to go along with the low fence.

The other ones are a add-on "mouse hole" for using the BT3 fence with a router mounted in the extension area and a sacrificial fence for buried dado stack use.

Just strips of 3/4 inch leftover plywood the same height as the stock rip fence. I didn't have the smarts to insert dowels to hold them slightly above the table as Loring did. A good idea!

mpc

cwsmith · 09-13-2021, 06:54 PM

Great post Loring, very well written and illustrated with your terrific photography.

I've not had a need for a tall rip fence, but if I ever do you've certainly showed the best way to do it; so, thanks.

I too like those HF Forstner bits and I've had my set for a few years now. Incredible buy.

CWS

Jim Frye · 09-13-2021, 06:40 PM

This one has been in use since the article was written. Actually it stays on the rip fence all the time. Right now there is a sacrificial piece screwed to it for some rabbeting work I was doing.

https://www.sawdustzone.org/articles...-panel-raising

capncarl · 09-13-2021, 05:24 PM

That’s a great use for Rockler clamps! This is high fence is right on the top of my gotta build one of these. I’ll put my own spin on it, I think mine will have the access holes drilled from the back, but not all the way through, probably slots holes cut with the Festool domino.

LCHIEN · 09-13-2021, 11:25 AM

I just did a little playing around. If I was to do it again, I would just drill a 1-3/4" to 2" hole with the bottom edge 2" from the bottom.
That's enough to get the Rockler clamp pin in the hole.
Nothing wrong with 1/2" wide slot if you want to, but leaves just 1/16th clearance if your 3/8" hole is perfectly centered.

But 1-3/4" hole so much easier than the oval and you're not going to have any issues with support from the big holes in any conceivable item on the saw. shown below is a 2" hole and a 1-3/4" hole in a piece of test scrap:

One of the best purchases I ever made for my drill press is the $36 HF 16-pc Forstner set 1/4" to 2-1/8" diameter. https://www.harborfreight.com/14-in-...-pc-62360.html

In my my PDF drawing I put the bottom of the hole a little higher... to make the screw foot of the clamp on the ridge of the back side of the rip fence and not end up between slots. What I have decided I will do in the future is to use a 2" high x 24" long piece of thin wood strip to protect the back side of my rip fence.

A user in the Rockler product reviews suggested using a soda bottle plastic cap to cover the end of the screw foot to make it less likely to damage "non-marring" stuff, I wonder if that works or makes it too slippery. Another user suggested oiling the screw-screw foot joint to make it smoother.

nicer20 · 09-13-2021, 10:17 AM

This is a great write up and details for construction. And I have bought those Rockler clamps.

One thought - do I need 1" wide opening given the clamp bolt being only 3/8"? How about just 1/2"?

TIA,

NG

jlhumbert · 09-13-2021, 05:50 AM

I have resisted making a tall rip fence for my saw because of the hassle of putting it on and taking it off. This is a great idea. Thank you for sharing!