Source for custom saw blade?

[David King]

I'm looking for a reliable saw shop that can make me a custom blade for doing curved truss rod slots. I'm hoping for a 6" dia blade with 5/8" hole, a .188 kerf and beveled teeth. If anyone has ever seen such an animal or can recommend a shop to braze one up for me I would be very grateful.

[Bob Gramann]

Thurston www.thurstonmfg.com made me a custom blade several years ago. They were easy to work with and weren't that expensive.

[Alain Lambert]

There are several 6" in saw blades on the market, not with this lage kerf though. Have you considered stacking 2 blades (like in a dado), This might work.
Most of the 6" are 1/2 bore, but there are some with 5/8. If usable for you, the 6 1/2" blades have 5/8 bore.

[David King]

Thanks Bob,
Thurston looks like the place, they can do a radius tooth in HSS. Perhaps they can do that in a brazed carbide too.

Alain, I've thought about stacking blades to get the proper width but I'd still like to get the bevel or the round bottom slot.

My problem has been that I can't find a spiral router/mill bit that has a long enough extension (I need about an inch). The one I have now is 3/16" shank and 4 flutes and that's two many flutes by 3. Also a saw blade can do this slot in a single pass whereas a router will need at least 3 or 4 to get to depth (.400"). With multiple passes the slot tends to get wallowed out.

[John Hamlett]

I got a 1/4" slotting cutter several years ago. It has four carbide teeth, it's 6 1/2" diameter, cuts a round-bottomed slot, and has a 5/8" hole. It will cut a 1/2" deep slot in hard maple, in my Unisaw, without seeming to notice. I'm pretty sure you can get them that cut square slots too. I don't see why a good sharpening shop couldn't grind the teeth down to whatever width you'd need. Now, the bad news. I spent so much time looking for it and contacted so many suppliers, I'd have to look through my tax records for the past 10 years to figure out where I got it, but an internet search might turn up something like it.

[Alain Lambert]

Here is one close to your specs.
Not sure about the theet shape, It is for flat bottom groove.
http://www.toolsxp.com/toolsxp/pc/Saw-B ... 0p3108.htm

[Chuck Tweedy]

David if you find one please let us know because I'm interested in this as well.
If you would like to have a group of us go in on having a batch made with round-profile teeth, I'm in for 1 or 2.

[David King]

Chuck, I hear you loud and clear, I was hoping someone would pipe up to prove that I wasn't crazy to move ahead with this.
I heard back from one place that said a round-topped tooth saw would be limited to 6 teeth on a 6" blade. I don't know why that would be the case.
I'm tempted to get one of the slotting blades linked above and have the teeth beveled. I could work them round from there with a diamond file if I felt that was worthwhile. It may not be necessary as I've heard that many just embed the rod in epoxy after waxing it.

[Clay Schaeffer]

A couple of other possibilities would be to use a molding head for a table saw and grind a set of HSS insert cutters to shape, or cut a flat bottomed slot and use a "scratch stock" tool ( a reground chisel) to round the bottom.

[Mario Proulx]

I have to ask: with all the excellent choices for truss rods we have today, why bother with an antiquated and less-responsive compression rod(which also adds zero stiffness to the neck itself) at all? Are you replicating a vintage design to the T or something?

[David King]

Mario, that's an excellent question and really the heart of the issue. I'm all about building the lightest and most balanced solid-bodied instrument possible so obviously doubling the weight of the truss rod is not going to help keep the weight down. I've also come to believe that compression rods sound different and at least in a bass guitar they sound better in terms of maintaining a solid fundamental. Lastly my necks are extremely stiff and I've struggled to find a rod that works efficiently and so far the single-acting bent rod seems to respond the best.

I'm certainly open to counter arguments. I'd love to stick to the easy/painless installation of the double acting rods if it was easily proved to be better.

[Mario Proulx]

I'm actually not a fan of the double-acting rods, but am a big fan of the aluminum U channel rods. they all work, but I like the low weight and added stiffness of the U channel system.

But I understand what you're doing, and since it works and is indeed very light weight, cool. I was just wondering if you had a unique take on it, and you do.

Say... Ever consider an aircraft cable type of system, for the ultimate in weight reduction? Works on the same principles as the compression rod, but uses a SS aircraft cable instead of a solid steel rod.

Another avenue that may be simple and effective without custom tooling would be to cut a square channel a bit deeper than you presently do, and solidly glue a properly shaped and curved bottom filler strip, which could easily be made with a ball-shaped router bit and a curved template to hold the strip.

Just tossing out ideas....

[David King]

Mario,

I've seen a curved rod "cassette" that could be inlayed easily into a fixed width and depth slot. I'm sure it works but it's always down to a matter of time. It's a fairly quick process to change a table saw blade, set the height and the fence. You get all the depth you need to go up through the guide jig and into the neck.

The stainless cable is interesting but I'm afraid it would exhibit much more stretch compared to a rod with less tensile strength and always the problem of reliable termination. How do you keep it from twisting inside the neck as you tighten the nut? .

Agreed that the aluminum channel rods work well but they are prohibitively heavy in a bass neck. I essentially to the same thing by using the CF reinforcement as the walls of the channel.

[Clay Schaeffer]

Could you use half of a carbon fibre tube to give the slot a rounded bottom? It should be fairly light weight.

[David King]

Clay,
I like the idea but it puts the CF in the bottom side of the rod when it want's to be on top to help the rod work effectively. Also how would you go about splitting the CF tubing? A thin diamond saw works but it's slower than molasses and makes a mess.

[Steve Senseney]

It was pointed out by someone in the past on the forum, that the CF is very good in tension, but not in compression.

[David King]

Steve the compression strength is largely dictated by the matrix, under perfect conditions compression strength can be up to 60% of the tensile strength. It's quite strong in both directions as long as the forces are aligned with the fiber orientation. When you encapsulate an extruded CF rod completely in wood I'm sure it's compressive strength will equal that of aluminum and almost certainly exceed the tensile strength of a 3/16" steel truss rod. I don't think anyone has ever experienced a CF failure but I can think of more than one rod failure.
If you want a strong and stiff neck then more steel is your obvious answer but when you are trying to save weight, it's tempting to look elsewhere.

[Clay Schaeffer]

"I like the idea but it puts the CF in the bottom side of the rod when it want's to be on top to help the rod work effectively. Also how would you go about splitting the CF tubing? A thin diamond saw works but it's slower than molasses and makes a mess."

Not all ideas are good ones! It does seem like it would be putting some stiffness in the wrong direction.

[John Hamlett]

I'm about to divulge one of my secrets...
I'm in a somewhat similar situation when I make mandolins, particularly those mandolins with long necks, like F5 mandolins. I want the neck as light and stiff as practical because the instruments tend to be neck-heavy. Not like bass guitars, perhaps, but unbalanced on a strap none the less. Here's a picture of the truss rods I make (with the help of a machinist friend) and use. It is a piece of 3/16" welding rod, a small anchor welded to one end and threads cut on the other, the top half of the rod milled away. The flat top, half rod accomplishes several things:
-it is lighter
-the center of the rod is effectively moved slightly toward the back of the neck
-the rod is not torqued for it's whole length when tightened because the flat filler stick above the rod prevents the rod twisting, so there is no torsional load on the neck shaft from the rod (less likelihood of a twisted neck).

Drill rod hardens too much when I weld the anchor on the rod and can be brittle, the welding rod does not. The main place strength is needed in a rod is at the threaded end, and there is no loss of strength there, it's sort of a "double butted" design. Although this is a 3/16" rod, I use a 1/4" cutter (because it's what I could find) and since the rod lies in the rounded bottom of the slot with a flat filler stick above, it works fine.

[Chuck Tweedy]

"Drill rod hardens too much when I weld the anchor on the rod and can be brittle, ..."

John, you should be able to anneal / temper the welded assembly back to a non-brittle state. Maybe you have tried with with the drill rod and it didn't work - that may be, but I'm sure it would work if you used O1 oil-hardening steel rod.