why does a folder-washer NEED to be round?

B

Bart student

Joined
Nov 17, 1999
Messages
676
Hello folks,

I'm plotting to make an attempt at making a framelock folder this summer ( so stay tuned), I have acces to some hi-tech precision machinery, and the guy who operates them daily proposed to make a few folder this summer.

I was working on plans and diagrams and so on, and it struck me that the liner or lock side needs a much smaller washer. Then I went to check on folder that have huge washers, like a MT LCC, and it struck me that the bigger the washers, the higher precision required, but also the more stable your knife feels.

Then I tried to figure out why a washer needs to be round. I checked, and on ALL my folders, the washers don't move at all, the blade slides between the washers. theoretically, they could be square and have the same effect. Of the BM 750 framelock, I even suspect that the washers are GLUED to the scales. Then it hit me.. if this is so, then why don't you make a washer that is almost as wide as the entire blade, with cutouts for the lock? It would greatly increase stability of the folder blade.

Are there some framelock folder makers out there that are willing to give this a test and potentially ruine a bit of teflon ? Insted of making round washersm try and make a washer that's lot's larger in surface, much larger blade contact, with a cutout for the framelock? I think you can keep it from rotating if you let it extend to the blade stop, so it's jammed.

or am i just missing something here? :D
It's all theory so far, but I like to study my theory before actually doing it in real life :D

greetz and take care, Bart.
 
Bart, you are absolutely correct. The washer could be any size or shape and the bigger the better as far as stability is concerned. In the case of the washer encroaching on the lock area you can simply cut out the washer to go around it. It is best to then afix the washer to the frame in some way to keep it from rotating and interfering with the lock. You could glue it or press fit the washer or you could employ some sort of fastening means such as a recessed screw or pin.

Currently I use phosphor bronze for my washer material but you could use any othe materials such as nylatron or teflon. I have epoxied a few lockside washers and pinned others. I use a 1/8" stainless steel dowel pin press fit into the frame with a match drilled hole in the washer to keep it from spinning.
 
First of all, I've never made a knife. All of my experience with bearings and washers comes from designing high-speed high-temperature rotating machinery. Everything I'll post will be based on experience gained from these other machines, things may work completely different with knives.

One of the problems with increasing bearing size is that while it frequently increases stability, it also increases friction.

I'll use the washer out of my BM550 Griptilian for an example.

This circular washer is roughly 16mm accross and the center hole is roughly 6 mm accross. Using the formula Area=Pi*Radius^2 we get that without the hole the washer has a surface area of 201.1 square mm and the hole has an area of 28.3 square mm. Subtract these out and we find that the total surface area is 172.8 square mm.

If we double the diameter of the washer to 32mm the surface area jumps to 804.2 square mm but the area of the hole remains constant at 28.3. Subtraction gives us a result of 776.0 square mm.

By doubling the diameter we have increased the surface area by a factor of 4.5 which has also increased the surface friction by a considerable amount. That would be a very bad thing in a high speed rotating member, I'm not sure how bad it would affect a knife.

The reason that washers are generally round is that having an eccentric shape frequently results in some areas having a different clamping force than others. When used to hold two pieces of parallel metal together a screw imparts clamping force in an even circular pattern centered on itself.

Think of the washer as being a series of lines radiating out from the center of this screw. If the washer is circular all of these lines will have the same area and therefore experience the same clamping force.

If the washer is some other shape (square, for example) the lines that extend the farthest (to the corners of the square) will have a different surface area and therefore the clamping load will vary around the surface of the bearing. This increases friction and causes uneven wear, and in extreme cases can even cause bearings to take on a "crimped" appearance which greatly increases drag.

So in my experience washers should be round unless there is a clearance issue that cannot be designed around or some other unavaoidable complication. With that said, I'd recommend that you try your idea and see how it works out. Most of the important advances in engineering were made by people just trying an idea in spite of plenty of evidence to the contrary.
 
Hey Bart! I'm no help. I just wanted to pop in and say hi. Good to see you on the forum again.
 
Fishbulb, you da man! :D Thanks for the excellent explanation. I knew there was some very good reason for round washers aside from the obvious aesthetic ones. I still think it's OK for cutouts near the lock though, if the washer is encroaching on it. But you may be right that it will eventually result in premature wear in that area.
 
Originally posted by Peter Atwood
I still think it's OK for cutouts near the lock though, if the washer is encroaching on it. But you may be right that it will eventually result in premature wear in that area.
Click to expand...

Like I said, knives are a very different application than the stuff I'm used to working on.

Something spinning at 1,800 RPM near the boiling point is going to put far more wear on the bearings than a folder that is cycled maybe a dozen times a day at room temperature; so it's entirely possible that the effects that I described wouldn't be a concern for a long time, if at all. I doubt that having lock cutouts would cause any problems.

I seem to remember having a Gerber Air Ranger that had one of the washers cut away in order to make some clearance for the liner lock. Or maybe it was a Camillus EDC. In any case, it is something that has been done on occasion by the big manufactyrers.
 
Washer can be any shape you want. Friction can be a problem but but ut depends on the materials you use. I use nylatron which is self lubricating nylon with molybdenum disulfide and is hard. Teflon tends to be squishy and can causes slight side play sometimes. BOB
 
I am no expert, I have never even tried to make a folder. What I do have is some experience with the folders that I have bought.

Strider uses a larger bronze phospher washer with a cut out for the lock. This seems to work just great in my AR, opening is very smooth and easy. The washers don't rotate, but I know Strider uses some type of adhesive to prevent this. The Buck/Strider uses a smaller diameter washer on the lock side for clearence. The opening is also nice and smooth, and I don't notice much if any movement of the washers.

So obviously you can use a washer that is not a circle to allow for a larger washer. I would think that it becomes somewhat of an issue of what exactly you want in the folder. If you use larger washers you might be getting more friction, and thus the opening wouldn't be as smooth. The upside with this arrangement is that the lockup will be firmer. If you use smaller washers you would probably get a smoother action, but a bit less firm lockup.

I would think the best way to go is take a round washer and make a cut-out for the lock. This way it would be easy enough to try the knife both ways, and see how it works best.
 
Heheh, Bart came over for dinner today, and we discussed the exact same thing... I'm gonna post my comments here anyway, in the hopes that someone can either prove or refute my theory.

btw, first post on this forum, so hi guys. :)

Anyway, here goes... I'm gonna describe what I'd like to call a worst-case washer. Take a regular round washer, only a bit bigger, then draw some lines trough the center (let's say at 60 degree angles) and a circle somewhere halfway trough the diameter of the hole and the outer diameter. Now cut off parts of the washer between two adjacent radial lines and the middle circle. You now got some weird looking washer, kinda like the "radioactive danger" symbol. It will have more surface area, but with edges perpendicular to the blade motion. See the problem forming? The blade rotates perpendicular to the washer, thus creating extra stress on the radial edges. This might, or might not, result in extra friction. That's something that can only be determined by experimentation. Secondary problem: I don't know if any washer material has a layered structure, but imagine using some material that has, you will peel off the layers along those edges, they would curl between the rest of the washer and the blade a little, but little by little this peeled-off curled-in area would extend. This will create even more friction, up to the point where it creates so much friction that your blade will open so difficult that it's necessary to loosen the pivot pin thus negating the whole extra stability factor.

The washer I described is a worst case, but the same effects will also appear in a square washer, albeit to a far smaller extent.

However, this is just my theory; I might be completely off, and I doubt there's some washer material with a layered structure. But even if the washer isn't "layered", the same peeling off effect might also be present in regular plastic-like materials with long molecule strings.
 
I think the biggest reason they are round, is that it makes them pretty much universal.They can be mass produced and used for any knife, or any other application you want.
 
nope it don't need to be round
and if you have too much drag you can take material out as mentioned
I'd take round spots out of the outer center to reduce drag if you have to much
but of course the clearance is your biggest adjustment to keep.
these washers take a lot of working to wear out.
keeping the pivot at one adjustment is the key I think.
I make my own anyway so it workes out ok. just my opinon:)
 
Both washers used on the Buck Strider folder are held in a fixed position and cannot rotate.
One is round with a cut-out, the other almost key-hole shaped.
Exactly what the thinking behind this configuration was, I am unsure of, but the action is not unduely impeded.
Dirk
 
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