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The Folding Knife (& Switchblade) Forum The materials, techniques and the designing of folding knives.

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  #1  
Old 09-29-2003, 09:56 PM
Webster Webster is offline
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Bronze Bushing

I am using bronze bushings for my lockback folders. Is the blade suppose to spin on the bushing or the bushing on the pin.

I use a 1/4 bushing, and I ream the hole to .250. The problem is the bushing measures .251. Should I press fit the bushing? I use brass liners and I have always brought the bushing down to about .249 and the blade spins on the bushing after it is peened.
It works great, but on this last folder it hit me, and I began wonder what others are doing. Any feedback will be appreciated.

Thanks
Bob


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  #2  
Old 09-29-2003, 09:58 PM
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Jamey Saunders Jamey Saunders is offline
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My understanding from reading the book "How to Make Folding Knives" is that the bushing is press fit into the blade, and rotates on the pin. As a practical matter, I'm not sure that it makes a difference.

Of course, you can think of it this way: If the bushing spins on the pin instead of the blade spinning on the bushing, there's a lot less surface area in contact, thus easier opening and less wear.


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Old 09-29-2003, 11:16 PM
Mail4Tim Mail4Tim is offline
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Mechanical Engineering 101

The idea behind using a bushing in any machine is to provide a ?replaceable? bearing surface. The bushing should be a press fit into the movable part, in this case the blade, and should slip around a shaft, or pin in this case. The bushing, being the softer of the two materials that are moving against each, should theoretically be the only surface that wears. The problem is, as I said, it?s only theoretical. In reality where you have movement you will wear both surfaces. In that case it?s better to have the wearable surfaces the pin and bushing since they are the easiest and cheapest to replace.


Tim
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Old 09-29-2003, 11:47 PM
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HermanKnives HermanKnives is offline
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I disagree. The purpose of a bushing to me is to keep the frame from binding the blade when all is peened together. The bushing should be about 1.5 thou thicker than the blade and when set in solid and the blade spins around it. If the bushing is a tad big I would hone it done to size so it moves freely inside the blade hole.
The idea of a replaceable wearing part dont make much sense in a peened together knife to me.
Also I would use something harder than bronze for my bushings as the bronze will expand/squish and bind up the knife if peened in to hard. I use either aluminum bronze or had some made in 440c and hardened them. Just my thoughts on the subject.


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Old 09-29-2003, 11:58 PM
Mail4Tim Mail4Tim is offline
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Tim,

You make a very good point. I guess I have too many knives that are assembled with screws, or maybe not enough that are assembled with pins. I guess it comes down to whether or not you can easily disassemble and re-assemble the knife. You can tell where my mind is at.


Tim
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  #6  
Old 09-30-2003, 03:37 AM
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HermanKnives HermanKnives is offline
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Tim,

Yes with screw together knives the blade spins around the "bushing" but in those knives I call it a pivot. Since he originally said his lockback folders I thought of bushings in the pinned lockback method of construction. The screw together pivots dont revolve around a pin though so the blade would still revolve around it also.
Sorry for any confusion


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Old 09-30-2003, 02:28 PM
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Don Robinson Don Robinson is offline
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I use bronze or brass bushings in all my folders. The bushing is usually .002 - .003" longer than the sum of the blade thickness plus two washers. That means the liners are pushed up against the ends of the pivot bushing, then when the screws are tightened, the blade automatically has proper clearance to swivel smoothly. The washers are also free, since the bushing extends thru them. No adjustments to the pivot screw are necessary. Just tighten them up.

This method forces the blade to rotate around the bushing, since the bushing can't move. The benefits of this are smooth action, less wear, since there is a larger bearing area, long life, since the hardened blade can't wear, and not having to adjust the pivot clearance. Also, no lock tight.

The same method will also work great with peened pins. since over peening the pin won't bind the blade.
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Old 09-30-2003, 10:02 PM
Webster Webster is offline
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Thanks guys, you have given me something to think about. It seems that the overall feedback is the blade should spin on the bushing, since the bushing can,t move after it has been peened.

Hey Don, what type of washers are you using and how thick are they. I run my bushing about .002 bigger than the blade, If I use .001 washers won,t that lock everything up?

Bob Cannon


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Old 10-02-2003, 08:25 PM
ron p. nott ron p. nott is offline
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I use brass bushing in my folders ( lock backs ) and at times i get blade wobble from side to side.. how can i fix this problem ..


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Old 10-02-2003, 09:07 PM
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Quote:
[i]Hey Don, what type of washers are you using and how thick are they. I run my bushing about .002 bigger than the blade, If I use .001 washers won,t that lock everything up?

Bob Cannon [/B]
Yes, unless the washer I.D is large enough to pass over the bushing.

As I said, my washers ride on the O.D of the bushing, just like the blade. I usually use .010 thick washers for small pocket knives, thicker and larger dia. washers for larger folders. I use Nylatron washers, which do not wear because they are free to rotate with the blade, The liners are squeezed up against the ends of the bushing by the pivot screws, leaving the washers and blade free, with side play limited to the extra length of the bushing. Again, the sum of two washers, the blade thickness, plus .002 to .003" for clearance.

If you are interested, I have a book, "My Way", listed on my web site that explains in detail how to make and fit the pivot, lock, and detent while making the complete liners.
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Old 10-02-2003, 09:19 PM
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Don Robinson Don Robinson is offline
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Quote:
Originally posted by ron p. nott
I use brass bushing in my folders ( lock backs ) and at times i get blade wobble from side to side.. how can i fix this problem ..
Ron, see my replies above. Make your bushing and washers like that and it can't wobble more than the clearance you build in.

Also, if you're making lockbacks, I suggest you consider using a threaded pivot pin and screws in the pivot instead of peened pins. Then it's easy to control the clearance, and you can easily remove the blade for maintenance.

I made lockbacks and slip joint folders for years, until the linerlocks first came out using screws for assembly. Then I changed over to a threaded pivot and used hidden pins everywhere else. Looked fine to me and my customers, but what do I know?

I admire your engraving work. Beautiful.
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Old 10-03-2003, 08:00 AM
ron p. nott ron p. nott is offline
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Hi Don.. Thanks for your info and advise .. i will try that .. I like to pressure fit my pins so i can get a clean flat surface.

I like that because it give me a good canvis to engrave on with out any interuptions in the surface .


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Old 10-03-2003, 08:54 AM
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Quote:
Originally posted by ron p. nott
Hi Don.. Thanks for your info and advise .. i will try that .. I like to pressure fit my pins so i can get a clean flat surface.

I like that because it give me a good canvis to engrave on with out any interuptions in the surface .
Ron, you know, you can hide the head of the screws under the bolster. That way, you still have an uninterrupted surface in the pivot area.
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Old 10-03-2003, 04:57 PM
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HermanKnives HermanKnives is offline
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Don, this all works great on screw together linerlocks but lockbacks especially interframes, a showing screw would ruin its looks and engraving area. And interframes have no bolsters to hide a pivot screw. Plus you would still have the 2 small screws holding the bolster on.

Ron, in lockbacks I use a taper pin pivot system taught to me by Steve Hoel. Years playing with bushings and still finding blade play somewhere drove me nuts. With the taper pin a few extra peening taps will eliminate any sideplay if there is any after tha main peening of the pivot pin. I believe the taper pin is the best and strongest folder pivot to be used but they dont work well when doing linerlocks. But this discussion was originally posted for lockbacks, how it got off on linerlocks I dont know.
Back to taper pins and bushings. Using bushings and straight pins you have a hole on the blade and a hole in the bushing. Now all these being at 90 degrees tells me that for a perfect fit with no play you absolutely must have the holes so precise that to me the blade would not spin freely around that bushing because somewhere there has to be some play to let it spin. With taper pins everything is measured with calipers and the fit is perfect as the blade hole and pin match together perfectly. The holes are reamed so the pin has to be press fit into the frame .150 past your standard hand press so it pretty much welds itself to the frame. When peening the knife together i use a piece of .002 heat treating foil as a shim on one side of the blade for the main peening of the small side of the pin. After the arbor pressing of the pin that additinal .150 you really dont need to peen anything but i do just for security After the shim is pulled if there is any sideplay left then some light peening on the small pin side will pull the frame perfectly together and eliminate that side play. The advantage here is thst the frame is in contact with the blade but is not exerting any pressure on the blade as a straight pin would do if peened harder. So you yave perfect fits on the slight angle of the taperpin and no play in about 1/8th the time trying to polish and hone bushings and get extremely accurate reamed holes for them. Doing the taper pins sounds confusing but I could show you easily in the shop in minutes.


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Old 10-06-2003, 10:21 PM
Frank J Warner Frank J Warner is offline
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Quote:
Originally posted by HermanKnives
Doing the taper pins sounds confusing but I could show you easily in the shop in minutes.
Yes, it is confusing but sounds extremely interesting. Is there a way you could post a couple of exaggerated drawings to illustrate the concept?

Also, how do you drill a tapered hole through bolsters, liners and blade/bushing?

-Frank J Warner


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