Lets Talk Bushings

David Schott

David Schott

Joined
Sep 27, 2004
Messages
3,041
Hello,

Im getting confused over various types of bushings on the market. Can someone answer my questions below, as I think I may be over complicating things here.

Type 1: Bronze bushings:
bsh_b_25093_1_600.jpg

Are these press fit into a blade? Do they roll around a pivot pin? The description on texasknife.com says that they roll around a pin as follows:
"This little guy fits between the main blade pin and the blade so that the bushing rolls on the pin instead of the blade rolling on the pin."

What, then, becomes the advantage of them since my understanding was that bushings help to eliminate pinching of the liners on the blade. If the bushing rotates, wouldnt any pressure on the bushing pinch the same way as without it? The only way I've ever heard of bushings being used was when they were made to be slightly wider than a blade, used with or without washers, so that when bolsters pere peened or pivot tighened, the liner crushed and locked the bushing in place while the blade was free to rotate without the majority of the friction of the liners pressing inward.


Type 2: Precision pivots with bushings:
precision_pivots.jpg


I am going to assume these are designed so that the blade rotates around the stationary bushing that gets locked in place when the pivot screw is tightened. Am I also right to assume that the bushing width should equal the width of the blade plus washers, which should also equal the backspacer width?
 
pivot bushings and spacer bushings are two different animals. spacer bushings hold your liner spacing so your blade is not pinched, pivot bushings act as a bearing so your blade opens smoothly and doesn't bind. properly done the bronze bushinds should be what's called oilite bronze, sintered porous bronze with oil in the pores.

-Page
 
sunshadow said:
pivot bushings and spacer bushings are two different animals. spacer bushings hold your liner spacing so your blade is not pinched, pivot bushings act as a bearing so your blade opens smoothly and doesn't bind. properly done the bronze bushinds should be what's called oilite bronze, sintered porous bronze with oil in the pores.

-Page
Click to expand...

...So is the texasknife description wrong? Should it say that the blade rotates around the bushing, which acts as a spacer for the liners?

...Do the pivot bushings work as i described, with the blade also rotating around the bushing in the same manner?

Crap...now im more confused.
 
my use of such bushings has always been pressfit the major diameter of the bushing,(the blade) the inside diameter (pivot pin)is where the movement is going to happen I'm not generally a folder maker, but I've done some reblading on some, and I do design other things where pivot bushings are appropriate. the bushing usually rotates with the blade, the pin is stationary, the second ones I believe work similarly except the pin is a hollow sleeve with a setscrew either way I would personally make the bushing flush with the blade and leave half a thousandth to either the liner or washers, personally I don't like washers unless a recess is cut in the liners to recess them. they leave more room otherwise for crap to gum up your action, but then again, I'm not a folder expert, there's no action in ost of my knives to gum up.

-just my preferences

-Page
 
I haven't read it in a while, but if I remember Tony Bose uses the bronze bushings in his slip joints. Best I can remember the blade rotates around the bushing that is locked into place by the liners.
 
Tony uses a bronze bushing and the blade rotates around it. He also leave it .001 thicker than the blade. This is so when he peens the pivot pin material he can never pinch the blade.
 
So all these comments seem to indicate that for slipjoints, the bushings are designed to remain stationary and be rotated around by the blade. This makes sense because peening wouldn't bind the blade. It doesnt make sense to have the bushing rotate around the pivot pin or else you're leaving the square-ness of the pivot hole to the manufacturer wheras with a stationary bushing, you can ream and ensure the blade is square to the bushing.

Now that i think I understand the bronze bushings used in slipjoints, I just want to understand the threaded bushing pivots designed for screw-together folders...based on what others have said it seems they work in exactly the same manner, except replacing the peening of the pin with slipjoints with tightening of the screws.

Im interested to hear more on this, as it sounds like some do things differently (IE having the bushing .001 wider than the blade vs having it wider than the blade plus using washers (sebenzas use this method) vs having the blade flush with the bushing and leaving clearance (but im not sure how this is at all advantageous over not using a bushing at all.)
 
I think you'll find that each maker uses the same bushings in a little different way....just to solve issues, or bring out a desired characteristic.

Personally, I use both bronze and 416 bushings, along with bronze washers. I use them is such a way that the bushing is clamped between the liners, with the bushing being .0005 to .001 longer than the blade is thick. The blade rotates on the OD of the bushing. I personally do not like the bushing/pivot combos that are sold. I suppose that if an individual is making a number of identical folders they might be a good thing, but since I create mostly one of a kinds, I find them too limiting.

As for the pivots themselves, I personally use 1/8" OD "threaded barrels", with 2-56 internal threads. I match this with a bushing that has a .250 OD X .125 ID. As you mentioned, they work exactly like peening a pin, with the exception that the folder can be disassembled without destroying any part of it.
The type of pivot system that a maker uses is very often dictated by their personal likes/dislikes, along with how the specific parts lend themselves to that individual makers tools and methods.

Its not complicated, its just that when you first dive into folders, you have to realize that the tolerances you likely "got away with" on your straight knives, simply will not be good enough to make a smooth operating folder. The biggest difference between folders and straight knives is that TINY things in a folder can make a HUGE overall impact on the finished product....mechanically.
 
Ed Caffrey said:
I think you'll find that each maker uses the same bushings in a little different way....just to solve issues, or bring out a desired characteristic.

Personally, I use both bronze and 416 bushings, along with bronze washers. I use them is such a way that the bushing is clamped between the liners, with the bushing being .0005 to .001 longer than the blade is thick. The blade rotates on the OD of the bushing. I personally do not like the bushing/pivot combos that are sold. I suppose that if an individual is making a number of identical folders they might be a good thing, but since I create mostly one of a kinds, I find them too limiting.

As for the pivots themselves, I personally use 1/8" OD "threaded barrels", with 2-56 internal threads. I match this with a bushing that has a .250 OD X .125 ID. As you mentioned, they work exactly like peening a pin, with the exception that the folder can be disassembled without destroying any part of it.
The type of pivot system that a maker uses is very often dictated by their personal likes/dislikes, along with how the specific parts lend themselves to that individual makers tools and methods.

Its not complicated, its just that when you first dive into folders, you have to realize that the tolerances you likely "got away with" on your straight knives, simply will not be good enough to make a smooth operating folder. The biggest difference between folders and straight knives is that TINY things in a folder can make a HUGE overall impact on the finished product....mechanically.
Click to expand...

Thanks!

Your last paragraph rings so true for me. I am shocked at how tight tolerances need to be. All those "this pins fits close enough that it will hold just fine" are simply not good enough. If nothing else, these first few folders have taught me what a POS my drillpress is.
 
Ed pretty much summed it all up!!

When i used bushings,i used the same method! you want your liners to pinch the bushing,not the blade.this eliminates pinching blade between handles,and makes the knife operate very smooth.the trick is getting the bushing with in
.005 of blade thickness,square on both sides :)

i'm waiting for a reply from,Bill.was'nt he making bushing lappers??
 
Balialistic: I have one of those bushing lappers and they are great. I lap mine 1-1.5 thous over blade thickness at tang. It is very easy. You can lap about 10-15 thous of the bushing if so inclined in about 30 seconds. I lap at220 grit and then with 4-5 thous remaining I switch to 1200 grit. It makes for a slicjk rotating blade.
 
John L said:
Balialistic: I have one of those bushing lappers and they are great. I lap mine 1-1.5 thous over blade thickness at tang. It is very easy. You can lap about 10-15 thous of the bushing if so inclined in about 30 seconds. I lap at220 grit and then with 4-5 thous remaining I switch to 1200 grit. It makes for a slicjk rotating blade.
Click to expand...

Cool!!! where did you get yours??

i want to use bushings on my insert knives :)
 
Bill Vining over on the tools and stuff for sale. He is now selling a scribe. He was selling an indicator a few months ago. His work is flawless.....and it works.
 
Got pictures and prices of one? I've seen those listed on his website, but it says coming soon. Thanks Ryan

edited to say I'm taking this to pm sorry for the hijack.
 
Do keep in mind that drilled holes are not adequate for semi precision work like this. Drill bits are for removing bulk material in a basically roundish hole. The drilled hole is not very round, accurately sized, accurately placed, perpendicular, or smooth. Following a drilled hole with a reamer address the first two concerns very nicely, and when done properly will usually also make a good finish.

The hole in a folder blade should be reamed. Drill your hole about .010-.015 undersized and follow with a reamer turning fairly slow (500-1000 RPM) and fed relatively fast, and feed back out at the same rate. This is a good application for an oil.

In "machine shop 101" you're taught to spot dill, drill, single point bore, then ream (with a surface plate, tooling buttons and a co-ax after drilling, God I don't miss that). Today we generally just circular interpolate. But for the thickness of a blade, and the placement precision needed for a folder pivot - I think a drilled hole followed by a reamer should be perfect.

edit:
My point being - don't scrap your drill press because you don't like the holes you're getting, try a reamer to get a good hole.
 
Last edited:
Nathan the Machinist said:
Do keep in mind that drilled holes are not adequate for semi precision work like this. Drill bits are for removing bulk material in a basically roundish hole. The drilled hole is not very round, accurately sized, accurately placed, perpendicular, or smooth. Following a drilled hole with a reamer address the first two concerns very nicely, and when done properly will usually also make a good finish.

The hole in a folder blade should be reamed. Drill your hole about .010-.015 undersized and follow with a reamer turning fairly slow (500-1000 RPM) and fed relatively fast, and feed back out at the same rate. This is a good application for an oil.

In "machine shop 101" you're taught to spot dill, drill, single point bore, then ream (with a surface plate, tooling buttons and a co-ax after drilling, God I don't miss that). Today we generally just circular interpolate. But for the thickness of a blade, and the placement precision needed for a folder pivot - I think a drilled hole followed by a reamer should be perfect.

edit:
My point being - don't scrap your drill press because you don't like the holes you're getting, try a reamer to get a good hole.
Click to expand...


Thanks! I do need to refresh on my precision stuff...

I wont be scrapping the old drillpress just yet...I'll turn her into something else before I do that!
 
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