Detent ball on liner lock

Matt Rochester

Matt Rochester

Joined
Nov 28, 2014
Messages
1,864
I am trying to figure out how to go about installing the detent ball in my first liner lock. I plan to press it into the end of the lock. I have some 3/32” detents and am wondering how small I need to drill the hole? I don’t have a mill. I do have some #31 drill bits and a 3/32 reamer. When trying it out on some scrap titanium the hole is too sloppy. Do I need a smaller bit and reamer? Can I do this without a mill? Thanks.
BSpbkcu.jpg
 
I can't tell for certain, but from the pic it appears that installing the detent is the least of your problems.

It doesn't appear that you'll have much, if any, room to place it correctly. It needs to stay up on the blade through out its entire travel, except when it comes off at the very end of the open position.

Are you sure your design is sound in that respect?
 
And yes, you can do it easily without a mill.

You'd probably want to use a #43 drill to press a 3/32" ball into a titanium liner. No reamer is necessary for that.
 
For a precision hole you really need to ream. HSS twist drills don't really drill round holes if the center web is engaged in the work, they drill somthing more like a Reuleaux triangle. If you don't have a reamer, you can get closer to round and on size by drilling a pilot hole first, to relieve the center area for the drill of the target size.

There are a lot of variables that go into precision hole making, so in general if you want a press fit on a .0937" ball, you would be shooting for a .0927-.0930" hole. One repeatable way of getting there would be to drill with #44 (.086) drill, and then reaming with a .0927" reamer. If you have a drill press with little run out, sufficient spindle speed and good drilling practices (allowing the drill to cut, rather than forcing, etc) you may be able to get a sufficient press fit by drilling with a #44 bit and then following that with a #42, but I doubt it. A #43 drill (.089) with no pre-drilled hole may go over size enough to get the ball pressed in, but that's not very reliable either.

But drilling and reaming .0937 when your ball is .0937 (size on size) will never give you a good secure press fit. Not one that lasts more than a couple open-close cycles.
 
John and I were posting at the same time. In matters of precision drilling, I will happily defer to John as I've seen first hand he definitely knows what he is talking about and is correct.

My comments were specifically pointed at setting a detent ball in titanium only as that's the only material I can speak to. You want a hole smaller than your detent ball. The titanium is springy and will deform and 'grab' onto the ball. So a #43 would probably be sufficient for this task and reamer wouldn't be necessary as you're forcing a ball into a hole that's too small for it anyway.....you're counting on the titanium to deform to the ball.

For what its worth, I've never used a reamer for that particular task and my detents perform flawlessly.
 
Hey if you can get a 3/32 ball into a #43 drilled hole that's perfect. I never tried and made some assumptions that are based more on hardened steel:hardened steel press fits than steel:titanium.

Something else I neglected is that the precision of the circularity of the hole for a permanent press fit of a ball detent really is less critical than it is for say, a slip fit alignment pint.
 
On that topic, are 3/32 ball detents more commonly used than 1/16? I've only tried 1/16 so far and they're a PITA to deal with.
 
In full disclosure, I've only ever used 1/16" detents, and don't foresee any reason to change at the moment.

I press a 1/16" detent into a #53 hole, which is 3-4 thousandths undersize (just going from memory), so the concept would be the same for a 3/32" detent. A #43 is 3 or 4 thousandths undersized for that.
 
J. Doyle said:
I can't tell for certain, but from the pic it appears that installing the detent is the least of your problems.

It doesn't appear that you'll have much, if any, room to place it correctly. It needs to stay up on the blade through out its entire travel, except when it comes off at the very end of the open position.

Are you sure your design is sound in that respect?
Click to expand...
Thanks for the reply. I am not certain mine will work but this is how the Case Trapperlock I took apart works. The detent doesn’t ride on the blade the entire time. It only hops on it about 7/8 of the way closed. As I said earlier, this is my first liner lock and ,although I’ve made a few slip joints, I’m no expert at all! I got my bit numbers mixed up when I said I had #31 bits as those are for the pivot. I’ll see what size my other bits are but I believe they are 43’s. The top of the hole is a little loose but the bottom is good. I did not center punch it so the bit may have walked a little at first.
 
The detent is in the end of the lock arm, not in the liner. I still haven’t trimmed the lock arm as I was going to wait til after heat treat.
 
kuraki said:
For a precision hole you really need to ream. HSS twist drills don't really drill round holes if the center web is engaged in the work, they drill somthing more like a Reuleaux triangle. If you don't have a reamer, you can get closer to round and on size by drilling a pilot hole first, to relieve the center area for the drill of the target size.

There are a lot of variables that go into precision hole making, so in general if you want a press fit on a .0937" ball, you would be shooting for a .0927-.0930" hole. One repeatable way of getting there would be to drill with #44 (.086) drill, and then reaming with a .0927" reamer. If you have a drill press with little run out, sufficient spindle speed and good drilling practices (allowing the drill to cut, rather than forcing, etc) you may be able to get a sufficient press fit by drilling with a #44 bit and then following that with a #42, but I doubt it. A #43 drill (.089) with no pre-drilled hole may go over size enough to get the ball pressed in, but that's not very reliable either.

But drilling and reaming .0937 when your ball is .0937 (size on size) will never give you a good secure press fit. Not one that lasts more than a couple open-close cycles.
Click to expand...
Thanks Kuraki. I’ll see if I can find a smaller reamer and will try a pilot hole.
 
If it's titanium I'd give a #43 drill another try in a test piece. Try pre-drilling it with a smaller drill and following up with the #43. If you're having trouble with the hole being bigger at the top pre-drilling will help resolve that.
 
Yeah the detent has to go in the lock arm. It will technically work with that design then....it just won't lend itself to nice smooth action.

The sooner the blade can get up on that detent and the longer it can stay there, the smoother your action will be.
 
J. Doyle said:
Yeah the detent has to go in the lock arm. It will technically work with that design then....it just won't lend itself to nice smooth action.

The sooner the blade can get up on that detent and the longer it can stay there, the smoother your action will be.
Click to expand...
I gotcha. The original one had a bearing in it but I’m using a bushing. I will try to get the detent as far to the right (as pictured) as I can so it will contact the blade as soon as possible.
 
Last edited:
kuraki said:
On that topic, are 3/32 ball detents more commonly used than 1/16? I've only tried 1/16 so far and they're a PITA to deal with.
Click to expand...
The most commonly used detent ball is .0625" (1/16"). The next size .0787" (2mm). They are the first go to when a mistake is made. The last size is .0937" (3/32"). For most knifemakers, this is the last chance to fix detent ball errors by drilling a new hole.

Starting with .0937" does not leave much room for error correction.

Chuck
 
Last edited:
Thanks Chuck that makes sense. I had not thought about it in those terms. I have a liner with a 1/16 ball right now that I dorked up, I tried peening the hole smaller but it won't hold a ball securely. It didn't even occur to me to step up to another size because .093 is too big for where I have it located. But 2mm might just work.
 
Matt R said:
Looks like a great book and exactly like what I need.
Is $200 the norm for a used copy? Apparently it isn’t being printed anymore.
Click to expand...

Yes

I paid damn near $500 for a slipjoint book

there's a poor scan pdf for free, but the paper book is so much better.
 
You must log in or register to reply here.
Back
Top