Slipjoint/lockback issue

Sean Yaw

Sean Yaw

Gold Member
Joined
Feb 26, 2019
Messages
417
I finished up my sixth knife tonight and have an issue I am looking for help/insight into. When I am peening a knife together, I start with the pivot and try to get it just tight enough to eliminate side to side play. The problem is when I accomplish that, the blade tightens up (sometimes fairly significantly) as it is closing. So, just tight enough when open and quite tight as it closes. This is leading to challenges, especially with lockbacks that don't have as much spring pressure to close as slipjoints do (at least mine). I am using precision ground steel straight on 410 liners (i.e., no mill relieving or washers). It seems reasonable that there would be more friction as the blade closes and the top of the tang enters the liners, but there is much more resistance than GEC and other factory slipjoints I have handled. Any idea what my issue is and how I could address it? Thank you.
 
Have you milled a raised area on the tang or using washers to act as a clearance spacer? There needs to be a minute gap to prevent the tang from binding on the liners.

Using a pivot with screws solves most of the fit-up problems. You can remove the blade and polish down any high spots or change the washer size as needed until it is just right. The screws also allow adjusting the blade play and tightness. There are many types of pivots available. Here are just a few:

Pivots | KnifeKits.com

Pivots: Over 9000 knife and holster making supply items. We feature knife kits, blade blanks, fixed blade & folder parts, blade grinders, pocket clips, automatic springs, carbon fiber, knife handle materials, KYDEX, HOLSTEX, BOLTARON and other holster making sheet and supplies. Superstore of...
www.knifekits.com
 
If you see witness marks on the Tang then you have clearance issues of pinching to tight. Don't over look the fact that the Pivot Pin actually swells in the blade pivot hole if you over peen to eliminate side to side blade play, this can create an over tight blade movement and can't be easily seen.
 
Possibly bowed liners? Are you using a shim between liner and tang while peening? What is the thickness of the spring compared to the tang? I’ve always addressed the blade pivot last, unsure if that matters tho.
 
I haven't found a way to use washers as I can't reliably thin and flatten blade tangs to accommodate them with the tools I have. I don't think my issue is a swelled pivot pin, though I could be wrong, because I have the same problems when I use a bushing and the tight movement is only 30 degrees or so of movement while closing. I also don't think it is bowed liners. They looks pretty flat on the granite surface plate when I am done with them. I do use a shim when not using a bushing. I have been making slipjoint springs as close to the thickness of the tang as possible, and make lockback lock bars slightly thinner than the tang.

I definitely have witness marks on all of my blade tangs. It seems like there would be those marks with a tang of uniform thickness and flat liners without mill reliefs. I did not do any milling on the tang as Stacey suggested. Perhaps I should try taking a tiny bit of material off to thin the top of the tang where the makers mark is?
 
You can get bronze pivot washers in very thin size. This leaves just the right gap.

Busto brings up another possibility. Over peening can bend/swell the pivot pin. This can make the blade twist as it opens or closes.
 
Since your not relieving the liners are you using a pivot shim when you peen? If not get yourself some .002 ss shim stock. I used to use 2, one on each side when I was modding gecs but gec parts are not even close to flat. Once you pull your shim/shims if there is any side to side play gently, very gently tap the pin to work it out. Now on the knife in question, have your tried slackening the blade a little? Sounds like it's just rubbing the liner as it closes. Possibly your spring is slightly thinner than your tang. From the center pin to the front of the spring is critical for thickness. It can be no less than the thickness of the tang and no more than .0002 over the thickness, at least when using a bushing. But if too thick you'll always have play. If that makes sense.
 
I am using two .002 shims when I don't have a bushing. When I have a bushing, I was not using any shims. I did try slackening the blade, but it got to the point that it introduced some play when open and still get quite tight when closing. I may need to keep tabs of spring thickness more than I have been. Up until now I was thinking that a spring that is slightly thinner than the tang couldn't hurt anything, but now I am seeing how the center pin location being thinner could pinch the liners together at that point.
 
Spring thickness in relation to the tang thickness is definitely a critical measurement. I use my granite sanding block and 600 grit paper to get mine dialed in.
 
Welp, I think it may have been a spring thickness issue. I was much more careful on this build to have the spring in the range Jason specified and this is the first one that did not have any tightening on closing. I think my springs were a touch thinner which made the middle pin narrower than the pivot, which left less clearance as the tang entered the liners down closer to the middle pin on closing. Not one does this one run great, she's a beaut too. Thanks for the help.
DB4E4A81-F3BE-4357-BFBC-54E469AF6D80.jpeg
 
Ahhh, I should have looked at your name on the left of the screen... duh....

Beautiful work, by the way.
 
Thanks.

My grandmother always claimed it’s a “good British name”, but we never believed her. It’s a pretty weird name for a blonde haired white dude.
 
I wonder if it comes from yew, like the wood used in England to make those powerful longbows. My last name also stems from a type of wood (no pun intended).
 
Possibly. I’ve never looked into it. Believe it or not, it has paid off to be named the same as the third axis of aircraft rotation though.
 
You must log in or register to reply here.
Back
Top