Slipjoint smoothness tips

Sean Yaw

Sean Yaw

Gold Member
Joined
Feb 26, 2019
Messages
417
How do you slipjoint makers get a super smooth action? I am guessing it seems to be a tradeoff of tang/spring-tip sanding grit, tang corner rounding radii, and spring tension. I have a slipjoint from Bill Ruple that is exquisitely smooth, but I haven't been able to get mine to feel like that. Even on my good ones, I can feel slight grittiness when opening/closing the blade slowly without letting it snap to the next position. I'd appreciate any tips people have. Thank you.
 
I should also add: When I pulled some bad ones apart, I can feel the bumps on the spring, perpendicular to the direction of tang travel. I think this explains the gritty feeling action as the tang catch/slips on the bumps. They are not there when I put it all together. I oil it heavily (not lithium grease though) after assembly before I start breaking it in. That is making me think that the tang corners are too sharp and/or the spring has too much preload.
 
I sand the spring where the tang rides to 100 grit with the sand marks running parrallel to the tang. I sand the tang 400-600 grit all sanding parallel to the tang.

This prevents galling with stainless.

Also a bit of lubrication
 
There are 100 ways to skin a cat here. During initial profiling I finish the inside of the spring to 400 grit on my horizontal. From there I never touch the running surface where the tang makes contact again. As your working the action throughout the build it is breaking in. For the blade I finish the back square to 2000 grit micron then hand polish out any vertical belt marks so the scratches run parallel to the spring. As I'm dialing in half and closed and get to within 2 thou I'll slap a 600 grit micron on until about a half thou. Then touch it up with 1000 grit micron and finally 2000 grit micron to hit zero. Sharp tang corners are not going to be friendly unless maybe you are heating back your tangs. I've yet to try this but the guys I have talked to swear by it. Rounding down the edges of your tang is also another good practice. It's really just about doing some experimenting and figuring out what you like and what works for you. As far as spring tension. Do yourself a favor and purposely make a knife with a lighter spring. It'll help your calibration going forward. Heavy pulls are an issue for almost every new maker. Everyone I have talked to has suffered from it to some degree early on. I tricked myself into thinking a 7 or 8 was a 5 or 6 because it was smooth. Then I handed a knife to a very well known maker last year and he gave me some great feedback.
 
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most of what's already been stated. I also buff all sides of the tang plus the spring walk as well. Finally, when the knife is all together and peened, I put a liberal amount of brasso into the pivot area and then cycle the knife a couple of dozen times. Usually smooth as silk after that.
 
My springs are around 46 RC and are sanded to 400 grit on the horizontal grinder. I will knock the corners off the tang, and polish the tang lobes on the buffer. Therefore, you have a polished 61rc tang running on a 400 grit sanded 46RC spring. I typically run washers and my 3/32 pivot hole is slightly oversized. I also use lithium grease for the break in. I found all of this makes a smooth action - def interested to hear what others are doing!
 
So a smooth tang and a smooth spring?

I always thought that they shouldn't be finished to fine so the grease has "lines/scratches" to sit in.
Don't you loose the lithium grease if the tang and spring are to smooth?
 
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Signalprick said:
I tricked myself into thinking a 7 or 8 was a 5 or 6 because it was smooth. Then I handed a knife to a very well known maker last year and he gave me some great feedback.
Click to expand...
What do the numbers mean?

I am interested because several of the slip joints that I've bought are awfully hard to open and close, and one of these days I may try to fix them. But I'm not a knifemaker--that's way beyond my ability.
 
Another Shepherd said:
What do the numbers mean?

I am interested because several of the slip joints that I've bought are awfully hard to open and close, and one of these days I may try to fix them. But I'm not a knifemaker--that's way beyond my ability.
Click to expand...
It's a very subjective way to judge the pull strength on a slip joint. Scale from 1 - 10. 10 being a bear trap.
 
Hengelo_77 said:
So a smooth tang and a smooth spring?

I always thought that they shouldn't be finished to fine so the grease has "lines/scratches" to sit in.
Don't you loose the lithium grease if the tang and spring are to smooth?
Click to expand...
Even a mirror polish has scratches. Personally found that the smoother the finish, the smoother the action. You don't even need bushes to get it right.
 
On stainless steel it will gaul if you do not have a difference in grit.
 
Another Shepherd said:
What do the numbers mean?

I am interested because several of the slip joints that I've bought are awfully hard to open and close, and one of these days I may try to fix them. But I'm not a knifemaker--that's way beyond my ability.
Click to expand...
Chris Crawford has a interesting video of measuring pull weight with a scale.

What is still missing is calibration of pull weight in (lbs) to rating of 1-10. I heard from one person who calibrated 2-2.5lbs to 4 to 6 pull rating.
 
ashwinearl said:
Chris Crawford has a interesting video of measuring pull weight with a scale.

What is still missing is calibration of pull weight in (lbs) to rating of 1-10. I heard from one person who calibrated 2-2.5lbs to 4 to 6 pull rating.
Click to expand...

Thanks, that is very helpful! It gives me a standard of comparison.

My wife has a large collection of those A-shaped spring clips, but I cannot find any that are strong enough to open most of my non-locking knives. Maybe I'll try locking pliers with some masking tape on the blade.
 
ashwinearl said:
Chris Crawford has a interesting video of measuring pull weight with a scale.

What is still missing is calibration of pull weight in (lbs) to rating of 1-10. I heard from one person who calibrated 2-2.5lbs to 4 to 6 pull rating.
Click to expand...

Another Shepherd said:
Thanks, that is very helpful! It gives me a standard of comparison.

My wife has a large collection of those A-shaped spring clips, but I cannot find any that are strong enough to open most of my non-locking knives. Maybe I'll try locking pliers with some masking tape on the blade.
Click to expand...
On a HT day, I actually made a sort of a column using crap around the shop, and an acme threaded rod to go up and down, using a fish scale(ala Chris Crawford).Using extended middle spring pin to secure. I barely get over an lb . It ain’t much, but it’s on my Instagram if interested. The images are supposed to be movies, but It’s apparently above my pay grade to post😜.
 

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Its nice that you guys are coming up with way to measure it but then who's standard do you go by to interpret the numbers you are getting?

Bottom line, seems like a little bit of a waste of time no offense. Unlees you find the 1 guy or group of "experts" that everybody can agree his/their interpretation of the pull is the standard its kinda still subjective no matter what you tell me or your customer your "measurement" is. Outside of that don't let me stop you from having your fun. :)
 
Jason, I know the friggin numbers do not mean squat ,and are subjective. However, this helps me dial it in to what I am looking for, With this, it’s repeatable for me. As far as it being a waste of time, I have neurological issues (not crying the blues here, just making a point)and have a hard ass time dialing in the tension, this alleviates this problem for me. By finding the sweet spot, that ”I’m” looking for, I can now be more consistent. As far as this 1-10 scale, I could give a rusty f… about it and don’t use it. I do see you use it though, where did you get your scale of measurements?
 
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