Looking for input on a design of a slip joint

S

Stevenj369

Joined
Dec 21, 2013
Messages
42
Hi,
So this design is a little out of my normal area of work but I have had it stuck in my head for a couple of weeks. I design in cad to make sure everything will work (at least to my knowledge which is limited to reading so far). I mostly design and build chef/kitchen knives full time so this is all new to me.

It is a 2.5in blade with a 3.75in handle. Blade thickness is .060in and I was planing on doing a 8in hollow grind on it (only wheel I have for now). I am pretty sure I have the slip joint part design correctly but ????? I am probably going to make a test one out of plastic to make sure before I start cutting metal, but no idea when since I am slammed on chef knife orders right now.

Design 1 2-22-15 Closed.jpg
Design 1 2-22-15 ISO 2.jpg
Design 1 2-22-15 ISO.jpg
Design 1 2-22-15 Open 2.jpg
Design 1 2-22-15 open.jpg
 
:eek: Nice CAD model. Only thing I can say is that the thumb ramp corner on the spine of the blade looks rather extreme and pointy to my eye.
 
nice, but if the thickness is 0.060, i think the spring height is too short to give a snappy action (i may be wrong). Another thing is that the spring center hole lies on very thin webs, i would reinforce that area in the fear of spring failure.
I would make the run-up 1/3 of the blade height, from the model it seems shorter. Otherwise the design of the tang/joint is really good with the joint contacting 2 points+pivot, and should make for a nice walk and talk.
 
Last edited:
Nail nick is upside down and your spring should be just a very bit short of the corners of your blade for best action.
 
NeilJBorja said:
:eek: Nice CAD model. Only thing I can say is that the thumb ramp corner on the spine of the blade looks rather extreme and pointy to my eye.
Click to expand...


Thanks, its funny every time I went to change the blade the point kept growing. I thinking of putting a little more radius like this:
Design 1 2-23-15 Front view.jpg



stezann said:
nice, but if the thickness is 0.060, i think the spring height is too short to give a snappy action (i may be wrong). Another thing is that the spring center hole lies on very thin webs, i would reinforce that area in the fear of spring failure.
I would make the run-up 1/3 of the blade height, from the model it seems shorter. Otherwise the design of the tang/joint is really good with the joint contacting 2 points+pivot, and should make for a nice walk and talk.
Click to expand...


For the spring Height are you talking about this area?

Spring Heigth.jpg



When you draw something and you think it looks ok, then you measure it and it only .030" thick. Thanks at least this time I changed it before cutting. Now it has .093" thickness on each side.

Design 1 2-23-15 New spring hole.jpg


Is this the area you are talking about for the run-up? Right now I have it at .35" with a blade height of .75" from belly of grind to above finger nick. Or am I lost?
Run-up.jpg


John L said:
Nail nick is upside down and your spring should be just a very bit short of the corners of your blade for best action.
Click to expand...


I woke up at about 3am last night and realized what I did. Which area are you talking about? The corner of the plunge to the spring? or the tip of the blade to the spring?
Design 1 2-23-15 Iso view.jpg


Thank you guys for all the feedback. I'm excited about making this knife.
 
Steven, it's been mentioned before, but is there a reason you've got the nail nick upside down?

I draw my folders up in CAD also to check rotation clearance, shape, design etc. You sure look like a good design there. I hopped over to your webpage and you kitchen knives are very reasonable priced - looks good.

Ken H>
 
It's upside down because it was late and I was getting tired. I ended up fixing it this morning while have my coffee. Thanks for the feedback on the kitchen knives. Thats my bread and butter right now.
 
Put your blade at half stop. Spring should now be just shy of the outside corner of blade. Same is true when in closed position. Not much...just a bit.
 
Design 1 2-22-15 1233.jpgDesign 1 2-22-15 1234.jpg

John L said:
Put your blade at half stop. Spring should now be just shy of the outside corner of blade. Same is true when in closed position. Not much...just a bit.
Click to expand...


So shorten the spring and the rest area at full open? Does that help with the transition from open to close? Would it help to have a small radius on the bottom edge of the spring?
I'm grinding 12 blades today so when I get inside tonight I'll change the model and see what you think.

Thanks for all the help. I glad after 5+ years of watching and learning that I finial decided to share my work and talk to you guys.
 
Steven, with your beautiful family and your wife working with you in the business, you are in the right group. KD are GREAT folks and a very family family friendly site. As the children get older, you won't have to worry about them seeing/reading things you don't wish on KD group.

John, Do you really mean the end of the backspring should be "shy" of the outside corner of blade? I have read the backspring should extend just past outside corner to allow the blade to rotate smoothly. If the backspring is just shy of outside corner, would the outside end not "hang" on end of backspring as it rotates around causing a "bump" in closing?

Please do understand, I've only made 6 slip-joints so I do NOT consider myself an expert by any means and rely on folks here to keep me on track.

Ken H>
 
If you make that backspring any more at all than just a hair short (better to keep it even) its
going to load up on you when going into the open position . Also most slipjoints should be right
at 1" less blade length than the knife when its closed.So a 3 1/2" knife closed should have a blade
@ 2 1/2". With the knife as is in the last pic it will work well.
Ken.
 
If you want a spring with more snap (more depth) take it off the bottom of the blade prfoile
and a bit more off the kick. If you add more to the top of the spring instead it can start to
get "clubby" real quick. Only CAD Iv'e ever done was with paper and pencil. YMMV.
Ken.
 
Ken H> said:
Steven, with your beautiful family and your wife working with you in the business, you are in the right group. KD are GREAT folks and a very family family friendly site. As the children get older, you won't have to worry about them seeing/reading things you don't wish on KD group.

John, Do you really mean the end of the backspring should be "shy" of the outside corner of blade? I have read the backspring should extend just past outside corner to allow the blade to rotate smoothly. If the backspring is just shy of outside corner, would the outside end not "hang" on end of backspring as it rotates around causing a "bump" in closing?

Please do understand, I've only made 6 slip-joints so I do NOT consider myself an expert by any means and rely on folks here to keep me on track.

Ken H>
Click to expand...


Ken: He already has his corners rounded perhaps a bit too much on the tang of blade. The spring now is way too far beyond the corner. Shorten up to even or....I think...just a hair behind corner. On this drawing it would still be on that radius by quite a bit.
 
OK John, we're on the same page. I agree the radius is a bit large, I like to just "break" the point so there is a very small radius to the corner. Not enough to be "rounded", but enough so the corner isn't "sharp". The end of backspring, as you say, just "just" extend past end of the backspring... enough so the tang will rotate without "hanging" on the end of backspring to cause the "bump".

We're on the same page. I draw up in cad, and see the rotation, but once I get to the steel, it just doesn't follow the pattern that close. Got to "feel" right.

Ken H>
 
I would agree with stezann that I think the spring height is too short. From what I understand the spring height should be approximately 1/2 the height of the tang. I say this as an observation from time spent researching, not practicing, so take that for what it is worth. :foot:

Here is one of the best tutorials on design I've seen. http://www.culverart.com/Slip-Joint Folder Designing.pdf
He also has several other good tutorials on his site.

Good luck,
Chris

Edited to add that I looked at your website. Nice work there Steven! :thumbup:
 
Hey, that's a good pdf file you linked to. I've been reading and studying it. I've saved it to HD so I can study off-line. Thanks.

Ken H>
 
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