Large Sebenza/Insingo FULL BACK SPACERS...

Carbon fiber's rigidity or stiffness is measured by its Young Modulus (measures how much a material deflects under stress). It is over 4 times stiffer than glass reinforced plastic (G10), and 2.5 times greater than aluminium... no casual issues will be had with it flexing or bending the end resting on the blade stop.

I will however need to investigate the Micarta version when I get to machining those. Micarta doesn't have the stiffness nor strength... so as I stated previously I may have to go with a thicker spine and machine a blade clearancing kerf or slot as I did in the Small Sebenza back spacer version.
 
Sorry... but I'm unable to answer that. The back spacer was designed using an Insingo blade shape which by default will also accommodate the Sebenza blade. The tanto is a complete unknown.
 
I do have the prototype machined.

I'm on a 'sort of' hiatus. Taking a break to work on some new designs and new products... things that are almost impossible to do with the shop in full swing.

I'll be getting back to shop ops come July and make the Large back spacer available at that time.

Steve
 
Just an update...

I'm back in the shop however we're having a protracted period of 90's+ temps where the unconditioned shop gets into the 110-120 degree range. That causes comfort issues for me BUT also problems with the CNC where differential expansion of dissimilar metals introduces precision errors. I do not run the CNC at all in those conditions. So nothing getting done until cooler weather.
 
I just purchased a Large Sebenza 21 plain jane from a fellow on the Chris Reeve Knives - BST Facebook group. It should arrive late next week given Monday is Labor Day.

I felt the need to acquire my own Large 21 to finalize the full back spacer development and finally make some available. I should be able to offer some carbon fiber and black canvas Micarta back spacers for the Large 21 in the Exchange once I get the knife in hand and lock down the G-code machining files. As a guess... that could be late September.

We're still experiencing a protracted string of weeks and weeks of temps in the 90's and 100's here in the PNW. I do not run the CNC in such temps. The heat causes too many issues.

Can't believe I haven't completed but a couple jobs this entire Summer. Fall can't get here soon enough for me...!
 
BOOMER52 said:
I've began working up what hopefully will result in a full back spacer for the CRK Large Sebenza and Insingo. There are a couple of issues right off the bat that make this more difficult than the back spacers for the Small Sebenza/Insingo... however I think these can be resolved with design tweaks.

Forum brother 91bravo has generously supplied one of his Large Insingos for me to disassemble and scan. The scans will allow me to be able to work the knife up in CAD and then CAM applications to arrive at machinable files.

The first hurdle I've encountered is the very tight tolerance of the Insingo blade to the lanyard hole. It turns out to be so close that my idea of machining my own stepped lanyard pin to solve the back spacer free rotation issue is not feasible. Even a small shouldered or stepped pin will have a strike issue. It also appears that the lanyard pin hole in the back spacer cannot even be full circumference for the same reason.

I'm still going to machine a carbon fiber lanyard pin however it will not be stepped or shouldered. If I can maintain a non-strike clearance with a straight lanyard pin it will require fixation into the back spacer with a dab of CA adhesive or epoxy.

We shall see... more as it happens...!

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The tolerances are quite close indeed. On my Small 21 the tip of the blade slightly cuts the lanyard string when it is closed. Not enough to sever it but enough that it frays it and bothers me. Then I have to worry one day it cuts through and I lose my pretty blue lanyard pin.
 
Do you think it will fit on every Large 21 insingo? Could slight variances in each knife be enough that it would be a problem?
 
Lapedog said:
The tolerances are quite close indeed. On my Small 21 the tip of the blade slightly cuts the lanyard string when it is closed. Not enough to sever it but enough that it frays it and bothers me. Then I have to worry one day it cuts through and I lose my pretty blue lanyard pin.
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No worries! The Small 21 has stepped or shouldered lanyard pin. It is fully sandwich captured by the scales and cannot fall out. The Large lanyard pin however is not stepped or shouldered... it is a straight pin and only prevented from falling out by the lanyard itself.
 
BOOMER52 said:
No worries! The Small 21 has stepped or shouldered lanyard pin. It is fully sandwich captured by the scales and cannot fall out. The Large lanyard pin however is not stepped or shouldered... it is a straight pin and only prevented from falling out by the lanyard itself.
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I'm pretty sure for whatever reason my small 21 does not have the stepped pin. I didn't know about it potentially falling out until I took the knife apart and noticed that it would happen without the lanyard.
 
Lapedog said:
Do you think it will fit on every Large 21 insingo? Could slight variances in each knife be enough that it would be a problem?
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That's the exact issue I have had with tolerancing the back spacer so closely using just one example of an Insingo blade profile. I understand that CRK water jet cuts their blades which is a CNC operation. All blades start out exactly the same... however their grinding/sharpening operations are all hand done which introduces slight variances into the final profile.

I have had a small number of blade contact issues with my Small 21 back spacer. Dozens and dozens have been machined and sent off without problems... but there were however a total of three instances (so far) where slight blade contact issues were observed. I've had to tweak the machining operations and hopefully eliminated this issue with the Small 21 back spacers. I say hopefully as there MAY still exist a blade having a slightly larger finished profile that hasn't been accommodated in my attempt to keep the tolerances tight as possible.
 
Lapedog said:
I'm pretty sure for whatever reason my small 21 does not have the stepped pin. I didn't know about it potentially falling out until I took the knife apart and noticed that it would happen without the lanyard.
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Hmmm... in attempting to suss out the definitive answer to this I came upon this discussion... http://www.bladeforums.com/threads/lanyard-pin-without-a-lanyard.756289/

I'm not certain it actually answers the question... but I believe ALL Small 21's originally came with a shouldered pin... I could be wrong as I am rather new to the CRK world...
A3c5tTQ.jpg
 
BOOMER52 said:
Hmmm... in attempting to suss out the definitive answer to this I came upon this discussion... http://www.bladeforums.com/threads/lanyard-pin-without-a-lanyard.756289/

I'm not certain it actually answers the question... but I believe ALL Small 21's originally came with a shouldered pin... I could be wrong as I am rather new to the CRK world...
A3c5tTQ.jpg
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I guess there is only one way to find out. I gotta take it apart again. If the actual hole size the pin sits in on the Large and Small then maybe they just ran out of stepped ones when mone was made.
 
We got off topic a bit with this shouldered/straight pin discussion... BUT it's a fairly critical issue for me since I machine a single style of a Small 21 back spacer that requires the stepped or shouldered lanyard pin. I have made the assumption that all Small 21's come with a standard stepped/shouldered pin based on the multiple dozens of these Small back spacers out there in Forum member knives and never having anyone say the spacer didn't work due to their knife having a straight pin.

You are the first to mention your lanyard pin is a straight non-shouldered style so I'm going to assume your straight pin is not OEM to your Small 21. To get back on topic... I wholly agree that the CRK knives have extremely close tolerances (with the Insingo blade especially) right there at the metallic round back spacer and lanyard hole!
 
My Large Sebenza 21 PJ is inbound!

Tracking says Friday for expected delivery. I'll hop on the CAD and machining code tweaks as soon as my Sebenza arrives. Could have the design completely locked down by the end of the weekend. We'll see...
 
The Large Sebenza 21 I purchased from a fellow on the CRK-BST Facebook Page arrived this afternoon! The card's 'born on date' was December 16, 2013... so this plain jane Sebenza is just shy of four years old. The knife is in fine shape... with no visible warts. Other than multiple snail trails which I would expect for a used knife... the blade appears new and unused. As I purchased this Sebenza strictly as a 'catch and release' fitment mule... I'm pleased with my purchase and won't have any trouble recouping my money when I put it back up for sale.

I've already disassembled the knife... placed packing tape on the blade to prevent marring... and just because I could... buffed all the dome headed hardware to a chrome like finish.

My large 21 back spacer was originally developed using a borrowed Insingo and now that I have a Sebenza to work with I've already needed to tweak the CAD/CAM files slightly and need to proof this new g-code in some scrap G10.

Temperatures have come down a bit so I may (fingers crossed) be able to fire up the CNC over the weekend and test machine the NEW modified profile. It's a simplified profile version as I'm strictly looking for the blade clearance at the stock round metal back spacer and lanyard hole. Once that is nailed down... everything else is ezee-peezee!
 
Machined the TEST spacer out of scrap G10. As a starting point... I began with the Large back spacer CAM file developed around the Insingo blade with a few tweaks I made at the stock round back spacer bulge. Once machined and fitted it is apparent the Sebenza blade has a slightly deeper belly. In the attached pic you can see between the two red arrows the blade has zero clearance. I thought I could get away with thinning the back spacer's spine to clearance the blade's edge profile... but with the deeper belly on the Sebenza's blade... clearancing the blade profile will leave too little spine. So... I need to abandon that idea and go with a deeper spine and slotting or kerfing to create the required clearance. It's an additional machining operation and necessitates the machining of a special jig... BUT... it is what it is...
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Going with the deeper spine will at least consolidate the machining file so the same one is used to machine both carbon and Micarta. That's a plus...

Here's a few CAD renders of the two styles of scallops available when I wrap this up. Bowl scallops and squared 'V' scallops...
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