I got an MC Etcher and want to be able to do custom etching on knife blades, but I am having trouble figuring out a good, repeatable way to hold them down. I have three specific knives I currently work with over and over. My first idea was to carve a pocket in a piece of HDPE for the blade to sit in. Problem there is that the blade will be at a downward angle compared to the Z axis. Second idea was to use clay. I pocketed a 1/4" deep rectangle into the HDPE and filled it with air dry clay. I then pressed the blade into the clay and let it dry. It shrunk by about 1/8". I watched a youtube last night where a woman mixed silicon and cornstarch to make molds, so I might try that next.
The ultimate goal is the have a mold with known dimensions so I can grab it, drop the balde in the mold, zero to known location, and go from there. Any suggestions?
I think you were correct in your first thought. It may not be obvious but you can just shim your raw stock to account for the angle drop. One of my favorite “ that’s so obvious.” techniques
If you want to share some pictures of your blade and setup I’d be happy to ideate with you further as well. Lots of fun approaches to be had.
Here’s what I’m shooting for. Female mold I can drop a blade into, and zero off the bottom left corner of the white stock. I’d have a template file that has the stock dimensions, and position of the blade with in those dimensions.
You’re idea of shimming brings me back to my original idea of pocketing out a female base for the blade to drop into, and have set screws come up from underneath to level it out.
Only reason I strayed from that idea is getting the pocket perfect takes 2 - 3 attempts. Using some sort of clay or goo, for lack of a better word, would save time.
That’s gonna be a blast once you’ve locked in a good process
For the goop, my biggest concern is rigidity in the final mold. Most mold materials that have ~0 shrinkage tend to be floppy. (Silicone is a no go)
A way to mitigate this could be an epoxy. I’ve heard of great results from a dumb little trick like pressing the master into JB Weld for example
You could also do a standard two part 5 minute epoxy if you wanted to play around a bit.
Most folks either slather their part in vasoline or tightly wrap with Saran Wrap to prevent permanently adhering their master to the mold material. Perfect, no. Good enough? Maybe
The idea behind shimming the female mold is that you wouldn’t need to shim anything in actual use. You’d shim the inverse angle of your blade when cutting the mold. That way when the mold is sitting flat against your table. the blade would have the correct angle.
(With this kind of stuff, the pockets will take awhile to get right, especially if you’re newer to the process. It’s pretty common to undersize your pocket slightly and “sneak up” on the final dimension with a few iterations )
I’m looking forward to seeing how this turns out.
I do not have a CAD file for the part. I have a process, detailed here, that I’ll use. I’ll start the pocket small and scale up slightly until it fits.
I think you’re missing the positioning and clamping opportunity with those mounting holes in the blade.
Build a fixture to use those holes and add some support under the blade length. The support probably doesn’t need to follow the the intricate profile of the blade; just support it against the etching bit.
You should look into Sculpey clay, an oven-bake polymer clay. You can find it at any well-stocked craft store. Maybe even the craft section of your local Walmart store.
Long working time and zero shrinkage.
@CrookedWoodTex for the win! I traced the blade and used that tracing to make a rough-ish polyline in CC using this method. I then used “offset vectors” +.25" to create a pocket I knew the blade would fit in. I left the large circle in the blade untouched. This created a HUGE pocket for the blade to fit in with one constant feature, the Trademarked “Spyderco Round Hole”. I did this for both sides of the blade on a single piece of 1/2" starboard. With the pocket carved I placed the knife in the pocket so it would pivot on that single huge hole in the blade. I roughly centered it in the pocket and marked the next largest hole, the one the blade pivots on, and drilled/tapped that. Now the blade has a jig it can fit in and will always be in the same position relative to X/Y zero (front/left) of the jig. I also drilled and tapped 8-32 set screws from underneath to support the blade near the sharp side.
Next step was to locate the blade within the jig. I placed the blade in the jig, set my X/Y zero to the lower left corner of the starboard stock using a 30* bit. I then jogged to the blade tip, and wrote down the coordinates. Moved right .3" and jogged north along the Y until the point of the bit was at the upper edge of the blade, wrote down those coordinates, rinse and repeat every 0.3". Did the same for the lower edge. Now I have known coordinates of the blade relative to the stock’s lower left corner.
Armed with those coordinates I return to CC and loaded the file for the pocket cut. I then make rectangles using the X and Y coordinates I recorded for height and width of said rectangle. I drag the lower left corner of each rectangle the lower left corner of the work space. I then draw another polyline from the tip of the blade coordinates to upper right corner of each rectangle. Now I have an accurate shape of the blade as it is actually located within the jig. Bit of node smoothing, some adobe illustrator wizardry, and I have a jig and template file I can use for repeatability.
I really appreciate everyone that chimes in with help on all my posts. I try to make it a point to go into detail how my problem was solved. If any one has any questions I’m happy to answer.
First engraving: ignore the “N”. That was me just dragging the bit across the blade to see iff it would make a mark. This knife is one of me EDCs, so the blade has some wear on it already.
that’s so obvious.” techniques
