WIP: Designing and building the new Resolute with the help of CNC.

aarongough said:
Hey mate!
Is that for vacuum forming or injection? How does shrinkage affect the part when vacuum forming, I must admit I hadn't even thought of that as an issue, will be fun learning this :)
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The values are very similar. I believe it is a function of the coefficient of thermal expansion and the glass transition temperature of the material and not the process used to process it. It's also not written in stone, shrinking in an injection molded part can be reduced with increased packing pressure and lots of things can affect it with thermoforming too, particularly how long you let it sit on the mold, if it's a male or female mold, textures and details, sheet and mold temperatures etc. so .006 is a rule but it could be +-.003.

The other thing with thermoforming is the Z axis often shrinks more than the X and Y because there is material spring back as well as plastic shrinkage, particularly in an amorphous material like Kydex. This can be affected by how quickly the part cools and which side (tool side or outside) cools fastest.

This makes it sound hopelessly complicated. It's not, you'll get it. Just don't be discouraged when it doesn't work perfect the first time.

Sometimes second op fixtures are cast (bondo etc) from a molded part rather than machined from a file because it's hopeless to get all the weirdness compensated perfectly.

Also, sometimes you want somthing to shrink a little. Kydex sheath makers aren't really compensating for this, they might build up a little thickness on the blade or the scales etc to get the fit they want and I'll bet most of them are not aware their sheaths are a little smaller than their knife, and they probably wouldn't work right if they weren't.

Just remember, it's pretty typical for a 12" dimension on the mold to be about 1/16" shorter on the finished part.
 
Nathan the Machinist said:
The values are very similar. I believe it is a function of the coefficient of thermal expansion and the glass transition temperature of the material and not the process used to process it. It's also not written in stone, shrinking in an injection molded part can be reduced with increased packing pressure and lots of things can affect it with thermoforming too, particularly how long you let it sit on the mold, if it's a male or female mold, textures and details, sheet and mold temperatures etc. so .006 is a rule but it could be +-.003.

The other thing with thermoforming is the Z axis often shrinks more than the X and Y because there is material spring back as well as plastic shrinkage, particularly in an amorphous material like Kydex. This can be affected by how quickly the part cools and which side (tool side or outside) cools fastest.

This makes it sound hopelessly complicated. It's not, you'll get it. Just don't be discouraged when it doesn't work perfect the first time.

Sometimes second op fixtures are cast (bondo etc) from a molded part rather than machined from a file because it's hopeless to get all the weirdness compensated perfectly.

Also, sometimes you want somthing to shrink a little. Kydex sheath makers aren't really compensating for this, they might build up a little thickness on the blade or the scales etc to get the fit they want and I'll bet most of them are not aware their sheaths are a little smaller than their knife, and they probably wouldn't work right if they weren't.

Just remember, it's pretty typical for a 12" dimension on the mold to be about 1/16" shorter on the finished part.
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Thanks Nathan, much appreciated!

I will try to keep that stuff in mind when working on the mold! As you said I think it's unlikely it's going to work the first time, that's fine... Always a learning experience!
 
So yesterday I focused on getting my engraving sorted out:

H2QjYyYl.jpg


This was done with the tip of a Maritool 3/8" diameter 60º chamfer mill that I use in another operation for cutting the window-breaker on the butt of the knife. I originally tried to use a separate tool but the other tool had too wide of a tip and made really awful looking engraving!

On this batch the engraving itself was a pain to do because I had hand finished the blades which meant the thicknesses varied quite a bit. I had to set the Z axis height for each one individually and it took a while!

The next batch will be much more consistent in this regard so I don't think it will be an issue. If it does continue to be an issue then I will switch to using a spring-loaded engraving holder. I'm hoping to avoid that though as the spring loaded holders seem to produce less nice engraving from the photos I've seen.

Pretty happy with how they turned out! Today I'll be working on handle scales!
 
Had a pretty big milestone yesterday! First I machined the first production scales:

HFGKV0Ul.jpg


And then I assembled the first complete Resolute MkIII!

hC7mpXNl.jpg


Very pleased with how it's come out! Fit and finish of the tang to the handle scales is bang on. Very, very close to being the same as if I'd ground them together after glue-up. Consistency of the finish on the edges of the tang is simply way above anything I can do by hand, same with the window-breaker and finger groove details.

Very very pleased that it's come out the way it has!

This knife is actually a 'blem' (plunge line has a mark in it on one side) and will end up being my personal knife. I'm taking tomorrow off to head up to a friend's cottage, will spend the time doing some carving and so on with the new knife, looking forward to it!

On the down-side I'm having some trouble with the driver for the spindle motor in the CNC... Yesterday it kept faulting out, I think it might be on it's last legs unfortunately. It's kind of an expensive part to replace (somewhere around $2-3k) so I'm going to try to get it to limp along a bit further, here's hoping it can make it through the next batch so I actually have money to replace it! It may be getting sensitive to heat in it's old age (it was 85F/30C in the shop yesterday) so I will be doing what I can going forward to keep it running cooler... If I can get it to limp along for a few months that would be ideal, we'll see.
 
Spent the weekend up at a friends cottage, did a bunch of woodcarving while I was there!

t2o2rAsl.jpg


These were carved from dry poplar. very happy with how the knife felt and performed. Spent about 4-5 hours with it in-hand over two days. No hot spots, no blisters. The knife is also still shaving hair nicely.

Very pleased overall!
 
Aaron,

Considering you are doing it all by CNC have you thought about getting rid of the pins and using bolts to secure the scales? You could eliminate glue up altogether and also offer different color scales to swap out.
 
AVigil said:
Aaron,

Considering you are doing it all by CNC have you thought about getting rid of the pins and using bolts to secure the scales? You could eliminate glue up altogether and also offer different color scales to swap out.
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Hey Adam!
Yes, I have gone back and forth about that several times... However I really like the look of the pins (corby bolts). Eliminating the glue-up would be great as long as I don't end up with corrosion/contamination issues inside the handle and so on.

I am planning to try VHB tape for the glue-up, that would be attached to the backside of the G10 stock before machining, then machined to shape with the handle scales. There's a good chance it will turn into a gooey mess around the edges, but it's worth trying!

Corrosion inside the handle really shouldn't be an issue given that the whole thing is nicely machined and Cerakoted, but I will have to do more testing before feel confident relying on that! I treat the glue more as a sealant than anything as the corby bolts are plenty strong...

-A
 
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Hey Aaron, how'd you do the corbies on this one? Did you just grind them off on your KMG, or did you also do them on the mill? On that topic, did you hand finish that first Mk III? Loving this thread btw
 
Corrosion really would not be a problem because you could break down the knife and clean it.
 
NeilJBorja said:
Hey Aaron, how'd you do the corbies on this one? Did you just grind them off on your KMG, or did you also do them on the mill? On that topic, did you hand finish that first Mk III? Loving this thread btw
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Hey Neil!
The corbies were ground flush by hand on the KMG. I don't foresee automating that step as it's a bit hard to hold onto the knife when it's in that nearly finished state...

The knife shown above was hand finished basically to fix some issues that I had caused on the grinder. The next batch will hopefully just be finished on the grinder with no need for hand sanding. The Cerakote is all applied by hand for now, as is the sandblasting, although I would like to build robots to automate both those stages!

-A
 
AVigil said:
Corrosion really would not be a problem because you could break down the knife and clean it.
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I have been considering whether I should do an easier to make and less expensive version of the Resolute (still very much up in the air on that one) and the bolts might fit well on that knife... For the current knife I really want the look of the flush-ground pins... I will definitely be working on that though as the glue-up stage is a big opportunity for screw-ups and I would like to get the whole process humming along as much as possible.
 
Don Nguyen said:
Aaron this is inspiring. I am also a little bit jealous :)
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Hey Don!
Given your engineering schooling I'm very sure you wouldn't have too many problems turning to CNC if you so chose! It is a very different way of doing things, but I really like it because it allows me to focus more on refining the process, rather than on one knife at a time... It's definitely made the process more fun for me!
 
Aaron, do you think that once you have your resolute program built should it be quick to introduce variations in the design, build modified fixtures and run another different model?
Or do you have the feeling it's gonna be starting from scratch for every model?
It is something i wonder, but presume it depends on the software adaptation capabilities, isn't it?
 
stezann said:
Aaron, do you think that once you have your resolute program built should it be quick to introduce variations in the design, build modified fixtures and run another different model?
Or do you have the feeling it's gonna be starting from scratch for every model?
It is something i wonder, but presume it depends on the software adaptation capabilities, isn't it?
Click to expand...

Hey mate!
It kind of depends on the nature of the change... If I wanted to add jimping for instance that would be a pretty quick change (less than a day) because it's just changing the outline of the knife a little.

If I wanted to change something that affected my fixtures (how I hold the blades while machining) like say changing the size/position of the handle pins, or the overall length of the knife, then I would be looking at having to re-make all my fixtures. In that case I'd estimate it's probably about 2 weeks worth of solid work to get everything made, assuming I'd just be making different versions of my current fixture designs...

It's definitely waaaay more up-front work than making them just by hand, but I think it will pay off very quickly once I settle into production. Right now I'm set for the blades themselves and the handle scales, just working on getting the sheaths sorted. Once that's done I'll be assembling and shipping the first batch, then starting on the second!
 
rustyrazor said:
yep... taking words right out of my "cant afford to get a CNC and don't know where to start" mouth
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At some point I really want to make a 'getting started with CNC' video... Likely still more than a few months away unfortunately.
 
Thank you Aaron,
yes the thing i had in mind was if you had to do something "simple" like making i.e. longer fixtures and longer blades, altering just the lenght of the blade, leaving all the other parameters pretty much invariated. I was wondering if the software would easily allow for a command like "insert 1 inch more of X axis in this point" and run the fixture and then the blade programs in just a few hours since your decision.
 
It might be better to ask when you're in full production mode, but how are you finding tooling costs? It didn't bother me at the time, but I feel pretty guilty breaking all those little end mills in machine shop now that I know how much they cost.
 
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