Hey everyone, Aaron here from Gough Custom! Today I really want to take you through the process of
trying to fix an issue that's been bugging me for a while, and that is the fit between
my handles and the tang of my knives. With this particular knife I can rub my finger over here,
and there's just a tiny little step. It's not offensive in any way but I can feel it,
and I really want to get rid of that step. I want these to be exactly the same size,
like they've been made as one piece. So I think I've worked out what the problem is,
and today I'm going to try and take you through the process of fixing it!
So here you can see the fixture that I use to machine all the components for my knives,
for the Resolute, this station here is the one where I machine the outside profile of
the blades. An end mill comes in from the side and cuts the parts out. The problem is that I think
that these pins are actually very slightly in the wrong locations. I made this fixture quite a long
time ago, when I was less experienced, and because of that I actually just drilled these holes with a
solid caride drill. And at the time I thought that that would be more than accurate enough,
but my more recent experiences taught me that any kind of drilling operation
is pretty much always going to be slightly off the position that you hope it's going to be.
So what I'm going to do is I'm going to pull these pins out, I'm going to weld these holes shut,
and then helically bore, with an endmill, these holes to exactly the right size and position
and that will make sure that when these get placed on the fixture
they're in exactly the right position to within like a ten thousandth of an inch.
I don't particularly want to have to remove the fixture from the machine in order to work on it,
so I'm just gonna protect it with some stainless steel foil, and also some anti-spatter spray.
Next I tried a couple of quick ways of removing these dowel pins from the fixture.
I was really hoping I'd just be able to get them out with vice grips or something, but it seems
like I did too good a job of putting them in in the first place! With the easy options not working
it's time to bring out the big guns, and that requires some welding! Note that I'm putting the
ground clamp on the fixture itself, as close as I can to the place where I'm going to be welding.
This is to make sure that no current goes through the machine ground via the bearings or any of the
more important bits in the machine. So what I'm going to do now is actually tack the ends of some
socket head cap screws to the top of the dowel pin. This lets me use the socket head cap screw
as a convenient handle for a really amazing little device called a slide hammer. The slide
hammer allows me to produce a ton of force to yank these dowel pins right out of the fixture!
Hey that worked beautifully!
Here you can see one of the socket head cap screws with the dowel pin tack welded to it...
Now it's time to weld the dowel holes shut! Of course I immediately stick my fat head in
front of the camera, but that's fine because now you guys can't judge my welding skills!
The welder I'm running is this little Millermatic 211. Having a welder in the shop is one of those
things where like I personally don't use it very often, but when you need it there is no
substitute! Now that the initial welds are done I need to come in with an endmill and actually
cut the top of the welds off so that I have a flat surface again. It's immediately obvious
that I wasn't able to fully fill the dowel holes unfortunately, but this isn't really unexpected.
There are two things that are working against me here. One is that the air that gets trapped
in the dowel hole actually expands as it heats up and that helps push the molten weld material out.
Number two is that the arc wants to go to the top of the hole, not the bottom, so filling a
blind hole like this is kind of tricky. If you guys know any tricks to do this well let me know.
I ended up just giving it a second shot, running the weld a bit hotter
and also trying to make sure that I was angling the MIG gun straight down, rather
than at an angle, to try and put as much heat and weld material down into the hole as I could.
This time I don't see any voids at all which is fantastic! So with
a final skin pass over the face of the entire fixture I'm ready to go!
The next step is to bore the holes for the locating pins.
To do this I'm using a tiny 3/32 inch endmill and I'm helically boring the holes.
Helically boring the holes, rather than drilling them, allows me to precisely adjust the size
in tiny increments by starting small and then enlarging the hole step by step,
and it also helps ensure that the holes are exactly in the right location.
With the initial holes bored I can now check the actual size of them using plug gages.
Plug gages are tiny rods of steel, ground to a very precise size.
If the plug gauge fits in the hole then the hole is either that size or larger.
Now that I know the exact size of the current holes,
I can enlarge them just the right amount to fit the pins that I'm going to use!
Perfect! For the locating pins themselves I'm actually going to cut small sections
off a gage pin. This is because gauge pins are very hard compared to standard dowel pins, and
they're also much tighter in tolerance. This will allow me to get the most perfect fit possible.
To get the locating pins to the exact length that I need, and also to put a nice chamfer on
the corners, I put them in a cordless drill and then grind them on my belt grinder.
Here you can see the finished pins with my finger for scale. They are
only 125 thousandths in diameter, and 350 thousandths of an inch long.
I then quickly test fit a couple of the pins in the fixture... They're perfect!
The finished pins are then permanently assembled
into the fixture using a tiny drop of superglue to hold them in place.
I then tried to quickly test fit one of my blades onto the fixture, and it wouldn't
fit at all... This is because when the pins, and the holes, are really tight tolerance and really
close in size to each other, if there's any variation in the position of the holes at all
then the pins won't fit. A common solution to this problem is to make one of the pins into what's
called a "diamond pin". This is a special type of pin that only has contact on two of its faces
rather than around its entire periphery. Diamond pins are used in a pair with a round pin.
The round pin locates the part in x and y, and the diamond pin locates the part rotationally.
This fully constrains the part without over constraining it and making it difficult to fit.
To make the pins into diamond pins I actually just machined them in place using my tiny 3/32
endmill. This worked really well! Previously I have made the diamond pins by grinding them by
hand on the grinder, but this is a much more accurate and much easier way of doing it.
After machining the pins I used a fine diamond stone to take the burrs off the corners.
It's really cool seeing such an intricate little detail, on such a small scale!
After doing this the blades fit on amazingly well!
They're easy to get on and off, but there is absolutely zero slop in that fit.
Now I need to go through the whole process of machining a
blade blank in order to test the final result!
In order to get the maximum benefit out of the newly accurate fixtures,
I need to make sure that the holes in the blade itself are also held to a very tight tolerance.
Doing this by helically boring with an endmill will work, but it's really fussy to keep the hole
size right because every time you have to change tools you have to dial the hole size in again.
So instead I'm going to use a small tool called a reamer which is specifically designed
for really accurately making a hole a certain diameter.
After reaming the hole size is checked with a pair of plug gauges called a "go no-go gauge". The go
side is 125 thousandths, and the no-go side is 125 and a half thousandths. The go fits and the
no-go doesn't which means we're right in between those two sizes, which is perfect! With that
sorted out I'm ready to move on to the next step which is cutting out the profile of the blade.
First the majority of the material is removed with a roughing tool. This is a tool that's already
been previously used for my finishing step, and I don't really care if it's a little bit worn.
Then I come in with a fresh tool and do a finishing cut.
This ensures that the final surface is as smooth and as accurate as possible.
All the parts are then moved one position right on the fixture and the process is repeated again
on the edge side of the knife. After all the machining is done I get this beautiful final
result. I can then check the exact size of the blade blank using a micrometer.
There's only one dimension that's easy to measure which is from the tip of the finger
guard to the back of the blade. In this case I'm only 0.0003 of an inch off the exact dimension.
So I have my finished test blade here with a pair of test handle scales, and it is beautiful!
Now obviously there are tons and tons of improvements like this that I've done over the
years, and I haven't really gotten to share them with you guys because I just haven't had time...
So hopefully going forward I'll get to show some more of them as I work on them and hopefully
it's something you guys enjoy seeing! I love chasing down improvements like this
it's a lot of work but it's also a lot of fun, and it helps meet my goal of making every knife
better than the last which, is something that I think is really really important. So
hopefully you guys enjoyed the video and I will see you again soon!
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