Hey everyone, Aaron here from Gough Custom!
At the end of 2020 I wanted to really push hard to get caught up on all of my back orders,
and part of my process for doing that was to get both of my CNC machines up and running machining
blade bevels! But unfortunately you can't just stick a block of steel into a CNC machine and have
a knife come out, you need special fixtures and so on to hang onto the blade while you machine it.
Especially for doing the bevels because you have very little material to hang on
to around the edges of the blade, while you're still trying to get full access to the bevel.
So I needed to make new fixtures in order to do this, and in this video I'm going to show
you how I went from this, which is one of my old prototype fixtures, to this guy which is the new
generation of my blade beveling fixture! The first thing that I need to do is to update my
3D model and to incorporate all the design improvements that I've thought of. I want
to move the pitbull clamps and also add an extra pitbull clamp. The reason for this is that having
just two clamps was allowing the blade to chatter, to move, when it was being cut. Having three
should improve the clamping pressure and stop that resonance. Then I want to move the bolt hole
locations that allow me to bolt down the blade blanks. Moving these just a little bit closer
to the blanks will allow me to bolt them down without making any special washers or adapters.
The next step is to set up all of the tools for the machining operations.
I have to insert the tools in the individual tool holders,
after cleaning each tool holder to make sure that there are no chips or anything in the taper.
With each of the tools set up physically, now I have to set them up digitally. I have to measure
each of the tools, the way they stick out from the holder and so on, and then set them up in
the tool library of my CAM program so I can use them for creating the toolpaths. To create the
toolpaths you have to go through and pick out each individual feature in the CAD drawing and then
choose what kind of operation you'd like to apply to them. There's lots of parameters to change,
but once all the parameters are entered the CAM program automatically creates the final toolpath.
Once the toolpaths are generated I then go through and simulate each of them to make sure
that the tool holder or the tool shank doesn't run into the material in some unexpected way.
With all of the tools set up and all the toolpaths generated it's time to start loading
the tools into the machine and measuring each of them. I have to measure the length of each tool
individually so that the machine knows where the tips of them are, and can guide them accurately.
As you can see there's a fair bit of work involved in setting up the CNC machine to make a part,
this is the reason why making many parts is often more economical than just making one or two.
With all the tooling set up now I have to set up the workpiece! In this case I'm using a block
of mild steel to make the fixture. The vise is carefully cleaned and then parallels are added
to hold the block of steel up off the base of the vise. Now I need to store the exact location
of the block of steel in the CNC machine so it knows where to cut. To do this I'm using
a "Haimer 3D Taster" which is a type of dial indicator that works in all three dimensions.
First I measure the top of the parallel, that's where the bottom of the block is going to sit,
then I measure the left edge of the block and the back edge of the block. This creates our
fixture offset, or our origin point, that all of the toolpaths are measured from.
With all of that laborious setup out of the way now I'm ready for the fun part,
cutting some steel! To begin with I'm using a half inch diameter roughing endmill with one
inch length of cut. Ideally you should always use the shortest tool possible, and obviously I could
shorten this tool up quite a lot, but this is what I had on hand so I just made do. Most of the top
surfaces of the fixture were then finished with a half inch two flute finishing endmill. Ideally a
shorter four flute endmill would be better, this would allow me to run faster and also to achieve
better finishes, but in this case I actually needed a square corner tool which is relatively
unusual for me, so I had to use one of the only endmills that I had on hand with square corners.
The square corners are needed on the tool so I can get right
into the sharp corner on this part of the fixture!
Next up is a little stubby quarter inch diameter four flute endmill.
I'm using this to machine the pockets that will hold the pitbull clamps.
Whenever I'm machining fixtures, or one offs, I tend to run fairly conservatively.
There's nothing worse than breaking a tool! If these were production parts then I would
be running this much more aggressively... Now I need to drill the holes for the 1/4-20
threads that I'll put in a bit later. These will allow me to bolt down the knife blades!
Have you ever wondered what the quickest and easiest way to spend 20 bucks is? There you go!
Small delicate tools like this are really intolerant of getting your feeds and
speeds wrong... Clearly in this case I was feeding a little bit too aggressively, so
time for a new tool and a second attempt! Before I come in for the second attempt though
I need to make sure there's no carbide chunks left at the bottom of that hole,
otherwise I'm just going to break the new endmill straight away.
These two little holes are the primary locating feature that will make sure the blades are in
exactly the right place. Because of this I need to make sure that their size and location are
very accurate. To measure the size I'm using plug gauges. Each gauge is a little precision ground
rod of an exact size, and if it fits into the hole then the hole is that big or larger. From
testing with the plug gauges I can see that the holes are 124 thousandths, they need to be about
125 thousandths so I'm going to come in and make a second pass to enlarge them just a tiny bit. Now I
can test the holes with the "go/no-go" gauge that I use for my handle pin holes. The green side fits
and the red side doesn't which means that we're in between 125, and 125 and a half which is perfect!
The final machining step is to drill the holes that
I'll then go on to thread for the pitbull clamps.
Now it's time for the dangerous bit, tapping all of these holes! If you break a tap off in
a part like this it is very hard to get it back out... To make sure I don't have any problems
I'm just using a little bit of molybdenum grease as lube and I'm taking it real easy!
Unfortunately I didn't have a nice spiral point tap on hand for these 10-32 holes
that I have to do for the pitbull clamps, so I had to use an old-fashioned hand tap instead.
These are slow to say the least!
A quick clean of all the threaded holes and then it's time for a test fit up!
Things are looking good so it's on to the next stage: making it pretty!
What good is a fixture if you don't make it pretty?? I want to quickly sandblast this to
give it a nice matte finish, but I can't risk getting any grease at all in my sandblasting
cabinet, so I ultrasonically clean the whole fixture first, then all of the bolt holes and
pin holes are masked off by simply screwing bolts into them and then we're ready to go!
Sandblasting is one of those things where it's a lot of fun to just do it on one or two things,
and really not fun to do it on like 50.
It does produce an amazing finish though!
Now I need to shorten a couple of dowel pins to perfectly fit in the locating holes in the
fixture. I do this using the "janky lathe" technique on my belt grinder. It actually
works very well! I decided that I would use cold blue to make the fixture black,
but unfortunately my SD card died, and so I actually can't show you that process.. Oh well!
Here it is after cold blueing and it looks great! I bet you wish I could show
you how I did that process eh! So now I'll go through and assemble the rest of the fixture,
install all the pitbulls, install the pins and then we're just about ready to put it to work!
With the fixture itself completed, now I have to go through and design the toolpaths for actually
machining the blades using the fixture! Because my CNC machines are not quite as accurate and
fast as a new machine I do have some tricks that I use in order to make the machines perform better.
One of those tricks is the use of these oversized blade models that trick the machine into changing
directions when it's not actually in contact with the real blade. This helps reduce gouging
and so on at the edges of the toolpath. With the toolpaths generated I can remount the fixture in
the vise and then get down to the real business of the day, which is machining some blades!
This blade is fully hardened A2 tool steel, and even though it's extremely hard at about 63
Rockwell C the machine and this tool combination has no problem at all cutting it. It's taken me a
while to work out the hard-milling process to this level, but now you can hear that it's so
quiet and smooth that you can't even hear the cutting over the air-blast, it's pretty amazing!!
With the roughing operation complete the next step is a semi-finishing operation.
This runs at 90 degrees to the previous operation and leaves
just a few thousandths of an inch of material for final finishing.
My first step with the finishing tool was actually to take a light surface pass over the ricasso
area. This makes sure that the relationship between the ricasso and the plunge line is
perfect on every knife! Unfortunately it became obvious really quickly that I'd screwed something,
up the finishing tool wasn't actually touching the blade bevel so it looks like I
accidentally removed too much material with the roughing pass.. Time to try again!
With all the little bugs and oversights worked out on some scrap pieces
I was finally ready to start machining actual blades using the new fixture!
I won't show you everything again, but I will show you some of the finishing
toolpath and then the final results. I'm really proud of my hard-milling
process these days and really pleased with the results that I get from it!
It's taken a lot of work to get it to this point but it's really been worth it!
As you can see the surface finish that you can get when hard-milling is just
vastly better than what you can do when you're machining annealed steel.
The final step in hard milling for this blade is to come in with a chamfer mill and engrave my
logo. The machining process then starts over again with the blade on the other side of the fixture.
Here you can see the final result ready for me to start hand finishing.
It's not perfect but it's really, really, good especially considering that my CNC machines
are more than 25 years old! Clearly I'm very pleased with it at least!
As I said I'm really pleased with how my blade bevels are coming out these days.
Getting the CNC machining process ironed out to this level has been
quite a journey, but it's been a lot of fun having to work all this stuff out! I really hope you all
enjoyed the video, and if you liked the video and would like to see more please make sure that you
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I'll see you guys soon!