How to mill a guard slot .............

[Karl B. Andersen]

..........or any slot, for that matter.
I offered, in another thread, to post up a little tutorial on how to accurately mill a slot for a guard.
So, I reckon I had better do it.
I may not get it completely done for a day or so, as I have had my middle finger on my left hand in a splint for a month.
Makes typing a challenge.
To facilitate this endeavor, I will copy and paste some posts I've made on a couple other forums over the past few years.
I will first say that I have milled no less than, I don't know, truly I don't, maybe 500 guards this way.
I will say, without hesitation, that you do not need a sophisticated mill to accomplish this.
I bought my grizzly bench-top mill in either '98 or '99.
Then about a year ago I bought a much larger round column mill.
I was taught this procedure by Jerry Rados, who has been making knives longer than many people on this forum have walked the earth.
He taught me on a Bridgeport, but, regardless of the mill, the steps are EXACTLY the same.
All you need is a mill - of ANY kind, a calculator and a dial indicator on a magnetic holder.
I will start out by showing a picture of a guard milled and slid onto a knife with absolutely not one other thing done to either the guard or the knife:

This is right off the mill:

 

[AVigil]

Thanks Karl,

I have subscribed to this thread

 

[Karl B. Andersen]

I have a couple philosophies in my shop.
One is:
"Slower = better. Better = faster."
In other words, take your time doing things right in the first place and it saves time down the road. Every time.
It seems like things are just dragging, going too slow, but in fact, you are saving yourself time later.
Just get that in your head now and it'll save you lots of headaches later.
It's true because then your mistakes a smaller and the corrections are easier and quicker.
I say this because we are truly going to be cutting in this slot just a few thousandths at a time, and it will seem like things are going really slow, but when it comes time to slide the guard on the knife, the fit time is reduced to almost nothing.
And that's a fact.
Spend your time MAKING KNIVES, not correcting things.
Also, I'm posting this because I have seen over the last few years all kinds of off-the-wall methods of slotting a guard, and just as many posts of people breaking all kinds and sizes of end mills.
I'm at the point now, in slotting guards, where if I break 1-2 end mills a YEAR, I could say that would be the average.
It's very rare.
I have often seen where people drill holes with drill bits creating webs to then be milled out, when, in fact, carbide end mills do NOT! like what are called "interrupted cuts". The end mill needs to be in CONTACT with the working surface at all times, not coming into and going out of material.
So, we're going to START the process with an 1/8" end mill, and we're going to completely cut the entire slot with the same tooling.
Stay tuned.

 

[Eric Kidwell]

Thanks for doing this Karl. Subscribed!

 

[mdubs]

I have a couple philosophies in my shop.
One is:
"Slower = better. Better = faster."
In other words, take your time doing things right in the first place and it saves time down the road. Every time.
It seems like things are just dragging, going too slow, but in fact, you are saving yourself time later.
Just get that in your head now and it'll save you lots of headaches later.

My old race instructor used to say "slow is smooth, smooth is fast" Loved the simplicity and truth

 

[Karl B. Andersen]

I have to say this, as this is just as important as the slot itself.
If we are going to be slotting a guard with a mill, we have to admit that both sides are going to be equal, parallel and symmetrical.
This means that the knife we're fitting the guard TO! needs to have the sides of the ricasso even, equal, parallel, symmetrical, etc.
Otherwise, things ain't a gonna work out.
So, get your knife flat and trued up first.
It can be done.
I now have a surface grinder, which makes things easier, but I didn't for the first 13 years of doing this!
Do whatever you gotta do. Get a granite surface plate. You need one any way. Just get one if you don't have one.
Use your dial caliper and a magic marker, sand paper and your surface plate or whatever, but get that ricasso to within .001" or less in dimension from side to side, where the guard is going to fit.
And we'll use a normal type knife with guard shoulders either filed in with a file guide or milled in with the mill.
But the guard shoulders also need to be true and straight.
Then we can proceed.
Preparing the knife itself can be an entirely separate thread, but here, we're just dealing with how to mill the slot.

 

[Karl B. Andersen]

For the benefit of this thread, we're going to suggest that our knife ricasso is .260" thick.

 

[Karl B. Andersen]

The first thing I do is get my guard material squared up on all four sides so it sits in the mill vice squarely.
I will be using an 1/8" end mill.
If we are milling a 1/4" guard, then no problem, we can mill it in one placement in the vise.
But if we're milling a thicker 1/2" piece, we'll need to mill 1/2 way through EACH SIDE!! So it's important that when we flip the material to mill from the other side, that it's sitting in exactly the same orientation. So, first thing is to get the material squared up.
You obviously have a mill, so get that done - first.

I don't really care how you do it, but get it cleaned up.
Either on a surface plate or on a surface grinder.

I will then take the FLAT and SQUARE material to the granite plate and lightly clean the surface at an angle, from corner to corner, so as to easily expose any scribe marks.

When you scribe a center line, it makes the line easy to see.

 

[Karl B. Andersen]

I do not use any type of stops on the vise to relocate the guard material if I remove it. I have not found that necessary.
As well, many of the guards I mill are thicker than can be milled from one side, so when we flip the guard over, any stops would be worthless. So, I've adapted to do the job without them.
What I have done, which can be seen here on the vise jaw, is to make a scratch as a reference point.
When I scribe the top and bottom of my slot location, I make sure to also scribe it on the side of the guard material.
This way, I just make sure it's lined up with the scratch mark on the vise jaw, and I'm always in the same spot within about 001".
You can get amazingly close each time if you move the material and have to replace it.
(see reference scratch on top of vise jaw)

 

[Karl B. Andersen]

So, we located the center line, as seen above.
Now locate the top and bottom marks by laying the knife on the guard.

Here we have our marks:

Now, I just want to find the center of the scribe line with the end mill:
(Notice how I have the slot height line lined up with the mark on the vise jaw)

Now, this is the important part!!
With the end mill centered on the center line of the guard material, lock the Y axis - in/out - and place your dial indicator and the magnetic base on the back side of the mill table and set the dial on ZERO.

Now find that top line with the end mill. This is a picture from an entirely different knife with a 1/2" guard, but shows the process quite well:

 

[Karl B. Andersen]

Now, at this point right here, when you have located both center and one end of the slot, you need to place stops on your X axis - left/right - to stop you travel when you reach the ends of your slot.
On my newer mill, I have locatable stops like this:

My smaller bench top mill did not have these, so I just used some C clamps and a small piece of steel on the bottom to bump up against mill when I reach the end of the slot.

Now, with a stop set in place for the first end, start creating your slot!
Just use the lever and drop the center cutting end mill onto the center line.
Move the table about 1/3 the diameter of the end mill and lower again.
As the end mill reaches the depth of the previous cut, you can feel it hit the bottom.
Then, just give it a tad more down pressure and cut another "step".

Repeat.
Repeat.
Repeat.

 

[Karl B. Andersen]

When you reach the other end of your new slot, place another stop in whatever fashion you have available, to stop the X axis travel at this end of the slot.
Now, you do not have to even consider your left/right travel for the remainder of the project.
Now, go back in the other direction and chew out those "steps".
When going backwards, you are either going all the way through, or all the way to your depth stop of the thicker material.

This is important.
I slightly eluded to this earlier, but if you are milling 1/2" material, you will only be able to go 1/2 way through in the first pass, so you will need to have set a depth of cut with whatever option your mill has.
If thinner material, you'll be going all the way through.

 

[Karl B. Andersen]

Here, in a piece of 1/4" material, we have a complete slot.

Now, I see that on this one I have marked " 68.5 ".
Here's the secret to that!

My 1/8" end mills measure .123".
I know that that knife ricasso area there was .260." (Forget that previously mentioned .250")
If I cut a slot in a piece of material .123" and NEED a slot .260", then I need to remove .137" MORE. Right?
Right.
But I need to remove 1/2 of that on either side of the center line, or .0685" in one direction, and .0685" in the other direction.
So, I lower the end mill into the slot.

Be sure to LOCK your downward travel of your quill to keep it as solid as possible.

Loosen the Y axis so it can go in and out.
Go all the way to one end until I hit one of the X axis stops and move the table either in or out, depending on what end I start at so I'm always cutting INTO the side, move the table out about 2 1/2 thousandths.
Crank to the other end.
Move the table either in or out the OTHER way and take out 2 1/2 thousandths off the other side of the slot until I hit the X axis stop going the other direction.
Then come out 5 thousandths.
Then 7 1/2 thousandths.
Then 10. Then 12 1/2.
Then 15.
Then 17 1/2.
etc. Back and forth until I hit .685 on either side of ZERO.

Here I am having gone all the way to .685 from zero:

 

[Daniel Fairly Knives]

Karl,

Thanks for doing this!

You do a great job of making everything easy to understand. Awesome photos too!

 

[Karl B. Andersen]

Of course, what we have done here is in material only 1/4 inch thick.
In 1/2" material, we can only go 1/2 way through with an 1/8 inch end mill.

When the first half is done, you'll need to FLIP the guard over - from END TO END - so as to keep the same side of the guard always to the front!
This ensures the center line is always in the same orientation to the quill.
Line up the hash mark on the vise jaw and your scribe mark on the side of the guard material and your X axis travel remains in the place and you don't have to change your stops.

 

[Karl B. Andersen]

Here is the completed slot.
Pretty, eh?

 

[Karl B. Andersen]

I realize we've been working with two different scenarios here with two different thicknesses of guards, but I hope you can catch on.
Here is what the 1/2" thick guard looks like milled half way through:

The finished guard:

And walked over and slid onto the knife:

 

[William Schrade]

Thanks Karl,

Now I need to buy a mill.

 

[Karl B. Andersen]

Here is the 1/4 inch slid onto the knife right off the mill:

You can see that the guard shoulders have a 1/8" radius.
I mill my guard shoulders, and do NOT back-cut the sides of my ricassos.
I leave them full thickness.
Regardless, the guard slot needs to be filed to fit this radius.
I lock the guard material in a rotatable vise and file the end of the slot to fit the radius:

This is what it looks like from the back side:

Slide on a piece of leather:

And tap the guard with a flattened pipe nipple:

If the guard is too tight, and I'm not dealing with already etched damascus, it will leave slight scratch marks on the ricasso:

They're a little difficult to see but they're the dark marks right behind the shoulders:

Do NOT!!! do anything to the guard slot!!
Take the knife to the lapping plate and gently sand the marks off!

marks are gone:

Re-try the fit:

Almost!

Little tap with the pipe nipple:

 

[SteelSlaver]

Thanks for showing a simple way to do this. Very efficient