Why *not* a six inch serrated tomato knife?

[Cushing H.]

Ok - how do folks like this idea for a profile. the spine is very slightly curved upwards, with the edge following the curve to maintain the blade width. The curve is barely perceptible, but to my eye it seems to break up the "clunkiness" of the first sketch....

 

[CallumRD1]

I have been aware of the o-ring around the contact wheel idea - but a couple things about it have concerned me. One, is the difficulty of getting the o-rings really accurately spaced, the second is that is strikes me that o-rings under the belt will produce pretty "washed-out" boundaries around the serrations.

It turns out that I *do* have a mini-mill, and right now am leaning towards using chamfer end mills to create the serrations. If you think about the geometry, you do not need to do this holding the blade vertically - you can just as easily clamp the blade flat on the table and come in from the side to create the serrations. With the indexing (or dro) on the mill, one should be able to get the serrations pretty consistent....

The problem that I see is your chamfer mill is likely 90˚ included angle or 45˚ per side. That's a pretty steep bevel for a knife (typically in the 20-35˚ range) and far higher than I'd want. The next option would be to tilt the knife on a fixture plate at say 25˚ so the effective angle of the cutter is 20˚. You're also going to have a lot of trouble if you do this after grinding the rough primary bevel because the steel will be too thin and lack rigidity. It will deflect away from the cutter and leave a poor finish at best. You'll need some careful fixturing to get enough rigidity to cut the serrations well.

 

[Cushing H.]

The problem that I see is your chamfer mill is likely 90˚ included angle or 45˚ per side. That's a pretty steep bevel for a knife (typically in the 20-35˚ range) and far higher than I'd want. The next option would be to tilt the knife on a fixture plate at say 25˚ so the effective angle of the cutter is 20˚. You're also going to have a lot of trouble if you do this after grinding the rough primary bevel because the steel will be too thin and lack rigidity. It will deflect away from the cutter and leave a poor finish at best. You'll need some careful fixturing to get enough rigidity to cut the serrations

Thanks for the thoughts. I have several serrated knives here - so I took a look at all of them (one bread knife, one sold as a tomato knife, and another two 2.5" "paring knife size), and all of them seemed to have serrations whose troughs seemed to be at an angle of about 45 degrees - so the chamfer mill seemed to be just about right. But then again, I was just eyeballing it. before I cut anything on a profiled blade, I should try out techniques on annealed scraps. an angled fixture plate is also something that occurred to me. Heck - if you get a steep enough angle, one could just use the side of an ordinary end mill.....

As far as when to grind - first I was thinking of doing it before hardening - but I think the concern there is erosion of that find edge due to decarb. But one approach there might be to do it pre-ht, then touch it up again after HT with that chamfer mill, using the existing notches as a guide. If done after (with a carbide mill), I would definitely do the milling prior to grinding the bevels (not sure how much risk there is there of catching a "tooth" on the belt and sending the blade flying..... probably much more likely to just grind off the tooth before you even know what happened?????

 

[Stelth]

You can't talk about tomato knives without mentioning the most famous ones.

Most people have seen them but may not recognize that they are tomato knives.

 

[Cushing H.]

Ive been struggling with how to clamp a blade for machining serrations at 45 degrees (or some other angle). I just cant think of any way to securely clamp the flat blade, on the long axis, at a significant enough angle (using any combination of angle blocks, 123 blocks, and or my vise) to machine those serrations.

The *only* thing i can come up with is an adjustable angle plate ... which i think will easily do the trick, but would likely be a single-purpose investment. Any one here have any thoughts on how i can do that clamping without using said angle plate?

 

[Richard338]

I file mine in.
I clamp the blade to a narrow board along the edge of a bench giving it firm support. Then by carefully controlling the angle of the file and guiding the spacing, I can get them precisely to my satisfaction. I file the blank before heat treat and before grinding the bevels. I go a little past halfway. Then later, grinding the bevel from other side exposes the serration.

 

[Hubert S.]

It is difficult for me to envision how you intend to machine the serrations with a chamfer mill. I assume you want to make scalloped serrations about 1/4" in size, not the small serrations (~1/16") you might see on a cheap steak knife set. The scallops could be made with a file at a shallow angle, filing from both sides to get a symmetric scallop. To get this type of serration on a milling machine, couldn't you just use a straight end mill and tilt your knife to ninety degrees minus the shallow angle you would have used when filing?

In either case, you have to hold the blade at an angle. If your vise opens far enough, you could just clamp a fixture plate at the correct angle and machine the serrations in the x-directions and space them using the y-axis. For a six inch knife, there should be enough travel to do this even on a mini mill. The fixture plate does not have to be anything fancy, just some scrap aluminum with a few 1/4-20 holes for securing the blade. If your vise does not open far enough, you could clamp a 1-2-3 block in the vise at the desired angle and bolt your fixture plate to it, but you'd probably have to cut away some material so the plate does not interfere with the vise. My 1-2-3 blocks have 3/8-16 holes in them, so it's easy to bolt stuff to them. Another option would be to build a mini pallet as illustrated in the video linked below. This would allow you to mill in the serrations in the y-direction and use the x-axis to space them out. The video is pretty long and I did not watch the whole thing, but watch around five minutes in to see how the mini pallet could be used for your application. Something like that could be useful for many other operations and would not take too long to make.

 

[CallumRD1]

It is difficult for me to envision how you intend to machine the serrations with a chamfer mill. I assume you want to make scalloped serrations about 1/4" in size, not the small serrations (~1/16") you might see on a cheap steak knife set. The scallops could be made with a file at a shallow angle, filing from both sides to get a symmetric scallop. To get this type of serration on a milling machine, couldn't you just use a straight end mill and tilt your knife to ninety degrees minus the shallow angle you would have used when filing?

In either case, you have to hold the blade at an angle. If your vise opens far enough, you could just clamp a fixture plate at the correct angle and machine the serrations in the x-directions and space them using the y-axis. For a six inch knife, there should be enough travel to do this even on a mini mill. The fixture plate does not have to be anything fancy, just some scrap aluminum with a few 1/4-20 holes for securing the blade. If your vise does not open far enough, you could clamp a 1-2-3 block in the vise at the desired angle and bolt your fixture plate to it, but you'd probably have to cut away some material so the plate does not interfere with the vise. My 1-2-3 blocks have 3/8-16 holes in them, so it's easy to bolt stuff to them. Another option would be to build a mini pallet as illustrated in the video linked below. This would allow you to mill in the serrations in the y-direction and use the x-axis to space them out. The video is pretty long and I did not watch the whole thing, but watch around five minutes in to see how the mini pallet could be used for your application. Something like that could be useful for many other operations and would not take too long to make.

I haven't watched the video, but the fixture plate in the thumbnail is exactly what I was implying when I suggested milling on a fixture plate.

 

[Cushing H.]

It is difficult for me to envision how you intend to machine the serrations with a chamfer mill. I assume you want to make scalloped serrations about 1/4" in size, not the small serrations (~1/16") you might see on a cheap steak knife set. The scallops could be made with a file at a shallow angle, filing from both sides to get a symmetric scallop. To get this type of serration on a milling machine, couldn't you just use a straight end mill and tilt your knife to ninety degrees minus the shallow angle you would have used when filing?

In either case, you have to hold the blade at an angle. If your vise opens far enough, you could just clamp a fixture plate at the correct angle and machine the serrations in the x-directions and space them using the y-axis. For a six inch knife, there should be enough travel to do this even on a mini mill. The fixture plate does not have to be anything fancy, just some scrap aluminum with a few 1/4-20 holes for securing the blade. If your vise does not open far enough, you could clamp a 1-2-3 block in the vise at the desired angle and bolt your fixture plate to it, but you'd probably have to cut away some material so the plate does not interfere with the vise. My 1-2-3 blocks have 3/8-16 holes in them, so it's easy to bolt stuff to them. Another option would be to build a mini pallet as illustrated in the video linked below. This would allow you to mill in the serrations in the y-direction and use the x-axis to space them out. The video is pretty long and I did not watch the whole thing, but watch around five minutes in to see how the mini pallet could be used for your application. Something like that could be useful for many other operations and would not take too long to make.

The chamfer mill idea was assuming that the blade is flat (parallel to the table), and the chamfer bit is then set to a known height, and the scallop then milled by translating the table in the y direction into the blade side a set amount. Disadvantage of this is that the radius of the cut will then vary by distance from the edge (the radius being smaller towards the edge - the idea is that the blade will be single bevel).

I would prefer your idea - holding the blade at an angle, then going in from the side using an endmill. Question: I thought of what you are talking about .... but how on earth would you securely clamp either a 123 block, or a fixture plate in the vise - with the thing angled, you would be clamping on the edge of the plate (block), not on a flat - and that seems pretty insecure to me.... ???

 

[Cushing H.]

I haven't watched the video, but the fixture plate in the thumbnail is exactly what I was implying when I suggested milling on a fixture plate.

So .... his fixture is round stock with a flat plate screwed into a slot milled into the round stock? That would work. Dont really want to make it, but if I needed to. Also, dont have that stock - would need to see if I could obtain small enough quantities so that I didnt have a bunch left over....

 

[Cushing H.]

I file mine in.
I clamp the blade to a narrow board along the edge of a bench giving it firm support. Then by carefully controlling the angle of the file and guiding the spacing, I can get them precisely to my satisfaction. I file the blank before heat treat and before grinding the bevels. I go a little past halfway. Then later, grinding the bevel from other side exposes the serration.

I'm afraid if I were to try to do that, it would just end up looking sloppy. Everytime I try to do something precise like that by hand, I just can not keep it consistent :-(

 

[fitzo]

One of those simple filing jigs based off the same idea as a lansky that I've seen people post here lately for filing a dagger might give the angle accuracy one needs to do it manually with a chainsaw file. There are 3/8" chain saw files (aka round parallel files) that would cut serrations that would fit a large ceramic rod wonderfully. I use the rod to keep my Richmond Artifex bread knife sharp and it cuts tomatoes superbly.

 

[Hubert S.]

Question: I thought of what you are talking about .... but how on earth would you securely clamp either a 123 block, or a fixture plate in the vise - with the thing angled, you would be clamping on the edge of the plate (block), not on a flat - and that seems pretty insecure to me.... ???

You would clamp two 1x2 faces and rotate to the desired angle, then bolt the fixture plate to the 2x3 face. If it's still unclear tomorrow, I can mock it up in the mill vise and send a picture.

 

[Hubert S.]

So .... his fixture is round stock with a flat plate screwed into a slot milled into the round stock? That would work. Dont really want to make it, but if I needed to. Also, dont have that stock - would need to see if I could obtain small enough quantities so that I didnt have a bunch left over....

If your milling machine has enough power to tap 1/4-20, making a fixture plate is really not that bad. I just made one last weekend to hold a workpiece on the rotary table, and drilling and tapping thirty holes did not take long at all.

 

[Daniel Carraher]

Clamp a 2” block 5.5” from the edge of blade. Use a file and keep it in contact with the 2” tall block. Would be way way faster than building a fixture for a one off knife

 

[Richard338]

Clamp a 2” block 5.5” from the edge of blade. Use a file and keep it in contact with the 2” tall block. Would be way way faster than building a fixture for a one off knife

This sounds simple and effective. The only challenge is getting all the depths even.
I might try this tomorrow...

 

[Daniel Carraher]

This sounds simple and effective. The only challenge is getting all the depths even.
I might try this tomorrow...

Just file to a center line. Depth and angle should be pretty simple to keep consistent across the board. In his case on a single bevel design would be even easier I think.

 

[Pinoy Knife]

if you p.m me we could talk a

I'm afraid if I were to try to do that, it would just end up looking sloppy.

if you contact me via p.m we could talk and i could tell you how to do it .. or you can try to figure it all out for yourself.. your choice

 

[Richard338]

Just file to a center line. Depth and angle should be pretty simple to keep consistent across the board. In his case on a single bevel design would be even easier I think.

Yes, I've been happy with the result freehand, but with the guide block I hope to be near perfect.

 

[Cushing H.]

You would clamp two 1x2 faces and rotate to the desired angle, then bolt the fixture plate to the 2x3 face. If it's still unclear tomorrow, I can mock it up in the mill vise and send a picture.

I maybe understand, but really not sure. Could you pls post a photo at your convenience?