Curved plunge

[Richard338]

Who cares

 

[Natlek]

Who cares

Yet another interesting project Natlek - looking forward to seeing the finished knives

I hope that I will grind radius on plunges like on right side of picture .Seems that on one on left plunge are not symmetrical , like I was done that
Thanks Mike

This is 52100 2.5mm thick blank , hardened .The jukebox/disc is outside and it's getting dark, so I haven't finished one side .I need to change little angle and make several pass to finish that side .I think the disc will last until I finish both sides for sure . I have grind bevels on quite a few kitchen knives on my big disk sanders , I forgot how much better finish they leave on steel compared to belt grinder .
Grit on disk is 60 AO ........................

Nice curved plunge

It looks silly but it works

Now I have million dollar question for you guys ..
Why in the name of God we use ceramic belts on simple carbon steel like 52100 , 1095 , 80CRV2 , 5160 ...etc WHY not AO belts ?????

 

[Backyard]

Now I have million dollar question for you guys ..
Why in the name of God we use ceramic belts on simple carbon steel like 52100 , 1095 , 80CRV2 , 5160 ...etc WHY not AO belts ?????

I don't. Tried out some ceramics a few years ago and didn't see enough improvement to justify the cost.

How deep is the curved plunge are you getting on that knife? Looks like you have just scratched the surface. I was going through the paper on my disc sander way too fast to be able to finish even one side. Less paper and more heat due to the speed was killing the paper.

 

[Natlek]

I don't. Tried out some ceramics a few years ago and didn't see enough improvement to justify the cost.

How deep is the curved plunge are you getting on that knife? Looks like you have just scratched the surface. I was going through the paper on my disc sander way too fast to be able to finish even one side. Less paper and more heat due to the speed was killing the paper.

It is 0.5mm deep now on edge , I want to end up with 0.2mm on edge before sharpening .So I need to change little angle , if I grind as it is I will pass spine . I will finish it this afternoon . So far I can t notice that paper is getting dull . This is first time I use AO paper on hardened steel for bevels .On my disks so far I used zirconia 40 grit and I was never happy .I try zirconia belt on grinder also , and they don t work for me .I can t explain why .They cut till they cut and then stop and start to heat steel too much . Zirconia grit should break to expose fresh tip as ceramic do but not in my case . What I think is good with AO is that grit wear /don t break/ and tip of grit round little and that s why they give much more nice finish ..
I will order some AO belts , the one I have are for wood

 

[Natlek]

Ok , one side done and it came excellent , I have nice radius close to plunge . When I finish other side I will have 0.20 - 0.22 mm on edge .I start to grind other side little , just to see how it would go with sparks flying right in my face and I don t like it I will finish somehow this one but I need to think what to do next with this problem .Shaft from motor /same thickness / protrude from back side enough so I can use this disk from that side to grind other side of knife or I should make completely new grinder with this thing and three phase motor ............
Disk still grind fine but I need to cool blade after every pass so I will change with new one for other side ....
I check label on motor , it is 6000 RPM and only 300 Wats , energy saving . . . With 6000 RPM and this 72mm disk I have almost 23 m/s on edge on disk , enough .

If I use disk from this side I need to cut jukebox

 

[Natlek]

Ok , let clear something first .When I open this thread I have NO idea how to do that task so I asked . I often came across pictures of knives with plunges grind this way and I asked my self how in the name of God they do that ?
Now , idea to use small disk come to me second day after I open this thread when I look in first picture in my opening post .I used that round *things* just to find which radius is good and a light bulb went on in my head .....why not make disk in that size and try ???????

So I finished with grinding , it came out perfect .

I stop grinding with same paper on other side here , no reason to risk to overheat blade

hardness and edge geometry matter ...... close to 70 HRC M42 steel cut sand paper without damage to edge .I will make small knife from tungsten carbide just for task like this one

I use that yellow glue for leather , rubber which need time to dry and then you joint part you glue .Easy to clean with gasoline , nitro solvent .........

new one

That steel part I attached it where I want plunges to start / from side of blade / then I glued that G10 and removed steel part .For other side I attached that steel part again on place , remove that G10 part and glued it on other side with gel CA ........ perfect !

finished blade

I try to get good picture from plunges from edge side and this one is best I can

I will shape back side of disk to get it thin on edge , I will have better control while I grind plunge radius on edge side and maybe I will glue thin aluminum for better visibility .I decide to cut back side and mount other disk on that side .In future maybe I will remake it .I make some math and I think that I can use 2 inch disk , under that would be ... I don t know SFPM speed fall dramatically.
Also I will put a 2-inch thick sponge inside on walls to muffle the sound, it is quite loud now . Maybe it's a better idea to mount some car audio and speakers in this grinding jukebox , neighbor will love me more

Edit

Of course I won't do it the same way the next time .
First I will grind on belt grinder blue bevels then on small disk only that green part to get plunges on right place and * Curved *
Paper speed would be between 15 and 22 m/s for that part of bevels and it would take minute to finish job

 

[Taz]

That is pretty slick Natlek!

 

[ea42]

Natlek this has been a great thread, very informative and awesome pictures. You've definitely got a knack for engineering a solution to a problem. I'm glad it all worked out for you!

 

[FredyCro]

Another win for Natlek

How do you finish the tang to ricasso/blade transition on hardened blades? I used the file guide, grinder and dremel with rotary tools but it's leaving too much marks on my nice carbide file guide.

 

[Natlek]

Another win for Natlek

How do you finish the tang to ricasso/blade transition on hardened blades? I used the file guide, grinder and dremel with rotary tools but it's leaving too much marks on my nice carbide file guide.

Now you know why it is called carbide *file* guide I will take some pictures how I do that this days ......

 

[Natlek]

Natlek this has been a great thread, very informative and awesome pictures. You've definitely got a knack for engineering a solution to a problem. I'm glad it all worked out for you!

Thanks
This juke box was a tool made for other purposes. There is an M6 thread in the shaft of the lower motor where disk is attached. I attached these Dremel circular saws to it to open a slot in the handles for my neighbors' kitchen knives repair .On other motor I use sanding bands also for Dremel

 

[FredyCro]

Now you know why it is called carbide *file* guide I will take some pictures how I do that this days ......

Thanks, I have to attack that a m2 blade soon..

 

[Natlek]

Ok , I finished this jukebox I cut backside , make another *disk* and mount some nuts for wood on back side of this plywood so I can use same work rest on both side without messing with grinding angle .I will make another two pair of disk , 5cm and 10 cm Dia . I give to friend some micarta and when he cut it in dimension I want , I will make new /small/ box for this *tool* .

 

[dwaterfield]

I built something very much like this. Based on the file guide but made to hold angle grinder. Positioned at the right length and for the sweep of the blade it makes those plunge lines that you want

Hey Backyard, I made something like this with a simple eyehook for the rod to pass through. I see you are using something that has an insert that can rotate. What do you call that and where did you find it?

 

[Natlek]

Hey Backyard, I made something like this with a simple eyehook for the rod to pass through. I see you are using something that has an insert that can rotate. What do you call that and where did you find it?

Uni ball bearing

uniballrod bearing - Google Search

 

[Backyard]

Hey Backyard, I made something like this with a simple eyehook for the rod to pass through. I see you are using something that has an insert that can rotate. What do you call that and where did you find it?

They are traditionally known as Heim joints but also can be called rod end bearings

 

[dwaterfield]

Uni ball bearing

uniballrod bearing - Google Search

They are traditionally known as Heim joints but also can be called rod end bearings

Thanks guys, I think I found a couple that would work to update my jig.

 

[Backyard]

Thanks guys, I think I found a couple that would work to update my jig.

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