Round edges flat platen

[JTknives]

I like my platen edges square because I feel it gives me the most control. This is the current shop project, and it was ground with a square edge platen.

If you're really set on a radiused edge... a file and a radius guage will get you there pretty easily. I showed it in the youtube video I did about hand tweaking plunges.

I am a sucker for a nice tight plunge cut like yours. Most knives I do have tight plunge cuts. I don't clame thy are anywhere as nice as yours but here is one I just finished

 

[LARRYZ10]

I use a square edge platten, I just brake the edge of the platten so it's not sharp and does not cut the belt. When I upgraded to a glass platten I just used the belt grinder to grind a very tiny radis onto the edge of the glass so it's not sharp. Let me say this up front, I suck at sweeping plunges but I give it my best try and this was done with a square edge platten. The problem I think with a large radius on a platten is that your stuck with it unless you change it out.

This was my most recent attempt at a sweeping plunge. This is a Damascus cutlass I'm working on for the WIP.

JT, I love your double edged dagger. The grind is beautiful. Larry

 

[Stromberg Knives]

Wow, this board is amazing. Such good advice from experienced makers.

I tend to wish for it, but there simply is no substitute for skill, experience and hard work.

I'm just going to knock off the very sharp edges of my platen and then setup and use the technique Mr Wheeler demonstrates in his video for perfect plunge cuts.

Surely it takes a little more time per blade. But I'm in no hurry, as long as my results improve.

 

[kuraki]

Last night I couldn't sleep so went out to look at this problem I'm having. My platen was some how out of kilter in regard to alignment across the face of the platen in relation to the axis of my platen wheels. So on one side of the platen, the belt ran against it, and on the other side, it flopped in open air. Definitely causing me a problem. I shimmed it square and that helped immediately.

I still don't like the sharp corners on my glass platen, so I just took a diamond file to them and knocked them back to about .030" radius.

Now I really need to get my 3ph motor and VFD wired up as belt speed is what's really limiting my ability to control what is happening. But at least I can get them even again.

 

[tim37a]

Valknut,

The reason for a rounded plunge is that if you have a square plunge it sets up a stress riser which may cause the blade to break at the plunge if you use the knife for prying. Although a round plunge is THE BEST way, with todays steels, it is not as critical as it was 50 - 100 years ago. Also, anyone who uses a knife for a pry bar deserves a broken knife IMHO.

 

[JTknives]

Ok I was in the shop today and thought I would show how I do it.
The plunge cut was already done but only roughed in. Roughing it in is something that's hard to describe but once you figure it out it's easy. I use the edge of the belt (50grit blaze) and carve it out and kinda like if you where carving it with a knife. When I first set the edge bevels I just make sharp even plunge cuts and leave to top of the edge bevel lower then the finished height. This way as I carve and shape the plunge cut I can sweep the edge of the belt in an arc down into the plunge and along the blade. It helps to have the platten tilted forward so you can see behind the blade and actually watch what the belt is doing. But this takes practi, first time I tried grinding while looking upside down and behind the blade I washed out the spine.

After your heat treated and ready to finish the blade I grab a nice gator belt. I start with a A300 gator and do the same roughing as I did with the blaze belt but this time I track the belt off the side of the platten just a tiny bit. This gives a little bit of flex so it does not dig in.

Then pop on a 100 grit and Keep it tracked off the platten the same amount. My belt has one edge rounded so it does not dig in. I round it with sand paper while the belt is running. Just dress it to the arduous you want. Here is how well the rounded edge fits my plunge. But a tip is only round one side, and flip the belt when you start on the other edge bevel. This way the belt still has a sharp edge if you need it and your using the same radius for both plunge cuts.

Here is what it looks like after grinding, make sure both sides match, your customer might not notice but you will and it will drive you crazy.

This is is where the rubber meets the road so to speak. If both cuts are not the same it will really look bad and is considered unprofessional. In fact a guy was elimanated from forged it fire because of uneven plunge cuts.

I go stright from A100 grit to a 220grit paper and start hand sanding. Here it is at 220grit does not take long at all.

Make sure you get up into the plunge cut, I kinda rock the paper into the cut.

Then flip it over and have a go at the other side. A big thing is protect the the nice crisp edge from the plunge cut to the ricasso. Guard it with your life don't let the sanding bar run up and over the edge. If this gets rounded it does not look good and is not fun to fix.

I then take it up to 400grit. It still needs a bit more but it's close enough for now.

 

[JTknives]

Man I just relazed I need a new name stamp. Just looked it over and the last few letters of my name are not crisp anymore.

 

[kuraki]

JT thank you for the tip of dressing the Trizact like that. I've been using Trizacts to do this because the height of the belt helped me feel and see what I was doing and even though I dress them sharp it never occurred to me to radius the edge like that. That's a great tip.

Can I ask how fast you're running the belt when dressing up your plunges?

 

[PaMtnBkr]

JT, Those are some great tips! I have to admit that getting plunges right drives me crazy. I like your technique too! One thing I like to do when hand sanding into the plunge is to use my file guide to keep me from running up and over onto the ricasso. You've been on fire lately! Thank you! Don

 

[Justin Schmidt]

Valknut,

The reason for a rounded plunge is that if you have a square plunge it sets up a stress riser which may cause the blade to break at the plunge if you use the knife for prying. Although a round plunge is THE BEST way, with todays steels, it is not as critical as it was 50 - 100 years ago. Also, anyone who uses a knife for a pry bar deserves a broken knife IMHO.

OK I understand what your saying. And with help from JTs picture tutorial makes more sense now. However if I ever sell a knife to a customer and he uses it as a pry bar, they're definitely NOT getting a refund. Pet peeve if mine when someone uses a knife other than to cut .
-Justin Schmidt