How to flaten the flats on the blade ?

Lerch

Lerch

Well-Known Member
Hi all

Over the last 2 years i have done pretty much only convex ground blades with the grind tapering all the way to the top of the spine. Since this is the way i have been doing things I dont have a lot of perfectly flat surfaces on my knives, i think it gives the knife a bit of a organic or natural look and i like it. anyway I have been wanting to do some more field/tactical knives with either flat or hollow ground edges. to develop the good sharp and crisp lines I always think about on tactical knives i need to have the flats of the blade well very flat. typically in the knives i have been doing only the area around the bolsters is flat and i do this by just pressing this area into the flat platen on my grinder but this usually rounds the edges a little bit where i bend the belt in. this method doesnt seem to work real well for long flat areas like i am wanting.

the only idea i have been able to come up with is to use a flat disc grinder and swap out the disc from 40 grit, 120 grit and finally 240 grit . I only have one disc grinder so this would be kind of a pain but I dont have any other ideas. any suggestions ??

thanks
steve
 
You are right. I switch up to 1000 grit to polish the flat before the bevels. I use 220,400,600,and then 1000.

I also have a 1/8 rubber pad on the disc to help smooth the operation.
 
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okay just to make sure im getting this right here. this is what i have Mike or anyone else reading. So since i cant find any 12" adhesive discs i should just use the 9 " discs i can find and use those for the flats to whatever grit i am wanting to take them too ? any particular kind of rubber on the pad to smooth it out ? since i only have one of these grinders im guessing that i would just want to do a whole bunch of blades at a time so i can somewhat limit the amount of disc switching i would be doing ?


thanks Mike

thanks
steve
 
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Steve, or lerch?
The trick with the 9" disc is that they are horizonal and there is a 1 degree bevel on the disc. When you have a blade over 4 1/2" you can flatten one side and not hit the middle of the disc because of the 1 degree bevel.
Then you flip the blade and go to the other side and flatten that side.

You can use rubber or cork? if you want some padding?

Also, you should be able to do flats on your Flat platen better than it sounds? What brand, model and thickness of belts are you using?
 
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Two thoughts come to mind. You mention "rounds the edges a little bit where I bend the belt in". The belt should be running in flat contact with the platen so it shouldn't have to bend in.

Secondly, I just wanted to get your mind working on the concept of a 1 degree bevel flat disc. Lots of people use them and love them. Having said that, there is no truly flat spot on a bevelled disc. That may be hard to visualize on a 1 degree taper, but to see it by exaggeration, think of a bigger angle - like an upside down ice cream cone or dunce hat. I had a tapered disc and found it completely unsatisfactory. Simlarly, cork padding will round an edge - not as much as your belt pushing in, but by the same mechanism.

These effects are small and don't much affect outcomes for many knifemakers, but you did request advice for "Very flat".

On that point, your belt should be flat against the platen and a disc should be high quality (Beaumont etc.) Flat (no taper) and without padding.

As with most things, you will probably find your answer somewhere in the middle.

My 2 cents (CDN$) :-D
 
If using the platen, try doing your flats with extra tension on the belt. Take out as much slack as possible and use the middle of the platen with the wheels slightly back from the front of the platen. If the wheels are flush or slightly forward of the platen, everything gets rounded off. I use a straight edge across all 3 surfaces and pull the platen forward just a hair.

http://www.trugrit.com/disc-psa.htm Just one of the many that has 12" discs.

Rudy
 
Your flat platen should be sitting proud of (or out from, in other words) your idler wheels so that the belt is flat and tight against the platen.

What kind of grinder/platen are you using?

If you don't have one already, you may think about installing a ceramic glass platen liner. This will minimize wear to your platen and give you a much flatter surface, much longer than a standard steel platen.
 
I am using a Bader B3 grinder with the combo attachment/flat platen

B3_COMBO_FIN0051.jpg

the belts i am using are generally Norton Blaze from 40grit to 120grit and then Klingspore J-flex yellow belts from 220grit on (though i am wonderign if i should keep using the klingspore belts)

the ceramic platen may help. I do the flats grinding holding the blade horizontally just like i do when grinding the bevels. it works okay for the bolster area but i just cant hardly keep it flat well enough farther out on the blade. I have been doing this progressively while i grind the bevels with the different grit belts, maybe if i did the flats all at once to the desired grit level and then procedeed to grind the bevels it would work better .

I do have the flat platen extended out a good .25-.50" from the drive and contact wheels

thanks
Lerch
 
sound advice

granite platens work well

ARCustomKnives said:
Your flat platen should be sitting proud of (or out from, in other words) your idler wheels so that the belt is flat and tight against the platen.

What kind of grinder/platen are you using?

If you don't have one already, you may think about installing a ceramic glass platen liner. This will minimize wear to your platen and give you a much flatter surface, much longer than a standard steel platen.
Click to expand...
 
From everything you're describing, it sounds like you might have a couple problems:

For one, you're platen may not actually be flat, but dished slightly? This would cause some rounding.

It could also be that you're not actually grinding completely flat as you do your "progressive" grinding. Incidentally, I use a similar technique.
Just make sure that as you change to more progressively shallow angles that you're not stopping yourself short.

Sometimes I'll actually leave my edge a little thick until the last "progression" and grind past where I've been stopping during the former passes.

It may help to dye your blade as you're grinding as well, so you can see exactly how evenly the metal is being removed, and how flat you're actually grinding.

Also, make sure you're using a sharp belt. A worn belt does nothing but cut unevenly and makes things all that more difficult.

Lastly:
It's also possible that you're pushing a little too hard and causing the belt to "bunch up" at the contact point. There's a little bit of a compromise between pushing hard enough to expose new grit on your ceramic belts, vs pushing so hard that the belt starts bunching. Increasing belt tension will compensate for this.
Honestly, I wouldn't use J-flex belts for finish passes on flats, as they're actually the most prone to bunching and rounding. Even with increased tension, they're just to flexible in my opinion.

Save them for handles and rounding your spines.
 
I agree with Andrew that you may need to Flaten your Platen or use a ceramic glass one. Sharp fresh belts and I asked about the kind of belts, because those J-flex are too thin the way I grind. try a heavy backing finish belt/belts and see if that helps?

Last, I do the flats vertically on my platen, the full tang up to the plunge line. This may be the main culprit?
I do grind the bevels horizontal.
 
here is a pic of my set up with the platen extended out where i have been using it

i am pretty sure the issue i am having is trying to use the J Flex belts when i am doing the flats. when i am using the blaze belts i dont have the problem. I also think i would benefit from a new platen, any suggestions on where to get one for a bader combo attachment ?
 
well i am gonna order me a glass platen from USAKNIFE , i looked at my platen and it does seem a little uneven in the middle.

on the belts what can you all recommend for a heavy stiff backed belt in 120-320 grit ?? i have been using norton blaze and the cubitron 3M yellow belts in 36,40 and 80grit and they seem to cut much for flat but i cant find any belts in higher grits. i would like to grind the flats to at least 220 if not 320 grit so i can bead blast away grind lines.

ideas ?

thanks
lerch
 
i have some Norax and some 3M micron belts, i will see if they do flats better than the jflex belts
 
If you are looking for finer belts that are still relatively stiff, consider the new(ish) Norax U936 ceramic structured belts - available from x200 (~100G) to X9 (~1700G) and they really last!
 
I will look for those Norax belts, does USA or Pops carry them ? Thanks.

Thanks for the tips on grinding the flats !!
 
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