Flat Grind Help?

WinDancer

WinDancer

Joined
May 15, 1999
Messages
720
I am pretty happy with my flat grinds through heat treating. When I go back with a 220 AO or finer belt, the seam in the belt causes the blade to bounce on every revolution.

I had my platten ground off flat at a machine shop and then mounted a flat piece of the cero ceran 'glass' on top of it.

It works just fine with the rough grits, just the thinner belts are giving me fits.

Are there different types of splices in belts? What kind do you use for the final grind on your flat grinds?

Thanks,
Dave
 
A thought just hit me, has anyone had any luck using a heavier backing on high grit belts....coarse belts usually have heavier(stiffer) backings than fine belts, perhaps that is the determining factor. Can't test the theory because I don't have a grinder with a platen.
 
The problem is not your platen. Welcome to the world of flat grinding. Are you running variable speed? If so, speed your belt up. If not, go to a Norton 220 or a Klingspor J weight belt, they are virtually seamless. I have gotten the J weight belts in 120, 220 and 400 grit but don't expect them to last very long on a flat platen. As a matter of fact, don't expect belts to last as long for flat grinding as they do for hollow grinding.

A flat platen is tougher on belt life that a soft contact wheel. I don't know if this will work for you but what I do is take it up to 220 or 320 grit on the grinder and do the rest by hand, starting with 220 grit and progressing through 320, 400 and ending with 600 for a hand rubbed finish. It really doesn't take too long.

Oh, I have tried the Trizact or Apex belts on a flat platen too. Not much luck with those either. These belts work very well with a soft backing (hence, contact wheel). Maybe someone else has had good fortune with these but I haven't had much luck on a hard, flat platen. They DO work well for hollow grinding.

C Wilkins
 
CL pretty much does it the way I do. The J-flex belts last about as long as a sneeze but if you are not that agressive with them and grind gently, you can take it to about 400 without much of a problem. With me, I find that only a sharp belt will work in the higher grits. With a dull one, I am constantly fighting belt chatter and usually screw up the grind. Good luck.

Hugh
 
it isnt much use to go much above 220/400 on the flat platten. I usually go to 220 and hand sand from there.
 
Everything that has been said is unfortunately true about flat grinding. Only when I am feeling really ambitious do I go past 220 grit. :)
I haven't seen my belt of choice in 220 grit mentioned, so I will plug for it. I use ceramic 707 belt from 3M. It has virtually no splice and lasts much longer than other flexible belts I have used.
Another problem could be using too much pressure at the higher grits. Since the steel is in contact with more surface area on the belt, you get better results with less pressure.

Brett
 
Hehehe. Guys, here is an idea. FLAT grind on the Wheel :) yes, u heard me right! Hold the blade tip up or down and flat grind on the wheel with the finer belts. U cant get right near the ricasso/plunge because of the size of the wheel, I use an 8", but u can go to 1200 or higher with the trizact easily, then hand sand from like 800 or so and get a nice finish. I also made some blades that I flat ground on the wheel completely. Smooth look with no plunges on them really, it all kinda blends and flows into the blade. I like this technique when I am using 1084 and doing an edge quench, less stress risers. Also, by using the wheel, u r changing the scratch direction by 90 degrees, so u can see if there are other scratches that need to come out from previous grits. Just be careful of the tip cuz it likes to burn. this trick also saves on hand sanding time, too :)
 
:SH&T,,NO WONDER iam haveing trouble at the final grind,i have been trying to grind as smooth as possible with higher grits,thank uall, royboy,,ps.how do they do the blade finish,,with the dark coating, or the matte finish.. royboy
 
Hmmmmm.... I sometimes have trouble with some residual scratches, but I just took a bowie blade to a mirror the other day on my platen...then sanded it out at 600x.

I'm running a variable speed Burr King with a glass plate on my platen...that's glued over-top of a 61 Rockwell D2 plate...the glass is just smoother.

I'm doing my finish grinding after heat-treat, so maybe that's a big difference.

I really wouldn't recommend doing what Taz suggested as you won't actually have a clean flat grind. With a blade done that way, if you hold it up to the light you will see the blade ripples as you look down the bevel. It will look clean just looking at it on a table...but if you have someone serious come up and pick it up and look at it like I said... they most likely won't buy it.

Of course all of this is just what I think... no foul thoughts intended here :)

Nick
 
Hmmmm....why not finish with a disk? No bumps or thumps. Windancer, you could use 2 different grits on either side of your disk and quickly flip it around....

Just a few "off the cuff" thoughts

Sincerely,
Rob
 
Well...I'm famous for doing everything wrong but for what it's worth...
I have the same problem as you if I try to take it too far down when it's soft. You didn't say if you had heat-treated it yet. If it's still soft, stop at 220 or so and save the final polish until the knife is hardened. I used to try to remove all the scratches before hardening so it would be easier after. I found it didn't work that way.:o
 
I ain't no steenkin' genius neither BUT I get a nice finish down to 600 off the ole platen. One trick that works for me is to let the belt do the work (no secret there) and to oscillate the blade slightly in a kind of small figure of 8 motion...seems to get them pesky scrathes all confused and they disappear. :)
 
I used to do a lot of hand sanding, but it's spirit breaking with stainless, so-

60 and 120 grit on the platten, then onto the disk grinder to 220 before ht. As per SR Johnson, 60 grit after HT, and straight to 400 on the platten. Some 400 and 600 on the disk, then 400 grit cork on the platten and hand finish from there. Ricassos only see the disk.

I use salt bath heat treat and there is a deep (like .003") salt affected layer that must be removed after HT. If you don't, it rusts.

I've been going to 220 pre HT, but I'm gonna experiment with 120 only. Important thing is that everything is even and flat pre ht.
 
You can go down to finish before polishing if you use cork belts. You will not get any bumping and if you get a fine one 600 regular or 1000p and get it worn even and load it with green polish you would be amazed at what it will do for you. Just ask SR Johnson. Cork belts work best it seems on harden metal and are not of any use on wood .
 
I flat grind on the platen up to 120 grit. Everything above that is done on a disk sander with a rubber disk mounted to the aluminum plate.
The rubber disk cuts out the chatter and gives a smooth finish. I use wet/dry paper and cheap spray adhesive. This method has cut my hand sanding time down to a minimum. I don't know how I ever made knives for years without it.
 
U just have to control the grind. I do this on full flat grind stuff, like kitchen knives. it helps get the edge down below your fingers, too. Also, for the ripples, it just takes a little practice..i do this step starting at 320 trizact, then 400 platen, 400 on the wheel, then 600 and 1200 trizact. If u watch what you are doing, you dont really get a ripple. I think Mad Dog knives does this, i saw it in their shop tour tutorial. And you can always go over it again when hand sanding.
 
WOW didn't know there were so many ways to flat grind. I cheat a little. I use a thin piece of canvas soaked in graphite on a 5160 platen.I don't quite get a FLAT grind.I grind 50 grit than 120 heat treat do 120 220 400 then satin brite belt. then a few strokes on a grey satin brite pad and call it good.
Take Care
TJ
 
I am grinding to 220 and then heat treating.

It is after heat treat, with the finer grits, that I am getting the splice / bounce problem.

I remember grinding on Nick's platten on his machine, and it was butter smooth, but we never went below 220.

I will give a couple of these belts a try and see if that helps.

Thanks, all, for your help!

Dave
 
this method works really well when making a curved Kris blade. as taz stated it works for a lot of removal, then i go back to the palten for a even clean up.
 
You must log in or register to reply here.
Back
Top