Flats...how do you grind them to where they look good?

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godogs57

Joined
Apr 16, 2004
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I need some good advice on how you folks grind your flats in the ricasso area...if there is any aspect of my knife making that I am not satisfied with, this is it!

I use a Wilton Square Wheel grinder...my flat platen has a hardened 2" x 7" piece of 440C so the face of the platen is supposedly very flat. This was necessitated by my having to take the platen to my local machine shop three seperate times to get it smooth...that soft metal just never held up well over time. After the third time I went with the 440C. Previously I had tried pyroceram and just could not take the static electricity pops generated every time I used it.

My process: I take the raw steel (CPM154 is my usual choice) and after cutting, profiling and the initial plunge cut, I then flatten off the ricasso area with 120, 220, 400 and then prepare for heat treat. No matter what, after ht and subsequent grinding down to 600 grit, I always seem to see 120 or 220 grit marks on the finished product AFTER polishing. I have made an effort to always use new belts in this process, so I will get a nice flat area...to no avail. I swear it seems that I could grind the damn steel down to the thickness of paper and I would still find scratches. I have made knives long enough to understand the concept of not using worn belts in a situation like this...but I am at a loss on this. It's just not up to my level of finish I like...

My hollow grinds or flat grinds??? No problems there...just in the ricasso.

Any ideas on how you fine folks deal with this would certainly be appreciated.


Thanks in advance,

Hank
 
Something else to consider is that even the higher grit belts will have the occasional mutant grit particle or grit clumps that are way bigger than their brethren. I grind up to 400 grit on the grinder, getting it to where it looks good, and then it's all by hand from there. Especially if you're polishing for a mirror finish, you almost have to do some hand work to get it perfect.

Start your hand sanding back a step and sand up to a grit higher than your desired finish and then back up a grit. Change the direction of sanding for each new grit. This allows you to see when all the prior grit's marks are gone. Use a bright light, and various light types. I have a halogen light I use for work, and a florescent light to check for missed scratches. I also take the blade out into the sun and to different areas of the shop for a different perspective. That way you know all the other scratches are gone.

The other thing I do for stainless steels, is I hand sand to 400 grit prior to heat treating. That way I can get all pesky deeper scratches out while the steel is soft.

I don't really do any mirror polishing, so I can't help you there too much, but I have fought scratch marks for many long hours. Scratches are our sworn enemies. Kill them. KILL THEM ALL!!! ;)

--nathan
 
Are you making sure that you change the direction of the grind every time you change the grits?? I used to think just tochange the belt was good enough but when you change directionsyou really can see the deeper scratches. It may be as simple as that.
 
A disc grinder will finish the flats much better than a platen.

If you don't have a disc grinder, I recommend trying some 220 and 400 grit Gator belts. The Gators are a structured abrasive that is much thicker than your usual 220 and 400 grit belts - about the same thickness as a 60 grit. This minimizes uneven spots or pieces of debris that get trapped on the platen, and gives a better finish.

I also use a pair of magnifying glasses to closely check the flats after each grit, to make sure all the previous grit scratches are out. If I just use my eyes (even with my prescription glasses) I tend to miss scratches. With the magnifiers, I make sure to get them all out.
 
silver_pilate said:
Something else to consider is that even the higher grit belts will have the occasional mutant grit particle or grit clumps that are way bigger than their brethren. I grind up to 400 grit on the grinder, getting it to where it looks good, and then it's all by hand from there. Especially if you're polishing for a mirror finish, you almost have to do some hand work to get it perfect.

Start your hand sanding back a step and sand up to a grit higher than your desired finish and then back up a grit. Change the direction of sanding for each new grit. This allows you to see when all the prior grit's marks are gone. Use a bright light, and various light types. I have a halogen light I use for work, and a florescent light to check for missed scratches. I also take the blade out into the sun and to different areas of the shop for a different perspective. That way you know all the other scratches are gone.

The other thing I do for stainless steels, is I hand sand to 400 grit prior to heat treating. That way I can get all pesky deeper scratches out while the steel is soft.

I don't really do any mirror polishing, so I can't help you there too much, but I have fought scratch marks for many long hours. Scratches are our sworn enemies. Kill them. KILL THEM ALL!!! ;)

--nathan
Click to expand...
Alternating direction above 400 grit is a bit of a waste of time unless you are going for a mirror finish or a VERY fine hand finish like 1200 to 2000 grit. I tend to make 400 my last crosswise grit and then go 600, 100 and back to 600 for the final finish. If i am going to a 400 grit "working" finish, then I go crosswise with 400, then straight with 400, 600 and back to 400. Another labor saver is NOT to go back to 120 when you hand sand. Start at no coarser than 180. 220 or 320 would be better if you can get a good even finish on the grinder up to maybe 600. I still have trouble sometimes with 400 and 600 belts so I often quit at 220 and go back to 180 to start hand sanding. I wish I could start art 320!!! The coarser the grit you start with, the longer you will be stuck at the next grit trying to get rid of the scratches. Also, don't be afraid to go back to the belt or disc grinder for a light touch on fine grits if you have any dips or divets.
 
I'll second all the recommendations to change direction, use different lights and magnification, structured abrasives, and the like. Having a perfectly flat platen or disk grinder is pretty much necessary too. I run mine at the slowest speed I can still make any progress, just to make as sure as possible I'm not letting the blade torque under the belt and grind the high side more than the lower. Yeah, that still gets me.

Where I differ from pretty much everyone else is that I grind the ricasso area before I do any other grinding. I always found that I would get the grind lines slightly out of symmetry trying to clean up those missed scratches in the ricasso when I'd ground the plunge first.

There's nothing more aggravating than to start getting in the higher grits and see some really deep scratch I have to back way up for... Close examination at every grit helps me a great deal.
 
Thanks so much for the suggestions. Brett, I have used Gator belts and I have just not seen them last too long in my case...that was my only grip about them. Perhaps I don't know a trick about Gators that most folks do? I don't know.

As for the dips and divots that JDM61 mentioned...yep, I get those too! Those really tick me off...

Any more suggestions are appreciated.
 
I want to add my voice to David's. Every knife blade starts at the ricasso.
The ricasso is finished, before the plunge cuts and before the tang is fashioned.

If distal taper is being incorporated in the blade, it should be accomplished as early as possible in its construction. In the order they should be completed is: Ricasso, tang and then the distal taper should be ground, followed by the plunge cuts.
The area at the ricasso should take only a bit of clean up after the heat treatment.
I have a note posted above my workbench that states:
"Its the ricasso stupid"
Trouble is sure to follow if the order is not heeded.

As far as getting flat grinds flat; a flat surface must be used to do the abrading. A belt running over a platen is not flat at all. It is everything but flat. If you would like to prove this to yourself; grind a 4 or 5 inch blade on your belt machine, take it to 120 grit, then place the blade on a flat surface and using a flat bar with 120 grit paper attached to it; abrade the surface of the flats from ricasso to tip. Every low spot will be glaringly apparent.
I use either a flat bar or a disc grinder, before heat treat, to make obvious, how flat the blade actually is.
The blade can then be put back on the belt to even these areas up.
If a "flat abrasive surface" is never applied to the flats of your blade one will never turn out a truly flat surface.

Every shop has its own way of doing it, this is just mine.

Fred
 
If you're having trouble missing scratches from previous belt grits, I think you might want to consider a quick hand rub with each grit after you finish on the belt. The ricasso won't take much time to knock out in each grit. You can be sure your 120 and 220 scratches are out this way, as you'll easily be able to make them appear with the respective hand sanding grits.

I picked that tip up from Fitzo and I think it's well worth using.
 
Honestly, I rarely go above 600 grit for hand finishes. I'm not a mirror finish person, so I don't go there. I do switch grits up to my final grit of 600, with 400 going at a slight angle and 600 going straight. For a heavy work knife, sometimes I'll keep 400 and 600 in the same direction. I rarely (if ever) start by hand below 320. Pretty much as clean as I can on the grinder, 320 hand, 400 hand, 600 hand.

--nathan
 
OK...stupid question here....how will a disk grinder enable me to make a "flatter" flat than a flat platen??? Also, can you suggest a good disk grinder (internet link if you can) for me to look at??
Many thanks for the suggestions....I appreciate you fine folks.
 
godogs57 said:
OK...stupid question here....how will a disk grinder enable me to make a "flatter" flat than a flat platen??? Also, can you suggest a good disk grinder (internet link if you can) for me to look at??
Many thanks for the suggestions....I appreciate you fine folks.
Click to expand...

My take is that you are not flat all of the time on a platen unless the blade is less than 2 inches long.
 
jdm61 said:
My take is that you are not flat all of the time on a platen unless the blade is less than 2 inches long.
Click to expand...

Even at two inches length, it is difficult to produce a truly flat blade on a moving belt.

The surface of a disc grinder plate is no flatter than a platen but a moving belt, running along the top of a platen, is not as stable as the abrasive that is applied to the surface of the disc.
A disc grinder is useful for many surfacing jobs around the shop. I could not do without one.
If you do not have access to a disc grinder, the next best thing is a
1/4" x 1" x 12" piece of flat stock with the desired abrasive adhered to the surface.
I buy rolls of sticky backed paper in 80 120 and 220 grits at the Lowes in my area.

Rob at KMG in Columbus sells machined disc. You just need a motor after that.

Good luck, Fred
 
Make sure you pay attention to how and where you store your higher grit belts.

If your 400 or 600 grit belt picks up grit from an eariler grind you'll be putting the scratches in yourself and not even realizing it.

I learned about this from Warren Osborn at the Guadalupe Forge Hammer in a few years back. He stores his 600 grit polishing belts in zip lock bags to keep shop grit out.

Also try sweeping the grit from around the grinder before you change belts. I always forget and end up running a brand new belt through the grit that was left over from privious grinding.
 
Mark Basford said:
Make sure you pay attention to how and where you store your higher grit belts.

If your 400 or 600 grit belt picks up grit from an eariler grind you'll be putting the scratches in yourself and not even realizing it.

I learned about this from Warren Osborn at the Guadalupe Forge Hammer in a few years back. He stores his 600 grit polishing belts in zip lock bags to keep shop grit out.

Also try sweeping the grit from around the grinder before you change belts. I always forget and end up running a brand new belt through the grit that was left over from privious grinding.
Click to expand...

Thats a good suggestion, Mark.

Using compressed air on belts as they turn on the grinder, really helps to keep them clean of oddball grits also. I have a hose designated for this at my grinder station.

Fred
 
Fred.Rowe said:
Using compressed air on belts as they turn on the grinder, really helps to keep them clean of oddball grits also. I have a hose designated for this at my grinder station.

Fred
Click to expand...

Me too. ;) Blowing all the crud out of belts helps them to cut longer too.
 
ddavelarsen said:
Me too. ;) Blowing all the crud out of belts helps them to cut longer too.
Click to expand...

I've been using the gator belts in 80 120 220. They won't clean any other way but forced air.

Thanks for your kind comments on the horn handled knife.
It went to Indonesia. It was a really fun piece to make.

Fred
 
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