How to scribe center of blade when steel isn't the thickness of the drill bit?

R

Rancho5

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Feb 10, 2015
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My 1084 from Aldo isn't .125 it's .145. I had planned on using my 1/8th drill bit to scribe the center line of the blade but when I tried the mark was off center. I flipped it over and scribed another line and now have two lines with a small space between.

Not having an expensive "center finder thing", and hence the drill bit trick, should I just grind to the line on each side and leave the empty space there, and then sharpen that for my final edge? Or do I go buy a .145 drill bit, if they exist?

Any inexpensive ways to find this center line? I really don't want to buy a "center finder thing" as a beginner. Maybe later.

Any tips and help much appreciated.
 
The steel is always going to be oversized and will vary, plus what I have in mind for edge thickness can vary- so the drill bit thing doesn't fly for me.

A Grizzly height gauge is less than $50

A knifemakers scribe can be found for less

Calipers work too
 
I assume you have not hardened and tempered the blade yet. You want to leave a bit of thickness before heat treating so what you have scribed should ideal.
 
Rancho, all you're trying to do is get that edge as well centered as you can. What works best for me is to have two lines about .040 apart (roughly) and grind to the line on each side. Because of that, it's not that important to get absolute center with the scribe, so anything that's a little more or a little less than half your blade thickness will do it.
The caveat, and it's a significant one, is that that blade has to be FLAT. If it has any burrs or the sides aren't parallel for some reason, or it's sitting on a blob of glop that you didn't notice on whatever surface it's lying on, your mark is gonna be crazy.
When I look at my drill bits, I don't see a perfectly centered point, the little ones tend to have sort of a chisel point (because I suck at sharpening them, probably) so I have some carpenters' nail set punches carefully ground to a point that I use instead.
Best answer, get a height gauge! :)
 
I get a drill bit that's slightly smaller and scribe two lines. Then I just eyeball it. Once I get down to .020 and thinner
 
Buy a set of calipers - they are cheap. measure the thickness of blade, set calipers to half wide, then use pointed end of calipers to scribe a line along center of blade. This will be slightly off center, so move to other side of blade, scribe another line. Now you've got two lines with a small space between that works good for the thickness you wish to leave for HT'ing.
 
I like the lines a bit apart depending what I am doing.

Try some inexpensive calipers to use as a scribe, just run one edge along the knife and one to mark. It sounds tricky but is quick and easy. I use mine a ton. I have some nice Mitutoyo's but use an old broken pair with a missing dial for marking so I don;t mar the teeth of my nice ones.

Another trick is to cut off a piece of the steel you are using, grind a corner to a steep knife angle, heat treat and use it for a scribe. The edge only needs to be close and you can still adjust it post heat treat, You only need a tiny scrap from the same bar.
 
My goal is also two lines for pre-HT edge thickness approximately .040"-ish. Once I'm down that far its not difficult to find the center post-HT. I also found that it is easier for my eyes to see two lines while grinding than just a single line down the center.
 
Try using a drill bit that's slightly larger, instead of smaller, than your thickness and don't let it roll when you scribe. It'll be easier to control, and as the others have mentioned, parallel lines may be a good thing. Also, keep in mind that your steel might not be precision ground.
 
Great input, thank so much. So doing the math (and PLEASE correct me if I'm wrong as I suck at math) my steel is .145 thick and my bit is .125 thick. The space between the two lines is .02 thick. If that's correct then I'm good to grind, right?
 
yes you will have about .02 flat. Another tip I didnt see mentioned here is to use a paint pen or sharpie. I like the paint pen better, the paint is not water soluble and heat of grinding wont mess with it. So just paint the edge of your blade and then scribe it. This will save the scribe edges of your tools from actually having to scribe the steel. Calipers work best for me as one will be able to deal with any thickness steel.
 
I have used a centered line and the parallel lines. Either is fine but the parallel lines may actually work better. I use the Dykem dye to paint the edge and use drill rod or a height gauge to mark the lines. With the drill rod, I get long bits that I use for drilling out handles for hidden tang knives. I cut off the length I need for the handles and the excess I sharpen to a point and use as a scribe. I started off by making scribes from steel scraps as was mentioned earlier but it was a hassle. If you forged the blade, get your ricasso flat first and clean up the sides of the blade so it sits flat on the surface before you scribe the lines.
 
Just use the 1/8" bit on both sides and take your pre-ht bevel just up to the line on each side. This will leave roughly .030" to .040". As stated above this is to make sure you don't go too thin pre-ht and to keep your grinds centered. I have some old lathe bits that I ground one side to a point that is .055". I mark both sides and that's what I grind to pre-ht.
 
Stick a .010 shim under the drill bit if you want a centerline. If you don't have any shimstock, cut some aluminum out of soda can, or stack some paper together.
 
i4Marc said:
I have used a centered line and the parallel lines. Either is fine but the parallel lines may actually work better. I use the Dykem dye to paint the edge and use drill rod or a height gauge to mark the lines.
Click to expand...

+1 this... Go with the 2 lines, you are being more conservative this way and it forces you be visually aware of how much you are grinding off.
 
Height gauge can be had for $45 from enco at times. Get one and a surface plate for $35 and you will find many uses for both. For now the above recommendations are solid and will deliver good lines.
 
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