Thread: flat as a concrete block

After seeing this article several months ago, it reminded me of watching my Grandfather flattening hones the same way.

So... I just lapped a Dubl Duck combination hone on a concrete block. Both sides. The hone is much flatter than when i received it and it sharpens a razor very well.

I'm not going to throw my DMT 325 plate away, but this might be a decent inexpensive way to get the job done for many. I am assuming that my concrete block is typical of the breed (flatness-wise).

I haven't tried lapping a harder hone, like a Swaty or Apart, yet. That's next on the list.

Could you do a pencil grid on the hone and do a few passes on the DMT to see how flat it really is?

I can believe that the concrete brick will abrade many hones, and that it may in fact be flatter than most old barber hones, but I would doubt that it is anywhere near as precise as the DMT for flatness.

Maybe it would be a good method for roughing in the flatness on a really worn hone, to be followed by the DMT.

I'd never heard of the concrete block thing. Only works if the concrete is harder than the hone, I'd guess.

I've heard of the grit on glass method, but its slow. If you have hard stones though its reliable.

Makes my glad I use the Scary sharp system on my razors, though it is a lot easier on woodworking tools that don't need to be as sharp.

Yeah, I just tried this on an old barber hone that I had considered unsalvageable because of some deep scratches in the surface and it worked pretty well. I actually found that the insulating firebricks that I use on my forge abrade much faster than concrete, but weren't as flat.

All in all I went through about 1/16 inch of hone in 5 minutes!

I wouldn't consider it flat enough to use on a razor with out a few laps on finer sandpaper or a DMT C, it was pretty rough on the surface as well.

A good option for reviving a really beat up old stone, but not for general purpose lapping.

I used a sine bar/plate and a runout indicator. The Dubl Duck was within 0.041 inch before lapping. Repeatability was the main issue as one spot on the corner was 0.015 inch all by itself. After concrete-lapping it was 0.0035 inch; over the entire 2 inch x 4.5 inch surface, both sides (I used pencil marks before starting on the block). I was, and still am, surprised at how well it worked. I then touched-up several razors to make sure that it was close enough to do the job well... it was.

My DMT D8C was checked, when purchased, to be w/in it's factory tolerance of 0.001 inch; over the entire surface. My particular concrete block isn't as precise as the DMT, but it is definently precise enough to work without any further flattening.

My test was mainly just to see if Grandpa's method really did work. He lapped all his hones, including razor hones, on one. On very rare occasions he would use a machinist's cast iron lapping plate. After reading the article several months ago I checked around at several local cabinet making shops and someone at every shop was aware of the method. Quite surprising and the main reason I finally gave it a test drive.

Talk about a low-tech solution! This might be a nice back-up method. One thousandth of an inch flatness over 24 square inches (like the DMT) is surely very nice, but not really required for practical purposes.

I've heard that a Swaty is capable of wearing a Norton lapping stone down. The Dubl Duck is quite soft compared to a Swaty. We'll see how the concrete block holds up to a Swaty as soon as I get an unlapped one to experiment on.

Originally Posted by Russel Baldridge

Yeah, I just tried this on an old barber hone that I had considered unsalvageable because of some deep scratches in the surface and it worked pretty well. I actually found that the insulating firebricks that I use on my forge abrade much faster than concrete, but weren't as flat.

All in all I went through about 1/16 inch of hone in 5 minutes!

I wouldn't consider it flat enough to use on a razor with out a few laps on finer sandpaper or a DMT C, it was pretty rough on the surface as well.

A good option for reviving a really beat up old stone, but not for general purpose lapping.

Worked really well for me. Different blocks maybe? Mine looks just like the one at the linked website. I found it to be faster than a DMT 325 coarse, also.

Originally Posted by Sticky

I've heard that a Swaty is capable of wearing a Norton lapping stone down. The Dubl Duck is quite soft compared to a Swaty. We'll see how the concrete block holds up to a Swaty as soon as I get an unlapped one to experiment on.

I can believe that about a Swaty. I picked up a 3 line last month and started lapping it on my Shapton GDLP with no weight other than the Swaty. I have gone through 4 sessions now now spending more than 20 minutes per session (I want to keep this fun rather than turn it into a chore) and it's still not there. During the latter part of the sessions I even dropped down to an unmarked 6x2 diamond plate I've had for over 10 years that's probably 200 grit range (definitely coarser than a D8C) for more rapid removal. Even on that, this Swaty is taking time!!! Surface wise and smoothness, by far the best quality barber hone I've handled.

Chris L

Originally Posted by Chrisl

Surface wise and smoothness, by far the best quality barber hone I've handled.

Chris L

I have two lapped Swatys that are among my favorite finishing hones ( a two and a three line version). If you like the Swaty's hardness and sharpening qualities, try an Apart when you get the chance. (credit to Randy Tuttle for that last advice)

Fortunatly when I got my swaty it was flat enough to use. I tried the draw a grid method and I wore off all the pencil lines really quickly, I don't think I even scratched the stone.

This is one of the most unique little tidbits we've had in this section for quite a while. Props to Sticky for trying it out and reporting back.

I've always wondered how folks were able to lap barber hones before DMTs came along.

What kind of surface does it leave on the hone?

Josh

[quote=Sticky;218551

Worked really well for me. Different blocks maybe? Mine looks just like the one at the linked website. I found it to be faster than a DMT 325 coarse, also.[/quote]

Yeah, mine looks like that too.

Come to think of it, I used the square end rather than the side (they were stacked up with my forge on top, and I didn't want to disassemble it to get to the concrete blocks) , so that could be the difference.

I'll give the side a try and see how it does.

Josh, I would compare the surface from the block I tried to ~150 grit sandpaper, but I used it dry so maybe the slurry would smooth things out.