Scraper Making & Sharpening/Honing

Hello people,

I've got an oddity, and I think I might know the answer, but then I could be well and truly wrong (probably am), so I'd like to throw it open for discussion.

I made myself a scraper from the instructions here: http://www.metalworkingfun.com/archive/index.php?thread-662.html.

All went well until I tried to use it - it was a total failure as the sharp edge immediately disappeared. A moments thought, and I reasoned that the file was most likely file steel and either not hardened right through, or I had inadvertently softened it whilst grinding even though I tried to keep the heat down. It was no use in its present state, therefore I had nothing to lose, so how about a bit of rough and ready heat treatment. Remove the handle, clamp the tang in the vice, and apply blowlamp until the tip glowed nicely, then plunge it into cold water. This I did, cleaned the scale off it, and tried to hone it with a medium and a fine diamond whetstone. Much to my surprise, I could not get a sharp edge - it was as if the material was too hard to be honed. I then tried to use it as a scraper and again was surprised to find that it performed very well indeed.

Since then, the cutting edge has developed unmistakable signs of wear, yet it still works as a scraper. I have tried, again, to sharpen & hone it, but it won't have it. I have not, as yet, tried the grinding wheel.

It seems to me therefore, that in order to restore a sharp edge, I may have to anneal, sharpen/hone, and then reharden. Which does seem rather odd.

Now, the diamond tool I am using is one of those 4 way jobbies which originally came from Aldi. I know that the coarsest side is worn out - in fact I do not think it was particularly good when I bought it, but the device as a whole has not had that much use and I would have thought that the other three sides would have been ok. It does leave scratch marks on the scraper, but progress, if there is any, seems extremely slow.

Your thoughts please.

Peter G. Shaw

Firstly I should start by saying that I have little experience in scraping ( I am fully qualified in scrapping though ). Most of the experts that I have seen on youtube seem to think that HSS or carbide is the way to go. I have several scrapers made from old files and all of them lose their edge pretty quickly. Some people say that this is because files are case hardened others seem to think that carbon steel isn't up to the task, what the answer is I don't know. Yesterday I decided enough was enough and got a piece of 20 x 6mm bdms, I cut a notch in the end to take a used triangular carbide insert and silver soldered it in place. on the other end I cut a tang and put a file handle on it.

I sharpened it at an angle of 5 degrees ( handle lower than point ) on both sides and had a go. The result is much better than anything else I've got and only took an hour to make.

Regards.

David.

Edited By David Colwill on 05/06/2017 20:36:13

Well I've got several scrapers made from old files, the two I use the most are triangular but there's a flat one and a half round too.

I wonder if you've got the hardness so far up the scale that the edge is brittle, and chipping off rather than cutting. Try tempering the end to a light straw and sharpen it again.

Makes no sense to me to have to soften, sharpen then re-harden, the scale from the heating will dull the edge. Putting a nice sharp cutting edge on would normally be the last operation.

FWIW I only lick the edge with a fine grind stone, quick and easy, sharpen it in 5 seconds.

Good luck Simon

Sounds like you hardened the cutting edge but did not temper it. You could try heating the cutting edge up to a light straw colour and plunging it into a tin of oil. One way of doing this is to play the torch/blowlamp on the blade an inch or two away from the cutting edge. You will see the metal heat up and change colour. The colours move outwards with the heat, so when the light straw colour moves outwards from the hot-spot and reaches the cutting edge, quickly plunge it into the oil.

I've never had to do this with old files. Usually they seem to be through-hardened and hold a reasonable edge. But maybe they just case harden them these days? IDNK. But as you already did the hardening step, you probably should temper it, as is usual procedure, to give a hard but not brittle edge.

Indeed, the thickness of the metal can play a crucial part in the tempering process, the temperature needs to be held for more than just a few seconds.(The hardening process on a molecular level isn't exactly instantaneous. The longer it's exposed to the given temperature the more complete the transformation will be.) 

This is why a furnace or some kind of heating rig can be better for tempering than just holding it against a blow torch, which will of course, just keep raising the temperature til it reaches the nominal burning temp. (although I suppose altering the distance you put between it and the burning gas might give you some result if you keep a keen eye on the colours!)

Michael W

Edited By Michael-w on 05/06/2017 22:50:45

Peter, I've got various (commercial) carbon steel scrapers including flat, triangular and curved ones, plus the type that holds a carbide blade.

Frankly, I don't do that much scraping, normally being pretty happy with the finish I can get with my machines (particularly the shaper) and when I do 'scrape' it's probably more to improve the general 'flatness' of an existing machined surface (let's call it removing any humps and bumps) rather than proper scraping. Basically, I don't have the skill, time or patience to do the kind of clever stuff you can see on YouTube and generally I don't need to.

However, when I do my "humping and bumping" I generally stick to the carbide scraper these days. I don't think they can be that expensive (although I purchased mine second hand at a GMES rally many moons ago) but if you are really going to spend a lot of time doing this kind of work (and it will take you a lot of time to do it well) then the cost of a decent tool to do it with should probably not be your biggest concern.

Just my two penny worth...

Regards,

IanT

I'd do it all the same again, but use clean oil rather than cold water to quench, and you should find you can hone the edge

I'm not sure about this ALDI brand sharpener, I suspect this may be the real trouble here, the diamond will only sharpen while it's adhered to the block, and I would guess it could rub off fairly easily. I have couple of diamond files/flats from Arc Euro Trade and they're great, the 6" flat file #200 very quickly shapes or takes back any edge, and then straight to the #1200 6x2 hone which puts a mirror finish on in just a pass or 2.

I made a set of scrapers around 1963/4 during my apprenticeship. All from old files heated and bent then hardened/tempered. They have kept their edge with minimum amount of sharpening ever since. Maybe the steel was different then ?

Could I ask what the state of the top and bottom surfaces are like. An edge only gets as sharp as the roughest side however much you polish the end. Forgive me if I have missed the point and am telling you things you already know.

regards Martin

Some answers.

I was aware that excessive heating can de-carburise a steel and so I did not keep it hot for too long. Having said that, I did not temper because by that time I was past caring having spent many hours getting "right". Plus, I didn't bother too much about colours in that I simply got it hot, held it there for a short period (define short!) and then cooled it. Frankly, it was more desperation than anything else and I really didn't expect it to work. I would point out that Bob Loader in his articles in MEW actually recommends not tempering for flat scrapers on the grounds that the edge will last longer.

Re the Aldi sharpener. Yes, I also wonder about its quality as Russ implies, especially as some, maybe most, of the coarsest grade appears to have rubbed off. As it happens I've ordered a replacement by Faithfull via my local hardware store. I am though, wondering about that quality of that device since I don't really know over much about Faithfull. Oh well, onwards & upwards.

Martin,

Before heating it, I had gone through all four sides of the sharpener and each one did indeed improve the surface to the extent that the cutting corner looked like a very thin line, if that makes sense. Since using the scraper, the corner looks to have gradually become wider. I'm not sure that the surfaces are as level as they should be, possibly my technique as it is the first time I've tried to make a scraper from an old file. But I think the finish adjacent to the cutting edge was probably ok.

Michael-W,

The actual cutting edge is less than 2mm thick so heat transfer will be very quick. I am aware of the 1 hour per inch rule so although I didn't time it, I did hold it at whatever temperature it was for a short while to allow for heat transfer. TBH, I was quite surprised when it actually worked.

OK folks, I'll try again.

Peter

No need to get too carried away with furnaces for a scraper blade. Heating with a torch has been done for at least the past 100 years to harden and temper tools such as scrapers, chisels, punches and the like. And has always worked OK for me.

You only need to harden the first inch or so, heat and quench in oil, next polish the steel, then to temper it start heating at the tang end of the body of the scraper keeping the colour blue at that end, and with the tip pointing up watch the colour travel to the tip and when the colour appears light straw quench it tip first in the oil, that way the scraper will have a graduated hardness and toughness.

Well that's how I did mine 30 years ago, my biggest problem was grinding the teeth off the file as I had only a hand powered grinder with a 4" stone on it.

Ian S C

Well now, it seems that the main cause of my problems might well have been me!

What I did was to carefully slightly regrind the tool, and then start to hone/sharpen it, but by accident I used a different grip, only to find that the diamond hone, all four sides, started cutting as it should do. I think that with the previous grip I was allowing the weight of the handle end to press down such that the business end was rotating, or perhaps pivoting might be better, around the point where the slope down to the cutting edge started such that the cutting edge was actually being lifted clear of the hone. The previous method of holding was to press down on the cutting edge using the fingers of the left hand whilst lightly supporting the handle and providing back and forth movement with the right hand. The new method is to still press down with the left hand fingers, but hold the tool much nearer to the cutting point with the right hand, whilst still providing back and forth movement. This way, I could feel when the cutting edge was actually in contact with the hone.

So there we are, I've learned something new. Which of course, I'm quite pleased about. I haven't bothered annealing, re-hardening & tempering because it works quite nicely as it is. Which suggests that I, completely by accident, got it just right first time.

The hone, by the way, is still, er shall we say, rather clapped out, indeed in parts it's bare. But it's still usable in places.

Many thanks for the assorted comments.

Peter G. Shaw