Is a hand scraper pulled or pushed?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Bob Worsley on 23/08/2020 10:47:17:

As is usual, after posting this, sat down with an ME off the pile to read and an article about scraping, 15 Jan 1988 issue 3817.

Their scraper, made from an old flat file, the end has the teeth removed and then slightly hollow ground. Use the periphery of the grindstone to put a slight hollow right at the very cutting end of the file. Grind the end with a slight curve and finally stone on an oilstone.

In use the description is "The tool is drawn steadily across the work with slight pressure applied to enable the cutting edge to make the cut.". My immediate reaction was 'ah, it is pulled'.

In use the scraper seems to be held at about 45 degrees to the work, so the 90 degree end face is at the same angle to the work if pulled or pushed.

Must say that pulling makes more sense if you have a handle the length of a chair leg, 20" or so, plus the length of the old file, 12" or so. Internal scrapers can only be pushed but they are hollow ground and the trailing edge touching sets the cutting angle.

Another problem solved! Thanks to everyone who read and contributed.

Coincidence! Looking for something else I just came across Part 2 of 'Forms of Scraping' in Novice's Workshop, by Duplex in ME3284 (1 Nov 1965)

Three reasons for scraping;

1. removing metal to true up a surface, or
2. providing a key for lubricating oil , or
3. removing burrs

I believe metal removal was usually done by pushing a long handled scraper with considerable force if necessary. Scratches to hold oil are made with a short handled scraper applied more gently to an already flat surface, and usually pulled to mark a regular pattern of crescents. Truing and keying are skilled operations while removing burrs isn't. Burr removal and other rough work can be done by either pushing or pulling.

Scraping to remove metal is much less common than it was in Victorian times. Whitworth's surface plates were flattened by comparing 3 plates with Engineer's Blue, and methodically removing all the high spots until the 3 plates all aligned perfectly. Not because it was the best or fastest method, but because he didn't have an alternative. Skilled work, very time consuming and expensive, so quickly replaced as far as possible first by planing machines, and then by grinding.

Ground slide-ways are too perfect because very smooth surfaces don't retain oil unless the oil is deliberately sticky (Way Oil). For that reason slide-ways are often scratched to improve lubrication, and – as a sign of 'quality' – a number of different pretty patterns such as frosting may be applied. Although crescents were made by pulling, other patterns were created by pushing.

So the answer is scraping can be push and/or pull depending on why the scraping is being done.

As scraping is associated with quality, it was and is widely applied for cosmetic reasons, possibly making things worse. Beware! In 1965 Duplex said: 'Care must be taken to avoid in anyway destroying the accuracy of the surface either by excessive or haphazard rubbing.'

Duplex mentions Carbon-steel and Carbide but not HSS. I guess it's because the heat resisting properties of HSS aren't applicable to scraping and Carbide is considerably harder when that matters. Carbon-steel is said to give the most polished finish and the scrapers shown in the 1965 article are all made from old files.

Dave

[Ex contributorParticipant @mgnbuk]

Scratches to hold oil are made with a short handled scraper applied more gently to an already flat surface, and usually pulled to mark a regular pattern of crescents.

That might have been how Duplex did it, Dave, but it wasn't how my former collegues "frosted". They just used the same scraper, but manipulated it differently (still pushing, though) to put a pronounced "curl" on the surface – some refered to "frosting" as "curling". To get an even pattern, lines were chalked onto the surface which were used to align the row of curls. When the first set of lines were completed, another set of lines were chalked on at right angles to the first & the process repeated.

Mostly, though, "frosting" was accomplished with a Biax power tool. This was not the same as the Biax power scraper (my collegues refered to the two types as "The Digger" and "The Froster&quot & when pushed firmly across a surface produced regular half-moon shaped cuts. The same method of chalking lines then chasing those lines was used. Using this tool took quite a lot of brute force & it was not easy to get a regular pattern – varying the rate the tool was pushed over the job varied the size of the half moons. I saw one of these Biax frosters mounted on a planer at Landis Lund grinders to get a really nice, even pattern. I was not strong enough to use one !

As I said initially, I have not seen pull scraping used in the UK . Scraping was only prevalent because surfaces could not be machined accurately enough at the time. My former employer didn't like having to employ skilled fitters because he reckoned that they were only needed because the machinists couldn't do the job he was paying them to do accurately enough.

Now scraping is a bit of a "lost art" because it isn't needed as much – castings can be machined to tighter tolerances & better surface finishes than in the days of planers, so what was once "fitting" is now "assembly".

It does seem, though, that some are treating it some sort of high art form, rather than the widely practiced rather mundane necessity it once was.

Nigel B.

[Bob WorsleyParticipant @bobworsley31976]

To answer Paul, no, I didn't do the scraping.

At the time, near 35 years ago, I had a friend who rebuilt and mended machine tools, he did it. It was on a Hassison L5A, which I still have and use, bought from Rotagrip. It wouldn't turn anything. Undid the few capscrews to remove the top of the saddle, bit of marking blue, front left, under the chuck, side of the saddle Vee ways no blue for 2-3 inches. Scaped the centre of the Vee ways, only contacts at the ends for 2" or so. I think he used a power scraper but only took minutes to get it done, blued and checked. End result was amazing, could turn to a size, repeatedly.

The difference I see between push and pull scraping is that pushing is digging into the metal, pulling isn't. With a 90 degree end, held at 45 degrees then the angle of the scraper to work is the same. Just seems more controllable pulling.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 24/08/2020 14:22:15:

[…]

Whitworth's surface plates were flattened by comparing 3 plates with Engineer's Blue, and methodically removing all the high spots until the 3 plates all aligned perfectly. Not because it was the best or fastest method, but because he didn't have an alternative. Skilled work, very time consuming and expensive, so quickly replaced as far as possible first by planing machines, and then by grinding.

.

Dave

In defence of my Hero … I must object !

Whitworth was a purist:

He understood that three plates are necessary, because any one of them must ‘blue’ with both of the others to demonstrate that its surface is flat [as opposed to being part of any other sphere].

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 25/08/2020 10:03:08:

Posted by SillyOldDuffer on 24/08/2020 14:22:15:

[…]

Whitworth's surface plates were flattened by comparing 3 plates with Engineer's Blue, and methodically removing all the high spots until the 3 plates all aligned perfectly. Not because it was the best or fastest method, but because he didn't have an alternative. Skilled work, very time consuming and expensive, so quickly replaced as far as possible first by planing machines, and then by grinding.

.

Dave

In defence of my Hero … I must object !

Whitworth was a purist:

He understood that three plates are necessary, because any one of them must ‘blue’ with both of the others to demonstrate that its surface is flat [as opposed to being part of any other sphere].

MichaelG.

I agree, Whitworth is my hero too. Far more important than Brunel, who I also rate highly. Whitworth worked out how to make precision flat plates with the technology available at the time, a truly major step forward. Genius. However, his contribution wasn't scraping as the be-all and end-all of making flat surfaces, it's true value was enabling flat surfaces to be produced inexpensively by other technologies. It led to modern machine tools, which in turn opened the door on almost every other technology since. Without ways of making precision flat surfaces, we wouldn't have the Internet.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 25/08/2020 11:13:14:
[…]

However, his contribution wasn't scraping as the be-all and end-all of making flat surfaces, it's true value was enabling flat surfaces to be produced inexpensively by other technologies. […]

.

I can’t disagree, Dave … but I didn’t want readers to miss the significance of the three-plate test.

Whatever method is used to manufacture plates, this remains the best way of checking them for flatness.

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

I see the 'three plate' test often quoted but it's not very relevant in these days of good quality affordable granite plates. They make a more than adequate reference for scraping in other references such as straight edges and smaller iron plates.

[Roger BestParticipant @rogerbest89007]

All this conversation has been about improving the quality of something by careful manual attention. Its still a useful skill, if you want it better than the best machine you have, hand finishing is a good way to go.

[Ex contributorParticipant @mgnbuk]

I see the 'three plate' test often quoted but it's not very relevant in these days of good quality affordable granite plates.

Used to be part of the apprentice training school tasks for trainee machine tool fitters at Asquiths in the '60s.

3 finish planed castings to be scraped together to a prescribed standard. If the instructor though the trainee was trying it on with a heavy application of blue to make them look good, he scraped a deep gouge across all three & sent them back for another go. This was recounted to me by one of the victims, who also said they went home with bleeding hands in the early days. They used scrapers they had forged themselves in the training school, which were then cyanide hardened in the work's heat treatment facility.

After the training task had been successfully completed, the plates were sent back to the machine shop to be finish planed for the next set of victims.

Nigel B.

[Pete RimmerParticipant @peterimmer30576]

Apprentice masters needed something to keep them entertained through the mayhem I suppose 😀

I wonder how much scraping work was required from fresh-planed to finished article?

[Nigel McBurney 1Participant @nigelmcburney1]

Back in the 1950s/60s I worked for a firm who made scientific instruments,one product was spectrometers which need an accurate "slit" of light ,the slits made from nickel silver,had a fixed and sliding jaw to adjust the width of light slit. To get the edges of the jaws absolutely straight the jaws were lapped on a cast iron plate which had been "loaded' with very fine abrasve, to prepare a lapping plate ,tthere were 3 circular plates about 9 inches diameter and fitted with circular hardwood handles, which screwed into blind holes in each plate with a very coarse thread, A steel threaded circular plate was fixed to the bench with wood screws,so you have one lap plate fixed to the bench and one plate with handle screwed on held in your hands ,some abrasive was sprinkled on the lower plate,the top placed placed on the lower plate and the top plate was lapped against the bottom plate with a circular ,cum figure of eight motion,hard work ,until the plates had an even grey colour,then the top plate was removed and the third plate lapped against the bottom one, following a pattern all the plates were lapped against each other in turn and thats when I learned about Whitworths motion. the pairs of light slits were mounted in pairs in a small fixture and then lapped to get straight edges, great care had to be take to avoid "rolling" the fixture resulting in slightly cureved slits.Long time ago now but I think the lapping lubricant was water. On every bench there was a circular surface plate ,Long before I started these plates had been made from iron castings and faced up in the lathe,they were then flattened by the Whitworth lapping motion,as they were surface plates rather than lap plates the abrasive grains in the surface were killed by carefully rubbing the plates with a very fine oilstone.A five year apprenticeship plus a further year was enough of that though it was very good training I went down the road making prototype parts for early automatic typwriters for another pound an hour,lot of money then.

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