Pull scraper angles?

Luke Rickert · Sep 4, 2020

I am trying to add a little pull scraping for those times and situations where it makes sense. I built an adjustable head scraper today but an having trouble dialing in the angle of the cutting edges. I will make some flexible scrapers even I get the geometry figured out.
For normal hard cast iron push scraping I use between 7 and 5 degrees negative. Is there an equivalent rule of thumb for pull geometry.

TGTool · Sep 4, 2020

The angle of the cutting edge to the work in push scraping is the sum of the negative angle on the blade face, PLUS the angle of scraper to the work. That might come out to more like 25 - 35 degrees negative. Pull scraping doesn't have the same muscle behind it, so it seems like it could benefit from being less negative. I've done a little but not enough to generalize on a target angle. Drawing conclusions from my experience is also muddied by the actual pull scrapers I've got to use. I made them so they're just my best guess for configuration. One problem I have is not keeping the blade/scraper square to the stroke gouges on one side or the other. It seemed like adjusting to a more negative angle (one is adjustable) enhanced the caster effect to try to hold it more square. That's also affected by the length of the vertical holder so it's juggling several variables at once.

I'd also be very interested to hear from scrapers with pull scraping experience about what to look for or how to set up the best conditions. Don Roberts I think has some good experience and is an occasional contributor here though I can't remember his screen name right off the top.

thermite · Sep 5, 2020

whidbey said:
I am trying to add a little pull scraping for those times and situations where it makes sense. I built an adjustable head scraper today but an having trouble dialing in the angle of the cutting edges. I will make some flexible scrapers even I get the geometry figured out.
For normal hard cast iron push scraping I use between 7 and 5 degrees negative. Is there an equivalent rule of thumb for pull geometry.
View attachment 298484

Contact Peter in London. He made up a batch to his own design. Might even have one to sell.

I have one. NICE item! VERY!

Most especially for a weakening, but 65 lbs lesser-mass oldster who no longer has "belly putsch" muscles a la "Da King!!!

TrueBor · Sep 5, 2020

TGTool said:
The angle of the cutting edge to the work in push scraping is the sum of the negative angle on the blade face, PLUS the angle of scraper to the work. That might come out to more like 25 - 35 degrees negative. Pull scraping doesn't have the same muscle behind it, so it seems like it could benefit from being less negative. I've done a little but not enough to generalize on a target angle. Drawing conclusions from my experience is also muddied by the actual pull scrapers I've got to use. I made them so they're just my best guess for configuration. One problem I have is not keeping the blade/scraper square to the stroke gouges on one side or the other. It seemed like adjusting to a more negative angle (one is adjustable) enhanced the caster effect to try to hold it more square. That's also affected by the length of the vertical holder so it's juggling several variables at once.

I'd also be very interested to hear from scrapers with pull scraping experience about what to look for or how to set up the best conditions. Don Roberts I think has some good experience and is an occasional contributor here though I can't remember his screen name right off the top.

I pull scraped for five decades. More than two and a haf in new new production. The rest in refurbishing. There is no rule. You make your angles to your height, shoulder, knees and eye sight. You stay as negative as you feel comfortable for the time you spend on work, strength etc. If you are not enough negative you defeat the advantages to pull scraping. The blade does not stay square to work because you do not sharpen the right way.

Luke Rickert · Sep 5, 2020

The rule is there is no rule

I guess more actually there are too many variables for there to be a rule. It is nice to hear from a professional at least.

There is very little information on pull scraping available in English and from what I can find in German. Does anyone know of any books etc on the topic?

I am getting a little better, as mentioned the sharpening is very critical. I have been using carbide which I lap and it cuts quite well but I think the edge is fragile so I might as well use HSS which is easier to work with.

thermite · Sep 6, 2020

whidbey said:
The rule is there is no rule I guess more actually there are too many variables for there to be a rule. It is nice to hear from a professional at least.

There is very little information on pull scraping available in English and from what I can find in German. Does anyone know of any books etc on the topic?

I was taught it - and "carding" - by a Schwabian who had learnt it at Daimler. Around 1900 and a bit, was a master of it War One and right after.

Not sure Herr Pelz was even a full five feet tall?

IF here are books, they might have been written in countries where the "Mechanics" as they called themselves in that era were sharp of mind, but physically SMALL men. The bigger, stronger guys were blacksmiths, farriers, farmers, miners, teamsters/draymen, stevedores, masons, sawyers, and Ironworkers!

Machine-tools were already recognized as "force multipliers" where brain counted more than brawn. Fine fits were still "new technology", needed finesse and smarts, not a "BFH" and hand-forged HCS chisels.

The reason for "pull" becomes apparent when you have tried both "push" and "pull" and recognize that they had large areas to cover by HAND and had to remain mentally alert and muscle repetition sharp a full ten sweaty hours in, paced as if to music, not be worn-out and making mistakes.

Carbide will pay-off. Stick with it.

Yah just need to develop the auto-muscle finesse to the cyclic touch to not "impact" that edge, each stroke.

Marcuschrist · Sep 7, 2020

I have very little experience pull scraping and don't have anything of real substance to add, The only Pull scrapers I own are forged from what I would guess to be O1 tool steel or something similar and even after touching them up with the accufinish I never had a lot of a luck with them. I have always just ended up finding a way to make Push scraping work in awkward slideways. However Pull scraping was recently bought up in the verktøymaskinklubben group on facebook and Edvind Wold posted these pictures of his Pull scrapers so I thought I should add them here as an example of what a real pro pull scraper uses.

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Luke Rickert · Sep 7, 2020

Marcuschrist said:
... However Pull scraping was recently bought up in the verktøymaskinklubben group on facebook and Edvind Wold posted these pictures of his Pull scrapers so I thought I should add them here as an example of what a real pro pull scraper uses.

Yep that was me asking the question in the Norwegian group

I have found more information in German and French forums. There isn't a huge amount of info anywhere but the English world seems to be dominated by push scraping.

I will share my findings and geometry as I figure things out.

Luke

thermite · Sep 7, 2020

MANY thanks for those fotos, Marcus!

Luke,

As is apparent, the design Peter in London sent me has a shorter, stiffer, spring section to it than the one on the left. In practice, "it depends" on where one grips Edvind's one, so I'd expect it has a wider range of optimal application.

Peter's also "reaches" from arching OVER, rather than from under.

And therein may lie another contributor to preference, either way.

- Push scraping, hand OR power assisted, the working edge and its position is always in the scraper's direct line of sight, never obscured.

- Pull scraping the working edge and its position is nearly ALWAYS obscured, very little of it even as visually useful for estimating the set-down start of stroke location. More reliance on "feel". More trained hand-eye finesse required?

Even so, Edvind's designs both have fair-decent indication off the visible part of their blade holding components as to where the edge will be.

One must learn to work off that.

2CW

Bill

dian · Sep 8, 2020

i seem to be using 70°/110° negative.

Luke Rickert · Sep 8, 2020

dian said:
i seem to be using 70°/110° negative.

Thank you Dian

How do those angles correspond to the diagram I have attached. Are you saying your cutting angle (Beta) is around 70 and the bend is 110? The text says the cutting angle is less than 90 degrees anyway. I found it on the Zerspanungsbude forum.

I have decided to finish my grinder with the Biax and then get back to pull scrapers, they show just enough promise that I keep messing with them but I can't get it to work well enough to actually use on the grinder or gages.

I think one reason I am having mixed results is that I don't have the correct stone to sharpen the scrapers, I had a carbide blade that was working quite well as I could lap it on a diamond disk (flat on the workbench) but my whetstone for the HSS isn't very large and I am having trouble maintaining the angle. I thought about making an attachment for my wet grinder (for woodworking tools) but that should be unnecessary.

thanks for all the input everyone, while pull scrapers might be more complicated than push I don't think it is impossible to figure out in a reasonably systematic way to go about it.

TGTool · Sep 8, 2020

My technical German isn't good so I've missed some of the points they make in the text. Just intuitively I'd think that delta, the angle from the work surface is the most important in determining the a action of the blade against the work. Or gamma back from 90 degrees if it's easier to think in negative cutter terms. Beta would establish a clearance on the cutting edge so if it were 90 degrees you could never get a cut with zero or a positive tool approach. 130 - 140 degrees suggests a reasonable angle for the handle in normal use. I've seen photos of scrapers holding a handle almost parallel to the work face which would develop the most negative cutting angle and maybe? the most pressure on the tool. The shoulder scraper looks like it would be easiest on arm muscles over time, but the vertical position might also limit the down pressure that could be easily applied.

This is all just thinking out loud, but if there are good tips in the text for us language Luddites I'd appreciate hearing them.

dian · Sep 9, 2020

angles from surface. (why make it complicated?) also you dont need any relief.

Luke Rickert · Sep 9, 2020

dian said:
angles from surface. (why make it complicated?) also you dont need any relief.

I am making it complicated as I can't get pull scraping to work reliably

TGTool · Sep 9, 2020

dian said:
angles from surface. (why make it complicated?) also you dont need any relief.

I think too that angle from work surface is most important. You technically do need relief in order to cut but if tool end angle is 90 degrees and angle from work is 80 degrees there's 10 of relief by definition.

dian · Sep 9, 2020

complicated: i was referring to the drawing. germans are specialist at it. i have no idea what all those angles are.

i find pull scraping easier, it needs less skills. of course you need a sharp egde, especially on some cast irons. my scraper has a head simply attached with a m10 bolt that can be rotated. a flexible handle is important.

Luke Rickert · Sep 9, 2020

The more I work with pull scraping the more I think it really comes down to sharpening, the flat edge is even more sensitive to sharpness than a radiused push scraper.

Does anyone have a recommendation for stones we can get in Europe. (Norton isn't as common)

dgfoster · Sep 11, 2020

whidbey said:
The more I work with pull scraping the more I think it really comes down to sharpening, the flat edge is even more sensitive to sharpness than a radiused push scraper.

Does anyone have a recommendation for stones we can get in Europe. (Norton isn't as common)

It sounds like you are asking for finishing stone recommendations. Rather than suggest a particular stone, I would suggest using diamond paste on an aluminum or iron lap with the lap resting on a bench top. The plate I use is only about 1x4 inches and 1/4” thick. I have used 1 micron and 5 micron paste on alternate sides of the lap to get a mirror polished sharpened edge on push and pull scrapers. I have used a “drag-from-the-edge” technique and a “parallel to-to-the-edge” technique to determine sharpening stroke direction. For a dead flat edge I like the pull technique. For a convex edge I hold the scraper nearly vertical less the selected degrees of sharpening angle and more or less hold the handle still with one hand and use the other hand to draw the edge toward you. A tiny bit of paste goes a long way. I roll or press it into the lap with a small bearing or just a random flattish piece of bar.

A mechanical device would be more convenient and faster, but there is no reason an equally sharp edge can’t be made with just a little patience. I am surprised how rapidly the diamond paste cuts.

Denis

Luke Rickert · Sep 11, 2020

That sounds like lapping is worth a try , I use diamond paste on a iron disk for my push scrapers and it works great (5 micron) I have some sectons old iron I can try out to lap the pull scrapers.

Luke

dian · Sep 11, 2020

i use cheap diamond disks mounted to a bench grinder. 300-3000 grit.

Pull scraper angles?

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