Scraper Questions

[John K Jordan]

One other advantage of the negative rake scraper is it applies almost no force against the wood so you get less chatter than you do with a regular scraper. This is especially true on thin platters with wings such as natural edge bowls. I used to think that holding a scraper handle up high was the same thing as a negative rake scraper if they both had the same included angle to the edge. It's not. My older tear drop scrapers were ground about 75 degrees. So flipping them over does produce a negative rake but it still works like holding a handle high on a regular scraper. Sharpening a scraper to a more acute angle like 45 degrees and giving it a negative rake on top is a much more controllable tool and leaves a fantastic finish.

I think holding the handle high is equivalent to the NRS in the geometry of the edge relative to the wood (if the included angle of the tool is identical) but not in the presentation and the amount of control you get by holding the tool horizontal and flat against the rest. With the handle high and the edge down it seems the wood would more easily deflect the tool downwards and not make as even a surface.

Funny thing about these scrapers today - yesterday I read from a woodturning book written by F.Pain in 1957. The guy showed how he ground curved edge scrapers with profiles that look very much "Rudy Lopez's" grind - Pain ground them from old files with a sloped top similar to negative rake scrapers but he doesn't call them that. He said they worked better with this grind but didn't attribute it to the grind angle but to the idea that he was grinding down into softer steel in the middle of the file. He raised a burr with a hardened rod.

Another thing he recommended 61 years ago - "Small flexible hand card scrapers shaped with a curved end are extremely useful for troublesome places." Hey, I like that idea.

JKJ

[Reed Gray]

Best explanation for why a standard scraper doesn't work like a NRS, and it seems to make sense, is when you hold the handle high like that you get a 'trailing cut', which would be like taking a card scraper and tipping it to 45 degrees or so instead of say maybe 80 degrees. The burr is turned too far over and works more like a rake than a cutting edge. I have applied that thought to my shear scraping too. So you start by rubbing the bevel without it cutting, and then roll it slightly past the bevel rubbing cut. It does seem to cut more cleanly.

Tool steel..... that could mean a lot of things... I did find out with the bimetal blades from Lennox that the teeth are M42 HSS.... Maybe we should find out if the M42 is available in 1/8 inch thickness.... Think the guy in the video was using that scraper on some rosewood....

robo hippy

[Kyle Iwamoto]

Kyle, I read your post again, and I think I misunderstood the first time - I thought you might be trying to cut what would otherwise be the bottom surface and the obtuse angle on the ground bevel.

JKJ

Thanks for the info! I was cutting with the top sharp surface, although handle level and "upside down". Did try sheer also, not working well..... Just trying to find a "cheap" alternative to regrinding and repurposing a high dollar scraper...... I use my skews as NRS.

Oh, I remember your cabinet scraper post from a while ago, and I've been using them. Not on the lathe though. I do know they cut skin much faster than wood...... DAMHIKT.

[Ralph Lindberg]

Sharpening scrapers "up-side down", Dave (D-Way tools) and Jimmy Allen (Boxmaster Tools) are both big fans of sharpening scrappers upside down.
Besides conventional scrapers Dave has negative rake ones, largely due to Jimmy and another local (Scott) encouraging him
Jimmy's tools are (I think) exclusively NRS.
(for those not in the Seattle are, Jimmy is well known for his box work. Dave encouraged Jimmy to develop his own tools to do boxes with, so he did. The "plan" is for Dave and Jimmy to have adjoining booths at the Oregon Symposium)

[Reed Gray]

Oh no!!! Not more tools..... If Jimmy wants to demo box turning, he is welcome to play on the lathe in my booth.... I do have a bunch of dried box blanks...

robo hippy

[JohnC Lucas]

I wish i could be a that symposium. I just checked and didn't win the lottery so guess I'll stay on this side of the Mississippi for a while.

[John Keeton]

I should have been more explicit - my post was in reference to that of John Lucas.

[John K Jordan]

I should have been more explicit - my post was in reference to that of John Lucas.

Ok, nevermind, then! The handy "qoute" feature can minimize ambiguity.

BTW, I didn't make it to the Knoxville club meeting last week so Ii don't know what tilted/offset platters were shown. The May newsletter should be out soon, I think.

JKJ

[John K Jordan]

... I would be willing to bet that a carbide burnisher would turn a burr on it...

Reed, I tried using a carbide burnishing rod on one of the 1/8" thick StewMac scrapers a few minutes ago. It certainly did raise a burr, even with light pressure. That's not surprising since it does with 10v steel.

I'm running on 10% today and wasn't able to test it on wood but I'll try to in a few days. Perhaps using them with a burnished burr would work better for woodturners than luthiers. Or at least get extended use from them with each sharpening.

JKJ

[Randy Heinemann]

Thanks for the replies. For a beginner like me, there is more information here than I can assimilate and use. I did buy a 1" Sorby round scraper and was able to sharpen it fairly well on my Tormek. I will work on refining the sharpening once I use it and find out how well it works. I've briefly tested it and it seems to work as intended. I'm sure that technique figures in to the final result as it does with all turning.

I was interested in the honing responses, though. The instructor who taught me some basics does hone his scraper with a flexible diamond hone and it does appear to yield a smoother surface than mine did when I tested it last night. Again, it's probably, to some degree, technique.

From the responses, it appears that scrapers are meant to be used with the tool rest at about middle of the piece and angled down at least slightly. Or maybe a little below center with the tool level? Is that correct?

[John K Jordan]

From the responses, it appears that scrapers are meant to be used with the tool rest at about middle of the piece and angled down at least slightly. Or maybe a little below center with the tool level? Is that correct?

Randy,

A "conventional" scraper, that ground with a bottom bevel only and flat on the top, is indeed held against the tool rest about in the middle of the work and angled down slightly (handle held up). Just where "about" in the middle depends on a few things. On the inside of the side of a bowl, for example, it is better for the tool to contact the wood a little above center. That way if the wood grabs the tool it is forced downward into air. If held below center, if the tool is grabbed a bit it will be forced down into even more wood and the resulting catch might be notable. The opposite for the outside of a bowl. For the inside or bottom of a bowl or platter I usually touch the scraper to the wood about on the center line or a little lower.

You might sometime try grinding a scraper with an upper and lower bevel to make it a negative rake scraper. These are easier to use, held horizontal and flat on the rest and simple pushed gently towards the wood and drawn along the surface. It can make very fine shavings to remove tool marks and is almost impossible to catch. I can't remember if it was mentioned in this thread but some people have ground most of their scrapers with a negative rake - I've done that too and rarely use conventional scrapers any more.

JKJ

[Thomas Wilson80]

Is there a good video how to grind a NRS from a regular scraper? Or is it just as simple as flipping it upside and grinding it the same way but at a different angle?
thanks,
Tom

[Reed Gray]

Honed scrapers.... Never considered a scraper and scraping cut as a finish cut on side grain/bowl oriented wood as a finish cut tool till I saw Nick Stagg of the Salem, OR club demo it on a lamp base. Hone off both the top and bevel of the scraper. So, I had to try it, and I found out it does work nicely on hard and dry woods like sugar maple, but no way for some thing like soft maple, or pine, or alder.

As for a NRS, the first ones were skew chisels where you didn't hone off the burr, angles of 25/25 or 30/30. There are lots of variations. Most of the ones from standard scrapers are more in the range of 20 to 30 on the top, and more blunt on the bottom. I think I said up above some where that I am liking the 30/45 to 30/60, but with a burnished burr rather than the grinder burr. I am also starting to prefer a 1/4 round nose profile. which is great for bowl work. Many other applications. Yea, I do really need to figure them out and post a video on them.

robo hippy

[John K Jordan]

Is there a good video how to grind a NRS from a regular scraper? Or is it just as simple as flipping it upside and grinding it the same way but at a different angle?
thanks,
Tom

Thomas,

I don't usually follow videos so I don't know. I posted this photo earlier of my favorite NRS ground from Thompson scrapers and a Thompson skew:

scrapers_neg_rake.jpg

Grinding these was in fact exactly flipping them upside down and grinding the same way.

However, I grind these with the same angle on the top and bottom just like several well known turners I've seen. Using the same angle gives some advantages. One, I can leave the grinder tool rest at one setting to grind both sides of all three. Two, making the same bevel on the top and bottom lets you flip the scraper over and use it with the curve in the other direction by putting a burr on the other side. I actually keep two of these as "left hand" and one as "right" and mark them so I know which is which without feeling for the burr.

The included angle on these is about 55-60 degrees, or about 30 or so on each side. A "sharper" (smaller) angle will cut better but the edge will not last as long. (no surprise there!) A blunter angle will not remove material as well but is capable of making a smoother surface on some materials.

I grind these in a bit different profile from what some turners use - I've seen them with a curve at the tip but I like the curve transitioning into a flat at the tip. This lets me use use the flat on mostly flat wings of pieces and more easily smooth other flat areas.

Most of my other NRS are one-sided and have a smaller angle on the top than the bottom. These little scrapers (also posted earlier) are ground from Thompson steel with a rather blunt included angle. They work extremely well in end grain on hard, fine-grained wood on things like box lids. I on many woods I get a glass-like surface that needs no sanding.

scrapers_small_thompson.jpg

BTW, I use all the scrapers shown here with no handles, even with not-so-small bowls and platters. As finishing tools there are no downward forces such as you might get from using a conventional scraper to remove wood. I do have sturdy handles on my box scrapers and other negative rake scrapers where the extension over the rest is larger.

JKJ

[Thomas Wilson80]

Thanks for the replies - my regular scraper seems to be kind of grabby lately and I've been toying with the idea of turning it into a NRS but didn't know the technicalities (angle, etc). Now I think I have enough info to play around. Thx