Thread: is scraping done in turning?

Japanese woodturners use hand-held scraper 'shims'.

Some European crafts, such as mold makers, still use something similar.
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I have used thin scrapers on bowls, which tend to chatter at lathe speed. The scraper lathe tool is used to smooth after the bowl gouge.

For example see: Serious Scrapers - Wood Turning Scrapers

Right off the grinder there is a little burr just like on the burnished hand scraper and it works the same way when the scraper is used in the trailing position.

The weight of the handled scraper and being held on the tool rest keeps it from chattering.

My favorite scraper is made from a high speed steel planer blade, 10mm thick X 50mm wide X 300mm long. It is heavy enough to not bounce around.

I grind it upside down at about an 80 degree angle, which gives me a nice burr. I run over the whole bowl with this, resharpening as soon as I stop getting shavings, then go over the bowl again, this time honing off the burr with 220 grit paper on a flat surface.

The last pass is a very light touch, making very thin shavings. With hard wood I can start sanding with 180 or 220.

Lathe speeds seem to fast for scraping using the bur. It disappears very fast. Some turners here use extremely steep angled scrapers and get very fine shavings. Also sheer scraping works well. (There is a thread about it here somewhere. )

I often use a curved cabinet scraper to help finish the middle of bowls and platters,

With the lathe stopped !

Phil

I have a homemade HSS curved scraper I use in a trailing mode on the lathe at low speed, mainly for final clean up on bowls.

thanks for the replies folks. I think I will have an experiment with it myself as I liked the theory of it but never given it a crack.

Originally Posted by Paul39

I have used thin scrapers on bowls, which tend to chatter at lathe speed. The scraper lathe tool is used to smooth after the bowl gouge.

For example see: Serious Scrapers - Wood Turning Scrapers

I believe the OP was asking about cabinet scrapers, not conventional woodturning chisel scrapers.

Something like these:
http://www.mikestools.com/images/products/520-5510a.gif

Originally Posted by sjm

I believe the OP was asking about cabinet scrapers, not conventional woodturning chisel scrapers.

Something like these:
http://www.mikestools.com/images/products/520-5510a.gif

My reference to thin scrapers above should more properly have been "curved cabinet scrapers" like the one in the middle in the above referenced photo.

I use the thick scraper in the trailing position, the angle being determined by the production of a thin shaving.

The burr does get worn off rather quickly, usually one pass across the inside or outside of a bowl. When turning, my grinder at the foot of the lathe is always running, when the sharpness of the scraper is diminished, a step to the grinder, a 2 second swipe, and back to scraping.

The 1725 rpm 8 inch grinder is set up with 2 120 grit wheels, platform on one side for scrapers & parting tools, and bowl gouge jig on the other. Roughing and spindle gouges I do free hand. The accursed skew is touched up on 220 grit sandpaper on a piece of MDF.

Originally Posted by Paul39

The burr does get worn off rather quickly, usually one pass across the inside or outside of a bowl. When turning, my grinder at the foot of the lathe is always running, when the sharpness of the scraper is diminished, a step to the grinder, a 2 second swipe, and back to scraping.

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Raising a burr on the grinder is quick, but it is also fragile. Raising a burr/hook by burnishing is slower but the burr will last longer. In the end the overall time required by both methods comes out to about the same, so you settle on your preferred method.

My preferences is to maintain the burr with a fine diamond card used in such a way that it partly burnishes and hones at the same time. That way I don't have to leave the lathe so frequently.

Polishing the face of the scraper to a mirror finish is critical for whatever method you use.
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you are absolutely correct SJM thats what I was refering to. But its all good I learnt some more info I wasnt expecting about the burring.

While I do use card scrapers on my flat work, I don't use them on turnings. Main reason, after considerable experimenting is that there is nothing that I can do with a card scraper that can't be done with a bowl scraper, and the bowl scraper had a big handle on it. If you want to use a card scraper, they work best at very slow speeds, or with the lathe off.

A good burr can be gotten off the grinding wheel. I have CBN wheels which go give a better burr than conventional grinding wheels. Actually pushing the scraper into the wheel as opposed to just kissing the bevel on the wheel makes the burr stronger (note here, I do hone off the old burr on a flat 220 grit diamond plate, top side of the scraper on the hone). A burnished burr works a little bit better and is a slightly finer edge. I seem to get the best burrs if I use a triangle burnisher rather than the round burnishers. It doesn't take a lot or pressure, a few light passes with the burnisher 90 degrees to the top. There is also a fancy one available from one of the catalogs which screws down to your work bench. I have tried the honed burr, and haven't found them to be worth the effort. When making finish cuts with a scraper, I have it on edge at a 45 or higher degree angle. I do round over my scraper edges to make this easier.

robo hippy

Originally Posted by robo hippy

When making finish cuts with a scraper, I have it on edge at a 45 or higher degree angle. I do round over my scraper edges to make this easier.

Robo hippy - am I right in thinking that it is the scraper bar side edges that you 'round over' to allow for better control when tilted up at 45deg as well as smoother maneuvering of the scraper over the tool rest when at that angle?
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PS - I found when I was experimenting with various methods of burr raising (reported here) that there is a correlation between the level of polish on the face of the scraper and the durability of the burr. The higher the polish the more durable the burr. But, with all things, we each find our own time-effort-benefit sweet spot with such things. Honing the scraper face up to #12000, as I did, may be an interesting thing to do as an experiment but totally impractical as a working method...

PPS - it occurs to me that a firm push of the scraper against a CBN or diamond wheel is going to have both an abrading and burnishing action on the formation of the burr. The plastic deformation associated with burnishing hardens the surface and generates compressive residual stresses in the burr that will make it more resilient.
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I do round over the side bar, and I believe a lot of skew chisels come this way. Mostly it makes it easier to hold up on its edge and slide across the tool rest.

I don't know all the metal scientific factors in creating burrs, and it has been so long since I have used conventional grinding wheels that I can't remember what those burrs were like. I do know you can overburnish (taking too many passes, and/or pushing way too hard) the edge in turning a burr so that it is like a wave that has crested and fallen over as in the burr turns too far over, and that makes it almost worthless. A few light passes is all it takes. It does take more time to resharpen the scraper face when you take it to the grinder again. Not sure if the CBN wheels kind of burnish the burr or not, but the raising of that burr yields a cutting edge that is as durable as any cutting edge I have gotten on a gouge.

robo hippy