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pull scraper
- Thread starter dian
- Start date
- Replies 9
- Views 5,606
Screwmachine
Titanium
- Joined
- Mar 8, 2001
- Location
- Switzerland
http://www.practicalmachinist.com/vb/general/hand-scraping-dixi-jig-mills-186035/
That's a good thread with lots of pull scraping info. I like to just barely kiss the corners so they aren't dead sharp. The face or 'business part' of the scraper is flat, no radius, at least that's how I was taught by the fellow from Dixi.
That's a good thread with lots of pull scraping info. I like to just barely kiss the corners so they aren't dead sharp. The face or 'business part' of the scraper is flat, no radius, at least that's how I was taught by the fellow from Dixi.
Forrest Addy
Diamond
- Joined
- Dec 20, 2000
- Location
- Bremerton WA USA
Don Roberts is my go-to guy for pull scraping lore.
I suggest you tweak the end radius to suit the texture of the scraping job.
Before you tackle the end radius problem take a big flat washer and lay one edge on a flat surface holding it at varying inclinations. Look at the radius of the trough it would plow if it was a scraper.
Think about the scraper's end radius and its geometry in use. The projected radius is a sine function of its angle of inclination. A 3" radius inclined to 20 degrees above the work face has an effective end radius of 8 or 9 inches. A pull scraper end radius is inclined to 70 degrees and the effective radius is nearly equal to the end radius. Therefore the end radii of pull scrapers has to be 2 -3 times larger than a push scraper's to acheive the same results.
I prefer nearly flat end radius for assembly joints, gaging faces, and steam joints and varying degrees of radius depending on the spots per square inch and the depth of the "trough" between cusps or bearing points.
Be careful here: you can get lost in infinite subtleties. I suggest you start with a radius about like the rim of a 3 lb metal (getting scarce) coffee can - about 3" and go from there. The cutting angle of the edge of a push scraper is 15 to 30 degrees to the work face' depending, etc. A pull scraper has the blade angle rotated about 90 degrees and pulled so adjust your scraping geometry accordingly.
Make it the cutting-edge angle tweakable by screw adjustment or bending. Also make the cutting edge feature removable for easy sharpening.
It aint rocket science. Scraping - especially pull scraping - is a personal thing where your preferred scraper design is strongly influenced by your anatomy. What works for the other guy may not work well for yoiu. Fortunately, the time to make a pull scraper is brief and materials not expensive. You will probably do a few iterations of making and trying for a few days before you settle on something that works for you.
But yes, blunt the sharp corners just a little.
I suggest you tweak the end radius to suit the texture of the scraping job.
Before you tackle the end radius problem take a big flat washer and lay one edge on a flat surface holding it at varying inclinations. Look at the radius of the trough it would plow if it was a scraper.
Think about the scraper's end radius and its geometry in use. The projected radius is a sine function of its angle of inclination. A 3" radius inclined to 20 degrees above the work face has an effective end radius of 8 or 9 inches. A pull scraper end radius is inclined to 70 degrees and the effective radius is nearly equal to the end radius. Therefore the end radii of pull scrapers has to be 2 -3 times larger than a push scraper's to acheive the same results.
I prefer nearly flat end radius for assembly joints, gaging faces, and steam joints and varying degrees of radius depending on the spots per square inch and the depth of the "trough" between cusps or bearing points.
Be careful here: you can get lost in infinite subtleties. I suggest you start with a radius about like the rim of a 3 lb metal (getting scarce) coffee can - about 3" and go from there. The cutting angle of the edge of a push scraper is 15 to 30 degrees to the work face' depending, etc. A pull scraper has the blade angle rotated about 90 degrees and pulled so adjust your scraping geometry accordingly.
Make it the cutting-edge angle tweakable by screw adjustment or bending. Also make the cutting edge feature removable for easy sharpening.
It aint rocket science. Scraping - especially pull scraping - is a personal thing where your preferred scraper design is strongly influenced by your anatomy. What works for the other guy may not work well for yoiu. Fortunately, the time to make a pull scraper is brief and materials not expensive. You will probably do a few iterations of making and trying for a few days before you settle on something that works for you.
But yes, blunt the sharp corners just a little.
Last edited:
Tyrone Shoelaces
Diamond
- Joined
- Apr 19, 2006
- Location
- Manchester, England
I worked with a guy from SIP many years ago. He came to the place I was working to re-scrape the cross rail on a SIP jig borer that was starting to bow in the centre of the rail. I was asked to look after him for the week it took to do the job.
The scraper he used was a pull scraper but it didn't look much like the ones in the DIXI photos. He encouraged me to make one like his, I've still got it and I use it from time to time.
It was made from a piece of 3/8" silver steel ( drill rod in the U.S. ? ). The end was beaten out to about 1/2" wide and looked like flat blade screwdriver end. It was hardened and tempered and then bent at about 80 degrees about 3" from the end. The scraper itself was about 14" long in total, it had an ordinary file handle glued on the silver steel. It was sharpened on a standard emery stone. It was pretty easy to make but required pretty regular sharpening.
You just pulled back in a straight line making little squares about 1/4" square. It took me a while to get the hang of it, I was taught to scrape in a half moon type scraping style and I kept wanting to rock the scraper blade. Regards Tyrone
The scraper he used was a pull scraper but it didn't look much like the ones in the DIXI photos. He encouraged me to make one like his, I've still got it and I use it from time to time.
It was made from a piece of 3/8" silver steel ( drill rod in the U.S. ? ). The end was beaten out to about 1/2" wide and looked like flat blade screwdriver end. It was hardened and tempered and then bent at about 80 degrees about 3" from the end. The scraper itself was about 14" long in total, it had an ordinary file handle glued on the silver steel. It was sharpened on a standard emery stone. It was pretty easy to make but required pretty regular sharpening.
You just pulled back in a straight line making little squares about 1/4" square. It took me a while to get the hang of it, I was taught to scrape in a half moon type scraping style and I kept wanting to rock the scraper blade. Regards Tyrone
jCandlish
Titanium
- Joined
- Jun 1, 2011
- Location
- Oberaargau, Swizerland
The particularly cool thing about Screwmachine's pull scraper is its castor angle. That is an important detail.
oldbrock
Hot Rolled
- Joined
- Feb 22, 2008
- Location
- Glade BC, Canada
We used to use a radius pull scraper to rough out large ( 6" to 24" babbit bearings when I was a kid eons ago. We called them tomohawks. Peter
so 70° included angle between blade and work you say? thats what the dixie amd screws scrapers look like.
this guys blade seems to be nearly vertical (1:25, 1:50):
Le grattage à l'épaule - YouTube
i dont want to bother to make an adjustable head, as this is for a little job i plan to do, so i need to get the angle right. (i wont bother whith any radius on it either, just touch off the corners. my blade will be 10 mm wide.
this guys blade seems to be nearly vertical (1:25, 1:50):
Le grattage à l'épaule - YouTube
i dont want to bother to make an adjustable head, as this is for a little job i plan to do, so i need to get the angle right. (i wont bother whith any radius on it either, just touch off the corners. my blade will be 10 mm wide.
Last edited:
Forrest Addy
Diamond
- Joined
- Dec 20, 2000
- Location
- Bremerton WA USA
That's scraping into crevices so naturally your scraping tools have to be designed for the job. You will not be able to use a single tool if you are to scrape in alternalte directions inside a dovetail's interior angle. You will need two scraping tools: one right hand and one left. The ergonomics have to work: the axis of the scraper has to center on the scraping edge otherwise you will have to muscle the tool to keep the correct tilt and that is fatiquing.
I can visualize the tool design but right now I can't verbalize it in simple terms. Trust me, my imaginings are absolutely brilliant and easy to make. If you could only see my sketches you will be smitten with awe and wonder..
Note to self: learn how to post images.
Last edited:
jhruska
Titanium
- Joined
- Jul 5, 2009
- Location
- Munster, In. USA
Forrest,Take and save photos to your computer.
Get an image/photo resizer.
This one is for Win XP and is free from Microsoft/Power Toys
Windows XP downloads - Microsoft Windows
It self installs. Use is right click over a photo. "Resize Pictures" now appears in the drop-down box when you right click.
Choose "Resize Pictures". The 'Small' size is perfect size for P.M.
When replying to P.M.
use:
"Go Advanced"
Scroll down in the new window to "Manage Attachments"
A new screen opens: choose "+ Add Files"
Then "Select Files" this is where 'My Pictures' on your own computer or what ever file the image is stored on is chosen. Then select that resized small photo. For XP its 'My Documents' and then find 'My Pictures' as that folder resides within 'My Documents.'
The file is chosen, then click 'Upload Files.'
Finally 'Insert Online' and that is it.
Here is a sample photo that was resized from a PDF to 61.7 KB
Regards, John
Get an image/photo resizer.
This one is for Win XP and is free from Microsoft/Power Toys
Windows XP downloads - Microsoft Windows
It self installs. Use is right click over a photo. "Resize Pictures" now appears in the drop-down box when you right click.
Choose "Resize Pictures". The 'Small' size is perfect size for P.M.
When replying to P.M.
use:
"Go Advanced"
Scroll down in the new window to "Manage Attachments"
A new screen opens: choose "+ Add Files"
Then "Select Files" this is where 'My Pictures' on your own computer or what ever file the image is stored on is chosen. Then select that resized small photo. For XP its 'My Documents' and then find 'My Pictures' as that folder resides within 'My Documents.'
The file is chosen, then click 'Upload Files.'
Finally 'Insert Online' and that is it.
Here is a sample photo that was resized from a PDF to 61.7 KB
Regards, John
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