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T Wise
03-08-2003, 08:14 PM
Like a lot of people out here I'm new to this whole scraping thing and look forward to hearing any words of wisdom from some of our more experienced scraping masters.
With that in mind, I think I finally figured the geometry of the scraping tool and I now am getting decent results(for a beginner) I thought I'd throw what my interpretation is onto this board and take it in the chin if I'm completely off base. I am using an Anderson Scraper with carbide inserts.
Step 1, grind a radius on end, 3".
Step 2 using a 600grit diamond stone hone the radiused edge as well as both flats.
Step 3 hone a 15deg bevel along the radiused edge, both sides.
Step 4 incline insert 15 deg and hone the flat sides.
Step 5 after all is done repeat steps 2-4 using 1200 grit diamond hone.
After reading and re-reading the connelly book and sharpening the tool I think that this is what they meant by it all. If I'm off base please advise.

As for scraping techniques I've tried the push methods as described in the book with fair results, but today I tried a method briefly described in the Moore book, "foundations of Mechanical accuracy" and they used a semi circular motion that produces crescent shaped marks, rather pleasant looking. I guess I was wondering if any others out there have used this method, and if you could describe how it's done properly?

Thanks in advance for all your help

Tim

Oso
03-09-2003, 01:00 AM
Are you grinding a 3" radius on the end?

I tried one about like that, but I was not pleased with the width of the scrape marks. I got too narrow for roughing, seemed like it was very much a pin-point tool. But since I am self-taught, and haven't done much scraping, I could easily be wrong.

How big a scrape mark do you get with your scraper doing the regular scrape technique?

jr45acp
03-09-2003, 07:45 AM
Oso, let me jump in for a minute. I made my scraper out of a file. As for the radius, an old German tool and die maker said to grind the radius using the curvature of a 10 inch circle as a reference. so far, it seems to work.

------------------
John B

T Wise
03-09-2003, 08:26 AM
That's right, 3", I was getting pin-point results as well until I honed step 4. lay tool flat, incline heel 10-15 degrees and hone the edge, you will get a "D" shaped edge.(on the edge against the work) The first time I tried it on my previouse attempts it just plowed off the high spots, leaving a nice smooth surface, still have to spot for high spots, but I got a much more controlled scrape. As for the radius I think that for pin pointing they use about a 1.5"rad on the tool. I haven't gotten there in my attempts yet.

Still learning

Tim

Oso
03-10-2003, 01:59 AM
Well, that all makes sense. I went with Forrest Addy, who has scraped a lot of stuff, he said radius like a 1 lb coffee can.
I must not be very good, cuz I'm with you guys, didn't like that shape, I like the .25 meter radius idea better. I had a nother scraper tool which is a short piece of tool steel in a handle. That has a very wide radius, and it worked a lot better for me.

Oh, and since Enco finked on me, I made mine from a file also. Seems to work, other than the radius issue.

Thrud
03-11-2003, 01:38 AM
Oso:
Enco finked on you? Wassup?

Ragarsed Raglan
03-11-2003, 03:00 PM
Anyone tried a flat end with an involute like radius form on the edges ...so that as the scraper is 'rolled' back an forth you get a fine feather edge with a thick crescent in the centre? Eclipse sell a steel flat scraper with a similar ground end to this, which I found was very similar to the scraper I was given by a retiree back in the '60's ~ he passed it on with the words along the lines of " Here son 'ave this an' see if ya can git scrapes like that in the next 40 years" ... Sadly I have to admit I can't, but they are almost as nice!

RR

Thrud
03-12-2003, 02:40 AM
RR

I have good new for you me lad! Dapra makes a Biax light duty power scraper that does crescent flaking. http://www.dapra.com/html/biax.htm

Great for those of us who are too old to learn any more cuz our brains are full. And you would not want to "push" something out of our brains - we might forget how to eat or fart or something - I seen one guy explode from that once. Not a pretty sight. http://bbs.homeshopmachinist.net//biggrin.gif

Ragarsed Raglan
03-12-2003, 12:59 PM
Thrud,

That was the ending to a '70's Art House French B film called 'The Big Blow out' wasn't it? An every day story of French Bourgeoisie who took to their scoffing weekend with enthusiasm. One swollen individual died on the terrace with excreta pouring out of his shirt cuffs and trouser legs, another passed on (and upwards!)when the Kharzi had a blow back whilst she was enthroned; in fact everything one would wish on 'Monsewer Chirac' at this time!

The old guy who gave me his scrapper managed a letter 's' - with the centre section the crescent shape, the tails being superfine feathers. I only occasionaly manage to do this, more through luck than judgement. My normal scrapes being effective rather than decorative!

RR

Forrest Addy
03-12-2003, 01:58 PM
Don't worry about the fancy stuff when scraping. Worry about getting the bearing and working clean.

Flaking (or frosting) is of dubious importance. Here's something I wrote some time ago on the subject.
---- ---- ---- ---- ---- ---- ---- ---- ----

Here's one of the best kept secrets of the machine tool rebuilding racket: that pretty frosting pattern so much admired on exposed hand scraped ways is strictly for appearance and it works against the owner shortening the life of the machine.

I've heard old hands sincerely speak in glowing terms of a "proper frosting job" as though it was both the crowning glory of a machine's appearance and a conscienciously applied means of retraining oil and reducing friction. Given a free hand a master scraper would apply an artistic scraping pattern to all exposed bare metal surfaces mush as a prideful bosun's mate applies fancy ropework to all quarterdeck fittings and appurtinances.

The master surface plates at Hunter's Point Shop 31 scraping bench had a handsome logos scraped in the center of their reference faces and the logos and all had near perfect bearing.

I've seen case haedened machine tool purchaser of vast experience be so takes with a beautifully frosted way surface they completely ignore the hazard it represents to machine tool longevity. They admire its glistening irredescent surface, run their hands over it'shypnotic indentations and breathe "It takes a master srraping hand to do this>"

I think BS, I used to do that by the acre with a Biax half moon power scraper and the brilliance of the scraping came from lapping the scraping edge with 9 micron diamond compound to a mirror finish. You can cover up a multitude of machine discrepancies with pretty frosting. It's eyecatching and beautiflu. It's also the used machine tool sales equivalent of putting a banana in the rear axle of a used car to silence failing gears.

Most machine tools feature way wipers either of felt or sophisticated molder rubber designed to exclude grit and chips plus retain oil at the ended of the ways. Frosting doen with a heavy hand may go as deep as 0.002 below the scraped surface and if done for maximum effect the frosted depressions are abrupt intersections ideally configured to trap dirt.

I'm a firm believer of frosting as much as 5% of the area in any fully housed way bearings as a means of lubricant retention and reduceing "stiction" but never in ways intended to be exposed to chipflow or airborne dust. There the ways should remain scraped smooth so the way wipers can better conform to the surface, excluding dirt and retaining oil. When the hand scraping pattern fades from the exposed ways in a few years, it's time for a re-scrape.

My suggestion to MDM is to consider my above remarks with his application.

Push frosting is easy to describe but it requires a great deal of practice if a good appearance is desired. You select a sharp scraper with only a little crown, apply the edge firmly to the work, and give the heel of the scraper handle a sharp bump eoght with the heel of the hand or a rubber mallet. Ideally the frosted depressions should be oriented alternately 90 degrees and be near perfect squares.

Acvocates of hand frosting frequently make a "mushroom" consisting of a knurled aluminum handle of normal proportions having a 1 3/4 dia mushroom knob on the heel. There is a #1 Morse internal taper in the business end designed to take the welded on shanks of a selection of frosting scrapers having end radii suited for each of a variety of frosting paterns.

Masters of the skill can produce a perfect checker board in alternating bearing points where the frosting is of uniform size and its orientation is in alternating direction. If done correctly any percentage of original bearing can be attained.

For half moon frosting, imagine the mushroom end of the scraper handle as a clock dial. The tool is used by gently striking the clock dial with a soft rubber maul or the heel of the hand. A right hander firmly grasps the scraper by the snak of the blade (not the handle) and applies it to the work with the left edge held firmly down. He strikes the mushroom at about 4 o'clock with a repeated slightly down handed blows. A series of half moons progress with each blow. The blows have to be absolutely consistant in force and direction.

Oso
03-12-2003, 02:12 PM
So what about the radius of a regular scraper tool?

Radius 3", 10", 3" modified?

What's best width and radius for

large surfaces, say 6" wide?

medium surfaces, say 2 or 3"?

small surfaces, V way sides maybe 1/2 to 1"?

For initial truing to get a basic bearing, not finishing.

[This message has been edited by Oso (edited 03-13-2003).]

Thrud
03-13-2003, 03:32 AM
RR
Sounds like it would have been very pretty. Many great scrapers have their own "hallharks" that others can tell their work by. You just want to sign your initials - don't you! http://bbs.homeshopmachinist.net//biggrin.gif

Oso
AS you learn to scrape you will pick the tools that work best for your abilities and techniques. As Forrest says a mirror honed edge is essential to proper scraping.

What is important is the appropriate number of bearing points per inch for the application at hand.

Oso
03-13-2003, 09:43 AM
Thrud:
refer to thread on old codgers.....

People have been scraping for longer than any of us have been alive. Therefore, some things are known to work best, and I for one, don't need to re-invent 250 plus years of precision scraping knowledge.

So If what is known to work best doesn't work for me, I am probably wrong. I don't like being wrong, it wastes time and makes fun fade away.

So, I ask the rest of you codgers for advice on where this codger ought to start out. When I have 50 years of scraping behind me, I will be able to make a more informed decision for myself...........

Ragarsed Raglan
03-13-2003, 12:08 PM
Thrud,

Yep!.....
Let me know when someone can do an M! One's gotta leave their mark in this world one way or another! I like looking for the carpenters marks on medieval oak beamed buildings. There's a particularly neat one in the Gents bog in my local pub!!!!

RR

T Wise
03-15-2003, 09:59 PM
here's what I dug up from a biax flyer,
regarding tip radius

5 1/2" radius, area prep, roughing, up to 8 bearing spots. Cut width approx .275
3 1/2" radius, 8-18 bearing spots. Cut width approx .236
2 3/8" radius, 18-26 bearing spots. Cut width approx .196
1 9/16" radius, 26-32 bearing spots. Cut width approx .157
3/4" radius, 32-40 bearing spots. Cut width approx .120

Don't get me wrong, I don't get these results yet, but if my cutter is getting close to these results I can't be too far off base. That power scraper seems like a good idea, but for now I'll have to be content with the arm-strong method. Thanks for all your input

Tim

Oso
03-16-2003, 02:05 AM
Excellent, thank you.

Mind, I am not getting those results either, and I wonder if the Biax may hold the tool at an angle other than what we do.

I had a 3" radius, and got barely an eighth width of scrape, no matter what I did with the angle.

Loafer
04-23-2003, 06:52 AM
Have you tried internal bearing scraping, have you any tips?

I am trying to fit some bronze bushes to a 7/8" bearing rod, but its been plated and is now slightly larger than the internal diameter of the bush.

Thanks