Want to get into Hand scraping

[BillH]

Well, I searched the archives, and it appears I missed out on a great group buy on that book about reconditioning machine tools.
For those of you who bought the book, and done some hand scraping, can you post some pics of your work? It is a skill I really want to learn.
Now I understand it is for getting surfaces really flat. So how about the checkering that was done on south bend lathes, and some bridgeports? Is that another type of scraping? Or is that the natural look of scrape marks?
I have an urge to scrape some steel plate, perhaps one day use it to restore lathe beds.

[Rustybolt]

Here, it's call flaking and other than appearance it holds oil. There is a way to hold the scraper that produces that effect. I havent done all that much of it myself.

[Thrud]

Bill

A surface can be scraped flat, but for bearing surfaces like lathe beds you want a "pebbled" surface - so to speak with equally spaced high and low spots - the number per square inch would be dependent on the quality of the work. In effect, we want a controlled roughness so the two bearing surfaces do not experience "stiction" (almost a vacuum welding effect similar to the "wringing" of gauge blocks) to one another. Hard drive makers found this out the hard way, machine builders have known it for a hundred years.

Granite flats naturally have air pockets around the hard quartz particles where the softer material breaks off during the grinding operations and leaves a slight depression around the "Quartz island" - this is why flat surfaces do not stick to granite flats.

The "frosting" on ways you speak of can be as scraped or it can be quite artistic to the point where a particular design is a tradmark of a particular man's work. The Half-moon crescent design is done with a certain model Dapra power scraper - any idiot can do it. These frosting designs are purely decorative and serve no useful function - but some sure are beautiful!

If you want to try it yourself, practise on some cast iron angle plates - they are cheap and easy to come by. Buy the Connolly book and get started.

[BillH]

I wonder how deep those crescent marks are, they sure are a neat guage to determine wear.

[Thrud]

Bill

Pardon the pun, but "they barely scrape the surface" (ha, ha)

[SGW]

I like Thrud's idea of practicing on a cheap cast iron angle plate. The angle plates made in India may actually be useful for something after all, and you can turn them into a worthwhile product.

The Machine Tool Reconditioning book may not be the best place to start; for one thing, it's pretty expensive. Lindsay Publications has, I think, some relatively inexpensive reprints of how to do scraping that might be a better source of basic information.

Quick course:
Basically, all you need is a reference surface plate, a tube of Dykem Hi-Spot Blue or equivalent, and an old file ground to a large radius on the end, square to the top and bottom faces of the file, for your scraping tool. Smear a THIN film of blueing on the surface to be scraped, place it on the surface plate, move it back and forth an inch or two a couple of time, lift up, and you should see some bright spots where the blueing got rubbed off. Take your scraper and scrape those down, smear the blueing back over those spots, and repeat. And repeat. And repeat. Etc.

[mochinist]

I don't know much about scraping myself but the older guys I work with do it for a living. I was told by them that the crescent shape that they put in, is done for the lubrication. I guess the ways can hold a little more oil. I have watched them scrape and put in the crescent shapes many times and it is truely an amazing thing to see.

[beckley23]

Thrud's suggestion about practicing on an angle plate is excellent.
By all means obtain a copy of Connelly's "Machine Tool Reconditioning", it is the cheapest tool you will buy, for value recieved.
The way to treat the angle plate is to; apply marking medium to the surface plate, place the surface to be spotted on the plate and move 1 or 2 strokes about 1/2" back and forth in straight line, take it off, scrape the blued spots, clean and debur, respread the marking medium on the surface plate, repeat the foregoing procedure, and so on until the surface is scraped in. The proper procedures are discussed at great length in MTR.
Harry Bloom

[daryl bane]

If you can BORROW a copy of the Michael Morgan
Scraping Video, it will really set you on the right path.I never rec'd my order,so I can't recommend buying from him, but it's a good
instructional. I have found a good Sandvik or
Dapra carbide scraper is the way to go, and
learn to sharpen with a diamond wheel. Find a real scraping hand and see if he will give you
a lesson or two. And lastly practice, practice,
practice.

[BillH]

Thank you guys for all the advice, when I get a chance, I will do these things, perhaps sooner than I thought.
You know, I bet the airport screeners would not like a hand scraper!
Im on the road at the moment, this hotel actually has high speed internet hookup in each room.

[T Wise]

I received my goods from Mike and I can say it fills in the gaps nicely if you are just learning the scraping trade. He has a new web site under new management, looking for people with outstanding orders to contact them. It looks like he's still committed to cleaning up the mess of the past couple of years.

Tim

[Ragarsed Raglan]

Bill,

First thing to get is a decent scraper. I can thoroughly recommend the Sandvik carbide inserted tip scraper. It will cut just about any hardness material and keeps its 'edge' well. Infact it is probably too sharp 'as received' as it will cut too much material if you 'go to it' on Cast Iron. I also have an 'Eclipse' proprietary scraper which is a carbon steel tool and is good for most light work.

My favourite scraper is one I was given when an apprentice by one of the 'old hands' as he was retiring (it was made in house by the machine tool company I worked for) - the tip is what was referred to as 'magic steel' (I suspect a high speed [with cobalt] steel, something along the lines of M42 grade) I can do nice crescent patterns with this tool, but not so good with the others!

As has been said ~ practice makes perfect, but also a range of scraper forms needs to be tried to find one which suits your style.
Don't try to make pretty cresents straight off, that is just decorative. The important aspect of scraping is to get a flat surface with spot heights in the 15-20per square inch region, a beginners target should be around single numbers. As you practice so the accuracy will develop. Eventually you'll be putting 'crescents' on all sorts of bits of metal, my daughter even has here light switch in her bedroom adorned with an aluminium surrond which is bevelled (on the mill) and finish scraped! My vice is 'Tattoed' with scrape marks all over!!

RR

[Forrest Addy]

Scraping can be back breaking work. Unless you're young and fit and have a strong back you'll wish you were long before the scraping job is done.

The tools are simple and not that expensive. A $40 import granite flat (glass will not work - no texture), a couple of good second cut 12" square files with handles, a 2" - 3" long stencil or rubber ink roller from the art supply store, some old mill files ground to make scrapers, a bench grinder and an oil stone - plus a $4 tube of Prussian blue from the auto parts store. Oh yes, plenty of rags and hand cleaner. Also have on hand a shop vac with an old hose to pick up the scrapings and filings.

First an important message. Prussian blue is a pigmented transfer medium. Be aware of your fingers when they are smudged with Prussian blue. You will have visible evidence of their progress between initial smudge and realization all over your shop. One smudge on your finger will transfer to the light switch, your shirt, your nose, your ear, the back of SWMBO's silk blouse when you smooch her "thank you" you for the coffee she fetched. Wherever there's a smudge is another transfer-to-finger waiting to happen. Prussion blue is communicable like the plague.

The granite flat (Many call them "granite surface plates" but to me a surface plate is cast iron and made to be portable. Somehow I can't get past my training: to me the granite gizmo that does the same thing as a cast iron surface plate is called a flat.) is available from Enco Mfg. 1-800-873-3626 or www.use-enco.com. Their Model 640-120 for $39.96 12" x 18" flat may seem largish for a small shop but it's long enough diagonally to rework most small machine tool slides with a minimum of overhang. A little overhang properly addressed poses no problem to final flatness. You can get import granite flats for about the same price from most any catalog site serving machine shops. MSC, Travers, etc. 10" and up mill smooth flat files are the best starting point for home-made scrapers. Any junky old thrift store file will work. Dust off the worst of the teeth with an angle sander and provide it with a handle.

Advance to the bench grinder. Holding the file at a 5 degree (roughly) angle to plane of rotation and using the side of the wheel, remove the teeth for 5/8" back from the tip. Then grind an arc on the end of the scraper using the wheel periphery. The arc should be about the same as the rim of a 3 lb coffee can. Stone both surfaces smooth but leave a sharp intersection. You've made what amounts to a chisel with a 95 degree included angle on the edge.

There are superb store bought carbide scrapers on the market. I suggest the hand scraper sold by the Dapra corporation (http://www.dapra.com/html/biax.htm) but they are expensive ($90 to $150 depending). The home shop typically doesn't have diamond sharpening equipment. If you know a rock hound having lapidary equipment consider him a scraper sharpening resource. A keen carbide scraper outlasts carbon steel about 100 to 1 (I'd almost swear). If you can fit a carbide scraper in your budget and you have several projects to justify it, I'd reccomend the purchase.

Here's a flat statement: you absolutely cannot satisfactorily sharpen a carbide scraper on a green silicon carbide wheel. The edge micro-chips and the effects of the crumbled edge will show in the ugly appearance of the scraped surface and the sweat dripping from your brows and elbows. Only diamond abrasives work well on carbide.

Carbide stones remarkably easy on those flat diamond plated stones such as those made by DMT and Norton.

Carbon steel doesn't last long scraping. It will dull rapidly. Resign yourself to touching up the edge every few minutes.

The first step is to stone the work surface prior to scraping removing all bumps and dings. Scraping and and stoning is a task involving all the senses and lends itself to a Zen-like contemplation.

Apply a few 1/8" dabs of blue on the plate and spread them with the ink roller. Vacuum clean the casting and wipe it down. Work cleanliness anywhere near the blued flat is absolutely vital. Apply the work to the flat. Be careful you don't rock the work on the flat. You can scrape a perfect convex if your're careless when taking a "print".

There will be a few smudges of blue on the work. Scrape only the blue. Refresh the blue with the roller. Take another print and scrape some more. Scrape crossways to the first strokes. Proceed for up to several evenings until the work shows a scatter of blue patches all over. Sooner or later you'll discover just how hard to scrape (don't rub the scraper on the work, make it cut) and just where.

As work progresses the transferred blue will fade. You'll need to roll out more dots of blue to the flat every now and then. How much is a judgment call. Gain the skill.

Cleanliness is important. a single filing chip or piece of lint will screw up a blue reading (called a "print"). Get a foot switch for the shop vac. If you see flecks of metal stuck in the blue, wipe the flat clean and re-blue. Use the shop vac and keep the scraping area clean. I've seen scraping benches that looked like a coal cellar. The work produced there was poor and expensive. Clean is cheap.

Proceed with the scraper. Practice a little on scrap cast iron until you can predictably make little flaky chips and nice parallel scrape marks. You'll soon learn to tip the scraper this way and that to catch blue spots not quite in line and to relax the downward force so the scraper's edge glides across low metal without cutting. You'll also learn to consciously relax your shoulders and neck. The little short controlled movements required for scraping force you to oppose one muscle group with another muscle group. Persist and your whole shoulder girdle and lower back will become one big knot you'll have to stew your bones and muscles loose in the hot tub.

It does no good to rub the blue off with the scraper. You have to apply enough force and effort to remove metal. The skill is acquired through practice. Make chips and study them through a 10X loupe. They should look like miniature cornflakes. When old timers hand scraped for stock removal the powdery cast iron fountained 3" above the scraper but we're looking for control just now.

After scraping, lightly stone the scraped surface with lighter fluid (evaporates quickly, has a low latent heat, and helps keep the stone free from clogging) to remove any raised burrs. Clean the stone with a rag and lighter fluid as you go. Let it evaporate and give the scraped work another rub on the refreshed blue. Scrape some more from another direction. I like to scrape from two or three directions; each in rotation.

A Norton made, 2" x 5" fine India stone is an invaluable aid. Also handy are triangular and square slip stones. Regular bench stones are poorly adapted for scraping - they're frangible and leave abrasive behind.

When new India stones are too sharp. Condition one side by rubbing it on 220 wet or dry. Be sure to clean it with soap and water and a nail brush. Tramp abrasive is worse than scraping crumbs.

Some of you may be alarmed at using flammible stuff like lighter fluid as a cleaning agent. I can only say it's the best solvent I've found for hand scraping. It's flammibility is balanced by its other properties mentioned above plus the stuff I prefer, "Ronsonal" in the yellow bottles, has little propensity to rust cast iron.

There's a time element as well. Lighter fluid evaporates in seconds and while doing so doesn't carry away much heat from the work. It's a major time-saver. Lacquer thinner is harsh on the hands and has a higher latent heat. Plan on waiting up to 30 minutes for mineral spirits paint thinner to evaporate and an hour for real Stoddard solvent. Flammibility isn't a real issue in my shop. I don't smoke, I'm careful with rags, and my scraping area is well ventillated.

Water based cleaners like 409 work surperbly but they have a high latent heat of evaporation. They cool the work causing it to go concave - meaning as you work you'll scrape more than necessary off the edges of the work. I once used a water based machine cleaner while scraping a 60" precision straight edge. Worked great!!! But: the next morning the straightedge had reached thermal equalibrium. My first check against the master flat showed the straight edge turned 0.0006" convex over-night. It was the cooling effect of the water based cleaner that did it. If you don't think water based cleaner won't have an effect on the scraping of a little old machine slide, try it and report back.

Proceed with scraping until all the file marks disappear and you get 4 spots per square inch - more if the work is small. If you're careful with heat input at the final stages, and you scrape with a keen edged scraper, final flatness will be equal to the granite flat you're using. A small import flat is typically in the 0.0002" to 0.0003 range of a geometric plane per square foot.

I wouldn't suggest you stone out the all scraper marks when done. For one thing there a belief that the slightly interrupted surface results in lower working friction. I believe this to be true but I have no numbers to support it except a maybe little less sweat. For another thing, a hand scraped surface is a bragging point and a handsome feature in its own right.

Precision scraping is a skill best learned under the guidance of a mentor but a crafty individual can discover most of the tricks for himself after getting a push in the right direction.

Some remarks on frosting or flaking. 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 with about as much practical benefit.

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 hardened machine tool purchasers of vast experience be so taken 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 its hypnotic 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 beautiful. 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 molded rubber designed to exclude grit and chips plus retain oil at the ended of the ways. Frosting done with a heavy hand may go as deep as 0.002 below the scraped surface and if done for maximum effect the frosted depressions have abrupt intersections with the scraped surface 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.

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 with 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 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.

You have to experiment. Individual anatomy has a pronounced effect. I have a muashroom handle and some odds and ends of frosting scraper. While I've acquired the knack many time I have to re-learn it if a few years intervene frosting jobs. It's a skiil that has to be maintianed through frequent practice.

[This message has been edited by Forrest Addy (edited 04-29-2004).]

[Ragarsed Raglan]

Forrest,

You should write a book!

That's a very accurate description of scraping, I like the warnings of the dangers of Prussian Blue!

I did mean to add to my earlier response that there was a surface treatment aspect of scraping that becomes apparent when a finger is run over a freshly scraped surface. The silkyness of scraped cast iron is apparent even against fine milled, or planed finish.

RR

[Evan]

Forest,

I think you just wrote an article. Excellent.