more questions about metal

[Noah Wagener]

The Veritas cast iron "stress relieved" lapping plate costs less than a comprable sized piece or raw iron at McmasterCarr. Can someone explain this. The Veritas one has all kinds of channels in it, has been "stress relieved", and made flat. I see prices in the thousands for a single 3 foot bar of iron on some online suppliers. What i am i missing?

Could someone explain what the "cast" in cast iron signifies and is it the same for cast steel. On another thread George said that steal and charcoal sealed in crucibles were cast into ingots. Cast as a verb to me means flung. Only other meanuing i am familiar with is a mould. I am sorry I have to ask here but I could not find this stuff on wikipedia and i trust people here more anyways.

Would mild steel make a suitable substitute as a surface/lapping plate.If so is hot or cold rolled more dimensionally stabel? I want to try and make one using the Whitworth method of matching three planes together thereby insuring they are flat. Seems a handy thing to know how to do. And any future adjusting could be done oneself.

[David Barnett]

Would mild steel make a suitable substitute as a surface/lapping plate.

The short answer—not really. Cast iron, and especially iron which is continually cast, such as in the Meehanite process, has a grain structure absolutely suited to embedding and presenting diamond. Steel, quite simply, does not. The graphite content of cast iron is also an advantage.

Try this thread for more information. Other substrates are mentioned in addition to iron, as I recall:

http://www.sawmillcreek.org/showthre...50#post2065650

[Noah Wagener]

THanks David,

I can't claim to have read that whole thread as it is epically long, Rapunzelesque. Most of it is about diamond lapping compounds which is not what i am looking to do. I am really just looking to make a reference plate that I can put blue on and check where to scrape planes.I am just concerned with what material to use that will shift the least as on machinist forums they have written that even granite must be trued every few years and not all granite is even suitable as a surface plate. Of course they have a lot less tolerance than i would. I was possibly thinking of using one (i would be making 3 as per the Whitworth method) for the initial lapping of blade backs and maybe even scraping out a groove for cambered blades. But my principal concern is with dimensional stability.

I noticed on that thread that your a fellow scraper, you metal me knuckles. The method you recommend to Metold i think involves already having a reference plane. I want to try matching three unknown bars of metal though it looks cheaper to buy actual certified flat lapping plates. Can you explain this discrepancy in price where raw materials cost more than finished plates? I think people would have to have security guards for rebar based on the prices im seeing for iron. This is why i wanted to use mild steel as a local supplier has cutoffs about a foot long for next to nothing. I think it is real mild as it scrapes almost as nicely as plane soles.

Can you give me any advice in scraping? Do you use actual machinist scrapers or the ground file route? I sacrificed a chisel and found it a little better than the file though the length is not adequate. I think i am more abrading than scraping though. It just goes easier when i sharpen the scraper real roughly, like 80 grit giving the blade some teeth. When i hone it like a woodworking tool i dig in and raise burrs and have a generally unpleasant experience.

thanks again

[David Barnett]

I realize I answered only one of your questions but was in a hurry and so answered the easiest—sorry about that.

I am really just looking to make a reference plate that I can put blue on and check where to scrape planes. I am just concerned with what material to use that will shift the least as on machinist forums they have written that even granite must be trued every few years and not all granite is even suitable as a surface plate. ... my principal concern is with dimensional stability.

Regarding dimensional stability, aging and stress-relieving cast iron, solid vs. webbed, and so on, I'm a mere piker compared to machinists and metrologists who haunt such specialized fora, so couldn't offer you anything but speculation. I have been told, however, that granite plate recalibration has much to do with wear and how the surface plate is used (or abused) and that if a granite plate is used for reference alone rather than as a substrate for flattening, woodworkers can expect flatness to be less an issue than for day-in-day-out use by machinists, toolmakers, and so on.

I want to try matching three unknown bars of metal though it looks cheaper to buy actual certified flat lapping plates. Can you explain this discrepancy in price where raw materials cost more than finished plates?

For anyone wishing to produce plates through automatic generation of gages, abrading and scraping three matching workpieces together systematically to cancel aberrations until the workpieces arrive at their limits of accuracy (or an acceptable degree of accuracy), I highly recommend Machine Tool Reconditioning and Applications of Hand Scraping*, by Edward F. Connelly, 533 pages of entirely readable, illustrated information, in which Whitworth's method and just about everything else related to scraping is thoroughly covered. Although this runs near a hundred dollars in reprint, you can usually borrow it through interlibrary loan.

This is why i wanted to use mild steel as a local supplier has cutoffs about a foot long for next to nothing. I think it is real mild as it scrapes almost as nicely as plane soles.

Really, my experience with mild steel was for laps (unsatisfactory), not reference surfaces, so can't speak knowledgeably to that. While I've not made surface plates, I have made steel straightedges using the three-piece method with good success and found the steel easy enough going although nowhere near as pleasant as CI, but that may well say more to my having started scraping my own CI laps after having used the Harris Meehanite laps for years.

Can you give me any advice in scraping? Do you use actual machinist scrapers or the ground file route?

I don't know how useful it would be to you, but I'll try and describe what I do.

I've used both commercially-made and file-steel scrapers and have had variable results with both, although the commercially-made scrapers have been more consistent, probably due to both steel and heat treat.

Early on, I moved to homemade HSS scrapers and have never looked back. I usually sharpen these scrapers on the 80-grit Norton 7" white wheel—sometimes on the 120-grit—on a slow-speed Baldor, but for HSS, faster would work fine. I'll then work it in few circles flat against a lap charged with 1µ diamond and that's it. I do think I add an almost imperceptible bit of extra pressure on the cutting edge, though, but never so much as to be noticeably lifting upwards—at least so it seems to me.

My stroke is probably idiosyncratic but works for me; left hand over the bar just back enough to establish a shallow angle with the fingers slightly curled over the scraper side. The left hand acts like a spring, while the right hand presses in short downward strokes while pushing lightly forward—a light scalloping motion—so light, though, as to be more of a notion than an actuality.

Sometimes I wrap the fingers of my right hand around the handle, wrapped with leather rather than round wood, but mostly I leave my hand open in comfortable and natural pronation. At any rate, it's definitely more a scraping than an abrading stroke but might very well look and sound to observers to be abrasive.

This may or may not make any sense to you, but that's as best as I can describe it.

As to the price of one cast iron blank or finished plate to another, it's a mystery to me, as well.

Hope this helps rather than confuses.


*The first five chapters—

1. The Art of Scraping
2. Professional Requirements
3. Characteristics of Metals
4. Tools
5. The Hand Scraper
6. Manipulating the Scraper

Chapters 21 and 22 respectively cover Frosting Techniques and Automatic Generation of Gages.

[Noah Wagener]

It helps. You seem to be saying the same thing as the only video i could find on the technique: http://www.youtube.com/watch?v=AkYyWcflMy8

do you know what is referred to by "hook" ? What bevel if any do you put on your scraper?

I still can't get over the prices for raw iron. 2 inch thick, square foot plate at K-mac corporation goes for $640.02. I have to misreading this somehow.

[David Barnett]

You seem to be saying the same thing as the only video i could find on the technique: http://www.youtube.com/watch?v=AkYyWcflMy8

Gorbant's right hand position is closer to my own than the first student's (a lefty) but Gorbant does gently grip the entire handle. I tend to leave mine open and more prone, but the built up handle I use—only the top is built up, by the way—is somewhat like Jeff Peachey's bookbinder's paring knives, but thicker at the rear before tapering steadily to the front, which works better for me than round turned handles [the scraper's longer than the parer, of course]. Such a handle puts the thrust and contact point at the heel, protecting the sensitive nerves in the palm, similar to graver handles. My paring chisels also benefit from this handle paradigm.

Do you know what is referred to by "hook" ? What bevel if any do you put on your scraper?

The pulled scraper, or "hooked" scraper uses a different geometry and scraping motion than straight scrapers. It's so named because of the sharp hook at the end. I'm afraid I don't have a picture of this. Both styles of scrapers work well—it's really a matter of preference. Some mix it up, preferring hooked scrapers for final frosting, for example. I have heard some describe a hook across a straight scraper's cutting edge akin to the burr formed on turning tools or bookbinder's French parers, but this is wholly unorthodox to my praxis.

I bevel only about 3° to 5° at most on carbide scrapers, but a cambered 90° grind on HSS allows me to scrape for a few minutes before retouching the edge, giving sufficient bite without digging in. I prefer a camber to simply rounding the corners. Back when I used to a lot more of this than now—it's been awhile—I'd leave the grinder going, something I'd not do if I was using a carbide scraper. A carbide scraper benefits from a slight bevel more than the HSS, by the way, but those need to be ground on diamond.

More importantly is the gentle camber across the front edge, say 4, 5 or maybe even 6". All of these things can be achieved freehand, of course—it's not critical.

I wish I could better describe the scraper, its preparation and maintenance, but it's so better explained and illustrated in the aforementioned Machine Tool Reconditioning, I can't begin to approach it.

I still can't get over the prices for raw iron. 2 inch thick, square foot plate at K-mac corporation goes for $640.02. I have to misreading this somehow.

I shouldn't think iron need be anywhere so thick as 2" for a 12" x 12" plate. Granite is one thing, iron quite another. Cast iron in that thickness places high demands on pour technique, slow cooling to control stresses, ensure grain homogeneity and crystal orientation, and so on, and would intuitively seem to be much more expensive than webbed plates left to season before surfacing.

[Jessica Pierce-LaRose]

For anyone wishing to produce plates through automatic generation of gages, abrading and scraping three matching workpieces together systematically to cancel aberrations until the workpieces arrive at their limits of accuracy (or an acceptable degree of accuracy), I highly recommend Machine Tool Reconditioning and Applications of Hand Scraping*, by Edward F. Connelly, 533 pages of entirely readable, illustrated information, in which Whitworth's method and just about everything else related to scraping is thoroughly covered. Although this runs near a hundred dollars in reprint, you can usually borrow it through interlibrary loan.

FWIW, if you search at Scribd.com under Edward F. Connelly, the book David references is the first hit for a PDF version. I don't know if you need a payed membership to download the PDF, but you can read online for free. Scribd actually has a fair amount of older books, and is kind of a neat place to look for these things. (They have Whelans wooden plane book, for instance)

[Trevor Walsh]

For your material prices, it all boils down to supplier, McMaster is an expensive place to get certain things, you are paying for a reliable supplier that in my experience is one of the best in the business.

If you want a surface plate for scraping, and for spotting plane soles, I'd buy one. For granite the size and grade you'd need woodcraft can supply for under $100. If the goal is generating your own plates, I'd look into someone in the machining world who could supply rough castings to machine and scrape. I'd think that any cast iron you are likely to find is going to need a heat treat to release the stresses, and another after the rough machining.

[David Barnett]

FWIW...

I'd say it's worth a lot, Joshua, as I see it finally went out-of-print—apparently Machine Tool Publications has no plans to reprint it. Good find. Thanks! Now that Lindsay's Learning the Lost Art of Hand Scraping is down to a few remaining copies, it's about the only game in town.

Also, for those who enjoy reading from original sources, Sir Joseph Whitworth's On Plane Metallic Surfaces and the proper mode of preparing them, from his Papers on Mechanical Subjects, is available through Google, et al.

https://play.google.com/store/books/...AAAQAAJ&rdot=1

[Noah Wagener]

THanks for the tips,

David, Gorbants talks about a "hook" on the actual work service i think. He says you'll be struggling scratching up the piece and then all of a sudden you'll have a "pattern; a beautiful hook..." I don not think i'll get there though. I can not get the hang of it. I either dig in or skate over the surface.

I did read the Whitworth essay. He recommends using an old file sharpened on a "Turkish" stone. I think that was emery. So i can not blame my lack of proper carbide or HSS (high speed steel?).

Thanks for the info on the online version of the Connelly work Joshua. I'll look into it.

Trevor, would hand scraping and filing be the same as rough machining and a plate would need to be heat treated afterwards? People on a machinist forum say cold is good for "stress relieving" iron. The Woodcraft plate is only $40. I just wanted to be able to produce one on my own hoping i then would be able to maintain it myself.

David, how thick would you recommend an iron lapping/surface plate to be. My Bailey plane looks like it is about 1/4" and feels like it flexes. Someone is selling 1/4" angle iron on Craig's list. Would that be thick enough? Could it laminated to 1/2"? If so with what?

thanks