Cast Iron Surface Plate Constuction

I was writing an answer to one of the other threads and thought we needed a new thread so more folks can read this info. The other thread asked if they could use a wood working machine table as a master plate. Here is what I wrote.

"As one of the guys said...for practice scraping you can use it, but trying to use it as a master NO WAY! A waste of time as there are no supports under it and it will bend and sag to what ever it is used on."

Reminds me of a story I have told on here a few times before. 35 years ago (or so) at Midwestern Machinery Company in Minneapolis they hired a fellow named Bill Tracy who was a top engineer and service tech who worked for Fellows Machine for several years. He came to Midwestern originally to help their men to scrape and calibrate Fellows gear testers. They eventually hired him as an employee. He was a chain smoker and developed a bad cough and died of lung cancer. He was a pain in the butt type of guy but really knew his stuff. I contracted scraping for them back then in the rebuild floor, but never worked with him as he trained a couple of their men to scrape the lead checkers and testers.

Well after he died those 2 guys he trained quit, one started up his own company and the other went to work for Honeywell. So Midwestern hired another guy who had worked for Fellows after they closed the doors. Midwestern had ran want ad's in Springfield VT the birthplace of Fellow. This guy told them he worked with Bill Tracy so they hired him as Bills replacement. They asked me to work with this guy to rebuild the lead checkers.

Well to make the story short and getting back to the plates...He had them make up a wood pattern and cast a "dummy" that is a special straight-edge that has both flat & V cast into the "dummy" so you blue and scrape both ways at the same time. The dummy is calibrated in the lab before the job and no need to check the machine ways with a tester like a King-Way and straight edge.

It was about 3" thick X 30" long and 12" wide and was cast with shallow ribbing in the bottom and had 3 point legs at the far extreme corners. 2 on one end and one in the middle of the other end.

I told that guy and Midwestern management that I felt the plate was weak and would bend. This guy, I forgot his name, but we could call him "That Guy". That Guy insisted I was wrong and seeing he worked for Fellows they had me scrape it to 40 PPI and .00005" flatness and parallel when it was setting upright on it's 3 points. It looked and was super in that position. I used a 36" Camelback straight-ege and a King-Way to test it. He also had me use a dowel pin in the V and a gage block on he flats measuring off a granite table to make it parallel to the 3 points in both long and width directions. This was something I also questioned, but did it as I was being paid by the hour and That Guy was the leader of the Fellows Dept. at Midwestern. He could not scrape, That Guy told everyone he was in the Test lab at Fellows and never scraped.

We started to scrape the ways of a 24 M lead tester using the Dummy. I used it as he watched me scrape the ways. It definitely was fast using it to scrape the Flat and V ways all at the same time. After we were done scraping the lead testers ways to 40 PPI we started to match fit the Tail stock of the tester to the base ways. But when we indicated the quill of the Tail-stock with my Best Test .0001" indicator it would change .002" when we reversed directions when we pushed it in and out when we were trying to make the quill parallel and pointing a little up in front to the base ways (rocking chair). He would scratch his head and said my indicator was bad.

He had them buy a brand new Inter-Rapid and set it up and again we got the same reading. LOL.. He was beside himself...The management came back and finally looked and asked me what I thought was going on. I told them the Dummy plate was bending and the Fellows Base was high in the middle. I then took the same 36" camelback and set on the Fellows Base and hinged it and it was super high in the middle. The dummy would follow the contour of the base and we could not "hinge" the Dummy we never knew it was getting high in the middle (rocking chair). They looked at That Guy and fired him on the spot. Poor Ba__tard had moved out from Springfield VT but he got what he deserved as after that Midwestern did some investigating and he had lied about what he did for Fellows, he had worked in the shipping and receiving dept. and not the calibration lab. They figured he had seen the scraper hands using the dummy and tried to design it from memory, not understanding the ribs or spine of the Dummy had to be designed deep and thin to support the plate when flipped over. That Dummy ended up in the dumpster and I went back to the old way or 36" camel back and King-Way.

So the moral of the story is thin plates not designed to be surface plates when flipped over that don't have high webbing and lots of it will bend. The wood working cast iron table designed to slide wood over it will bend and will not work as a master. Next time you see a old fashion cast iron surface plate look inside the bottom and if it has a lot of webbing, it can be flipped over, but if it does not have webbing and 3 points it was designed as a bench plate to sand on and not be used as a master plate. Rich
PS: Good CI plates are heavy as heck too...

Thanks, Richard. I've been trying to wrap my head around what is needed to test and lap a surface plate. I have watched videos of people using cast iron lapping plates and I was wondering what kind of ribbing they have between the two lapping surfaces?

Hello, my name is Brian and I'm a toolaholic

Rich,
I worked with Frank Kline for a year at Stintson Honeywell
nice guy but we had no lead checkers in the company.
He did give me some good advice.
It looks you had a dummy plate designed by a dummy, In Moore's Book he shows what masters should look like.

I gotta go along with Rich much as it pains me to agree with him on anything (you listening Rich?)

We still have gravity and even cast iron sags from its weight. My way of thinking suggests everyday shop scraping tooling like straight edges and surface plates should be proportioned so the depth of the webbing and stiffening is 1/6 or greater of the length.

I would call the general class of the fitted plate Rich described as "full fitted scraping tooling" where all scraped features are present as a negative of the production parts to be referenced from it. Here I'd suggest a length to stiffening depth of 4 to because of the mass of the face. The necessary face thickness of such a plate may involve undulations measured in inches making it a weighty appliance indeed. Considerable longitudinal and triangulated lateral stiffening would be required if it was to stay within tolerance regardless of its orientation in space.

The naif would think the more iron the better. Not so. The minimum material properly distributed to enhance stiffness is the design goal within the practical limits of a working foundry and a tooling budget. Thus scraped references are webbed and triangulated instead of boxed and celled. Looking at illustrations in Moore's "Fundamentals of Mechanical Accuracy" their master reference plates looked to me 1/3 the depth of their length of the reference surface. Nice, but we lesser mortals inevitably have to compromise.

Those of you who may be tempted to design their own surface plates and straightedges look carefully at similar tooling made generations ago and draw inspiration from them. Remember everything is (from a deflection and gravitational sense) made of rubber.

Well I don't suppose I should mind entering the world of BOHICA again so I'll ask:
IF one wished to make a straight edge, let's say 36"X3-4", and had the proper size surface plate to scrape it to. Could one not use something like an old CI piece from an old tractor or maybe even some other old (seasoned??? ) CI piece of proper dimensions?
I see CI parts so quite often buried in the ground or covered in weeds etc. What would make these finds bad candidates?
I know I'll catch feces for asking but I really don't care. I am brand new for sure. Even still I don't see why a straight edge has to originate from a purpose casted camelback or whatever other straight edge "styles" there are?

Galaxy S4, Slimkat
If I wasn't married I'd quit fishing

I don't come here to debate or guess. If someone wants to answer such silly questions, go ahead. I was hoping we could keep this thread clean from silly questions as that. I started this new thread to discuss professional scraping tools and not junk science. As someone said, Challenger maybe you should go to another forum and have fun. Charles our Moderator in his sticky's above made it clear we want to share information to teach rebuilding equipment and not farm equipment. Forrest gave us his professional knowledge, just what I was looking for.

Please tell me how this is a silly question.???
I know you have a problem with me but the question I asked isn't a silly one. It's a legitimate question. I honestly thought you would be the first to substantiate the question alternative sources for straight edge "raw materials". That's no lie. I'd have bet money, Richard, that you would have given potential alternative sources for a "to be scraped" (or machined and scraped? ) straight edge.
Maybe some clarification is needed.
Many old pieces of farm equipment use a sort of "I" beam front axle made from thick, heavy cast iron. I've learned from you, and others here and elsewhere, that a straight edge cannot be some light weight, thin, rigid etc. It has to be able to be constructed so it will not deflect (sag) or bend, twist, etc while being used for it's intended use. If I am. Missing other qualities a straight edge needs to be deemed the right tool for the right job please inform.
My question wasn't to light up,your thread and I'm not trying to illegitimize the value of this thread because it is valuable information that you are providing in it.
You yourself gave a long, and enjoyable imo, story about an example of what NOT to do when making a proper scraping tool WITH an explanation of why the casting was doomed from inception.
Are you saying, then, the only thing that could become a precision Straight edge is a casting produced solely for the purpose of becoming a straight edge?


Galaxy S4, Slimkat
If I wasn't married I'd quit fishing

There are many recipes for " cast iron" so you will never know if that old cast iron part you are trying to use is suitable for a precession measuring tool.

Also just because it is old and "seasoned" is not really a good reason to use it... There is a thread here on PM that references a study on the stability of cast iron that shows aging does not help at all. Only proper heat treating increases the stability of cast iron.

I will post a picture of my cast iron surface plate in an hour.. Maybe seeing one will help you..


Sent from my SM-N900V using Tapatalk

If you want a reference for scraping the most important quality it needs to have is to be dimensionally stable. This quality is best met by two materials cast iron and granite. Granite for its wearing properties and cast iron because it can be easily worked in the shop. When you go get a piece of mystery metal (like a tractor front axle which by the way is a drop forging)your failing before you even start. As I said in another post if money is that tight you need to find something else to do. Like every other hobby or line of work there is a price of admission it's partial knowledge and partial an investment in tools. The other thing is when you come on here with a bunch of guys that have spent their lives in various types of shops and suggest some of these asinine pieces of metal you're just making yourself look stupid. And lastly if you or anybody else is going to scrape machine tools for geometric accuracy you have to display a certain level of craftsmanship. You can't be some kind hack that gets his tools from the junk pile.

Rich,

If you could pick three books that your scraping students would read and absorb, what would they be?

Pictures of a good cast iron surface plate. Notice the webbing that supports all areas of the thick plate..








Scraping is not rocket science but it does require good tools, good work habits and stable references. Without those you will be forever frustrated because you are now working with .0001 of an inch measurements and that is very difficult.

Challenger, just buy an import surface plate from grizzly, shars, or woodcraft and use it. Get the best grade you can afford, 12x18 is fine. A tube of permatex blue or oil paint will suffice as dye for now.

Use a HSS parting blade and a simple holder to use as a scraper until you can rig up carbide sharpening stuff. I can tell you that HSS works just fine, but needs a touch-up every pass or so.

Watch scraping class videos on YouTube or attend one! Lots you can learn from forums and videos.

We often tease Richard about writing a book, but in reality he ha's already written one. It's scattered all over in hundreds of different threads; you just have to find them.

Once you can get a part reasonably flat, then you can invest in carbide, better spotting dies, a better plate, and good measuring tools. Until then, make chips.

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carlquib said:

Thanks, Richard. I've been trying to wrap my head around what is needed to test and lap a surface plate. I have watched videos of people using cast iron lapping plates and I was wondering what kind of ribbing they have between the two lapping surfaces?

Hello, my name is Brian and I'm a toolaholic

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Brian, It depends on what size ad what you want to use them for?

Spencer in NH said:

Rich,

If you could pick three books that your scraping students would read and absorb, what would they be?

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I bring to the classes 3 books for the students to look at. Machine Tool Reconditioning by Edward Connelly, Testing Machine Tools by George Sleshinger and The Foundations of Mechanical Accuracy by Melcom Moore. (spelling might be a bit off, sorry) Rich

I'll comment for Challenger regarding straight edges. He'll likely come to the same conclusions others have but it just takes some time to converge on the good answers and know why the other suggestions go no where.

Rich and Forrest have both commented on proportion in order to have enough stiffness to be useful. If you find a piece of cast iron, consider whether it can be tall enough for the length you want, or conversely, given its height one direction, how long (or short) must it be to avoid sagging and introducing inaccuracies. (Read Rich's story) It's entirely possible you could find a piece that can be cut and be sufficient but the odds are slim. The front axle mentioned, ignoring the fact that it's a forging for the moment, would only be 2-1/2" to 3" tall so couldn't be a good straightedge longer than about one foot and likely less.

Then there's the issue of weight. This is a tool that you're slinging around regularly and if it's really heavy you'll wear yourself out fairly quickly. Forrest mentioned the issue of not just "more iron" but iron used judiciously. Think about and look carefully at the camel back straight edges by Brown & Sharp and others. They're proportioned to be tall for their length but the sections aren't very thick. I've got two straightedges from different sources, one 24" and one 36". As it happens, the shorter one weighs more.

If you're serious about finding junkyard material for a straightedge, try looking for some place that has old mining equipment or big industrial stuff. I'm imagining a large gear reducer that has ribbing on it. So now all you need to do is cut up the casting to include one long rib for the base and then you can cut the curve of the camel back out of the part around it. A Sawzall with a couple packages of blades should do it. Then think about drilling some lightening holes like you see in the photos. You probably don't have annular cutters big enough, so think about using the boring head to whittle them out to size. An angle grinder will help smooth things out and you'll want a fairly good mill or planer job cutting into the rib to make the surface you'll subsequently scrape.

To be honest, it sounds to me like a bitch of a lot of work and a less than 100 percent chance of success, but have at it yourself. If you'll take some pictures as you go along it would make an interesting discussion thread.

Richard King said:

Brian, It depends on what size ad what you want to use them for?

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I would eventually like to use them to lap my surface plates. The plates I would like to lap range in size from 3' x 4' to my smallest which is 6" x 12". All the plates I have are used, so I have no idea what kind of shape they are in. I would like to eventually get an autocolimator and a repeat-o-meter so I can check them myself.

Hello, my name is Brian and I'm a toolaholic!

TGTool said:

If you're serious about finding junkyard material for a straightedge, try looking for some place that has old mining equipment or big industrial stuff. I'm imagining a large gear reducer that has ribbing on it. So now all you need to do is cut up the casting to include one long rib for the base and then you can cut the curve of the camel back out of the part around it. A Sawzall with a couple packages of blades should do it. Then think about drilling some lightening holes like you see in the photos. You probably don't have annular cutters big enough, so think about using the boring head to whittle them out to size. An angle grinder will help smooth things out and you'll want a fairly good mill or planer job cutting into the rib to make the surface you'll subsequently scrape.

To be honest, it sounds to me like a bitch of a lot of work and a less than 100 percent chance of success, but have at it yourself. If you'll take some pictures as you go along it would make an interesting discussion thread.

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After you cut that rib out of a big gear case or cut the spoke out of a gear and drag it back to your shop and start to mill a bunch of it away you are going to find it's full of voids. The unfortunate truth is all castings have voids. On something like a straight edge casting the designer and foundry man are going to take great pains to minimize them but even on the most well made castings a void appears on the final cut now and again.

Why is it that all hobbiest are fatally cheap. You can buy a piece of Dura-Bar to make a 24" straight edge for about $100.00 with shipping. You will be starting with a piece of material of known quality that you can make into a tool that you will use the rest of your life.

carlquib said:

I would eventually like to use them to lap my surface plates. The plates I would like to lap range in size from 3' x 4' to my smallest which is 6" x 12". All the plates I have are used, so I have no idea what kind of shape they are in. I would like to eventually get an autocolimator and a repeat-o-meter so I can check them myself.

Hello, my name is Brian and I'm a toolaholic!

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Simple way to check plates. How to determine if your surface plate is out of tolerance. - YouTube
Good video on laping the plates Surface Plate Calibration and Conditioning - YouTube

I have watched both of those videos and they are very good. Basically what I got from them is I have a long way to go to get a good handle on this fine meteorology stuff.

Hello, my name is Brian and I'm a toolaholic

carlquib said:

I would eventually like to use them to lap my surface plates. The plates I would like to lap range in size from 3' x 4' to my smallest which is 6" x 12". All the plates I have are used, so I have no idea what kind of shape they are in. I would like to eventually get an autocolimator and a repeat-o-meter so I can check them myself.

Hello, my name is Brian and I'm a toolaholic!

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I used to be like that, want to do everything myself... Turns out I now have tons of tools that get used very little just so "I can do it myself".

I am getting better and learned I just can't take on every project.

Working at precision required for an B, A or even AA takes a lot of practice, special and expensive tools. You will probably never need to check your plates again so buying the equipment and learning the skill is just not worth it. Pay the money to a specialist and be done with it.