Scraping The Bottom


This isn’t another one of how my luck usually goes posts.

This is an actual post about scraping.

Scraping you say?

Scraping WHAT, paint? Gaskets?

Nope. Scraping Cast Iron.


Yep, pretty much what I said the first time I had ever heard of it too.

If you have ever owned a precision machine like a metal lathe or a milling machine, the odds are that at some point during the final assemble and test fitting of parts, one or more of the parts that slide along another one were scraped to insure maximum flatness and contact between the two parts.

There is a very quick way to tell if a cast iron machine piece has been scraped to fit better.

You will see a pattern like this on the fitted parts.

There is an art to this process and in the past it was all done by hand in a back breaking and extremely tedious manner using a special hand tool which was obviously called a scraping tool. These weren’t just any kind of scraping tool, they had hardened tips. With the advent of exotic metals, long handles had Tunsten Carbide scraping wafers clamped in the ends and the intervals between having to sharpen the edge got much longer and you could replace the scraping bit. These things ain’t cheap. The one pictured here is $85. Just the replacement bit is $50.

I looked into getting one of them until I saw that.

Eventually, electric powered scrapers were invented which cut the amount of time and effort down to a small fraction of what it used to take to finish scrape pieces. IF, you can get it into where you need it.

One good look at the size of the piece being worked on in that picture ought to give you a clue.

There are literally HUNDREDS of Youtube videos on this process but relatively few classes one could take and this is Old School shit that still has a very real need in the world to this day. It’s a pretty involved process from start to finish which I am not going to go into in detail

but you need Dykem bluing stain, a true flat surface to put the bluing on like a Surface plate and then you rub the piece on the flat side across the surface plate with the dye on it to find high spots that need to be scraped down. You can also put the dye on one piece and then slide the matching piece across it to find the high spots. You do this, scrape the little high spots and then repeat until your tongue is hanging out.

Now you are probably asking yourself what in the hell any of this has to do with me, right?

The Battle of The Mini Lathe continues.

I bought another Tail Stock for my Mini Lathe last year and recently went to do something and discovered that the center line height on the Tail Stock is way too high compared to the spindle.

If it was too low I could just shim it.

Too high is a whole nuther kettle of fish.

I did finally get a surface plate a month ago so that is another weapon in my arsenal but this particular problem involves one piece that a surface plate is useless for, The prism on the ways of the bed that the tail stock slides on.

That bumpy thing on the left..

So I bought some GIANT Sharpies to use instead of Dykem bluing ink and found that the base of the new tail stock is riding way up high on that prism.

Scraping the high spots inside the “V” on the base would allow it to fit lower and thus reduce the center line height.

Unfortunately, this is a relatively small part, about the size of a pack of cigarettes and I don’t have a hand scraping tool.

I ain’t paying $85 to $175 for one either. Even if I did, it would be way too big for this job.

So I made one.

I ordered a little thin strip of Tungsten Carbide off the internet a while back, $12 for a 1/16th by 1/2 inch by 6 inch strip.

I made a holder, broke off an end of the Tungsten, clamped it in the tool and then ground it down on a Diamond encrusted wheel mounted to my old belt driven bench grinder.

Then I dug in my crap, found an old wooden file handle and stuck that on there. Then I tested the scraper on a POS Chineseium Cast Iron Anvil I bought a long time ago that is a beauty of a paper weight because it ain’t no kind of real anvil.

I’m gonna put that in the Win Column.

So now, you can see the strips of blue in the Vee of the bottom plate for the tail stock.

Before I started messing with it, the blueing was right at the very top edge of both sides of that V which was causing it to ride way too high on the prism.

I need to do some scraping with the tool on the blue parts, clean it, reblue the prism on the mini lathe and slide the bottom plate along it again. I want that blue strip to look more like the other side, mostly blue from one end to the other.

That was a whole bunch of post just to get to this point but it was also a whole bunch of work making that little scraper.

Even that is a drop in the ocean compared to how much scraping is going to get done on that damn mini lathe. The cross slide and compound both need to be gone over and scraped after I get done with this tail stock.

32 thoughts on “Scraping The Bottom

  1. I never did that but I have scraped plain bearings on industrial engines and
    double-acting air and gas compressors. Spray a little Dyken on a journal
    rotate the crankshaft a full after torquing the connecting rod cap. Shiny
    spots indicated a tight fit. Using a bearing scraper, shave the shiny parts
    down to till you get an 80+ percent fit. Here is the tool:

    Liked by 2 people

      • Hey!
        I’ve dug shit house holes.
        My grandfather beat the shit out of me once.
        Well, more than that
        Grew up next field to him
        Did a shitty job as a youngster, mostly because I didn’t want to do it.
        …after the beating.
        and this is something I’ll never forget.
        “I don’t give a fuck what you do in your life, you make sure you do it right. If your job is to dig a shit house hole, you do it fucking right. You make sure the walls are straight.”


  2. a long time ago, my dad showed me how when we rebuilt a engine for his truck, he was taught
    by the navy,or rather the fucking navy as he called it. but he was in before pearl harbor, so
    he did get some good schools in before it hit. i still have some of his old tools from his navy days.
    don’t use them much, more like a link to him. but what you are doing takes time and skill few people either care to learn or brother with. stick with it as it is worth doing the right way.
    i was lucky, i grew up with a south bend in the basement to play with.

    Liked by 1 person

    • Richard McKenna was a career squid and a China sailor before WWII and only wrote one book, but made it a good one: The Sand Pebbles. You will remember the Steve McQueen movie based on it of course. A good bit of the book was about McQueen’s character’s relationship with the ship’s engine and he talks about scraping bearings and aligning bearings and all that stuff hardly anybody knows how to do these days. It’s well worth the reading; find the Naval Institute Press edition because it talks about where McKenna came from and how he got to be who he became. It’s a dang shame he didn’t live longer.


  3. That is almost a lost art. Well, doing what you are doing will keep you out of the bars, keep you out of trouble and keep you out of your wife’s hair, so it is a 3+ advantage to you. I do something similar when I rehab old tools to get a better fit and clearances. I too use a sharpie but I don’t get anywhere the clearances or tolerance you do, nor do I have too.


  4. Lacking English here since I don’t need technical terms a lot in this language.
    I remember having seen a guy using a special kind of paste to get a smoother sliding of the mechanics of his rifle – bolt slide ans such.
    He had to apply that paste, slide the bolt a hundred times, apply some more and so on until the roughness was gone and the bolt worked like a charm. I think it was something like honing or lapping. Lot of work but still easier than what you describe.
    Wouldn’t that also be a way to achieve your goal?


    • You can use valve grinding/lapping compound to get a super smooth fit on parts like that. Just make sure you clean it all out!

      Phil has waaay too much metal to remove to lap off. Normally, you’d grind this with a surface grinder, and then possibly lap the parts together if you need extreme precision.

      My Dad was an Old Skool Tool and Die Maker, and taught me how to do this. He was quite surprised that one of my Mechanical Engineering courses in College taught us how to do it, as he considered it an “obsolete” practice in the early 70’s. Still, he said it was good to know how it used to be done “Just In Case”.


      • Besides having a lot of material to remove I would also have to lap in two pieces onto the same prism. The cross slide and the tail stock use the same one to register on.
        It would change dimensions every time you lapped one or the other in.
        I agree with your Dad that it is good knowledge to have and the experience of actually doing it is seriously challenging. Most definitely not something you are going to get out of a book.


    • Lapping or valve grinding compound. I bought some diamond paste to do that kind of stuff with. It comes in fine, finer and holy crap is that smooth grits. See my comment below about lapping two different pieces onto one register.


  5. Serious question.
    How do I answer this?
    . Please describe how you manage multiple projects and clients at one time, and how you report that information.

    I’ve got my own ideas, but for HR, how does this work?
    I’m not shitting about this. A good HR (and I hate these motherfuckers) answer would help.


  6. Phil, a larger radius on the scraper will help a lot. Run about a 5 degree angle on the cutting edge. Use some green diamond paste on a piece of flat hardwood to hone it after the grind.
    And use the absolute thinnest layer of dykem you can- almost rubbed thin like a wax.
    How high is this tailstock, anyway? Might be worlds ahead to mill it close then scrape it in.
    Scraping is addictive, it is like meditation for gearheads.

    Liked by 1 person

    • This is the base for the actual tail stock. I already took that bigger piece to work milled it flat. That alone was probably more than enough to correct the height issue. I am also fucking with the base because sitting so high up on the prism makes it unstable. Unrepeatable when you slide it back and forth because it wobbles back and forth front to back.
      It was kind of pivoting in the middle where all the contact was as you can see in the picture.
      When I put it back together I can shim it to the correct height now.


    • At one point in my early days , I hand scraped big end bearings and main bearings on a aincient diesel engine , it took around four hours per bearing .


  7. I worked at a tool and die shop for several years making progressive die sets
    The punches (upstairs) were floated into alignment with the dies ( downstairs)
    Then the locating dowel pin holes for the punch holders were finish lapped
    They called it squealing the pig because that is what it sounded like


  8. I learned old school methods in the ’70s before moving on to CNC programming in the ’80s and Cad/Cam in the late ’90s
    Before Cad/Cam was widely available, you really had to know your way around geometry, trigonometry, and algebra.


  9. Around 2005 or so, I was on a job for the month of October in Auburn, Wa. Enumclaw area
    Very beautiful
    Encounterd some really weird people though.


  10. I always like reading your tales of machining and the mastery of things mechanical.

    Now, off topic – does anyone have an effing clue when the DNI report on foreign election interference is going to be submitted to The President, if not the public? The topic has gone silent on the internets.


    • Couldn’t give you a time frame, Steve, but you can betcher ass the Trump team is keeping things as close to the vest as possible, so that when the hammer comes down the lowlifes won’t be able to scurry/slither out of the way in enough time!

      Popcorn! Getcher popcorn riiiite heeeere!


  11. Been there, done that. Scraping and fitting is a time consuming, tedious operation, but it pays off in the end. Fortunately I haven’t had to do that in many years


  12. Very ambitious project. Looks like you have a good game plan.

    Have you seen RotarySMP serioes on his mini-lathe on YouTube? Lots of scraping at the beginning.


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