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  1. #1
    Join Date
    Nov 2004
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    Default Tuning a combination square with a hardened head

    I have an older Starret combination square that has the hardened cast iron head. It is no longer square.

    I've seen plenty of videos on requiring a combination square. My problem is, I think, that being hardened; I cannot make any impression on the nubs in the slot.

    I've tried files, sandpaper (most of the common types) and even tried with a burr I ground on to an old file.

    From what I can see, the "hardened" label on these square heads is not just marketing!

    Anybody got any suggestions?

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  3. #2
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    Dec 2007
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    Sydney
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    Default

    Diamond file?
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  4. #3
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    Nov 2004
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    Default

    Quote Originally Posted by clear out View Post
    Diamond file?
    H.
    Yeah, I think you're right. Certainly nothing else does anything except polishing!

  5. #4
    Join Date
    Mar 2004
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    Brisbane (western suburbs)
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    Default

    Mark, if the head nibs are so hard, it begs the question, are they worn or is it the slider (rule) part that has worn unevenly? Perhaps you have already done this, but I'd be making good & sure which bit is causing the problem before getting too physical with anything.

    I'm pretty gung-ho when it comes to dealing with tools that aren't doing what they should, I "fixed" my out-of-square Rabone combination square by filing the nibs (which filed pretty easily) but I would have a few long, hard thinks before getting stuck into a Starret. Maybe I'm just intimidated by the name....

    Cheers,

    P.S. The thought just hit me as I pressed 'send' - wouldn't the stock of your square be case-hardened? If so, you would need to be mighty circumspect about how much you filed hose little nibs, you could easily cut through into softer iron & exacerbate your problems.

    I'm off to do a bit of "google research".....
    IW

  6. #5
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    Default

    OK, a quick search turns up that Starret make two types of stock: hardened steel & cast iron (the latter seems to be the most common). Can't find any mention of case-hardening of the cast version, & I can't find any info on its composition, but I guess we can safely assume it's formulated to end up mighty hard. I never realised before how much you can vary cast-iron properties by the various heat-treatments employed after casting - I thought you just took it how it is after it cools in the mould!
    Cheers,
    IW

  7. #6
    Join Date
    Jun 2005
    Location
    Helensburgh
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    7,696

    Default

    Starrett offer a refurbishment service for old tools.
    CHRIS

  8. #7
    Join Date
    Jul 2011
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    In between houses
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    1,784

    Default

    Check the blade, I’ve seen plenty of worn down ones before, only take a 1/4 of a mm and it would throw it out a fair bit over 12” of blade.

  9. #8
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    Nov 2004
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    Default

    The rule is relatively new. I bought a Starret metric rule. It's about 18 months old. I'm not saying it isn't the problem, but it seems unlikely.

    I will have a look tomorrow.

    I have order some diamond needle files. Nothing special and I'm not expecting a lot from them for the price. If they get this one job done, they've paid for themselves.

  10. #9
    Join Date
    Nov 2004
    Location
    Redlands area, Brisbane
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    Default

    I got the diamond files I ordered. Cheap and nasty; $11 including delivery from Amazon.

    But, they did the job and they still have life left in them. So totally worth it.

    I also ordered a dedicated square from Banggood that claims to be DIN875/0 for about $26. DIN875/0 is a pretty darn high standard. This standard has allowed deviations measured in single digits of microns.

    I received it today and I will do a follow up tuning now that I have a reliable reference to work with. I was pretty close though and certainly way better than where I started from.

    Can't say I have the tools to test to DIN875/0. But Dennis took the same square in his China Tools episode seven to someone that could get pretty close.

    I'm pretty satisfied with the new square and I recommend it. It will be put away and only pulled out to test other squares.

    I discovered my other engineering "squares" were way off. I tossed them in the recycling bin along with a try-square that was also way off. I found that the blade was not even the same width across the length of the blade.

    To replace the little engineering squares, I bought an iGaging 100mm double square. It is dead square against the reference square and modestly priced. I also recommend it.

    I did not buy the 150mm iGaging square as I have a Starrett 150mm combination square as well. Though until today, I was not 100% certain about how square it was either.

    While this is bordering on obsessive, I was driven down this road by problems that I could never reconcile. For some of these problems, the only logical answer was the squares. And sure enough they were not all okay.

    That said, I'm creative enough to continue making expensive sawdust.

  11. #10
    Join Date
    Jun 2005
    Location
    Helensburgh
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    Default

    Did you use a surface plate for your comparisons?
    CHRIS

  12. #11
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    Nov 2004
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    Default

    Quote Originally Posted by Chris Parks View Post
    Did you use a surface plate for your comparisons?
    No. I don't own one.

    I can see the use for one, but I would not be able to justify one for the little use I would get as a reference surface.

    For flattening waterstones, I have one of those DMT diamond plates. In my defense, I bought it before the prices of them went through the roof.

    I was referencing the squares to each other.

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