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Thread: How do I ensure a straight edge is straight?

  1. #16
    Join Date
    Dec 2010
    Location
    South Coastal Massachusetts
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    6,647
    Quote Originally Posted by Pete Costa View Post
    I've got an opportunity to buy a used 72" Starrett Ruler C416R.
    Setting aside the utility -

    Are these sought after on a secondary market, with high resale value?

    Can you purchase it for less than this resale value?

  2. #17
    Join Date
    Aug 2013
    Location
    Princeton, NJ
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    6,691
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    Quote Originally Posted by Malcolm McLeod View Post
    To be rigorous, it would be wise to spec that an edge should be compared to the other and then swap end-for-end and compared again. Certain shapes, symmetric about the center, could ‘pass’ this test otherwise (think about a gentle s-curve :: all 3 could mate).

    Admittedly this would be virtually impossible to create on a jointer, but after the art-work-as-end-stop thread, I just had to toss this grenade over the fence.
    Hah! Good point, so swapping end for end or moving them around would reveal a matching s-curve. Anything is possible especially as they become flat and minor inconsistencies reveal themselves.

    For what it is worth I setup a jointer with a pair of high precision spirit levels after checking each table separately for flatness. I have a 40” long box square (cast iron tube that has been scraped flat/true on all sides) to compare to the tables.

    Check the tables in an x pattern then length wise and note any errors. Set the outfeed parallel to the head across its width. After which check them for parallel both along the lengths and across their widths. Set their heights, then cut the wood.
    Bumbling forward into the unknown.

  3. #18
    Join Date
    Jan 2020
    Location
    Saratoga, NY
    Posts
    49
    Quick update - I ended up getting the ruler. At $95 is was almost too good of a deal, so I was cautious. I borrowed Mel's suggestion to use a tightly stretched wire to check for straightness. It looked good to me, although due to Covid, I was working on the sidewalk illuminated by my headlights. Not recommended, esp. by yourself. I got it home and checked it against some large windows, but it was quickly apparent the glass had a bow in it. I then did the draw a line and flip exercise (thanks again Mel) and it was as good as my eyes can tell. It can flex a bit if I push hard in the middle when only the ends are supported, but that should not be an issue for setting up my jointer. Once that task is done, I may just try and sell it at something closer to market price and put those proceeds towards my next toy. Thanks all for your advice and insight. Pete

    Starrett.jpg

  4. #19
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    5,589
    store it carefully. The recommended way is hanging straight down on a nail in the wall. Rust will destroy the accuracy as will a coat of grease not wiped off before use.
    Bill D

  5. #20
    I use this straight edge for my PM parallelogram jointer, PM 2000 and MM FS30 Smart 12" J/P. It worked perfectly for all and was reasonably priced.https://www.leevalley.com/en-us/shop...s?item=05N6305

  6. #21
    Join Date
    Jan 2020
    Location
    Saratoga, NY
    Posts
    49
    Quote Originally Posted by Bill Dufour View Post
    store it carefully. The recommended way is hanging straight down on a nail in the wall. Rust will destroy the accuracy as will a coat of grease not wiped off before use.
    Bill D
    Thanks Bill, good advice. It's hanging in a safe corner of my shop, although my picture orientation skills may not show that!

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