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Starrett Back Plunge?

Discussion in 'METROLOGY - MEASURE, SETUP & FIT' started by Buggy Chief, Nov 28, 2016.

  1. Buggy Chief

    Buggy Chief United States Active Member Active Member

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    Looking at buying a pre-owned starrett indicator and prefer a plunge indicator. When I look on eBay all of the used sets with wooden boxes are back plunge. Can someone share the rationale for back plunge? I am obviously new to this hobby and understand how to use a normal plunge, but can't understand the back plunge? Thanks in advance!
     
  2. higgite

    higgite General Manger - Proofreading Dept. Active Member

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    I don’t have a back plunger type DI.... yet, but I can see how one might be handy for checking things like mill table X-axis tram using just one indicator without needing a mirror. I'm sure others will chip in with other uses, too.

    Tom
     
  3. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    It seems to me that the back plunger was a step in the process, earlier than the 'through the body' types. All the ones I've seen were old looking, well used.
     
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  4. westsailpat

    westsailpat United States H-M Supporter - Premium Content H-M Supporter-Premium

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  5. mikey

    mikey Active User H-M Supporter-Premium

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    Starrett and others made back plunger indicators many years ago. The advantage was that the indicator faced the user. This was an advantage when tramming your mill so you didn't have to bend over to see the face like you would with a standard indicator. They typically came with an arm that allowed you to also read things that were out of position or in a deep hole. As far as I know, they were only made to read 0.001" increments and I've seen a lot of them in auto mechanic's tool chests. They tend to need more force than the typical AGD-type indicator but are still accurate and useful. I have one that I use on occasion, mostly for tramming.
     
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  6. Buggy Chief

    Buggy Chief United States Active Member Active Member

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    thanks for all the replies and input....very helpful!
     
  7. projectnut

    projectnut United States Active Member Active Member

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    I'm not sure I would buy any measuring tools sight unseen unless the seller offers a return guarantee. The Starrett 711 or "last Word" indicators have been around for in the neighborhood of 70 years. Many on eBay and other auction sites are from the 50's and 60's and show their age. One of the main problems with them is the older they get the more tendency they have to get sticky. I have 4 in the shop and 3 of them have started to stick. The only one that is still flawless is the one I purchased new in the early 1980's. The other 3 came from fellow workers that retired and sold off some of their tools. They all worked fine for a while but I know they are much older than the one I purchased new. I can send them out for repair, but past experience has shown that the cost of repair is nearly the same as the cost of buying new.

    I also have a Brown & Sharpe 321b test indicator and a Mitutoyo 513-202 test indicator. Both of these are about the same age as the Starrett I purchased new yet work much smoother.

    As a side note the first indicator I purchased new was a Starrett 196 back plunger style like this.
    http://www.ebay.com/itm/Starrett-di...322683?hash=item3d2c6ca4fb:g:3EEAAOSwEzxYO50C
    Again it was in the early 1980's and it still works flawlessly today. They're great for use on a surface plate, between centers, and of course foe tramming the mills.

    A few years ago a former fellow employee offered me another one at a price I couldn't refuse.
    http://www.ebay.com/itm/Starrett-No...384786?hash=item3d2c9b5e52:g:LmcAAOSwux5YPjou
    It's much older than the one I purchased in that it's in a wooden box. This one must have led a sheltered life because it to works flawlessly. The only drawback to both of these indicators is that they only measure in increments of .001"
     
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  8. Bill Gruby

    Bill Gruby United States Global Moderator Staff Member H-M Supporter-Premium

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    I use the back plunge gage on a weekly basis. I check model airplane engine crank shafts for bends and out of round with my bench centers.

    "Billy G"
     
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  9. chips&more

    chips&more United States Active User Active Member

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    I have collected through the years many, many indicators and from all makers (except China and the like). But when I want to use an indicator and not just make a pile of them in the shop. I use the Interapid test indicator.
     
    Last edited: Nov 30, 2016
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  10. westsailpat

    westsailpat United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Last edited: Nov 30, 2016
  11. Buggy Chief

    Buggy Chief United States Active Member Active Member

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    LOL...I have a test indicator. Love all the old vintage Starrett stuff, especially the ones that come in the wood boxes. What stories they must have...

     
  12. projectnut

    projectnut United States Active Member Active Member

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    The key word here is OLD. Given these tools can be nearly 70 years old there is always the possibility they have been dropped or otherwise abused by a previous owner. Even if they haven't, given their age and the environment they work in there's always the possibility they may just be worn out.

    I have no problem with the quality of Starrett instruments. When I started in the trade they were among the best on the market. The great majority of the measuring instruments I have in the shop are Starrett. The big difference is I know their history, so I know I can trust their accuracy and repeatability. Those being sold on eBay and other auctions sites are often being sold by people who have no idea of how the tool was treated, how to test it's accuracy, or whether or not it's worn out. There are very few instances where retired tool and die makers or machinists are actually selling their own tools.

    Essentially it's a case of buyer beware unless the seller offers some kind of return policy. I understand the allure of being able to purchase a tool at a fraction of the price a new one sells for. However in order for the transaction to be successful the tool has to be in good operating condition, or returnable if not. If it doesn't work properly and can't be returned you've just wasted however much money you've spent.

    My rule of thumb when buying anything used is that if the item isn't as advertised, or doesn't perform its normal expected function it should be returnable. If I go into the transaction knowing the item isn't returnable the total cost of the item (including any repairs that may be necessary) should not exceed 30% of the cost of the same item purchased new.

    There's nothing more frustrating than machining a part, measuring it, believing more material has to be removed, removing the measured amount, measuring again to find the part is undersized due to an inaccurate measuring tool. You've wasted both time and material, and can no longer trust the measuring tools' accuracy.
     
  13. ericc

    ericc United States Active User Active Member

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    If you want an indicator that works, buy a new one, even a cheap import one. I love the look of the old tools, though. I bought a Starrett 196 back plunger indicator at a garage sale. It did not have the hole attachment that makes it useful for measuring bores, so it was not used much. I tried using it once for centering a bar, and I noticed that the magnetic stand shifted as the bar rotated in the lathe chuck. There was a little sticky spot. When I pressed on the plunger, it just got worse. Soon, the indicator was useless, and I had only used it once, unsuccessfully. I called Starrett, and they said they could repair it if I sent it back. It cost $70 or so plus postage. It is perfect now, but I have not used it. It looks so beautiful. They even shipped it back in a nice cardboard box with their logo. That Harbor Freight indicator looked really terrible, but turned out to be a MUCH better deal and has gotten a lot of use.
     

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