Shortening a DRO Scale
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  1. #1
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    Default Shortening a DRO Scale

    A while back I asked if anyone had shortened a DRO scale, without success, so heres a story of what I did.

    A seller on Ebay with little feedback was selling a complete Mill setup C-80 Newall DRO. I bought it arrived complete and undamaged. This is for my 10EE not the BP, so one scale would need to be shortened to use on the crosslide.
    About this time I see on Ebay an odd C-80 setup, all in a large plastic case, for sure a Demo setup, and one of those scales was a Microsyn scale that would fit perfectly on the 10EE crosslide. For less than the price of a Microsyn scale I got a complete setup.

    The installation on the lathe went fine, but now I have a 13" scale and a useless 10" scale as it has a nice 2" slot milled in the tube to show the balls inside. From one of the members here I bought a 48" scale.

    The scale of a Newall is a SS tube filled with ball bearings, the tube is plugged on each end with fittings that are staked in. So I have one tube for practice, and one for the money. Chucking up the tube in the lathe, it was turned down until it was about .010 thick, then a bolt was threaded into the fitting with a spacer and a washer just pulled the fitting out. As can be seen in the photo.




    This is the fitting with setscrew that is used to adjust the scale after assembly


    After shortening the scale it was staked back into place. Surprisingly a 8oz hammer and a 3/32 drift produced the same depth dimple as the factory marks. These are the factory dimples.


    These are mine.

    Before the good scale was cut, it was chucked into the lathe and fitted with a reader head attached to the tool post. Over a 6" lenght the varience on the lathe to chuck mounted scale was .0014" , thats more than I expected. Assuming the new lathe scale was closer to correct, than a used scale, I thought I could get better that that. After assembling the scale it did not take long to adjust the altered scale to within .0002 of the lathe scale over 6".

    The Newall is a nice DRO, and getting it cheap makes it better.

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  3. #2
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    Tom,

    What do you think of the idea of making a home made scale 80 inches long?

    I have a scale that is 4.5 meters long on my planer mill that I could use to calibrate it.

    What is the diameter of the balls in that thing?

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    The balls are .500 dia. Newall calls them nickle chrome, they are magnetic. I don't know how critical the alloy is. The tube is SS non-magnetic. The OD is 15mm yes, the ID is just .500? as a ball will very slowly travel down a vertical tube if I cover the vent with my finger.

    Keep you eyes on ebay there was a long scale for sale last month. The tube might be tough to find, metric OD, imperial ID. You could CL grind a .625 to 15MM, but for that cost you could buy a scale. just a thought.
    Last edited by Toms Wheels; 06-03-2010 at 06:27 AM.

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    Nice work, Tom.

    What takes place when you adjust the scale? Are you just tightening the setscrew, and does that stretch the tube/jam the balls together? I have some with plastic screws in the end, are they the adjustment or just plugs over the adjustment?

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    There are 2 plastic plugs, one screws in has a slotted head, the other is like a plastic rivet, just pushes in. The threaded end holds the setscrew that adjusts the pressure on the balls. A drawing in the Newall site shows a spring arrangement, neither scale had that when disassembled, possibly only used on very long scales, or discontinued.

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    I recall when this question came up a few months ago, I thought it would not be a difficult job to shorten a Newall scale. Others said it was impossible. I am always glad to see an impossible job done, and done well.

    Larry

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    Tom,

    I have a 40 inch scale - and can likely get another one used . . .

    what do you think the chances are that there is enough material to bore / thread one end of one scale and externally thread the end of the other scale and make an 80 inch long scale from the parts of both scales?

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    The wall thickness is about .050" not much meat to thread. But the biggest worry I'd have is accuracy. The reader head induces a magnetic field that is disrupted by the balls as well as by the tube, this distortion is read and based on how much it is distorted, the result is a number. Even though the tube is not magnetic, I'd guess it distorts the field somwhat. The short tube I have that has a slot milled in it, the readings are in error as the head passes over that slot, I recall the reading was .010 off compared to the lathe scale. A threaded joint might be more or less. There is the ability to crank in error factors on the display, so carefull measurement could provide enough data point that you might smooth out that ripple. Call Newall for a price on the tube, then you'd need 160 balls.

    Check on the board here if anyone has a 80" scale. I purchased the 48 from Bob.

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    thanks for your comments Tom - I have kept my eye open for an 80 inch scale and posted several ads - I guess I need to pony up and buy the right scale. I bought a DRO for a 14 x 40 lathe with scales and it cost less than the price for a new 80 inch scale . . .

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    I scored a Newall DRO with an 80" scale on ebay a while ago, in fact I bought 2. The first one had the 80" scale slide out of the packing tube and was badly bent. The 2nd one got out, but somehow wasn't bent. The weight seems to be able to pound through the tube caps, so if you do find one, send real specific instructions to the seller about packing it with wood on the ends. I did on the second, but he didn't believe me and shipped with with just the Newall caps and tape.

    BTW, I have one of the Newall swinging center tube supports for long scales if you need one.

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    I have a similar problem. My Sheldon lathe has 62" carriage travel, more that I want to pay for a DRO scale. I have never had a reason to need a DRO for more that about 20" from the chuck, but using a shorter scale would require restricting the carriage travel to avoid damaging it. I have considered making a slide for a shorter scale I have with a spring or weight pulling the sensor downwind and a dog on the carriage that picks it up when near the headstock. Has anyone done anything similar?

    Bill

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    IIRC, Newall actually has hardware for that situation. You put a funnel on the headstock end of the reader head to guide the scale back into the reader head, and a swinging bracket on the tailstock end of the tubular scale to allow the reader head to pass as it slips off the end of the scale.

    If that's not workable, it wouldn't be hard to unclamp the end of the scale and allow it to move when needed. Newall routinely mounts scales with only one end when they are short. My Lathe X-axis scale is only mounted on one end, and it's the 1/4" diameter microsyn.

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    Interesting. The scales I have are glass, not magnetic, but it would not be hard to make a setup where the scale could move the whole length of the bed. Then you could move it to the area where you were working. That doesn't come up often, but recently I turned a new bearing seat on the end of a 4 foot shaft. I was able to hold things close enough with the carriage handwheel dial, but a DRO would have been better. A couple of stops that clamp on like a taper attachment bed clamp would reduce the chances of damaging the scale. Sounds like a good weekend project.

    Bill

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    Anyone have any guess as to the cost of just the rod (filled with bearings, ready to use) for 60 inches of travel from Newall ? Don't need the reader head, just the rod.

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    $500++ or so

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    Quote Originally Posted by bob View Post
    $500++ or so
    Yikes....that's twice as much as I would have expected...

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    what do you think the chances are that there is enough material to bore / thread one end of one scale and externally thread the end of the other scale and make an 80 inch long scale from the parts of both scales?
    Newell does make 80" and longer scales, but they use a spring loaded support in the middle on longer scales like that. It looks like a tensioner pulley and flips down when the reader head passes by.
    The scales I have are glass, not magnetic, but it would not be hard to make a setup where the scale could move the whole length of the bed. Then you could move it to the area where you were working.
    Glass scales are much more sensitive to alignment; Acurite recomends that their scales are aligned within .010" total in all planes. I do not think they would work on a sliding fixture, I believe that you would get read errors.

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    Quote Originally Posted by misterT View Post
    Glass scales are much more sensitive to alignment; Acurite recomends that their scales are aligned within .010" total in all planes. I do not think they would work on a sliding fixture, I believe that you would get read errors.
    I'm aware of the position accuracy requirement with glass scales. The idea would be to make a slide, possibly Thompson bars, that would mount on the carriage and have a link that clamps on the bed in the same manner that a taper attachment is connected to it. Probably I would want a clamp on each side that the carriage would hit at the end of available travel to avoid damage to the scale. The alignment of the scale would be all from the slide. For that matter, you could mount the scale on the taper attachment and set the taper to zero. I might try that just to see how it works out.

    Bill

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    I also purchased a Newell DP7 from an auction it came with 3 scales two of which are too long to be used on my BP.
    I called the Newell tech support and was told that can not shorten the scales.
    But figuring I have nothing to lose I might as well try. So far I have cut one if the scales and found that it did contain the spring mentioned in the first post.
    So wish me luck and I will post how it all turns out.

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    Reassembled and everything works like it should. I'll have to get it mounted on the BP before I can test accuracy but it should be fine for my home shop.


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