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  1. #1
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    Default Advice Needed Cylindrical Comparator

    Hi all,

    Just a quick question if I may;

    I was thinking of purchasing this and using it (amoung other uses) as a cylindrical comparator setup. I know it's actually designed as a height comparator but I'm thinking that the type of base wouls allow it to be used as a cylindrical comparator.

    What do people think?

    Simon

    s-l1600-2.jpg
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  2. #2
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    Jul 2016
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    Default

    Do you mean comparing cylinders by rolling them under an indicator and comparing the high points? If so you would only be limited by the throat.

  3. #3
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    Default

    Hi Cask,

    No it's used to compare an engineers square (or the squareness of a part) to a known precision square reference.

    Stefan has made one in this youtube video. Nicely made as you would expect. If you want to get to the guts of how to use it, go to 30:10 into the video.

    https://www.youtube.com/watch?v=4F-bUiyFmWc

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  4. #4
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    Default

    Nothing but crickets here!

    Decided that I will make my own.

    Had some very heavy scrap off cuts so I've fashioned a base at this stage.

    I've roughed it all round on the SG. Did 6 sides on one wheel dressing you can see the finish is requiring a final pass with a freshly dressed wheel but I'll do that later.

    I have ordered a 300mm length of hardened and ground linear shaft for the post.

    Not sure if I will go 3 or 4 feet but I like the idea of pressing some ball bearings into a hole in the base and grinding down for the feet.

    Probably should move this into "projects" folder.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  5. #5
    Join Date
    Apr 2019
    Location
    Adelaide
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    589

    Default

    I would have thought the item you showed would be suitable however it looks like there is no allowance for a fine adjust to get the gauge smack on zero.

  6. #6
    Join Date
    Oct 2011
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    Norwood-ish, Adelaide
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    Default

    Quote Originally Posted by simonl View Post
    Nothing but crickets here!
    Sometimes grasshopper, that happens...

    Quote Originally Posted by simonl View Post
    Not sure if I will go 3 or 4 feet but I like the idea of pressing some ball bearings into a hole in the base and grinding down for the feet.
    3 points define a plane. With 4 it may rock, although if you grind them down after pushing in they should not - but if you are going to do that, why bother with ball bearings? A dowel pin would do as well.


    I don't usually watch Stefan and I just skipped to the 30' mark as you suggested, but from what I understand of the process, he is only doing half the job. He is assuming that the square he uses to set up is 100% accurate and so just comparing to that. What is more conventionally done is to measure a cylindrical square top and bottom to see that it is actually a cylinder then check with something like this in dimetrically opposite locations. The difference in reading will tell you how much out of square the base is to the cylindrical surface is so that you can then use that (with corrections if necessary) as a master, comparing all other squares to that.

    There is actually nothing special about the set up as shown; provided that the radius on the base is greater than the diameter of the indicator tip and not close to flat, moving the indicator should be able to find a minimum (so your original plan would work).From a set up perspective, the key requirement is that the plane that the indicator tip moves through should be perpendicular to the surface plate and the axis of the base radius should also be on that plane. If not, errors could creep in.

    It does beg the question though why do it that way? If he has a 'reference square', it would be quicker to use that to see if things were square. Knowing that something is say 0.002mm out is only useful if you are working with geometric tolerancing (GD&T). For those not in the know, GD&T uses datum surfaces and axis to define a geometric feature, so if on his toolmaker's block the requirement was defined as square to within 0.005mm (there are special symbols to represent these things), that is represented in abstract as two parallel plains 0.005mm apart and the whole surface must lie within the two planes to be acceptable. Horribly complicated and not something normally done in non-commercial settings (it has pluses when trying to get mass production parts to fit together) as it adds an extra level of complexity.

    Perhaps to save yourself some work I'll mention I've seen this done by putting a radius piece on a height gauge and replacing the stylus with a DI. Same end effect.

    Michael

  7. #7
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    I just want to make a squareness comparator so that I can compare relative squareness of (say) my granite square to my angle plate.

    Also if I decide I want to make a cylindrical square then I can check how square it is simply by rotating.

    It will also double up as a indicator base on the SP.

    I think it's a simple but nice thing to make.

    Still trying to work out the advantage of using a test indicator (with s stylus) as opposed to just a DI with a plunger.

    I have seen many with a test indicator but I can't see the advantage.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  8. #8
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    Nov 2017
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    Geelong, Australia
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    Default

    Tom Lipton (Ox Tools) on YouTube has a good video on squareness if you haven't seen it.
    Titled "It's hip to be square"

    Steve

  9. #9
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    Default

    I would be happy to give a bunch of old flat carbide chunks, you could them lap them for contact.

  10. #10
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    Default

    Here's a link to a blog version of the Ox Tools comparator build in case you struggle with Tom saying "right" every 5 seconds
    The photo of a different comparator using a ball bearing as the pivot might be of interest too.

    "Nothing Too Strong Ever Broke": Squareness Comparator Part 1

    Steve

  11. #11
    Join Date
    Oct 2010
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    melbourne, laverton
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    1,910

    Default comapitor

    hi mate loos nice. how much is it?
    aaron

  12. #12
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    Oct 2008
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    N.W.Tasmania
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    Default

    Quote Originally Posted by simonl View Post
    I like the idea of pressing some ball bearings into a hole in the base and grinding down for the feet.

    Simon
    Hi Simon, I can't remember where I heard or saw it, but most likely from one of the gurus, Tom, Stephan Robrenz etc, but whoever it was specifically said that he wasn't going to use ball bearings for feet on a comparator base because small particles of crud will wedge under as you slide the base over a granite reference plate, whereas if you use flat carbide inserts (which he then lapped on a diamond lap,) there is a much better chance that the feet will just push any dust particles away like a dozer blade instead of riding up on them. something else for you to consider.

  13. #13
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    That's an interesting point. Doubt it was Stefan as he used the ball bearing idea on his.

    I like the idea if TC feet but I'm not exactly sure if I have the means to lap them?

    BB are easily ground with a SG and it fun watching it spark out. There is a sense satisfaction watching the SG go back and fourth, up and down until no sparks come off!

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  14. #14
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    Default

    I wishI could remember the build, but I would have to look over a heap of YouTube video content, which while it is very interesting, is also very time consuming and right now I have lots of stuff to get done. Good luck with your project though Simon, I enjoy hearing about your exploits so keep us posted,
    Rob.

  15. #15
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    Default

    Bit black on those angled faces/edges but maybe just your lack of wheel dressing, must of been producing a lot of dark sparks but then again it may of just been the way you took the photo, not using the correct lighting or a not so good camera, just extremely dark.

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