How to inspect this feature? Arc on part with center off some distance - Page 2
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  1. #21
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    Quote Originally Posted by Gordon B. Clarke View Post
    There's an easy way to measure all three so think harder.
    ^^annoying. If you know an easy way I’m all ears.

    Quote Originally Posted by Gordon B. Clarke View Post
    A drawing in metric and then a dimension (0.005") in inches.
    Welcome to my crappy world I prefer to work in metric, but because I’m in the US, I have to converse in both. If I tell someone I need to take a couple thou off that makes sense, but if I told them I need to take off 50 microns not so much.

    It can be as thick/long as you want. 1 mile extrusion, but we can lop off an inch for measurement. Whittled is fine if you can hit the tolerances. +/-.005” is pretty standard for machined parts over here. Yes, the sizes vary as I do job shop work (primarily whittling with a sharp pocket knife, but I do have a 3 axis VMC).

    The quick sketch I made was sized to demonstrate the need: If it were a small radius, I’d use a pin or turn one. I’d also turn a no-go and check for daylight. I have no formal education as a QC inspector, so my default approach could be wrong. When it is a 4” radius (or whatever), it gets a little inconvenient and inaccurate to make 8” diameter “pins” to check it.

    Seems most on here are understanding my question and providing some good ideas. Thanks!

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  3. #22
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    Quote Originally Posted by Gordon B. Clarke View Post
    ....

    The distance from the edge for the arc radius?
    The arc diameter?
    Me? I'd want more dimensions than just those 3 plus tolerances.
    Distance to either edge is of no matter as it will vary with height and length and lets go with these being +/- .050 inches.
    Height and width of blank and their tolerance are of no matter but may change how to do it.
    The feature is fully dimensioned to the datums by these three numbers, only tolerances are missing.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    Distance to either edge is of no matter as it will vary with height and length and lets go with these being +/- .050 inches.
    Height and width of blank and their tolerance are of no matter but may change how to do it.
    The feature is fully dimensioned to the datums by these three numbers, only tolerances are missing.
    Bob
    I don't disagree but what the OP wrote was "Can anyone tell me a good method for checking this feature?"

    Without tolerances there's umpteen ways to do that.

    I regard it all as a waste of my time but those that wish to give suggestions can of course continue to do so. IRL my first response to the OPs question would be "What's you suggestion?".

    When my son was 14 he started asking me what this and that was in English for his homework. Kids here learn both English and German. I answered him for a few weeks before asking him "Why do you keep asking me when I'm sure you know the answer?"

    His reply? "It's much easier asking you." and with a smile. Now and then I asked to read what he had written and rarely had any comment. I stopped "helping" and he ended up getting top marks.

    My daughter got top marks too in school in English and I as good as never speak English. I have smart kids Probably takes after their mother.

    My wife speaks fluent (apart from Danish of course) English, German and French.

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    My God man. +/-.005", +/-.127mm would be the tolerance. Lots of helpful people here, great forum.

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    Quick check- place the radius against an edge on a surface, then drop in a pin of some diameter. If all 3 are correct, the pin can only be in one spot.

    However, this will not tell you anything about the errors should there be any.

    Sent from my SM-G973U using Tapatalk

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    Quote Originally Posted by CosmosK View Post
    My God man. +/-.005", +/-.127mm would be the tolerance. Lots of helpful people here, great forum.
    I try and help when I can. I don't baby sit.

    You've now doubled what you originally wrote ("but that doesn't do very well for radius as finding a .005" discrepancy seems very iffy.") to a ±.

    Given what you have available how would you do it? You can then be given advice you can use.

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    Quote Originally Posted by Gordon B. Clarke View Post
    I try and help when I can. I don't baby sit.

    You've now doubled what you originally wrote ("but that doesn't do very well for radius as finding a .005" discrepancy seems very iffy.") to a ±.

    Given what you have available how would you do it? You can then be given advice you can use.
    I understand not wanting to do the homework. I am puzzled, and stumped how thickness changes how to measure 'this shape'. I have a b+s dial caliber, pec ruler, and Lufkin tape measure. If I use caliber I want +-.004", ruler+-.015, tape +-.05".

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    I'd have taken a ".005" discrepancy" as a bilateral tolerance
    Five thou one side, five thou the other.
    Yet how to check this rad at +/-.005 if it is not a perfect round rad and is short. True to form? Best fit circle or master round to X/Y?
    Functional gauging is always best but expensive in small runs.
    Bob

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    I would like to know what difference material or thickness makes. Seems,but may not be,an unnecessary post.

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    Quote Originally Posted by camscan View Post
    I would like to know what difference material or thickness makes. Seems,but may not be,an unnecessary post.
    More surface area to get a good reading on a 1" thick part than a 1/32 thick part.

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    Quote Originally Posted by crazygoat View Post
    More surface area to get a good reading on a 1" thick part than a 1/32 thick part.
    Good thinking Batman.

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    Of course it matters what the part looks like to measure

    a tiny piece of sheet metal or a feature on an engine block.

    Be serious

    As much as you want to pretend Gordon has no point, he does metrology for a living, and you all do not seem to.


    With the equipment in my shop, assuming it is a milled feature[we don't know since schoolboy didn't say] I would program it without rounding the corners and grab a parallel and a group of pins. Calculate the chord height. You ought to be able to measure with reasonable certainty the chord height.

    You cannot measure the actual radius for that short a segment of a large radius to any degree of accuracy with common tools. IOW the difference between a radius .006 larger and .006 further away is not going to be significant

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    I have to agree with Gordon on this. If the operator brings this in he has the print with tolerances for the part complete with the part and can provide other info. Today most inspection can call the whole print up on the computer and print the print out. I don’t blame him for the skimpy info.

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    Here's rev B if that helps (in inches). The dimensions are arbitrary for the most part (3 axis machined part). I'm trying to illustrate that it's bigger than what I'd usually use a pin gauge for. I've seen this type feature on several parts, so this is a hypothetical example. Seems like a PIA unless you have a CMM which I don't. Haggling with the designer is not an option. Function unknown. QTY 1. Definately some good ideas here.

    temp.jpg

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    what we've done before, but with much tighter tolerances, is to clamp down a piece of sacrificial material so you can machine a full, or near full circle. Then it's easy to check.

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    Even CMM's can be "dodgy" when reading partial large arcs so what I've done before is the attached.

    #1 Put a piece of scrap in the machine and mill a diameter with the same cutter in the same holder as will be used for the proper job.
    This guarantees the cutter is cutting size with no runout etc...

    #2 Make the part like this (for a 1off or to prove program/process). The part is finish machined to over thickness using the same cutter in holder as #1, and add a good sized drilled hole as shown.
    Verify using a calliper check.
    Bandsaw through the channel and flash the back off and done
    Attached Thumbnails Attached Thumbnails capture.jpg  

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  23. #37
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    Good idea on machining the full circle! I suppose you could also machine out 4 of them in a circular pattern then cut them out with the bandsaw and finish.

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    I’m a bit intrigued that a toolmaker or old-timey detailer (draftsman – engineer) hasn’t replied to this topic with “why don’t you just lay this out”? For tool & die makers this is where they really separated the sewage from the good, just detail on vellum & paste it on the weird looking part.

    In the past I have made locating templates using plotters. If set to plot 1:1 my old roland is within .005” from origin to max size on the surface. Using a .25mm pen tracing on the center of dimensions given, the visual line extending outside that part edge would be .005” (about the line width of a good machinists’ scale). A plotter example (old tech) attached...

    I have some sympathy to a post about the power shutoffs happening in California where a poster references Victor Davis Hanson, RE: how pitiful we are getting compared to prior generations of builders. → Victor Davis Hanson: Members of previous generations now seem like giants — When did we become so small? | Fox News

    Good luck, Matt
    Attached Thumbnails Attached Thumbnails tweco_plug_350_174hxl.jpg  

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  26. #39
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    My 2 Canadian cents worth if I had to check this part.

    1: Get X0/Y0 for the bottom left hand corner of the part with an edge finder.
    2: Put a test indicator (e.g. Interapid) in the spindle and move the table in either x or y to the value of the radius.
    3: Hold a gage block or something really flat against the face of the part and adjust the indicator until it reads 0.
    4: Move the table to the center of the radius and slowly spin the spindle by hand against the radius of the part.
    If it's off anywhere, you'll know right away.

    I realize the radius on the part is probably a bit of a stretch with an Interapid type indicator in the spindle, you may need some sort of extension for it to work properly. However, I'd be confident measuring to .001" or less like this.

  27. #40
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    Has anyone else noted how much putting +/-.005 on print one has now been tighten up by a lot in Rev 2 and the added numbers?
    Double dimensions, much reduced room to work inside.
    Bob


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