Grinding centers, how precise must included angle (60 degrees) be?
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    Default Grinding centers, how precise must included angle (60 degrees) be?

    I want to touch up some centers that will be used in the workhead of a universal cylindrical grinder. It's easy, right? I just offset the head by 30 degrees, dress the wheel, and kiss the center.

    My question: how precisely do I need to offset the head? If I eyeball the 30 degrees from the engraved scale, I can probably get within 0.2 degrees, say between 29.8 and 30.2. Is that good enough? Or do I need to use a precision angle gauge or a sine bar to get this angle more exact?

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    Unless the workpiece has had its centers lapped, and lapped co-linear, the contact the center makes with the workpiece is never perfect anyway, so having the centers perfectly ground on 60 degrees is not that important. Their uniformity is. Eyeball the angle and clean up the center, it will work fine.

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    I'd think that would be plenty good. I always warn people that I've gotten center drills that didn't give an exact 60 degree hole. For accurate work both center and center hole should mate up well. I used to use radius center drills with good success. Perfect contact and if the end got dinged a bit it didn't matter. Better if you need a slight taper by offsetting a lathe tail stock too. Radius center drills are harder to find than they used to be, but IMO, worth the effort to track down.

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    We make gages for a tier 1 automotive manufacturer and their parts all have centers made with radius center drills like you describe. They have to control the dept of center accurately for CNC cylindrical grinding.

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    Is my brain failing or did someone make spherical centers that contacted the 60* drilled parts more in a circle than a cone ? It was supposed to let shafts be less affected by misalignments than normal centers ?

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    Yes, those are the radius (Type R) type centers I'm talking about. Radius Type (R) – KEO Cutters

    Lately I've found it's way easier to find pictures and catalog numbers than anybody that actually has them in stock. Don't confuse them with bell type centers, which sound like what you'd want, but aren't.

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    Depends on the class of work you are doing.
    Seems counter to all the effort you've put scraping and aligning the machine to just set the angle off the scale instead of using a sine.
    A good center manufacturer will hold something like 60 degrees +15/-0' or better, and the best work will likely involve lapping the females on your part.

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    Cash, thanks for checking in here. The advice I get from you and others here means a lot to me.

    Quote Originally Posted by Colt45 View Post
    Depends on the class of work you are doing.
    The first thing I will be making (after adjusting the height of the grinding wheel spindle to agree with the workhead and tailstock) are some more test bars and some MT5 adapters for 5C collets and chucks. This is to make it easier to use the grinder in the future, and also to get some experience with making stuff on it. I am able to hold 1 micron tolerances on the machine (0.00004") and would like the centers to help with that.

    Seems counter to all the effort you've put scraping and aligning the machine to just set the angle off the scale instead of using a sine.
    I don't currently have any tools that can measure angles very precisely. So I might need to make or buy something. But I was not sure if it is needed here.

    A good center manufacturer will hold something like 60 degrees +15/-0' or better
    Let's see, 15 minutes of arc is 1/4 of a degree. So this is between 60 and 60.25 degrees. Interesting, that means that a fatter angle is OK, but a skinnier one is not. So this means it's OK to make contact on the larger outer diameter of the center drilling, but not on the smaller inner diameter.

    To hit this tolerance would mean that I need a workhead offset angle between 30 and 30.12 degrees. That's not so hard. I should be able to cut/mill/grind a 30/60/90 triangle out of steel and use that as a "setting gauge" to get that accurate. How do you set angles for grinding centers?

    the best work will likely involve lapping the females on your part.
    I have purchased a couple of center point laps and tried them out, once is 80 grit and one is 150. In fact I have exactly the same question regarding dressing them. The manufacturer said to just dress them by hand with a open-pore carbide stone (and even sent me one for free to try out!). But it seems to me that I should do this on the lathe or grinder using a diamond dresser set at precisely the correct angle.

    Can this sensitivity to the center-point angle be avoided by using the radius-type center drills that Conrad described?

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    Default Thread Revival

    Sorry for the thread revival. Very interested in the female radiused centre approach mentioned earlier.

    I have a high accuracy grinding application I'm working on. We are working with tolerances fine enough that the quality of centres can make a difference. Whats the optimum setup for a small pencil sizes shaft? Female radius centre at each end of the part with carbide male machine centres?
    What about if I'm limited to a male part centre in at least one end of the part.....we usually grind these male centres in a collet. Anything better?
    Also I have a load of hardened steel shafts with conventional female centres in them.....we usually lap them with a CBN cone but even that leaves nasty score marks....does anyone lap with a brass cone + lapping paste?



    Quote Originally Posted by Conrad Hoffman View Post
    Yes, those are the radius (Type R) type centers I'm talking about. Radius Type (R) – KEO Cutters

    Lately I've found it's way easier to find pictures and catalog numbers than anybody that actually has them in stock. Don't confuse them with bell type centers, which sound like what you'd want, but aren't.

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    "I have purchased a couple of center point laps and tried them out, once is 80 grit and one is 150."

    where did you get these 60° "laps"?

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    Quote Originally Posted by dian View Post
    "I have purchased a couple of center point laps and tried them out, once is 80 grit and one is 150."

    where did you get these 60° "laps"?
    Haven't lookd recently but there was a place called Cen-T-Lap that made machines for doing this. They used abrasive cones that went on over a hard rubber mandrel, sort of ?

    But if you want accurate, Jones & Shipman center grinder.

    A friend tried the lapping method, he didn't like it and said it didn't work for shit. He does thousands of shafts a year and is generally pretty good, so I tend to believe him.

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    Quote Originally Posted by EmanuelGoldstein View Post
    Is my brain failing or did someone make spherical centers that contacted the 60* drilled parts more in a circle than a cone ? It was supposed to let shafts be less affected by misalignments than normal centers ?
    "Ball end" tips are still common in sets of live-centres with swappable tips.

    Their PRIMARY use is to manage offsets for turning tapers, 'coz the reduction of contact area to a narrow "tilted ring" of swept area of travel reduces the load they dare apply when NOT on a decent live center, before they are galling and ruining the socket, most common materials, from too stingy a contact area.

    The Old Skewl trick if you had no such critter - or had just trashed one - was to grease-up a bearing ball and run it in a cup center.

    Given it ain't hard to gather a suitable collection of those hardened bearing-balls, some among us figure the fallback is actually easier to support with clean and undamaged goods than the bespoke ball-end center tip is.

    Back to the question: If a precision GRINDER is the horse you wish to saddle, not just vanilla lathe work?

    You will want to meet or TRY to beat the primo maker's of store-bought dead centers who do it as Day Job.

    See Stark, Riten, et al for their current specification's and pricing.

    If/as/when the specs have gotten tighter and better over the years? Well.. the folks USING them have had reasons to pay for better goods.

    Truth, is I keep my one of each "top end" ones set aside for measuring and assessment of the lathes. I don't USE them for actual turning atall.

    Ordinary work I use bog-standard commodity centers, carbide tipped, some of them even Chinese-made. Cheaper and easier to keep reminding myself that dead centers never WERE going to last "forever".

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    ^ wtf ? My reference is a camshaft manufacturer which grinds thousands of shafts per year. They were interested in improving the product, tried lapping the centers and were not satisfied with the results. What you do in the garage is not relevant to the question asked.

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    Quote Originally Posted by EmanuelGoldstein View Post
    ^ wtf ? My reference is a camshaft manufacturer which grinds thousands of shafts per year. They were interested in improving the product, tried lapping the centers and were not satisfied with the results. What you do in the garage is not relevant to the question asked.
    LOL!

    Well. ain't it just too damned - and EXPENSIVELY - bad they hadn't paid attention to what "garage" folk who had been INDUSTRIAL folk with a bit of metallurgical book-learnin' fifty-sixty years earlier already knew , wasn't it?


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    He can not speak very well, everybody knows
    But to me he sure looks swell in his oldman clothes
    I asked him a grinding question and he only goes (yeah)

    Un dat un dat un dat dat, un dat un dat, dat dat
    Un dat un dat un dat dat, un dat un dat dat

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    Quote Originally Posted by EmanuelGoldstein View Post

    He can not speak very well, everybody knows
    But to me he sure looks swell in his oldman clothes
    I asked him a grinding question and he only goes (yeah)

    Un dat un dat un dat dat, un dat un dat, dat dat
    Un dat un dat un dat dat, un dat un dat dat
    Yah never needed anyone's permission to remain HUTA stoopid or noisy, either one.

    But I'm easy. Yah HAVE it.

    "Just in case" of accidental exposure to daylight or such....

    60-degree metal-on-metal or ball-tip, either one was such an effing DURABLE "bearing" that lapping cudda improved it, Colonel Rockwell (New Departure) and Harry Timken (cable TIMROSCO) wudda BOTH starved clear to death.

    They did not.

    The rest is history if not also obvious.

    High precision, trivial loads, else short service life. "Dead" centre is OK for metrology and low-RPM grinder mount-ups. "Position" is paramount, not running load management.

    ELSE

    "Bearings" roller, fluidic, wotever. Longer life. Precision according to budget.
    Better for volume balls-to-the walls production use. "Cams to be shat", even.

    Pick either one. TANSTAAFL


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    This is as much fun as grinding!

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    Quote Originally Posted by ballen View Post
    This is as much fun as grinding!
    It IS "grinding". Or maybe "grating"?

    Abrasion is abrasion. Pointy things seek the center of orifices.

    Mostly, we just DEAL wit' dat!



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