Way to build up or plate an overground, undersized arbor?
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  1. #1
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    Default Way to build up or plate an overground, undersized arbor?

    Nmtb50 arbor shown has been over-ground and touches spindle only a little at large end. I’m pretty sure additional grinding won’t help. A new one with the necessary 2 1/4-10 threads is $550. and used ones are like hens’ teeth. So I’d like to see how it might be built-up. Welding? If so what rod?Plating? Aluminum duct tape? Can’t be done?

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    Last edited by Cannonmn; 10-26-2020 at 09:44 PM. Reason: Use good English

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    I have had many parts hard chromed and reground. Bet $200-250

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    Thanks, do you recall the thickness of plating you got? Cost varies with thickness applied I guess? What’s max thickness or is it only limited by your wallet? Recommend a shop that does this? Same shop chromes and regrinding or separate shops?

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    You can put it on as thick as you want. If it's done right it's pretty tough stuff. Most chrome shops I've worked with do grinding also if it's fairly small stuff. You weld on that adapter you'll be remachining the whole thing and you'll lose any original hardness it had. Don't do that.

    Is there some reason you can't just grind the taper to the correct angle then grind a bit off the taper side of the flange?

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    Quote Originally Posted by eKretz View Post

    Is there some reason you can't just grind the taper to the correct angle then grind a bit off the taper side of the flange?
    That was my first thought

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    Quote Originally Posted by eKretz View Post
    Is there some reason you can't just grind the taper to the correct angle then grind a bit off the taper side of the flange?
    That's exactly what I suggested in op's previous thread on the subject - OP, I thought you were going to do that, was there a problem with it?

    How much nmtb arbor/spindle contact is enough?

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    Quote Originally Posted by gregormarwick View Post
    That's exactly what I suggested in op's previous thread on the subject - OP, I thought you were going to do that, was there a problem with it?

    How much nmtb arbor/spindle contact is enough?

    I took the suggestion from that thread, set up the grinder by copying the taper from a new arbor, and ground the old arbor. I noticed that when the indicator stayed as close to zero as it was going to do while cranking the new arbor back and forth, the Pointer on the upper table of the grinder was well-above (numerically) the numbered taper scale. As suggested I ignored the scale And kept the table set where the indicator wanted it. When I ground it, the sparks looked pretty evenly-distributed along the taper. After grinding and cleaning it, I thinned out he blue paste coating in the spindle as much as possible while leaving what seemed like an even coating. I pressed the ground arbor in by hand and got a nice even ring of blue less than 1/4 in. “Long” extending from gauge line. So the area of contact with spindle was reduced from previous grinding, not what I expected. There was about same length of arbor surface visible between flange top and spindle bottom, about 1/8 in. With no improvement in spindle contact after hours of additional work, it looked like I wasn’t going to get there and didn’t have time to keep working on it, so the idea of starting over (Plating, grinding by someone with better grinder and skill) looked good. If I was sure what went wrong with what I did, I could fix it, but lacking same, I’m pretty sure I won’t get there continuing with that grinder.

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    I would buy new 50 taper end mill holder and adapt that to have the needed thread. 50 bucks from ebay and you are starting with known good taper instead of this fiasco.

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    If you can't regrind the existing taper, how are you going to regrind plating?

    Indicating an existing taper is just a starting point. Grinding tapers is an iterative process. You grind, blue it, check fit, adjust. Rinse and repeat until you are pleased with the contact. Now go put the arbor back in the grinder, bump the little end into the wheel by .0005 and try it again. You don't get to quit after the first try. Think of it as trying to get laid. You didn't give up after the first time you were turned down, did you?

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    So, gotta ask. Was your indicator on center? Was your grinding wheel?

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    Quote Originally Posted by MattiJ View Post
    I would buy new 50 taper end mill holder and adapt that to have the needed thread. 50 bucks from ebay and you are starting with known good taper instead of this fiasco.
    That’s a good idea that’s crossed my mind in a similar form, namely picking a holder we have that’s either a dupe or one we probably won’t need, that has a protrusion with o.d. over the 2 1/4 in. We’d need to cut the 2 1/4-10 threads. Not sure how hard the protrusion area normally is, thought they were case-hardened, so a larger o.d. protrusion would have enough meat to grind or turn the hard stuff off for threading it.

    I did lookup the Eboo arbors, they’re certainly options if I want to fit a pre-threaded bushing on, then it’d have to have a never-slip joint with Dutchmen, keys, or whatever.

    I’ll Probably summarize several options with cost and risk on paper then pick one.

    NMTB 50 Taper 1" Tool Holder new | eBay

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    Quote Originally Posted by eKretz View Post
    So, gotta ask. Was your indicator on center? Was your grinding wheel?
    I had the indicator as close to where wheel contacts arbor as possible. But might be worth revisiting that setup. Was it on center, I’m sure u mean vertical center as with lathe cutter position, well probably not.

    Grinding wheel isn’t vertically adjustable on this machine, it has same center height as the two dead centers holding the work.
    Last edited by Cannonmn; 10-27-2020 at 09:20 AM. Reason: Mobettah

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    Quote Originally Posted by gbent View Post
    If you can't regrind the existing taper, how are you going to regrind plating?

    Indicating an existing taper is just a starting point. Grinding tapers is an iterative process. You grind, blue it, check fit, adjust. Rinse and repeat until you are pleased with the contact. Now go put the arbor back in the grinder, bump the little end into the wheel by .0005 and try it again. You don't get to quit after the first try. Think of it as trying to get laid. You didn't give up after the first time you were turned down, did you?
    Nah, didn’t go to that length, maybe oughtta go back and spend some more time with it. As to the initial question, we’ll never need to regrinding it after it is put right once, not used that often and shop will close in a few years for retirement/lease expiration. Am hoping, if that option selected, to find a shop that will both plate and grind it.

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    when you copy an existing holder by putting it between centers in that grinder and indicate it in to set the taper angle, you absolutely MUST have the indicator right on the centerline of the taper, else you're setting some random angle depending on how much off of the center you're are - this is probably the problem you're having there

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    Quote Originally Posted by Cannonmn View Post
    I had the indicator as close to where wheel contacts arbor as possible. But might be worth revisiting that setup. Was it on center, I’m sure u mean vertical center as with lathe cutter position, well probably not.

    Grinding wheel isn’t vertically adjustable on this machine, it has same center height as the two dead centers holding the work.
    So you are using an actual O.D. grinder then? Grinding wheel height should be fine in that case. You need to have your indicator pretty close on center in order to set the taper even somewhat accurately that way. Generally you get it close that way then make the final tweaks per your bluing print.

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    Quote Originally Posted by jz79 View Post
    when you copy an existing holder by putting it between centers in that grinder and indicate it in to set the taper angle, you absolutely MUST have the indicator right on the centerline of the taper, else you're setting some random angle depending on how much off of the center you're are - this is probably the problem you're having there

    Ok got it, will revisit that this pm.

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    Quote Originally Posted by eKretz View Post
    So you are using an actual O.D. grinder then? Grinding wheel height should be fine in that case. You need to have your indicator pretty close on center in order to set the taper even somewhat accurately that way. Generally you get it close that way then make the final tweaks per your bluing print.

    Yes, B&S no. 1. It is old but I think accurate where it counts. I know the manual says always grind in automatic feed, but due to some too-exciting events where the left travel stop didn’t hold and the wheel banged into the arbor flange, I oscillate the table manually.

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    So, just got done with more grinding. I checked for correct center height of dial indicator then ran arbor along it, no deviation seen on 1/2 thou indicator. I put it in Undamaged spindle I’ve blue-checked vs. new arbor and this is the little blue that printed (link). The neck’s diff diameters either side of groove, are 1.548” on top, and 1.532” on bottom included in my grinding. Maybe that means it is hopelessly overground? Anyway seems to me I need to shave more off the big end in order to get any contact above it.

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    Last edited by Cannonmn; 10-27-2020 at 03:50 PM. Reason: Fix

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    Well thanks for all the advice, I learned from this even tho the arbor never fit. It got so slim it rattled in the spindle after my last grind, so I’m not working on that one anymore. Maybe some day when more time is available I’ll cut down the arbor so the nice threaded end remains attached to a remnant that’ll fit into a good nmtb50 holder we already have, that can transfer the high torque to a large boring head.

    We have another identical large Criterion boring head with same problem, somewhat rough surface on the taper. I’ve had enough of taper grinding for a while so I plan to swing that one in a lathe with ram removed, and hand-stone the roughness off. The blued finish is still on it so it should be easy to see when I get the very small high spots down to a smooth surface.


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