Getting a reamer running true in a er collet chuck
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  1. #1
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    Default Getting a reamer running true in a er collet chuck

    The easiest way to get a reamer running true in er collet chuck using a dti when trying to clock it within 0.01mm or less on tight limit bores what way when you have a low spot to move dti

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    If (big if) I understand what you're asking, it's how to true up the cutting head of a reamer when a properly assembled ER collet still allows it to run out of true.

    Well, sometimes you can't, and you shouldn't. If the shank of the reamer is bent, even if you nominally true a section of the cutting diameter to "0", you've actually set up a conic cutting geometry along the rest of the diameter. If the reamer is really out, you should either regrind the shank true (and have it likely move on you later), or best, return it to its manufacturer with a nasty note.

    Other tricks are to shorten the shank to allow a closer to the flutes clamping. This cuts both ways (sorry), as it'll be truer, but stiffer, so remaining error will still allow a incorrect hole to be reamed. Or set up a couple Al "V" blocks, and use a press or a vise to try to bend the shank true. Wear good safety googles and don't be surprised if something snaps.

    Best choice is to use carbide chucking reamers. I've never had one with a bent shank, although I guess it's possible. Or, make a solid holder with an oversize hole and two groups of ~M6 set (grub?) screws, four near the nose at 90 degrees to each other, then another four identically arranged about 30mm above the first set.

    Now you can tediously adjust two levels of the reamer flutes to run true, which will give you as close a proper cylinder of cut relative to the hole as you're going to get. Only recommended when you're doing a bunch of holes, or can keep the assembly for future use. Small flats in the shank to match screw placement will help with stability and drive consistency.

    Go carbide. It's worth it, in my so very humble opinion.

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    First you have to establish if your error is centricity (runout) or coaxiality. Centricity will show a similar error in the same angular position near the top of the tool and the end of it. Coax error is almost always the greater of the two errors on ER collets using longer tools like reamers. Coax error will show up as greater error near the end of the tool than at the top near the collet.

    Centricity can be addressed by rotating the collet in the holder in small increments, while maintaining the angular relation between the tool and the holder, to even out any concentric error in the collet/holder. If using high quality, good condition holders and collets this error is usually in the sub 10μm range anyway and you really need a 2μm indicator to tweak effectively.

    If while doing the above you find that the error remains more or less the same, and in the same position on the tool, then switch the rotating the collet, with the tool, in the holder.

    If you still find that the error remains consistent with the tool, then it's safe to assume that the error is in the tool itself and not the assembly. At this point you have to accept that you will not get it perfect and move on to mitigating the error as best you can. If the error is small and you are able to change it to some degree using the collet rotation method above, then you can try and split the difference along the length of the tool.

    Severe coax error can be tweaked by reseating the collet in it's taper. Do this by setting the nut hand tight, then tapping (TAPPING!) the face of the collet nut with a soft face mallet as you tighten it. The top of the tool will move towards the side that you tap down.

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    You don't say what size reamer.
    For small ones, under about 3/16, I hang them way out. The hole you're reaming will straighten it up.
    For bigger, up to about 5/16, I still hang them way out, but I tap it around with a piece of brass to get it running true.
    For bigger than that, the guys above answered that pretty good.

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    Search for adjustable ER tool holder. There are several different styles and manufacturers with a "buckable" style head.

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    jeez, don't make a mountain out of a mole hill. Just bang it with a hammer till it runs true. Ok, so it takes a little more finesse than just banging on it, but a couple taps and you can easily get it within a couple tenths.

    Obviously, you also need to make sure all components are clean as a whistle and burr free.

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    Maybe I'm a little out of date, but I was always taught a reamer follows the hole which is the reason for the chamfer on the front end. Obviously, within reason, it can't be running .03" out or anything silly, but dialing it to .0002" ?

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    Quote Originally Posted by Mike1974 View Post
    Maybe I'm a little out of date, but I was always taught a reamer follows the hole which is the reason for the chamfer on the front end. Obviously, within reason, it can't be running .03" out or anything silly, but dialing it to .0002" ?
    I think a lot of guys think that reamers are sharpened along their flutes. However, they are not, they are circle ground, and only the chamfered ends are given relief for cutting. So oversize reaming is due to damage to one or more of the chamfered edges which forces the reamer to flop around as it mashes a chip. Also, because the flutes are circle ground, they very easily pick up material and form built up edge on top of a flute, which also forces an off center deflection.

    An out of true running reamer will tend to chatter on the top edge of a sharp hole. Good reason there to precision chamfer the top of the hole. If the hole was drilled, it is going to be a sloppy edge, so a few revs with a sturdy chamfer tool could help get the reamer into position quickly. Otherwise while that chatter is going on, the reamer is also in the process of 'hunting for position' and it may take a few thousandths of penetration before it forms a close fitting guide hole.

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    Depends on the reamer.

    I use cavity reamers a lot in aluminium. They do not have a cylindrical land.
    It takes less than nothing for them to leave scores and swirls in the bore. The edges have to immaculate (the tiniest nick will ruin the bore) and runout has to be absolutely minimal for them to cut acceptable holes.

    If OP is talking about some shitty £20 parallel reamer then sure, whatever.

    But there are legitimate reasons to need this kind of accuracy. OP didn't state, so I answered his question.

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    Another reason for tapping a reamer in after chucking is the aesthetics of the reamed hole. A reamer that is out a tenth or two will still likely ream an on-size hole, but the hole will have a visible groove pattern from the outermost flute dragging a bit. It is probably a small fraction of a tenth, but still visible and gives a bad impression.

    Note that tapping a reamer in is not banging on it so hard it bends. Rather, you are affecting the reamer + collet + collet chuck stackup. Light taps on the shank just above the flutes.

    Regards.

    Mike

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    I like these

    https://www.commandtool.com/assets/u..._true_zero.pdf

    Yes, for general purpose a thou or two runout on a hss reamer is fine. But for high precision roundness, size and finish I have found runout is critical (shocker alert).

    I started using those collet nuts on a job along with an Urma reamer. It's been a few years but I think it was 16 finish that was required on cast aluminum. Obviously, regular reaming methods were nowhere near where I needed to be. Actually used a little polishing wheel in the CNC to get the finish until the Urma reamer came in.

    Or.....depending on what you sizes you are reaming, step up to a boring head.

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    I have found that for smaller reamers, say 5/16" and down, concentricity matters for hole size if your trying to hold a tenth or two. I start off my tapping on the collet with my small brass drift, then on the reamer shank if needed, then try not to remove the reamer from the holder for as long as possible. Maybe the best solution is a better collet design, I think ER is pretty piss poor since it relies on the nut for alignment and 40% of the collet is proud of the holder taper.

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    Am I the only one here that uses a floating reamer holder?

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    Quote Originally Posted by moonlight machine View Post
    Am I the only one here that uses a floating reamer holder?
    Since most of my holders are made of steel, none of them float. Can't say I've ever seen a floating reamer holder. Picture?

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    Quote Originally Posted by gregormarwick View Post
    Depends on the reamer.

    I use cavity reamers a lot in aluminium. They do not have a cylindrical land.
    It takes less than nothing for them to leave scores and swirls in the bore. The edges have to immaculate (the tiniest nick will ruin the bore) and runout has to be absolutely minimal for them to cut acceptable holes.

    If OP is talking about some shitty £20 parallel reamer then sure, whatever.

    But there are legitimate reasons to need this kind of accuracy. OP didn't state, so I answered his question.
    What is a cavity reamer?

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    Quote Originally Posted by Mike1974 View Post
    What is a cavity reamer?
    Probably a penis implant for some.

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    For shits and giggles, I indicated a .187" reamer I had set up (without checking concentricity at setup) to do a job right now. It's running out about .010" and reaming a .1872" hole. How much more should I bend it to get it to ream to .1875?

    It's like claiming the sharpening of a drill point off center will make it produce an oversize hole. So I take a 1.75" drill that is worn enough that it squeeks a bit when it gets an inch in, and deliberately shim it with a .010" shim in the Oliver drill pointer and grind the point off center. It doesn't shift the hole diameter at all. Not even a little.

    Why do all these cause and effects seem to be so damn stubborn when you want them to work in reverse?

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    Quote Originally Posted by Mike1974 View Post
    What is a cavity reamer?
    A form tool for reaming hydraulic ports and valve cavities etc.


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