stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Sept 4, 2021 9:04:15 GMT
Dan, Forgive me if I'm missing something here, but if you mount your collet holder in a self-centering 4-jaw chuck, you are never going to be sure that the body is running true (unless you have an exceptional chuck). I would think that if you want to hold the collet body in a chuck, it should be an independent 4-jaw, and adjust the chuck jaws until the collet body runs true. But that then begs the question "Why use a collet chuck at all?". With an independent 4-jaw you should be able to adjust the work in the chuck jaws to run as accurately as you desire. Yes indeed, that’s how I read it too. To make sense, the collet chuck should be a direct fit on or into the lathe headstock or the mill spindle. Nothing else makes any sense to me. But oh deary me, a 4-jaw is no substitute for a set of collets, life is too short for that. I know there are highly skilled craftsmen who can set up a 4-jaw quite quickly, but that person is not me! The joy of being able to switch work around from one collet to another in seconds, and know it will be accurate, is beyond price. I hardly ever need to use my 4-jaw independent now; it gets less use than the 4-jaw self-centring chuck (which is a little-known and under-rated piece of equipment IMHO) Gary I agree Gary. A collet chuck, fixed directly to the lathe/mill spindle is the ideal solution. I merely mentioned that if Dan is going to hold his collect chuck in the 4-jaw, he may as well hold the work in it. That's not meant to imply that having a 4-jaw independent is any substitution for a good collect chuck.
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abby
Statesman
Posts: 927
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Post by abby on Sept 4, 2021 14:17:18 GMT
The purpose of this post is to verify by my own findings that some cheap Chinese made tooling does not meet the claimed quality/accuracy and is often money wasted.
Sorry ,I thought it was clear that for the purpose of quickly checking the accuracy of the collets I used the previously described method.
Yes I could have set up the ER chuck in my independent 4 jaw but it would have been an unnecessary step , I have a very accurate 4 jaw self centering chuck fitted which I rarely remove Holding the collet chuck in my 4 jaw SC then clocking the runout gives me a known standard , any deviation from that standard gives me an idea of the accuracy of the collets.
BCA type jig borers are incredibly useful ME machines that don't appear for sale often. Spares and collets are rare and expensive and fitting an external chuck to the existing spindle reduces the useful height above the work table.
My BCA was made in 1942 ,there is wear in the spindle , in the few original collets that I have and in the bearings. In order to put back it's accuracy , especially for very small end mills , I have firstly made new bearings.
The second stage will be to make a new spindle which will be built around the ER16 chuck , and hopefully accuracy will be restored to 1/2 a thou. However if the bought in items are not accurate to start with the whole exercise will be a waste of my time.
I hope this clears any confusion. Dan.
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Sept 5, 2021 18:47:42 GMT
The purpose of this post is to verify by my own findings that some cheap Chinese made tooling does not meet the claimed quality/accuracy and is often money wasted. Sorry ,I thought it was clear that for the purpose of quickly checking the accuracy of the collets I used the previously described method. Yes I could have set up the ER chuck in my independent 4 jaw but it would have been an unnecessary step , I have a very accurate 4 jaw self centering chuck fitted which I rarely remove Holding the collet chuck in my 4 jaw SC then clocking the runout gives me a known standard , any deviation from that standard gives me an idea of the accuracy of the collets. [Snip] Hi Dan If you can eliminate run-out altogether with your ‘ER chuck in a 4-jaw SC’ then you can be very specific about collet run-out. The trouble is, if you have run-out already in the chuck set-up, then the collet, also with run-out, might cancel out the original runout, or add to it, all depending on the luck of where the run-out is located relative to the chuck when mounted in it. If you have (for the sake of argument) .001 run out in the chuck, and .001 in the collet, then the measurement you read from the collet might be anything from .002 to zero. So strictly speaking, deviation of the collet from the chuck run-out gives you a range of uncertainty of + or - whatever the original reading was. And on re-reading, I think this is what you were saying in your original post on the subject, but I’m afraid I didn’t grasp it first time round! In extolling the virtues of a set of collets, yes, mine will have less-than- perfect precision, but perfect precision costs a lot to achieve, and most of us don’t need it; they were not expensive and I’m happy with what I’ve got, others might not be. I guess the VFM calculation with the Chinese products is the old conundrum of how much price vs how much inaccuracy is tolerable. (I’ve no idea if mine were Chinese; I suspect they may have been Indian) You are lucky indeed with your 4-jaw SC, both my SC chucks have too much run-out for fine work, and what is worse, it is inconsistent AFAICS, so I don’t see a lot of point in the usual suggestions of grinding the jaws etc. But there are usually ways around; indeed there have to be, because the max capacity of ER32 collets is so much less than a SC chuck. Gary
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