Reducing collet nut play by electroplating thread?

[Adam HarrisParticipant @adamharris13683]

I have a Nikken NX-5 spindle speeder that I picked up very cheaply on account of the owner crash-driving the collet with cutter so hard into the spindle nose taper that he could not get it out and the wedging created a hairline crack down one side of the spindle nose thread. I have managed to remove the collet and everything seems to work surprisingly well, but obviously I want to keep the crack closed when tightening the collet nut and to this end I am thinking nickel electroplating the nut thread to make it a tighter fit onto the nose makes sense. I think I have read here that some firm(s) do a nickel electroplating job to a user specified thickness in microns. Is this so, and any recommended places to get it done? My other question is how to calculate the absolute minimum play twixt nut thread and nose thread to avoid binding? The thread is M20 x 1.0mm pitch. Any advice much appreciated.

[Adam HarrisParticipant @adamharris13683]

How long should nickel electroplating by a few microns an M20 x 1.0 nut take? If a matter of minutes/hours, perhaps best would be to visit the shop and specify a number of microns and repeat according to trial and error until fit just tight enough ?

[DiogenesParticipant @diogenes]

I think the fundamental problem with that is that parallel threads only exert axial and not radial pressure with any great efficiency.

I don’t think you will get it to be a tight enough fit to eliminate flexing under cutting loads, without it being almost impossible to undo.

If there’s enough ‘meat’, machining off the old thread and shrinking/pressing on a sleeve to receive a new or modified nut would be a much better solution.

Edit; using the existing thread to receive a slightly tapered / ‘unfinshed’ nose extension on a ‘once-only’ basis might be possible, but will leave you more stick-out, probably not a good thing..

[HopperParticipant @hopper]

Yes it seems rather hopeful to retain the taper with plating on the nut. Might you be able to silver solder the crack up instead? Or machine down and instal a band as suggested already.

Re plating, if you wanted to try, maybe a home zinc-plating kit would allow you to build it up in stages until you got it how you wanted it. I think to plate an internal thread, you will need to set it up with the electrode down inside the hole, otherwise plating usually does a poor job of going inside holes.

Very hard to measure how much thickness you need though. Measuring the OD does not tell you that. It will be undersize for tip/root clearance, but it is the bearing surfaces on the flanks of the V groove that take the load and will need building up. You would need to measure them with the three-wire method.

[Hopper]

On Hopper Said:

…
Very hard to measure how much thickness you need though. Measuring the OD does not tell you that. It will be undersize for tip/root clearance, but it is the bearing surfaces on the flanks of the V groove that take the load and will need building up. …

For which reason, it might be easier to deliberately over-plate the thread thickly, and then machine it back to size with a die or lathe.  Removing metal accurately is generally more straightforward than adding it!

More fundamentally though, is this repair likely to be satisfactory?  Gut feel from the comfort of my armchair, is that a precision speeder running in the 10000 to 40000rpm range that’s sustained metal cracking damage is likely to misbehave under load.    The speeder might seem OK spun up off-load, but will it cut accurately?   Might get an idea by padding the thread more-or-less thickly with PTFE plumber tape and experimenting.

Plating will cost time and money and results in the sort of repair I would hope not to find on a second-hand tool bought from ebay!   Adam is the man on the spot though; he’s best placed to judge if plating is a brilliant fix or a horrible bodge!

Dave

[Clive FosterParticipant @clivefoster55965]

There are specifications for modified threads to make room for plating. One of my 1950’s engineers handbooks (Newnes?) has a short section on the subject giving specifications for BSF and Whitworth threads.

Maybe something modern and comprehensive covering this subject could be found on the internet. This would at least give you some idea as to what can be achieved and how much plating thickness would be needed.

That said I’m firmly in the turn down, shrinking a band on and cut a new thread camp.

You don’t say what breed of collet you have but if space is short is there any reason why you can’t make the band oversize with a larger thread and make a new nut to suit. Obviously the thicker the band the more support it will give to the cracked area.

it appears that collet nut threads are made a bit slack so the nut can shift a touch to be properly centred on the collet. It would seem that if the threads were made really tight there is a danger of pushing the collet slightly out of line should there be any errors in concentricity between the thread and the rest of the system ie both collet taper and the collet itself.

Clive

[Tony Pratt 1Participant @tonypratt1]

Sorry to say I’m absolutely sure plating is not your answer, some sort of sleeve over the nut may work though.

Tony

[SillyOldDuffer]

On SillyOldDuffer Said:

…machine it back to size with a die or lathe

It is the nut he wants to plate. That is the piece with a female thread in it. Hard to use a die on a nut.

[Tony Pratt 1]

On Tony Pratt 1 Said:

…some sort of sleeve over the nut may work though.

It is the spindle, with a male thread and tapered hole up its centre, that is cracked. Sleeving the nut, which is undamaged and has a female thread, will not achieve a great deal.

[Michael GilliganParticipant @michaelgilligan61133]

Being unfamiliar with the aforementioned device … I had a look at Nikken’s web-site, and am suitably impressed:

https://www.nikken-world.co.uk/products/spindle-optimisation/spindle-speeder

Whatever is done deserves doing very well.

MichaelG.

[ going off to ponder ]

.

Edit: __ some useful info. here:

https://www.nikken-kosakusho.co.jp/en/product/index.php?seq=23

[DC31kParticipant @dc31k]

It has already been touched on twice above, but the whole idea is misguided from a mechanical point of view.

Look at the degrees of freedom of the three parts (spindle, collet and nut) and how each degree of freedom is eliminated.

Think of a lathe chuck that goes onto a threaded spindle nose. The register provides concentricity; the threads are supposed to be loose enough so that they only provide axial restraint. The collet/nut/spindle assembly works in a similar way.

If you tighten up the thread clearance so that it does attempt to provide radial as well as axial restraint, it will fight whatever mechanism is already in place to assure concentricity.

Tightening up the radial clearance of the thread will also tighten the axial clearance and could lead to skewed contact (unequal pressure) between the face of the collet nut and face of collet. You need a (relatively) rattling fit on the thread in both directions so the taper in the spindle is the only thing influencing the collet’s radial location and the face of the nut is pushing it smoothly and evenly into that taper.

[Tony Pratt 1]

On Tony Pratt 1 Said:

Sorry to say I’m absolutely sure plating is not your answer, some sort of sleeve over the nut may work though.

Tony

I didn’t read the OP’s original post thoroughly, as it is the spindle that is damaged obviously sleeving the nut will do nothing to solve the problem.

Tony

[Adam HarrisParticipant @adamharris13683]

Thanks everyone. The crack is hairline albeit all the way through and stops short of the base of the threaded part. I think turning it down in a lathe for a sleeve is not viable for 2 reasons – 1) whether in lathe or on mill, the action of a cutter might well exacerbate/extend the crack catching on it at each revolution and two 2) I am loathe to attempt to disassemble the head to extract the spindle for working on, especially when Nikken say it must be returned to their facilities for any disassembly, and without removing the spindle there is great difficulty in holding the nose as the body is vast and the opposing flats at the base of the nose very narrow. It would have to be a milling job with a complicated set up.

[DC31k]

On DC31k Said:

On SillyOldDuffer Said:

…machine it back to size with a die or lathe

It is the nut he wants to plate. That is the piece with a female thread in it. Hard to use a die on a nut.

Impossible to fix then!  Unless Adam knows about taps.  Bet he does!

Dave

 

[Adam HarrisParticipant @adamharris13683]

[Adam HarrisParticipant @adamharris13683]

You can see in the 3rd photo how the crack opens when a collet is pushed in. Not easy to know how much more/less it opens with the nut tightened up hard on the collet as obviously cannot view crack when under the nut. You can see in the 2nd photo the width of the head’s body compared with the 2 little flats to hold the spindle (18mm long and 5mm high at the highest point). Excuse the horrible clutter on the bench!

[Adam HarrisParticipant @adamharris13683]

I could press a very short but fat sleeve (ring) onto the base of the threaded nose where there are a couple of surplus threads in order to prevent the crack extending. I could bore out a bit of the nut to enable that sleeve to be a bit longer but then I am reducing the nut’s own ability to counteract the widening of the crack…

[Adam HarrisParticipant @adamharris13683]

The body of the nose is quite a lot thicker at the bottom of the threaded part (tapered socket for SK10 collets) than the top so it is rather worrying that the crack does go all the way to the bottom of the threaded part, albeit it does not appear to go any further than that.

[Adam HarrisParticipant @adamharris13683]

By the way, a new threaded spindle from Nikken is £678 and they imagine it may need other parts, thus totalling £1169 excluding labour so a bodge followed by very tender use is what I am looking for! A new NX5 is just shy of £4000

[Michael GilliganParticipant @michaelgilligan61133]

This may be bonkers, but:

I would consider making a solid ‘blank collet’ to fill the hole … then smear it with an anaerobic retainer and set it in place using the existing  [well-greased] nut.

Then remove the nut, and machine the blank, in situ, to take a ‘next size down’ collet.

[ if you see what I mean ]

MichaelG.

[simondavies3Participant @simondavies3]

Have you considered tightening a collet to open the crack, apply one of the mega-strength Loctites (or whichever brand you prefer) like 601 or 648 ( exact to be proposed by more expert than me, then swiftly remove collet to allow crack to minimise and the Loctite to (hopefully) permanently re-join the crack.

 

[Adam HarrisParticipant @adamharris13683]

Might be a good idea Michael – they do an SK6 collet which takes up to 6mm cutter which would be good enough for me. I could make an SK6 taper sleeve (same taper externally and internally) and glue it into the SK10 sleeve somehow. Then put some weld onto the nut nose and bore it out for the SK6 collets. What glue/anaerobic retainer would you recomend? I could hold the crack tight closed while gluing with an appropriate jubilee clip. Do you think the wall of the SK6 sleeve would be thick enough for purpose?

[ZanParticipant @zan]

If the crack opens when the collet is pushed in this could be worth a try it’s non destructive and relatively simple non destructive and no heat

1 machine a dummy collet

2 put a flat on the taper

3 clamp in situ to open the crack

4 dribble Locktite on crack and it may wick into the crack

 

Edit…….opps already mentioned above. didn’t see it!

 

[Adam HarrisParticipant @adamharris13683]

Do you think Loctite could really stop the crack opening when torquing down the nut on the collet?

[Adam Harris]

On Adam Harris Said:

Might be a good idea Michael – they do an SK6 collet which takes up to 6mm cutter which would be good enough for me. I could make an SK6 taper sleeve (same taper externally and internally) and glue it into the SK10 sleeve somehow. Then put some weld onto the nut nose and bore it out for the SK6 collets. What glue/anaerobic retainer would you recomend? I could hold the crack tight closed while gluing with an appropriate jubilee clip. Do you think the wall of the SK6 sleeve would be thick enough for purpose?

I would think it worth a try

… up to my ears in domestic stuff at the moment, so [sorry] can’t go searching the Loctite specs.

There is one that’s nearly as strong as 638, but’s more fluid

MichaelG.

[Author]

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