A2-3 5C threaded spindle nose cracked - replacement ? Takahashi TNC-LT-0

Hi

I had crash in X on a long part being held in my 5C threaded spindle nose, this has cracked the spindle nose to the point where the runout is excessive. The Lathe is an older Takahashi TNC-L-T0 running Fanuc - 21T. I took the spindle apart and from measurements it appears to be A2-3 spindle however with metric bolts (3xM10). I am wondering who might be able to supply a 5c threaded spindle nose in A2-3 ; I've looked around but no one seems to list this type of spindle nose .

I've taken a crack at reverse engineering one but I'm not clear on the 5c tolerances as I use a lot of threaded collet closer tooling and my home-made version I'm not sure on where to bottom out the closer.

Any tips on suppliers in North America or should I look at making mine better ?

Thanks
-P

I've attached pics you can almost see the crack but it actually goes down into the nose about 1.5", it flexes way too much now to use. I am still able to use it with an external collet closer (because it tightens down on it) but cant use anymore with normal 5C collets.

Also attached pic of my home-made one semi-complete. You can see the issue I am having is how deep to cut the taper and the "bottom" seat for the closers. Wouldn't be an issue if I was just using it for normal collets but need it to work with both normal collets and oversize collets with closers...

You could look at making a threaded collar with a very close fit at the thread to act as an external support when using regular inside taper mate collets. Even split the collar so you can clamp down to "0" clearance on the threads.

While not a perfect solution, it would be quick to implement and let you take some time to get a better setup in place. Doesn't need to be hardened or a fancy steel, just reasonably carefully made to function well.

If I am understanding. Is the issue that you dont have an accurate way to measure the TSC of the tapers?

High Quality Precision Dimensional Inspection Gages

model 77M with ball styli look on ebay, thats where I bought mine.

You have a qualified part or "benchmark" so setup of the gage is much less fussy than just using gageblocks and grinding to a print dimension.

My issue with making the replacement is I am uncertain of the proper specification for the 'closer'. i.e. is it bottoming on the threads or on the lip at the bottom of the threads (I assume the lip because why else would it be there), and also on the inside is bottom face of the closer supposed to sit flush with the spindle nose or ?? I have seen the 5c specs on the site so can get the taper cut, but its the external threaded closer spec I am fighting with. For only doing a single I'd be happy to buy one but cant find one anywhere :-)