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Tailstock Tantrums


Not a good start to the day.  Drilling some Delrin blanks and my drill chuck spun, no biggy it has done that before.  Huh, not this time it has ripped a few rings in the taper.   Now I'm pretty sure the taper was clean, the lathe hasn't turned metal in quite a while so all swarf is plastic.   Mmmm, what to do ?   Ring Warco and see about a new tailstock barrel, possibly.   I haven't got a MT3 reamer, plus I wouldn't be sure it would cut true with the burrs.  As the taper is ground it HAD a nice finish, that doesn't mean it was accurate !!!

OK whats the worst I can do but bugger it up in true MAD modder style.  I have a little bit of experience in scraping so break out the tool.   "First cut is the deepest"  cut out the burr raised and remove the damage from the drill chuck taper, this was a little brutal, I didn't fancy grinding it as I have better feel with the scraper.   I didn't think to get photo's before I started so you only get to see the tailstock bore after I worked it, cut out the damage and then level all round the bore lightly using the scraper to make sure its all parallel and material was removed evenly.   This was the biggest gamble as I could pretty well ruin it at this stage making the bore bell mouthed.

At this point both bore and taper had been cleaned up and I tried them together to see if they fit and would twist (with oil) also see if they bind, OK so far, but need another taper to test so used the live centre.  Left a burnished ring on its taper so more scraping needed and slight work on the live taper now....

Finally sorted and both tapers feel OK, another problem I have at this stage is that I hadn't any idea how good the taper was before the damage so all I could do was blue up my best taper and blue the tailstock bore.  Once inserted and gentle twist to transfer blue, check bore with light and angled mirror.  The taper when I withdrew it showed where blue had gone, or not.

Next apply the chuck taper by firmly pushing in and get it blued.  The slide in contact doesn't look great, but more on that later.  I cleaned the taper and did a twist test to transfer more blue and check the overall contact pattern, not too bad.  Finally conduct the slide test with the taper in different orientations and look at the blue patterns.  Pretty much consistent pattern, so never wow contact all over.  At least we have no contact in the damaged area's so hopefully a taper binding in the bore due to this damage won't occur again.

Once cleaned up it was time to do some testing and see how things really are.  Sliding in the different tools the taper felt good, no tight spots and pushing it in firmly the taper locked.  Now that isn't something I could say before about this tailstock, it wouldn't always lock even with a firm clunk.  Tried muliple orientations of the tooling and feel how much force needed to eject the taper.   This actually feels better than it was !!!

My final testing is to see if the taper is still true and what deflection I get.   Remember I said I didn't know how good the taper was origionally, all I could go by was feel and how it had changed.  First setup was vertical deflection, I set up the "TEST" bar as true as I could and checked for runout along the bar, this was done multiple times moving the centre round, again checking how much force was  needed to eject the taper.  All OK, some deflection when pressing the centre at full extension of the tailstock barrel, so normal for this lathe as I have had to compensate for that before.  Finally do the horizontal, all the same as before.  Happily it all seems to work and a bit better than before.   Anyones guess how the taper was ground, but not sure it was that accurate.  My scraping will have made lots of little contact points, but looking at the blue it seems consistent at the nose and reasonable coverage further back, however the rear of the taper has very little contact.  I suspect this has always been the case as opening up the taper should have moved the contact further back, or resulted in less contact at the nose.   As before, the overall feel is much better for now.  Not sure I would recommend this method for repairing a taper, but if these are the tools and skill you have, what have you got to loose.  I very much recommend people learn to scrape, both flat and bearing surfaces.  It's one of those hand tool skills you can call on for such an event as this.

Cost me a days work, but the lathe is working again and not going to damage further tooling, or incur more cost getting it fixed.

I should maybe clarify for anyone unfamiliar with the deflection measurement used here, I am looking for a none return to zero on the indicator.  This might signify a problem in my scraping or an issue of wear in the tail stock.   You push-pull the live centre, not swing on it and see some deflection, the needle should come back to zero if all is well.  Any perceived click is bad, i.e the taper pivots, very cheap MT drill that doesn't match the taper its put into as a worse case example I have come across or the tail stock barrel is a poor fit / worn in its casting.   You are testing the whole assembly this way, so be careful not to jump to a conclusion, you might just have forgot to lock the tail stock.


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