Live center modifications

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ccfl
Posts: 118
Joined: Wed Jun 01, 2016 9:14 am

Live center modifications

Postby ccfl » Tue Jun 13, 2017 8:00 pm

Since I recently put my lathe back into a working state after however many months on the Healing Bench(h/t AvE), I decided to test it with a project entirely inappropriate for a cheap, flimsy 7x12 lathe: making a new extended nose for a cheap live center (http://www.shars.com/products/toolholdi ... e-center-2). This should really be done on a cylindrical grinder, or at least a grinder of some sort, right? Can I make something at least as good as the original?

original_nose.jpg


Per the listed specs, runout is touted as .001" or less (wow!)(also claims to be hardened to 58-62HRc, but I promise you, it is not). Removal is easy without disturbing the bearing stack inside. The shank is hollow, insert a rod and tap-tap-tap and it comes right out.

Material started as 1"OD 1144 about 4" long. I do not have a collet chuck or anything fancy that would make this easy, just a 5" 3-jaw (though, it's a good'un, from Japan, even) on a homemade adjustable backplate. In the first setup I turned the bearing journals and established the final OD where it passes through the front retainer/o-ring. (I overshot the rear bearing journal by a really tiny amount and had to knurl & re-turn. Oops, managed to save it, but no one will ever see it unless I show pictures of it on the internets.) Then flipped it around clamping on the front bearing journal and adjusted the chuck to zero and turned the nose features. Final finishing was done by hand with a medium India stone & WD40.

new_vs_old.jpg


Another thing, the body OD was ridiculously huge, the wall thickness at the front bearing was like .235" thick. I cut .200" off the OD for more toolpost/compound clearance. I don't know what that material is, but it is HORRIBLE STUFF. The chips behave like Stressproof but oh man, it's not. Nothing I tried would cut it without tearing. Not conventional HSS, not HSS in a tangential/shear holder, not coated carbide, not uncoated/hand-sharpened carbide. I gave up and left it ugly.

finished.jpg


As finished, the best measurement I can do on it shows runout on the 60* point is bit less than .0001", I was not expecting that but I'll take it. At any rate, the new nose is more accurate than whatever no-name bearings are inside, so I'm happy with how it turned out.
"Never trust a man who puts a witty quote in his sig line." -Mark Twain

pete
Posts: 1278
Joined: Tue Feb 10, 2009 6:04 am

Re: Live center modifications

Postby pete » Wed Jun 14, 2017 2:44 am

Those are real good run out numbers. Some very expensive well made live centers have about that. And even better you managed that with any 3 jaw. Since it's soft you might want to think about preserving it for only your most accurate needs. And trying to off set the tail stock and using it while taper turning will seriously wear the tip. Since the original outer body was likely designed to be ground as a finishing step, they probably didn't care too much about the materials surface finish qualitys while turning it to size.

Sometimes when I've had surface finish problems no matter what I try then upping the feed rate can help. Not always, but enough to make it worth trying.

ccfl
Posts: 118
Joined: Wed Jun 01, 2016 9:14 am

Re: Live center modifications

Postby ccfl » Wed Jun 14, 2017 2:04 pm

This little toy lathe only has one gearset for turning, I think feed rate is .008"/rev(!). I tried all of everything. Hand feeding, spindle speed, tool nose radius... oh well. When even the shear bit taking a .001" cut didn't work I realized it wasn't anything I was doing wrong. Even hand-filing left it with big gouges and streaks. It's smooth to the touch now, just ugly as sin.

I haven't needed to offset the tailstock for anything yet, if I ever do I'll burn that bridge when I come to it. I do have halfway decent MT2 & MT3 carbide tipped dead centers stashed away for really fiddly stuff.

I really, really did not think this would come out usable, much less with that little runout. If it were a part I could do all the critical bits in a single setup, sure. That I would've had confidence in. But the flipping around and re-chucking was where I thought it would fall apart. My chuck is really very nice, it's got excellent hard (very hard) 2-piece jaws, and I've reground the jaws with the chuck properly preloaded (inner, outer, & top faces). I like knowing that I can trust it. It was an ebay score, covered in goo and sawdust(?) with no markings visible, paid an embarrassingly small amount of money for it, about half what a new generic Chinese chuck sells for. Even though I put a lot of work into it it still feels like I stole it. Disassembled, ultrasonic cleaned, deburred, polished, converted to front-mount, jaws reground, new flush ball oiler made from brass stock...

chuck_before.jpg


chuck_after.jpg

Cast Iron backplate made from the original SB9 threaded one, only .400" thick (not counting the front register inside the chuck). 4x #10-32 adjusters...
adj_backplate.jpg


I don't know how it's possible for an old used & apparently abused chuck but there is zero side play between the master jaws and the body. In fact there is negative clearance. With the scroll removed it's difficult to slide the jaws in the slots by hand. The chuck repeats, when re-clamping the same part, to less than I can measure with a tenths indicator (it does have a 'master pinion' marked and it does make a difference which pinion is used). There is some variation when changing clamping diameters which is inevitable just by nature of the scroll plate, but it is only around .0015" through the whole range. It's a true gem.
"Never trust a man who puts a witty quote in his sig line." -Mark Twain

pete
Posts: 1278
Joined: Tue Feb 10, 2009 6:04 am

Re: Live center modifications

Postby pete » Wed Jun 14, 2017 3:06 pm

Off setting the tail stock can be done accurately by measuring the off set with an indicator as it's shifted sideways. More important is getting it lined back up with the headstocks C/L. But isn't too tough with a good indicator attached to a chuck or the faceplate and sweeping either side of the tailstocks morse taper. However trying to check the tailstocks vertical alignment with the headstocks C/L with the same setup will drive you nuts trying it. Gravity will throw your readings off by a lot. It's a very real problem and there's a few threads on the PM forums about it. My small lathe doesn't have the ability to shift the tailstock over so I use an off settable dead center for taper turning on that lathe.

I paid a great deal for my Emco chucks and get about what you are after regrinding yours. There's not many 3 jaws that can do that without paying some large money. You'll be having a real bad day if you ever crash the top slide or tool post into it though. Mine have those master pinions as well and I've found the same. That one does make a measurable difference.

ccfl
Posts: 118
Joined: Wed Jun 01, 2016 9:14 am

Re: Live center modifications

Postby ccfl » Wed Jun 14, 2017 5:03 pm

Yeah, this tailstock is not meant for offsetting either, though it's technically possible. It has a lock screw on the underside and no jacking screws up top. No fun to mess with. It's roughly aligned now but I still have some headstock alignment work to do before messing with it any more.
"Never trust a man who puts a witty quote in his sig line." -Mark Twain

spro
Posts: 6753
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Live center modifications

Postby spro » Wed Jun 14, 2017 6:34 pm

Sometimes it is better to say nothing. Sometimes it is appropriate within the context of appreciating the work. This is a delicate balance and hope I don't blow it. The extended live center is probably too long. One way to check that is to mount an indicator on the saddle. This could be on exposed cross slide ways. The idea is to traverse a straight shaft between centers or between the fine chuck and tail center. In this case, use a blunt tool, reversed tool holder or something to which nominal cutting pressure would be applied in use. You can then measure the relative difference of linearity as it approaches the live center. This is an un powered check which will expose some things.

ccfl
Posts: 118
Joined: Wed Jun 01, 2016 9:14 am

Re: Live center modifications

Postby ccfl » Wed Jun 14, 2017 6:54 pm

Not sure I understand. You mean applying pressure with a [blunt whatever], while measuring deflection along the mounted shaft?

I already know not to waste time on messing with tailstock alignment (yet), since I know from previous measuring that the headstock is quite a bit off (chuck-held-only turning cuts are tapered .001" per inch, smaller towards tailstock end). I have a spare headstock with tapered rollers in it I need to swap in and align, one of these days. Headstock currently in place still has the little toy radial bearings.

So... knowing that the headstock alignment is way off, and that means the tailstock alignment is also not gonna be right, will I learn anything useful checking deflection while traversing along a shaft between centers?
"Never trust a man who puts a witty quote in his sig line." -Mark Twain

spro
Posts: 6753
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Live center modifications

Postby spro » Wed Jun 14, 2017 7:12 pm

Probably, as it doesn't take much time. The deal is, is that you are really into this now and would be making parts even before everything is perfect. (I did) It is just a check and you can place the shorter one in there and check the differences. No surprises when you need to figure out why something is tapered more than something else closer to the chuck. If one records these differences, their improvements in alignment are noted right there. Believe me; it is better than just trying to remember every thing as long as you can still find the notes :)

ccfl
Posts: 118
Joined: Wed Jun 01, 2016 9:14 am

Re: Live center modifications

Postby ccfl » Wed Jun 14, 2017 9:34 pm

OK, but just keep in mind this is a machine I can pick up and carry across the shop without hurting myself. I would not be surprised or disappointed if I found I could deflect the bed by maybe .002" just by pushing down real hard by hand. I'm working on making it accurate, it will never be robust. It'll be a nice backup once I finally get that 14x40...

I never posted an update in that other thread, but I finally got off my butt and finished the saddle/cross slide epoxy job. Added flush oilers on the rear legs of the saddle, ports up to feed the cross slide ways, and so on. It works fantastic. The alignment is correct, it's smooth as butter, and hopefully the magic epoxy will prevent it from wearing out prematurely. If the headstock were properly aligned with the bed, the x-slide alignment I ended up with would make facing cuts that are concave by .0005" over 6" which is just silly. Right now, with the headstock sitting crooked, it faces more concave than that (.001" per inch, same as the taper on turning, since it's a right angle) - but before the recent work it made CONVEX facing cuts which was just unacceptable. It'll get there eventually.
Last edited by Harold_V on Thu Jun 15, 2017 1:53 am, edited 1 time in total.
Reason: to remove unacceptable language
"Never trust a man who puts a witty quote in his sig line." -Mark Twain

spro
Posts: 6753
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Live center modifications

Postby spro » Wed Jun 14, 2017 10:06 pm

There is another thing which slowly escapes and then goes really fast: Time. It is best to get the concepts down while you have time for them. Even with the better, larger machines, what you learn now relates to what you call a toy now. I think I know why you call it a "toy" because there are so many larger and more serious lathes being discussed here and elsewhere. The stuff you learn know .. and not saying that you are a newbie any more than me. You've posted pictures and examples of work to benefit us.
I've been around a long time but sort of stuck in the old ways. Maybe only good for relating back to the concepts or grinding tooling but I can be replaced in a day. I/We have seen, right here, newer members advance so quickly they are understanding and building engines or knowing software of advanced control and employed in industry now.
There is that window by which you can only learn the other side and why and why not, things work. I think this knowledge from our smaller machines is useful to the future.
Okay. Just read your reply. It is clearer to me now. Maybe I should've deleted the above but something must resonate.


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