Author Topic: eBay Accuracy Humour - Live Centers That Is  (Read 788 times)

Carpenter84

eBay Accuracy Humour - Live Centers That Is
« on: July 11, 2019, 05:59:10 AM »
I noticed my live center smoking last night. Lol... i put new bearings in it and packed it with grease about a year ago... gonna assume I screwed up and she no good. Haha

Perusing eBay this morning looking at live centres. Check out the accuracy the Chinese advertise! They must have so little idea of what theyíre talking about that theyíre just making up numbers at this point. Check out the first photo... what is that number? Is that even a measurable amount??

I want a center with that long nose. I always have a problem getting my tooling in close to my center.

The second photo. 20 thou?!
The third photo is the only one thatís reasonable.
And the fourth photo is shars. Which i would buy, but on every item Iíve looked at from shars in the past all have ridiculous shipping.. really, just outlandish shipping for somewhere thatís not actually that far away.
« Last Edit: August 25, 2019, 09:40:54 AM by 4GSR »
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

woodchucker

Re: eBay accuracy humour
« Reply #1 on: July 11, 2019, 10:46:05 AM »
can't talk about the accuracy, but I will say, that I would be bothered by 3 bearings.
it's easy to align two things, it's hard to align three.  would it be better with 3... maybe, but in my mind, a thrust bearing in the back, and a bearing in the front should suffice. would 2 in the front work better...??? maybe, but aligning that thrust to the two in the front might cause more problems if not exactly located.


my 2 cents... That's why there are flex couplers for motors that allow multiple bearing surfaces to be slightly out of alignment.
would an integral set of bearings be better aligned.. probably, but there's still room for error.
Jeff
Clausing 8520   SB Model 9a - power hacksaw, Milwaukee band saw in a table.  Delta Rockwell Surface Grinder (not online yet .. being rebuilt where am I going to stick this)
For pics: https://imgur.com/user/woodchucker/posts

Carpenter84

Re: eBay accuracy humour
« Reply #2 on: July 11, 2019, 12:46:16 PM »
Ya I wondered about that too. I asssssume it's 2 front one thrust. Unless it's actually just three big balls rolling around....
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

4GSR

Re: eBay accuracy humour
« Reply #3 on: July 11, 2019, 02:12:18 PM »
If they are angular type of bearings, the front two take the thrust and the rear one keeps it in alignment radially.  It also provides a preload for the bearing stack when designed correct.  I bought a live center made in India to go with the 13" lathe I used to owned.  I could wiggle the center point up and down, but when I applied thrust to the point, it straighten up and ran true.  Never seen one made like that!

Most of mine are dumpster dive Rhone (sp) live centers that the center point was damaged.  Set them up on my T & C grinder and re-sharpen them.  They run good as new.  Oh, the bearings were in very good shape.  I have a couple of home made bull centers that just run on two bearings.  Because they are on two bearings, not double row bearings, they still wobble when holding a work piece.  Probable if I shimmed the bearings to give it a preload, the wobble would go away.

Carpenter84

Re: eBay accuracy humour
« Reply #4 on: July 11, 2019, 02:47:00 PM »
I think I could take a stab in the dark and say that Chinese $20 3 bearing center doesn't have angular contact bearings. Lol.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Bill Gruby

Re: eBay accuracy humour
« Reply #5 on: July 11, 2019, 02:51:04 PM »
 It may not be three, it could be a double row in front and a single in the rear position.

 "Billy G"
Don't sweat getting old, you'll still do dumb shit, just slower.

An Optimist will tell you the glass is half full, the pessimist half empty, the engineer will say the glass is twice as big as it needs to be.

Carpenter84

Re: eBay accuracy humour
« Reply #6 on: July 11, 2019, 02:56:24 PM »
Just a bunch of roll cages with washers for races? Lol
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Carpenter84

Re: eBay accuracy humour
« Reply #7 on: July 11, 2019, 02:56:58 PM »
Hey... I'm still standing by my prediction of there just being 3 big balls rolling around a shaft.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Carpenter84

Re: eBay accuracy humour
« Reply #8 on: August 23, 2019, 05:57:00 AM »
So, just in case anyone was wondering...

I bought two of these Chinese centres... and boy-o-boy, are they ever Chinese.... like... more Chinese than I bargained for ... *le sigh*


I got the skinny pointed centre because I always have issues with tool clearance, and I got a pipe centre, because Iíve run into numerous times when my centre was too small. Both are softer than butter, neither of the mt2 tapers have tangs on them and do not pop out of my TS (even tho they advertise ďextra longĒ Morse taper arbors...), the pipe centre only has two 6006 bearings, and I can pull the top of the centre off by hand to expose the bearings. No thrust bearings at all. (I know this because it came of very easily when I got the damn thing stuck in my ts...) The pointed centre I cannot pull off. Itís all pressed into a blind hole with no punch hole in the rear of the arbor....

If I indicate and spin the centres by hand thereís .0005Ē~.001Ē run out, as advertised. But when engaged in the work the pointed one imparts almost .003Ē runout on the work - however! I know my ts is not centred on my spindle... I need to do some work there. Iím obviously getting off centre holes with my centre drills. However, even after taking skim cuts thereís still runout, so, the centre is definitely deflecting or thereís runout in the bearings under load.

So, all in all, wasted $40. Iím not really even sure thereís enough in these centres for me to even improve on. Thereís a bunch of false advertising. They claim hardened materials that arenít - tho, I did forget to check if the MT is hard, the points certainly arenít. Thereís certainly not three bearings either. No tangs/short arbors.

Usually the Chinese eBay purchases arenít thiiiis bad... bummer.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Bill Gruby

Re: eBay accuracy humour
« Reply #9 on: August 23, 2019, 07:39:35 AM »
OK, ebay does not set the tolerances so they are not at fault here. THE SELLER IS. Ebay gets a bad enough rap with out this. It's buyer beware. My 2 cents worth.

 "Billy G"
Don't sweat getting old, you'll still do dumb shit, just slower.

An Optimist will tell you the glass is half full, the pessimist half empty, the engineer will say the glass is twice as big as it needs to be.

4GSR

Re: eBay accuracy humour
« Reply #10 on: August 23, 2019, 07:43:12 AM »
To get a good live center, you're going to spend some money.  Over $100 USD to start.  Forty years ago I bought a Rohm live center for the 9" SBL, with a no. 2 MT.  Been used a lot over the years, no runout, still good as new.  Paid a whopping $59.99 for it back then.  I know the same one today is I'm guessing around $150 USD.

They do come up used once in a while.  The few I've bought, the points were all buggered up.  I set up on my T & C grinder and re-ground the points.  They now have very little runout.

4GSR

Re: eBay accuracy humour
« Reply #11 on: August 23, 2019, 08:03:24 AM »
Shawn, If you can figure out a way to pull the live center apart, Might be worth getting a set of real bearings to install in place of the OEM bearings.  Again, maybe just as cheap to buy a good center for the price of a set of high precision bearings.

4GSR

Re: eBay accuracy humour
« Reply #12 on: August 23, 2019, 08:16:02 AM »
Out of all of the Chinese and Indian made centers, this one is probably the only one I would trust...

https://www.ebay.com/itm/NEW-2MT-PRECISION-DOUBLE-ROW-LATHE-LIVE-CENTER-MORSE-TAPER-2-FOR-CNC-LATHE/230922241103?hash=item35c409c44f:g:SvoAAMXQAwNRC~6f

This one is identical to my Rohm center I use on my 9" SBL.  With most of the tooling I use on that lathe, it does fine.  The only tool I have an issue with is the insert threading tools, the center point will get in the way.   I have an old school live center with a small OD point that will allow me to get the threading tools down to about 3/8" in diameter with problems.  Anything smaller, I can't see good enough to thread.  That's when the geometric die head comes in use or good old die for threading.
Ken


4GSR

Re: eBay accuracy humour
« Reply #14 on: August 23, 2019, 08:35:37 AM »

Machinists Gazette

Re: eBay accuracy humour
« Reply #14 on: August 23, 2019, 08:35:37 AM »