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Live center disassembly .

I wonder if the way they assemble those less expensive centers is to heat the cup assembly hot & drop the center/bearing assembly cold. It could generate a lot of cup/bearing grip force making press / driving force removal more difficult. Grinding precision surfaces for bearings to have the right fit takes more time & effort. Hard to say if/where corners get cut with this stuff, just a guess.
 
PeterT said:
I wonder if the way they assemble those less expensive centers is to heat the cup assembly hot & drop the center/bearing assembly cold. It could generate a lot of cup/bearing grip force making press / driving force removal more difficult. Grinding precision surfaces for bearings to have the right fit takes more time & effort. Hard to say if/where corners get cut with this stuff, just a guess.
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I wondered exactly the same thing.
 
DPittman said:
Is there any chance that if I made a tight fitting collar/pipe to fit over the two straight diameters of the nose/point and used permanent loc-tite on them that would give enough holding power to pull the assembly out? I'm doubtful. Any other suggestions? Ya I know it's probably not worth it but good bearings are cheap and my time is even cheaper.
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I think that is a good idea, maybe that and a slide hammer. If you use 609 with a bit of heat you'll be able to get the cemented bits off again. In theory the bearings should be an interference fit on the shaft so should come out....if they end up stuck in the blind hole its more futzing about, but there's ways to handle that as well
 
PeterT said:
I wonder if the way they assemble those less expensive centers is to heat the cup assembly hot & drop the center/bearing assembly cold. It could generate a lot of cup/bearing grip force making press / driving force removal more difficult. Grinding precision surfaces for bearings to have the right fit takes more time & effort. Hard to say if/where corners get cut with this stuff, just a guess.
Click to expand...
So do you think just pressing them in isn't a likely scenario? I would think that would be cheaper than heating? I'm guessing they would slap bearings on the center cone shaft press it together and then do finally grinding on the cone center.
I can get a replacement center from china for under $30, but I don't like the idea of throw away and the replacement ight not be any better anyhow. There is a good chance I destroy this one in trying and have to replace it in the end afterall, but I get the opportunity to learn with not much to loose in my attempt.
 
What’s your take on the seal or shield? Is it just pressed in? I’m guessing it is relatively thin material and can be pried out (destroying it in the process). Once it’s out you’ll have a better idea of how it’s assembled.
 
Johnwa said:
What’s your take on the seal or shield? Is it just pressed in? I’m guessing it is relatively thin material and can be pried out (destroying it in the process). Once it’s out you’ll have a better idea of how it’s assembled.
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It's part of the center cone and it's possible that is what is rubbing on the body and not the bearings making the rough feel.
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You could drill a couple of holes 180 deg apart on the back in-line where the bearing outer race should be and punch it out.
 
DPittman said:
Yup that's an option I didn't think of. I wonder how hard of material this is
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Doesn't matter. You can always get drills that are harder up to and including diamond drills.

But the front and back corner machining marks "suggest" that it isn't that hard. Try a file scratch.
 
What if you were to capture a flat section of the point in a collet chuck or 4J and then jack the body off with jacking screws or machinist jacks? Maybe a ring with 3 threaded holes for jacking screws where the ID just captures the body or a locking ring around the body proper?

Is the end of the MT2 taper threaded for a draw bar?
 
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All great ideas fellows, it's great resource to be able to put our thinking together.
As it's turns out, as @Susquatch suggested, I figured I'd try a small drill bit on the taper end to see how hard it it was to drill. To my surprise it was not hard at all. So I drilled up to 1/4" all the way through and then took a rod and tapped the assembly out. Well some of it anyhow. Two of the three bearing are still in there. I will try some "techniques" to extract that. I was also surprised to find 3 bearings in the little thing.
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The bull gear bearing on my Hartford was a stubborn beast to remove. None of the conventional methods worked.

So I fabricated a special expanding collet for the job. It was a fun project and well worth the effort.

The top side of the collet is threaded to fit a 3/8 adapter that came with my slide hammer. I drilled out the bottom side of the collet a bit bigger than the slide hammer thread to allow the collet ears to bend a bit easier and also to take a tight fitting button. Before the Collet is inserted into the bearing, an expander button is positioned at the top of the slits in the collet. After that, the collet is inserted into the bearing till the lips snap into place behind the bearing. The button is then pushed to the bottom to hold the collet ears solidly against the bearing ID and the lip behind the bearing. The button is made from a 5/16 nut turned round in the lathe precluding the need for more threading. The button needs to be threaded so it can also be pulled back up to the root of the slots so the collet can be withdrawn if need be.

Here is a pic of the collet, button and bearing.

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This shot shows it in the top bearing and if you look down inside, you can see the button ready to be pushed into place to expand the collet tight to the bearing.

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Here it is assembled in the bearing so you can see what it is supposed to look like before pulling the bearing.

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After the button is positioned as above, I installed the puller adapter, and then the slide hammer. A few raps on the hammer and out it came.

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As I had mentioned above, I wasn't entirely sure it was the bearings that were causing the rough feel to the center but that it could be the part of the ground cone that caps the bearings in the body as it rotates in the body of center. I believe that was the cause, as the bearings feel fine to me. I'm not sure why they made that part so imprecise while the rest of it seems good. That part doesn't need to be precise it just needs clearance from the body wall.

I figured this would be a good opportunity to practice with my tool post grinder to fix the problem. I did initially try turning a bit off in the lathe with a hss bit but the material is too hard for that. I didn't try carbide but went straight to the tool post grinder instead.

Once I was set up to grind I realized that I should have taken most of the material off with a carbide lathe tool first as it was way out of round. However it was about experimenting with the grinder so I took it very slow as there was alot of material to remove. It was surprising how practically breathing on the compound was enough travel inwards to make sparks fly again when grinding. Of course I didn't need to make this part as precise as I did but I got it impressively precise with a nice finish.

Two really short videos: one to show how out of round the part was to begin with and one to show finished part.

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