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Gordon

Gordon

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I have this ball bearing center which got too close the the tool bit. I would like to regrind the point but I cannot figure out how to get it apart. There is no hole through from the back and the front seal or shield does not appear to be easily removed. Some centers appear to have a front shield with spanner wrench pin holes but this is just flat. The option is to put it in the headstock and find some way to keep the point from turning while it is being ground. Any ideas?
 

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You don't take it apart. You need a proper fixture to preload the bearing and mount it by the morse taper and then regrind it.
Send it out and have it reground.
 
In my area of the US, a new MT3 center like that ranges in price from $10 to $30. Buy a new one. Regrinding will likely cost much more.
 
OK I will try to regrind it in the headstock and if that does not work I will just buy a new one. I should be able to cobble up something to keep it from rotating.
 
Hi Gordon
2 Hose clamps a a piece of sheet metal bent to go underneath both clamps should hold it from turning.
Before doing that I would hold it in a 4 jaw and dial it in to make sure the body and point run concentric, then clamp the 2 together.

Just an idea.

Scott
 
You can also mount it in the Lathe Headstock OR Tailstock- NO power needed
and use a rubber O ring around the straight section of the center.
Drive the O ring with a Dremal tool and that will spin the center and you can rework there, or even grind it . Wash the straight section with lacquer thinner first,, no oily surface allowed
Rich
 
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Remove the face sheald off the center and the cap off the rear of the shank. The bearings have to come out the front. There also could be a nut and a threaded portion in the end of the taper. You have to figure how yours is made. A new center with a longer center step is what you are looking for?
 
I wonder if this was pressed together, and thus is held together by press fits. If you could heat up the outside (including the bearing) and cool the center spindle, maybe it would come apart without needing persuasion. Not sure how to achieve that, other than perhaps heating up the whole thing (giving a good heat soak), then dipping the nose in a bath of alcohol + dry ice, or something like that. Not sure what the thermal shock would do to it ...

Another thought, though likely more trouble than it is worth - drill a hole through the center of the MT3 shank (assuming it is not too hard to drill) up to the area where the center spindle should be. Thread a portion of this hole, then screw in a bolt with a spacer to put pressure on the back side of the spindle.

Honestly, I have doubts about either of these ideas working, but ... just brainstorming ...
 
Richard Carlstedt said:
Drive the O ring with a Dremel tool and that will spin the center...
Click to expand...

What is a reasonable estimate for the minimum speed that a Dremel would spin the centre at?

How does this speed compare to the speed items are spun in a traditional cylindrical grinder?

Would it be one, two or three orders of magnitude different?

I suspect a cordless drill could be a better option for this task.
 
The tool used does not matter, any rotary source can be used.
The speed is determined by the pulley or rod being held to drive the belt. The surface area of the driven diameter is 3-4 times greater than the point being reworked , so the forces are favorable. I would estimate that 3,000 RPM max for the center would be appropriate to allow remachining or grinding
Rich
 
Gordon said:
I have this ball bearing center which got too close the the tool bit. I would like to regrind the point but I cannot figure out how to get it apart. There is no hole through from the back and the front seal or shield does not appear to be easily removed. Some centers appear to have a front shield with spanner wrench pin holes but this is just flat. The option is to put it in the headstock and find some way to keep the point from turning while it is being ground. Any ideas?
Click to expand...
Ideally is a MT3 ID & a precision ground OD to hold onto, but since that isn’t the case your live center could possibly have a threaded cap on the end. Any way to grip on the cap & spin the MT3 shank off? Might be difficult since could have been glued when built. If that works it could help determine what’s next. The center (angled end that goes into workpiece) is normally pressed into a bearing, let’s hope. Let us know how you make out & we’lll proceed from there.

Good luck
 
The MT3 and the main body are one piece and the retainer/seal at the end does not have any obvious way to remove it. I assume that it is pressed in place. At this point I have discovered another problem on the headstock end. The adaptor to hold the MT3 center is not accurate. I suspect that the adaptor is actually a MT5 to MT3 and not the proper South Bend non standard taper. It is almost MT5 but the taper is just slightly different. I will try to rework the adaptor since the proper one is extremely rare. I seldom use the center in the headstock so I have not run into the problem before and if the adaptor is put in square it can be OK.
 
The taper is .602/ft. #4 1/2 is .624 /ft and #5 is .631/ft so it is just something that South Bend used. I have no idea why they chose that taper instead of using something standard.
 
The story of my shop life. In order to do that I have to repair the other piece of equipment and in order to that I have to make a new piece for that and then I need some material to do that.........Now what project was I working on last week when I started all of this?
 
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