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Thread: Runout on jacobs chuck
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24th January 2014, 08:38 PM #1Senior Member
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Runout on jacobs chuck
Dear All
I have just got my Waldown 8SN wired for 3 phase and discovered considerable wobbly-ness of drill bits when fired up. The chuck is Jacobs on Jacobs taper (JT6?) directly on the spindle (no morse taper). I put DTI on it and no runout on chuck body (measured at nose just below the key holes). On this basis, my view is that spindle is running true. I looked up into the chuck and the jaws seem ok/undamaged. But everything I mount in chuck has very noticeable wobble. Thoughts? If I decide to remove the chuck, how do I get it off the Jacobs taper without damaging the drill.
David
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24th January 2014 08:38 PM # ADSGoogle Adsense Advertisement
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24th January 2014, 09:56 PM #2Distracted Member
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24th January 2014, 11:40 PM #3Senior Member
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Thanks
Many thanks. I saw some references to using wedges when searching other threads. I will make some/buy some and give it a shot. Unclear to me why the bit wobbles when chuck looks ok...perhaps some past trauma that has pushed things a tiny bit out of alignment which is then magnified by the drill bit.
David
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25th January 2014, 05:01 AM #4Distracted Member
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Yes, a small error will be 'leveraged'. The nose is not a reliable reference, and looking at the jaws proves nothing. First I would chuck something like a ground pin or an end mill and clock it close to the chuck. Then - assuming there's runout - remove the chuck and clock the spindle nose. If that wobbles inspect the bearings. If they are smooth and not loose you may have a bent spindle. If you eliminate all those things the chuck is the culprit. Like most things they can be damaged by crashes or ham-fistedness. I believe they can be dismantled and rebuilt but I've never done it. No I lie, I did press one apart once but don't recall the outcome. Probably still in bits somewhere.
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25th January 2014, 04:14 PM #5.
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And even rebuilt, there can be problems Bryan.
I have a small collection of 1/2" and 1/8" Jacobs ball bearing chucks and with a desire to fill in the gap I'd bought a 3/8" capacity 11N that appeared in good nick for a reasonable price on US eBay. I also bought replacement jaws, ball bearings and the split nut that houses the bearings and drives the jaws. Assembled with the new parts, the chuck has about 5 thou runout. Useless. It wouldn't be too difficult to bend the body of a chuck out of whack in a crash without there being obvious external damage. Imagine tailstock drilling and your workpiece comes adrift.
Probably what happened to the also useless 1/4" Albrecht I got gouged on too.
BT
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26th January 2014, 08:36 AM #6Senior Member
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A further thought/observation
Thinking further on the question of removing taper mounted chucks, the persistent theme in my reading of threads is how hard they are to remove. Assuming the JT6 tapers on my Waldown spindle and the Jacobs chuck itself are very accurate and smooth, then the possibility is that the two are "wrung" together. Further, if they have been wrung together for 25 years, the possibility is that they have effectively become "bound" at the molecular level (based on my reading of the view that you should not leave gauge blocks wrung together for too long).
If true, this does not help my removal of the chuck in question but it does help me manage the frustration I will inevitably experience and perhaps stop me doing damage.
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26th January 2014, 12:02 PM #7.
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David ,
There is another way to remove the chuck but it does involve some mucking around.
A chuck can be removed from its taper by drilling a hole on the axial centreline , through the body of the chuck and then with the aid of a suitable drift, the arbor can be hammered out. The spindle is easily removed by disengaging the pinion from the rack, the return spring is the only fly in the ointment. A pair of pointy nosed Vise Grips could possibly be used to prevent the spring from unfurling. Another way is to partially extract the spring and wind some wire around it for constraint.
Wedges need to be hammered also. Could be a tricky thing with the chuck mounted on the drill.
Bob.
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26th January 2014, 08:43 PM #8Senior Member
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Chuck removal options
Thanks Bob. I did see refs in threads about axial drilling of chuck and keep it as an option. I am trying to practice a far too recently learned approach to analysing mechanical problems...that is to test/do the most obvious simple things first and the most complicated/invasive last. My tractor hydraulics book repeats this as a mantra at the beginning of the fault finding bit of each chapter. So, wedges it is (once I have made them....I am planning a very gentle taper to max the force they exert). Failing that, disassemble the spindle and go to work on the chuck off the machine.
David
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26th January 2014, 09:07 PM #9
If you use a pair of wedges at 180 degrees from each other then you can use a clamp to force them together so you don't have to hammer them. It reduces the chance of damaging the bearings and spindle.
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26th January 2014, 09:16 PM #10Senior Member
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Clamps
Thanks Gavin...I will give clamps a go as first cab off the rank
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