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Acceptable runout? Bench Drill Press

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Fitzroy

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My Fobco star has a wobble at the end of the drill bit. I’ve ignored it for the last few years but this lockdown has given me time to investigate.

The chuck is a Jacobs 34-06 on 6 taper. I’ve taken the chuck off and taper and chuck are in good condition. I’ve put the chuck on in multiple positions and the outcome below occurs similar with regards to chuck rotation not spindle rotation.

With the chuck off the taper runout is considerably less than the 0.01mm increment on my dial gauge, in fact barely discernible. This is at any point on the taper.

With the chuck in place the runout on the chuck body is just over 0.01mm. With a round bar chucked up the runout close to the chuck jaws is about 0.02mm. 125mm down the rod the runout is 0.5mm.

The min and max points of runout are at the 3 and 9 o’clock on the chuck, from an arbitrary 12 o’clock. I’ve chuck up the same bar, and a different bar, in different positions and the runout and min max positions remain constant.

These data indicate to me the taper is good, but the chuck is not holding the bar in line. Is this level of runout ok, am I expecting too great a level of accuracy?

A new 34-06 chuck is c. £40, will it fix the problem, or is this correctable by taking the chuck apart and conducting some ‘maintenance’?

Thought and ideas welcomed. Fitz.

Videos of runout.
Runout at chuck

Runout at 125mm
 

Fitzroy

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Any thoughts before I drop £40 on a new chuck for nothing?
 

Doug B

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Have you tried taking the chuck to pieces cleaning all the parts, regreasing & putting it back together ? Might be worth a try it will also tell you if there’s damage or excessive wear on the internal parts.

This was mine off my old Meddings it was in a poor state but some TLC got it running nicely

94C5146A-FCBD-4294-BDA5-47299184945C.jpeg
 

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AES

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First off, I would say that the run out you show at 125mm down that rod is NOT acceptable (and excuse me for being "daft", though it sounds very much as if you do know what you're doing, are you SURE that test rod is straight)?

If YES, (as I assume is the case) then apart from Doug B's suggestion of taking the chuck apart and cleaning it thoroughly, my only thought is to ask if the taper adaptor (which I assumes screws into a female socket at the back end of the chuck (?) is OK? By that I mean not the tapered face itself (from the checks you've already done that sounds as if it's OK), but the screw thread itself (damaged, small burr, etc?) or the threaded socket in the chuck itself has perhaps a bit of hard muck sitting somewhere on the thread/in the socket?

If that all checks out OK - and the strip/clean of the chuck itself, as per Doug B doesn't improve matters - then I have the feeling you may well be lashing out on a new chuck, sorry.

(Please note: As I don't know that particular chuck/taper adaptor combination I am only ASSUMING that the taper adaptor does indeed screw into a socket on the back of the chuck!).

HTH
 

Fitzroy

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To close this out. I disassembled the chuck and cleaned it out. The jaws seemed in good shape with no mushrooming of the contact surfaces. Reassembled and no change in performance. I discovered that whilst the jaws were in the correct order they were not in the correct jaw slots, which shouldn’t have mattered, but I rebuilt it again as per Jacobs instructions. The runout remained but moved 120 degrees, so the body is good and the jaws are duff.

A jaw replacement kit was £40 and a new Rhom Prima chuck £45. New chuck order, delivered and installed. Run out at the jaws is c 0.02mm and 125mm down a rod is 0.07mm. Overall I’m happy with the money spent.

I’ll keep a lookout for a cheap jaw kit as the Jacobs chuck is much prettier.

Thanks all for the help and advice as always.

Fitz.
 
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