Changing an Arbor on a Jacobs Drill Chuck

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Anyone who owns old machines probably scours Ebay for orphaned tooling for their pride and joy. One of the benefits/curses of that pastime is that you tend to accumulate broken/wore out tooling. Some of the broken drill chucks I have acquired over the years are starting to look pretty good to me considering some of the prices I’m seeing online, these days. Last year I bought an Llambrich drill chuck (made in Spain by Jacobs Chucks) at the CAMS Yard Sale with an R8 arbor that worked real nice (initially, anyway). The last time I used it there seemed to be an awful lot of runout, and I put it aside for future investigation. Today I decided to take a look at it……………..



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Here is the chuck in the Bridgeport. I set up an indicator to measure the runout, and was surprised to find .013″.  Now, a certain amount of runout in a chuck is to be accepted (MAYBE .001 or two), but .013 makes this chuck pretty much junk, as is.  I remembering checking the runout when I bought it, and it was in acceptable limits. I suspect I dropped it, and bent the arbor at some point.  The taper part of this chuck is very narrow, and is the weak point on the chuck/arbor combination. I suppose I could have damaged the jaws of the chuck, but my money is on a bent arbor.

As I don’t have the proper fitting Jacobs wedges to remove the chuck from the arbor, I ordered some, so I can remove the chuck from the arbor and determine what taper arbor to order. Most Jacobs chucks are labeled with the chuck taper (Jacobs taper) right on the chuck. This one is not.


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These are Jacobs Chuck Wedges. These are the tools that are used to remove chucks from their arbors. I used these to remove the Jacobs chuck from this arbor, but they were not a perfect fit, and as you may be able to see in this pic, are slightly deformed from mis-use. I used this as an excuse (Like I needed one) to buy a complete set of Jacobs Chuck Removal Wedges. I have several chucks that need either replacement arbors, or I need different tapers on them , so the wedges will get plenty of use. They are about $7.00 a set, so I bought all four sizes (should be here tomorrow or the next day).


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This is how they are placed on the chuck for removal. The wedges are squeezed in the jaws of a vise, and (at least in theory) will pull the chuck off the arbor. I will tell you from experience; this is rarely as easy as the instructions make it sound. I will do a walk-through on this when I pull the chuck off the Llambrich.


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This is what you will get if the chuck has spun on the arbor. This is a  Jacobs 1/2″ chuck I got off Ebay (real cheap), which needs more than just a quick arbor change. You can see some pretty bad scoring inside the chuck arbor. Cheapskate that I am; I tried to polish the arbor and chuck taper, to get rid of the runout.  Try again, fool! This didn’t help at all, and I bought a Phase II arbor (probably about 12 or 13 bucks), and will try this one again once I get my toolpost grinder set up, and grind the chuck taper smooth. This chuck is here for illustration purposes  for the time being.


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A better shot of the scoring in the Jacobs taper.


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And here is the Llambrich chuck set up for evaluation. You can see the thin Jacobs taper at the end of the arbor. I suspect this is where I will find the runout on this chuck. Once I get the new wedges, I will get some pics of the removal process and reassembly. More in a few days…………………………..


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OK; its a couple of days later, and the wedges arrived. I bought the “whole set” of Jacobs Wedges #1, #2, #3, and #6), kind of expecting the #6 to be larger than the #3 (which I already had). I am a little confused/surprised to find that the #6 is actually SMALLER than the #3. I need just a little more opening to get the #3 to spread the arbor off the Llambrich chuck off the arbor, so it looks like I will have to modify the #3 that I tweaked last time I used it. Another one of life’s little mysteries.

At least I now have about all the wedges I will ever need for Jacobs chucks, but maybe NOT for other chucks. It shouldn’t be a big deal to get this chuck loose, just a little grinding on the wavy wedge I already have. Thought maybe this was going to be a textbook job……………………………………………..


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First, I thought I’d try the #3 wedges. I didn’t think they’d be rigid enough to get the chuck off, but had to at least try.


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OK, this ain’t gonna work. I had heated the chuck up, hoping the heat would expand it enough to pop loose from the arbor. I just didn’t have enough pressure on the taper to brake it loose. It did loosen the ring on the chuck enough to get it apart though.


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With the cap off, I could slide the base collar back, and unscrew the jaw section of the chuck off.


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Base slid back, ready to unscrew the jaws…………..


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Here it is apart. I always wondered how these things worked.


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All that is left is to get the arbor off the base of the chuck. Next I’ll try a worn out, broken bearing splitter I ran across the other night while I was cleaning up. This splitter might be stout enough to work, even though its a half step away from the scrap barrel. The Wilton has a ton of squeezing power, and a little more heat couldn’t hurt, either. I put some heat to the chuck with a small propane torch, and gave the stationary jaw a good hard rap with a 16 OZ ball pein hammer, and the chuck popped about six inches in the air. Success!


*** I probably should mention here that when a chuck and arbor part company; they do so violently! It is best to be ready to grab the chuck (and/or the arbor), so that no damage is done. I was prepared with a pair of leather gloves, so not parts were harmed this time ***


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The chuck taper looks pretty good (no grooves), but the arbor taper has seen better days. Curious, because it doesn’t appear to have spun at all. It is in better condition than the pics would indicate.


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I haven’t indicated the arbor yet (still hot), but would guess its slightly bent. I still have to figure out what Jacobs taper it is, but will figure that and get one ordered.




After determining that the arbor is a JT #6 (Jacobs taper), I ordered one from ENCO. I had a few other small items that I needed, so I ordered them to qualify for free shipping. The arbor came to a little over $20.00 for a Phase II, but I’ve had good luck with their stuff. Not US made, but the Jacobs arbor was $78.00. The other 7 items ordered where US made. I would have liked to make it a clean sweep, but business is business. I’ll get started cleaning up the chuck itself, so I’m ready to go when the arbor shows up.


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I ended up down in the shop and started playing with the parts again, first step is to dunk the parts in some of Eric’s Bio-Diesel for a soak.


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I was a little concerned about what the condition of the chuck taper, given the shape the chuck arbor was in (kinda groovy). I got the crud out of the taper bore and planned on grinding the bore smooth (DON’T GET EXCITED!)


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Heres the set-up. Chuck the chuck base up in the lathe, and spin it as fast as you can. Grab the Dremel (with a 320 grit roll on it) near to the chuck as you can, so that the roll will be the pivot point, and run it in and out a couple of times. With a 320 grit roll, you’re not doing alot of cutting here, Its just a light scuff. The shot above is about 30 seconds of grinding total, and the bore is pristine and shiny. No high spots or grooves at all. I think the key here is to have the lathe running fast, and never let the Dremel stop moving. Don’t hold the Dremel hard; let the roll follow the taper, don’t guide it. This is one of those operations where less is better than more.


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The only thing left to do before the arbor shows up is to fix the knurled ring. It spins on the chuck base, and it is used to hold the chuck stationary when you tighten the jaw collar. The smaller jawless chuck I have has a split ring that you can tighten, and thats the way I think I’ll go with this repair. I really don’t want to weld the ring on. I’ll drill, tap and counterbore the hole before I split the ring.


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Thats it for now; just need to split the ring, so its back in the drink till I’m ready to reassemble.





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Just so I don’t confuse you; I had all my tools out, and I decided to work on the ragged Jacobs chuck that spun on the arbor. It was pretty rough, and I didn’t have much faith that I could clean it up with the Dremel. Turns out with a 220 grit roll, and just a few more passes, it didn’t look too bad. I HAD to know how close I got it, and just tamped it on the arbor (lightly) and threw it on the mill to indicate it.


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Look at this! I got .0005″ runout (thats half a thou). I’m just gonna send it home and call it a day.


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This is how I drive the chucks home; a stout dowel in the jaws and a convincing nudge with a 3 pound sledge. Be sure to place the base of the arbor on a soft piece of metal (copper block in my case), so that you don’t distort the upper register.  I put the chuck back into the mill and re-checked the runout, and ended up with .001″ (the runout doubled when I sent the chuck home). I’m sure I can do better than that, so I’m going to pull the arbor again, and re-grind the chuck. The high spot should be fairly evident, now that the chuck has been mounted. I might just put a Morse 3 taper arbor in it and use it in the lathe. Runout won’t be as critical in a stationary chuck, and I would probably be used just for short center drills. We’ll see what shakes out, when I get the Llambrich chuck gets straightened out. More later, but thats it for the Jacobs chuck right now…………..


******************************************BACK TO THE LLAMBRICH CHUCK*****************


8-25-2014 UPDATE:


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Well, the chuck arbor came in and I finally got some free time to work on it. The chuck itself has been soaking in Bio-Diesel and good and clean and I got to work on the spit ring. First thing is to determine the center line of the ring (both vertical and side to side) so I can install the pinch bolt. I have to create a flat spot to start the center drill on, then countersink for the cap screw that will pinch the ring together, once its split.


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Heres the flat, and drilling the through hole for tapping.


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I counterbored the ring to accept the head of the 10-32 screw. I didn’t have a whole lot of meat on the ring, so I trimmed a thousanth or two off the head of the screw.


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Here it is with the boring, threading and counterboring done. I split the ring on the band saw,  de-burred it and was ready to assemble the chuck.


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The cleaned parts of the chuck.


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All assembled, with the new arbor and ready to join the two parts. About 2 minutes after I took this shot and drove the arbor onto the chuck; I realized that I hadn’t installed the split ring. This time the Jacobs chuck removal wedges worked like the instructions said they would; smooth and easy. Theres alot to be said for clean, polished parts.


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Finally, assembled and ready for the spindle. I spun it in the spindle, and found that I still have .002″ runout. Bummer. I took the chuck out again and looked at the jaws, and see some dings in them. I guess the jaws are next. I don’t think I’ll ever find a source for jaws, and plan on grinding them. All in all; I’m happy with the arbor replacement; I got rid of .011″ of runout. It has gone from really, really bad to not really that good, but I am confident that I can get it a little better with a chuck grinding (once I figure out how to do it).  More later…………………….

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