# Chuck jaw holding problem.



## littlejack (Jan 20, 2014)

Hey guys:
  I just came in from playing with the Atlas 10" QC54. I was playing with threading a piece of 1/2" stock, and found a problem.
  When I put the stock into the chuck and tighten, the jaws only clamp tightly on the back end (drive end). There is a slight gap
  between the stock and the jaw on the feed end. There is enough gap that it can definitely be seen with the naked eye. 
  I removed the jaws and checked them with a machinist square. They look to be square, no gap along the holding surface. 
  I installed them back into the chuck and checked for play. There was a minute amount, but not much. Would this be wear?
  Can I have the jaws milled so they hold the piece correctly?
  Do I need to buy a new chuck?
  Anyone ever have this problem?
  Jack


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## DAN_IN_MN (Jan 20, 2014)

Your chuck is worn a bit.  That is called "bell mouthed".

Here's how one member fixed a worn chuck.

http://www.hobby-machinist.com/show...aw-Chucks-(17-pictures)?highlight=chuck+grind


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## kd4gij (Jan 20, 2014)

Typicley you regrind them with a tool post grinder. Scence most home shops don't have a toolpost grinder. You can make a mount and use a drimmel tool or die grinder.


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## rafe (Jan 20, 2014)

Are you sure it's the chuck and not the piece you chucked


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## littlejack (Jan 20, 2014)

It is definitely the chuck. I did try 2 pieces of stock, and both had the same results. 
  Thank you all for your replies.
  Jack


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## wa5cab (Jan 21, 2014)

Jack,

As Dan said, the jaws are bell mouthed.  This can happen from any combination of three reasons.  Wear on the outer ends of the jaws.  Wear on the slots in the chuck body.  And wear on the keys on the jaws that run in the slots.  You can also have wear on the jaw teeth that run in the scroll (the disk that the tightening gears drive), on the lands in the scroll, on the scroll pilot or bearing, and on the hole in the chuck body that the pilot runs in.  But from your description of being able to see a gap between the workpiece and the outer ends of the jaws, that is probably your worst problem.

To fix the bell mouth, you need a high speed grinder mounted firmly on the carriage, and a fixture to load the jaws in the proper direction during grinding.  You can't just put a steel or aluminum ring around the inner ends of the jaws and back them out against it because that will cock the jaws in the opposite direction to that in which they cock when gripping the OD of a workpiece.  There are two common fixture types.  The simpler one requires a ring with three holes at 120 deg. and a hole drilled in the flat front of each jaw, with pins in the holes in the jaws and in the ring.  When you tighten the jaws, they will cock outwards just as they do in actual use.  However, you do have to drill holes in the jaws, which I never liked the idea of.

The other fixture consists of a round plate with a hole in the center and three holes at 120 deg. just large enough to fit over the jaws.  The three intersect the center hole just enough for the inner face of the jaw to stick past so that the stone doesn't hit the ring.  This also loads the jaws in the proper direction and requires no whittling on the jaws.  If the scroll pilot isn't badly worn, this should return the chuck to usability.

There was an article on making such a plate in the Downloads section but since we started resurrecting Downloads, I haven't come across it.  I have a local copy of one of them that I can send you if you want it and will send me your email address in a PM.

Robert D.


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## iron man (Jan 21, 2014)

As Wa5cab pointed out the method shown is incorrect for grinding a chuck you must load the jaws correctly in the right direction I use a method that is very simple you cut three equal size pieces of key stock and place them inbetween each jaw but not far enough down so they get in your way when grinding close the jaws down tight until all three are secure and start your grind. Feed slow and take your time. Ray

- - - Updated - - -

Here is a post with some pictures.

http://www.hobby-machinist.com/show...huck-Jaw-Alignment-Issues?p=102483#post102483


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## littlejack (Jan 21, 2014)

Thanks again guys.
  All of this help is great for the beginner/novice/ME.
  The method used by Ray "iron man" looks to be very easy to do. I will need to get a bigger Dremel. I will need to make a Dremel holder.

  Just thinkin out loud, but would it be feasible to load the chuck as iron man did, and then run a very sharp hone of the appropriate size into  
  the jaws via the tailstock? 
  Just askin.
  Jack


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## iron man (Jan 21, 2014)

I dont believe that would work the last one I did I used a die grinder it does not take very long. Ray


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## littlejack (Jan 23, 2014)

Hey guys:
  Range report on fixing the jaws of my lathe. I did as instructed by you fellas. 
  It took me a few hours to fabricate a holding fixture for my Dremel tool. I did pre-load the jaws in the closing manor. After getting  
  everything set up, I began. I ran the lathe on the slowest speed with the Back Gears engaged. I ran the carriage feed on the slowest 
  setting also. I crept up on the jaws until I began to see sparks in the rear, the highest points. After that, I backed the stone out and made
  my first cut. Each cut from there on was .001. A few times, I re-run the previous cut without moving the cross feed. 
  After all was said and done, to get the back of the jaw the same as the front, it took about .012 off. After cleaning the jaws up, I made a  
  couple extra passes just for fun. 
   The jaws came out absolutely perfect. I tried different size pieces of stock, and it took very little effort with the chuck key to lock them into
  place.
  I thank all of you for your experienced input. It is very much appreciated. 
  Regards
  Jack


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## kd4gij (Jan 23, 2014)

Glad it worked out for you:thumbsup:  It feals good when we achive the results we where looking for. Have a great time with the lathe now.:drink2:


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## robinj66 (Jan 28, 2014)

I caught up with this thread a couple of days ago and have done some reading on www and watched a few You Tube videos - very interesting and something I definitely want to try.

Since toolpost grinders are as rare as hen's teeth over this side of the pond (or prohibitively expensive) I aim to use my dremel-type thingy.  

How have people made their mounts?      Do the grinding stones need to be anything special?


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## littlejack (Jan 28, 2014)

Hey Robin:
  I don't know what lathe you have, and what tool post you have on your lathe, so, I don't know if this will work for you.
  I have an Atlas QC 10" x 54. It has the original lantern type tool holder. Here's what I came up with.

  The chuck is a 5". I used 5/8" key stock to pre-load the jaws with. There was only about .060 of key stock engaging between each jaw. 
  That was all the room there was to clear a 5/8" dremel grinder bit.
  I used a piece of 3/8" x 1 1/4" flat bar 6" long to mount in the tool holder. 
  Then, I figured the dimensions needed from the tool holder to the center of the chuck needed to make the dremel holder. 
  After getting the measurements, I sawed a piece of 2x4 6" long to hold the dremel with.
  I used a hole saw to cut an undersize hole (1 3/4") in the 2x4. I then used sanding drum in my drill press to enlarge the hole. I enlarged
  the hole ONLY enough to allow a TIGHT twist fit to get the dremel in place. I also drilled and tapped two opposing 3/8" holes, top and
  bottom in the 2x4 to hold the dremel as well. Although, I do not think it was necessary. 
  I then drilled and tapped three 3/8" holes in the flat bar to mount the 2x4 to. 
  I then transferred the hole pattern to the 2x4 using the d&t flat bar. 
  I then drilled the 2x4, and bolted it to the flat bar.
  All that was left, was to situate the dremel bit to the proper starting point. Then I used the cross feed To feed the bit into the jaws, .001 per run.

  All the best with your project.
  Regards
  Jack


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## robinj66 (Jan 29, 2014)

Hi Jack - many thanks for that. I'll try to give it a go :thumbsup:

I have a 10F  Atlas (TV36)  with a 4 way tool post but otherwise pretty standard.  Should be able to attach something to the tool post but I was wondering whether people had bought holders for their dremel or made them (one or two on Ebay (UK) but expensive:shocked: )


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## littlejack (Jan 29, 2014)

Robin:
  You should be able to make one rather simple, to be held in your QC tool holder. I don't think I would put a whole lot of money into buying 
  one, as it will not get used much in ones lifetime. 
  Jack


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## wa5cab (Jan 30, 2014)

Robin,

Here's a link to a commercial one made to fit a QC tool holder.  I think it should fit your 4-way turret holder, too.

http://alisam.com/page/1gu8y/Metalworking/Dremel__tool_holders.html

I also have a drawing of one that I made out of a piece of 4X4 wood post.  Requires a milling attachment vise on the cross slide in place of the compound.  I can email a PDF if you're interested.

Robert D.


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## robinj66 (Jan 30, 2014)

Thanks for the info guys.

Jack - I agree, no point in spending loads of dosh if you don't have to (and I fancy the idea of being creative:scared: )

Robert - I can't believe how cheap things are over there. You guys should count yourself very lucky) .

Plans for a wooden creation would be great (I'll pm you an email address :thumbzup: ) -I have seen one on a You Tube video . It was something I hadn't thought about before but should be within my capabilities (famous last words :rofl: )


ETA I do have the Atlas milling attachment but have yet to use it in anger. I have bought a 1/2" end mill which should fit directly into the "holder" I have - it fits onto the drawbar. I don't have any collets though - do you need them to mill?


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## wa5cab (Jan 30, 2014)

Robin,

Just so that I'm sure you understand, you only use the vise off of the milling attachment.  It will fit in place of the compound (as will the table off of the Universal Compound Vise).

If all of your cutters had 1/2" shanks, no, you wouldn't need any collets.  However, that's unlikely.  Atlas sold a set of four reducing bushings to go with the cutter holder, one each with an ID of 7/16", 3/8". 5/16" and 1/4".  However, they tend to be what most would call "expensive".  I bought one set new from Clausing that cost as I recall about $63.  For about the same money, there's an outfit in Hong Kong called CTC Tools who sell an excellent quality set of 3MT (and 2MT) collets in 1/16" increments.  The 3MT set covers 1/16" to 3/4" in sixteenth increments. It uses the same 3/8"-16 drawbar as the cutter holder does.  If you find that you need smaller increments that 1/16" (most collets have very little "adjustment" range) you can use 3AT (what was originally sold by Atlas), 3C, 5C or that short European type whose name always escapes me.  But you will have to acquire the appropriate draw tube for the first two or a front-mounted collet chuck for the latter two.  All of which are more expensive to much more expensive than the 3MT or Atlas cutter holder and bushings.  But any of the 4 are either available in 1/64" increments or have a have a larger operating range.  And all can hold much longer work if it will pass through the spindle or somewhat longer work if it won't.

If all that you need collets for is to hold milling cutters, the cheapest solution is the 3MT set.

Robert D.


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