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Thread: Grinding Jacobs chuck jaws bigger

  1. #1
    Boolit Master Traffer's Avatar
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    Grinding Jacobs chuck jaws bigger

    I am in the process of rigging up a horizontal drill press. It will be used exclusively for drilling dies from 7/8 14 bolts. The drill press head I am using has a JT 3 male for a typical JT 3 chuck. I have purchased two JT 3 chucks both in 3/4". I have looked a long time for a 1" chuck but the only ones I have seen are way past my budget. I don't recall seeing anything for less than $120. Whereas I bought two 3/4" chucks for under $20 apiece.
    My plan was to run one of these chucks on the drill while running a cylindrical grinding wheel on a rotary tool against the inside of the jaws, taking them down until they will accommodate a 7/8" bolt.
    What are your thoughts on this? As I said, the only thing that will ever go in that chuck are 7/8" bolts and it will only be used for drilling and reaming, no side pressure. And by the way I have a MT5 to JT3 arbor if anyone needs one cheap. Unless anyone thinks I can use it for something else, I will never have a machine that will use anything that big.
    AKA hans.pcguy

  2. #2
    Boolit Master

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    Hmmm... O.K.--after giving it some thought. I have a floor model milling machine and a fairly large floor model drill press. I also have two 3/4" Jacobs chucks, one for the mill and one for a lathe. The drill press has it's own chuck, but I'm pretty sure it will go to 3/4". Given the equipment you describe and the method you intend to use my thoughts are that you will not be able to grind it with sufficient precision that you will then get the precision you require to drill the dies. I think that there will be some wobble. I have been able to obtain slightly unusual and expensive tooling as your desired 1" chuck by utilizing the internet. Not only are there wholesale tool companies, but there are used tool companies as well offering either tools made overseas in strange places (like India, Indonesia, or Turkey) at reasonable prices. It takes patience, persistence and perhaps some research. Then, there is always the odd item that turns up on e-bay, but you have to keep checking to connect. It is my belief that although tools can be modified, the best tool for the job is usually one that was made for that purpose. If you have to go with the modification of a 3/4" chuck, then it might be better done by disassembling and machining each jaw.

  3. #3
    Boolit Master

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    Getting the chuck out that far may be tricky as there may not be enough "jaw" at the outside end. Also not sure the body opening is going to accept the 7/8+" size with out modification. Another issue is universal chucks need to be ground with the play taken out of them, on lathe chucks a needle bearing race or fixture is use to grind the jaws with the chuck tightened to it in the back ( or removeable jaws it on the chucks fixed jaws so the outer jaws can be ground in one set up, Then the fixture race is moved to the outer jaws and the inner jaw is ground .005-.010 bigger. We did lapp some Jacobs chuk jaws to improve accuracy and remove damage from bits spinning. we used a small short bearing to hold the play in one direction then lapped the jaws. With out the race the jaws aren't held tight and have some give or play making accurate work hard.

  4. #4
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by country gent View Post
    Getting the chuck out that far may be tricky as there may not be enough "jaw" at the outside end. Also not sure the body opening is going to accept the 7/8+" size with out modification. Another issue is universal chucks need to be ground with the play taken out of them, on lathe chucks a needle bearing race or fixture is use to grind the jaws with the chuck tightened to it in the back ( or removeable jaws it on the chucks fixed jaws so the outer jaws can be ground in one set up, Then the fixture race is moved to the outer jaws and the inner jaw is ground .005-.010 bigger. We did lapp some Jacobs chuk jaws to improve accuracy and remove damage from bits spinning. we used a small short bearing to hold the play in one direction then lapped the jaws. With out the race the jaws aren't held tight and have some give or play making accurate work hard.
    Thanks, That makes sense to me. I think I will try a ring of 3/4" or something to hold in the very bottom of the chuck jaws and grind out the jaws to the desired diameter. The latest chuck I bought (made in China) measures actually .835" so there is not that much to go to get a 7/8 inch bolt in there.
    As far as the suggestion by Die Gebirgsjager, to be dilligent and shop for a 1". That is a good idea also. However the price range I am looking at does make it a very daunting proposition. Especially with a JT3 socket.
    AKA hans.pcguy

  5. #5
    Boolit Master PaulG67's Avatar
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    How do you intend to hold the "Rotary tool"?
    Paul G


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  6. #6
    Boolit Master

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    I made a mount that held a 1/4" die grinder in aloris lathe tooling to use as an ID grinder for grinding lathe chucks. Couldnt cut very heavy but it gave a good finish and once it sparked out a very straight true cut. On the Lathe chucks when cleaned and relubed, installed at 0 on the spindle, and the 0 marked chuck key used after grinding they would normally run and repeat around .0005 until someone over tightened them or used a mallet on them. I had an air muffler mounted on the grinder I used for this so I didn't have to listen to the scream for a couple hours at a time.

  7. #7
    Boolit Master

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    Traffer Keep in mind you will need to disassemble that drill chuck to remove grinding ash ( metal and broken down wheel grit) or it will not last long. Grinding the drill chucks will be worse than the lathe chucks since the jaws are enclosed more in the body.

  8. #8
    Boolit Master woodbutcher's Avatar
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    Uhhhhhhhhhhhhh.Instead of going to all that trouble why don`t you get some reduced shank bits.Silver&Demming pattern I think is what they are called.
    Good luck.Have fun.Be safe.
    Leo
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  9. #9
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by country gent View Post
    Traffer Keep in mind you will need to disassemble that drill chuck to remove grinding ash ( metal and broken down wheel grit) or it will not last long. Grinding the drill chucks will be worse than the lathe chucks since the jaws are enclosed more in the body.
    I have never disassembled one of these. They look like they are crimped together and do not open up. As far as cleaning, I use Jacob chucks for holding work that I use diamond bit grinding wheels on and they are constantly getting full of grit. I have developed a couple of ways to clean them. One way is to stick a vacuum cleaner hose on the jaw end and blow carburetor cleaner on the outside of the chuck in the cracks. And with the fluid in the chuck I use an air hose to blow on the outside of the chuck. I do this while opening and closing the jaws. This draws the cleaner through the chuck from the outside through the inside coming out of the chuck end. That way it doesn't get the grit deeper into the racks in the chuck. Then I finish with WD 40 in the same way to lube it. HOWEVER, if there is a better way, I would love to know it.
    AKA hans.pcguy

  10. #10
    Boolit Master


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    https://www.youtube.com/watch?v=hCgWNpE-STk

    Shows how to take apart a Jacobs Chuck.

  11. #11
    Boolit Master
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    Some notes on larger chucks-may be something of use in this discussion.
    http://www.practicalmachinist.com/vb...indig-339696/?
    I would disassemble both chucks and select the most used for initial effort(s) in any grinding fitting etc.
    I'd also visit local flea markets. I've found a lot of machinist equipement.
    Also local machine shops may have some equipement useful to you which they deem unuable for their efforts.
    Friend used my tool post grinder to true up jaws on lathe chuck.
    Almost deleted this as I feel it dwells on bigger items but thought something might jiggle some thinking in another direction.

  12. #12
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    garandsrus's Avatar
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    Why not just mke a holder for the bolt? Use the chuck to hold the tool holder, which is bored out to the right diameter. A set screw would secure the part to the holder. Since you aren't doing long parts, the added length shouldn't matter.

    Sort of like a collet holder, but no slits. The runout should be good if you never remove the holder from the chuck.

  13. #13
    Boolit Master Idz's Avatar
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    since it sounds like you want a 'chuck' for only 7/8 rod the easiest thing to do is use a 1/2" bolt in your chuck. Then attach a 1 1/4" aluminum block to the 1/2" bolt and bore the block to fit your 7/8" bolt. 3 brass set screws can secure the 7/8" bolt into the aluminum block.

  14. #14
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by garandsrus View Post
    Why not just mke a holder for the bolt? Use the chuck to hold the tool holder, which is bored out to the right diameter. A set screw would secure the part to the holder. Since you aren't doing long parts, the added length shouldn't matter.

    Sort of like a collet holder, but no slits. The runout should be good if you never remove the holder from the chuck.
    Great Idea. I have already made a similar holder. I bored out a piece of 1" round stock with 7/8 14 threads on one end and a reduced diameter to fit into the chuck on the other end. However, it adds length to the chucked bolt and exaggerates the run out. I may go back and bore it deeper to make the bolt fit very close to the jaws. This would make it work better. Because of it's length it is also difficult because I don't have much length from my chuck to my improvised tail stock. But it can work and I will use it if modifying the chuck to accept the 7/8" bolt will not work. It is a pain to work without a lathe. For instance the "holder that I made was made from 1" round stock center drilled and tapped to 7/8 14. I had to take it to a machine shop to make the pilot hole because I cannot chuck the 1" round stock. Even with a pilot hole it was very tricky to bore the hole on center. But it worked. I usually have to unscrew it and work with screwing it back in with differing torques it to get to spin on center though.
    AKA hans.pcguy

  15. #15
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by kywoodwrkr View Post
    Some notes on larger chucks-may be something of use in this discussion.
    http://www.practicalmachinist.com/vb...indig-339696/?
    I would disassemble both chucks and select the most used for initial effort(s) in any grinding fitting etc.
    I'd also visit local flea markets. I've found a lot of machinist equipement.
    Also local machine shops may have some equipement useful to you which they deem unuable for their efforts.
    Friend used my tool post grinder to true up jaws on lathe chuck.
    Almost deleted this as I feel it dwells on bigger items but thought something might jiggle some thinking in another direction.
    That is an excellent thread. I may just pull it apart and grind the jaws independently returning them and checking, repeating until it runs true. It is interesting about the ring. As I have already thought about this from Country Gent's post. I could remove the chuck and clamp the jaws onto a rod in another drill press and grind from the other side. My burrs are long enough to do this and the jaws would be loaded at the tip so it should work well. When I got the done I could finish the jaws by either pulling them out and continuing the same line or load it back in a little deeper and finish the tips. But armed with all this new understanding I am confident that I will get the job done very satisfactorily. Thanks to all very much. I learned so much in this thread. I didn't even know how to take a chuck apart before this.
    AKA hans.pcguy

  16. #16
    Boolit Master

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    If you can disassemble the drill chucks you may be able to modify the housing or jaws to ride in a little deeper opening them the last bit you need. You stated they now open to .835 so another .045-.050 is all that's needed. That's probably the minimum amount of "extra" to easily insert a 7/8" bolt. grinding off the back of the jaws or deepening thining the housing a small amount may gain what you need with out modifying the jaws.

  17. #17
    Boolit Master
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    I may be misunderstanding what you are trying to do but it appears you are taking a drill press, converting it in to horizontal boring machine to perform a repetitive operation. If I understand correctly, you want to hold the workplace in the chuck - i.e. 8/8" threaded rod, to rotate into tooling to drill, ream,etc? I'm thinking such things as push through sizers, etc.

    What are you holding the tooling in opposite the 3 jaw chuck on the drill press spindle? Instead of putting your workpiece in the chuck, since the workplace will remain a constant size - diameter and length - why not hold the workplace opposite the chuck in a special made holder - similar to a collet and instead of feeding the workplace into the tool, feed the tool into the workpiece with the drill press spindle - the spindle acting the same as a tailstock would on a lathe if you are boring/reaming?

    But, as I said, I may be misunderstanding what you are attempting to accomplish? Have you got any photos of your "set-up" that you've put tegether so far?

  18. #18
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by bedbugbilly View Post
    I may be misunderstanding what you are trying to do but it appears you are taking a drill press, converting it in to horizontal boring machine to perform a repetitive operation. If I understand correctly, you want to hold the workplace in the chuck - i.e. 8/8" threaded rod, to rotate into tooling to drill, ream,etc? I'm thinking such things as push through sizers, etc.

    What are you holding the tooling in opposite the 3 jaw chuck on the drill press spindle? Instead of putting your workpiece in the chuck, since the workplace will remain a constant size - diameter and length - why not hold the workplace opposite the chuck in a special made holder - similar to a collet and instead of feeding the workplace into the tool, feed the tool into the workpiece with the drill press spindle - the spindle acting the same as a tailstock would on a lathe if you are boring/reaming?

    But, as I said, I may be misunderstanding what you are attempting to accomplish? Have you got any photos of your "set-up" that you've put tegether so far?
    OK, now I think I know what you mean here. You are correct in the fact that I am holding my work in the chuck and moving it onto the drill bit/reamer. I am using another chuck mounted to the drill press table as a tailstock. The reason I have to do it this way is that it is the only way to get a hole true in the middle and straight through the piece. If I simply drilled a hole in a round bolt it would not be centered perfectly and would probably not be straight through. So basically I am using the drill press just like a lathe for boring. Spin the work on to a centered bit.
    AKA hans.pcguy

  19. #19
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by country gent View Post
    If you can disassemble the drill chucks you may be able to modify the housing or jaws to ride in a little deeper opening them the last bit you need. You stated they now open to .835 so another .045-.050 is all that's needed. That's probably the minimum amount of "extra" to easily insert a 7/8" bolt. grinding off the back of the jaws or deepening thining the housing a small amount may gain what you need with out modifying the jaws.
    Yup that is the first thing I am going to attempt. Since it is the least destructive.
    AKA hans.pcguy

  20. #20
    Boolit Master

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    If you want to get a 3 jaw chuck accurate you grind it. You will use a ring on the outside of the jaws to keep them stable and then grind the inside of the jaws to true with a grinder on the lathe. This will give you a jaw that with care alnd luck will be true to 3 thousnads of an inch.

    This works with lathe chucks as they are inside outside and have a nice flat for the tension ring. A drill chuck has tapered jaws outside so I don't know how you will hold the jaws in tension. If you just back the all the way out the chuck will only be as true as the body and most cheaper Jacobs chucks won't hold 10 thou or so. Now add in the tolerance of the machine itself and it looks like you are trying to make a donkey do a horses work. I don't use bolts for die stock as they are not cut with very accurate threads. I prefer to thread the die after setting it to run true with the bore.

    All that said you can give it a try as I have seen some very good work done with some very rough tools. Just depends on how much care you put into the job.

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