# plead for 3 jaw chuck knowledge



## casca92 (Jun 1, 2017)

Greetings  wise ones
hopefully soon I will have this     JET BD 920 N  lathe out of your hair.
my confusion today is the chuck jaws do not square up.  lathe was pre-loved probably more than once when I purchased it.
jaws are marked with what I believe is the correct location by stamped number.

I have juggled the jaws into different jaws and still same effect. 

2 jaws will center up nicely with one always short of target.
not sure if it is always the same jaw not squared or if it is one slot out of wack..

jaws appear to be in good condition, and has been oiled and fairly clean.  it mounts to spindle square and runs square.

                                                               OR
Am I not being a realist and my expectations are to high.  would like to hold off on a new chuck for a little while until I return to work from medical leave.

I a wait your wisdom and guidance.
casca


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## Superburban (Jun 1, 2017)

Often the jaws are marked 1.2.3 or something, It is a pain getting them in right. First, you need them in the right slot, and then you need the first one (hopefully marked 1), to engage the spiral first, then turn the spiral to the next slot, and put the second jaw in, and so on.

If they are not marked, mark them with tape, and  also mark the slots. then try your luck. remembering that they all need to follow the spiral. Whats it? 27 possible ways to assemble them?

If you have 2 jaws fit nicely, it might just be that the third jaw needs to be put in its slot before the other two.

Also, if you flip the jaws over, you can see that one has the first thread closer to the tip, then one is a bit further back, and the other is back more. I think that is your 1, 2, 3. or 3,2,1.


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## casca92 (Jun 1, 2017)

ahh a light is starting to come on ,  not real bright  but that is some guidance I was hoping for.


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## mikey (Jun 2, 2017)

Casca, try looking at this thread: http://www.hobby-machinist.com/threads/chuck-run-out.50125/

I showed some pics on how the jaws of a 3JC are installed. Does this help?


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## Superburban (Jun 2, 2017)

Good write up there Mikey.


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## mikey (Jun 2, 2017)

Superburban said:


> Good write up there Mikey.



Thank you!


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## hman (Jun 2, 2017)

Superburban said:


> Often the jaws are marked 1.2.3 or something, It is a pain getting them in right. First, you need them in the right slot, and then you need the first one (hopefully marked 1), to engage the spiral first, then turn the spiral to the next slot, and put the second jaw in, and so on.


I'll beg to differ just a bit here.  The _order_ in which you insert the jaws is important.  But which slot the #1 jaw goes into is a lot less so. If the spiral inside the chuck, the teeth on the jaws, and the angular locations of the three slots are made correctly, it should make no difference at all.  Sometimes it will make a small difference in how well the jaws center the work.

None of the chucks I've bought have had the slots numbered.  All of them have had the jaws numbered.  Per a suggestion I'm pretty sure I read about in a HM post, I tried marking the slots in one of my 3-jaw chucks A, B and C.  I then tried all three positions of the #1 jaw and measured the runout of a test part.  IIRC the difference between the best result and the worst was something like .002" runout.  I've since done this with my other chucks, and recorded the "sweet spots" for all of them.  Of course, all of this was at just one test diameter.  It might well vary for other diameters, depending on the various various factors mentioned above.


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## Superburban (Jun 2, 2017)

John, That certainly does make sense, and in a perfect world should work.  I have a small 5" 3 jaw that I got off E-bag, To fit in the flat rate box, the seller took the jaws off. Neither the jaws, or the slots are marked. Took me awhile to get them in right. Once I got the right order, they were close, but they all still had to move over one slot to close right. Now you have me wondering if the jaws are cut right. I have used it on a rotary table, so would not notice if they are centered. It was obvious they were re-cut.

Your explanation, along with Mikeys make the 3 jaw sound so simple. Now I'm going to have to go out, and  check that 3 jaw.


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## chips&more (Jun 2, 2017)

I buy high quality chucks because the chuck is the heart of the lathe. All of my chucks have numbered jaws and slots. If it has more than one key hole, one key hole will also be marked. And all of my 3-jaw chucks are ajust-tru type. I would not buy anything else. If you buy a cheap chuck or a worn out one you will probably get frustrated with your project results. I would not regrind the jaws either. That whole picture means something is really wrong and you will end up with an iffy chuck. Yes, I know a good chuck can cost as much as the lathe. But, the results of your effort will be money well spent…Dave


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## markba633csi (Jun 2, 2017)

Remember chips this is a HOBBY forum;  lots 'o folks here 
(myself included) do just fine with the cheap-o chucks.  I can get work within a thou with
my little chinese sow's ear with a bit of tapping.
Mark S.


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## mikey (Jun 2, 2017)

Every high quality chuck I've seen has numbered jaws and jaw slots. Typically, the factory will hand fit the jaws to make sure the jaw fits without binding before numbering them. Some chucks, like Rohm, will fit the jaws and certify the accuracy of the chuck by tightening only one pinion; that pinion will be marked and the chuck should be tightened onto the work with that pinion. Otherwise, the accuracy of the chuck may not fall within specs.

The point: if your jaws are numbered then use them as marked. If not, then as long as the jaws fit without binding it should be okay. If you want the best accuracy from them, swap the jaws and check run out with a dowel pin until you find the best combination, then mark them yourself and mark the pinion that produced that best result. Once done, it should hold the tolerances the combination can produce.


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## Rustrp (Jun 2, 2017)

mikey said:


> Casca, try looking at this thread: http://www.hobby-machinist.com/threads/chuck-run-out.50125/
> 
> I showed some pics on how the jaws of a 3JC are installed. Does this help?



So the link took me back to the older thread and it's all good stuff. -Russ


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## Rustrp (Jun 2, 2017)

markba633csi said:


> Remember chips this is a HOBBY forum;  lots 'o folks here
> (myself included) do just fine with the cheap-o chucks.  I can get work within a thou with
> my little chinese sow's ear with a bit of tapping.
> Mark S.



I agree, but what chips&more posted is correct. If someone is on here as a hobbiest or machinist who worked in a facility that only bought less than quality or precision they wouldn't know. When people don't know, a lot of opinion gets pushed and passed along, and we get a lot of what I call backyard fence mechanics. i.e. The neighbor knows a neighbor who said do it this way and so on. **That's good enough** is okay for anyone who chooses to work this way but knowing how to make it a couple steps better is never a bad thing. I get on my soapbox about imports but it's the cheap imports which I'm referring and if a person wishes to go there that's okay, but with the correct information they can quit struggling with why they don't hit tolerances.


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## chips&more (Jun 2, 2017)

Rustrp said:


> I agree, but what chips&more posted is correct. If someone is on here as a hobbiest or machinist who worked in a facility that only bought less than quality or precision they wouldn't know. When people don't know, a lot of opinion gets pushed and passed along, and we get a lot of what I call backyard fence mechanics. i.e. The neighbor knows a neighbor who said do it this way and so on. **That's good enough** is okay for anyone who chooses to work this way but knowing how to make it a couple steps better is never a bad thing. I get on my soapbox about imports but it's the cheap imports which I'm referring and if a person wishes to go there that's okay, but with the correct information they can quit struggling with why they don't hit tolerances.


You nailed it! And we also get what I call “internet authors”. The people that sit in front of a key board typing away with misinformation, know-it-alls that don’t really have a clue or they could be just typing to be typing because they are bored.


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## Rustrp (Jun 2, 2017)

chips&more said:


> You nailed it! And we also get what I call “internet authors”. The people that sit in front of a key board typing away with misinformation, know-it-alls that don’t really have a clue or they could be just typing to be typing because they are bored.


Good information is exactly that, it's good and it shouldn't be bad for anyone. So due to this conversation, I had to go out to the shop and crank out the jaws on the old lathe. It's a three jaw and I couldn't remember what my father-in-law told me was the correct order away from the brand stamp in the face of the chuck, CW or CCW. With the info he gave me I knew it would be one of the jaws on top where I positioned the brand, which is a Gisholt BTW. The way he expalined it was the #1 would drop in first as you face the chuck and rotate it clockwise. The first slot past the brand stamp is #1` and the #3 is to the right of the brand and goes in last. The jaws are numbered and I'm guessing the chuck is as old as the lathe, late 1800's to early 1900's.

Edit; The information was given a long time ago but I knew the first jaw to pop out would be #3.


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## Rustrp (Jun 2, 2017)

casca92 said:


> ahh a light is starting to come on ,  not real bright  but that is some guidance I was hoping for.


I'm a neopyte in the machinist occupation, so with everything stated you have three jaws with three different thread amounts. The #1 would have the most threads and the #3 the least.


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## mikey (Jun 2, 2017)

A 3 jaw chuck is a 3 jaw chuck. It will have some run out; even the best chuck do. However, the run out is of little consequence as long as the part is not removed from the chuck; it will always be concentric with the spindle as long as we don't unclamp it from the chuck. 

Run out values matter when we try to re-chuck a piece that is already turned. In this instance, an adjust-tru type chuck will get the part as concentric as possible for that specific diameter only. Otherwise, an adjust-tru chuck is like any other 3 jaw chuck. 

I think it is always a good idea to buy a good chuck, primarily because the quality of the machining is better, tolerances in construction is tighter and they tend to function better for a longer period of time. However, this has little to do with concentricity of the results when you first turn a piece. As long as the chuck holds the work solidly and does not allow it to shift, a cheap Chinese chuck will be just as good as my Rohm/Emco/Samchully chucks on a first turning. 

Hobby guys have various financial capabilities and Chinese chucks that hold solidly are just fine, in my opinion. I don't expect them to hold up as long or as consistently as a better chuck would but for hobby guy, I think that's okay.


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## Superburban (Jun 2, 2017)

Thank you for stepping back in Mkiey. For a few minutes there I thought this had turned into a rich mans only board, and us on limited budgets were not wanted.




Rustrp said:


> I'm a neopyte in the machinist occupation, so with everything stated you have three jaws with three different thread amounts. The #1 would have the most threads and the #3 the least.



I beg to differ. Not the number of threads, but the position like has been stated a few times already.


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## RJSakowski (Jun 2, 2017)

I have often thought that if someone told me that they would give me a million dollars to spend on equipping a shop not including the building, on the condition that I had to spend it all within 24 hours that I could do it. 

Unfortunately, I have a limited budget for equipping my shop.  When I am considering purchasing new equipment, I always ask myself "Is it enabling?".    By that I mean will it allow me to do something that I couldn't accomplish with my existing equipment.  I bought my Tormach for that reason.  I had projects that couldn't be accomplished by any other means. 

I could spend $1K to 2K on a quality name brand chuck but it wouldn't enable to do anything that I can't do already.  Spending that money on a TIG welder or plasma machine will permit me to take on projects that would be difficult if not impossible otherwise.   I recognize the value of quality equipment and if this were my livelihood, it would be prudent to invest in same.  But it is not my livelihood.

We have seen many examples of exquisite workmanship turned out on machines that would be considered toys at best by professionals and I personally have seen junk work come off quality machines.


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## RJSakowski (Jun 2, 2017)

To further clarify the order in which chuck jaws are reinserted, here is a photo.  Line the jaws up so they are all even and the distance of the tooth to the inside of the jaw is increasing.  The jaws will now be in their correct order.  

The chuck jaw with the tooth nearest the inside of the jaw (the left one, in this photo) is the first jaw seated. I place the jaw in the slot and turn the scroll backwards while maintaining gentle inward pressure on the jaw.  At some point, the jaw will come off the scroll and drop down to the next position on the scroll.  Turn the scroll forward to engage the jaw.  Now insert the second jaw in its slot and continue turning the scroll until it captures the jaw.  Repeat the process for the third jaw.  The jaws will now be in their correct orientation.


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## mikey (Jun 3, 2017)

Superburban said:


> Thank you for stepping back in Mkiey. For a few minutes there I thought this had turned into a rich mans only board, and us on limited budgets were not wanted.



Nah, that's the nice thing about HM - everyone has something to share, teach, learn or joke about. The vast majority of us are hobbyists, which is what makes it so nice for all of us. One thing I have seen repeatedly is that a new guy may be new to machining but will often have skills in another area that astound me. So enjoy the community, learn and have fun. Well, that's what I try to do anyway.


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## markba633csi (Jun 3, 2017)

When you get to the point where you are asking yourself "what do I need to make or fix" instead of "what do I need to buy" then your shop is relatively well equipped.
For a while anyway.  Till the next Harbor Freight catalog comes. 
Mark


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## Wreck™Wreck (Jun 3, 2017)

On a 3 jaw scroll chuck the threads on the jaws are offset 1/3 of the scroll thread lead from the part holding surfaces. In the case of a .125" lead .041xxxxx", it does not matter which slot the master jaws are in so long as all three are in the same thread in the correct order. To simplify jaw changes it is useful to number the slots and jaws but is not required, as seen below.

Turn the scroll until you see the beginning of the thread and install jaw #1, rotate the scroll until the start appears in the next slot and install jaw #2 and so on. The relationship lies between the threads of the scroll and master jaws. Keeping each jaw in the same slot helps with repeatability  as any error remains in the same place, if indeed the OEM finish ground the hard jaws in place then slot placement is important as the error in radial slot location either advances or retards the work holding surfaces.

Many chucks that I have used  have the slots numbered inside the groove where they are not easily seen much like the jaws are numbered down in the slot which can not be seen until removed.

I do not know why this is done but surmise that it makes for a cleaner looking product, high end products often have the numbers laser/chemical etched where they may be seen. Also take into consideration that the employees at the chuck factory need to know where the parts belong in a given assembly.

Buy yourself a set of number stamps and mark it for your own use, you will not be able to to do so on the hard jaws however.


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## dlane (Jun 3, 2017)

Kinda the same as a Jacobs 16n super chuck , as far as jaw placement go


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## Rustrp (Jun 3, 2017)

Superburban said:


> Thank you for stepping back in Mkiey. For a few minutes there I thought this had turned into a rich mans only board, and us on limited budgets were not wanted.
> 
> 
> 
> ...


I was incorrect by stating the number of threads vs the thread offset. I suppose the number of threads are important for strength  when larger stock is in the chuck. When I took the jaw out of my chuck I didn't count the threads and I didn't take all three out so I didn't have a comparison. I do have the mechanical aptitude to understand the installation order sequence based on thread offset or number of threads if that were the case.  I stopped posting because I didn't want to become more verbose, specifically in regards to numbered jaws and slots. The link to Mikey's earlier explanation covered this. This was my atempt to convey in post #15. If the jaws and slots are numbered then this is the position they should be installed. Mikey, RJ and Wreck Wreck gave good examples and photos (including your photos). If a person isn't familiar with installation sequence they could miss the timing on the end of the scroll and end up with major misalignment, which takes us back to the OP.

This topic got deeper (and this is good) when we started discussing quality versus mystery metal imports where the jaws or slots are not numbered. Then we took a turn on what is spent, e.g. rich vs. poor. The reality here is this isn't about $$$ it's about information given that's correct. It shouldn't make a difference if you do this for your daily paycheck or you do this for a hobby, correct information is important and I'm not willing to get knotted in semantics. The real $$$$ issue comes in when we move into the **time is money arena**. If I have three jaws that are numbered I'm ahead of the game on installation after repair, restore, etc. If I have jaws and slots numbered I'm ahead of the game on accuracy in regards to runout, i.e. accuracy.  Everyone who visits here isn't a hobbist and we shouldn't pretend that's the case. On the other hand if it were only hobbist a lot would be missing if you leave out the professionals who are willing to spend their time here dispensing valuable information. As a business owner I'll estimate I have 100K invested in equipment, and I have friends and acquiantances who have 1-2m invested in equipment and they still come to me to get projects done, so if you think the comment was about rich or poor you missed the point.


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## Superburban (Jun 3, 2017)

The information in this thread would be good to pear down just to the pertinent info, and make it a stickey, or FAQ, some where.

I was only trying to correct your thread count comment, there was no intention to slam you, and I hope you are not taking it that way. The only part directed at you, was what was posted after the quote from your post. The rest was aimed at the others that were just showing off, and contributed nothing to the OP's question.


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## Rustrp (Jun 3, 2017)

I was only trying to correct your thread count comment, there was no intention to slam you, and I hope you are not taking it that way. The only part directed at you, was what was posted after the quote from your post. The rest was aimed at the others that were just showing off, and contributed nothing to the OP's question.[/QUOTE]

As I stated I was incorrect to state thread count, but if we look at you correction can you see that technically you correction is incorrect too. If the chuck and jaws are not numbered then there is no correct location(s) unless the owners manual instructions detail the direction the jaws are inserted. The importance would be placed on the offset of the threads, as in RJ's photo in post #20, and the #1 jaw would be on the left. It makes sense for a manufacture to cut the threads the way they do so all of the jaws have the same number of threads. The jaw number would be accomplished by offsetting the jaw in the manufacturing process to match the insertion sequence. In regards to location, if the manufacture doesn't mark the chuck there is no correct location. You can install the #1 jaw at any location. I'm guessing from your photo that the jaws and chuck are numbered based on the 679 which I am also guessing is the S/N of the chuck, and I'll add that the jaws were matched to the chuck.

One thing I got out of this will be directed to anyone choosing to purchase from CL or EBay, especially if the lathe, specifically the chuck isn't assembled. It would be easy to end up with two jaws that are the same based on visual inspection if the jaws were not aligned as a set.

In regard to being slammed. I didn't take it that way, and as I stated I'm a machinist neophyte, although I addressed the rich man poor man based on your comment and I'm not sure how you arrived there. I didn't read any comments from anyone showing off. I made my comment based on casca92's post. I hope we didn't lose him.



casca92 said:


> ahh a light is starting to come on ,  not real bright  but that is some guidance I was hoping for.



Casca 92 I hope the light is still on and you're healing. Arrange your chuck jaws as RJ's #20 post and watch this from around the 17 minute mark.


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## silence dogood (Jun 3, 2017)

RJSakowski said:


> To further clarify the order in which chuck jaws are reinserted, here is a photo.  Line the jaws up so they are all even and the distance of the tooth to the inside of the jaw is increasing.  The jaws will now be in their correct order.
> 
> The chuck jaw with the tooth nearest the inside of the jaw (the left one, in this photo) is the first jaw seated. I place the jaw in the slot and turn the scroll backwards while maintaining gentle inward pressure on the jaw.  At some point, the jaw will come off the scroll and drop down to the next position on the scroll.  Turn the scroll forward to engage the jaw.  Now insert the second jaw in its slot and continue turning the scroll until it captures the jaw.  Repeat the process for the third jaw.  The jaws will now be in their correct orientation.
> View attachment 234712


 Laying out the jaws is the way I do it.  Sometimes, I forget and get the order backwards.  Once you put the second jaw in, it becomes obvious.


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## RJSakowski (Jun 3, 2017)

If your chuck jaws are not marked in any way, you can designate the order easily by drilling one, two, and three small dots on the non-contact faces of the jaws. I use a carbide printed circuit drill bit to mark the hardened jaws.  Lacking the carbide drill bit, short light lines made with a Dremel will also work.  The face of the chuck should be marked as well.  It is not hardened so you will be able to drill the spots with a HSS bit.

Double check that you have the orientation correct and mark with a marker to avoid mis-marking. Should you make a mistake, there's nothing wrong with having three, four, and five spots.  Just don't go too crazy.


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## casca92 (Jun 3, 2017)

thanx
YOU all were a great deal of help

glad I did not ask which came first the chicken or the egg 

thanx


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## Wreck™Wreck (Jun 3, 2017)

Casca 92 I hope the light is still on and you're healing. Arrange your chuck jaws as RJ's #20 post and watch this from around the 17 minute mark.





[/


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## Rustrp (Jun 4, 2017)

Wreck™Wreck said:


> On a 3 jaw scroll chuck the threads on the jaws are offset 1/3 of the scroll thread lead from the part holding surfaces. In the case of a .125" lead .041xxxxx", it does not matter which slot the master jaws are in so long as all three are in the same thread in the correct order. To simplify jaw changes it is useful to number the slots and jaws but is not required, as seen below.
> 
> Turn the scroll until you see the beginning of the thread and install jaw #1, rotate the scroll until the start appears in the next slot and install jaw #2 and so on. The relationship lies between the threads of the scroll and master jaws. Keeping each jaw in the same slot helps with repeatability  as any error remains in the same place, if indeed the OEM finish ground the hard jaws in place then slot placement is important as the error in radial slot location either advances or retards the work holding surfaces.
> 
> ...



Good info especially the thread lead offset. I was flying by the seat of my pants when I stated the jaws would have fewer threads based on the sequence they were inserted. I was basing this on the #1 moving towards the center without thinking the movement may not be a full thread width when the scroll end reached the next slot. Thanks, -Russ


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## USMCDOC (Jun 10, 2017)

I liked this guys vid.. easy peasie!


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