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Getting the workpiece straight in the chuck.

Tailormade

Iron
Registered Member
#1
So, I've got a question so basic it seems no one else has even had to ask it. (Or if they did, I didn't know the right terms to search on)

In my 3 jaw chuck, I have yet to figure out a way to get the work piece even close to straight in the chuck.

I feel like there has to be some better way than what I'm doing. If there is some method that is well accepted for getting things aligned in the 3 jaw chuck, I am all ears.

What I *thought* would be the way would be to use a center finder, scribe some lines, and then center drill at the intersection. However, with the longer shafts I cant even drill there, the chuck is so far off. Longer as in, 15-20 inches.

I also have a four jaw chuck, but haven't tried switching the chucks just yet. I anticipate the same problem with this though, as I seem to be missing something basic about getting the shaft at least close to parallel to the ways perpendicular to the chuck face.
 

markba633csi

Active Member
Active Member
#4
Well first off, 3 jaw chucks (especially cheap ones) don't have great repeatability. If they did we wouldn't need collets and 4 jaw chucks.
What I do with mine is try inserting the piece in several times and see what happens. Sometimes it's right on the money. Other times it's all over the map. Another trick is "tapping" on the workpiece to help center it. Some people can do this with remarkable accuracy. But when it absolutely has to be perfect, use a collet or a 4-jaw.
Also for long pieces you must use a steady rest. I don't own one, but I suspect the day is coming soon when I'll have to break down and buy or make one.
Mark S.
 

scwhite

Active Member
Active Member
#6
Yes, it seems like a bad idea to me to, but the piece won't fit through the head stock, so I didn't see another option.

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If you have a steady rest set it up for anything long .
I don't know what size lathe you have but it is most
Likely a small lathe like my 10" swing Clausing 4900
It can run about 2-7/8 dia. In the steady rest . And to set the steady rest on center and the right dia. You
Put a short piece os stock in the chuck turn it down to the size of you 15" shaft . Put you steady rest right up close to the chuck where you just turned the location to the size of the 15" shaft . Set your steady ready up on that short piece . Open it up do not move any of the jaws on the steady rest . Open the three jaw chuck and take out that short test piece you just set your steady rest to . Now in clamp the steady rest and move close to the other end of the shaft about 13" form your chuck . Put your shaft in the chuck
Snug it and best it on the bottom two jaws of your steady rest . Now you have to make sure you have you carriage on the side of the steady rest you plan on working . Close the top jaw on the steady rest . And clamp the bed clamp and the steady rest clamp .
Don't run any work in a steady rest very fast no faster than your back gear will run .
Check all of the jaws make sure you have them all
In the right slots . Each slot is numbered and each jaw is numbered and must go in the proper slot .
If you have two peace jaws the also should be a match with its number and should have the same number on it as the jaw slot.
You will have to take the all out a start number one first in the slot and the scroll must catch the number one jaw first then don't turn the scroll past number two slot make sure you catch number two the same thing on number three . Now you can screw them on in . Your chuck should be right now .
And just like markba633csi said I will tap on the face with the lathe in motion with a brass mallet
Don't run it to fast or to slow it should be about
250 to 350 rpms
 
Last edited:

scwhite

Active Member
Active Member
#8

kd4gij

Active User
Active Member
#9
I use a dial indicator and a soft mallet ton get the part running true. For a longer bar indicate out near the end first then check up near the chuck.
The roller posted me Frank works great on shorter parts.
 

Glenn Brooks

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#10
Here's a method I adopted from my master machinist friend, who learned this from from old time master machinists 35 yrs ago when he was starting out in the trade.

Loosely Chuck up your part in the three jaw, and turn on your machine at slow speed (50-100 rpm or thereabouts).

Lightly tap the high part with a light hammer 2 or 3 times as it spins around.

After you get the hang of it, this will true up the part 9 times out of 10. If not, loosen and repeat.

Tighten up the chuck enuf to hold the work.

I hardly ever use a dial indicator with my three jaw now, after I learned how to do this.

Glenn
 

DAT510

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#12
What part of the work piece are you trying to machine? If it's the end, then as others have suggested a steadyrest would be a way to go, since it sounds like piece is too big to fit through the bore. If it's the "side" of the work piece, what about mounting it between centers and using a dog drive?
 

Tailormade

Iron
Registered Member
#13
If you have a steady rest set it up for anything long .
I don't know what size lathe you have but it is most
Likely a small lathe like my 10" swing Clausing 4900
It's a 12X36, but its headstock has a pretty narrow openning, so I assume I'll be getting to know that steady rest pretty well.
Don't run any work in a steady rest very fast no faster than your back gear will run .
I'm pretty sure the prior owner didn't listen to that advice, the arms on the steady ready rest are.. a bit rough at the ends. I don't see any indexing on the arms, can I just dress up the ends of the arms or must they be replaced? On that same topic, are those steady rest arms with bearings on the ends worth having?

Here's a method I adopted from my master machinist friend, who learned this from from old time master machinists 35 yrs ago when he was starting out in the trade.

Loosely Chuck up your part in the three jaw, and turn on your machine at slow speed (50-100 rpm or thereabouts).

Lightly tap the high part with a light hammer 2 or 3 times as it spins around.

After you get the hang of it, this will true up the part 9 times out of 10. If not, loosen and repeat.

Tighten up the chuck enuf to hold the work.

I hardly ever use a dial indicator with my three jaw now, after I learned how to do this.

Glenn
I'm going to give that a try with a wooden mallet tonight, thanks.

A few years ago I saw franks tool on his web site. So I found a good use for those useless single wheel knurling tools that come in tool sets. Replaced the knurl with a bearing.
View attachment 232689
I haven't seen a tool set with a single knurl, what makes them useless? Of course with the existence of google and ebay now I've seen many of them. Still not sure why useless.

What part of the work piece are you trying to machine? If it's the end, then as others have suggested a steadyrest would be a way to go, since it sounds like piece is too big to fit through the bore. If it's the "side" of the work piece, what about mounting it between centers and using a dog drive?
Thanks for mentioning the lathe dog. I'd heard the term turning between centers but not understood how it would be done.
 

Frank Ford

Active User
Active Member
#14
I haven't seen a tool set with a single knurl, what makes them useless? Of course with the existence of google and ebay now I've seen many of them. Still not sure why useless.
NOT useless, but quite useful! Great for straight knurls on the lathe to avoid double-tracking, among other regular uses.

Here's an irregular use, renewing the knurling on a bar clamp:



 

dontrinko

Active Member
Active Member
#15
I use the tail stock to put a little pressure on the work as I tighten it. This helps but I still end up trying several times until I get it close.
If you are not using the part that is in the chuck you can turn the extended part and it will end up round even if you do not have it perfect in the chuck. I have done this on long pieces: turn one end then turn it around and turn the other. This helps if the work is not perfectly round to start with. Don
 

jlsmithseven

Active Member
Active Member
#16
Sorry for asking, but what exactly does this little wheel do that touches the piece. Is it meant for tool height or runout of the piece? I am just a little confused on how this little tool works, but it looks like a good tool to have?
 

mikey

Active User
H-M Supporter-Premium
#18
Sorry for asking, but what exactly does this little wheel do that touches the piece. Is it meant for tool height or runout of the piece? I am just a little confused on how this little tool works, but it looks like a good tool to have?
It's just a bearing mounted on a piece of square stock. In use, the work piece is mounted in the 3JC and lightly snugged. Then the lathe is run at low speed and the bearing is gently brought into contact with the work. Initially, only the high spot contacts but as you slowly feed the tool in, the work is brought into relative concentricity with the spindle and you will see the work start to run true(r). At that point, you stop the lathe and tighten the chuck firmly and you're set.

This works for shorter pieces or even thinner work like a washer that you're trying to get to run true in a 3JC (you bring the tool into the face of the washer). It is not a precise method but it is better than nothing. Its actually a good tool; I've had one for years but I cannot recall who came up with the idea to use a bearing. An old machinist friend of mine used a piece of maple with a rounded end that worked just as well.

In the case of the OP, this tool would not be useful due to the length of his work piece. A steady rest and a dial indicator would allow him to center drill for live center support but that has been discussed already.
 

jlsmithseven

Active Member
Active Member
#19
Oh so you're saying loosen the chuck jaw a little bit, run it at like 35 rpm or something and it will true it up and then just tighten the screws. Sounds simple and awesome, not sure if I will be able to do that though.
 

benmychree

John York
H-M Supporter-Premium
#20
Not always necessary to turn a blank piece to line up the steady rest; I just get it close, then put a center drill against the shaft end lightly and see what trace it leaves on the shaft end if not on center, then adjust the SR jaws until the center drill hits the shaft dead center and drill the center hole, With a bit of practice it is easy and quite accurate. There is nothing wrong with running things fast speed in the steady rest as long as the jaws are not overly tightened and a lubricant is used; way oil, center lubricant, white lead or whatever is at hand. If the jaws are roughed up, they can be re machined. I have thought of using a hand reamer in the spindle and carefully adjusting the jaws, one at a time against the rotating reamer, but have never tried it; same could be done using an end mill, the more flutes the better.
 

mikey

Active User
H-M Supporter-Premium
#22
Oh so you're saying loosen the chuck jaw a little bit, run it at like 35 rpm or something and it will true it up and then just tighten the screws. Sounds simple and awesome, not sure if I will be able to do that though.
Just run it at the lowest speed you have. It works well but don't expect to be dead on concentric this way. It will get you close enough, though, and the tool is worth making and using.
 

benmychree

John York
H-M Supporter-Premium
#25
I had quoted jlsmithseven who apologized for asking a question.
I want him to know that asking any question is fully encouraged here!

-brino
Yes, there should be no need to apologize for asking any question, no matter how basic it may be; that is what this forum is for.
 

scwhite

Active Member
Active Member
#27
Not always necessary to turn a blank piece to line up the steady rest; I just get it close, then put a center drill against the shaft end lightly and see what trace it leaves on the shaft end if not on center, then adjust the SR jaws until the center drill hits the shaft dead center and drill the center hole, With a bit of practice it is easy and quite accurate. There is nothing wrong with running things fast speed in the steady rest as long as the jaws are not overly tightened and a lubricant is used; way oil, center lubricant, white lead or whatever is at hand. If the jaws are roughed up, they can be re machined. I have thought of using a hand reamer in the spindle and carefully adjusting the jaws, one at a time against the rotating reamer, but have never tried it; same could be done using an end mill, the more flutes the better.
The best way to dress the end of the steadyrest
Jaws is to make a leaping mandral and run the mandral with a live center in the tail stock
The bring in the jaws on the mandral with the laping
Compound on your mandral
 

Chipper5783

Active User
H-M Supporter-Premium
#28
The above responses are all good and will likely give a better result than simply putting that piece of bar into the chuck and cranking down on it. Of course, a 3 jaw chuck does not hold perfectly, either on center or aligned to the axis of the bed. If you pay lots of money and get a new top end chuck and then mount it correctly - it will be closer to "perfect" - but it will not be zero runout up close to the chuck and well out along the bed (assuming you have an accurate test bar).

However, very few people here would actually spend that kind of $$. It really is not necessary. Using techniques like the ones described above will get a pretty good result, with a pretty ordinary chuck (cheap or well used). Don't sweat it. I actually don't do any of the tap/bump/rolling techniques. I have been through the whole chuck mounting/tuning - and for 3 jaw work, I simply snug the stock - and go. The run out is 0.003 close to the chuck and twice that 6" out. The reason it is no big deal is because after the first couple passes it will be running as true as the machine is capable of!

I have never checked using an unsupported bar, 15-20 inches out from the chuck. I can't imagine very many situations where it would be relevant (center drilling something too big for the spindle hole, even then there are other ways to get'er done)?

Another excellent solution (not mentioned above) is to set yourself up with soft jaws: load the jaws, skim them and then the work will run very close to true.

You said that it is running way off? Take some measurements (make sure it is an accurate piece of material), and check the run out at several locations out from the chuck. Maybe there is an issue with how the machine or the chuck are set up?

Let us know how you make out. Regards, David
 

Glenn Brooks

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#29
One essential use for the tap/bump roll techniques in a three jaw is to true up a part that has been previously turned.

Glenn.