I Understand
Thanks for the replies.
The top jaws I replaceda are hard jaws.
I use a four jaw, collets, six jaw,and a three jaw in that order. I turn between centers when it is applicable; however, there are instances when a three jaw is unbeatable. For example, when turning something with three or six sides.
This is something I started to do today. I am turning down the ends of some socket head cap screws to fit them with brass caps. They are for a spider that fits the left side of my head stock to support long stock that runs through the spindle. I take three nuts and cut a slit long ways on one of the sides. I screw three of these on the screw I want to cut a tenon on. When I tighten the chuck, the nuts compress, holding the screw, without damaging the threads.
I chucked the "drill rod" in my six jaw and checked it. The total indicator movement was less that .". Divide that by two for the run-out. I believe it is straight enough for the task at hand; however, I do agree something turned between centers is better.
The body is running true. I am going to take it apart again and make sure there is not something obvious. If not, what chuck service would yall recommend and is it worth spending any money on?
I understand a three jaw is going to be far from perfect. To rephrase my question, what should I expect from this chuck, new. I could not find any specifications on it.
I have to add this to keep Forrest from giving a lecture. I have three four-jaw chucks, a six, an eight and a ten. The reason I have three is I can grab things with the eight I can't hold with the ten and I can hold things with the six I cannot hold with the eight. The ten in a monster Cushman that is great for holding large stock. It was given to me by a friend that is a machinery dealer. It is accurate and a dream to set up. I use my Buck 8" direct mount most of the time. It does not have quite the holding power of the big Cushman but it is easier to pick up and it handles smaller stock better. I use my Buck 6" for really small stuff that the eight will not hold. I started using a four jaw when I was getting started for two reasons. It was the best chuck I had with my ENCO and I took Mr. Addy's advice. That is something I do not regret.
Also, to be more specific, If I can get the the Bison three jaw within 0." run-out, for a reasonable amount of money, I will fix it. If I can't fix this one, and a new comparable three jaw, will provide accuracy in the 0. range, I will replace it. If 0. to 0." accuracy is not achievable in a standard three jaw, I will eat my Wheaties and save my money an buy a "set true" or an "adjust true" thee jaw chuck.
Sorry for the long post. I felt a better explanation of my goals was in order.
Thanks again and have a great week.
Grits
Thanks for the replies.The top jaws I replaceda are hard jaws.I use a four jaw, collets, six jaw,and a three jaw in that order. I turn between centers when it is applicable; however, there are instances when a three jaw is unbeatable. For example, when turning something with three or six sides.This is something I started to do today. I am turning down the ends of some socket head cap screws to fit them with brass caps. They are for a spider that fits the left side of my head stock to support long stock that runs through the spindle. I take three nuts and cut a slit long ways on one of the sides. I screw three of these on the screw I want to cut a tenon on. When I tighten the chuck, the nuts compress, holding the screw, without damaging the threads.I chucked the "drill rod" in my six jaw and checked it. The total indicator movement was less that .". Divide that by two for the run-out. I believe it is straight enough for the task at hand; however, I do agree something turned between centers is better.The body is running true. I am going to take it apart again and make sure there is not something obvious. If not, what chuck service would yall recommend and is it worth spending any money on?I understand a three jaw is going to be far from perfect. To rephrase my question, what should I expect from this chuck, new. I could not find any specifications on it.I have to add this to keep Forrest from giving a lecture. I have three four-jaw chucks, a six, an eight and a ten. The reason I have three is I can grab things with the eight I can't hold with the ten and I can hold things with the six I cannot hold with the eight. The ten in a monster Cushman that is great for holding large stock. It was given to me by a friend that is a machinery dealer. It is accurate and a dream to set up. I use my Buck 8" direct mount most of the time. It does not have quite the holding power of the big Cushman but it is easier to pick up and it handles smaller stock better. I use my Buck 6" for really small stuff that the eight will not hold. I started using a four jaw when I was getting started for two reasons. It was the best chuck I had with my ENCO and I took Mr. Addy's advice. That is something I do not regret.Also, to be more specific, If I can get the the Bison three jaw within 0." run-out, for a reasonable amount of money, I will fix it. If I can't fix this one, and a new comparable three jaw, will provide accuracy in the 0. range, I will replace it. If 0. to 0." accuracy is not achievable in a standard three jaw, I will eat my Wheaties and save my money an buy a "set true" or an "adjust true" thee jaw chuck.Sorry for the long post.I felt a better explanation of my goals was in order.Thanks again and have a great week.Grits
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Post
by Harold_V » Wed Jan 18, 2:30 am
Ramv wrote:For instance, does 'a' represent TIR at d1? If I chuck in a "perfect" ground drill rod measuring 25mm, I will see at the most a 0.03mm deviation in measurement?
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I interpret the reading as you suggest, but keep in mind, a three jaw chuck tends to be diameter specific. It may be within a particular region of error at one diameter, yet better or worse at another diameter. That's due to the relationship between the scroll helix and dead center, which may or may not be true. To be perfectly clear, it is most unusual for ANY three jaw chuck to provide identical readings in regards to runout when the chuck is used for different diameters.
What happens when I rechuck the part? Should I expect it to have a TIR of at most 0.03 + 0.015 = 0.045? That doesnt really make sense because TIR just went up for no reason.
There's more to it than you might think. For example, if your chuck has been sprung (a crash, or by over tightening with only the tips of the jaws engaged, the piece being chucked may not be gripped dead parallel with the spindle centerline. In such a case, you can expect strange readings, often not repeatable, and they'll get better (or worse) as you traverse the shaft in either direction. And, as suggested, above, you can expect different readings as you change sizes in regards to the pieces being chucked.
If you hope to grip pieces with great precision, you have a few options. One of them is to use collets (questionable quality may result), or to use a four jaw chuck and dial the part to the level of precision you desire, and, thirdly, soft jaws. If you understand how they're properly applied, you can generally achieve a level of repeatability of less than a half thou in concentricity, and if machined according to the given application, virtually dead perpendicularity. All with the added bonus of the ability to chuck parts without jaw damage.
It is VERY important that you understand proper use of soft jaws. If you do not, none of the above will be true.
Harold
I interpret the reading as you suggest, but keep in mind, a three jaw chuck tends to be diameter specific. It may be within a particular region of error at one diameter, yet better or worse at another diameter. That's due to the relationship between the scroll helix and dead center, which may or may not be true. To be perfectly clear, it is most unusual for ANY three jaw chuck to provide identical readings in regards to runout when the chuck is used for different diameters.There's more to it than you might think. For example, if your chuck has been sprung (a crash, or by over tightening with only the tips of the jaws engaged, the piece being chucked may not be gripped dead parallel with the spindle centerline. In such a case, you can expect strange readings, often not repeatable, and they'll get better (or worse) as you traverse the shaft in either direction. And, as suggested, above, you can expect different readings as you change sizes in regards to the pieces being chucked.If you hope to grip pieces with great precision, you have a few options. One of them is to use collets (questionable quality may result), or to use a four jaw chuck and dial the part to the level of precision you desire, and, thirdly, soft jaws. If you understand how they're properly applied, you can generally achieve a level of repeatability of less than a half thou in concentricity, and if machined according to the given application, virtually dead perpendicularity. All with the added bonus of the ability to chuck parts without jaw damage.It is VERY important that you understand proper use of soft jaws. If you do not, none of the above will be true.Harold
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