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Machine Shop and Tool Talk

Self Centering Lathe Chucks


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  #1  
Old 06-27-2005, 08:42:23 PM
Smoke Smoke is offline
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Default Self Centering Lathe Chucks

I have a lathe with self centering jaws. Every once in a while I will change the jaws to do different jobs. My question is, many times I have to fool with the jaws while turning the chuck key to get them in center. What is the correct way to center the jaws while turning the chuck key. I know there is a faster way than trying to do it 4 or 5 times. Thanks !
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  #2  
Old 06-27-2005, 09:25:03 PM
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Gene O. Carpenter Gene O. Carpenter is offline
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Default Re: Self Centering Lathe Chucks

Smoke,
I had a 9" South Bend and on the back of the chuck there were numbers stamped in, 1,2 & 3 each of the 3 jaw's will have a corresponding number, turn the key til the leading edge on the spiral plate is at the #1 pos,insert # 1 jaw,turn key to #2 insert jaw #2 and the same for #3! I had the inside jaws and the outside jaws also there was a set that I never could figure out what they were for so they became paper weights,til I sold the lathe. The guy that bought it was happier than "a pig in a poo pile"!
Gene
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Old 06-28-2005, 08:53:17 AM
John G John G is offline
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Default Re: Self Centering Lathe Chucks

Smoke, it depends what you mean by "in center". A self centering three jaw lathe chuck is only so good, as far as being truly on center and reproducible. You could chuck a piece, turn it true, and then if you remove it from the chuck and re-chuck it, the piece will not be on center. To chuck a piece closer to on center, you need a four jaw independent chuck, a dial indicator, and patients.

Good luck.

John
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Old 06-28-2005, 03:58:30 PM
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Craig A Craig A is offline
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Default Re: Self Centering Lathe Chucks

One word is missing in all this and the word is DECENT.
A DECENT 3 jaw scroll chuck CAN be amazingly accurate.
I have one that we have used for 15 years and it is STILL dead accurate.
I just wish the name tag hadn't evaporated as I would buy another one just like it in a minute when the time came.
On another big, old, South Bend we have an ancient 3 jaw chuck that is still dead on after having been through hell and high water over the years.
I think the Swedes make the best chucks but you pay for them!!!
I hate to say this but the Chinese, besides SOME of the junk they STILL make, are turning out some very good machine tool stuff too.
Like everything else...you have to watch for the quality.
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Old 06-28-2005, 09:46:06 PM
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Gene O. Carpenter Gene O. Carpenter is offline
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Default Re: Self Centering Lathe Chucks

The 3 jaw that I had was also "right on" IF I reposistioned the work stock back in exactly the same posistion it was started at ! For that reason I centerpunched a spot by the #1 jaw and one on the stock which I aligned under the center of that #1 jaw.. ( something Red taught me,see below)
I used it for hobby work, mostly brass cannons from 6" w/3/8" bore up to 20" w/3/4" bore.
Make quite an impressive report when charged with a cap full of fffg black powder!

I had the lathe for 25 years and it had sat in a garage for 45 years or so where is was used for turning and truing up armatures on the old 6 volt starters and generators. Was never abused and Big Al, the guy that bought it, pulled it apart, beaded it and repainted it South Bend grey, did something to all the tooling,a few decals and it looks like it did when it left the factory.

In another post a few months ago I mentioned an old man that we called "Red", don't know why as he was as bald as a billiard ball. Anyway he was an engineer and machinist and when I picked up my 1st lathe , a 12" Atlas, was about worn out. His eyes lit up when he saw that old machine and he could do anything on it !

He said that "any lathe is only as good as the guy running it".. He was one of those learned men that you hate to lose to that "final calling",if you know what I mean.
He told some amasing stories on how "his company" built some of the big gun's used in WW2,they built their own long bed lathes, he showed me how to make the boring bars I used to bore out my cannons. He designed and built the garbage disposer that many of you have in your kitchen sinks ! Had the proto type in his celler, he was under contract to "his company" in Medina Ohio and they hold all his pattent rights..Miss that old fart!

Gene
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Old 06-28-2005, 10:37:19 PM
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Craig A Craig A is offline
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Default Re: Self Centering Lathe Chucks

Quote:
Originally Posted by Gene O. Carpenter
The 3 jaw that I had was also "right on" IF I reposistioned the work stock back in exactly the same posistion it was started at ! For that reason I centerpunched a spot by the #1 jaw and one on the stock which I aligned under the center of that #1 jaw.. ( something Red taught me,see below)
In another post a few months ago I mentioned an old man that we called "Red", don't know why as he was as bald as a billiard ball. Anyway he was an engineer and machinist and when I picked up my 1st lathe , a 12" Atlas, was about worn out. His eyes lit up when he saw that old machine and he could do anything on it !
He said that "any lathe is only as good as the guy running it"
Gene
RED sounds like MY kind of guy! We witness mark parts also if there is a need to remove the part in question from the chuck.
For REAL accuracy, turning between centers is the only way to go for TOTAL repeatability.
Craig
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Old 06-29-2005, 07:38:01 AM
Smoke Smoke is offline
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Default Re: Self Centering Lathe Chucks

Thanks for the replies fellas. I will try looking for the numbers on the chuck , as soon as I ever get time get out there and play. Thanks Again,
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Old 06-30-2005, 03:59:03 PM
Timberman Timberman is offline
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Default Re: Self Centering Lathe Chucks

Hi, Smoke , I suggest that you mark the jaws and body with a felt tip pen before you take it apart.
Its likely that they are numbered ,on the jaws in a side groove and on the body, on the large diameter of the slot.
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Old 06-30-2005, 07:18:43 PM
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Craig A Craig A is offline
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Default Re: Self Centering Lathe Chucks

I got so sick and tired of looking for those darn numbers I got ticked off and took the jaws to a cutoff wheel and ground notches in the outside ends... ...on ALL our 3 jaw chucks.
NOW I can change jaws in a flash...
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Old 08-27-2005, 06:15:34 PM
Steve Adams Steve Adams is offline
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Default Re: Self Centering Lathe Chucks

Many times over the years I have resorted to "tapping" a part true with a big piece of brass and an indicator. A lot of chucks have some give in them if they aren't to tight. Just put your part in and snug it up a bit, put the indicator on and tap down on the highest jaw and you should be able to get it pretty good. Tighten the chuck up, recheck it and away you go. Some chucks are more forgiving than others.
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Old 11-27-2005, 08:08:27 PM
StevenG StevenG is offline
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Default Re: Self Centering Lathe Chucks

Its right whats been said about the matching numbers, also always tighten & slacken the jaws with the same screw each time. As was also previously said its all down to quality & condition - a chuck been a precision instrument & not just a tool. They make some good tackle over in Europe, but i still think we make the best here in the UK, with such firms as Pratt Burnard been regarded as one of the best. We certainly used to make the best Lathes in the world with such firms as Dean, Smith & Grace here in West Yorkshire always been known as the "Rolls Royce of lathes" - if you ever get chance to use one you`ll see why
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Old 11-28-2005, 04:00:16 PM
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Forrest A Forrest A is offline
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Default Re: Self Centering Lathe Chucks

A set-true self centering chuck is the only way to have concentricity when removing and replacing stock in a SCTJC.

Forrest
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Old 12-08-2005, 08:47:07 AM
George Andreasen George Andreasen is offline
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Smile Re: Self Centering Lathe Chucks

I had to throw in my two bits worth here........
An old machinist friend showed me how to true up a three jaw and save buying a new one. Assuming the scroll inside isn't totally bunged up, place a timken bearing race at the REAR of the jaws and tighten down. Use a toolpost grinder and make repeated passes up to the race until you have even sparks all the way around. Remove the race and run the grinder in to the rear of the jaws and grind MORE jaw material at that end. What you are doing is bringing the jaws down tight on a KNOWN accurate piece (the bearing race) and grinding them to truth. You then grind the rear of the jaws slightly recessed. The chuck will now take stock and turn it accurately, although as mentioned before NO average three jaw is 100% accurate unless you pay top dollar for one that has individual adjustments for wear. Let's be honest....much of what we do doesn't call for "space shuttle" accuracy!
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