[pzzamakr1980]

After nearly 6 months after I purchased my lathe I was finally going to make something which is a prototype for my own business venture. I ran into a considerable problem however. I mounted some 7/8 aluminum stock in 5" 3 jaw chuck that I purchased from Lathemaster along with the 8x14 and other assorted accessories. I center drilled it and then extended the piece out of the chuck to be supported by my live center. Thats when I noticed something was amiss. The live center was pushed a bit to get into the hole. It was deflected from the center line of the spindle. I then started turning the outside diameter of the piece down and immediately noticed that with the light cut i made only half of the diameter was actually being cut into. Thinking the tailstock was to blame or something was amiss with me I tried another piece of 7/8 aluminum and extended the aluminum only about 1.5" out of the chuck. Same thing occurred. I then used a piece of drill stock and a dial indicator to determine where the misalignment was occurring. There were two places. The first was at the mounting point of the 3jaw chuck. It was miscentered by about .003. The second was by far the more serious. When a piece of drill rod was placed in the jaws I was getting about .0150 of runout. Thinking I was making an error in my readings I tried other pieces of round material all with the same results. While a beginner machinist I know enough to realize that that is substantial. I also cleaned and rubbed down the jaws and remounted the chuck after cleaning it thoroughly. There were no chips or grit or anything else. Any suggestions on how to fix this or whats causing this. Thankyou

[HuFlungDung]

Perfect 3 jaw chucks are rare animals. There are so many things that affect runout, that the correct question is "Why does my part run true when rechucked in a 3 jaw?"

However, the backplate for the chuck needs to be checked first of all. Take the chuck off and check for runout. It should be dead perfect, there is no excuse for any eccentricity or wobble of the backplate. If you don't get that part correct, then the error exaggerates the further you get from that critical mounting surface.

The current state of wear of the chuck may also be a source of frustration. If it has had some use, and a part has slipped in it a time or two, there may be some slight scarring or wear at the front of the jaws. Carefully stone off any burrs, or, I usually use a round file for this, just lay it on the inner gripping surface of the jaw, and push the file in and out of the jaw. Let the file 'grab' any built up material that is stuck to the jaws. When any buildup is gone, the file will 'skate' over the hard jaw surface. Stop filing at that point

Even a 3 jaw in good condition will likely not hold the stock exactly the same way after rechucking. The potential for runout after moving the stock and rechucking is actually at least twice as great as the actual runout of the chuck to begin with.So if you can, center drill and do not move the stock.

Another trick is to use a collet chuck if you are gripping on good round surfaces and need to do a lot of secondary operations. Collet chucks are quite a bit more repeatable for positioning.

However, for certain work, I have made do with a 3jaw in the following manner: center drill the one end of the stock. Now, move the part way out of the chuck, so that the chuck only grips maybe 1/4" to 1/2" of stock. Put the part on the tailstock center, and then close the chuck on the other end. Because the grip of the chuck is extremely short, it does not have as much leverage to force the stock to run offcenter on the tailstock. Its almost getting close to running the part between centers, which is the surefire way to make sure that there is no misalignment being imparted to the work by the chuck.

On fussy work on a cnc lathe with a power chuck, I will do as described. Then, I will back out the tailcenter and see how much runout the center hole has. It is usually within .01 or .02" (depending on the job length), so then I will smack the outboard end of the stock to bring it into a true running condition. Otherwise, the part will turn a taper due to flexure of the tailstock.

[pzzamakr1980]

Thx Hung. What bothered me so much about this was the fact that the chuck is literally brand new. It has never held anything. Luckily, I have two 4-jaw chucks that I can use tomorrow to start again. I got real tired of spending 30 minutes to remove the chuck from the back plate. I dont have a stubby hex wrench so I was having to cram the hex in between the spindle housing and the back plate to loosen the screws holding the chuck to the back plate. Tomorrow I'm going right away to Lowes to get stubby hex's because of that miserable exercise. On top of problems with the 3 jaw I also was unable to practice knurling because the knurling tool that came with my chinese made qctp was unable to center my workpiece. It was too high and nothing I did could get it to line up. Its the one that has the dovetail built right into the post and it looks like they reversed the holes of the knurlers. It was a disappointing and frustrating day.

[in2steam]

Pizza, you might have alot of runout in yourjaws, thats a problem with 3 jaw chucks, that can be corrected, so can the problems that hung stated with the faceplate. It seems that the sieg 3 jaw chucks come with alot more then normal runout, alot of people have bought bison chucks to replace them.

Also, you are doing something atleast the way I was taught wrong. After center drilling, if the piece is able to be turned with out aid of steady rest the 3 jaw should be removed. The faceplate and centers, and dog should be then used, the dead center on the tailstock being more accurate then a live center. I have cheated and done it with a 3 jaw were tolerances were not as critcal for OD of the part but, it will be better on C2C then with 3 jaw and center. I know its a pain but unless this piece is under a couple inches you will have a hard time doing with the 3 jaw on this type of machine. The next step down that ladder was to mount a homemade center in the three jaw chuck and take a truing cut on that so it was on center and use that like a taper mounted center. This worked well on worn out chucks that I was taught on in school, we made it as a project I think it was out 12L12 or 12L14. I was always taught that the 3 jaw on manual machines was always the least accurate of mounting methods, short of strapping to a facplate(btw collets were the most accurate). The really nice high end cnc machines don't have as much of a problem, they are almost like big collets in that right.

chris

[pzzamakr1980]

I have used a 3 jaw chuck before to make decent parts. When I took my classes about a year ago we always used a 3 jaw chuck and a live center. I routinely had no difficulty with holding .005(+-3) for my beginning projects. This was with lathes used at a community college that saw 10 different people using them a week. I realize that the 3 jaw is not a precision item but having .015 of runout is excessive. I absolutely agree that to make precision work I should not use it. I have never used the knurler that came with my qctp I bought with my lathe. I wanted to try it before I used it for actual production so I wanted to turn the part down a bit so the knurling would be noticeable. I didnt even care about precision as long as the part was turned down, it wasnt. Half was turned, the other half was not. So where I got a bit frustrated was that the chuck wasnt free with the lathe, it was 60 bucks so it shouldnt be this bad. The same with the qctp knurler. That thing is useless junk. I routinely get the cheap stuff when I think it will be good enough and too many times I get stuff that isnt even useable. Okay that was a bit of a rant and now im done. And Chris dont think I do appreciate the advice I really do, advice from guys like you is how I managed to cnc my mill and reading other posts is how I got this far and decided to make a small business of this hobby.

[pzzamakr1980]

The one thing that i forgot to ask was Chris you had mentioned adjusting the 3jaw to make it more precise. What does that involve. I intend to use a 4 jaw and just take the extra time to dial it in and collets when I really need precision but for quick work I would still like to be able to use a 3jaw because of its convenience. Thx again.

[in2steam]

The one thing that i forgot to ask was Chris you had mentioned adjusting the 3jaw to make it more precise. What does that involve. I intend to use a 4 jaw and just take the extra time to dial it in and collets when I really need precision but for quick work I would still like to be able to use a 3jaw because of its convenience. Thx again.

A couple of things can be done, some are not worth the bother though either esp for the price you paid. truing a chuck is more or less like truing any thing else you turn, but be for you proceed you need to be absolutely sure that were your problem is, trying to true up jaws and finding out the closing mechanism is bad does you no good. I have only tried truing jaws once on steel jaws, its not easy to do and depending upon how hard they are, some have pads which can be replaced, although from what i see thats not the case. Not to get to involved in the process but you take a known diameter ground piece of steel, preferably around half the diameter of the opening in the form of a ring that you use on the outside to backward clamp, and insert it with it sticking out. You then observe the TIR, mark each jaw in reference to a similar mark on a the steel, I use 1 2 3 stamped into a washer for my taig but that is a little bit different as its alum jaws. At anyrate you then take and push that piece of steel back into the jaws as far as it will go, with out slipping off and keeping your reference points in the same spot. Then you take very very light cuts with a very very sharp stout boring bar, in all honesty you may even need to have them ground. You are stuck with that area were the steel was sitting untill you do one of several things, take a ring of a similiar nature and clamp it to the chuck outward(backwards from normal). You could do the exact opposite, the results are the same you have a nub that you need to clean up when you are done, I suppose you could do all from the outside, and move the ring but I have never seen it done that way. The piece you use in the jaws needs to be very very tight tolerance preferably ground. I have heard of people making a hone of sorts, and using a similiar ring to hone the inside of the chuck jaws, but I could not tell you exactly how they do it.
Once this is done you need to make some witness marks so you make sure the chuck is remounted the same way, this system does not work well on screw on chucks. I have to true my taig all the time, its got alum jaws, so the flex alittle when you crank on it, for that a simple washer works well and I normally don't clean it up, untill its very large nub. If your TIR is around .15 then plan on taking around .005 to start, but go based on your TIR from the steel piece. The person that showed me used a steel ring of about 4" diameter and this was done on a 8" chuck. He used around 3/4 solid boring bar, and then took the ring and clamped it to the outside after doing the inside about 80% of the way. He had 1 dot 2 dots 3 dots stamped on his jaws and matching are on the chuck and had a cam lock chuck. He said doing the step side was easier, but you had to pay attention to the TIR for each step on the jaw. This method will take up problems with the chuck itself and bad jaws, not the mech, nor a bad mounting. If you have agresive hatch patterns in the teeth you may break bits, and this will wear them down.


chris

[in2steam]

In the end I would check into a bison, they are cheap and very nice.

chris

[RICHARD ZASTROW]

Don't no body bore soft jaws no more? When you get your new chuck (you will eventually) get an "adjustru" type with replaceable jaws. If the machine is a high rev type, consider a steel body to avoid shrapnel. If you get a BIG bonus or a rich relative sends you a bunch of cash, go for a counter centrifugal, cast steel bodied, replaceable jaw adjustru chuck complete with a carbide boring bar and a set of boring rings. OR take a vacation in Italy.
Ciao,

[in2steam]

Don't no body bore soft jaws no more? When you get your new chuck (you will eventually) get an "adjustru" type with replaceable jaws. If the machine is a high rev type, consider a steel body to avoid shrapnel. If you get a BIG bonus or a rich relative sends you a bunch of cash, go for a counter centrifugal, cast steel bodied, replaceable jaw adjustru chuck complete with a carbide boring bar and a set of boring rings. OR take a vacation in Italy.
Ciao,

Can't say for sure how soft the jaws are, thats why I said be careful and you might have to grind instead.
Its just a lathemaster 8x14,, the passport costs more then the chuck does, then again now that I see $2.85 at the gas station so does the tank of gas to get it, 31 degrees and windy, given the weather here italy sounds nice, but then again so would las vegas of course my luck I would get stuck on a Jet Blue flight or Midwest would be bought out by Air Tran while I was away and get stuck.

chris

[skmetal7]

hmm, are u sure u have the jaws in the right order? they should be marked. the cheap Chinese chuck i got with my 8x14 wasn't even that bad! but it did look like i was cutting a cam, lol. so i went with a Bison, i want to get a 4 jaw 5" independent chuck, but cant find a good one yet (anyone have some pointers? and where i can get a adapter plate?)

[RICHARD ZASTROW]

Chris, I was refering to removeable soft jaws not the serrated hard jaws. I used to work for Kimberly-Clark when what is now Midwest Airlines was KC Aviation, a fleet of corporate jets AKA the Kimberly-Clark air force. If AirTran gets their hands on it, I'll never fly on it again. Having spent time in Italy, I'd go back in a heartbeat. That chuck of choice was a tonque in cheek poke at the price one would have to pay for what I consider best of all worlds.

[pzzamakr1980]

Alright I'm gonna pick up a bison in the next round of purchasing. I have a 5" 4jaw chuck that i can use in the meantime. Its a cheapie but since I can dial it in I should have much less difficulty in getting it to run true even if it does take a bit more time. I considered trying to fix it as per the directions and just said screw it, it will make a nice vase holder. Thx for the input guys its appreciated.

[pzzamakr1980]

What have you guys purchased for your lathes. I was looking at the bison set-trues but they only come in a minimum of 6" as near as I can tell. What did you buy and if you have it post a link too. Thx.

[skmetal7]

i got this chuck

http://www.use-enco.com/CGI/INSRIT?P...PARTPG=INLMK32

[Cruiser]

I just bought a new enco 12 x 36 and may know what you can do to fix your chuck. I pulled the pins from both chucks and face plate and mixed up some lapping compound, then by hand i lapped each chuck and the face plate to the taper on the spindle till they'd locate against the locating face, It worked great ! right now i have the four jaw mounted with the three jaw in it and it still runs true but i also had to relieve the relief faces of the jaws of the four jaw chuck to eliminate interferance.