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hwingo
02-16-2009, 01:03 AM
Hi Guys,

Once again I visit the Lodge of my brothers in search of Light. I need a wee bit of your infinite wisdom.

Ordinarily, the work I do on my lathe is not so critical that I need to use a 4-jaw chuck. Historically I simply chuck a piece of metal in my 3-jaw chuck, turn to size then part the piece.

I recently purchase a piece of aluminum that's 2.5" OD X 12" length and I desire to keep it as close as possible to 2.5" OD. I have no aversion to reducing the OD by a few thousandths but I do have a problem with reducing the OD by .010". In this case that would be unacceptable.

Using my new 4-jaw chuck for the first time I began indicating using my indicator which measures in .0005". I tried to pick as smooth a surface as I could find fearing every little bump and dip would be recognized by the indicator. And I was right to have this fear.:eek: Resigning myself to the fact that I was indicating a rather rough surface, I was happy getting the piece indicated within .001" near the free end. Problem begins.:rolleyes:

When I power-up the lathe, the end runs quite smoothly but the work that's closest to the chuck has an observable wobble. Moving the indicator near the chuck I re-indicated and re-adjusted the work until I was within .001". Great .... but now I have noticeable runout at the end. I'm faced with a .010" difference any way I go. I have not tried using a steady rest. I assume this would be advisable? Should I first indicate at the chuck and make jaw adjustments and then use the steady rest and indicate near the end to get the work running as true as possible?

Since this was a piece of extruded aluminum that was pulled off the rack and shipped to me, should I assume this is as close as I will come (.010") to getting this work running true due to the rough surface? Seems like I should be able to do better than that.

Both ends need to be faced off and I need to drill (bore) a hole through the entire length. My goal is to keep this piece as close to 2.5" OD as possible and get everything running true along the length of the piece. What are your suggestions in accomplishing this?

Harold

.RC.
02-16-2009, 01:22 AM
How big a hole needs to be drilled???

Is the OD going to need to be turned in any way??

You could try a cathead and steady??

winchman
02-16-2009, 01:47 AM
Chuck the part in the 4-jaw with the indicator near the outer end. Drill a center hole. Repeat for the other end. Mount the bar between centers, and indicate the OD in several places with the indicator mounted on the carriage. This checks the OD and also makes sure the tailstock isn't offset, which would result in a taper.

If the amount you need to remove to true the OD is to your satisfaction, go ahead and true the OD.

Proceed with your project as before, and report back.

Roger

hwingo
02-16-2009, 02:18 AM
How big a hole needs to be drilled???

Is the OD going to need to be turned in any way??

You could try a cathead and steady??

http://i234.photobucket.com/albums/ee38/hwingo_2007/Vince4.jpg

The largest hole to be bored is 1.75", the next largest is 1.5", and the smallest is .95". Refer to image.

Harold

hwingo
02-16-2009, 02:20 AM
Chuck the part in the 4-jaw with the indicator near the outer end. Drill a center hole. Repeat for the other end. Mount the bar between centers, and indicate the OD in several places with the indicator mounted on the carriage. This checks the OD and also makes sure the tailstock isn't offset, which would result in a taper.

If the amount you need to remove to true the OD is to your satisfaction, go ahead and true the OD.

Proceed with your project as before, and report back.

Roger

Thanks Winchman. I'll give this a go. I appreciate your reply.

Harold

gmatov
02-16-2009, 02:24 AM
Is the piece straight to begin with? If it is, you should be able to hold a couple thou of size. You say .010 under is too much, and you are telling us that you have runout that is about that much, end for end.

Bowed some.. You ain't makin' no 2.499 out of that.. Does it actually mike 2.500 over its length? You might have a couple to play with.

Cheers,

George

doctor demo
02-16-2009, 02:45 AM
What has not been mentioned yet is to take a mic and check if the piece is round, it sounds like it may suprise You just how much it is out of round. As mentioned earlier it may also be bowed.

Steve

.RC.
02-16-2009, 02:46 AM
If it is 12" long and your spindle bore is smaller then 2.5 inches you will have to use a steady to bore it...

Paul Alciatore
02-16-2009, 03:02 AM
Round stock is not necessairly round. Or straight.

In my limited experience, steel is worse than aluminum, but both are not all that accurate to size and may have low spots almost anywhere along the length. A reduction of 0.010" in OD (that's just a 0.005" cut) is not an excessive amount in order to get the OD uniform and I have seen stock that required more.

I would first center punch both ends as accurately as I could. Then mount between centers using these punch marks and check for any excessively low spots. If there are any, mark the location(s) and how deep they are. The pattern of low spots will determing how much you must take off and where.

You can then adjust the location of those punch marks and center drill both ends. Mount between centers again and reduce the OD until the lowest low spot is removed. You now have an accurate OD that you can base all the other operations on.

If you really need a 2.5" OD, it is probably best to purchase oversized stock. This is available in some sizes and alloys without stepping up to the next fractional size.

torker
02-16-2009, 09:01 AM
Harold...I used to face the same problem you are having. It was due to my chuck jaws being out of whack.
Get the far end true...the chuck end would be out....get the chuck end true..I'd have a big wobble on the far end.
I always got around it IF I could center drill the far end when it was true. I'd then run that end on a dead center then I'd true the four jaw end.
I kept the piece running on the center for all the truing operations...and for setting up the steady rest. Since then I've trued up the jaws for my four jaw and it's made life a whole lot easier.
Russ

JoeFin
02-16-2009, 09:31 AM
2 piece soft jaws are made for just these sort of occasions.

Cut a piece of scrap of the right diameter to fit down in the Hard Jaws and hold the Soft Jaws to the correct opening Dia. Clean up to True with boring bar. When I do that they run with in .001 every time

http://i198.photobucket.com/albums/aa83/Freakindj/000_0008.jpg

MickeyD
02-16-2009, 09:38 AM
The quick way to check is to put it on your surface plate (or reasonable substitute) and take a couple of height readings as you rotate it. Unless you pay extra (usually a lot) for precision stock, the dimensions are all over the place.

tony ennis
02-16-2009, 09:48 AM
Regarding having to keep it at 2.5" in dia... Why? Apparently this part is going inside of something else, or has to support something else.

If so, then it likely has well-known contact points. Can you turn it round, bore the center hole, and then sleeve the contact points back to 2.5"?

Lot of extra work, but your desire for a precise diameter and bore hole is at odds with leaving the stock as-is.

JCHannum
02-16-2009, 10:05 AM
This is what centers and steady rests are for. The likelyhood of holding a longer piece true is very low. Turning between centers is probably the simplest and most accurate method. Be sure to check for taper in the early stages and adjust the tailstock to compensate.

hwingo
02-16-2009, 11:21 AM
Good Morning Guys,

If I can get the far end "zeroed in", faced, and then drill a center hole for a live center, then change ends and go through the same procedures, is it possible to place the work between centers without using a dog (using a dead center at the head stock and live center in the tail stock and apply "holding pressure" via the tail stock) and take a series of very light cuts along the length until the work is turned round? Stated differently, can I apply enough pressure between the two centers using the tail stock that would allow the work to turn so that I could make light cuts along the entire length? If I used a dog, I would be unable to "true" the entire piece.

Harold

Oldbrock
02-16-2009, 11:40 AM
Right, you had it running true at the four jaw chuck and reasonably tight. Now indicate the end near the tailstock. With a small bashometer ( hammer) hit the high side until it is also running true. My method is to have the lathe running between 50 and 100 rpm, have the indicator on the outboard end and hit when the indicator reads +. NOTE. you should always hit on the indicator side of the work. If you hit on the opposite side when it reads "0" you will shock the indicator doing damage to the guts. Pick a speed that suits your kama, just joking. You will find an rpm that you can easily time your hits, I like 100, that may be too fast for the first time. If the little hammer won't move it the get a bigger hammer and you can hold something in between it and the work to avoid bruising it like a piece of junk plastic. That's my method anyway. Peter

winchman
02-16-2009, 12:52 PM
I doubt you can apply enough pressure with the tailstock to drive a 2.5" diameter piece between centers for truing the OD.

If you don't need the entire length trued, put the outer end on the center in the tailstock and just grip 3/8" or 1/4" with the 4-jaw.

If you extend the tailstock ram far enough to put the steady around it while you're truing the rod, you can fit it to the finished OD before removing the tailstock to do the drilling and boring. That'll save some setup time.

Maybe I'm too careful, but I don't think dial indicator and hammer should be mentioned in the same paragraph.

Roger

lane
02-16-2009, 07:11 PM
Right, you had it running true at the four jaw chuck and reasonably tight. Now indicate the end near the tailstock. With a small bashometer ( hammer) hit the high side until it is also running true. My method is to have the lathe running between 50 and 100 rpm, have the indicator on the outboard end and hit when the indicator reads +. NOTE. you should always hit on the indicator side of the work. If you hit on the opposite side when it reads "0" you will shock the indicator doing damage to the guts. Pick a speed that suits your kama, just joking. You will find an rpm that you can easily time your hits, I like 100, that may be too fast for the first time. If the little hammer won't move it the get a bigger hammer and you can hold something in between it and the work to avoid bruising it like a piece of junk plastic. That's my method anyway. Peter

brockley got it right . But just roll the chuck by hand and tap the high side once true re check the chuck end . May have to move back and forth a few times but it will indicate in with end reason. Do what is called a 4 side indicate using the chuck jaws as a reference . Make indicator read 0 at jaw 1,2,3,4, on both ends that is as close as you may can get it with stock that is no round.

hwingo
02-17-2009, 03:15 AM
Hi Guys,

I'm reporting back after a day of semi-frustration. Conversely, it's been a day of learning (which is really the object of any exercise while a completed job is secondary).

To respond to several statements, I give you the following:

1. I checked tail stock center using a .0005" indicator. Thinking back, I likely messed up things when I dial-indicated and attempted to zero my tail stock. I'm certain I need a lesson on how to zero the tail stock because the work piece ended up with a slight taper.

2. I started with a work piece that's 12 1/8" long X 2.5" dia. I needed to end this Chapter with a piece that's 12" in length and 2.5" dia. The "long & short" is, I had nothing to grab hold of so I had to turn the piece between centers. This was a "first for me" (turning between centers).

3. The work piece was as most suggested ..... "out of round with peaks and valleys along its length"; a new lesson learned. To the best of my ability I "zeroed" the far end, then drilled a large center hole using a large center drill. Took the piece from the 4-jaw and using the same process I did the same thing to the opposite end of the work.

4. I was not shop-prepared to turn between centers as I didn't have a dog for my faceplate so I removed the 4-jaw, installed a center in the head stock, placed the work between centers and applied sufficient pressure via the tail stock to over come work-slipping when taking VERY THIN cuts. This worked! Because of inexperience and poor working knowledge I really didn't think all things through finding that I was unable to turn the entire length of the work when set up. Reasoning that I was turning between centers, I turned the piece within 4" of its length and switched ends and finished the piece after switching ends about 10 times.

5. After the piece indicated round (and the same at both ends), I decided to measure midway between the two ends. This is when I learned that mid point was about .004" larger in dia than the two ends. This tells me I was cutting a taper. Had I been able to turn the entire length without swapping ends, I am certain that one end would have been larger than the other, hence, a taper. By swapping ends as cuts were made, what would have been a long single taper was compounded by cutting tapers from both ends. I think I'm right on this. Those having experience should correct my thinking about these tapers if you find my thinking flawed. Comments would be appreciated.


POSTMORTEM ANALYSIS

Had I known what the hell I was doing when indicating and zeroing my tail stock, regardless of poor-planned-setup I would have realized a straight, round piece when finished. In passing, when the work was turned round, I lost a total of .008" OD at both ends.

Comments are appreciated as well as instructions on how to center my tail stock.

Harold:)

JCHannum
02-17-2009, 08:04 AM
When turning between centers, I use a spud in the chuck. This is just a short piece of stock that has a 60 degree point on it, turned in the chuck and left in place. It is tha most accurate way of getting a true center.

Get, or make a dog, they are usually cheap on eBay. Homemade ones need not be elaborate, two pieces of square or flat stock bolted together with a third bolt or one piece bent to drive it.

Center the tailstock to the best of your ability before starting. When taking the first cuts, take very light cuts. As soon as enough stock has been removed to get a good measurement, check for taper. It will be there. Using a dial indicator on a mag base, the T/S can be adjusted and another test cut made. It will likely take a couple of tries to get an acceptable reading, so go lightly.

I do not know what you are making, but in some cases, such as a shaft running in a couple of bearings or bushings, the journal areas where the bearings will run are turned to size individually and a relief of a few thousandths is cut between them. This speeds the machining and removes some of the angst.

winchman
02-17-2009, 08:21 AM
I don't understand why you couldn't turn the entire length between centers without swapping ends. It's OK to move the tool around on the topslide and to reposition the topside itself as long as you're careful to pick up the same OD when you continue. I've found the results will be better than swapping ends.

I'm not surprised the bar was irregular as you say, but my experience has been that larger bars are oversized enough to allow for cleanup to nominal OD over a one foot length. Maybe I've just been lucky.

I'm sorry I didn't suggest checking the tailstock offset with something else before mounting the work between centers. The irregular OD of the bar probably made it impossible to distinguish the offset from the other variables.

To check the offset, mount a piece of bar between centers, and make as long as cut as you can without changing the position of the bit with respect to the carriage. Measure the OD at the tailstock end and at the end near the chuck.

If the tailstock end is larger, move the tailstock toward you one half of the difference. If it's smaller, move it away from you. Take another pass on the work, and repeat the measurements.

It's a good idea to check the offset with the tailstock ram extended the amount you'd normally be using it for turning between centers, i.e. not much.

Roger

Scishopguy
02-17-2009, 01:12 PM
If you are working with rough stock (extrusion, etc) and have ends that are not faced, be sure that you don't seat the stock against the face of the chuck while trying to true it with the indicator. I leave about an eigth of an inch between the face of the chuck and the stock so that I am working off the gripping surface of the jaws and not being thrown off by the rough face of the stock.

If you chuck an extrusion and it it out of round at the chuck, you can sometimes get it closer to true by loosening and rotating it a little to the right or left (your choice) and re tightening it. Extrusions are not usually even close to being true round as they come from the mill. Some materials are worse than others. Aluminum and plastics, like acrylic and PVC are the worst, in my experience.

Truing a long piece can easily be done if you are able to get the part to indicate true at the chuck. First, indicate it at the free end and center drill it. Repeat on the other end. Then indicate it at the chuck end and turn between chuck and center. Rotate end to end and finish that last little bit that was gripped in the chuck. The part should now be easy to chuck and should be pretty close to true in the chuck. (here is where you rotate and bump to get it dead on). Now, face the ends down as close to the center as you can without touching the center point. You can now bottom the piece in the chuck and it should be sure it is pretty much true. At this point you are probably going to start drilling it out and the little bit that didn't clean up on the end will not be an issue. At this point you can swap ends to rough out your hole, meeting in the middle and be sure that they will closely meet up (as drills tend to wander a little it will not be absolutely perfect but this is a roughing cut to ready the part for the boring operation).

(Just my opinion you can take or leave, claiming no expertise other than my own trial and error);)

hwingo
02-17-2009, 06:07 PM
Winchman & Scishopguy:

Thanks for hanging in there with me on this project. I am currently at work and not at my home shop. I will attemtp to take pictures of my work set-up so you can see why I was unable to turn the entire length. It's only 2:17 PM in Alaska and I don't get off work until 4:30 PM so it will be several more hours before I can submitt a picture.

Harold
(KD5DNA)

hwingo
02-18-2009, 12:41 AM
As previously stated, I failed to properly plan during setup. I tried to keep the quill on my tail stock as short as possible and when doing so, close proximity of the tail stock to the saddle prevented me from accessing the end of the work. At the head stock end, I had about 1/8" of travel before the saddle engaged the gear case on the head stock.

Having re-positioned the compound and extended the tail stock considerably, I now have barely enough clearance (~1/2" between saddle and tail stock and 1/8" between saddle and gear case to make a full pass without the need for switching ends. See red arrows in pictures.

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Winchman2.jpg


http://i234.photobucket.com/albums/ee38/hwingo_2007/Winchman1.jpg

Scishopguy
02-18-2009, 01:10 PM
Hmmmm.....I see the problem now. You need a friend with a longer lathe. I think that is the main reason some of us advise the neophyte machinists, looking for their first lathe, to get one bigger than they think they will need. It is just no fun to try to do a big job on a smaller machine and eventually, you will run into a job that requires it.

hwingo
02-18-2009, 01:43 PM
The lathe is a 12" X 36". I still had 2 feet of bed avaliable. Having longer centers would really help. A longer center at the head stock would allow more travel past the work and having a longer center at the tail stock would provide me with more space when working near the tail stock.

Harold