[HuFlungDung]

To take a slightly different tack on this chucking problem, it seems extremely difficult to rechuck anything in a 4 jaw and to indicate it back to true running. I think the condition of the chuck jaws and slideways has more to do with this than actual bearing faults. As tightening pressure increases, the tiny bit of wear and slack in the jaw slideways, and possible worn taper effect on the jaw grips becomes significant. The increased tightening pressure may at some point not move the part predictably, instead causing a degree of tilt to occur which spoils the setup accuracy attained thus far.

A tilted circle is an ellipse and will not indicate round.

First of all, it is necessary to indicate the part in two spots, either a face and an annular ring, or two annular rings spaced some distance apart. You achieved much the same result by switching to a chuck and steady rest.

To use the 4 jaw alone will require the use of a hammer and an indicator. The only way to align the face of the part (if available) is with the hammer, to tilt the part. If two annular rings are used, then adjust the chuck to center the closest annular ring, and tap the part with the hammer to center the outermost ring.

It is necessary to keep going back and forth as an adjustment to either position affects the other one. But you can keep splitting the difference until you get down as close as you have the patience for. IF you find this is impossible to do, then your chuck is no good (assuming your part is straight) and needs to be reground. You may find that the 'natural position' of the chucked part is a few thou off 6" out, but that you can persuade it into position with a hammer. For precision work, this is still not the best condition to start out with. Rework your chuck.

Collet chucks may also suffer this misalignment phenomena a wee bit. 5C collets are bad for this, because the easy fit at the back end of the collet makes the outer end of a long piece float off center. You can tilt a part chucked in a collet with your hammer as well. If you cannot get zero runout a few inches from the collet, then suspect that your collet is no good. Get some real Hardinge collets.

Chucking a part between chuck and tailcenter is also prone to 'getting you' when doing precision work. The 4 jaw may have a mind of its own, and inexperienced users may think that plugging a tailcenter into the end of the part negates the effect of the part being misaligned with the axis of the lathe. Not so, the part will flex the tailcenter, and machining in this condition will create an offsize diameter with a bit of taper thrown in for bad effect.

Turning between chuck and tailcenter is best accomplished by chucking on a very narrow band on the end of the piece. Then, this acts as a crude universal joint, and the tailcenter may then have enough influence to actually align the part with the rotational axis of the lathe, and it will cut straight and repeatably.

[ozzie34231]

Suprisingly this cheap chuck was pretty good at holding the piece parallel to the ways. The differance was nearly unnoticable over a 5" distance.
After getting close but still with fairly loose jaws I put the far end in the tailstock center, snugged the piece up more and then pulled the center away. As I kept working it stayed aligned. At the end I was .0005 TIR #4 jaw high at both places. I thought one little tightening would do the trick.
What you say about the unpredictability was why I quit the first day and started this thread. Sometimes a high at 4 would move to 3 or 1 but always at least .0005".

Thanks,
Jerry

[HuFlungDung]

Did you actually mike the part across the corresponding diameters to see if if was really round to begin with? How or what did you make the part on? Could you have suffered from misalignment when doing the initial machining, as I described above?

Drilling a center hole in the end of a piece of rough stock, and then moving the part for machining is enough to create some headaches when you are trying to be really careful. Ideally, drill the center hole, and machine it without moving it, or, I suppose turn between centers (which I never do because lathe dogs scare me ) or thirdly, chuck a wee bit of the end and hope the tailcenter will align up.

[HuFlungDung]

~snip~ I then put the hanging end in my steady rest and got virtually no movement on the dial Gage.

Jerry

That is correct I've clued in a few new apprentices who have tried to 'dail in' stuff in a steady rest. It's always dials in perfect, no matter whether it is lined up or not with the chuck

Since the steady is using the questionable surface itself for guidance, it can introduce false confidence in the setup and previous workmanship on the part.

[sizmo]

Finished a Quorn a few months ago. And it being about the 100 th spindle i have built over the years. I do them different than any one else and they all have worked fine . Do the bore work first .Then turn the rest of the spindle off the bore.by making a male piece to match the bore and never unchuck it slip spindle on and finish as between centers.

[ozzie34231]

I turned the exterior between centers, the dog leg wrapped in tape to not distort.
If there were an out of round condition the high spot would not have moved during adjustment, ,,,,I think.

Sizmo,
I thought of that, and in fact that's how I'm going to make a much smaller spindle for a toolpost grinder that I'm building from a toolpost grinder. :-) Soon as I can dope out the taper. I have the male taper so it shouldn't be too tough.

Jerry

[handlewanker]

Hi all, there is another factor with the 4 jaw/3 jaw and steady combination.
Most turners will know about this, as it's common logic and is taught first hand as an apprentice or trade school person, but for those who use a lathe and are self taught then it is vital to know.
When a longish shaft is set up to be held in the 4 jaw and supported in the steady for end working, the shaft MUST be rotating true BEFORE the steady is applied.
Failure to do this will result in the shaft being off centre, as the steady has no indicating capability to show that the job is actually flexing, if it is slender, or about to "walk" out of the chuck if it is a bit more substantial.
This phenomena happened to a work mate I worked alongside and who should have known better.
It happened in 1973, and the job was a steel shaft weighing about a ton, approx 10 " in diam and 8 foot long.
The shaft was set up in the four jaw while held in the crane and the steady brought up to support the other end.
Initially the chuck jaws were set by measuring with a tape to get approximate centrality, then the half finished shaft was gripped in the 4 jaw with copper protectors, and supported on the open steady.
After setting the chuck end true with dial indicator the steady was adjusted to support the shaft.
The steady had been set in the beginning to have the legs approximately equal length out for the diam of the shaft, and then when the steady was mounted to the bed of the lathe it held the shaft while the ropes were removed.
Going like clockwork, you'd say. How wrong you can be.
There is NO method to get the shaft running central while held in the steady, unless that is you cunningly move the tailstock up and use the centre to gently touch the shaft end and so indicate the centre point which will start off as a scribed circle and so get smaller as the steady is adjusted to it.
Great, I do this all the time you'll say, so do I on my own lathe, but on someone else's lathe you rely on the fact that the tailstock is centralised to the bed and has not been set over for any reason.
And hereby lies the lesson. Never assume that the obvious is reality.
In this case, a job had been turned two weeks previously and necessitated having the tailstock set-over about 2". Since that date and to this particular moment in time it had stayed that way.
The aforementioned shaft was now "central" to the tailstock but 2" off centre to the lathe, and it walked almost out of the chuck due to the twisting and flexing motion like a universal joint.
It was only spotted when one of the 4" square 1" thick copper protectors fell onto the floorboards and woke the dead.
A very near miss, and a jolt to the nervous system of the guy who was seated up on the tool post while the machine was turning.
This is a example of unforseen circumstances that go to make up the industry.
Getting back to normal turning requirements, with say for argument sake a smallish lathe about 6" centre height, or as the USA mob term it "a 12" swing", then with any job requiring 4 jaw and steady combination work, it is really necessary to hold the previously machined section in the 4 jaw, by narrow copper strips, probably about 1/2" wide for an 8" -10" diam chuck.
This set-up will allow the job to be gripped, but not influence the set-up by being too firm as to making the shaft flex.
It is also a false sense of security to allow the job to remain in the steady for too long due to the uneven wear on the steady seats, which require constant adjustment as the job proceeds.
Whenever possible cut a centre in the shaft end and do all the roughing wth the centre in and a packing piece in the 4 jaw to stop the shaft moving bacwards and off of the centre.
For final finishing the steady can be used to get the concentricity required.
All these thing are learned in basic training, and never forgotten.
Incidently when getting that final "thou" off the clock it is better to slacken and retighten the opposite jaw rather than trying to crush the living daylights out of the job.
Ian.

[ozzie34231]

Hi Handle,
Well I'm not school trained in machine work but I was lucky that most of it occurred to me,(except the last part of course). When this part was running .0005TIR, I pulled the tailstock up and it pushed about .003" on the close dial. I adjusted that out then, and then slowly and carefully brought in the steady rest jaws. I was aware that the rest still might have been a thou off, but at this point the other end was in a 5-c so I did the boring that way.
If it doesn't run real well, I'll make it again with all my newfound training.

Hi Sizmo,
I was trying to think about why I rejected your way and I think I was wondering how I could be sure the bore would be in line with the tail center drill hole. Do you drill the center after you mount the piece on the mandrel you've made.
My shaft is fairly long so what would keep the center drill from wandering?
If you drill before you bore, how do you know you're in perfect alignment?

Jerry

[handlewanker]

Hi all, just looking at the method Sizmo outlined. I state here and now that this method, no matter how juicy is not ACCURATE, but cannot be proved to be so on the finished job.
Here is a hypothetical spindle, 9" long and 1" diam. Using the Sizmo method the shaft is held How?
Assuming it is held in the 3 jaw for roughing out and then boring to finish, the next operation will be to turn it around and having made a male taper in the three jaw, mount it on the taper and support the other end on what? A centre? OK, when the centre was cut it would have been made accurate to the OD of the end, fine, but when the taper was cut the centred end was halfway up the pipe and unless the three jaw was gripping the shaft dead true (unbelievable) then it is running out by who knows how much, just can't be measured, and so the taper is cut, and the shaft is mounted on the new male taper, used as a centre, and the other end running on a revolving centre, or if you are a masochist from way back in the old school days, a dead centre dosed with copious quantities of graphite grease etc.
If you now apply a dial indicator to the tailstock end, the shaft is running true, because it was centred so, and if you dial up the chuck end it is also running true. Go for broke?
Not on your life, if the accent is on accuracy, then the taper is only true at it's end and the farthest point of the tapered bore will be out.
It can't be measured, but it is OUT, due to the fact that it was cut on a shaft that was running out on it's farthest end. The amount that it is out will not be detected by most means, but this does not give it a pedigree of accuracy that you get when the job is confirmed accurate.
If you had used a 4 jaw chuck in place of the three jaw then you are still relying on the end of the shaft running true when the tapered bore was machined and have no way of checking the allignment axially.
To test this theory, grip a 1" diam X 9" long bright mild steel bar, or preferably a 1" diam ground steel bar 2" deep into the chuck of your choice, and test the run-out at the chuck end and then at the other end as it rotates in the air.
It will have a run out depending on how much the chuck had been abused in it's working life.
They all do, due to BELLMOUTHING caused by overtightening the jaws to get a job to move that last 'thou, in the case of a 4 jaw, and overtightening to hold a job when less pressure would do.
The way to go is with the four jaw and steady method, and no other way.
Ian.

[ozzie34231]

Hi Ian,
I think it will work on a stout relatively short spindle, because you can drill the tail center after mounting the workpiece on the male taper. Also the taper needs to be self holding like a morse.
I think it will work on the little toolpost grinder shaft I'm going to do. Its smallest diameter is 17mm and it's only about 6" long. The male taper will penetrate the shaft by about 1 1/2" so it should be stiff enough to center drill.

Jerry

[Geof]

Hi Ian,
I think it will work on a stout relatively short spindle, because you can drill the tail center after mounting the workpiece on the male taper. Also the taper needs to be self holding like a morse.
I think it will work on the little toolpost grinder shaft I'm going to do. Its smallest diameter is 17mm and it's only about 6" long. The male taper will penetrate the shaft by about 1 1/2" so it should be stiff enough to center drill. Jerry

The wander you get drilling the center hole could be enough to throw it out. Taking a finish cut on the center with a little single point tool would probably give you better accuracy.

[handlewanker]

Hi ozzie, I'm a die hard from the old school, so I won't offend you by being dogmatic. If you've got a digi cam, let's see some pics of the project.
As a matter of interest, that method that you mentioned about grinding the spiral sides of end mills and slot drills by the CNC method has a big advantage in that it cuts out the slender finger support that "generates" the spiral.
One of the members of a model club I used to go to in the mid 90's was building a small cutter grinder with this method in mind.
The helix angle was read off by a computer sensor along the cutter axis and this allowed a whisker to be ground off of the OD instead of chopping the end off of the cutter.
In addition it will also allow you to make spiral reamers and do thread grinding on a small scale etc etc.
Ian.

[ozzie34231]

Hi Ian,
I'm not far enough along that pics would help much.
I'm drawing in Inventor, but most of the drawing is of the wheelhead side of the job.
My idea is to use some off the shelf stuff as components of the project
An 18" cross slide table mounted on end and turned backwards will hold the quill and motor mounted on its base.
Another 18" cross slide table will serve as the work holding base. A 5-C spin index will hold the actual work piece. The index will be mounted to the table with all the mobility of a Quorn, ( rotation in 3 axis, slide on one axis to adjust the center of rotation).
If I CNC the shaft of the spin index and the long axis of the table it's mounted on, I'll acomplish what you've suggested.
If I CNC the other axis of that same table, the ceiling of what I could sharpen or create would go through the roof.
I'll see if I know how to grab a picture from Inventor and post the part I've drawn.

Jerry

[ozzie34231]

Well, Let's see if this works.

[handlewanker]

Hi ozzie, like they say, one picture is worth a thousand words.
I draw 2D in cadkey, nothing fantastic, but it does help to get the proportions right.
Now I've seen the 3D bit I'm just going to have to have a go at 3D to visualise the projects, especially the different colours for various parts of the machine.
I hope you're going to counterbalance the work head.
I've got a Macson surface grinder that the previous owner had some dramas with.
The counterbalance system was missing and he did not realise what it was used for.
On winding the head down it would stick and then fall a bit, making a mess of the job and a few stones as well.
That was when the learning curve came to an abrupt halt and he got rid of it.
After I stripped the machine down the counterbalance system was found inside at the bottom of the column casting. It consisted of 5 springs on a frame and wired to a pulley at the top of the column.
I'm going to replace the springs with an iron counterweight, as this will give constant positive up pressure to the head when winding down and back up.
Ian.

[handlewanker]

Hi ozzie, while I remember it, to overcome the combined weight of the spindle and drive motor, have you considered having two slides for the Z axis?
Mounted on the same column but on opposite sides, one slide would carry the motor and the other slide would carry the spindle.
Both slides would be driven by two acme screws or ball screws and would be geared together at the top of the column to a stepping motor.
This would enable the belt tension to remain constant as the two slides moved up and down the column.
To adjust the belt tension, the screw driving the motor would be disengaged and turned a few turns so moving the motor away from the spindle, after which it would be re-engaged again.
This method would also lend itself to a vertical milling machine where the combined weight of a spindle, drive motor and gearbox is carried on the same slide.
Using two seperate slides would mean that a milling head could move up and down without the need to have a sliding quill to give it sensitivity.
Ian.

[ozzie34231]

Hi Ian,
I've been using various drawing programs for over 20 years starting with one in an Amiga computer in about 1984 or 5. Many times I had the feeling that I could almost do it better with paper, pencil and eraser.
But this "Inventor" absolutely blows my mind! It works the way you think. You draw lines or shapes and then you can put dimensions to them and it adapts. You draw one part and then you begin an assembly adapting the new parts to what you have, and if something you did earlier doesn't work, you change it in the most simple manner and the assembly adapts. If I lost what you see above, I could recreate it in about a half hour. I love it.

Now as to the counter balance. I understand your point, but in this case it would involve a tremendous amount of additional work and I'm not sure it's needed. The vertical slide will be very solidly mounted, (unlike a Quorn), and is itself a sturdy hunk of iron. I don't anticipate frequent movements of that axis and with the dovetails I can lock it in place if needed.
If you look at the drawing there is a hole through the two green plates. This will be the location of a large pivot pin so I will be able to tilt the grinding wheel within about 15 degrees each way. This may turn out to be a redundant capability, but for now I'll leave it in the design. I still have to work out the system for securing the plates together. That system will require extensive modification of what you see drawn so far.
perhaps two large bolts in curved slots would work. For a start I'll just bolt the two together and see how the whole thing works and then go to improvements.
I've started drawings of the workpiece table and holder. If you like I'll post them when I get further along.
Regards,
Jerry

The spindle is bored, halfway. Now I'm waiting for a new chuck, to flip it and do the drilling from the other end.

[handlewanker]

Hi Ozzie, I remember the Amiga well, my daughter still has one, but only because she's got games on 5 1/4" floppies.
Most of my ideas are sketched up using a Wacom drawing tablet in Photoshop, to get an idea of a layout, (beats backs of envelopes), and then formalised using Cadkey to get a working scale drawing with dimensions.
The counter balancing issue will only become a problem if you want to do any serious surface grinding, and this is where you just must have negative gravity compensation. Tight slides to overcome weight don't work, that is if you're trying to get tenths off a job.
For the bit of surface grinding that crops up from time to time, I reckon the method you propose will work OK. However I like to see the "cut" go on and so I'd back it up with a clock tied to the slide to make sure the slide moved the amount I wanted it to.
On the other side of the coin, if you were to contemplate CNC for the Z axis,(hardly likely) then weight compensation would have to be an important consideration.
I'll be watching your progress with great interest, as I've also got a cutter grinder project in the between stages, and only need a bit of spare time to get stuck into it.
I aquired an X Y slide assy from a very basic Clarkson cutter grinder from way back, and the head assy from some other machine also from way back.
The grand plan is to be able to do cutter grinding and some cylindrical grinding, external and internal, so that all bases are covered.
Ian.