3jaw chuck alignment problem

[Anatol]

I have an alignment problem with my 1980s Frejoth 12x37 lathe (very like a Grizzly 4003, and various ENCO etc) and 6” D1-4 3jaw chucks. I know 3 jaw chucks are not that accurate but I think it should be better than what I’m seeing. D1-4 backing plate is running acceptably true - within 1 thou radial and axial. The back edge of chuck (where I can get a gauge) is also running within 2 thou of true.


A rod set in the jaws describes a cone. Close to the jaws, the rod is 10-15 thou out, but 4” down the rod the error increases to 30 thou or so. Tracing back along the rod into the chuck, this would suggest the minimum error on the rod - the point of the cone - would be back inside the chuck - if you could measure it.


Thinking is was a jaw issue, I got a new-to-me 6” 3 jaw d1-4 chuck, chinese, relatively new and in good condition. It shows almost the same error! I then tried slipping a shim inbetween backing plate and chuck. Oddly this did not change the error much.


I’m quite confused and would be grateful for any insight or advice.

 

[Wizard69]

The idea that the “new” chuck performs the same as the old suggest to me a spindle nose problem.

Your runout values could be good or terrible blue depending upon where the measurements where taken. You really want a high precision dial indicator because measuring to a thousands isn’t good enough. You would have to do a bit of trig to find out if the axial runout is enough to cause your issues.

Given that I’d mark your spindle nose so that the marks can be seen with the chucks mounted. After which I’d mount and test both chucks to see if the high point is consistent with both chucks.

Actually at first it might be a good idea to check for burrs or dings on the spindle nose. Also take the cam lock mechanisms apart and clean. It takes very little at the chuck nose to cause significantly can’t chuck issues.

 

[DJP]

Try test rods of different diameters to confirm that it's not a worn scroll problem. I have scrapped a few 3 jaw chucks once the scroll causes runout. There is a solution to bore out the jaws when clamped on a bearing ring at the back of the chuck but this only fixes the problem for that diameter.

A new chuck is my preferred solution.

 

[Lloyd-ss]

New guy here, but I might as well jump in and embarrass myself right away. Because I don't yet know you guys, my apologies if my suggestions are things you've already done or thought about or just too basic. But alignment problems are usually harder to diagnose than you think they should be. I had the same problem with my Grizzly 5" chuck and was able to improve it noticeably.

First off, I am assuming you haven't had a bad crash on the machine recently, I know that only happens to other people. Also, I guess you've removed and cleaned the jaws in the chuck.

The condition you are describing, 15 thou in 4" is pretty extreme. First, remove the chuck and check the squareness of the spindle nose as follows.

1, Lightly stone the mounting face of the spindle nose to identify and remove any burrs. No high spots should show up.
2, With a mag base on the cross slide, and dial test indicator tip on the face of the spindle nose, rotate the spindle and check the face for runout. Anything other than zero (or darn near zero) would be surprising, and bad. A machine problem, not the chuck.
3. With the indicator still mounted to the cross slide, adjust the location of the indicator tip so that you can traverse the the spindle mounting face from front to back, covering as much of the spindle face diameter as possible. Basically tracing a chord across the spindle face. Again, anything other than zero would be surprising and again mean a machine problem. Without moving the carriage or indicator, rotate the spindle at 60 degree intervals and traverse the cross slide front to back at each location. All readings should be near zero. Anything else is a machine problem.

If the spindle nose checks out ok, and I hope it does, next is the chuck.
4. Lightly stone the mounting face of the chuck to identify and remove any burrs. Load your chuck into the lathe. Load a known straight rod at least 1" in dia x 8" long into the chuck, with 5" sticking out. Set the mag base on the cross slide and the dial indicator tip at 12 o'clock on the rod at one inch away from the chuck jaws. Rotate the spindle to find the high point of the rod. Note the TIR and mark the 12 o'clock high point of the rod with a sharpie. Also mark the chuck, the nearest jaw, and a visible part of the spindle nose, all at 12 o'clock. With the indicator still at the 12 o'clock high point on the rod, move the carriage along the length of the rod. You said that showed a 10-15 thou rise on the indicator, correct? Rotate the spindle to verify that the high point at the end of the rod is aligned with the high point near the chuck. Mark the rod at 12 o'clock.

You should now have a series of lines marking the high point at 12 o'clock on the rod, chuck, jaws, and spindle. Also, at this time, number the individual chuck jaws and chuck slots as 1,2, and 3.

5. With the rod and spindle still in the 12 o'clock orientation, move the indicator and its base so that the indicator tip contacts the front of the rod, near the chuck, at 9 o'clock. Traverse the carriage along the length of the rod and hope to see zero movement. If you see more than zero, adjust the indicator tip so that it follows along the centerline of the rod, not too high, and not too low. If you are traversing the length along the CL of the rod, the curvature of the rod would only show a 2 tenths movement of the indicator. But if you are 50 thou above centerline, you'd see almost 2 thou movement. Kind of a false positive. The point of this part is to find out which way things are "bent", and get some baseline marks in place. So, everything should be marked, and "bent" upward toward 12 o'clock.

Up to this point, there should have been no surprises and everything should have gone as described. I hope, LOL.

6. OK, now to finding the real problem.
With everything back at 12 o'clock, re-set the indicator to touch the top of the rod at it's 12 o'clock high point near the chuck face. Rotate the spindle and set the indicator to read zero at 3 and 9 o'clock and high and low at 12 and 6.

7. Check the rod. Leaving the spindle at 12, barely unchuck the rod and rotate it 180 degrees to 6 oclock. Indicate your rod again at 12 oclock at both ends. The indicator readings should not have changed. If they changed, either the rod is bent or the chuck repeatability is really bad. But lets assume the readings stayed the same.

8. Leaving the rod chucked in the chuck, remove the chuck and reinstall it rotated 120 degrees. Now, with the indicator again at 12 oclock and the chuck and rod at 12, and the Spindle off by 120 degrees, recheck the dial indicator readings. If the indicator readings are the same as before, that means the runout is following the chuck and not the spindle. Move the chuck to the next set of holes to verify that the runout stays with the chuck.

So what happened? Did the runout follow the chuck or the spindle?
Move everything, including the chuck and spindle, back to the 12 o'clock position.

9. Now check the chuck jaws. With everything back at 12, verify that the indicator readings are the same as they were in step 6.
10. Remove the bar and the chuck jaws after making sure that everything is still marked. Reinstall the jaws indexed to the next set of slots, and rechuck the bar. Align all the marks at 12 oclock except that the chuck jaws will now be off 120 degrees. Set the indicator back up and check the top of the rod and see if the readings are the same as in step 6. My guess is that they will Not be the same. You'll probably find that the runout has kind of followed the jaws, but not exactly.
11. Now, rotate the spindle to get the high point of the bar again at 12 oclock. So, is the high point still in relation to the original jaw? If it followed the jaw, you are lucky, because it might just be a jaw problem.

12. You will probably find that the readings are best with the jaws installed in one particular position, and that the runout is tied to the location of the jaws. As previously suggested, try some different diameter bars to see if its a scroll problem, too. But if its mostly the jaws you can clamp a ring deep in the chuck and bore them out just enough to clean up. Make sure to permanently mark the number one jaw position. After boring the jaws, you'll have to hand finish the section of each jaw that clamped onto the ring.

I had to go thru this procedure with my 5" 3 jaw and I got the runout an repeatability from about 9 thou down to 2 thou. I would have liked better, but that is why we have 4 jaw chucks, right?

My apologies for the long winded post, but i hope it might help somebody.
Lloyd-ss

 

[Anatol]

thanks everyone and especially Lloyd for great advice.
I think I figured it out. No Lloyd, there was no crash, but maybe something dumber
Thinking my process through I realized I measured the straightness of the d1-4 backing plate with a gauge mounted on the end box. But I measured the bar in the chuck with a gauge on the saddle.

This immediately suggests the misalignment is between spindle and ways.
The lathe might be a bit old (40years?) but it hasn't had much use, ways are clean and I believe spindle bearings are good.

Then I remembered...the lathe is on a ply shed floor, and is a bit unsteady. But the shed is not mine, so I can't pour concrete or cut holes in the floor. So I bought some slabs of 1/4” steel plate and a couple of weeks ago I slid them under both ends of the lathe. But I had no helpers so I had to lift each end separately with a pry bar, and hold the bar down with my foot while I bent double to slide the plate under - quite athletic.
In doing this I think I ‘bent' the join between the ‘box’ and the ways. Makes sense? Its a sheetmetal base, not cast.
(one day I should get/make a more solid base for it.)

So now the question: is how do I find out and how do I fix it.
To calibrate, I’m guessing I need a long straight bar in the chuck, and two gauges at 90 deg on the saddle. Maybe one in a tool holder.
I guess I’ll figure hout how to align the ways with the spindle axis by adjusting mounting bolts, maybe shimming?

Thanks all, I really appreciate this supportive community.

 

[Lloyd-ss]

Wow, I can hear the grunting and cussing while you were muscling that around. How about first just checking the base to see if its level? Maybe a shim or 2 in the right place will get you back in business. Fingers crossed.

 

[MRA]

If the spindle is out with the bed, it'll bore tapered holes, so this might be a way to check? On a previous (ancient) machine with a flat-top English bed I could make such an adjustment, but with my current V-way bed machine the headstock is either right, or something is Very Wrong!

 

[Anatol]

How about first just checking the base to see if its level?.

yeah but,... the base is two sheetmetal cabinets, I'm not persuaded they're too rigid, I could have bent them a bit or put a tiny bend in the place where the headstock meets the ways. As far as I an see, the way to test is with a very straight bar I note chuck, and a couple of gauges.I don't have such a bar... I guess a foot of 1" drill rod would give me some indication.

I lifted the far end of the headstock, so if theres a bend, its a 'valley' at the meeting of the headstock and ways. So I guess I could jack up the join with a screw jack?

 

[Anatol]

If the spindle is out with the bed, it'll bore tapered holes,

I don't think I need to do that, I already know its not straight by putting a gauge on a straight bar. Or am I m missing something?

 

[Anatol]

I'm not near the lathe right now but I had look at a diagram. Clearly the bed/ways are well attached to the headstock, I'll need to do some dismantling (taking off cover panels) to find what screws to adjust and where to shim. Good practice I guess. Always learning experience

 

[goldstar31]

At the risk of further castigation, might I querulously ask whether the lathe bed is 'in twist' or not?

Over the years, I have written on this matter and seemingly no no avail.

Again, risking further censure, this sticking a rod in a chuck- and possibly cutting two test rings is not the answer to someone with a lathe -- which hasn't just come out of the factory.

True, I have a test bar with a No 2 Morse taper shank and I have a thing to cut ( hopefully) two identical rings. However, my lathes are 'new' or recently returned from being slideways ground. ALL of them have been subject to having a precision spirit level put along the ways and across the shears- at least twice and the necessary adjustments made.

Be assured- there is nothing revolutionary or even new. It is and always was standard practice.

My Sieg4 sits on a steel drip tray but that lives on the top of a 1" topped computer desk whereas my Myford ML7B lives on a steel sheet drip tray on a steel lathe stand which is bolted down.
That's not the end of things on a Myford because a 7 is out of balance because the motor- well, mine is attempting to tilt everything backwards. Once the motor was installed, I re-checked everything.

Somewhere in what I laughingly call my library, there is a similar sort of note by none other that Tom Walshaw writing as Tubal Cain of his workshop in the English Lake District- where the ground under his lathes- isMOVING!

I hope that these comments might point the way to solving your own problem.

Norman

 

[Lloyd-ss]

This is very interesting and enlightening. It is funny how someone else's comment or situation can make one sit back and evaluate their own situation. I am new to the forum and trying to absorb and learn what I can from the wealth of knowledge that is freely offered, hopefully without being an annoying pain to people.

I have a Grizzly benchtop lathe similar to, but a bit smaller, to the lathe that Anatol is diagnosing right now. It got me to pondering how my lathe is mounted, and then Norman's comments made me think even more about it. My lathe is 11 years old and has been setting in the same place for 4 years now. It is mounted on one of those old WW2 military office desks, reinforced, topped with a large piece of 1-3/4" thick solid core door, with the legs removed and now sitting on a solid box base of 2x6's. I very carefully leveled the top with shims placed under the 2x6 base when I did the initial installation. But the lathe itself is really just setting on its two 4"x6" rough finished cast iron pads about 36" apart, with a single 1/2" bolt thru the middle of each one. As Norman asked, is the bed twisted? Darn Norman, I am just having my first cup of coffee and now have a task to do because I don't know the answer to the question.

So I had to check it, and honestly, it only took about 30 minutes. I don't have a precision spirit level, but I do have a 4 foot carpenters level that has tight vials and is repeatable. I removed the rear chip guard from the machine so that the 4' level could lay across the ways. The chip guard only had 3 screws. I wanted to lay the level across the ways near the headstock, and then at the tailstock end of the ways. I used a pair of ground tool blanks, one on the flat of each way, to get the level above the V's. The tops of the V's aren't ground like the flats are. I wiped the ways and tool blanks clean and also stoned the bottom of the carpenters level in the middle 6" so that it would set repeatably on the tool blanks. I laid the level across the tool blanks at the tail stock end first, noting exactly how the blanks were placed and how the level was placed on top of them. The bubble looked to be centered perfectly between the lines, but with progressive eye glass lenses and old eyes it was hard to tell. I ended up putting a .010 feeler gauge under the level, on top of the rear tool blank to shift the bubble ever so slightly to the edge of a line. With an eye loupe I could see exactly how the bubble touched the line in the level. So I had my reference point. Then, again noting exactly how everything was placed, I moved the entire set-up to the headstock end of the lathe. And guess what? Instead of a .010" feeler gauge, I had to use a .012" feeler gauge to get the bubble in the same alignment. Hmmmm. The tool blanks supporting the level are only 4" apart, so that is .0005" of twist per inch front to back, but it is spread out over the 30" spacing that was between my 2 measurement points. Does it matter? I don't know, but zero would certainly be better. And maybe I could "push" on the headstock with my hand and get it to move even more than that. IDK. But shimming it to get the two ends level with each other ought to easy enough to do.

Norman, thanks for your thoughts, and Anatol, I apologize for my long windiness in your thread, but hope there is something useful in there.
Lloyd

 

[mu38&Bg#]

The question is are you measuring runout or aligning the bed to the spindle? They are not the same thing.

 

[goldstar31]

The question is are you measuring runout or aligning the bed to the spindle? They are not the same thing.

Happily, first things first. If you don't get the bed sorted out, the alignment of the spindle becomes nigh impossible.

If the bed is twisted at all, one must assume that Friend Pi will multiply the error when a longitudinal cut is taken. I need not utter the word 'Ouch!' Surprisingly the twisted lathe bed changes from a a rectangle to a part of a cylinder. This is why people like Georg Schlesinger(Sp?) writes and writes and the whole thing is accepted by people who are charged with getting things right. If you want bed time reading, get stuck into Edward Connolly's Machine Tool Reconditioning- which is available on the 'net. A wet towel, a crate of aspirin and match sticks to prop eyes, but brother, that is the dog's doo daa's.

And somewhere, Dieselpilot, you will find that most spindles have a toe in-- and invokes the wrath of an instructor when resting elbows on convenient tailstocks.

Incidentally, I'm not an engineer but have family share certificates for failed machine tool manufacturers.

Repeating myself---- OUCH!

Norman

 

[mu38&Bg#]

Norman, let's go straight to the point. How is spindle/chuck/tool/work runout related to bed leveling or spindle alignment? It isn't. So what did the OP measure/observe? You can level the bed and align the spindle all you want, but it won't fix runout.

 

[goldstar31]

If you are talking about the runout caused by a worn chuck, I agree but if you are talking about machining a a piece of work which should emerge truly parallel from a twisted bed, I have respectfully disagree.

To attempt to correct a worn chuck by grinding the jaws when the scroll is worn only produces an accurate position in one diameter. One needs something like a curvilinear chuck to cut a scroll which will allow (say) three jaws to open and close throughout the chucks range- accurately. Bazmak and I were happily prattling about soft jaws some time back.

I think that we fondly follow Euclid and imagine that everything follows straight and parallel lines but a machine tool improperly adjusted or worn- or Heaven forbid-- both, certainly doesn't follow any of the Euclidean postulations.

I'm writing as someone who has scraped several lathes over the years. In fact, in the vdim and distant past I described in Postbag in 'Model Engineer' how I reconditioned a friend's Myford ML7 which earlier was only fit to turn bananas. It ended up with a reasonable accuracy of 'half a thous' runout at 6 inches on a homemade test bar. I had to scrape a reference from a reference which came from 'Blancharding' his worn lathe bed.

I hope that this throws a bit of light onto what is clearly a very misunderstood procedure.

Regards

Norman

 

[mu38&Bg#]

I am not "talking" about anything. I asked for clarification of what was measured to give the proper answer.

All that typing and we still don't know what the OP actually did! Nothing you say is wrong, but I don't think it's the answer the OP needs, yet.

A: Did he use a dial indicator to check spindle/chuck/work runout?
B: Did he turn a piece of stock and measure diameter which showed taper?

The OP's first post in this thread implies he did A, while his post #5 indicates he thinks B is the problem.

This should bring up red flags if you understand how to inspect a lathe. As we know A and B are unrelated! I'm not sure Anatol understands this. This lathe has V ways and the chances of the headstock moving or being worn are extremely small.

 

[goldstar31]

I am not "talking" about anything. I asked for clarification of what was measured to give the proper answer.

All that typing and we still don't know what the OP actually did! Nothing you say is wrong, but I don't think it's the answer the OP needs, yet.

A: Did he use a dial indicator to check spindle/chuck/work runout?
B: Did he turn a piece of stock and measure diameter which showed taper?

The OP's first post in this thread implies he did A, while his post #5 indicates he thinks B is the problem.

This should bring up red flags if you understand how to inspect a lathe. As we know A and B are unrelated! I'm not sure Anatol understands this. This lathe has V ways and the chances of the headstock moving or being worn are extremely small.

Obviously, I haven't a clue as to how the poster conducted his 'tests'. Probably the proper test would be to rig a taut wire from the spindle to the tailstock 'poppet' and use a dial gauge on the saddle to record the deviations along the bed. Seemingly, at the end of the day, the chuck- worn or otherwise seems to be somewhat irrelevant.

I suppose that. some 'dollar a dozen' lazer could be rigged up to to find out what really is happening.
I recall 'Exactus' writing years ago in Model Engineer doing something similar which was entitled "Microscope on the Lathe'

I think that the original article still appears on the 'net.
Of course, you are pushing an old man who to rack his almost 89 year old brain to find a solution which really should be subservient to others who haven't macular degeneration like me. The necessary information is, I
believe, still available as I have suggested.

In all sincerity I cannot condense a tome of more than 500 pages into a ' a few lines' of difficult for me to read script.
Maybe someone else should have a go.

Regards
Norman

 

[goldstar31]

Thanks Lloyd ss. I didn't know that anyone was actually 'reading between the lines' or V ways.

Gosh

Norm

 

[Anatol]

Thankyou Norman, Lloyd, dieselpilot for helpful advice. I'm afraid I've spent my available time tonight reading (some of) Edward Conolly's book on scraping (recommended by Norman). I thought it was only about scraping, but its a goldmine of machininst's knowhow-thankyou! So I only had time to gloss the thread.

I will return as soon as I have time, but meantime, let me summarise:
A dial indicator (1 thou divisions) mounted on the headstock plate behind the chuck was used to check the chucks, radially and axially. The 'new' chuck was better than 2thou, the old chuck about 3 thou.
A rod locked in the jaws - sequentially of both chucks - was tested with the dial indicator in a mag base on the saddle - this showed the rod describing a cone. I believe this is called axial runout. The point of the cone originating about at the plane of the back of the chuck.
I understand that the 'datum' is different for the two readings.
I am having trouble visualizing what kind of misalignment can result in the rod in the chuck describing a cone, with respect to the plane of the ways.

I have a precision level 0005/ft, I bought it on eBay and it was not packed well . I checked the ways with this in three places (middle and at each end) rotating it 180 deg in each test location to (presumably) cancel error. The ways seem to have no (minimal) twist. BUT my methods may be sloppy.

I will try the 'taught wire' test, maybe that will help me understand the problem better.
It is also obvious I need to re-level the entire machine, and I know this can only be temporary due to the nature of the floor.

I am a beginner and am keen to learn. The exactitude of the machinist's art is something mere mortals cannot comprehend, and I must admit being a bit awe-struck by the precision that can be achieved by skill, precise method and concentration, using simple, but accurate, tools. I am also thoughtfully impressed by the fact that diagnosing such seemingly simple geometrical problems in the metal objects right in front of me can be as intellectually challenging as anything I've ever done.
thanks again.