Rollie's Dad's Method Help?

[beckley23]

On page 18, Sep/Oct 2004, "Reconditioning a Lathe-Revisited", issue of HSM there is a lathe test card. For the most part the tests are performed in the order shown. The logic will be obvious. Test #22 is "Lathe must turn cylidrical with work mounted in the chuck"(I'm assuming this is "the two collars test"). The tolerances for; Toolroom lathes is .0008", Engine lathes ; 12-18" sizes .0015", 20-36" sizes .002". The bar is 12" out of the chuck and 4" D.
The same test/check is in every SB HTRAL book I've seen, it's in Connelly's "Machine Tool Reconditioning"(the whole test card is spread through out the lathe section).

The 4" D bar is a bit large for small lathes, IIRC, I used a 2" D for the 12" CK in the article, and a 2-1/2" D bar for the Series 60 in "Another New Toy" in the Monarch forum of PM.
Harry

[sasquatch]

I'd just "BIN" the sucker, go buy a better one!!

[Forrest Addy]

Just to clarify, the version of the two collar method I prefer is one where the two collars are machned separately if need be to within 0.0005" of the same size. The object here is to obtain two precisely sized reference diameters widely separated that can be scanned with a dial indicator mounted on the carriage. It's a means of quantifying the parallelism in the horizontal and vertical planes of the lathe spindle in respect to the carriage motion.

This way any number of readings can be taken as leveling and alignment progresses. If care is employed to not disturb the chuck or the two collar reference piece, the headstock can even be dismounted and adjustments made.

If you rely on turning tests alone eventually you will run out of material on the collar.

Success and consistancy of course depends on the condition of the lathe. If the saddle's fit to the bedways and the bedway's linearity is sufficiently degraded it may be impossible to secure consistant results. Then the decision has to be made to live with machine as-is taking time for every feature cut to sneak up on sizes by many cuts and hand finishing to size and finish/. Or to re-condition it, sell it down the river, or part it out/scrap it.

In answer to the other question about my using test bars. Hell yes, if one is available and it's straight. A good test bar makes the work so much simpler. However a good test bar costs $300 to $800 depending on size and quality. When the need comes the budget is scant and the lead time is long.

A test bar is a manufacturer's, re-conditioner's, and installer's tool. It seldom pays for a small shop to own one. A test bar is used once when the machine is first erected and then it sits on a shelf until you need it years later when the machine is surveyed for refurbish/replace. A test bar in its years on the shelf may become battered, rusty, even damaged; possibly modified into shop tooling, possibly lost. If a bar is not available and determinations have to be made, we have to resort to the expedients we are now discussing by their initials.

[J Tiers]

Just to clarify, the version of the two collar method I prefer is one where the two collars are machned separately if need be to within 0.0005" of the same size. The object here is to obtain two precisely sized reference diameters widely separated that can be scanned with a dial indicator mounted on the carriage. It's a means of quantifying the parallelism in the horizontal and vertical planes of the lathe spindle in respect to the carriage motion.

Ah, perhaps THIS is the issue that makes people consider it so much MORE fussy and demanding.....

I prefer the "take a cut and measure" method. You will run out of material, but chunks of pipe are not hard to find. presumably you will always have a mic around (or if not, why is this matter even an issue?).

On the theory of "use once in a very great while", I simply make another test bar when needed.... A piece of pipe and a few minutes cutting the valley between collars takes care of another few years, and it is no issue sitting it on the shelf after use..... costs very little, works fine, tests the machine in actual use.

You CAN make a test bar with great effort, but you will still have the issue of re-seating it in whatever the holder is..... chuck, taper, etc. And then you have errors.

if you make your own at time of use, and never remove it until done, you KNOW it is consistent. No re-seating required, one less cause of errors.

[Forrest Addy]

Ah, perhaps THIS is the issue that makes people consider it so much MORE fussy and demanding.....

I prefer the "take a cut and measure" method. You will run out of material, but chunks of pipe are not hard to find. presumably you will always have a mic around (or if not, why is this matter even an issue?).

On the theory of "use once in a very great while", I simply make another test bar when needed.... A piece of pipe and a few minutes cutting the valley between collars takes care of another few years, and it is no issue sitting it on the shelf after use..... costs very little, works fine, tests the machine in actual use.

You CAN make a test bar with great effort, but you will still have the issue of re-seating it in whatever the holder is..... chuck, taper, etc. And then you have errors.

if you make your own at time of use, and never remove it until done, you KNOW it is consistent. No re-seating required, one less cause of errors.

Which is why I default to the two collar method for one test of lathe condition. Yes there are a few others.

[GadgetBuilder]

My view is all three headstock/bed alignment methods are in essence the same: if you have a precision test bar then you use it. If you don't have a precision test bar, you simulate it. With TCT you turn two accurate test areas on a bar and use them to simulate the precision test bar. With RDM you remove the error sources using arithmetic thus simulating a precision test bar. However it's done, the same information must be extracted from the test used. The goal remains: measure the deviation between spindle axis and bed ways.

I march to the beat of a different drummer in many areas and so it is with RDM. I consider John Wasser's paper on RDM to be a concept paper rather than a test plan ready for execution. The paper identifies error sources that make chucking a generic test bar differ from measuring a precision test bar fitted in the headstock taper. And he indicates how these errors could be compensated for mathematically. Finally, he describes how the results might be used to improve the situation.

In reducing the concept to practice, one need not (in my view should not) simply follow what he wrote. I believe the reason the error sources are identified is so the user can figure a way to minimize them. For example, providing a method to allow using a rod whose diameter isn't constant and removing the difference mathematically would be plain silly - I think it is included so people understand that rod diameter is critical to the measurement. Using an accurately ground rod with a major bend in it would be silly too. But, if the rod used has a slight bend the calculation should prevent it from affecting the result, where his logic on this seems reasonable.

The test bar will have some runout from chucking which is unavoidable. Runout at the far end can be minimized easily by snugging the chuck in increments, measuring the high point and pushing it down with your thumb, tightening more, etc. It's easy to get TIR within a thou at the far end. This makes it more closely simulate the perfect test bar we wish we had, making the mathematical corrections needed smaller. Then, set the indicator up for horizontal or vertical measurement and set indicator zero so the reading for runout at the chuck end goes equally above and below zero, making John's Near End Average = 0 so it can be ignored in the calculation. Now, the RDM calculation is reduced to adding the high and low readings at the far end together and dividing by 2. (This result is analogous to the TCT result except with TCT the result reads directly off the indicator since runout has been removed by machining.)

A detail John's paper ignored is test bar sag. All test bars sag, even precision test bars. A larger diameter test bar sags less. In all of the methods sag should be accounted for. Measuring the actual sag isn't easy so generally it is calculated and then used to adjust the vertical result.

John Wasser's paper suggests shimming the feet of the lathe to correct bed twist. He didn't say to check your common sense or experience at the door. It is reasonable to use whaterver means are available to ensure the bed isn't twisted before using any spindle/bed alignment method. Nor does his paper consider the effect of bed wear on the measurement so common sense and experience are needed there too.

Does RDM provide perfect results? Certainly not - although it looks like you're taking only two measurements per axis, setting indicator zero at the chuck end is really 2 more readings that enter into the calculation invisibly. So now there are 4 readings, each with a little error and if the errors don't cancel then it would be easy to be off half a thou. The ground test bar could have a diameter difference between the measurement points of a tenth since I can't measure better than that. The calculated sag in the test bar gets added in too and it's a calculated value which could be affected by the type of steel in the test bar. And so it goes -there is some noise in the result. It's random so sometimes it cancels and sometimes it adds. The question is, is the error in RDM greater than in other methods. And does it matter in a home shop - that is, there are some real world limitations imposed by Mother Nature when you try to use the results to adjust a lathe.

Straw man criticisms of RDM, things like twisting the bed into a pretzel, are constructed by taking Wasser's paper literally. Arguments like this suggest to me that people haven't considered the possibility that John Wasser's RDM is a concept paper with details left to the student.

As a student of RDM I find this thread very sad. The OP asked a question about RDM and was told it is a waste of time and that no competent craftsman uses RDM. Then things evolved to people apologizing for even mentioning RDM and on to people who fail to denigrate RDM feeling the need to qualify comments with "I'm not advocating RDM...".

If the RDM test is so fatally flawed as to be useless in the home shop then why not (unemotionally) post detailed reasons why so that students can learn?

John

[Forrest Addy]

I'm not sure how bed twist and spindle alignment became linked. They are two separate problems and the order in which they are remedied is important. Cart before the horse: the bed is first adjusted into a near perfect plane. Using a precision level across the flats is almost always the simplest way to establish it. If one attempts to improve spindle alignment to the carrage motion (commonly expressed as t"take out the taper") by deliberately twisting the bed the carriage will bear on two diagonal wings.

All other checks and verifications are determined from a lathe bed only after it is in a plane (level). Only then can checks and adjustments of the fit of the saddle on the bed, spindle axis to the saddle motion, fit of the tailstock base to the bed, etc procede.

All too often people take a cut or two and discover some unaccountable taper and announce to the world the spindle is "out". Then they procede to tweak, shim, whatever to shivvy the spindle into compliance with their notion of a correction. There is a difference between an axis and a parallel tool path just as there exists tool build-up tool wear, thermal expansion, tool deflection and a half dozen other factors that affect the cylindriciity of a turned or bored surface.

As John mentions, there are to the home shop machine tool user three roughly equivalent ways to determine spindle axis alignment: test bar, RDM, and (newly coined) TCM. I have full confidence in the test bar and the TCM PROVIDED preliminary checks verify whichever used qualifies as a true representation of the extended sindle axis. I'm very skeptical of RDM because so many readings and calculations are involved, evolutions almost sure to introduce "observation" error. In theory it's no diferent from the test bar and two collar method. In practice, it's error prone unless heroic care and precautions are taken.

In the photos I've seen those who demonstrate RDM use a slender rod extending twenty or more diameters from the grip of a three jaw chuck and a 0.001" resolution indicator. Gravity attracts all objects. A 3/8 rod extending 7 inches droops 0.0004" from its own weight. That's the allowable spindle axis rise in one foot. Add another 20 grams from the gaginbg force of the indicator punger and the droop increases if applied on top or decreses if applied on the bottom.

A test bar the diameter of the spindle taper or a pipe having a 6 to 1 overhang is correspondinlty stiff and being stiff and the same diameter over the gaging surfae(s) they elinimate the need for averating and calculation.

Just stuff think about. Those of you locked into less critical work may scoff at such fuss and feathers and rightly so. It far exceeds your requirements. Sooner or later you will be called on to do something critical and I have set myself to prepare (actually, nag) the complacent for their next step in machine shop evolution. And to do that I need to raise undertanding of a machine tool's limitations and pass along the mental tools to correct or compensate for them them. Thus these tedious lectures of mine.

[dp]

Imagine how long this thread might run if the OP had asked the following and gotten answers to his questions right away:

My question is, is RDM for aligning the headstock with the ways, and tailstock? Horizontal and vertical alignment by adjusting the headstock? Or is he talking about shimming the "feet" of the lathe in his discription to achieve alignment?

So - can someone please answer the following:

• if RDM for aligning the headstock with the ways and tail stock?
• is Horizontal and vertical alignment done by adjusting the headstock?
• is he talking about shimming the "feet" of the lathe?

[customcutter]

Imagine how long this thread might run if the OP had asked the following and gotten answers to his questions right away:


So - can someone please answer the following:

• if RDM for aligning the headstock with the ways and tail stock?
• is Horizontal and vertical alignment done by adjusting the headstock?
• is he talking about shimming the "feet" of the lathe?

Beings I'm to OP, I'll take a stab at it.

Yes, in RDM he is describing shimming the feet of the lathe, not the headstock.

Yes, Horizontal and Vertical alignment can be done by adjusting the headstock. However, that would be last choice, after verifying other causes are not the problem.

Maybe. I think RDM in my case was used more as a check to verify headstock alignment with the ways and tailstock. I have learned that after leveling my lathe that everything came more into alignment. Also after setting for almost a week since leveling that it has "settled" and "runout, deflection, alignment, etc" whatever the correct term for it is has dropped from .006" before leveling, to .004" after leveling, to now .002" after settling for the past 5-6 days. I haven't tried actually aligning using RDM due to a lack of time and not having used a "machinist level" to level with. I'm curious to see what the numbers are after getting it finally "leveled".

thanks,
Ken (OP)

[Forrest Addy]

The go-to machinist level is the Starrett 98. I use a 6" version but they come in multiples of 2" to a foot or more.

http://www.ebay.com/sch/i.html?_trks...tt+98&_sacat=0

It's accurate, handy and relatively low in cost. Further while it's graduated in 0.005" increments it can be read much closer than that provided you are willing to interpolate the bubble indications. The graduations are some distance apart and the bubble returns to the same indication when removed and replaced on the same slope.

In any case a half blind old fart like me can still eyeball a half or quarter graduation thus interpolating to just over 0.001" slope per ft.

If you pull a hair from your head (No hair? Rob one from SWMBO's hair brush) and tie it around the vial so you can move it along to align with the bubble allowing very consistent readings. If you reverse the level in its tracks and take readings both ways you can: a - calbrate the vial. and b - read the bubble consistantly (but with care to avoid parallax errors and the like) to 1/10 the vials graduations. That's 0.0005" per foot. Yes you have to be careful and yes its a PITA but my point is a Starrett 98 level if handled right can be a very accurate tool.

Can you do the same with a carpenter or a torpedo level? Not really, because they are commonly rated as 15 Arc minute levels and they have no graduatios besides the two marking the ends of the bubble.

So all is not lost if you dont have a master precision level costing $400 or even a clunky awkward cheapo import. You can do a good job with a gratuated machinist level if you know the slope each graduation represents. If will only take .longer.

Having said all that and run on forever over nuanced esoterica allow me one final comment. If your lathe is working OK then it's OK. Leave it alone and don't mess with it. If you're curious, and want to run some of the tests mentioned here go ahead BUT DO NOT suddenly feel a need to fix something that aint broke merely because you find it aint perfect.