Rollie's Dad's Method?

[jwmay]

I can’t speak to RDM from a position of strength. But I would say that if you decide to try a method, and then, because you don’t quite get why it’s done the way it is, and thus change a portion of that method to suit you, and then are disappointed with the results….its not the method at fault….probably.

Similarly, if the first step is to level the lathe, and a person decides to forego step one in favor of modifying RDM, and ignoring the impact of foregoing step one…it’s not the method at fault.

So if it’s me, I go back and follow instructions as they’ve been laid out. Because it appears those things might have been important.

So if step one is level the lathe, then level the lathe.

On a side note, I’m not even smart enough to understand RDM, and threw it out a long time ago. It’d take someone showing me in person.

Good luck! I think you’re headed in the right direction with RJSakowski.

 

[daved20319b]

I would not adjust my headstock in lieu of level or shimming to remove twist. I made that mistake years ago. I was able to remove the taper while turning but I now cut a dish when facing. One has to assume that when a lathe is assembled, that the headstock is aligned correctly.. It is more likely that the ways are twisted, either through rough handling or bolting it to a non flat surface.

My lathe alignment procedure consists. of first leveling the lathe to remove any twist that I may have introduced. Next I check the headstock alignment to the bed, I do this by mounting a bolt on my faceplate. The bolt has a polished head and I place an X with a Sharpie so that I can make measurements on the same point. It is position so that I can touch that point with my dial indicator in a position at the front of the lathe and at the rear by moving only the cross slide and rotating the spindle. I lock the carriage and with the bolt to the front, I adjust the dial indicator to contact the center of the X and zero it. Then I rotate the faceplate to the bolt is at the rear and move the cross slide to contact the X,, without disturbing the indicator. Any non zero indicator reading is due to headstock misalignment and I adjust to correct.

When I am satisfied with the headstock alignment, I then move to the alignment of the ways using the RDM method and shim as necessary to correct. Next, I run the two collar test to verify alignment . The next step is to align the tailstock. I do this again with the RDM method. I mount a bar in the lathe, but instead of running free on the tailstock end,it is run on a center. I made a special split ball for a 1" bar so I can mount the bar in my 3 jaw chuck without introducing any strain on the tailstock center. From there is it straightforward. Adjust the tailstock so the difference in the averages at either end of the bar are equal to the desired taper.

There is one more measurement to be made and that is for vertical alignment of the spindle axis to the ways. This is not normally done as there is no easy way to correct a misalignment and it has a relatively small influence on use of the lathe.

Thanks, RJ, lots to digest there, so I'm probably going to need to got through it several times, but I'm sure I'll have more questions for you once I get my head wrapped around it all. Appreciate your time, more later.

Dave

 

[daved20319b]

I can’t speak to RDM from a position of strength. But I would say that if you decide to try a method, and then, because you don’t quite get why it’s done the way it is, and thus change a portion of that method to suit you, and then are disappointed with the results….its not the method at fault….probably.

Similarly, if the first step is to level the lathe, and a person decides to forego step one in favor of modifying RDM, and ignoring the impact of foregoing step one…it’s not the method at fault.

So if it’s me, I go back and follow instructions as they’ve been laid out. Because it appears those things might have been important.

So if step one is level the lathe, then level the lathe.

On a side note, I’m not even smart enough to understand RDM, and threw it out a long time ago. It’d take someone showing me in person.

Good luck! I think you’re headed in the right direction with RJSakowski.

I wouldn't say I was modifying the method to suit me, more that I didn't (don't) understand the starting point. And based on what RJ and others have said, it also seems that there were some important details left out of the instructions I was working from, like the necessity of a perfectly round test bar. The instructions I have say the bar needs to be the same diameter for most or all of its length, but it doesn't qualify the precision of that diameter, i.e. within .010", .001" or .0001". The devil is in the details, as they say, and that's a pretty important detail that hasn't been addressed in any of the instructions I've found so far. I'm also still not clear on the +/- dimensions and where you start from. It may well be a simple and effective method, but there's a lot of apparently critical info left out of all the instructions I've been able to find. But I hope you're right and that RJ can get me on the right track. Later.

Dave

 

[RJSakowski]

One more thought concerning the RDM method vs. the two collar test. And that is precision. The RDM method makes two sets of two measurements with either a dial indicator or a dial test indicator. while the two collar test makes two measurements of diameter ideally with a micrometer. A micrometer has a resolution of .0001" and you are measuring a diameter so the taper measurement resolution is actually half that or .00005".

With the RDM method, you measure the minimum and maximum with a dial test indicator with a resolution of .0005"/div. or preferably .0001"/div. If you round the reading to the nearest division, your average could be in error by as much as one division.. You are making two sets of measurements, so the worst case, your measurement could be two divisions.

Personally, I was trained to interpolate between divisions and can reliably read to 1/5th of a division. I also prefer to use a .0001"/div. dial test indicator or a .00005" digital dial indicator. This brings my overall resolution on a par with the two collar test. Even so, I still will run a two collar test as a last word in alignment.

 

[mksj]

Per the RDM directions...
Common Error:
Some people will find the near-end average distance, turn the lathe till it reads that distance and then move the carriage down the ways with that mistaken assumption that the reading shouldn't change. That method will only work if your bar is known to be perfectly straight and the chuck is known to hold the bar in perfect alignment with the spindle axis. Do not confuse that method with this one.

It does help to have a concnertic rod for RDM, but I disagree that swing should not change as you move down the bar, as no chuck holds stock perfectly axially. I use a a 0.0001" dial indicator, I find further resolution of diminishing value on most manual lathes as the range is too limited if extending out 9-12". Highr resolution micrometer readings are of value when measuring cutting diameters, such as the 2 ring test. At the end of the day, the headstock may be perfectly aligned and you may still cut a tapper for various reasons. Same for the tailstock alignment, in some case I have to ever so slightly adjust the tailstock alignment forward based on the cutting dynamics and length of the cut to get consistent diameter end to end.

 

[mac1911]

So this post is mostly thinking out loud, but if someone has some insight, I'd like to hear it.

So in my ongoing effort to get my older Grizzly 12" x 24" dialed in, I decided to put the cart before the horse and try to align the headstock to the ways. I say cart before the horse because I haven't really done a thorough job of leveling this thing, there's enough twist in the bed that a precision level soon has me chasing my tail. But that's fodder for another post.

Anyway, RDM seems to be a fairly popular and respected alternative to the usual method of dialing in lathe alignment, so I decided to give it a try. For a test bar, I chucked up a piece of 1.25" aluminum heavy wall tubing in my 3 jaw, I figured that would be stiffer than a comparable solid bar, and it was a good length. And right away, I was having issues with the instructions. They say to record the high and low numbers and average them. But why/how are they getting high and low numbers in the first place? Why not just zero the indicator on the low point, then record total runout? Anyway, that's what I did, and I was getting about .002" at the chuck, and almost .060" at 16" from the chuck. Which seemed excessive, if I'm understanding the instructions, that would seem to indicate my alignment is out by ~.030" at the 16" mark. But that's about double what I'm seeing for taper when I turn something. For no particular reason, I decided to swap ends on my test bar, and I got totally different numbers, about half my previous measurements. So then I switched to a 7/8" 416 SS round bar, and got a whole new set of numbers nowhere near the previous checks, much lower and closer together end to end. So in 3 tries, I came up with an alignment error of ~ .030", .015", and .003". Not exactly useful info, what am I supposed to do with that, average all three readings?

My other issue with this method is correcting the alignment by shimming the feet. Seems like this is assuming the lathe is twisted, but if it's leveled when you start, as it should be, then why not go to the source and adjust the headstock directly? I realize not all lathes allow adjusting the headstock, but mine does, and once (if) I ever get mine level and straight, I'm sure not going to mess it up by twisting it again.

Maybe I'm totally missing something here, but it seems to me that if this is going to produce useable data, I should have gotten at least similar numbers from all three attempts. I was careful to make each measurement at the same location on the bars, and I made all the measurements multiple times. I've decided to set this aside for now and concentrate on trying to get my lathe properly leveled, but at this point, I won't be trying RDM again, I'll go with the more traditional method.

And BTW, yes, I'm working on the level/twist again, only this time I'm going to see if time and gravity can accomplish what I couldn't with brute force. More later.

Dave

I have a 12x20 thats had several owners , god knows how many transportation issues
Was definitely “out of alignment”
Im not a machinist but a auto mechanic and fixer of just about anything.
Any how :
I to had my run ins with RDM and the few videos out there are not very clear , at leasr to me

Can I ask some basic questions
1. What precision level are you using to check your bed twist.
2. Have you taking out all other possible issues like carriage/cross slide slop ir error.
3, curious , what method was used by the manufactured to assure gear head /spindle was aligned with the bed ways?

When I was looking at my head stock for possible alignment issues. I found that the head is attached to the ways with similar fashion to the cross slide lock.
Some angled hardened pins locked down with set screws along with a few bolts come up through the bed into the gear head.
So no real surprise these where all a bit “loose” So I loosened the “gib” style locks and the the bolts from below and snugged it all up evenly as I could .

I have left it at that for now.

Im eager to get back to getting it more aligned