Scraping in all bearing surfaces on my Wards/Logan 10"

Rex Walters said:
3.1 Test bars

The way you find the center of rotation is interesting. It requires a test bar: a precision ground bar about 12" long, with centers bored at each end, a morse taper at one end, and a precision ground cylinder for most of the length.

I bought a surprisingly inexpensive pair of test bars shortly after taking Richard's class for the first time (from India on ebay, I think). One MT3 and one MT2 to fit the headstock and tailstock tapers of my lathe.

The right way to validate a test bar is to put it between centers and check for runout. Since I, ahem, currently lack a fully assembled and precisely aligned lathe, I had to use a matched pair of vee blocks on my granite plate. Testing the cylinder portion was easy: just find top dead center with a tenths indicator, and carefully rotate the cylinder. Repeat at each end and in the middle of the bar.

I was shocked at how accurately ground the cylinder portion was. The needle on my tenths indicator barely moved. Total indicator runout of like 0.00005". Amazing.

You basically test for runout on the Morse taper portion the same way. Unfortunately, because I couldn't put it it between centers it was much harder to test. Even a tiny amount of movement axially while rotating the test bar will move the needle on a tenths indicator significantly. I tried sandwiching a small ball bearing between the center in the far end and a heavy block to push against while rotating. Using this method I measured about 0.0003" to 0.0004" TIR, but I'm not confident in the result — it may actually be better than this. Tenths indicators are unbelievably finicky beasts.

The last test for the test bar is for the taper itself. You ink a stripe down the length of the taper, insert it into a matching taper in the spindle, twist, then analyze the resulting smear.

The taper in my spindle was pretty grody from decades of misuse. There is a bit of surface rust, quite a few scores, and lots of "character" from use since 1947.

I cleaned it as best I could, then took a MT3 hand reamer (one of the most expensive cutters I've ever purchased) and very carefully removed any remaining burrs and crud, twisting the reamer purely by hand. I did NOT insert the reamer fully and turn it with a wrench to cut a new taper, of course, as there would be no (easy) way to precisely align the taper with the spindle axis. I just removed the burrs.

I then inserted the test bar with a stripe of spotting ink, and couldn't have been happier with the result:
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I checked mine yesterday between centers. Dead straight but the MT3 showed almost .0007" TIR. <1/2 that on the small end.
 
ddickey said:
I checked mine yesterday between centers. Dead straight but the MT3 showed almost .0007" TIR. <1/2 that on the small end.
Click to expand...

Maybe I did a better job indicating without putting it between centers than I thought. For the money, those things are surprisingly well made (even at 0.0007" TIR in the taper).

After removing and reinserting the test bar into my spindle several times now, I average about 0.0002" TIR at the headstock end of the cylinder, and anywhere between 0.003" to 0.005" TIR at the tailstock end. Not sure if it's the pitted and scored spindle taper or the test bar that's kicking the bar out of line most, but either way I'm doing my best to ignore that small amount of error.

Rotating to the halfway points with the indicator on vertical or horizontal, it's dead on along the entire length of the test bar, which is all I care about (proves the headstock and spindle axis are aligned to the bed ways).

It's all angels dancing on the head of a pin for the type of work I do, anyway. Only once every few blue moons do I insert any morse taper tooling into the spindle. For super accurate work, I turn between centers: I stick a center into the spindle and re-cut an accurate taper at the headstock, then adjust the tailstock set-over until I'm not cutting any taper in the part at all. I can't think of a single operation where a slight concentricity error in the taper will cause any issues.

Screw-on chucks register on the outer face, and don't even touch the taper. I don't count on scroll-chuck accuracy below a thou or two, and independent-jaw chucks need to be adjusted to center a part regardless.

I'm satisfied that the headstock, outer bed ways, and saddle are all aligned as well as I'm able.

The inner ways and tailstock aren't quite as perfect (yet :). For the record, trying to "tip in" to minimize scraping on one of the faces of the inner inverted vees was a mistake: I should have just scraped "straight down" I think.

It's not out all that much, and I just finished epoxying the phenolic between the two halves of the tailstock. I've got quite a bit of material to remove there, so there is no point doing any more scraping/alignment until I get it closer to the same vertical plane as the spindle axis. It scrapes like butter, though, much easier to scrape accurately than I expected.

I've started cleaning and painting parts (don't expect much, I'm NOT trying for a flawless museum piece, just a working tool protected from rust). I'll post more pictures soon of the final alignment and scraping (I didn't take any photos of epoxying the phenolic in place, but the process is pretty straightforward).

More soon. I see the light (of the on-rushing train) at the end of the tunnel.
 
Any update on the lathe Rex? Found this to be very informative and hope you would feel comfortable sharing your progress. I will likely be starting to attempt a similar process on my mill and I will be returning to this thread for information (and to catch pitfalls) along with all the other literature out there.
 
macardoso said:
Any update on the lathe Rex? Found this to be very informative and hope you would feel comfortable sharing your progress. I will likely be starting to attempt a similar process on my mill and I will be returning to this thread for information (and to catch pitfalls) along with all the other literature out there.
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Yikes! I really need to log in here more often. Sorry for the slow response.

I finished the lathe project quite a while back (before the plague even). Apologies for not updating this thread. I've been actively using the lathe with no issues whatsoever, so I must not have screwed it up too badly in my attempts to scrape it in.

My only real advice with respect to your mill is to just go for it. Patience, persistence, and logical thinking will see you through.
 
Rex Walters said:
Yikes! I really need to log in here more often. Sorry for the slow response.

I finished the lathe project quite a while back (before the plague even). Apologies for not updating this thread. I've been actively using the lathe with no issues whatsoever, so I must not have screwed it up too badly in my attempts to scrape it in.

My only real advice with respect to your mill is to just go for it. Patience, persistence, and logical thinking will see you through.
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Logical thinking, Rex is an amazing machinist.
He makes it look easy.
Rex, you should show your Quorn cutter grinder.
These kits are not easy. Most difficult imho.
 
The only amazing thing about my work is that any of it ever works.

I should make a thread for the Quorn. I've got some plans for finishing touches that I'm still working on, though. I left the blow-by-blow for that one to our local list — I'll publish the whole shebang for real once I'm satisfied with the result.
 
Rex Walters said:
The only amazing thing about my work is that any of it ever works.

I should make a thread for the Quorn. I've got some plans for finishing touches that I'm still working on, though. I left the blow-by-blow for that one to our local list — I'll publish the whole shebang for real once I'm satisfied with the result.
Click to expand...
Looking forward to it!
 
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