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

"Pretty sure I bought it from Shars (but possibly on ebay). I’ve been very happy with it. It’s as accurate and square as I’m able to measure (within a tenth over the long side)."

Thanks for the feedback. I've been debating about getting one of them from Shars. Would prefer an angle granite from Rahn but can't justify the $$$$.
 
I clamped that granite angle plate to my scraping project angle plate..
We clamped it up high and ran a test indicator along it's horizontal edge to check square.
Came in very handy. Someone said the error factor of that plate is + - .0002.
That's exactly the variance we experienced when we checked for square.
I wondered what the hole was for. :)
I was very happy with it. I didn't know it was yours Rex.
Thank you for bringing it.
Jon had a Suburban Tool, cylinder square with the magnetic base. That came in handy also for the smaller pieces.
 
When we checked Jeff's angel plate he was scraping with the granite . With indicator starting near the iron and moving out the square it was zero for about 6" and the jumped .0002" for about the last 3 inches. At the time I figured it was the square, but maybe the plate under the square was bad. One way or the other Jeff did a super job on it. I was fun watching him get mad and start to step scrape. :)
 
Haven't posted an update in quite a while. Neither the family nor the few people still paying me money occasionally seem content to let me spend all day every day in the shop. Even the Giants keep insisting on extra inning walk-offs. Such problems!

Anyway, some progress since the last post: I've only (!!) scraped in the outer ways, headstock, and saddle. The headstock is now aligned to [kisses fingers] near perfection:


There was a whole lot of learning involved for me to get it to this point.

1. Attitude

The first thing was to "get mad" as Richard likes to say. I finally got tired of seeing my lathe in pieces, and stopped repeating check after check after check before actually doing anything.

I think it's a natural tendency for beginners like myself to pussyfoot around for fear of breaking things. Watching my dad try to use a computer used to drive me insane, for example. I spent my entire adult and professional life with computers and have zero fear of hurting the darned things. With the lathe I'm terrified of making a mistake that can't be corrected. Most mistakes just mean more scraping. Occasionally, they require gluing on some Rulon or phenolic and then more scraping.

I'm still being careful and trying to think things through, but mistakes are unavoidable the first time you do anything in life. So I quit messing about with the inner ways and tailstock, and moved onto the important bits. That definitely paid off, as I learned quite a bit more.

2. Vee Way Angle

Before the change in attitude, I was quite worried about accidentally changing the angle of the inverted vee ways (90 degree included on a Logan). Then I remembered mentioning it to Richard who just shrugged and said to remember that you scrape the saddle in to the bed anyway. A slight change in angle is no big deal.

I think that as long as each side of the vee is FLAT, it doesn't matter if one side is, say 47 degrees off of vertical and the other 51 degrees.

I think what matters most is that the vee doesn't get wider or narrower at the tailstock or headstock end of the way. In other words, what matters is the center of rotation for each plane. As long as those two lines are parallel with each other, it doesn't matter if one or rotates more than the other.

Put yet another way: Imagine a tiny little man wearing a pair of skis, and resting each one on the outside of the vee. It doesn't matter how much the man's knees spread apart or come together. What matters is that he doesn't go pigeon toed or duck footed — his feet just need to be parallel no matter how bowlegged or knock-kneed he gets.

Keeping the angle of each side exactly 45 degrees off of vertical is hard (nearly impossible) because each side is only about half an inch wide. As long as both sides are flat, though, it's relatively easy to tell if one end or the other is narrower. One way is simply by feel and by sound: move the (roughly scraped in) saddle to each end test for play. A slightly more precise way is to blue up the ways, slide the saddle to the two ends and examine the resulting marks on the ways (each end should see roughly the same amount of streaked/wiped away ink).

The job of an inverted vee is to keep the saddle from rotating on the horizontal plane. As long as the saddle has full bearing, the precise included angle just doesn't matter (unless someone convinces me otherwise).

3. Headstock alignment

EVERYTHING
on a lathe references from the center of rotation of the spindle in the headstock (more specifically, the center of rotation of the Morse taper at the chuck end of the spindle). Unfortunately, it's a purely imaginary line.

You can't indicate an imaginary line! Nor can you throw a level on it.

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:

IMG_0769.jpg

That's an excellent fit. And a very well made test bar. The wider unstreaked areas were due to worn grooves in the spindle taper, not anything with the test bar.

3.2 Testing the spindle

Next, I needed to ensure the spindle and spindle bearings themselves were reasonably precise.

First I indicated for runout on the spindle itself. A little less than 0.0002" TIR. Honestly, not as good as I was hoping for (hey, even I can scrape to a few tenths) but probably as little as could be expected from a very old hobbyist lathe:


Logan's use a screw-on chuck. I also tested if the surface the chuck references against had any cam action going on. Again, the surface quality is far from perfect, but I'm still quite satisfied with the results (and some careful stoning should eliminate the one little bump you see):


3.3 Finding lines on the same vertical/horizontal planes as the center of rotation

Finally we get to the thing I found most interesting in the whole process.

I've now validated that the test bar is astonishingly accurate, and that the spindle itself is in reasonably good shape. Time to actually use the test bar for its intended purpose.

There is nothing like a tenths indicator and a 10-12" lever arm to reveal the tiniest little bits of dirt, inconsistent pressure, etc.

This is the very best result I saw with the test bar inserted yesterday:


That's about 0.0001" TIR at the chuck end, and 0.0009" at the tailstock end.

That's the best result, that I was never able to repeat. Results vary every time you remove and re-insert the test bar. Sometimes it would move as much as 0.005" TIR at the tailstock end!

No matter what, the spindle and test bar tapers aren't perfect. Minute specs of dust will invariably kick things around a bit. It doesn't matter how carefully you re-insert the test bar, the end is pretty much guaranteed to show some runout, and the bar will basically circumscribe a cone.

Here's the thing, though: it really doesn't matter too much! With one little trick, that cone can still reveal a line in the same plane as the axis of rotation.

Here is possibly my favorite passage in all of Edward F. Connelly's fantastic book, Machine Tool Reconditioning:

"To nullify the effect of eccentricity error, the mean position is located at the vertical diameter for this portion of the test."

That is some seriously opaque technical writing, especially for something so important to understand. It's impossible to read that without your eyes glossing over! I must have read it two dozen times without understanding until the penny finally dropped.

As usual, the underlying concept is critically important (and actually kind of cool):
  1. Place the indicator tip at roughly top dead center at the end of the test bar.
  2. Rotate the spindle to find a high point and a low point.
  3. Set a zero at the low point, then rotate to find the high point (which should be 180 degrees away). Let's say the high point reads 0.0016".
  4. Now rotate the spindle to find the halfway point precisely between those two values (rotate until the indicator shows 0.0008").
Since the test bar circumscribed a cone, the line formed at the top of the test bar is now on the same horizontal plane as the axis of rotation.

That is, the line formed between a point at top dead center at the headstock end, and one at the tailstock end will be twisted fore or aft around the vertical axis, but it doesn't tip up or down at the headstock or tailstock end — it's precisely aligned with the axis of rotation.

If you now sweep an indicator mounted on the carriage along the length of the test bar, with the tip at the top of the bar, you can measure exactly how much the spindle axis is tipped up or down.

The test then needs to be repeated once with the vertical plan, and once with the horizontal plane (once with the indicator on top, and once with it on the side of the test bar). In both cases you just rotate to the halfway point to find the true axis of rotation.

That is what I'm showing in the first video of this massive post: the outer ways of the bed are guiding the carriage along a path precisely aligned with the axis of rotation of the spindle.

Whew! I hope someone finds this as interesting as I do. (laugh)
 
Rex, I can't imagine how difficult scraping in your lathe must be to a hobby guy.
Scraping a flat bar is one thing, to correct a worn lathe and bring it back to better than factory specs is incredible.
Scraping both sides of a v way alone is daunting to me.
Well done sir.
We missed you last Saturday.
See you at the scrape fest.
 
Sounds like RDM. I find it very interesting.
 
Rex, I can't imagine how difficult scraping in your lathe must be to a hobby guy.

Nah, like anything I think it gets easier the more you do it. Now that the outer ways and carriage are a reliable reference, it’s easier to see just how poor a job I did with the first things I worked on.

It took me a month of pussyfooting around and fretting to get the inner ways and tailstock rough scraped. Maybe three or four days to do the more critical outer ways, saddle, and headstock. And they came out far better!

I like the puzzle of it. Everything you touch affects everything else.

If only Connelly had learned to write readable English! It’s all in there, but the man was clearly incapable of using the active voice.

Anyway, I’ve got a little more progress still to post, and I can see the light at the end of the tunnel.

I debated with myself whether or not to (shudder) paint the dang thing since I’ve already got it apart. After mulling it over in the back of my brain for a few days I convinced myself just to get the darn thing finished and put back together. Having a working lathe again is more important than making it pretty, right?

Yet somehow I seem to have just ordered some expensive gray enamel paint ....
 
Sounds like RDM. I find it very interesting.

RDM?

In my day job, RDM stands for raw device mapping storage to VMware.

Google also turns up “remote device monitoring” and, my favorite, “random death match”.

Suspecting you don’t mean any of those, though the last seems somewhat appropriate.
 
RDM?

In my day job, RDM stands for raw device mapping storage to VMware.

Google also turns up “remote device monitoring” and, my favorite, “random death match”.

Suspecting you don’t mean any of those, though the last seems somewhat appropriate.
Rollie's Dad's Method.
 
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