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

Rex Walters

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I've been working on my lathe off and on over the past several weeks or months, but I've been hesitant to start a thread documenting my progress (or lack thereof!) for fear of embarrassing myself.

I'm increasingly confident that I'm going to end up with a very precise lathe rather than a very large pile of cast iron dust and tears, so I'm finally willing to share my progress.

After creating a new cross-slide for my lathe some time ago, I'd already spent a lot of time scraping in the compound and cross slide. But I decided to tackle a far larger project.

I've taken Richard King's class twice now (and I'm about to help out with a third) but I know full well there is no way to really learn something without actually doing it (and even better, trying to explain what you're doing to others). So, despite my old Wards/Logan being in perfectly (well ... "acceptably") useable shape to begin with, I decided to scrape in the bed ways, headstock, saddle, and tailstock. I rationalized that this was "my first lathe" and even if I ended up with an expensive and shameful pile of worthless cast iron, I'd learn something in the process.

As expected, it's been a terrific learning experience.

I decided to attempt the inner ways and tailstock first before tackling the outer ways and carriage. I thought this wise because in case I totally screwed up, the tailstock is less critical than the carriage. It took an embarrassingly long time for me to realize that the headstock also rides on the inner ways, though, so if I screwed them up I was still pretty much SOL.

Anyway, I'm happy to report that after a LOT of work, I've got the inner ways and tailstock base scraped in to about 0.0006" with decent bearing over the entire 42" length of the bed:


If I'm reading Connelly correctly, I think the standard for this test is under less than 0.0008". The width of the tailstock base is only about 4" and the level is calibrated to 0.0005"/10" so, if my math is right, each division on my level shows about 0.0002" of deviation. Three divisions max deviation is under the standard. Whoopee. :cool:

Actually, I've still got just a bit more fine tuning left. I'd like to get a little bit more bearing points on the far side of the rear fee way, as well as a few more on the bottom of the tailstock base (it's bearing across the entirety of all three surfaces, but I'd like to get a few more PPI). I'm pretty sure I can improve 0.0006" slightly but I'm pretty satisfied already (considering the stack of tolerances).

Interestingly, the far side of the inner inverted-fee way needed the most scraping. Not sure why this would be unless it was out a bit when it left the factory.

I'm leaving out an awful lot of things that I didn't document, but here's the rough outline of getting to this point. I'll try to update this thread with more thorough details as I tackle the outer ways, headstock, tailstock top, and carriage.

Step zero was to scrape in a 36" straightedge. It's slightly shorter than my bed, but there's no way I'd have been able to manhandle a larger straightedge. As it was, I really wish I'd acquired a plain casting without the angled edge for large dovetails. The additional weight of the dovetail feature put it right at the edge of what I can manage by myself (my straightedge weighs about 70 pounds if I recall correctly).

Another (critically important!) preliminary step was to determine what to use as the "datum plane." I'd heard from Scott Logan himself that the flattened tops of the inverted vee ways on Logan lathes were ground at the factory at the same time and with the same setup as the ways themselves. Since the tops of the vees receive no wear, this eliminated a lot of what Richard calls "detective work." After a good stoning to remove the raised burrs from 70+ years of nicks and dings, I had an excellent (and convenient!) reference plane waiting for me.

Connelly calls this a secondary reference/datum. For other manufacturers, you'll have to look for unworn edges on the flat ways, or use the bottom of the rear way to determine the original datum plane. After just one lathe job I'm convinced that if I ever work on a lathe that doesn't have the tops of the vees pre-ground to be coplanar with the real datum (the ways themselves) the very first thing I'd do on a refurbish job would be to make the tops of the vees a secondary datum. It's incredibly convenient to be able to just lay something flat across the ways to indicate from instead of having to balance/clamp 1-2-3 blocks and parallels.

The datum plane is everything when it comes to precise alignment and an accurate lathe. Literally everything on the lathe is adjusted relative to this plane. It's worth spending an awful lot of effort ensuring that all points on this plane are as coplanar as possible. Many years ago, I tried to level my lathe using shims. Trust me, screws/nuts (or paired wedges) are the only way to go for the level of precision required. You'll drive yourself insane trying to get things level (planar) with shims.

While it's only necessary to ensure the datum plane is truly flat, and not to align it with any particular plane, trust me that it's worth the effort of making the datum plane truly level. It's awfully convenient to be able to just throw your level onto things to see if they are parallel to the datum plane.

It's also worth calibrating your level instead of always ensuring you have it oriented in the same direction (something I try to do anyway, but am bound to screw up occasionally). The process is easy and satisfying (and likely documented elsewhere on this site).

I carefully re-leveled the bed at the start of each day's work (and often once or twice during a session, especially after jostling the bed or causing heavy vibration from rough scraping things nearby. Just the tiniest movement of the nuts on the leveling feet is enough to move things out of level by a couple tenths. I have the whole thing supported by a massive maple workbench, but temperature and humidity variations are definitely enough to move the bed out of alignment slightly from day to day.

Here's what level looks like:


I started by scraping the inner flat way. The first blue ups showed more wear in the middle than on the ends, unsurprisingly. Because the area under the headstock is fixed and has no wear, I first tried to leave that area alone as much as possible. I thought I was being smart by "tipping in" the scraping and doing most of the scraping at the tailstock end. Naturally, this ended up with the way angled downward toward the tailstock relative to the datum plane. No bueno. So I ended up needing to remove a bit of metal at the headstock end anyway.

Note that the flat way needs to be coplanar with the datum plane in both dimensions (left to right, as well as fore and aft). It's very easy to confuse yourself when indicating in one direction if you're also out in the other.

In case it isn't obvious, here's how I indicated to ensure things are parallel to the datum plane:

IMG_0361.jpg

In this image, I've got a piece of precision granite across my datum plane. Just rest the the base of your surface gauge or indicator stand on this, and use a small parallel or side of a gage block to average out the points on a scraped surface.

I discovered a pretty significant nick in one corner of my mag base, by the way, that was causing me no end of grief trying to get repeatable results. A quick stoning fixed the problem, but for a while I thought I was losing my mind.

As I mentioned it's important to realize you may have tipped the flat way in one of two dimensions. At one point I was trying to determine how far the flat way was tilted toward the tailstock after my initial scrape, but I just couldn't seem to get repeatable results. After several attempts, lots of head scratching, walks, and countless cups of coffee, I finally realized the way was also tipped over a thou toward the back of the lathe as well as left to right. Because I wasn't always measuring in the precise middle of the way, my results would vary.

So I rigged up this ghetto King-Way to at least perform this one measurement reliably:

292410

I just super glued a couple washers on a flat bar to create a two point reference, and clamped it to the granite square or level I placed across the vees. This photo is a bit of a lie. I only used this setup to measure the flat way (and ensure I was indicating at the same offset from the edge of the way). I didn't actually use it for the vee ways. The front edge of my lathe is not precision ground (you can still see the rough abrasive grinder/saw marks). It's not flat enough for anything super critical, but it was enough for me to figure out how much I needed to correct left to right.

Hope this all makes sense. I've learned quite a bit in the process, and doubt I've covered half of it, but I hope this is at least somewhat interesting and useful.

Doubtless I'm still making other boneheaded mistakes, but I'll continue to share. Please don't hesitate to correct me if I'm doing something wrong or if there's some easier way.
 

Rex Walters

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A bit more progress.

I've scraped in:

• All three inner way surfaces (flat and both sides of the inverted vee), of the bed ways:

292764

• The bottom of the tailstock base to match the bed ways (the flat bed way is narrower than the flat way on the tailstock base - hence the stripe without bluing in the photograph).

292765

• The top of the tailstock base (scraped to be parallel to the datum plane). This was tricky to scrape and indicate parallel because of the guiding portion that sticks up in the middle. I was using it to mark up the top half when I took the photo (hence the bluing on the scraped surfaces — blacking?).

292766

• And I've just started to scrape the top half of the tailstock base to match the lower.

292767

I'm performing various checks along the way with straightedges, the surface plate, and indicators to ensure things are as flat/parallel/coplanar as I can get them.

The most difficult thing to get coplanar is the two parts of the top of the tailstock base, separated by the protrusions to guide the top portion. I neglected to get a photo, but the best way to ensure they were coplanar was to scrape the larger portion flat and parallel to the datum plane (indicating with the rig in the previous post) then clamp that surface down to a matched pair 1-2-3 block on the surface plate and indicate from underneath. I'll try to get a photo of this setup tomorrow.

Once both portions of the base are coplanar and parallel with the datum plane, I need to fit the top half to match the bottom. These were not precision surfaces from the manufacturer. They weren't even terribly well machined, so this will (eventually) be better than factory. This is definitely overkill, but its a learning project so there's no reason not to go overboard.

The "rubber meets the road" test is with a test-bar stuck in the MT2 taper of the tailstock (testing both for vertical deviation as well as side to side as I slide the tailstock along the ways):

IMG_0370.jpg


Because the top and bottom aren't yet a perfect fit, I've still got a thou or two of rock between the two halves. Once I've got a matching flat surface on the top half, I'll use the indicator tests above to step scrape the top half into alignment.

Between the four sets of mating surfaces (bed ways, bottom of base, top of base, bottom of tailstock top-half) the tolerance stack is a lot to control, but I'm extremely confident I'll be able to get less than a half thou or so of deviation along the entire length of the test bar.

All this scraping is lowering the tailstock significantly (possibly 0.010" or more). Once I scrape in the headstock, I'll see how much lower the tailstock quill is than the headstock. If it's less than a couple thou, I'll definitely just live with it. If its lower by only a 2-3 thou, I'll likely lower the headstock with a few extra passes. If it's more than ten thou, though, I'll probably epoxy some turcite or equivalent to the top half of the tailstock. That will require milling the bottom half even lower though, so I'd like to avoid it if possible.

Onward!
 

Janderso

Jeff Anderson
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Great fun!
Rex, how much time are you investing in this?
Perfect timing with the class next week. You will be the star pupil!
 

toploader

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Great read. I really want to take Richard Kings class at some point. And do exactly what you are doing.
 

Rex Walters

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This fellow is selling a Leblond/Regal with scraped ways.

Out of my price range, but I’d like to take an indicator to it to see how good a job they did scraping it in.
 

Bob Korves

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Between the four sets of mating surfaces (bed ways, bottom of base, top of base, bottom of tailstock top-half) the tolerance stack is a lot to control, but I'm extremely confident I'll be able to get less than a half thou or so of deviation along the entire length of the test bar.

All this scraping is lowering the tailstock significantly (possibly 0.010" or more). Once I scrape in the headstock, I'll see how much lower the tailstock quill is than the headstock. If it's less than a couple thou, I'll definitely just live with it. If its lower by only a 2-3 thou, I'll likely lower the headstock with a few extra passes. If it's more than ten thou, though, I'll probably epoxy some turcite or equivalent to the top half of the tailstock. That will require milling the bottom half even lower though, so I'd like to avoid it if possible.
Shimming between the upper and bottom halves of the tail stock is an acceptable way to get the spindle center lines to match. The scraping is to get the geometry correct. The interface between the two halves is not a sliding surface. Just get the geometry correct. Also, tail stock spindle dead level and dead equal height to the spindle center is not what is called out in Machine Tool Reconditioning (MTR) or in manufacturers' tolerance sheets. In MTR, the tail stock spindle for a 12-18" swing engine lathe shows it should be 0 to .0008" toward the cutting tool at the fully extended and locked down position while measuring the side of the spindle, and 0 to .0005" high when indicating the top of the end of the spindle in the same setup. This is to accommodate side pressure in use, heavy parts mounted, and wear over time (MTR 26.49 to 26.57)
 

Rex Walters

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Shimming between the upper and bottom halves of the tail stock is an acceptable way to get the spindle center lines to match. The scraping is to get the geometry correct.

Yes, using loose shim stock is common, but I'd prefer to have the shimming material permanently attached and scraped to ensure the alignment stays true. Putting loose shim stock on scraped surfaces just seems wrong to me. It's a little weird using turcite for a fixed bearing surface, but not unheard of from what I've read.

... shows it should be 0 to .0008" toward the cutting tool at the fully extended and locked down position while measuring the side of the spindle, and 0 to .0005" high when indicating the top of the end of the spindle in the same setup.

I read a "zero to 0.0008" spec as "just don't angle it away from the operator and if anything favor toward you slightly." No?

I don't think a few tenths of height difference will be detectable due to cosine effects, but I guess it makes some sort of sense to angle it ever so slightly toward the operator when fully extended. Since tailstocks are adjustable, though, what's the point? If I'm doing precise work and turning between centers you can be darn sure I'll adjust the tailstock to eliminate any taper anyway. I'll ask Rich his opinion next week.

I get adjusting the cross slide to cut ever so slightly angled, but intentionally scraping the tailstock off axis seems odd.
 
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