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

[Rex Walters]

I must owe you money.

 

[Richard King 2]

Rex is very talented, patient, methodical, good looking and rich

Jeff your a little behind the times...lol Allischicks post was from 2021. But your right about Rex. A very talented guy

 

[Janderso]

Jeff your a little behind the times...lol Allischicks post was from 2021. But your right about Rex. A very talented guy

Oops.

 

[dan.blasingame]

nice ...

 

[Rex Walters]

Apologies for posting to a very old (but apparently popular) thread of my own, but I just re-read reply #44 after receiving another like, and I really must correct a slight mistake I made toward the end. The post is too old to edit.

That post describes what some call Rollie's Dad's Method (RDM) to find the true axis of rotation. As far as I'm concerned, it's the only method that works accurately and reliably. The test bar only needs to be truly round, about ten or twelve inches long, and with a consistent diameter. Test the bar with a micrometer at multiple places along the length and repeating the test after revolving the bar a few times. It doesn't matter whether the bar is held in the taper, in a collet or in a chuck. A decent piece of TGP shafting won't break the bank and will work fine (the diameter isn't critical, but something reasonably stout like 3/4" is ideal).

I think I wrote it up reasonably well, but my mistake was this sentence toward the end:

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 procedure I described in that post establishes a line on top of the bar that lies on a horizontal plane that is parallel to the axis of rotation. But the end of the bar will now be pointing slightly toward or away from the operator.

If you were to sweep an indicator mounted to the cross-slide over the top of the bar by moving the carriage left and right, the indicator tip would also move toward or away from top dead center, even on a perfectly unworn lathe. The indicator reading will change slightly as you traverse, but the angled or curved line formed by connecting all the TDC points along the bar will be on a horizontal plane parallel to the axis of rotation.

To establish a straight line parallel to the axis of rotation, you need to connect two points at top dead center (one close to the chuck, one toward the end of the bar).

To summarize the absolutely accurate process:

1. Mount the test bar as securely as possible (held in the taper, in a collet, or in a chuck).
2. Mount the indicator base to the cross-slide or compound.
3. Place the tip of the indicator at the end of the bar, visually near top dead center.
4. Rotate the bar to find the maximum indicator reading, then feed the cross slide in and out until you find TDC (max indicator reading)
5. Continue rotating and moving the cross-slide to find the maximum reading at TDC and zero the cross-slide dial or DRO.
6. Rotate the bar to find the minimum indicator reading (180 degrees away if an accurately ground test bar) and zero the indicator.
7. Rotate the bar to find the indicator reading halfway between the minimum and the maximum reading.
8. Mark that point on the bar.
9. Repeat steps 4-8 with the indicator tip closer to the chuck and without zeroing the cross-slide dial or DRO.

The mark closest to the chuck should be on the same side of the bar as the one at the end if the bar is ground accurately and not bent with a compound curve. If your test bar is particularly well made and well-mounted, the cross-slide dial / DRO reading at TDC at both locations will be the same (but it doesn't really matter).

At this point, the imaginary line connecting the two marked points will be exactly parallel to the axis of rotation.

If the TDC points are on the same side of the bar, and your dial/DRO readings are close to the same, you can safely sweep the top of the bar by traversing the carriage left and right to evaluate the condition of your ways directly (but to be completely accurate, you must find TDC at each location without rotating the bar). Any change in indicator reading indicates that your ways are worn or twisted.

When reasoning about this process, it helps to imagine a test bar with a compound bend kinda like a crankshaft, with two U bends in the vertical and horizontal planes (hopefully your real test bar is more accurately made!). Imagine it's mounted in the spindle at an angle, too.



Imagine how you would need to rotate the spindle and move the cross-slide to find TDC and min/max/avg deflection at different points along such a bar.

The easiest way to measure and remove twist, of course, is with a precision level, NOT using an indicator (ideally, before starting the process above). But this is a really great method to evaluate the condition of your ways after leveling.

Hope this helps someone. I'll sleep better tonight now that I've corrected the mistake!

 

[ZenModeling]

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:

View attachment 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).

View attachment 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?).

View attachment 292766

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

View attachment 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):

View attachment 292768


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!

I’m interested into what the “Richard King” Class is about??? It sounds like something I’d luv to check out…Could you tell me what’s it about ect…I’m new to site & machining…
Thanks Lee

 

[ZenModeling]

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:

View attachment 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).

View attachment 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?).

View attachment 292766

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

View attachment 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):

View attachment 292768


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!

 

[Rex Walters]

I’m interested into what the “Richard King” Class is about???

Richard is still active on this site and elsewhere, but I think he is only holding classes at his home in Minnesota these days. You can find more information including his contact information at handscraping.com. He’s very responsive, but like all of us he isn’t getting any younger.

Regards,
—
Rex

 

[ddickey]

He's got a Facebook group called King-Way Scraping Consultants
As far as I know he is no longer on this site.

 

[Janderso]

You can find him on the PM site.
As Rex said, he has classes in his local area only.
The week long scraping class was outstanding imho.