Need advice for repairing damaged SB 14-1/2” lathe

[SLK001]

I'm saddened by your lathe tipping over (but then, we did warn you!!). Before you get too carried away with buying new parts, I would go thru the lathe, examining all the cast iron parts for cracks. As you say, CI is very brittle. A shock like your lathe saw may have propagated to other areas of the lathe and cracked castings right and left. Only a very close examination may reveal the true extent of the damage. I would suspect that the entire carriage suffered damage beyond the external visible exam.

The taper attachment you may be able to live without. As @Dabbler has said, he has never used his. I use mine all the time. You will have to decide if your usage warrants replacing the broken parts. Keep us posted.

SLK "saddened by your plight" 001

 

[rwdenney]

I have inspected the lathe, particularly the carriage, in detail. No, I haven’t magnafluxed it, but so far I can find no further damage. I think one reason is the rear saddle gib was not very tight providing some rebound space. The screw seems to have born the brunt, and I looked very closely at the front of the saddle through which the screw runs, and there’s no damage there that I can find. I really think the taper castings took the energy from the buckling screw—those are much lighter castings than the front of the saddle. The taper attachment acted like a crush zone. The next thing to contact ground after that would be the switch extension, but I don’t even see a scratch there.

But time will tell. I’m buying used parts at used-part prices. I can sell them that way, too.

As to the I-told-you-so, I’m beating up myself enough for the both of us.

Rick “has to fix it to see if it can be fixed” Denney

 

[rwdenney]

Parts arrived. One difference: The screw is for the later 14-1/2 with ball thrust bearings on the cross slide screw. It requires a sleeve with shoulders inside to capture the bearing washers, and my sleeve (which is for the older version that used solid bronze thrust washers) lacks that shoulder. No problem--the seller also had the sleeve, so that is on the way. I have new thrust ball bearings in hand.

The castings fit perfectly. My connecting bar is bowed by a sixteenth and binds when the slide is drawn to the ball handle end of its travel, so I will have to machine that flat. That surface provides no bearing when sliding, so it does not need to be precision machined except to be reasonably flat and square, and I will contemplate how to get that done. I need a milling machine! But that is only required for the taper attachment to function.

The nut is a replacement nut commonly found on ebay. It's very tight--a bit too tight. I need to study it to see what's making it tight. The screw is pristine, which is awesome.

(The outer smooth section of the screw is made for the ball thrust bearings, and has a smaller diameter than the same section on the damaged screw, so I need to make the full conversion to the ball bearings.)

Rick "progress being made" Denney

 

[Dabbler]

very nicely done!

 

[SLK001]

The nut is a replacement nut commonly found on ebay. It's very tight--a bit too tight. I need to study it to see what's making it tight. The screw is pristine, which is awesome.

Measure the threads on your new shaft (using the three wire method). It should be a Class 3A thread. The nut is a Class 3B thread and is most likely finished with a Class 3A tap. The original nut was bronze, but most of the ebay replacements are brass (I haven't found a bronze copy). You may be encountering a war between fits of different classes, especially if your two vendors aren't the same person. Color your shaft (no, the new one) with a Sharpie, then thread on the nut. If the problem is on the top of the thread, then you may be able to chuck up the leadscrew and sand some off the top. If the problem is on the flanks, you might have to lap the new nut (use the old leadscrew as the lapping device) until you get a good gliding fit.

 

[rwdenney]

Measure the threads on your new shaft (using the three wire method). It should be a Class 3A thread. The nut is a Class 3B thread and is most likely finished with a Class 3A tap. The original nut was bronze, but most of the ebay replacements are brass (I haven't found a bronze copy). You may be encountering a war between fits of different classes, especially if your two vendors aren't the same person. Color your shaft (no, the new one) with a Sharpie, then thread on the nut. If the problem is on the top of the thread, then you may be able to chuck up the leadscrew and sand some off the top. If the problem is on the flanks, you might have to lap the new nut (use the old leadscrew as the lapping device) until you get a good gliding fit.

I hadn’t thought of lapping it in. Good suggestion.

But I need to test a bit. I only hand-fit it on the keyed portion, which sees no wear (or use) at all, and didn’t go beyond that point. The thread looks pristine, but I haven’t mic’d it, so it may loosen up a bit when it gets past those unused threads. And I was testing dry.

I just had a hour yesterday to try some stuff, so the real work of fitting that screw has not yet begun.

Rick “needs to replenish the lapping compound stock anyway” Denney

 

[rwdenney]

Quick update: no pics today, but I installed everything on the taper attachment except the sleeve (still on the way) and the connecting bar. This includes installing new 5/16” alignment pins, which were quite tight.

The steel tie rod was bent, but I was able to straighten it in my 20-ton press. The taper attachment appears to work perfectly. I had to spend a good bit of time stoning the dovetails on the taper slides—I’m not sure that taper setup has been used in many decades and there was a lot of corrosion and dings.

But my big smile this evening as I sip celebratory Scotch is with the cross slide screw. Once I really cleaned the screw really thoroughly using a wire brush wheel on one of my grinders, and once I decided to just make the nut get past the keyed section, it started moving with just enough running tolerance to be smooth but with very little lash. I chucked up the end of the screw in a cordless drill (the shaft through the taper attachment is less than 1/2”) and spun it back and forth with Tap Magic to run it in. Installed and oiled with the operating oil it is now smooth over the whole range.

Backlash is 0.010 from the thread fit. I’d be happy with that in a new lathe. As long as I adjust the ball thrust bearings with zero backlash (which ball bearings will do), I’ll be able to preserve that value. The old screw was .050.

The tapered gib in the compound was kinked on one end and was adding a lot of drag at one end of the travel. I found a replacement gib and problem solved. All the gibs are now installed. The backlash on the compound is 0.015.

All that’s required for the taper attachment to be fully restored is to machine flat (or find a replacement for) the connecting bar. It would be easy to make one of these from steel plate, and I may do that instead of trying to machine the cast iron connecting bar. That can happen later.

Next task will be to install the proper sleeve for the ball thrust bearings, and it should be here Monday. That will restore normal lathe operation, and I can then make a few things.

And then modify the shoulder bolt I bought from McMaster for clamping the cross feed nut to the cross slide. As it is now it’s usable, but it sticks up and would prevent turning the compound in a full circle. At that point, the repairs will be complete and I’ll be on to the general overhaul the lathe needs.

Rick “there will be pics” Denney

 

[rwdenney]

Latest installment. TL;DR: Lathe is fully operational.

For the curious, here’s the difference between the older solid-bearing taper attachment and the newer ball-bearing model. First, the bearings themselves fit inside the sleeve that fixes the cross slide screw to the taper bed. The solid bearings were washers placed at the ends of the sleeve, not inside it.

The bearings:

They fit in the end of the sleeve at the left. Note that the opening in the sleeve is much smaller. The old one is on the right.

Because the later sleeve contains the bearings, it is longer.

The screw is narrower where it goes through the taper attachment. The old screw is at top. But the narrow section is a close fit in the sleeve.

The sleeve going in. It fixes the screw to the binder stud using a taper pin the runs in the slot. The grooves at the ends feed oil to the ball bearings.

All together. The tie-rod clamp is parked at the tail—no need to drag it around if not using the taper attachment. Installing it in the tie rod takes ten seconds. The connecting bar is damaged and needs to be machined or straightened before it can be installed, but its only purpose is to pull the cross slide with the taper (and to keep chips out of the screw when not using the taper). That will have to wait. I ran the lathe using the half-nut power feed through the whole range of the taper attachment, and it works perfectly, but for the connecting bar.

Using a dial indicator, I measured 0.009 backlash on the cross slide in the sweet spot.

I found an expensive shoulder screw from McMaster that works perfectly for clamping the cross slide nut. I made first chips drilling a hole through it for the oil.

I tapped the hole for 1/4-20 to use the original plug screw, but drove the cheap tap too deep and broke it. I’ll probably make the screw, but for now the big Allen-wrench cavity makes a good oil cup, and the oil just drips through the channels in the tap. That bolt is $22, but cutting the head off it and milling in a screwdriver slot (plus the oil hole) would make it just like the original. It sticks up too much as it is and interferes with the compound. I was happy to see that the tailstock drilled a well-centered hole.

I also carefully leveled the lathe using my Starrett 98-12. The leveling adjusters I used made it easy to match the level of the head and tail, and to raise the tail enough to level it longitudinally. That will be good enough until I can turn a test bar.

Rick “recovered from the mishap except for the bowed connecting bar” Denney

 

[brino]

Great photos and description.
I bet it will be useful for others in the future.
Thanks for documenting it all so well.
Brian

 

[rwdenney]

Quick question...I'm thinking about scraping in the connecting bar, just because I can do it here without a mill. I'll need to take off about .060 at the high spot. Is that nutty? And if not, what kind of scraper should I get? I see Anderson scrapers but don't know how to buy carbide inserts for them. There's also a guy in England who makes them and who supplies carbide inserts.

The part does not need ultimate flatness--probably 5-10 thousandths tolerance is plenty good enough--but I am hogging off a lot of material.

I am also rooting around for some steel bar stock, which I think I can use to fabricate a replacement connecting bar that might even be an improvement on the original.

The nose bows down at the tip. It's fine for the first 4 inches of the slot, but further out than that binds against the binder stud on the taper attachment.

(I just watched a Youtube of an Australian guy truing up the gasket surface of an exhaust manifold using a 4" hand grinder instead of a scraper--even that would probably be good enough except it would look terrible. His definition of flat was effective sealing against a gasket. I think his bluing showed about three or five points per square inch, but it showed them all over the surface. But he took off about the same amount of material I need to remove to flatten that connecting bar.)

Rick "a mill would be better" Denney