Headstock and spindle shaft upgrade question

Vazbro · Jan 20, 2018

Hi guys,
I am a new member and wonna be garage machinist. I say wanna be cause I haven't used a lathe yet. That being said, I have already purchased a SB 9C and tore it down completely to powder coat the parts and rebuild whatever necessary to bring the lathe to top shape before using it. However, I have a concern.

The headstock bearing area and spindle shaft have some scratches and I was wondering what would be the best way to address this issue. I've read somewhere in the forum that the SB9 is limited to 1400 RPM. If I've not mistaken, this is due to the metal to metal and the lubrication system. I wanted to upgrade to a DC brushless motor in the future as well and I thought the best way to get rid of the scratches and at the same time be able to take advantage of the higher RPM DC motor upgrade in the future would be to machine the headstock/spindle/both to press in couple of high speed/high temp capable bearings. What do you think of this solution? Are there any negatives about doing this?

I was also thinking to find a good used headstock and call it a day. Or even buy a used headstock from a newer year model with the copper bushing that I can buy and press into the headstock. Of course I welcome any other suggestions you may have. Here are some photos for your review. Thanks in advance for all the help.

iwananew10K · Jan 22, 2018

Not to sound negative but it's a horrible plan.

Can't see your pics either.

michiganbuck · Jan 22, 2018

QT: [bearing area and spindle shaft have some scratches] If not raised such scratches will do no harm.. If raise then a fine flat hone and then cleaning away any abrasive will do.

Dobermann · Jan 22, 2018

OK, I'll go ahead and sound negative!

Running an old SB 9 with cast iron bearings at high speed is an invitation for a bearing failure and spindle score problem. The RPM recommendations for those machines were pretty well thought out. Adding a high-speed DC motor to the mix is not going to do anything for you. The newer machines with the bronze bushings were not all that much more tolerant of high speeds either

Turning operations on a vintage SB lathes are all about sharp tools and moderate speeds. They are capable machines but they are not high speed heavy duty machines. You may want to re-think your machine needs.

iwananew10K · Jan 22, 2018

Another thing no one seems to consider is the threaded spindle...people go on about how dangerous it is to turn in reverse(which is fine IMO at low speeds) but don't think about the very real possibility of a spindle seizing at high speed...

johnoder · Jan 22, 2018

What do you think of this solution? Are there any negatives about doing this?

Pure sillyness

Forget high speeds with SB

Start educating yourself here, and do realize its entirely possible to make great parts with slow speeds - its been happening for at least 200 years

http://campkahler.com/files/How_to_Run_a_Lathe_SB_1of2.pdf

http://campkahler.com/files/How_to_Run_a_Lathe_SB_2of2.pdf

michiganbuck · Jan 22, 2018

I think to have a plane bearing that would be closes enough at cold-start and still close enough and not seize at full warm up is a factor..Likely a 3000 rpm PB spindle would be a little too loose at cold start. Perhaps a pressure oil system would be needed and an oil cooling system…. and still for much non production machining 1450 is pretty fast.
*Think one of my old books said about 2100 was a limit to consider..but don't what book that was.or what type or what machine.
Yes bronze grinder bearings run fast but many needed a warm up time to make them run at best.

These old CI bearing machines were designed to run around the clock with not a seize so likely they would run to 2,000 for a few hours if willing to chance a shot spindle. Likely if some people are doing that they could post it here...and we should not beat them up..IMHO.
Machines are best run to the manufactures specs..

Redesign the head is a poor idea..Yes some guys here could do that, even build a machine from ground up... ...

Derek Smalls · Jan 22, 2018

You've got a bunch of really good advise so far. Here's a bit more. Get your machine running, as is.
Being a 9c, it's a limited but capable machine. Use it to learn, both how to run a lathe, and to figure out what kind of work you will be using it for and how it suites that work. Then you will know exactly what it's short comings are, OR aren't, as the machine's abilities relate to you and your work. At that point, you will know exactly what you need and want in a lathe and you can modify what you have or upgrade as you see fit.
Until then, it's like talking about what kind of tires you want to buy but you don't know if you'll be running the Indy 500 or plowing snow with them. :nutter:

thomasutley · Jan 22, 2018

Some good advice above.

There are real-world physics problems running too fast. Plain bearings (aka hydrodynamic bearings when lubricated with oil) rely on a thin film of lubricant to keep metal from touching metal. There's a physical limit to the PSI the oil can support without the journals touching each other. Add too much side load, or get the oil too warm (thin), or cause the oil to cavitate from high speed relative motion and bad things happen fast.

I have a VFD on my 16" that lets me turn the spindle at nearly 1800RPM (or faster, but I have the max frequency output limited to 90Hz at the motor). Doesn't mean I can get away with running that fast for very long or any time at all under heavy off-axis cutting loads. I'm willing to spin it up for a minute for light finishing cuts on small diameter parts held in a collet, but I keep my hand on the bearing cap to feel for any heat creeping in.

Finally, there's also a safety issue with old-school cast iron chuck bodies. They can only handle so many RPM before centrifugal (centripetal?) force causes them to explode. I'd be nervous running my original 1943 10" Skinner chuck up to 2000RPM.

kitno455 · Jan 22, 2018

There is not really enough meat in the headstock casting to take a reasonable bearing. Run it at the speed it was intended, with good oiling, and it will outlive you. Doing otherwise will just ruin it.

allan

Rudd · Jan 22, 2018

The CI bearings and spindle on my 13 were/are scored, it's been 15 years since I've seen them so I don't recall if it was quite that bad. I stoned down the high spots and put'er back together 15 years ago (with new wicks). John Oder gave me the advise to do that IIRC. I keep oil in it, haven't had any problems. The 13's bearings are segmental, not pure cylindrical like your photos.
Give it a go, what have you got to loose?

v8packard · Jan 23, 2018

thomasutley said:
Plain bearings (aka hydrodynamic bearings when lubricated with oil) rely on a thin film of lubricant to keep metal from touching metal. There's a physical limit to the PSI the oil can support without the journals touching each other. Add too much side load, or get the oil too warm (thin), or cause the oil to cavitate from high speed relative motion and bad things happen fast.

To add to this, the bearings should be pressure fed with oil if you are going to run at high speeds for long duration. With the size of your spindle and the area of the bearing I would guess you would want a continuous 20-30 psi at speeds 2000-2500 RPM. Perhaps a bit higher under load. Unfortunately there is no practical way to add this to the spindle without considerable re-work and engineering.

Properly adjusted and lubricated the stock machine produces beautiful work within its capacity. The top speed of 1400 or so may be slow for small diameter soft materials machined with carbide, but HSS will get things done nicely on that lathe.

Best of luck to you!

Marc

m-lud · Jan 23, 2018

I have a few of those groves in my 16. When South Bend
designed those cast iron bearings with the lateral groves the intent was for the groves to fill with oil and distribute oil the width of the bearing.

My concern is with the wick in the center of the bearing if you have good oil coming into the bearing and flowing outward. The groves cut by earlier contamination could give the oil an escape from following it's full intended path.
In other words a damage cut grove a half inch from the edge of the bearing may not be getting oil distributed to that last half inch. The oil will follow the easiest path.
I would like to fill the damage groves with something to stop the flow of oil around those damage groves to prevent that possibility. I don't know if they could be hand filled with Babbitt or solder. Then there is the chance of that coming loose and causing damage. Being that soft it shouldn't.

iwananew10K · Jan 23, 2018

Ok, it can see the pics now.

For the bores simply stone any high spots, and add the felts back in to the groove at the top.

For the spindle stone those adhered lumps of CI off. Reassemble,oil,and adjust clearance to spec.
Use it as is or sell it.

johnoder · Jan 23, 2018

Thumbnail provides some visible WHYS the 9C is unsuitable for high speeds

Head stock casting DESIGNED for the huge superprecision angular contact ball bearings on the Hendey

Then scroll down to another essential - MASS - only a little more swing than the 9C, but a full TON of iron - or five times that of the longest bed 9C

m-lud · Jan 23, 2018

Your pictures just started showing on my computer.
That has been ran without oil. You can knock all the high spots off with a fine file but you may be out of luck with the spindle wear.
Either line bore and go brass/bronze or replace the unit.
As a printer I have seen brass bearings that ran twenty fours a day for years on end before needing replacement. It's all about keeping them oiled. There are to many factors other than the bearings themselves to try to make it run faster. Balanced upper and lower drive for example.
That's a different bearing design than my 16 so ignore my previous post.

v8packard · Jan 23, 2018

thomasutley said:
I'd be nervous running my original 1943 10" Skinner chuck up to 2000RPM.

I get nervous with mine at 900...

michiganbuck · Jan 23, 2018

I think a lathe should turn what it was designed for..Needing more one should buy that lathe.
For high production work the jobs should be able to afford the machine.
For one and few-ups a slow machine can do most anything..1450 is not that slow..

I am not seeing the photos... Guess one could fill groves with the likes of two part epoxy after cleaning with acetone..then hone/file to make surface true match.. likely I would just leave it alone..low Temperature solder might work.. think we had some for 180f degrees (have to check on that)
We had a plane bearing grinder glass coated the reground to needed specs. it lasted for years and was still good when we closed the shop..no not suggesting that on an old lathe.

Headstock and spindle shaft upgrade question

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