Downside to big spindle bores

I have noticed a lot of new machines are offered with large spindle bores where previously they never did..

An example of this is say 16" manual lathes, in the heyday of manual machine tool production in the 60's and 70's they would have had a D1-6 camlock and a 2" spindle bore..

These days a 3"spindle bore on this size machine is much more common....Considering realistically manual machine tools of today are not as well engineered as in years past due to CNC being king there must be a downside to these big spindle bore lathes, otherwise they would have been fitted as standard back in the 50's, 60's and 70's...

Decreased stiffness could be a problem but I doubt it. The old heavy iron was designed for large roughing cuts with carbon steel and HSS. This nowadays has been replaced with lesser cuts at high-speed with carbide. Lighter spindles would be an advantage in achieving higher speeds in the headstock. A comparison of the spindle speeds along side the spindle bore sizes would be educational.

The down side is probably the increase in cost of spindle bearings, in the past precision bearings were much more expensive (relatively speaking) because they were made in places like the US, Germany, and Japan. Today bearings are made in China, India, and Korea and they are cheap by comparison. I design machine tools for a living and I can tell you the bearings are the cheapest part of spindle assemblies.

I think the manual machine manufacturers of today have reassesed the applications their machines are used for and they have found the majority are used in one off and repair operations where the machine that has the most capability in the smallest space is king. In the old days shops bought a machine based on the work they did which was usually production and a machine was only expected to make a limited variety of parts.

I concur with JR. Precision grade spindle bearings are lower cost in proportion to what they were 40 years ago. They're also a bit more reliably precise thanks to sub micro-inch gaging apparatus now available and superior metallurgy.

If there is a downside it may be a less accurate axis tracking taking all spindle, bearing, and housing errors into account. Personally I don't think so. The few modern lathes I ran spindle roundness specimins for resulted in errors less than 50 microinches deviation from circularity Good enough for me.

Those of you who do work needing certifiacation for dimetral circularity really should consider running specimens and get your spindle certified. The rest of us can muddle along taking such things for granted. I ran tests on my lathe when it was new in 1971 and a few times therafter. It still turns pretty round. I think

Those of you who cheaped out and replaced your machine tools original precision spindle bearings with ABEC grade 1 and equivalent bearings should run a specimin. It's an eye opener when the cal lab returns a cert with a potato shaped trace and note the error runs in the low thousandths of an inch. I ran a lathe like that. Couldn't machine a globe valve seat to save your soul. Every one was a leaker.

The advance in materials and precision in bearings has also led to much thinner bearings that have the same or more, load & RPM rating than in the past. This allows a larger bore without a larger headstock.

downside was/still is lower rpm
my 5" youji will only do 1200 max

Once was a time when the thermal affects on a “Big Bore” machine were significantly greater as a condition of accuracy. Fluctuations in temperature and the resulting instability were overcome by running upfront warm-up cycles. I would imagine this would still exist on cheaper CNC or conventional machines.

J-Head said:

I think the manual machine manufacturers of today have reassesed the applications their machines are used for and they have found the majority are used in one off and repair operations where the machine that has the most capability in the smallest space is king. In the old days shops bought a machine based on the work they did which was usually production and a machine was only expected to make a limited variety of parts.

Click to expand...

I agree with this also. Likewise, gap beds used to be relatively rare, now they seem to be standard. Shops are less willing to buy more lathe capacity than they need just to get a large spindle bore, so builders are upgrading their machines to make the sale.

I have been told the larger bores are due to oil field work. This helped us out as we needed to buy a new lathe with a 3" bore. The work we run on this particular machine has nothing to do with oil field work. We actually got a machine with a 4" bore as that was the smallest they offered, we bought a 30" x 120" Lion lathe.

Big spindle bores do need a different approach to chucking smaller work. In general the common scroll chuck design has a maximum practical centre hole diameter of around 1/4 OD. So for real large bore you need either a plug in chuck system for smaller work like the common 5C systems or alternative means of holding small work. Not a problem for oil-country lathes as these are really bar work machines.

Often forgotten that the conventional lathe is a centre lathe designed for between centres or geometrically similar work when used anywhere near its design capacity. The drilled spindle is almost an after thought allowing bar type work on smaller material as a sort of handy extra. In the UK at least gap beds were pretty much the norm except for true tool-room lathes.

Thing that surprises me is that plain bearings haven't made a come-back. Modern materials and oils should have killed the old speed limitations. Modern seals should permit proper pump feed lubrication as per automotive practice. Shell bearings are cheap and very accurate these days.

Before the financial crisis killed any chance of funding the beast I spent a bit of time looking into doing a cheap, updated machine for the lathe in a corner with a semi-skilled operator firms. Currently the haunt of well aged South Bends, down at heel Colchesters, hacked off Harrisons et al. Base concept was a Heavy 10 (ish) size machine with 4" bore spindle in pump fed palin bearings with up to 5,000 rpm capability optimised for positive rake carbide insert tooling. Heavy exploitation of cheap PC derived technology to get rid of expensive bits, but not CNC (as you know it anyway). Gearbox, feed screws who needs em! Its amazing what can be done with web-cams and lateral thinking. Purely an "I can do it" indulgence to keep the post retirement brain cells active of course and I never did get round to tracking down the engineering references needed to sort my variant on a chucking system.

Clive

"Often forgotten that the conventional lathe is a centre lathe designed for between centres or geometrically similar work when used anywhere near its design capacity. The drilled spindle is almost an after thought allowing bar type work on smaller material as a sort of handy extra. In the UK at least gap beds were pretty much the norm except for true tool-room lathes."

Interestingly enough, the first lathe documented to have a through bore spindle was made in the Westford/Chelmsford Massachusetts area (about 10 minutes from here). Again, we see that changing industry needs have dictated lathe spindle design.

Thanks everyone, I was just curious whether in my never ending quest for a machine whether there was a disadvantage to having a big bore in a small machine..

The only disadvantage I can think of is that it's more difficult to mount small chucks because the large bore will mean a larger spindle face. For example, a 2" bore will have a D1-6 face and will easily take an 8" chuck, a 3" bore will have a D1-8 face and normally the smallest direct mount chuck for a D1-8 will be a 10" chuck. You can custom order them or mount a smaller chuck on a larger face place if desired.

"I think the manual machine manufacturers of today have reassesed the applications their machines are used for and they have found the majority are used in one off and repair operations where the machine that has the most capability in the smallest space is king. In the old days shops bought a machine based on the work they did which was usually production and a machine was only expected to make a limited variety of parts"

Also, I think it is just market forces, everybody wants that big spindle. Bad news is that the modern mid sized lathes are pretty lame and are basically a disposable item. Instead of a $200,000 100yr investment, they buy 10 of the $20,000 junk lathes.

Conversely, Mud, one may end up in the situation we are in on our Summit... spindle bore is 1/4" bigger than the chuck bore. Might go in the spindle, but you can't get the work there to begin with. Yeah, I know, you can bore out the chuck, but what kind of idiot sells a lathe with a chuck that has a smaller hole than the spindle.. especially when that big hole is the selling point (and the ONLY advantage that machine has over a boat anchor).

There is no doubt that a big spindle hole can be a great advantage in repair or one-off work. Working bar fashion rather than centre or chucking style can save material and, frequently gives much easier set-up. The extra room oop t'ole turning a lot of tricky jobs into simple chuck work.

However if you decide to design from first principles around a really large spindle bore on a fairly modestly sized lathe at an affordable price, ruling out tons of accessories, the thing evolves into something very different to a conventional lathe. The conventional way ends up as a slightly slimmed oil country lathe. Affordable and oil country don't go together. Modern technology and methods let you do things very differently. To my eyes the conventional lathe, especially the Chinee economy Kerry, Harrison, Colchester style near copies, is in many ways as obsolete as the Holtzapffel.

Just need a good lottery win to go out and prove it!

Clive

Clive,

You could do some pretty interesting things with a large spindle and pressure pumped bearings. Not just pumping a lot of oil, but using pressurized pads to center it, like an air spindle. You would only need bronze or whatever for moments when forces exceeded the pressure and caused contact. It should be very smooth. Certainly better than the 9" Logan, which in my opinion can only be called a lathe by the grace of God. At one point, I was making optical mirrors on one and had to lap out the sunburst pattern the cheap ball bearings printed on the face.

Bill

Interesting thread...

One way to get some of the undoubted setup advantages of a big bore lathe (mentioned by Clive) on a beer budget :

- Save, from the scrap yard, a heavily built, good quality old school lathe with a small bore and a long bed with most of the wear up near the chuck, then build a really long (ie deep) bell-housing style backplate for the chuck.

This is effectively a big bore spindle, mounted at the rear end to the spindle nose of the former lathe

Take a reasonable sized 4 jaw and bore it out to same ID as the bell housing. (A full sized chuck gets too heavy for the purposes of this kludge)

Make a beefy fixed steady to support the bell housing, right behind the chuck, with pressure lubed pads per 9100's post (for occasional use) or use a proper bearing, in a custom housing mounted off the ways, possibly braced back to the headstock proper.

IF the lathe is seriously big, or it has massive steadies, you could no doubt get by with just using the OEM item for occasional use.

The accuracy of the ways on formerly good lathes is often still good once you're a foot or more towards the tailstock. This kludge won't do big bar work, but very good for medium length things, like large hydraulic piston rods with integral flanges at the front end, as often used on big presses. You can fine tune the lateral position of the steady to make it turn exactly parallel.

The 'bell housing' can be provided with tapped holes at intervals for cat-head style internal support - something a bit difficult to arrange on a big oil country lathe unless the workpiece goes all the way though the spindle.