# Lathe size vs chuck holding size?



## Sparkynutz (Apr 12, 2022)

Looking at lathes and curious if there is any rule of thumb for lathe specs?

Can a 7x16 lathe turn a chunk of aluminum theoretically 7x16 or slightly under? 8.7x23?

Many times they advertise chuck size in description. 
What diameter material can actually be chucked up? Are all jaws reversible so a 4 inch chuck can hold something about 4 inches in diameter?


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## stupoty (Apr 12, 2022)

It can get dificult to get to the edge of a large part for od turning near the size capacity but booring a hole might be ok , also the "swing over sadle" is a factor for longer parts with large diamitor.

(Hope that makes sense)

Stu


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## graham-xrf (Apr 12, 2022)

stupoty said:


> It can get dificult to get to the edge of a large part for od turning near the size capacity but booring a hole might be ok , also the "swing over sadle" is a factor for longer parts with large diamitor.
> 
> (Hope that makes sense)
> 
> Stu


Ah Ha!
Is it that the common specified swing measure is the diameter of a part that will clear the ways, as opposed to being able to be over the saddle, clear of obstruction all the way to the tailstock?

Sure, it makes sense! The manufacturer would claim the larger number in the advertisements.


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## Cadillac (Apr 12, 2022)

A 7x16 lathe would probably max out at 4or5 inches on the diameter maybe 3. And probably 10” on the length. 
 You need to subtract for the saddle on the first number. Then the length you subtract chuck thickness and tailstock.


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## KyleG (Apr 12, 2022)

YMMV, but I find that I run out of horsepower before I run out of size capacity.


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## Bi11Hudson (Apr 12, 2022)

In many cases, especially for smaller machines, the swing and over center length is a marketing gimmick. The marketing 'genius' that came up with the numbers likely has never used a lathe. The only real use of overall swing is when comparing machines of the same general size. 

My small machine is a 9 x 19, between centers. With a chuck on one end and a live center on the other, it closes down real fast. A much more useful number is the swing over the cross slide. The overall swing is more an indication of the center height when divided in half. British machines use center height already, a much more reasonable measure. The swing measurement indicates the maximum size before fouling the shears. Tool positioning is not considered, nor are external chuck jaws.

.


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## addertooth (Apr 12, 2022)

And if you are using the stock chuck on a 7 X 16 lathe, you will run out of how wide it will open pretty early on too, unless you are using "outside jaws".   I have an extended cross-feed on my 7 X 16 (LMS 7350), even so, largest working diameter is about 4-5 inches with everything optimized, and doing small cuts. 

Without the extended cross feed, I lose an inch of travel, so my tool can only get about 1.5 inches from the center line of the lathe.


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## rabler (Apr 12, 2022)

If you are facing or boring on something that is short enough to be held in the chuck only, so that you don't need to run the carriage under the part, and can hold if from inside (i.e., it is already a hollow cylinder or has a recess in the headstock side) you can get pretty close to the swing over ways figure.   For example you might face off the bandsaw marks if you cut a short piece of 6.5" pipe.  But you'd have trouble turning the outside.  So it is possible to contrive a situation where could use very nearly the full 7" diameter.

The point being depending on what you need to do, you might be able to use the full stated diameter in some limited circumstances.  Similarly with the length.  But you'd never be able to turn a full 7x16 piece.  One of the challenges in machining is planning out the operations you need to do within the envelope of your machines.   There are tricks to pushing these limits, steady rests and through the headstock are examples, plenty more exist.  But as you push the envelop more, you generally take more time,  more setups, and have to accept larger tolerances.


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## addertooth (Apr 12, 2022)

Steady rests can help, but good luck finding a steady rest for a 7 X 16 lathe, which will pass a 5 inch diameter piece of stock.  I just measured mine, it has an internal diameter (ID) of 2.5 inches.  As I said earlier, you can only screw the cross-feed about 2 to 2.5 inches back from the center line, which limits the maximum Outer Diameter (OD) you can cut.  This is assuming he has additionally purchased the extended travel mod from LMS.  Here is a comparison picture below.  It shows the original on the right, and the extended version on the left.


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## Larry42 (Apr 12, 2022)

Disclaimer: I know nothing about mini lathes! I put this out there so you can see what kinds of loses you get from a stated lathe size to actual maximum work piece. My lathe is a PM1440. It can swing 14" over the bed and 20" if I take the gap bed out (have never done that.)Theoretically I could put 40" between two dead centers BUT I couldn't machine to the ends. I would need some way of driving the work. Dog on a Faceplate is probably the shortest. If the work was small enough in diameter I could just let it pass through the spindle bore. Mine is a MT5 so 1.5". Some lathes have started using a "MT5 1/2" but that is odd, it does allow bigger work to pass through. 

Now we get to the really true limiting things. Power! I suspect most mini lathes are using variable speed motors. As the speed is reduced so is the available power past a certain point. Depth of cut is a function of both available power and machine rigidity. (Perhaps plastic gears also?) Feeds on the carriage and  (cross slide?) Control finish and rate of material removal. Not normally a limiting factor. Available threading sizes w/o needing to do gear changes? Metric & imperial? Swing over the cross slide 8.5", cross slide travel 6.75", compound travel 3.5", Carriage travel 37". So for most things the maximum diameter would be less than 8.5" VS the 14" swing over the bed. 

Look at things being done online to get an idea of the size projects you can do with your lathe of choice.  It is also totally true that you will spend as much on tooling and accessories as what the lathe cost! Almost everyone does up grades to their Chinese lathes. Think of them as Kits. It is worth paying a bit more from a reputable supplier. Watch Blondihacks.

And one last thing you will want to spend $ on... a Mill. The two make a set.
Have fun, be safe, wear eye protection!


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## Aaron_W (Apr 12, 2022)

Sparkynutz said:


> Looking at lathes and curious if there is any rule of thumb for lathe specs?
> 
> Can a 7x16 lathe turn a chunk of aluminum theoretically 7x16 or slightly under? 8.7x23?
> 
> ...



No, but not in a false advertising sense. A 7x16" lathe can physically mount a piece 7" in diameter, but not one 16" long because the carriage / cross slide will interfere. Similarly it can physically mount a piece 16" long, but at nowhere close to 7" in diameter.

16" is the distance between centers, which specifically refers to holding work between centers. Using a chuck will reduce this by a couple of inches. Using tooling in the tail stock (boring bar, drill bit and chuck etc) may reduce this length by several inches.

The nominal swing specifically refers to holding work with a faceplate and there are severe limits on the work that can be done as the carriage and saddle will get in the way.

As to a realistic work envelope, the between centers distance is fairly accurate for turning, and even facing, but drilling or boring is probably more like 10-12" at most. The swing over the cross slide (a more meaningful measurement) on the 7" lathes is around 2-1/2". Lathe designs do vary so while the 7x16 mini lathes have a practical swing of around 2-1/2" another brand / design of 7" lathe could be a little more or less that that despite having the same swing simply due to the carriage being designed to ride a little higher or lower on the bed.

Also 7x16 (or whatever) is simply a nominal size actual is often a bit larger or smaller.

Same goes for chucks, a 6" chuck is 6" in diameter, some may be able to hold a work piece a maximum of 6" in diameter, some 6-1/4" some only 5-1/2" so when shopping for a chuck it is good to look at the specs, not all 6" chucks are made equal.
Also worth looking at the size of material that can pass through the chuck. Buying a chuck with a 3/4" bore to use on your lathe with a 1" spindle bore means you are limiting your options with the chuck. Rough rule of thumb is a chuck should be 50-60% the swing of the lathe so a 7" lathe will usually be found with a 3 or 4" chuck, a 10" lathe a 5-6" chuck. 4 jaw chucks can often be a little larger than a 3 jaw.
You could put a 6" chuck on a 7" lathe, it will fit and turn, but unless only holding a very tiny part the jaws will hit the ways of the lathe.


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