How is a Lathe Measured?

How is a lathe measured? I see one that is 7" x 10", then another more expensive one that is 8" x 12". Where are such measurements taken and what would be the differences?

Thank you.

Reply to
JWho
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OK, further Distance between centers: 10'' Swing over bed 7"

So, naturally, one questions causes more. Are lathes normally measured like this?

What is a "swing over bad"??

Thank you.

Reply to
JWho

In the US, the first number is the maximum diameter workpiece that can be rotated over the bed, in the UK it's apparently the radius. Note that this dimension may shrink when you crank the carriage in close to the work - there's a smaller number for swing over the cross slide.

The second number is the maximum length of workpiece that can be held between centers, one on the headstock and one on the tailstock, like on a wood lathe. If you install a chuck on the headstock this distance will shrink some.

Another number often hidden in the specs but of great importance is the size of the through hole in the headstock. This governs what size barstock you can feed through, allowing only a little bit to hang out of the chuck where you can work on it easily. While you can saw off chunks for each part, that's very wastefull. For your bushings for example, you'd probably want a lathe with at least 1" through hole. In practice, smaller 9" swing bench top lathes are usually just over 3/4", while larger 12-13" swing models can usually handle something like 1

3/8". Some of the little tabletop lathes like the sherline have a through hole less than 1/2", a major annoyance since 1/2" stock is so usefull.
Reply to
cs_posting

Cubits!

Reply to
Tom Gardner

Go here for more info on mini lathes and mills. Good info for beginners.

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Reply to
mlcorson

Hi. Thank you for the reply. I understand what you mean on the diameter of the workpiece. I am in AL, USA, by the way.

When you say chuck, is that similar to a chuck on a cordless/electrical drill, just special for a lathe? It's for holding a tube or rod or similar, correct?

Here is the one I am referring to.

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At the bottom, it has, "Through chuck capacity: 5/8" ". Is that the same as "through hole in the headstock" that you mentioned? Would that make it unable to use some size of solid rod, or would it just make it less convenient or use more rod?? I am not 100% sure what that means to me.

Thanks! This newsgroup is great!

Reply to
JWho

I'm there! Thanks!!

Reply to
JWho

That's advertised in their retail store for $369.99. They emailed me a 20% Off coupon. That makes it $296 That is very tempting.

Rex

Reply to
Rex B

Well, sorta in that it used multiple jaws to hold things, but it's much larger and heavier and designed to take side loads that a jacobs chuck (drill chuck) couldn't.

Yes, same dimension. What it would mean is that if you wanted to make something like your bushing out of stock thicker than 5/8", you would need to saw off a pice that you could hold in the chuck. You'd do all your turning, then probably use a parting tool to turn the section you want off of a wasted stub left in the chuck. Wheras if you had a larger through capacity, you could just work on the end of a longer piece and only part off what you need when you are done.

Reply to
cs_posting

wrote in message news: snipped-for-privacy@g14g2000cwa.googlegroups.com...

As another example, suppose you wanted to machine some fittings at both ends of a long shaft. Say 15 feet long or so and that you just wanted to turn 2" at the ends down to 1/2" say. If the through hole in the headstock is 1/2", then the largest diameter shaft you could turn would 1/2". If the headstock hole was 3", the maximum shaft diameter would be about 3" .. in both cases, the length is limited by the room you have in your shop to the left of the lathe because only a little bit has to stick out into the working part of the lathe -- the 2" length you wanted to machine. Now suppose that you headstock hole is 1" and you want to turn the ends of a 10 foot shaft, 1.5" in diameter. Can't be done on that lathe .. at least not with reasonable convenience. You would be limited to a length slightly less than "the distance between centers." The hole through the headstock is generally much less than the hole through a chuck. That's a property of the chuck, not the lathe. Of course, if you have a 3" hole in the chuck and a 1" hole in the headstock, you can't push your work further in than the point at which the work touches the spindle.... at least not twice on the same lathe. The size of the hole through the headstock is far more important in a production setting where the material is being fed through the headstock to the cutting tools. Since most home shop machinists rarely turn long, large diameter, shaftings, the issue is mostly a matter of convenience and wasted material, as pointed out earlier... until, of course, that day when you absolutely must have that larger diameter. That's the first order approximation. Now for some refinements of the idea. You should always keep the working part (the place you are cutting metal) as close to the headstock as you can. That cuts down on chatter (you'll learn about that soon enough), and makes it easier to hold accuracy all along the piece. A long piece much be held at one end by the chuck and at the other by the tailstock point. The longer that distance, the wobblier the work becomes .. with many attendant problems. For that reason, working long pieces not partly in the headstock means you'll have to use a steady rest or a follower rest or both. The third order approximation... For very accurate work you do all the machining between centers, with nothing stuch through the headstock hole.

Get hold of the lovely little book "How to Run a Lathe", originally published by South Bend, but now available very reasonably from Lindsay publication.

Reply to
Boris Beizer

HUM! I think I see what is meant now! One can work on a rod longer than

10" as long as it is 5/8" thick or less, correct? Assuming that is correct, then your points on it being more and more wobbly as the rod got longer makes perfect sense. Right now, I can only think of two parts I would ever make, and neither is longer than 10". Before this, I thought every rod had to be inside the two centers.

THANKS, gentlemen!

Reply to
JWho

Actually you can't work a thin rod anywhere near the capacity length of the lathe, because it will flex and chatter, rubbing against the tool rather than cutting smoothly. You can probably only turn something a few diameters long that is hanging out of the chuck, a bit longer if it is also supported at the tailstock end. With something really long and thin, you could work an area near the headstock, and a shorter area real near the tailstock center, but not in between. And you'd have trouble drilling the hole for the tailstock center, since you couldn't support the work near where you'd be drilling.

I'm going to guess that for half inch stock, the practical limit for chuck support is less than 3" maybe 4.5 or 5" if you support the other end with the tailstock. Could be wrong though, lathe has been in storage fora few years.

Incidentally, long piece hanging unsupported out of either end of a lathe's headstock can be quite dangerous - either the end you are working on, or spare stock hanging out the other side. They invariably flex, and the more they flex the more the rotation makes them flex even more - with the result that they can end up flailing around whacking expensive stuff like you, crashing into the bed, or in an extreme case even knocking the machine over.

Reply to
cs_posting

All that you mentioned is just for a rod that is over 10" though, correct? I think the thing I would want to make is about 8" or 9". I can envision what you mean on it wobbling. It would be like a fiberglass rod. Pretty soon it is like a lasso. :-| Sounds dangerous!

Thanks.

Reply to
JWho

The rule of thumb is never to go more than three diameters unsupported .. and that is pushing it. If the job is done between centers, or between a chuck and a tailstock center, then it is supported on both ends and you can go 4 to 6 diameters without intermediate support. You can go longer and thinner than this in two (actually, three) ways.

  1. Very carefully, with very careful adjustment of the tool height, light cuts, and very, very, sharp, properly sharpened, tool bits.
  2. Use a steady rest. This is an intermediate support that stays fixed on the lathe bed. Gives you an additional support point. A bit of a PITA if you're machining the whole length because you have to move the steady rest if it is on the spot you want to machine. Has to be reset for each pass.
  3. A movable steady rest.. called a "follower rest." This attaches to the carriage and moves along with it... typically behind the cutting tool. Has to be reset for each pass.

A word of caution on long things in small lathes that fit through the headstock. If the stock sticks out of the headstock's left end more than ten or twenty diameters, it will wobble, and eventually bend. This happens quite catastrophically since the more it bends, the greater the centrifugal force that makes it bend even more. The least it will do is bend your stock to uselessness. Somewhat worse is deep gouges in your workbench, or even worse, removal of sundry body parts that are in the region.

Boris

Reply to
Boris Beizer

Thank you for the additional information. I saw one of those steady rests on the HF site.

I had mentioned making a part besides some bushings. It turns out the final product is 10.5" and over 5/8" wide. So basically, I can not make it on the HF $350 7" x 10" lathe, correct?

Thanks.

Reply to
JWho

Correct----most of the time. The tag on my old South Bend reads size "14

1/2 x 72" The 14 1/2 is the swing diameter over the ways. The 72 is the total length of the bed! I've never measured center-to-center, but suspect it is around 32.

Bill

Reply to
Bill Marrs

Reply to
EdFielder

Thanks for the information. That "actual working distance" was the kicker on the Harbor Feight 7" x 10" lathe. :-(

Reply to
JWho

This is actually incorrect, at least in the US.

"Swing" is max diameter able to turned over the ways.

"Bed length" is defined as the *total* length of the bed.

In the UK it's swing radius X bed length between centers.

Jim

Reply to
jim rozen

You've got to be careful. The first number is the diameter that can be turned over the ways (though sometimes it's the radius, but that's usually pretty obvious). The second number is EITHER the total length of the ways, OR the maximum distance between centers. It's totally inconsistent. I've seen my Craftsman lathe sold on eBay as a 12" x 32" (length between centers) 12" x 36" (length between headstock and end of ways) or a 12" x 48" (length of bed). You have to be careful. I nearly bit on a South Bend ~10" x 24" one time until I looked closely at the pictures and realized the 24" was the length of the ways. Maximum length between centers, ~8" I'd guess.

Jim

Reply to
Jim McGill

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