I'm not a wood turner, but I do see some things I would like to do with a metal lathe. I would like to be introduced to the topic by understanding what makes a good metal lathe.
-Brian
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I'm not a wood turner, but I do see some things I would like to do with a metal lathe. I would like to be introduced to the topic by understanding what makes a good metal lathe.
-Brian
Acuracy: It may not make a difference if a turned spindle has 3/32" deep ring when 1/16" was desired... but a metal lathe is generally set up to handle single-mil accuracy... 0.001"-0.005" (and sometimes sub-mil).
Repeatability: You want to be able to create a 0.050" deep ring at the same spot, every time... not 60 mils one time and 40 the next. Try creating a screw without a jig... metal lathes usually come with this built in and automatic.
Speed: Metals generally require much slower speeds than wood. 50-100rpm is pretty typical. Most wood lathes with be several hundred rpm.
Tool stiffness: Holding a wood gouge removes a lot of your repeatability and accuracy. Not to mention it can be near impossible to cut some metals that way... this is where rigid tool posts come into play.
These are just a few of the differences...
I have a 10" South Bend metal lathe and am very happy with it. I am not a skilled machinist but I can machine metal to make it fit. I don't often build things. I use the lathe to repair things around my place. I also have a tool room mill that is made by Bridgeport but has a different name on the name plate. I work with metal more than I do with wood, most of my wood working is in the construction end of wood working and that is generally repairs and construction around my home.
According to a couple of metal working forums that I follow South Bend is one of the more popular lathes and parts are available for many of the older machines.
Accuracy would be the difference. How's that accuracy accomplished? Tighter tolerances, higher quality components. South Bend used to be a good, well built work horse of a lathe. I can't speak for them today, as I haven't run a new one. The main problem with all this stuff is that all the great manufacturers shut down or moved their production overseas. Clausing, Sout Bend, Hardinge all used to be great. You will pay for a good lathe. Good lathes are not cheap. I have a chinese lathe I bought many years ago for my personal use. I had a product I needed it for, just one product, and tolerances weren't a factor. I bought it, thought it was fairly specific to the company I bought it from, then I went to IMTS in Chicago and saw about 20 of the same lathe, each one branded the different. There was one company in China making them, and everyone was branding them as their own. So there wasn't any difference in that market.
I'm sure they have gotten a lot better now, and in most cases, they are all good enough to do small projects. A good one will take some serious cuts in steel with no issues. A cheap one will not.
Want to run the best of the best, run a Hardinge Tool Room Lathe. Oh my......those babies are a true dream to operate. You can't even hear them run.
Regardless of whether you're after a tiny bench top or massive floor model metal lathe you want the machine to be as rigid as possible. Others have said you want accuracy but to my mind accuracy is the responsibility of the machinist. Rather I would say that you want the lathe to be built to pretty tight tolerances so that it can hold a piece of work concentrically and have minimal flex and defelction when the cutting tool is in contact with the work piece.
When it comes to woodworking I have pretty much committed to North American and European equipment - expensive but well made. When it comes to metal working equipment I have used North American equipment and new Chinese made equipment and tooling. I simply can't afford new Western made equipment. This being said, you'll find that the Chinese lathes can be excellent value for the money. Grizzly, which is the preferred brand of woodworking equipment for many around here also carries a line of very reputable metalworking equipment. If you can test a used North American lathe I wouldn't hesitate to go this route either. A tired worn out lathe is good to no one unless they are experts in the field of refurbishment and this is very demanding work.
Sure, but you can only be as accurate as your machine and tools allow... wood lathes simply cannot offer the same accuracy as a metal lathe without major rework.Quote:
Originally Posted by Chris Fournier
As an apprentice working towards my journeysman card as a machinist, I got to run the old worn out lathe all day long. I polished a lot of stuff on that machine because I couldn't get it close enough. It was a bear of a machine and it was my "lesson". Everyone started on that machine. Then you moved to a Jet, which was about 40% crap, so your work got somewhat better, but not there yet. Then you could move up into the better machines. Clausing Colchester (sp?) was a nice one, then the Hardinge.Quote:
Originally Posted by Chris Fournier
If you're running +/-.002" or so, you can do pretty much anything you want on most any machine these days, unless it came from Harbor Freight.
Of course digital readouts make running a lathe a dream. Add a quick change tool holding system and you're in business.
Comparing Wood Lathes to Metal Lathes is like comparing Apples to Oranges. Each has there own purpose. Metal Lathes use a semi auto feeding system for cutting, cutting is done in mm or .001 of an inch. I agree the rigidity must be there. Yes you can only cut to the tolerances the machine was built too, but without the rigidity you wont get the tolerance either. A machine can be built with close tolerance but would not be able to achieve the tolerance without a rigid construction
I'm not sure how metal and wood lathes got compared as I agree, they are cousins at best. Now a wood lathe can be adapted to do metal spinning and these two types of lathes are more like siblings or brothers from another mother perhaps.Quote:
Originally Posted by Ed Harrall
My point was that a lathe is not accurate, the machinist is accurate. A lathe can hold tolerances, how closely a lathe can hold tolerances determines the ultimate accuracy that a machinist can achieve. Perhaps this applies differently when discussing manual versus CNC lathes. While this may seem like nitpicking or semantics, this forum will inevitably have the "tolerances" and metrology threads and then these semantics will be very important.
Ok I understand where you are coming from. I agree that a manual lathe the machinist is the true "tolerance" key. Only experience is the true teacher for this. Some concepts are hard to get though to some people. One thing I have trouble teaching to my students is the fact that the dial readout is 1/2 the diameter of the object that is being turned. It normally takes 3-4 projects for the concept to soak in. I still teach them to read a Mic instead of using a digital readout one. Mostly to make them think a little about the reading they are taking. I also require them on their first projects to grind their own bits. What fun it is for them! Some of the students will go though a full 4" piece of steel getting the first one right. Of course the biggest mistake is getting the steel to hot.
If you're looking to buy a metal lathe take some time and do some research. I'd recommend that you understand what you need for size, horsepower, rpm and feed rate as these can limit you. A small machine just can't do large work, but a large machine isn't very good at small stuff either. I'd never get one that couldn't cut threads.
Having run the best of the best in Engine Lathes, as they are called in the shop I can say that there are differences in the accuracy of the lathe. Being that the spindle bearings run in different classes of TIR ,total indicator runout, and whether or oit you have plain or tapered bearings.
The grade of cast iron in the ways, and whether or not they were hand scraped for parallelism, straightness and whether or not the was are V shaped or flat. Also the type of gears used in the headstock to transmit power effect the finish achieved because of vibration. Whether or not they are ground or milled, hobbed, spur gears or helical, and last but not least the casting material used for the bed, headstock, and carriage.
I have run between just about all of the best American made metal lathes, Pratt and Whitney,Hardinge,cincinatti,south bend,American TurnMaster, Colchester,LaBlonde,Monarch,Lodge and Shipley ,Jones and Lamson Turret, Harrison,, and a few I can't remember: and can honestly say that each one has it's own characteristics.
The lead screw should be hardened and ground to produce nice finish snd accuracy when cutting threads.
Check out homeshopmachinist there is a wealth of information on differnent lathes. I like my 1960's South Bend 10L or "heavy 10" as it is called. It has the ability to cut left and right hand threads. It also has power feed on the carriage and cross slide. The spindle accepts 5C collets. Many other accessories are available.