lathe capabilities

kmartin

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I'm shopping around for my first lathe. I've done all my research, compared models and feel like I know all the features of every lathe from 7x12 mini to 11x24 Logan's. The problem is I'm not sure how much lathe I need for what I need to do... can y'all help?
This will be my first lathe and prototyping LED flashlights and bike lights. I want turn aluminum mainly, not much bigger than 2"x3"x6"long. The catch is I plan on turning off center and cutting internal tapers. I will also be doing interrupted cuts, and cutting fine threads internal and external up to 3" diameter.
I feel like a 7x12 lathe would fit all my needs, but I'm worried about the off-center turning on such a light lathe.
My budget is about 1k and size will be limed to 500lbs. I'm in Oregon so second hand lathes are hard to find, especially Logan and South bend, although Craftsman 6" seem to be abundant.
So, what do you think I need?
 
Interesting dilemma kmartin. A 2"x3" chunk of aluminum turning off center with interrupted cuts and the larger diameter (you say up to 3" OD threading) is going to take some size. Remember you will need clearance for the tool post and cutting or threading toolbit in addition to the final size of the part. Even if it will swing the size stock you need, will the 7x12 lathe have enough crossslide travel? Will if have enough longitudinal length to allow tailstock support when needed? Bigger is better...heft and mass are helpful too. Before purchasing, if possible try to find someone with a lathe in the size you think may work and see if you can set up a chunk of aluminum and swing it, thinking about all the operations you will or may have to do to it to get a finished part. Even if you try it on a bigger lathe at work or maybe a local machine shop, i think the time spent will vastly help your decision process.., and may be a real eye opener too!

Bill
 
Kmartin

I started with 6x12 Craftsman lathe and found that the size was very limiting. Even small stuff with interupted cuts was a pain.

My next lathe was a Logan 9x28. From what you are telling us, that would probably do well for you, only that the spindle bore was 13/16" and you would not be able to pass stock through the headstock on much larger than AA lights. It weighed just over 300 lbs but with stand it clocked in at closer to 600 lbs.

I now have a 14x40 which weighs in at just under 2000 lbs.

The big thing is that you can do small work on a bigger lathe, but it is extremely dificult to do larger work on a small lathe. there are work arounds, but takes a lot of set up and fiddling.

Now anything bigger than 14 or 16 x 40 is getting into a really serious machine and if I had to use the full capacity of those lathes I would need a totally different shop set up with cranes etc as I could not lift the stock in and out.

So my opinion is that you probably want to be looking in the 9x to 14x range, probably settling for something in the 9, 10 or 12 range.

Walter
 
starlight_tools link=topic=2005.msg13073#msg13073 date=1304524449 said:
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So my opinion is that you probably want to be looking in the 9x to 14x range, probably settling for something in the 9, 10 or 12 range.

Walter
I absolutely agree. lathes smaller than 9"are too small for for general hobby machining. They may be adequate for doing things like model building. I have seen guys do jobs, right at the lathe's capacity but working on a machine that is at its max capacity is slow and no fun.

My comment on large lathes for making small parts is that even though you can make very small parts on large lathes, I have found that not to be much fun either.

For my needs and general hobby use, I think 12" - 14" is best. I've owner 10 lathes over the years. They were all 10"-14" I found that the 10's were too small about 10% of the time and barely adequate another 20% of the time. The 12" was too small about 5% of the time and barely adequate about 5% of the time. I moved up to a 14" gap-bed, 3 years ago and would not go larger. It has met all of my needs so far and is quite adjile even for very small parts.

I think a good starter/learner lathe is a 9"-12" belt-drive/back-gear lathe. Once you are comfortable with your skills, you may want to move up to a 12"-14" lathe with a spindle hole big enough for 5C collets (1-3/8" or larger) and posibly a gear-head.

Charlie W.
 
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Good advice so far. I'll add that the length is going to be a big factor too. Since you aren't likely to get a spindle hole large enough to pass a flashlight body, then you will end up using a steady rest . So, when you need to bore, you must consider the length of the part plus the length of the boring bar, all measured from the face of the chuck. 10" part, 10" bar (provided you want to bore through, rather than end-for-end) plus the tailstock which you won't want to remove every time you do a deep bore leaves you looking for a machine in the 28-32" Z length. That you won't likely find in a small, light, bench machine.
 
CharlieW

Let me re-address the comment I made about turning small things in a large lathe.

I find that I can do detailed work on small items in the 14x40 lathe that I have now and I really do not find it too cumbersome. I would however find turning those small items in a 50" x 50 Foot lathe to be absolutley ridiculous. The speed range of the lathe is another important factor. Larger lathes have a lower top end speed which can be a problem when turning small items. My 14x40 has a speed range of 30 to 2200 RPM which gives me really good control even for the really small stuff.

It is always best to get a machine sized properly for the work you are doing. sometimes a couple of lathes is the best solution so that work can be kept in the right range. A small jewelers lathe for the mini stuff and a bigger one.

It is possible to turn items that are longer than the bed on a small lathe as well, again lots of funky set ups.

Walter
 
Walter,
I understood your comment about large lathes. I wasn't considering a 1440 to be a big lathe. I agreed with you on the 10"-14" size being a great general use size. I was not saying that a 1440, especially a modern one, is too big for small parts. I don't type well so I often try and get by without trying to add every detail and exception possible.

I often hear the comment about large lathes and I was just saying that at some point large lathes are not handy for small parts. Your speed range comment is a good example. Many home shop guys go out and get large swing older flat belt lathes that are low RPM and very cumbersom to use on smaller parts.

As I mentioned, I also own a 1440 gearhead with 50-1850 speed range. I was also trying to get accross that lathes are best when sized to the majority of work you do.

I've worked in medical device design and manufacturing for the last 20 years and many of the parts are quite small. We used Hardinge and Levin lathes for some of the prototype parts we needed. Some of the parts were .020 in diameter and had a wall thickness of .0015.

Like we both said, "size appropriate".

Charlie W.
 
Wow! You guys are awesome. I got 10+ good postings in less than 12 hours.
Anyway, I shouldn't of even mentioned the 7x lathe. A 7x lathe is going to cost $500 + 200-300 for tooling and it seems like South Bend's and Logan's with tooling go for a little more than that.
500 lbs was a little arbitrarily made up from when I looked a 11x24 Logan 1920 that weighed that much and was about the biggest I could imagine fitting and moving... I'm graduating College in about 6 months and living in my girlfriends house, so I'll probably be moving withing the year. If i had a garage or shop to place it in I would consider buying bigger.
So, I'm going to scratch anything smaller than 8" off my list. That leaves with minimum of Asian 9x20... which look nice. Or Logan 10+ or SB 9+.... which look much better.
Here in Oregon there seems to be a premium for old iron. Infact, I just found a Logan 11x24 that was pretty "used" with fair amount of tooling asking $1800.... I offered $900 and he said he would get back to me if it doesn't sell.
I'm scouring craigslist and have it setup to contact me anytime a lathe is posted within 200 miles of me. I will also post a WTB on here also.
What do you guys think?
 
Ohh and I'm a long time poster on CPF (candle power forums). They got me started and trained me in the "way of the light" I looked on there for machine advise but didn't find anything. I'll check out that link.
 
You are going to be doing some rather precision work, with fine threads. Don't settle for anything with measurable bed wear. An expert machinist can compensate, but you don't need the aggravation.

My picks would be the Lathemaster 8x14, or the grizzly 10x22 for new lathes. Both are change-gear machines.

Used, a South Bend 9A or 10K, or a Logan 9x17 or 9x28, with QC gearboxes.
Clausings are also good choices, in a similar size range.

At the risk of insulting someone's machine, I'd advise you to pass on the Atlas machines, with the possible exception of a lathe-model squared-head 12x36 cabinet model. You probably won't find a mint machine in your $1000 range though.
 
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