Enough HP for mini-lathe?

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The_Apprentice
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Enough HP for mini-lathe?

Post by The_Apprentice »

I am very new to the hobby (though long ago I did have experience in machine-shop in high school).

I would like to purchase my first ever mini-lathe, but the horse-power is what worries me. I am wanting to work on creating some jewelry, as well as other small metal projects. This may involve working on 15mm diameter round bars, to 2-inch diameter tubes. The material will usually be either 304L stainless steel, or 316L stainless steel.

The main worry here, is if these mini-lathes have enough power for harder metals like that? I have read reviews of some of these mini's as stalling at times, to the point of being un-usable.

Being in Ontario Canada, there are mainly three choices to choose from.

Princess Auto sells a 1/3HP lathe for around a grand. I think enough is said on that...

BusyBeeTools is seeing a 1/2HP lathe for just under a grand (due to Father's day weekend sale).
http://www.busybeetools.com/products/la ... cx704.html

And the other choice I have is KING CANADA. Which is in the same range:
http://www.kingcanada.com/detail/7-x-12 ... 0712ML/308

Maybe I am over-simplifying things, but the last one does not mention HP rating on the motor. So doing some simple math, their motor is 5.5 Amp, and since voltage is 110V, 1 phase, 60 Hz....

That should give us:
(110 * 5.5) / 746 = ~.81 hp.

If I am oversimplifying this, please let me know of my mistake, LOL.

So, going with King Canada, I am getting more than 3/4HP of power on my mini.

Does this make sense, and would this seem sufficient for machining 316 SS material?

Thanks in advance all.
ccfl
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Re: Enough HP for mini-lathe?

Post by ccfl »

These all have permanent magnet brushed DC motors, with PWM DC speed control driver boards. Essentially the same drive system as treadmills.

I have found the typical 7x lathe motor fine, but the controllers have annoyances. There are adjustments for overcurrent, ramp-up speed, minimum speed, and so on. These adjustments are not documented, not marked which pot does what on the board, and likely different brands use different boards. The simple solution is to ditch the original control board and replace it with something robust and user-friendly. KB Electronics KBMG-212D has a lower minimum speed, higher max speed (current), offers brake-to-stop as opposed to the original board's coast-down, and it's all adjustable, and comes with full documentation. You can also use your own user-friendly controls, like a proper FWD-REV switch like a big boy lathe. It doesn't support start-stop via momentary buttons but you can do it that way with some additional electrical bits.

Watch ebay for them, normal average price is ~$100 but if you're patient they can be had for half that. Be careful when searching, there's a nearly identical model, KBMG-21D, that only does 1A output. KBMG-212D will do 10A (can be configured for less, if you feel the need).

My suggestion is to replace the controller first and keep the stock motor, see how you like it. A real controller makes a world of difference.
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Cary Stewart
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Re: Enough HP for mini-lathe?

Post by Cary Stewart »

I suggest that you take a look at Sherline at www.sherline.com
Their lathes have enough HP to do what you have described and are the right size also. Their build quality is excellent but not Jeweler's lathe level. The Unimat 3 would mount the sizes you state but are way under powered for that stainless 316.
Cary
John Evans
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Re: Enough HP for mini-lathe?

Post by John Evans »

I think HP is your least worries trying to machine 304 SS on those lightly built flexible lathes.
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Harold_V
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Re: Enough HP for mini-lathe?

Post by Harold_V »

Before making any decisions, you'd be well advised to consider the surface speeds that will be required to successfully machine those grades of stainless, neither of which are fun to machine. That said, each machines reasonably well, assuming you don't try to remove a lot of material in one pass, using a heavy feed. Work hardening is also an issue with those materials, so it's important that you not allow the tool to tarry in cuts. That's a recipe for instant hardening and failure.

If you attempt to remove material beyond recommended surface cutting speeds, your tooling will suffer premature failure, so you don't really have a lot of wiggle room, and some of those small lathes are notorious for spindle speeds that are way too fast.

To give you a guideline, 75 feet/minute would be the maximum you should entertain, and you'd be well served to run slower, especially if you run dry (no cutting oil). That said, the maximum speed for 2" diameter stock would be 143 rpm. At that speed you would require the greatest torque available from the motor, depending on the depth of cut and feed rate. Rigidity plays a huge role in what type of cut you'll be able to take, and none of the miniature lathes are known for being robust.

Shoot for a lathe that has a bottom speed of 100 rpm, or slower. You won't regret having slow speeds for the material you intend to machine---especially if you entertain the idea of machining titanium. You would be better served to buy a somewhat larger machine.

H
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earlgo
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Re: Enough HP for mini-lathe?

Post by earlgo »

The 1958 ATLAS 12" bench lathe catalog specifies a 1/2 to 3/4 HP motor. The lathe I have has been using a 1/3HP motor for 50 years or so, and it takes a stupid move to stall it out. I'd guess if you put a 1/3HP motor on a mini-lathe you will have enough to break things.
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SteveHGraham
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Re: Enough HP for mini-lathe?

Post by SteveHGraham »

Machining 304 is not something I would want to do often on a mini-lathe. It work-hardens like crazy, and any machine that just tickles the work instead of ripping through it seems likely to work-harden metal.

My mini-lathe has a 550W motor, and it seems fine for this size machine.

Don't get a 7x10 or 7x12. Get the longest one you can find. There isn't a lot of space on mini-lathes.

You can do fine work on a mini-lathe, so if that's your only choice, go for it. If you can go a little bigger, you will have an easier time, and you could get a quick change gearbox. The only real advantage of the mini-lathe, to me, is that you can carry it around by yourself.

Don't forget Littlemachineshop.com.
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The_Apprentice
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Re: Enough HP for mini-lathe?

Post by The_Apprentice »

Well, I picked one up on Friday, but it will be a while before I will get around to trying it out.

I will probably pick up some cheap carbon-steel first to do my trials on, been a long time since I worked in a shop. As I understand, I can always get a stainless steel with sulfur added to cut easier into it.
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Harold_V
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Re: Enough HP for mini-lathe?

Post by Harold_V »

The_Apprentice wrote: As I understand, I can always get a stainless steel with sulfur added to cut easier into it.
Correct, but you're not limited to sulfur. 303Se has selenium added for free machining, and it machines somewhat better than 303S. You also have the option of using 416, which is the best of all for machining, and offers the opportunity for heat treating, assuming you'd find it necessary. Both of the 300 grades are non-magnetic (although slightly magnetic in a work hardened state), while 416 is magnetic.

Stock lists also show 203S, but I have never knowingly encountered that alloy in my many years in the shop, so I can't address its qualities. It is reputed to have slightly better machining characteristics than either of the 303 alloys.

H
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RSG
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Re: Enough HP for mini-lathe?

Post by RSG »

The_Apprentice wrote:Well, I picked one up on Friday, but it will be a while before I will get around to trying it out.
What did you end up going with?
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The_Apprentice
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Re: Enough HP for mini-lathe?

Post by The_Apprentice »

I ended up with King Canada. But I've been soooooo busy this month, I haven't even had a chance to clean the lathe, never mind giving it a test drive. Will try to get around to it before the weekend is out.
RSG
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Re: Enough HP for mini-lathe?

Post by RSG »

Let us know how you like it!
Vision is not seeing things as they are, but as they will be.
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