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Minimum HP on mini-lathe for stainless steel cutting?

The_Apprentice

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#1
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...
https://www.princessauto.com/en/detail/1-3-hp-mini-metalworking-lathe/A-p8507659e

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.
 

markba633csi

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#2
Your equation neglects the efficiency rating, most likely the HP would be closer to 1/3 or 1/2 HP.
Mark S,
 

The_Apprentice

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#3
Your equation neglects the efficiency rating, most likely the HP would be closer to 1/3 or 1/2 HP.
Mark S,
I had been thinking on that. But when I did some research, I read that efficiency is only thrown in when going the reverse, calculating backwards starting from HP.

In any case, I get more suspicious on things. Even using 100% efficiency, the 3 Amps and 110 Voltage from the Craftex lathe (for example), is quite a bit under the 1/2 HP that is listed... either I am still missing something, or it's a little fraudulent where companies are rounding 1/3 values up to 1/2 when ever they can for a better sale...

In any case, I will try calling King Canada tomorrow and see if anyone is bright enough to know the hard HP value of theirs.
 

tq60

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#5
Lots of marketing simply do same regarding motor size.

Basic math to what it consumes but not what it does.

Just think how cars would be rated...

Issue with stainless is work hardening so small cuts are somewhat out but small power in machine tends to direct one to that.

No clue to how these will work with your plan but you could request test drive or demo of them if you have some material to cut then see how they operate.

If your budget is a grand one can go old iron and do far better where they can locate say an old sb 9 size then if a bit more power is needed simply swap the motor.

Many options

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

The_Apprentice

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#6
"Lots of marketing simply do same regarding motor size."

But does most marketing also claim their lathes come with a quick-change-gearbox, when this does not seem to be the case? I noticed these Chinese lathes keep indicating this, when I see so no such thing. Even after reading through the on-line manuals... no such thing. Yet outside box indicates there is a QCGB.

Grrrrrrrrr.
 

tq60

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#7
Them folks can work "quickly" to change the gears....

One can quickly change the gears since they are just under a simple cover...

"Quickly Changable Gears in a Box"...

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The_Apprentice

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#8
Well, I sent King Canada an email today of some information on their (hidden HP)...

"We typically do not use Horsepower because it can be very misleading. We are required to use amps as a rating. I will give you an example and you can draw your own conclusions. Grizzly has a very similar model that is 3.3 amps and calls it a 3/4HP, which is high by any calculations or conversions that you find online. Ours is a 5.5 amp. and therefore would be higher."​

I do know the KC looks almost identical to the Grizzly (with minor differences), but the Amps may be one of the better selling points. Especially since I can pick it up practically for the same price.
 

tq60

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#9
Amps at what volts and what power factor?

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shooter123456

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#10
I had been thinking on that. But when I did some research, I read that efficiency is only thrown in when going the reverse, calculating backwards starting from HP.

In any case, I get more suspicious on things. Even using 100% efficiency, the 3 Amps and 110 Voltage from the Craftex lathe (for example), is quite a bit under the 1/2 HP that is listed... either I am still missing something, or it's a little fraudulent where companies are rounding 1/3 values up to 1/2 when ever they can for a better sale...

In any case, I will try calling King Canada tomorrow and see if anyone is bright enough to know the hard HP value of theirs.
I had a Harbor Freight 7x12 which looks to be the same as the ones you are listing. They advertise as having 3/4 HP, but thats pretty much nonsense. I also have a HF mill advertised as having a 4/5 HP motor (roughly 600 watts), but it isn't even close. When tested, it was never drawing more than 350 watts. However, the motor says it is rated for 110v @ 6 amps which gets you to the 600 watts they advertise. I would say its dangerously close to false advertising, though technically they aren't wrong. The motor is rated for a max of 4/5 HP, but the mill itself is only capable of a little under .5 HP.

I am pretty sure the lathe I had was 250 watt tops. I cut plenty of 303 stainless with it with no trouble, I would just have to take light cuts. I also could never get HSS to cut well on that little lathe with stainless, so it was always carbide inserts. I cut 304 stainless a few times and it wasn't easy, mainly because of the lack of rigidity on the little lathe. I needed to cut at least .01" deep to actually take a cut, and there was so much deflection, I had to go in .0175" to get it to take that .01" cut. Not fun, but it got the job done.

I have a 10" lathe with a 1HP motor now and it cuts 304 with no trouble. If I was planning to cut that regularly, I would start bigger.
 

shooter123456

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#12

DAT510

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#13
HP ratings are misstated on equipment from from all parts of the world. My Campbell Hausfeld 30 gallon compressor was part of a class action suit a few years back. Turns out Campbell Hausfeld rated/marketed their compressors at "Max" HP vs "Continuous HP" My compressor was supposedly a 5HP 110v machine. To achieve 5HP at 110v is 34+ Amps, which is not 110v circuit one would normally have access too. In reality it was a 3 HP compressor. They ended up giving all effected owners $50 in Campbell Hausfeld products.
 

Bob Korves

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#14
My 110v shop vac is rated at 5.5 hp. As if. I suppose the motor might put that out for a few milliseconds under some scenario as it was undergoing self destruction and the white smoke was pouring out... Until we turn the boats around and send the misrepresented goods back, it will continue. And China is not at all the only bad guy. I see product misrepresentation everywhere. It is difficult to compare horses to ponies... Demand truth in advertising (and in politics...) In the meantime, we are watchdog and quality control as well as buyer.
 

Wreck™Wreck

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#15
Machine friction and the weight of the rotating components aside the determining factor for power required is the Metal Removal Rate, this is often expressed in cubic inches per minute.

In other words a 5 horsepower machine will in theory run a part 4 times faster then a 1 HP machine by way of higher speeds, feed rates and depth of cut, only you can determine what you time is worth.
 

Ken from ontario

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#17
So it sounds like that mini lathe with "1/2HP" motor and mediocre rigidity will most likely not be able to cut stainless steel as the op (the-apprentice) was hoping for.
 

mikey

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#18
So it sounds like that mini lathe with "1/2HP" motor and mediocre rigidity will most likely not be able to cut stainless steel as the op (the-apprentice) was hoping for.
I dunno' about that lathe but I've turned a fair amount of stainless on my little Sherline lathe with a good tool, and it has about 1/2HP with limited rigidity to boot. I will admit that it won't hog off huge chunks of 304 but it will cut it in small bites without too much trouble and will do so accurately. A lot depends on the tool and the user.

Looking at just HP is like looking at only one facet of a diamond. What about available speeds, spindle bore capacity, threading range, chuck mount configuration, longitudinal power feed and so on? All the features that separate one lathe from another can be very important and the power of the motor is only one consideration.
 

Desolus

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#19
I had been thinking on that. But when I did some research, I read that efficiency is only thrown in when going the reverse, calculating backwards starting from HP.
Unfortunately math can not be made to work that way.
 

The_Apprentice

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#20
I heard someone on here refer to the descriptions as "Chinese Horsepower"

LOL. It does seem we should make that catch-phrase stick, otherwise more hobbyists will run into these nasty surprises.

I also noticed a lot of sellers either purposely, or accidentally keep inflating the values of HP of these chinese lathes. 1/3 gets extrapolated to 1/2. And 1/2 to 2/3, and even now there is a seller on Amazon selling a listed 2/3 Grizzly as a 1 HP unit. Despite I saw at least one person leaving negative feedback stating a warning to inform others.
 

tq60

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#21
If one looks at LRA or locked rotor amps it is the amount of current the motor can pull under those conditions.

Others use a fully loaded to point of stalling or still others may use starting current that could be much higher than breaker rating for miliseconds.

Some time ago we found some documentation explaining how the different devices were over - rated this way.

Any type of motor will only draw the rated current when performing rated work so the little 600 watt motor very well could be running at 250 until the depth of cut is increased to the point that the spindle hp requirement gets there.

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Desolus

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#22
It has also been my experience that chinesium motors fry the first time you get close to stalling, where american made motors can generally take more abuse. It's not a hard and fast rule, but in my opinion should be taken into consideration when purchasing equipment.
 

shooter123456

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#23
I heard someone on here refer to the descriptions as "Chinese Horsepower"

LOL. It does seem we should make that catch-phrase stick, otherwise more hobbyists will run into these nasty surprises.

I also noticed a lot of sellers either purposely, or accidentally keep inflating the values of HP of these chinese lathes. 1/3 gets extrapolated to 1/2. And 1/2 to 2/3, and even now there is a seller on Amazon selling a listed 2/3 Grizzly as a 1 HP unit. Despite I saw at least one person leaving negative feedback stating a warning to inform others.
I have seen the same thing. Precision Matthews had a machine listing that said it had a 1.5 HP motor and noted "This is the same motor used on machines of similar size, but other distributors choose to round it to 2 HP."

Even when they are somewhat accurate with their HP ratings, they often do it on draw instead of HP at the shaft. So all the energy lost to heat, friction, sound, etc is included in the HP rating.
 

Bob Korves

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#24
I don't know if they still do it, but in the old days Rolls Royce (under)stated the horsepower of their automobiles as "adequate." If only manufacturers had that mind set instead of undercutting the competition today, we might have more top quality stuff made again...
 

darrin1200

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#25
I would almost say, that both the King Canada and the Craftex are the same lathe, just different labeling. If you are near a Busy Bee, I would recomend it over the King Canada. I have recieved good help from the guys at the Ottawa store.

As for if this will do what you want, I do not have any where near the experience to answer that. Hope you find what you need.
 

The_Apprentice

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I would almost say, that both the King Canada and the Craftex are the same lathe, just different labeling. If you are near a Busy Bee, I would recomend it over the King Canada. I have recieved good help from the guys at the Ottawa store.
I have indeed visited Busy Bee, and took a quick examination of their lathes. There are some differences though, maybe close but not quite the same.

Interestingly, I have seen quite a few very negative threads on this site in regards to Busy Bee.
 

Ken from ontario

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#27
I have indeed visited Busy Bee, and took a quick examination of their lathes. There are some differences though, maybe close but not quite the same.

Interestingly, I have seen quite a few very negative threads on this site in regards to Busy Bee.
That unfortunately is true , it must have something to do with their "after sale service" that some customers complain about ,I've heard there has been some improvements made in that regard, and to be fair , their good customer service varies .some say it depends on the individual stores and the people who manage them , I've never had a bad service from the Busy Bee store in Pickering/Salk road , good enough to keep me going back in year after year .also have heard praises of the one in Ottawa.
 
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royesses

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#28
I don't know if they still do it, but in the old days Rolls Royce (under)stated the horsepower of their automobiles as "adequate." If only manufacturers had that mind set instead of undercutting the competition today, we might have more top quality stuff made again...
Yes I've heard that. In the 60's and 70's GM under rated HP by up to 200 in order to comply with corporate rules and make insurance companies happy.

Roy
 

The_Apprentice

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#29
LOL, interesting stuff.

One thing I learned by Rolls Royce, is way back in the 60s they would make their machinists watch a medical video that showed what procedure one had to go through when getting brass swarf in their eyes. Everyone had to watch the video, which was very gruesome because doctors could not use magnets to remove them from the eye. Also, it was a procedure that involved no anesthetic at the time for these types of eye operations.

After people watched the clip (many fainted), people were much more dependable on making sure eye protection in the factory was worn at ALL TIMES.

Just reading about it, makes me never want to risk chances. I've seen my father undergo operations from milling/lathe slivers, and that was more than enough growing up.
 

jouesdeveaux

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#30
I have worked a fair amount of 304 round bar on a 7X12 (Grizzly G8688) with 3/4 HP and have had no problems with it. I use carbide insert cutting tools and have worked on bars from 0.060" in diam. to 0.50". I get the best finish using a relatively high RPM. On 0.25:" and 0.50" diam rods , I've dine cuts of 0.015" with no problem. The critical thing especially with small diameters is to use collets and work very close to the chuck to avoid deflection of the work piece..
 
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