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rustdreamer
08-01-2017, 03:31 PM
Lets say you have a lathe or mill with a 5hp motor when it came from the factory.
Will a machine run and function will with a smaller motor say 3 hp?

pinstripe
08-01-2017, 03:45 PM
Sure. The feed and speed calculators will tell you approximately how much hp a tool/cut needs. I think one spindle hp per cubic inch of metal removal per minute will get you in the ballpark. Remember that the machine will have internal losses, so you won't get all 3 hp at the spindle.

Toolguy
08-01-2017, 04:46 PM
Many home shop metal cutting machines are in the 1 to 2 HP range to begin with. Most Bridgeports have a 2 HP spindle motor.

Norman Bain
08-01-2017, 05:30 PM
My second hand lathe was purchased with a 3-phase dual speed 750/1400 7.5HP motor. Changed it to a single phase 4HP motor that ran at the higher 1400 RPM speed.

It works just fine. It does take a pretty deep cut to load it up and it never seems stressed to the point of risking a stall. In fact the whole lathe sounds/feels better when it is loaded up some.

Making cuts to change diameter by 3mm (1.5mm DOC) in steel is common for me and I do not mind the chips running blue. I can and do occasionally hack off 4mm and sometimes 5mm, but those in my amateur hands feel like abuse.

doctor demo
08-01-2017, 06:23 PM
Well, there is no substitute for horsepower except time, to a breaking point of nothing being accomplished.
I have run lathes with half horse motors and lathes with 50 horse motors.
My lathe at home (now) has a five horse motor on it and I would like it more if it were double that:).

When I had my Axleson (I had to give up during a move) it had a 25horse on it and was my go to machine for a quick job.
I have no idea what a phase inverter and step up transformer would cost or what it would do to my residential electric meter for that size, but my swmbo would not have allowed it anyway:(.

Steve

larry_g
08-01-2017, 06:43 PM
Lets say you have a lathe or mill with a 5hp motor when it came from the factory.
Will a machine run and function will with a smaller motor say 3 hp?

Yes, probably. Not all machine tools come with a standard frame motor so finding a replacement of any horsepower could be a challenge. The more specific you get on your questions the better the answers you get will be.

lg
no neat sig line

Tundra Twin Track
08-02-2017, 12:28 AM
Lets say you have a lathe or mill with a 5hp motor when it came from the factory.
Will a machine run and function will with a smaller motor say 3 hp?

My 18"x60" Lathe came with a 10 hp I changed it out with a 5 hp 1ph and has worked flawless.The milling machine I refurbished had a 7-1/2 hp and I changed it to a 5 hp as well.

flylo
08-02-2017, 02:10 AM
Plan on it doing 1/2 the work at the same speed as the original motor or 1/2 the metal removed at the same speed as it probably takes 1/2 HP just to keep thing turning you cut the available power in half which for a home shop may be fine. I have to ask as cheap & plentiful as 5 HP motors are why the switch?

J Tiers
08-02-2017, 02:25 AM
You probably need FAR LESS than you think.

Ever put a current meter on the machines?

I have a small horizontal mill that has a 1/4 HP motor. I have put a 2" slab mill on the machine, and pushed it to what I figured was the mechanical limit of the forces I was willing to apply to the machine, but have NEVER stalled the motor.

MattiJ
08-02-2017, 02:43 AM
You probably need FAR LESS than you think.

Ever put a current meter on the machines?

I have a small horizontal mill that has a 1/4 HP motor. I have put a 2" slab mill on the machine, and pushed it to what I figured was the mechanical limit of the forces I was willing to apply to the machine, but have NEVER stalled the motor.

Ha!
I have stalled my weeble 1.5hp lathe more than once, as well as tripped the thermal motor protector numerous times.
If you wish to use only HSS you probably hardly ever run on the power limitations but with coated carbide tooling most older lathes are under powered in many cases.

pinstripe
08-02-2017, 03:31 AM
Ha! I have stalled my weeble 1.5hp lathe more than once, as well as tripped the thermal motor protector numerous times.

I'd believe it. I've seen your parting off video :) 3 hp should be plenty for HSM though. That's about what you get with a 14" lathe these days.

Black Forest
08-02-2017, 07:59 AM
My mill has a 4hp motor for the spindle and sometimes I wish it had more. My lathe has a 14hp motor and I would miss those horses if I had less. Granted I use it for farm repairs and often have to turn a 50mm or larger diameter down to much less and I can do it quite fast on my lathe.

boslab
08-02-2017, 09:36 AM
I'd noticed newer 5hp are smaller than the old ones, better steels etc, but although they say 5 I'd guess it's really pushing them, we had lots of new motors of the same size etc on the plate that failed quickly, ran baking hot, the only choice was fit a bigger new motor than the old motors if rewinding wasn't practical
Mark

smithdoor
08-02-2017, 10:43 AM
Yes it will work just fine on 3hp
You find some will say bigger is better
If look at BRIDGEPOR mill start at 1/2 hp mill and for decades was 1 hp Today the same or Clone may as high as 5 hp on the same mill.

I did in my shop to save tool and the machinist.
Your machine gears will last longer by reducing the horse power
In home shop this also reduced the cost or wiring too.

Dave



Lets say you have a lathe or mill with a 5hp motor when it came from the factory.
Will a machine run and function will with a smaller motor say 3 hp?

Tundra Twin Track
08-02-2017, 11:45 AM
Plan on it doing 1/2 the work at the same speed as the original motor or 1/2 the metal removed at the same speed as it probably takes 1/2 HP just to keep thing turning you cut the available power in half which for a home shop may be fine. I have to ask as cheap & plentiful as 5 HP motors are why the switch?


I don't think doing half the work with half the HP covers the entire spectrum of work, when you are doing large dia pieces is where I could possible use the 10hp on the lathe.When I had 3" shaft in lathe was taking 0.125 cuts that I thought was pretty good,maybe with 10 hp I could take 0.250 cuts.

In the mill I have taken 0.250 cuts with face mill,there is a lot $&@? flying around,with 1" end mill I have cut aggressive enough to make me nervous but power never seemed to be issue.

The Lathe came with 4 B width belts going from motor to headstock,I only use 2 with the 5hp if they start to slip I have other issues!


Don't forget I am not a real machinist,just a farmer lol!!!

flylo
08-02-2017, 11:47 AM
I may be wrong but didn't the specs regarding rated HP change in the last 75 years? For some reason I thought the old rating hate to be sustained & the new rating just had to "make" the rating & not sustain it for a long period of time.

smithdoor
08-02-2017, 12:23 PM
Yes if trying to sell tools add more power it is cheep and they make more sales
Back in 80's I had lathe it used a 30 HP need 480 v it cost $10,000 for new power meter to run this lathe. If only just change to motor I would have save $10,000

Dave


I may be wrong but didn't the specs regarding rated HP change in the last 75 years? For some reason I thought the old rating hate to be sustained & the new rating just had to "make" the rating & not sustain it for a long period of time.

Forrest Addy
08-02-2017, 01:35 PM
These days of variable frequency drives and their low cost for 2HP and under (new) and their ready availability (used) in larger sizes leads me to suggest it would be a mistake to change out a three phase motor for a single phase in acquiring machine tools for the home shop.

There is no escaping a little analysis. Local availability, budget, connection, etc have o be considered as a whole.

A week or two of hassle selecting, buying, and installing a VFD compared to years of infinitely variable, very smooth and efficient motor operation make the VFD/three phase motor decision a no-brainer except in those cases where a small budget is an absolute deal breaker.

I've had VFD's on my machine tools since they became affordable in the mid '90's and never, ever had a problem with them that wasn't of my own making: perplexing mis-wire of a control station, noisy pot (don't use junk box parts for work intended to last), mis-entered parameter and that's about it. Diagnosis maybe an hour, fix in minutes.

wierdscience
08-02-2017, 02:10 PM
I may be wrong but didn't the specs regarding rated HP change in the last 75 years? For some reason I thought the old rating hate to be sustained & the new rating just had to "make" the rating & not sustain it for a long period of time.

Recommended service factors changed a bit IIRC.

J Tiers
08-02-2017, 03:26 PM
A few who have both semi-commercial operations, and industrial machines, are quite possibly needing more.

But I stand by the deal with the mill and the 1/4 HP. I think that motor could break something on the mill, when it is in backgear and munching away.

The Logan.... I have 1/3 HP and the motor is an intermittent duty door motor fully enclosed and has NO FAN. I have NEVER stalled it, the belts slip way before the motor is stressed. In the years I have used it, I have run into thermal limits two or three times. If it happened any more, I would put a cooling fan on the shaft.

old mart
08-02-2017, 03:51 PM
At the museum, the lathe runs 1.5hp three phase, and the mill has 1.5hp single phase, these ratings are plenty for HOME use.

MattiJ
08-02-2017, 04:19 PM
At the museum, the lathe runs 1.5hp three phase, and the mill has 1.5hp single phase, these ratings are plenty for HOME use.

HOME use can be virtually anything. 1.5 hp is plenty if you only make miniature steam engines but awfully little if you have 40 ton excavator bushes and axles on table..

I have coffee pot sized milling machine but I also know fella who has two monstrous milling machines and chinese 18' lathe with 4" spindle bore (and two smaller lathes) on his hobby garage. He is not even the one whose hobby train is 1:1 scale steam locomotive ...;)

J Tiers
08-02-2017, 04:29 PM
If you do industrial work, you need industrial machines. If you don't do that, well, then you do not.....

That should be obvious.

The machine makes a difference also. There are 12" machines that need very little, because they are Atlas, and would be twisted into a pretzel by too much of a cut. And, there are 12" machines that will use 3 or 5 HP and ask for more.

One size definitely DOES NOT FIT ALL. Some may need to be reminded of that from time to time, as they loftily sneer about folks with smaller machines "taking all day to get anything done, peeling off tiny threads of metal", and never considering that those people may not be trying to do the same things.

philbur
08-02-2017, 06:08 PM
Geared head lathes can use up a lot of hp at maximum revs.

Phil

flylo
08-02-2017, 06:37 PM
Lets say you have a lathe or mill with a 5hp motor when it came from the factory.
Will a machine run and function will with a smaller motor say 3 hp?

Yes it will, just not as well & not to the capacity it was designed for or do the work it's designed for. It it were the case I bet my truck would run on a 6.5 HP motor, probably go down the road but not have stellar performance & I dought the motor would last long.

Forrest Addy
08-02-2017, 09:43 PM
I've run lathes ranging from 1/6 to 200 HP and many in between. HP is roughly equivalent to stock removal capacity per unit of time. Machine robusticity could be said to equate to ability to resist cutting forces, shock, and vibration, transient overloads from collision and wrecks.

There is no virtue in accepting weak under-powered machine tools just as here is no particular glory to having the biggest and toughest. If your machine suits your work flow and you are satisfied with its performance cojnsider your blessing. If you are frustrated by lack of stock removal capacity and you feel a need to re-power consider the condition and robusticity of the available machine tools for a motor retrofit.

Some machines can be re-powered by motors up to three times that recommended by the manufacturer PROVIDED due caution is exercised in which speeds and feeds are selected for heavy cuts and which tooling is employed. Selecting the wrong combination may be a ticket to failure or machine damage. This requires insight and working up to the target operating level by gradual steps until you determine just what level of spindle speed, feeds and tooling the machine can withstand. You cannot bluffly walk uo to an over-powered machine tool and start hacking away at a large hunk of alloyw steel with the latest and greatest stock removal tooling without expecting anything from a spindle stall to disaster.

Most spindle transmissions are torque limited. My personal engine lathe has a 20 RPM bottom spindle gear. My present spindle motor has 5 HP at 1750 RPM. That works out to 15 ft lb at the shaft. The spindle transmission at 20 RPM has a, 87.5 to 1 reduction. 87.5 x 15 equals 1132 Ft lb torque. The final reduction gear on the spindle is 5 Mod 40 teeth. Using the Rush Gear HP calculator and entering tooth count, face width, alloy steel case hardened material etc such a gear will safely transmit 2.7 HP at 20 RPM at a pitch-line force of 2500+ lb. I calculated safe HP for every gear pair in my lathe spindle transmission because I once had a 10 HP motor on it. There were seven speeds suited for the full 10 HP and boy did I make chips when I used them.

You want to over-power your machine tool, this is the level of detail you have to consider before you commit. Work the numbers. If you don't want to get into it, stick with manufacture's recommendations. If under-power, stock-power, over-power works for you don't insist on yourself as a paragon of orthodoxy for others to emulate. Other folks may have sound reasons to stray from the path you would choose for them.

The OP lathe came with a 5 HP and his question was could it be run with a 3 HP. The answer is without question YES at minor sacrifice to stock removal. There are other considerations such as if a single phase motor was substituted for a three phase and the greater vibration might be a factor and of course the motor RPM, pulley size etc. But yes.

I understand a certain fondness for histrionics and dramatic exaggeration can attract anyone desiring to express skepticism toward a slight over powering a small delicate lathe but I hardly think a reasonable retrofit will "twist it into a pretzel" as was suggested earlier. Even a light lathe has a certain robusticity. The failure mode of witlessly overloading a SB 9A is likely to be failure of the second reduction on the headstock backgear. If in direct the belt will slip on the step pulley which is annoying but hardly a mechanical failure.

J Tiers
08-02-2017, 10:37 PM
.....
I understand a certain fondness for histrionics and dramatic exaggeration can attract anyone desiring to express skepticism toward a slight over powering a small delicate lathe but I hardly think a reasonable retrofit will "twist it into a pretzel" as was suggested earlier. Even a light lathe has a certain robusticity. The failure mode of witlessly overloading a SB 9A is likely to be failure of the second reduction on the headstock backgear. If in direct the belt will slip on the step pulley which is annoying but hardly a mechanical failure.

My definition of "twist it into a pretzel" is that the machine will deform under too much force, and lose accuracy, at least. It should spring back when the abuse is over with, of course. But meanwhile, the tool may dig in overly deeply due to the extra cutting forces, the machine may vibrate and chatter, it might even be damaged.

If you take the statement literally, you quickly run up against the fact that CI does not bend, no pretzels likely....so much for the literal interpretation of hyperbole

Given that the Atlas lathes specifically have been known to break the compound right off in some cases, usually from over-extension, WITHOUT any overpowering, and that there are known weak areas such as the die cast zamac handwheel gearboxes on some models, I suspect that overpowering could do sme real damage. It surely would not be LESS likely to break something.

More robust machines that are not in the Atlas and SB 9" class, will likely take considerably more, with nothing worse than extra wear on ways, screws, etc.

It also takes effective lubrication to work with higher power, as well as structure. Machines intended for industrial use generally have automatic pumps, one-shot oiling systems etc. Machines in the Atlas class, and to some extent in the SB 9" class, depend on the user to dribble oil on the ways from time to time, as the fit takes them. That sort of lube system is just not up to heavy duty usage.

There are many ways to "twist a pretzel".

Forrest Addy
08-03-2017, 01:04 AM
My definition of "twist it into a pretzel" is that the machine will deform under too much force, and lose accuracy, at least. It should spring back when the abuse is over with, of course. But meanwhile, the tool may dig in overly deeply due to the extra cutting forces, the machine may vibrate and chatter, it might even be damaged.

If you take the statement literally, you quickly run up against the fact that CI does not bend, no pretzels likely....so much for the literal interpretation of hyperbole


"Hyperbole"! That's the word I was looking for. Getting old. Yeah, I knew what you were saying and I pretty much agree but the noobs and lurkers who are always with us may not. Us old farts have to watch our words. I could show you PMs and emails where my incautious blurts confused or misled someone just starting and haven't yet distinguished between my colorful words and those that are golden.

I could challenge you: you got non quantifiable adjectives; you got numbers too? But nah!

I ran a small lathe some time ago when I had my Starrett 98 level on the cross slide I reached for it just as the tool entered the cut. The bubble moved a half graduation. Curious I gathered and sprinkled levels and indicators to pass the time as a series of long cuts ran out. I've done the same since and its interesting the deflections and movements possible in a lathe in mid-wear. New and those is very good shape hardly move at all. None of these deflections and movements were permanent but as you'd expect older lathes didn't repeat zero very well. I recall an ancient American lathe in an Oregon farmers machinery shed. Its carriage was so worn it slewed one way or the other depending which way you cranked the handwheel and you had to slip a couple pieces of step flashing under the leading edge of the tailstock to take out the rocking chair. I welded up and re-machined a bearing seat on an axle for him. What a way to spend a barbecue. Pulled pork sandwiches in one hand and the cutting oil in the other: be careful where you take a bite. Fateful words: "Hey you're a machinist..."

No particular point to make out of this except to confirm my faith in the old engineer's aphorism: "Everything is made out of rubber."

Ian B
08-03-2017, 02:11 AM
I have a lathe with a 10HP 3 phase motor (Harrison M400). The only time that I get anywhere near to using the rated power is when dropping the clutch with the gearbox set for 2,000rpm. How do I know the load? Simple, the first time that I tried it, the fuses blew :(

During any normal machining that I do, I'm working at nowhere near the motor's rating.

Ian

Forrest Addy
08-03-2017, 05:12 AM
Few home shop machinists exploit the full stock removal capability of their machine tools. Full journeyman machinists, the aggressive high ballin' kind use more than half their machines HP unless there's a ton of stock. Mitigating against full HP cuts are part strength or rigidity, limitations in tooling, machine condition etc.

Back in the day forge shops and foundries often had machine shops attached or down the street that "roughed off the bark" for their customers. Here you saw heavy full HP cut every day.

Most machine time is spent at substantially less then full power. A good aggressive manual machinist might spend 15% of his time is stock removal getting down to the finish cuts and details. CNC machines have no such limitations They can commonly employ max power cuts to near finish size before skimming off the finish stock in minutes unless there is a sculpted surface to contend with.

I prefer machine tools having ample power because they are generally stouter built therefore smoother running, more stable and consistent than their frailer cousins in comparable condition.

Personally I loved working a machine tool to full power where circumstances permitted. I recall Leonard Schmidt and I worked on neighboring 72" King vertical boring mills each equipped with a 75 HP DC drive. Our job was to rough a couple dozen steel winch drum castings, each about 3 ft in diameter and 4 ft high: rough, face, and bore for welding in the shaft. There was an inch of stock per side. Once the shaft bore was finished and weld prepped, we could rough the stock off in as few cuts as possible. This was 1973 before carbide had fully evolved to the present day's strong, tough, cutting tool technology. The GE tools we had were primitive and brittle but if you radiused the cutting edge properly you could get a full length cut except for the 3/4" held in the faceplate jaws.

75 HP in 65 KPSI cast steel on a 3 ft diameter works out to about 35 RPM, 3/8 DOC and 0.035 feed/rev on each of the two ram tool posts. That's roughly 60 lb of 800 degree chips per hour and they'd pileup on each side of the machine and char the wood block floor. We were assigned a full time helper to haul chips. The load meter was wavering on 95%.

The shop superintendent when he came by felt the radiant heat from the aisle and heard the jingle of the chips, looked to see what was happening and there Leonard and I were working the snot out of our two 72" Kings, each knocking out a drum apiece in about two shifts. I was looking his way. The superintendent smiled at all the productivity. He brought over a couple of his superintendent buddies after lunch so he could swagger and strut. Leonard and I got zip for awards and recognition but what can you expect?

Wow! I'm full of stories today.

MattiJ
08-03-2017, 05:55 AM
I have a lathe with a 10HP 3 phase motor (Harrison M400). The only time that I get anywhere near to using the rated power is when dropping the clutch with the gearbox set for 2,000rpm. How do I know the load? Simple, the first time that I tried it, the fuses blew :(

During any normal machining that I do, I'm working at nowhere near the motor's rating.

Ian

You just got too big lathe, I'll offer you a smaller one in exchange :rolleyes:

65mm workpiece would be still rather small for your lathe since it fits trough the spindle.
You could turn that 65mm mild steel bar @2000rpms with coated carbide and run out of power before you realize:
4mm DOC at 0.4mm feed/r is next to nothing on a M400 size machine, yet you would need 25kW or 33hp to take that cut at 2000rpm.

pinstripe
08-03-2017, 06:27 AM
You could turn that 65mm mild steel bar @2000rpms...

400 m/min in steel? Are you cutting or melting? :D

MattiJ
08-03-2017, 07:21 AM
400 m/min in steel? Are you cutting or melting? :D

Thats right in the middle of recommended speed for example on some Sandvik coated inserts like 4325 grade.
For example CCMT 09 T3 04-PMC 4325 recommended speed range is 345 to 460 m/min on steel. :eek:
That is still very small CCMT09 insert size commonly used on small hobby lathes, yet you need over 15hp to fully utilize it.

I got couple of boxes thumbnail-sized CNMG inserts, plugged in the recommended feeds and speeds to cutting power calculator and it tells me that 160kW would be needed ;)

pinstripe
08-03-2017, 01:19 PM
Very interesting MattiJ. Do you know why some inserts with the same grade are rated for different surface speeds? For example, WNMG 08 04 12-PR 4325 is the same grade, but vc is "only" 305 (365-230).

I thought it might be a positive/negative thing, but that doesn't appear to always be the case. The positives are generally faster for the same grade, but the difference between them is not consistent.

I tried the Sandvik calculator once. The smallest size machine I could choose was something like 20 hp! Not quite home-shop :)

MattiJ
08-03-2017, 02:50 PM
Very interesting MattiJ. Do you know why some inserts with the same grade are rated for different surface speeds? For example, WNMG 08 04 12-PR 4325 is the same grade, but vc is "only" 305 (365-230).

I thought it might be a positive/negative thing, but that doesn't appear to always be the case. The positives are generally faster for the same grade, but the difference between them is not consistent.



Your insert is -PR, for heavy roughing cuts. Finishing inserts generally have higher speeds than roughing inserts.
My example was -PM which is "Medium" cutting or something like that.

If you look at WNMG 08 04 12-PM 4325 the speed range is 405-250 m/min

pinstripe
08-03-2017, 02:57 PM
That makes sense. Thanks!