New Lathe, motor quandry...

All, I have now aquired my Harrison, an L5 (4.5" X24") from 1950/51 judging from the serial number and apperance.
It is fitted with a 3 phase motor. The ratings plate states: 1 Hp 930 rpm full load speed, 400-440V 2A 50z. Its a brook unit, looks original. Am I correct in thinking this is a proper 3 phase (415v ) motor only? I have not opened the conection box yet, but the ratings plate makes no mention of 240V. Given my original plan was a 240V inverter drive I think Im in need of a rethink. Suggestions please.
thanks
Dave
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Yes it is a 3 phase motor, you could use a single to three phase converter to get it going.
small.planes wrote:

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On Mon, 6 Mar 2006 15:25:03 -0600, small.planes

This is a 6 pole motor hence the low speed of 930 rpm. From the spec plate it looks as if it's just a 440v star would motor and not suitable for an invertor drive. Digging to star point out on a 6 pole motor isn't something for the faint hearted.
Best bet is to look for a modern 6 wire 440 / 240 4 pole motor rated at 1425 rpm. Should be plenty kicking about cheap at the 1 Hp level.
-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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On Mon, 6 Mar 2006 15:25:03 -0600, small.planes

judging
looks
I
of
This is a 6 pole motor hence the low speed of 930 rpm. From the spec plate it looks as if it's just a 440v star would motor and not suitable for an invertor drive. Digging to star point out on a 6 pole motor isn't something for the faint hearted.
Best bet is to look for a modern 6 wire 440 / 240 4 pole motor rated at 1425 rpm. Should be plenty kicking about cheap at the 1 Hp level.
-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
John, Having seen the unit, though not into the conections box yet, Im no about to start digging about inside it... Im not that brave/stupi (delete as appropriate) Would there be implications for running at ~50% overspeed? Or woul you also use an inverter drive to run the motor slower? I kno harrisons were specd with various speed ranges, and afaik th headstocks were the same internally. currently its 22-480 rpm (i think
Sorry if these are obvious questions, but this is the first time her for me.
thanks
Dav
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wrote:

your motor is a 400 V 3 phase... 240 V single phase inverters put out 240 V 3 phase, modern motors are normally convertible from 400 to 230 V.
As your motor is not readily convertible what you can do is get a converter, these will give a synthesised 400 V 3 phase supply ( fixed 50 Hz ) from a 240 V supply. These converters are best run with a slave motor ( acts like a flywheel on an engine ), some units have this built in. Converters are a little touchy, and need tuning to the motor load, however many modern units do this automatically.
Possible contacts, Boost Electrical.. tel 01959 534073, Transwave tel 0121 708 4522. there are other suppliers.
I use a converter to give 3 phase in my workshop.. it runs the lath, the mill, and a drill. It also allows me to run other equipment I am working on.. very handy
--
Regards Jonathan

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On Tue, 7 Mar 2006 02:22:52 -0600, small.planes

These early L5's were a bit on the slow side, why they chose to use 6 pole motors to slow these I'm not certain but 480 is rather embarrassing.
I used to own a larger L6 with the two speed motor with a top speed at 700 / 1400 depending on range. Most of the time it was spent around the 700 to 800 range with smaller work.
I wouldn't go for a single phase motor on one of these because of the losses in the gearbox. On a cold morning it was impossible to run the top two speeds without allowing the machine to warm up. The oil drag was enough to get the clutch to slip and single phase motors are not renown for great torque.
I think also your original post was incorrect in the makers details 2A sounds very low for a 1HP motor, especially a 6 pole which draws more current than a 4 pole.
I'd ask around and see if you can come up with a decent 1 hp 4 pole. Do you have any motor rewind companies near you ? These often have loads of S/H motors they can't sell as companies don't want S/H when new is relatively cheap to them.
At the moment I don't have any and I've worm my welcome a bit thin scrounging motors for others on the list. <g>
-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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On Mon, 6 Mar 2006 15:25:03 -0600, small.planes

Any reason why you couldn't pop a 1hp single-phase motor on there?
Peter
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On Mon, 6 Mar 2006 15:25:03 -0600, small.planes

judging
looks
I
of
Any reason why you couldn't pop a 1hp single-phase motor on there?
Peter
There is no reason, just that I was told single phase motors are not s good, pulsing etc, and lower starting torque. Currently Im trying t establish the 'best' solution, before I spend money, as the budget i limited (new baby) and there wont be a second chance.
What Speed ranges get most used for typical (myford sized) model en work? This might affect motor choice?
Dav
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On Tue, 7 Mar 2006 06:43:37 -0600, small.planes

I had an L5 years ago, converted it by fitting a 1.5hp 4-pole (1425rpm) single phase motor. It worked very well. I honestly can't remember what pulley I fitted to it, whether I tried to get back to the original speeds, but I still have the original 6-pole 3-phase motor here with the original pulley fitted.
Cheers Tim
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On Tue, 7 Mar 2006 06:43:37 -0600, small.planes

I don't know how relevant the pulsing is to small lathes (though as usual, others may have a different opinion), personally I wouldn't have believed it makes much difference. We're only aiming to cut to a thou rather than tenths of a thou, and there will be always be a fair bit of inertia from the chuck & work etc. On a surface/cylindrical grinder where tenths matter it may be more relevant.
On my ML7 I have a 1/4hp single phase motor which happliy spins the 6" 4 jaw with a considerable lump in it up to speed with no problem, yet at lower speed will also power some pretty chunky depths of cut.
When I first got it I was desperate to stick a 3/4hp motor on as I felt it would otherwise be vastly underpowered, but so far the itty-bitty motor has performed more than adequately.
Most machines will use a 1425rpm motor and the speed range will be determined by the pulley/gearing ratios. Ive used all 6 speeds on mine from 35 - 640rpm (and would have liked a few more!) at some time or other, and what you use depends on what the work needs. All materials have an ideal cutting speed in SFM, and you set the spindle speed broadly around this. The formula (CS x 4) / D = RPM will give you a starting point for the spindle speeds you need.
If anything is unclear in the above then ask away.
Peter
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I have had a Harrison L5 for a number of years... it was one of the last L5's and was metric from new. I converted mine to single phase when I bought it. It was a piece of p---. (Even I managed it without trauma)
The Harrison originally had an option of a 2kw Single Phase .. so I went and bought a new capacitor start unit from MachineMart when they first started to stock such things. It was a direct replacement ... especially as the rails on the rear of the Harrison are dead easy to adjust to fit just about anything. You need to rewire the reversing switch for single phase ( and because of the stand-offs during the rewire for single-phase I had to fabricate a slightly bigger enclosure for it from mild steel plate, ... the existing one was touching the terminals after the conversion). I didn't use the start and stop on the front of the cabinet relying on the main isolator on the side and the 'off' position on the rewired switch, but that was just laziness on my part. Because mine came with a lo-volt lamp I changed the transformer, and it also came with a 3 phase suds pump which I replaced with a secondhand single phase one from G&M Tools. That was all done in 1995/6, and it has been working great ever since. No need to faff around with convertors/invertors and it cost a lot less too.
IanB
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Slightly off the original topic, but related in the speed change o
motors way...
Is the problem with slower spindle speeds purely that you have to tak longer to do things? Or is there a minimum speed that you should tur things at.
If i calculate correctly then a 1450 rpm motor will give approx 34-75 rpm using the same input pulley as currently fitted.
If the slowness just means it will take longer then I am tempted to bu a 1.5hp static phase inverter (within budget :) , and run the lathe a is until I find a suitable 1450 motor, or can get more budget. Do you all see any problems with this? thanks for the help.
Dav
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On Wed, 8 Mar 2006 02:31:01 -0600, small.planes

Dave
Spindle speed needs to be set to a nominal point or range that is decided by the type of material to be cut and also the diameter of the material. The cutting speed of a material is normally expressed as 'Surface Feet per Minute' or SFM, and relates to the speed at which the circumference of the material moves past the cutting edge of the tool.
Have a quick look here:
http://www.frugalmachinist.com/speedsandfeeds.gif
This will give you a guide to the cutting speed (CS) in SFM for a range of materials. It is taken from an old Bridgeport manual but the speeds are the same for turning as milling.
Once you know the CS in SFM of a material and the diameter of the material to be turned you can easily calculate what your spindle speed should be set at to achieve the required SFM at the point of cutting. This can then be calculated by using the formula: (CS x 4) / Diameter=RPM.
Lets take for example, a 1" diameter Mild Steel bar: Cutting speed from the chart would be 80SFM, therefore (80x4) divided by 1" = 320 RPM. You would then set the spindle speed to the one you have that is closest to this.
Similarly, a 1/4" diameter piece of the same material would ideally require a higher speed, i.e. (80x4) divided by 0.25" 80 RPM.
I should stress that these are the 'theoretical ideal' speeds using HSS tooling, and clearly some of these just aren't available to us. The 1280 RPM shown above is twice as fast as my maximum available speed, but I have quite happlily turned short parts of 1mm diameter at only 640RPM. With carbide tooling the recommended SFM is ofter twice as high as HSS or more for the same material being turned. Very often a higher speed and smaller cut can improve the finish on parts but this is equally affected by the tool geometry too.
In summary I wouldn't worry too much about having a 34-750 speed range as I'm sure you will manage pretty much everything with this. It would be nice to have a 1500RPM or 2000RPM top speed for some jobs but high speed can be a little scary sometimes! One other thing to take into account is that most cast iron chucks have a maximum rated speed above which they can explode. Personally I've never seen one do this and have no idea what different speed ratings may apply, but if in doubt go slower! Regards
Peter
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On Wed, 8 Mar 2006 02:31:01 -0600, small.planes

take
34-750
buy
Dave
Spindle speed needs to be set to a nominal point or range that is decided by the type of material to be cut and also the diameter of the material. The cutting speed of a material is normally expressed as 'Surface Feet per Minute' or SFM, and relates to the speed at which the circumference of the material moves past the cutting edge of the tool.
Have a quick look here:
http://www.frugalmachinist.com/speedsandfeeds.gif
This will give you a guide to the cutting speed (CS) in SFM for a range of materials. It is taken from an old Bridgeport manual but the speeds are the same for turning as milling.
Once you know the CS in SFM of a material and the diameter of the material to be turned you can easily calculate what your spindle speed should be set at to achieve the required SFM at the point of cutting. This can then be calculated by using the formula: (CS x 4) / Diameter=RPM.
Lets take for example, a 1" diameter Mild Steel bar: Cutting speed from the chart would be 80SFM, therefore (80x4) divided by 1" = 320 RPM. You would then set the spindle speed to the one you have that is closest to this.
Similarly, a 1/4" diameter piece of the same material would ideally require a higher speed, i.e. (80x4) divided by 0.25" 80 RPM.
I should stress that these are the 'theoretical ideal' speeds using HSS tooling, and clearly some of these just aren't available to us. The 1280 RPM shown above is twice as fast as my maximum available speed, but I have quite happlily turned short parts of 1mm diameter at only 640RPM. With carbide tooling the recommended SFM is ofter twice as high as HSS or more for the same material being turned. Very often a higher speed and smaller cut can improve the finish on parts but this is equally affected by the tool geometry too.
In summary I wouldn't worry too much about having a 34-750 speed range as I'm sure you will manage pretty much everything with this. It would be nice to have a 1500RPM or 2000RPM top speed for some jobs but high speed can be a little scary sometimes! One other thing to take into account is that most cast iron chucks have a maximum rated speed above which they can explode. Personally I've never seen one do this and have no idea what different speed ratings may apply, but if in doubt go slower! Regards
Peter
Peter, I think I might not have been clear in my question, I have looked i several books, LH Spary, Tubal Cain etc and they have the idea speed calcs. I understand the ideal speeds, but given that currently my to speed would be 480rpm if I dont change the motor, vs 750 rpm if i do will it make any difference in terms of machining, other than a increase in time? The feeds are geared to be so many thou per rev, s the amount of advance is the same, but slower (if that makes sense) Will there be an adverse affect on small parts finish? ( ie if i ru under the ideal speed by a long way)
The limit on my budget means that i cannot afford the prefered optio of a 1450 rpm motor and VSD to run it. If the current speeds wil suffice then I will probably run the original motor with a cheap stati phase converter until I have more funds available. This would be abou the same cost as my original (no longer practical) plan of rewiring th motor to run delta on 240V and a 240V VSD from RS, which seemed like t easy way until I saw the motor... Then at a later point ( a few months time) I can get a more modern 1450 3 phase motor and use that at 415 or 240, and then if ness get a VSD as a third stage.
hopefully that makes sense, comments are appreciated, Im fairly new to all this.
Dave
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On Wed, 8 Mar 2006 09:06:09 -0600, small.planes

Dave,
you may be worrying a bit too much at an early stage. My advice would be just to use the lathe for a while and spend time getting used to the machine before you worry about changing motors for a faster speed.That way you may have a better idea of what you need.
Remember that small lathes used to be treadle powered before the advent of (relatively) cheap motors, and they seemed to get the job done OK back then. I'm sure they couldn't have managed to get it spinning all *that* fast.
FWIW I hand feed the carriage for most of the work I do. It's nearly all short-ish (<6") and not worth faffing around with the change gears as I don't have a gearbox. I'll use the feed for screwcutting or fine finishing cuts but I find that most of the roughing is quicker by hand. Getting a fine finish is more about the feed, depth of cut, and tool geometry rather than just down to spindle speed. You can always polish it or take the last thou or so off with emery/oil.
As I mentioned previously I recently turned up (down?) a set of 1mm dia silver steel pins with only a top speed of 640RPM. The 'ideal' speed from the formula tells me I should have been running much faster than this but it really wasnt a problem at all.
You could always turn a larger pulley as an early project and see what difference this makes to how you feel about what you need?
Peter
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>

static
about
the
te
to
Dave,
you may be worrying a bit too much at an early stage. My advice would be just to use the lathe for a while and spend time getting used to the machine before you worry about changing motors for a faster speed.That way you may have a better idea of what you need.
Remember that small lathes used to be treadle powered before the advent of (relatively) cheap motors, and they seemed to get the job done OK back then. I'm sure they couldn't have managed to get it spinning all *that* fast.
FWIW I hand feed the carriage for most of the work I do. It's nearly all short-ish (<6") and not worth faffing around with the change gears as I don't have a gearbox. I'll use the feed for screwcutting or fine finishing cuts but I find that most of the roughing is quicker by hand. Getting a fine finish is more about the feed, depth of cut, and tool geometry rather than just down to spindle speed. You can always polish it or take the last thou or so off with emery/oil.
As I mentioned previously I recently turned up (down?) a set of 1mm dia silver steel pins with only a top speed of 640RPM. The 'ideal' speed from the formula tells me I should have been running much faster than this but it really wasnt a problem at all.
You could always turn a larger pulley as an early project and see what difference this makes to how you feel about what you need?
Peter
Peter, thanks, thats about what I assumed, slow speeds are just not ideal, I not very experianced at this and wondered if I had missed somethin obvious that all engineers already knew... The original plan for vsd came about as I work for an electrica machines company and could probably 'find' one, so it seemed the pat of least resistance, with added plusses for speed control if the moto had been suitable. Ill stop worrying now and go have a drink before starting my firs batch of machined circular tuits <Grin>
Dav
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Peter Neill wrote:

Gawd I forgot all about those theoretical speeds! I turn for a living and just aim to chip the material, and obviously acheive the desired surface finish.

More like 4 times with modern carbides. Your example of 1" MS above, would be turned at 1500 or even higher here. Obviously I'm using flood coolant so that helps. I'd part off with indexable tooling at about 1200. At these speeds I'm also using high feeds, there's never any sign of distress, just smooth cutting and short chips.
Often if is sounds right it is right. But experience helps.
I had an L5 once, it was given away in this group. I cant even remember what spindle bearings they had. Maybe the low spindle speeds were more likely due to it being common in schools. I remember my school had one. I think it was the larger spindle variant.
I'm still a fan of 3ph motors and VFD's, makes for a much easier to use machine.
3ph motors also DO tend to give better finishes in my experience. When my Harrison M300 was single phase it always gave a regular and visable pattern on long turned parts.
Wayne...
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