Low speeds - any disadvantages?

Not strictly model engineering (motorbike engineering and supercharging!), but...
About to arrange a trip to the next town to look at a medium-sized lathe
(English, geared head 6.5/13" x 40", 20" into gap although the spindle bore's too small for e.g. fork stanchions, has a non-working suds pump and tank etc.) and may consider it if it's in reasonable shape, one concern is the speed range - 8 speeds from 30 - 750 RPM - and whether the low top speed is going to cause problems? The only issue I can think of (other than slow removal of material when cutting!) is that may be a bit slow for small-diameter work in work-hardening materials, but as this would be my first lathe since college over 30 years ago any hints and tips would be appreciated!
Another concern is that the quadrant lever and clutch knob for the sliding and cross power feeds (ooh, luxury....) appear to be missing - I've a fair idea how they (should) work and aptitude enough to rebuild car and 'bike gearboxes, so is this going to be a serious can of worms should there be problems with 'em? They were manufactured into the 70's and fairly popular (if a bit pricey new...) and had spares support into the 90's so there may be spares still around... Famous Last Words?
As manufactured it's Imperial, and bikes seem to all be Metric these days - apart from threading (which may need a 127 gear or similar made if it has gone missing over the last 50 years), am I making a rod for my own back by not going for a Metric lathe? I have a bunch of Metric (and Imperial) measuring tools and can probably remember 40 thou = 1 mm...
I should be able to see/hear it running so can check for noisiness and slop in the bearings, head, QC 'box etc., and I'll be able to check the ways and see what tooling's with it, anything else that I should be checking? Apart from how much trouble I'm going to get from SWMBO, of course...
Thanks in advance,
Dave H.
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Dave H. wrote:

All depends what you are going to be doing with it. Bit too slow for carbide tooling on small diameters but fine for HSS Is it a three phase machine? if so you could run it on an inverter and run it up to double the speed without much risk. Keep any eye on top speed for the big chucks etc and see if the bearings/gearbox warms up too much. Start remembering that 1mm = 39.37 thou as you home in on final diameters. These slightly bigger machines tend to be cheap as some home users are (wrongly) put off by them. Unless it has been abused then it should be fine.
Good luck
Bob
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On Tue, 9 Feb 2010 13:24:56 -0000, "Dave H."

Might be easier if you could tell us what lathe it is (make/model). Then people may be able to offer suggestions of weak or strong points from personal experience.
Regards Mark Rand RTFM
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"Mark Rand" wrote...

Good Idea...
It's a post-war (WW2, not the Great War!) Milnes 13", popping out to look at it in a few mins... NOT buying it while I'm there, need to see if it'll fit in the shed first!
Thanks, Dave H.
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Simple rule of thumb. More power in low gear and lower power in high.
Power - really torque or the ability to cut without a stall.
Large diameter requires lower speeds - it is surface speed not rpm that determine rpm and cutter and material.
Martin
Dave H. wrote:

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    O.K. That looks like an intersting machine, based on the description in <http://www.lathes.co.uk>. And it looks as though the spindle bore (1-5/8") is large enough so you could adapt a 5C collet closer to it.
    Aha! Hardened bed too. Probably in pretty good shape then, unless it has been used for toolpost grinding without sufficient protection.
    Good Luck,         DoN.
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Dave H. wrote:

One small detail - how much do they want for it and how much will it cost you to move it?
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"Dudley wrote...

They'll deliver at cost (having big wagon and being all of 8 miles away...) - and a reserve of 200 on it, which ain't bad if it's all there and working! Just off to see if it is.... And whether it'll fit in the shed :)
Dave H.
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The slow speed will be of a concern with small parts, but it may be possible to increase the motor sheave size or even drive the motor with a vfd.
I'm not familiar with this particular lathe but one other concern might be the minimum feed speed, some of the older slow lathes wouldn't feed less than .010", (even much more in big machines) , it may be tedious to do fine finish work. YMMV, and for the price it would still be a good deal.
basilisk
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"basilisk" wrote...

On investigation of the plate on the machine, the sliding (carriage?) feeds run from 2 thou/rev upwards, the surfacing (cross-slide?) from 0.7 thou (but see below) - I assume this should be OK for most purposes, can't imagine having tools with much less of a tip radius!
I like the VFD idea, although it's fitted with what looks to be a 2HP 240v motor - I guess that could be driven with a single-phase VFD if such a thing exists?
I went to take a look this evening, the ways look to be in pretty good order and there weren't any really offensive noises - the head and QC gears all looked pretty good (no chipped/missing teeth, not particularly worn) - the spindle bearings *might* be a little sloppy, but it appears to have taper rollers there so it could be just a matter of getting the preload right? Certainly when the clutch was disengaged it took a fair few seconds to spin back down from 120 rpm or so (with a hefty 10" 3-jaw chuck on it), so not on the tight side :o) It looks like as a minimum the 127 tooth gear's there, along with 3-jaw, faceplate, tailstock chucks and centres, plus an assortment of tools/bits, holders and the thread-dial: There is a problem with the feed selection lever / clutch though, but it looks like all the bits are there to work with, and the steadies have disappeared in to the same black hole as the handbook and the 4-jaw chuck...
It's a bit bigger than I was expecting - New Shed time, perhaps
It's starting to look like I may have to buy a *big* bunch of roses (and a bigger bottle of bubbly) for Sunday, and promise SWMBO that her trike will be one of the first projects... Aaaaarghhh.
Thanks for the input, Dave H.
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Dave H. wrote:

Single phase motors cannot be run from a VFD only three phase motors are suitable.
Bob
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    O.K. My 12x24" Clausing will produce even finer feeds -- but I don't think that I've ever used them. :-)

    I'm afraid not. Single-phase motors are quite frequency sensitive, because the value of the starting capacitor has to be tuned to the line (mains) frequency and the inductance of the motor windings. And a single-phase motor typically has a centrifugal switch which will re-engage the start capacitor when the speed drops below a certain point.
    What are the odds of finding a three-phase motor which will fit it?

    All in all, it sounds like a nice deal.

    It is worth it. :-)

    Very much so.
    Good luck,         DoN.
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On Tue, 9 Feb 2010 22:01:57 -0000, "Dave H."

What makes you think the bearings are sloppy? If they're not making nasty noises at top speed they're most likely OK. The preload is controlled by precision spacers and almost certainly not adjustable.
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On Tue, 9 Feb 2010 13:24:56 -0000, "Dave H."

When I had a Myford ML7 - top speed of 640 rpm - I still managed to use carbide and turn small parts. A number of 1mm x 5 long silver steel pins and a 4mm 316 shaft were no problem, although the final finish was with a bit of emery.
At the time I used a DCMT tool from Greenwood with IIRC Sandvik GC1025 grade inserts, with a 0.2mm nose radius. Very versatile tool which then became my almost universal choice for anything on the Myford.
Even now on my Colchester Bantam I rarely go above 1000rpm (next and top speed is 1600) and use carbide for everything except form tools.
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Dave H. wrote:

If you only have one lathe, this could be a pain. 750 RPM is not a massive limitation, but many times for smaller work you might want more. It may be possible to run this machine well above rated speed with a VFD on the motor. Depending on the bearings, lube system and such, you may be able to do this safely, or not. The only issue I can think of (other than slow

Missing, as in somebody took the handles off when moving, or broke them? or, missing, as in, this lathe never had any power feeds other than the main carriage threading feed?

If you are going to be doing a lot of metric threads, having to back up for every threading pass will drive you round the bend! The transposing gears get you proper feeds, but with an imperial leadscrew, you cannot disengage the leadscrew between passes.
Jon
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Jon Elson wrote:

I usually do that as standard practice.
You have to withdraw the cutter anyway, and running for a second or so in reverse is not significantly harder than winding the carriage handle - and then you don't have to bother with the thread dial indicator at all :)
-- Peter Fairbrother
The transposing

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On Tue, 09 Feb 2010 22:27:26 +0000, Peter Fairbrother

As a generall comment, it is common to reverse the Imperial machine between cuts of a metric thread, but it isn't mandatory.
Each numbered line is normally one inch of carriage movement. If you withdraw the tool and return the carriage a distance in inches equal to the 10th's of millimeter pitch of the thread you are OK.
eg for 0.7mm, 0.7x10 = 7" so count seven numbers on the chasing dial and you are OK to take another cut.
This is a short hand way of getting 254 thread pitches which will always be a line on the chasing dial and converting to inches. In this case you could obviously use 3.5", but have to keep closer track of the numbers and lines. Ffor some machines with a 6tpi leadscrew (rather than 8) you may have to use whole inches depending on your particular dial.
This isn't always quicker than reversing, but it is an option
Richard
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on a thread chasing dial

cocked it up editing, sorry Richard
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I too do bits for bikes ,i have a fully metric trick as you like Harrison 11" top speed 800 with a pulley mod ,can get down as low as about 1.5mm dia in most stuff but it can be frustrating at times ,so go pick up one of thise micro lathes from Arc euro ,strip it sort it and it will be nicely under the bench ready for that carb jet or silly size pin that will inevitibly be required. I have no connection with arc euro .
As to metric /imperial question i have an imperial mill and a metric lathe so i just have to be careful somtimes ,reckon its quite good to be able to do stuff in either size ,certainly the way they trained us when i did my time ,enjoy your big iron !!
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    Hmm ... for really small-diameter work (as long as you don't need to thread with it) maybe a small lathe like a Taig/Peatol or a Sherline in addition to the more serious sized one which you are contemplating. Granted, that top speed is going to be a trial on your patience. I'm surprised that you don't get up to about 1600 RPM on a 12" or 13" swing.

    It depends on how much is missing, and what the design is. If you know the maker, you can check it out on <http://www.lathes.co.uk> and perhaps get an idea just how they work on that particular machine. If it just the star shaped nuts like South Bend uses, and nothing from under them is missing you probably can do fairly well. If you have to make a stack of clutch plates, it may be a bit more tricky.

    Hmm ... actually, 39.37.... (repeating out after some decimal places). The easier one for me to remember is the totally precise 25.4mm/inch. Calculate using that, and you are there. It is totally precise because of a standards definition back in the 1950s IIRC.
    And for real convenience, check out the digital calipers and micrometers. You can switch between systems at the press of a button, including converting an already made measurement.
    As for the metric threading, even with the 127 tooth gear, you have to remember that the half-nuts have to be kept engaged until you have the thread completed, and you need to run the lathe backwards to get to the starting position for the next pass. If you disengage the half nuts, you will almost certainly wind up cutting along a different path each pass.

    Sounds like you have a pretty good handle on it.
    Good Luck,         DoN.
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