Low speeds - any disadvantages?



    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.
--
Ned Simmons

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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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wrote:

That doesn't bother me a bit, Jon. I often back up even when cutting inch threads. The threads I cut are usually short, often fine, and it's as easy to change speeds (gear head lathe) as it is to hit the right spot on the threading dial. I cut slow so I can stop in time, back up fast. I've found it works best for me to do it once slowly rather than thrice quickly get it right third try, since I very seldom make more than two or three of anything.
Carbide cutters work best at higher speeds, HSS works well at lower speeds. HSS can take a keener edge than most carbide. I can take finish cuts of tenths with HSS that produce fuzz or dust rather than chips. Carbide won't do that, at least not for me. I don't understand a preference for carbide in a home shop where production isn't an issue. It's useful when working with hard or abrasive materials, but for ally, brass, bronze, delrin, nylon, mild steel and some stainless I much prefer HSS. I often run it dry or with just a few drops of cutting fluid, still get good surface finish with sharp, carefully-ground bits.
I have never made anything thatcouldn't be made on a 9 or 10 inch Logan or South Bend or even a Myford Super 7, but what I have is a 15x50 import clone of a gearhead Colchester or Clausing that belonged to Mary's dad. Her mom wanted me to have it when he passed because she thought I might appreciate and respect it as he did. She was right. The difference in rigidity between it and the smaller lathes is huge and I like that a lot. Chatter? What's that? I could probably love a Monarch 10EE or Hardinge a lot, but I'm not in shop-building mode and I'm quite content with what I have.
I'm retired now, but these attitudes were formed when my shop time was as limited as that of most guys with a full-time job and a family. Shop time was relaxation, a respite from the competitive race and daily grind of bidness. Production efficiency has never been an objective in my shop. On my time, having fun is job 1.
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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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My Student has a top speed of 1200 I think it is but because I run it off a phase converter it's not too happy at starting up on the highest speeds. 900 is ok but I actually rarely run it at more than 650 and don't find that to be any sort of restriction. In high volume production you want the optimum speed for maximum metal removal but for odd jobs and home shop work most things will cut just as happily at lower speeds with sharp tooling for the sake of a few more seconds per job.
I always find the key is the right tooling. I use razor edged non ferrous carbide tips even for ferrous work because they cut better on small machines. Maybe for the occasional roughing job I'll use an actual ferrous tip but you can't get any sort of finish with them.
If the lathe is suitable otherwise I wouldn't give the top speed a second thought.
--
Dave Baker



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This thread has been interesting for the number of posters who have lathes with modest high speeds and who don't feel it's a problem.
I have a 10 x 24 Jet with a max speed of 2200 rpm +-. I have a controller for it that takes the FPM desired and the diam, and drives the VFD to give the right speed. I often find the the controller wants the spindle to go faster than 2200. In ordinary circumstances, e.g., mild steel & 1/2" diam. Such that I was considering re-pulleying it to get higher speeds (if the spindle bearings would be OK with it).
My assumption has been that the FPM is not just a matter of efficiency (i.e., production speed), but of surface finish. That too low FPM will produce a worse finish than a higher "right" value. Am I wrong? Is FPM just a max value to keep production up without destroying the tool?
As always I'm sure that the vast collective knowledge here will have the answer, Bob
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