Suppose I want to face 4mm off a 50mm dia surface in something hard.
Remembering that mine is a small lathe and can only take 0.25mm cuts in the hard stuff, that's 16 cuts. At 1mm per turn each cut will need about
30 turns, 60 if only cutting one way.
That's 960 turns of the handle, and it gets tiresome real quick - damhikt.
As to using the leadscrew to drive a carriage or cross feed, I just think it may be too much of a compromise - will the leadscrew still work properly as a leadscrew? Will the pin or whatever which rotates stick? will it cause the carriage to move?
I don't know the answer to either question, but I have doubts.
In which case ask Myfords, Boxford, South Bend, Emco and a host more companies who did and in some cases still do employ this situation of a combined lead and feed screw.
I have to say that, stopping the machine, reversing the direction of the feed shaft, re-starting and re-engaging the feed 16 times is also tiresome. I guess if I was going to do that job very often I would have to consider if the compromise of using too small a lathe was worthwhile. Although I have PCF on all my lathes, when facing something where I want a good surface finish right to the centre, I am more inclined to feed by hand. I can at least try to vary the feed rate to match the surface speed. With practice and using the "hand over hand" method one can produce a very good facing cut. With that in mind, I agree with an earlier comment that PCF is somewhat overvalued in small lathes. Lets be honest, it's a hobby (well it is for me) and if we don't enjoy twiddling hand wheels we possibly need to look at CNC anyway as we won't need to turn any hand wheels at all then.
This system for providing power feeds is well established, much used and reliable. I have a couple of PCF Myfords and a Boxford which all use a single leadscrew to provide power feeds, they all work faultlessly and have done so for many years. All also work very well as a "leadscrew" and produce accurate threads if I have taken the trouble to correctly set up the drive train. Again, these days many thread accuracy issues are down to compromises in trying to cut as many imperial and metric threads as possible with a couple of change gears (smaller are cheaper so 21 rather than 127) or with a simple limited range gearbox.
In fact, my BH600 which has both a leadscrew and a power feed shaft does tend to stick sometimes when I try and disengage it. I guess it is all down to appropriate design and manufacture. In my experience, the issue with sticking when disengaging feeds is much more prevalent on feed screws with very fine threads, something which is often used these days on the smaller, cheaper lathes. Trying to disengage the feed on my old Naerok 920 when approaching a shoulder at speed was guaranteed to provide an increased heart rate. I would also point out that if facing, particularly with a hard material, good practice would have the saddle locked anyway; supposing the facility is available of course.
Not sure I totally agree with your suggestion here Mark, it wasn't "nasty" enough to stop Schaublin using "the robust, buttress-thread,
4mm pitch leadscrew, for both screwcutting and the sliding feed", and I don't think many describe them as compromised down to a price - at least not a price I could afford :-)) To be fair though they didn't bother with power cross feed at all and the drive system for the leadscrew was far from simple, so as you say you pay your money and choose your compromise.
Helps with the sale of replacement half nuts as well, at least it does if the lathe is good enough in other ways to last a reasonable amount of time.
Sorry to reply to my own post but on reflection after another glass of white, I need to clarify my comments which were merely intended as a "humerous reposte" to Mark's comment.
I don't want anyone thinking that Schaublin actually used anything as vulgar as a "slotted leadscrew"; although the leadscrew does in fact do both tasks it is "an exceptionally large (40 mm diameter and 4 mm pitch), hardened and ground, running in angular-contact bearings and clasped by long nuts provided with positive oiling" (see Tony's Lathes page). On the later 125/135 and later machines they do also provide power cross feed but use a shaft that runs down the back of the machine driven by bevel gears. They still do though use the leadscrew to provide both threadding and sliding feed, so that part of my hunour is correct.
I regret my earlier 'troll' remark, it was undeserved and I apologise. I have actually emailed you to say so but it was bounced. I really didn't mean it to be quite as abrasive as it actually appeared, I see you have made a considerable useful contribution to the mini-lathe debates. The UK model engineering group is outstanding in the helpfulness of the characters who use it, I didn't really mean to introduce a discordant note and I'm sorry if I might have offended - please accept my apology.
I don't know - I'd rather like to be an armchair machinist, standing up all day does my back (and feet) in. I do have a swivelly office chair next to my lathe, but that's not the same.
As for buying another lathe, I am in the market or will be soon - need more grunt and mass than my minilathe can provide - I now have £550 put aside and can borrow a bit more from myself, so looking at £750 or so. I would like PCF though.
Don't need big, can use a borrowed lathe occasionally for big, need grunt and precision. Don't think I will be buying a C4 however - maybe a C6 or a used Boxford?
-- Peter Fairbrother (who doesn't have nits either)
So what about the Chester DB-8V or Warco WM-240? Both are available for £700. These appear to be essentially the same lathe. Similar capacity to the Comet, similar size, can do left hand threads (they say), variable speed, reversing. The Warco has a slotted cross-slide. Can't be sure about the Chester model. They also come with accessories that would cost an extra £100 with a Sieg C6B from Axminster although the C6B has a slightly bigger capacity. Doubtless both would want some fettling to be useful.
I too am looking for a lathe in this range and these are what I am considering at present. They seem to tick all my boxes. Anyone used either of these and willing to comment. Better yet, anyone near South Staffs want to let me have a look at one in action?
The C6B is a crap lathe. It does have a tumbler reverse IF you are prepared to remove the drive pulley to swap gear over at the back. The variable electronic drive is a waste of time, useable low speed is around 250 rpm, below that it stalls if you piss on it.
I had one that I fitted a two speed poly vee drive belt system to in an attempt to make it more useable. It made it 100% better but 100% of crap is still crap.
There is no substitute for mechanical speed reduction that increases torque unless like the big boys do and over spec the motor by a factor of 7 or greater.
On or around Tue, 26 Aug 2008 16:02:28 -0700 (PDT), John S enlightened us thusly:
well, I'd go along with that. The Student has all gears, and OK, being 1960 it doesn't run all that fast (1200 max) but it does also go down to 54 in low gear. It's reasonably capable with a 2HP single-phase motor (original would have been a 3HP 3-phase), although to be sure I only do light work on it anyway.
The more I hear about the lower end of the new-machine market, the less I'm likely to buy one. OK, my student has had quite a hard life and has some issues (and some missing parts, like the brake, which would be hard to find or expensive). I did actually find out that I can get a new crossfeed screw and nut, but that would've cost more than the machine did.
All the time there are decent machines like that available second hand, that's going to be my preference...
If you decide that you want to go with a =93proper=94 British built lathe, I have a good Boxford AUD (power feeds to saddle and cross slide, thread cutting gearbox, single phase from new, coolant pump) that I could be persuaded to part with. If you are not too far from junction
17 of the M4 I might also deliver it (within your stated budget) as long as access is OK your end. You would need to be fairly quick for that though as my son goes back to university in a few weeks time and I wouldn=92t do it on my own.
I=92m not going to push it at you because from your earlier postings it might not be right for you and I am not really that bothered about selling it. If you read some of my earlier posts you will see that this is not my amateur sales technique it is just how I feel. I bought it from a fellow member of this group who didn=92t use it much and as, in size (4.5=94), it is in between my other lathes it doesn=92t get much use here now either. From your earlier posts these are the reasons I think it might not be ideal for you, still only you know what is right I guess.
It is an imperial machine. While in first class mechanical condition it spent all of its=92 working (standing about?) life in the education system so has the odd chip and mark typical of the breed. It is a long bed model (30=94 between centres) so will need a minimum of 56=94 length although it only needs to stand out 23=94 from a wall. The three jaw chuck is a Burnerd and seems to be in good condition, the 4 jaw is much older but works as they say. It does not have any steadies with it but does have a QCTP built to the JS design.
Anyway, enough from me, if you think you might be interested send me an e-mail and invest an hour or two in popping down the M4 to have a look. I can send some pictures but would be happier if you came and had a look at it. I am an hour and twenty minutes from junction 18 of the M4, a journey I have been doing at least twice a week lately.
For other group members, sorry but at the moment this offer is for Peter Fairbrother only due to location etc. If he doesn=92t want it I might part with it if you can make the transaction =93painless=94 for me, otherwise it can stay where it is and I can enjoy using it occasionally.
As it happens I'm breaking a complete mk2 Student. (an ill-advised buy - lets not go there!) The brake looks and seems to work OK. For a few beer tokens I'll remove it and leave it at IF for you. Crossfeed shaft and nuts are s*****d though. Contact me on the email below if interested
Sounds pretty good overall, except for being Imperial and perhaps a little larger than I want, though it will fit nicely.
Access is tricky - up one flight of stairs - but not impossible, and I could round up a few local chaps to help. Also I have moved lots of pianos, so am used to moving similar large top-heavy narrow objects. Could even leave it downstairs if needed. How big are the holes under the bed?
I'm in Trowbridge, about 20 miles south of J 17 - is that anywhere close?
OK Peter, got your e-mail but I'm just off out so I will reply tomorrow with a couple of pictures and some more details. We can then take it from there if you decide you want to.
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