Turning small diameters

Chas explained :

That and smaller can be done and even hallow tube on a C3 (also known as a Chinese 7x14), with the right tools and technique - but not by me yet. The lathes do need to be tidied up a little to get best performance out of them. You can get them for under £350 via ebay.

Any clue on what the right tools and techniques are?

Yes, I might well go for the ebay 7x14 that is actually from the US Big Dog , which I think is not a Sieg but very similar. But if someone tells me I'd be better off with say, a Taig, for the small stuff, I'd get something like that.

On 11 Nov, 22:50, "Chas" wrote:

Turning long (relatively) thin pieces requires some skill, the correct tool, and a little luck. High spindle speeds are useful, IIRC I rarely ran my unimat below the top 2 speeds (2500 and 4000 rpm). small diameters have low surface speeds, so going flat out is not usually going to fast. Generally ignore carbide, for small diameters you want the minimum cutting force, to reduce deflection, and for that using HSS, or CS if you really get into it, is best. Sharpen the tools with more top rake than normal, and hone them to a sharp edge. An easy way to asses sharpness is to run the tool *lightly* over you thumbnail. you should be able to shave a tiny thin curl off. Brass is usually cut with no top rake, but I found that a sharp tool worked for small diameters as long as the lathe is not 'sloppy'. The cutting force trying to move the tool into the work that is generated by the top rake is small compared to the force required to move the crossslide generally. Take small cuts, and be patient, its very easy to spend a couple of hours getting a tiny part done. Its also very easy to scrap it on the last cut (DAMHIKT...) Use 'free cutting' variants of metals, in the real world there is potentially a strength loss issue here, but in tiny scale it will not matter, and every help you can get will make it easier. Make temporary steadys from bits of hardwood. parquet flooring is useful for this. On small parts you can help steady by just holding a piece of hardwood against the part. Make sure your tools are on center height, *EXACTLY* as there is less scope for error, if you are a little low your part will catch, bend and then run over the top of the tool, to high and you will increase the cutting force considerably, assuming it will cut at all.

The cons of a little lathe (C0 / unimat etc) are that you very quickly run out of size and power. The myford size (3.5" center height) has been around for a while, and so I guess it must have proven to be a reasonable compromise wrt size vs weight. A general truism is that you can do small work on a large machine, but not the other way round. A not quite on topic illustration of this are the rc helicopter parts I used to make. They weighed about 0.5g, and would fit comfortably on a penny, but I made them using a 1700 kg 10x50 (IIRC) knee mill. As for specifics a chinese 7x lathe will work just as well as a more expensive lathe, but you may have to 'tweak' it a bit to get it working nicely. A friend of mine had a Taig, and did a lot of good work on it, but he also had to tweak that, as it has no leadscrew. He has recently 'upgraded' to a Seig C3 (Arc Euro Trade is just down the road from here), and seems very happy with it.

I started with a super adept (tiny old lathe), but quickly got a Unimat, which I made a lot of small parts on. Works fine, and is still in the cupboard for the occasions when a smaller lighter and faster (4000 rpm) lathe is appropriate. TBH though it hasnt had a lot of use since I got an L5, and then recently a CVA. Most of my stuff, turning wise anyway, is just nicer to do on the larger lathes. You can take large roughing passes, and then finesse the last bits out, where as the smaller Unimat doesnt have the power to do more than a finishing pass every time. The C3 sizes are somewhere in between IMLE.

HTH

Dave

Dave, Thank you very much. Very helpful. So I should probably look for a machine with a reasonably high spindle speed. These seem to be the smaller ones, I suppose it's easier for them to make a small one run faster. I suppose that narrows it down in my budget bracket to a Chinese 7x (max

2500 rpm), a Unimat 4 (max 4000 rpm) or a Taig (max 7000 rpm)

Obviously you know what you are doing - so would you be confident about making a brass piece 0.5mm dia, 20mm long, on something like your Unimat using your accumulated skill and tooling?

I suppose the exact on-centre tool setting must be quite an issue at small sizes - 1 thou high/low on a 20 thou dia piece is out by 10% of the radius, which I guess is a lot. So I suppose the more precision engineered the lathe, the easier it is to achieve this. But I don't see any conclusive evidence for any difference in precision between the machines in my budget bracket.

Chas

Chas,

Talking about tool holders for modeller's lathes, have a look at the toolholders for the Fonly lathe in this article.

You will probably want to do free hand turning for items like chimneys and domes and these tool holders let you do it very well. You would have to supply a flat surface for them to sit on but this coould be as simple as a piece of metal plate on the cross-slide.

I started on a Super Adept which was treadle driven (converted Singer sewing machine table, so speeds for small diameters were not too high. For very thin work, the travelling steady was my finger :-).

Another way of turning thin work is to take one cut fron a larger stiffer piece. This minimises the work deflecting from the tool, but you do need a lathe with a bit of grunt to take the cut.

Also for small diameters, you can use a tailstock mounted tool which combines a cutting edge and a steady - i.e. the body of the tool has a bore which is just clearance on the machined diameter and the cutting part of the tool is right at the front.

Jim.

No problems. I assume you are a usenet noob? Try not to top post (answer at the top to a question) it

*REALLY* winds up some people, and makes it harder to follow the topic. Ive mixed my answers into your original questions, but a full post at the bottom is also used...

Whilst fast top speed is useful I wouldnt get to hung up on it. (My L5 is about 1000rpm) Are you only ever going to do small stuff? (the answer to this is no incidentally, machining is addictive...) I found the unimat limiting in its smallness, the taig is better in this respect, but the 7x chinese is better again, for no more real bench space. If you want it to go faster I would venture that turning a new pulley set is a simple lathe job ;)

Dont forget that the lathe is just the start of the expense, you will also need to budget for tooling, chucks / collets / a bench grinder to sharpen toolbits (assuming you dont have one), metal to turn into scrap etc etc...

Turning 0.5mm x 20mm I could do on the unimat, on the harrision, and on my CVA. however no matter what the machine Id reckon on probably scraping 2 out of 3 if I was having a bad day. This thread (

) shows a picture of some brass parts I made, IIRC they are 1mm in diameter, about 5mm long, but they have a 0.5mm hole cross drilled in the middle. I used the unimat and my *big* TOS mill to make them, as I could have the unimat sat on the mill table and it made the various ops easier. I wouldnt limit yourself to brass either. use the appropriate metal for what ever it is you are making. FC steel turns really nicely for instance, silver steel can be hardened which makes axle point bearings run nicely etc. guide bars from old printers are really nice metal to turn, some sort of precision ground steel.

Setting the center height has very little to do with the quality of the lathe. Pretty much any new lathe will hold the same tolerances at the price level and size we are talking. Some may 'feel' nicer, or have a better finish and paint, but paint doesnt make parts. A quick change toolpost makes getting c*ck on simpler, but I dont have one for my unimat, just a large selection of shims.

Dave

But be careful! Whilst superb to machine it is I think plated, probably nickel. I made some pillars for a job recently and bunged them in with the rest of the job for blacking. The areas that I had machined blacked ok, the original diameter did not!

Back to the subject line. When I first fired up my Viceroy (10" swing) I played with some tools and happily turned a length of 8mm printer bar down to 1mm (over about 10mm long). Pleased with that I then drilled it up the middle with a 1/64th drill, even more pleased with that I shoved it on the mill and cross drilled it again 1/64th.

The max speed available for the Viceroy was 1300 odd rpm so I woul not worry too much about a high speed capability. As has been stated sharp HSS on centre tooling is a must! Richard

Jim, Many thanks.

I get the general point, which seems to be that small diameters are more about the skill of the lathe operator than the features of the machine.

I have seen descriptions of the cut-in-one-pass approach, and it makes sense - but mostly these seem to be of the order of 1.5 - 2mm dia.

Yes I have looked at length at the Fonly lathe. I kind of assumed that it's a way of getting some sort of lathe for next to nothing, and whilst I am cheap, I'm not that cheap. On topic, one of the things that put me off about the Fonly, which I still don't understand really, is that it is ungeared, driven from a multitool. So a Dremel, as a good example, runs from 10000 to 33000. They don't all go quite as fast as this, but part of the point of multitools is the substitution of speed for torque. It really surprises me that this vast difference in speed from normal lathes doesn't totally mess up the cutting process. Obviously it works, but it destroys my confidence that I understand how lathes work and the logic of lathe feature selection!

Chas

Dave,

OK, no more top posting. Yes, a noob. I suppose I'm used to email chains in reverse order, but of course this isn't email.

Hmm, I'd have thought the maximum speed of these things was set by the balance of the rotating chuck and associated stuff, and maybe the bearings, so I think I'd be a bit worried about just gearing it up to double or something. Maybe an experiment for when I'm really skilled and confident, in about 2019 or so.

Just what I wanted to understand, thanks again.

I'm getting more confident now that some sort of 7x is the right compromise for me. Tiny things beyond my turning competence will just have to be made some other way. There's always wire.

Chas

In article , Chas writes

Chas,

Dave Sanderson has given you lots of good advice, which I will try not to repeat.

You don't say how *long* the very small diameters are to be. This is important, as workpiece deflection is one of the biggest problems with turning very narrow parts. Varies a bit with material stiffness, but once you get to more than a couple of times diameter the finished part will taper (wider at the outboard end) too much to be any use. As Dave said, you can use a steady, but the conventional type with fingers will almost certainly not close down far enough (you could try making the fingers more "pointy"). Probably a better solution is to use a rose bit (think of an end mill with a hole up the middle) or one of these small diameter turning tools:

This has advantages: unlike a rose bit, which has to be home made and only works for one diameter, it can work for a variety of diameters (you have to make a bronze insert for each) and it is ready made (and it is quite cheap). It also allows the turned part to have indefinite length.

Even a steady at the end won't help if the turned part is more than a few diameters long - the middle will deflect away. The above devices overcome this.

I suspect the use of hand gravers has in part to do with the fact that not all the turning is parallel, with some curved sections etc, but I'm not a watchmaker, ever. Also, AIUI, the tolerances in watch/clockmaking may not be what you think, I believe sloppy (= very low friction) fits are the norm.

The other issue you need to consider is maintaining concentricity. Very often you will need to work on the end few mm of the part, by pushing most of it into the chuck (to minimise deflection) then to work on the next bit you pull it further out, and with most chucks you will be lucky to have it concentric with the bit you turned first. The best solution is to use collets, which are much better at maintaining concentricity - they are pretty standard on watchmaker's lathes for that reason. This is something to look at when selecting a lathe. The best and most convenient system I have used is that on Myford's 7 series lathes, which has 2 MT collets held in place by a screwed nosepiece. Not cheap, and I suspect from what you say that the Myford lathe option will be outside your price range anyway. You can get MT collets with threaded rears which are held in with a drawbar, work for most lathes with an MT headstock; never used these. Collet systems using adapters for ER collets are an alternative, though in my experience the concentricity straight from the box is not as good, you may need to true up the taper on your lathe, not for the faint hearted.

On the question of lathe size, then up to a point go for something larger than your immediate needs. It is, as you say, always possible to do small work on a big lathe, and not possible to do big work on a small lathe. I say "up to a point" as big lathes tend to be much more awkward to do small work on. I have a Myford S7 (3.5" centre height) and a Harrison M300 (6.5" centre height) but would always prefer to do small work on the Myford (the collet system is part, but only part, of the reason for that). In addition to looking at what collet systems work on your potential lathe, it is very helpful if it has, or can be fitted with, a finely graduated leadscrew handwheel, like the S7. Something I really miss on the M300. Thus means you can position the cut to within half a thou, which is difficult to do with the topslide (as (a) the graduations are too small and (b) you have to set the bloody ting to turn exactly parallel in the first place).

For fine work you need to ensure your slideways are smooth but without a trace of slop; this is one area where a cheap lathe will need fettling. A topslide lock (you will have to do this yourself) will aid security. For getting really fine cuts with a topslide (as opposed to one of the above devices) set the topslide to a fine angle so that 1 thou on the dial gives 0.1 thou of cut (but don't forget to allow for the extra movement towards the headstock, DAMHIKT).

One final thought: tool shape for turning narrow parts should be knife types with a sharp corner, not round-nosed. The latter will cause much more deflection force than a knife type; the latter should have a very, very fine radius to reduce stress raising in the sharp corners, but no more. (This is because almost all the cutting force with a knife tool is parallel to the axis, towards the headstock.)

Hope this helps. If you give more detail about the things you want to make, I'm sure the collective expertise here will be able to add more. I myself have just re-activated my interest in RM after a gap of 30 years, investigating recent commercial N gauge stuff, but have not yet got involved in re-engineering any of it.

David

In article , David Littlewood writes

Forgot to say, you'll have to scroll down, the thingy is right at the bottom of this very long page....

David

Dave,

I thought this might be a problem.

The link seems to be broken but I found the Chronos page and tool, thanks. It's obvious I'm going to have to get used to some very precise and careful setup - at first sight it looks like even a minute tailstock alignment problem will just break the turned part as it goes through the hole. Obviously yet another skill to add to the very long list.

Ah. This makes sense.

This seems to be available for Chinese 7x lathes. e.g.

Hmm not sure whether this is available, even as an accessory, on any of the lathes in my size bracket. No photos really show the hand wheel properly. Google searches (hampered by the difficulty of knowing what search terms to use) don't find me anything. On the basis that if it isn't advertised, it isn't there, I assume I won't have this. Anyway, I don't really understand, I'm sorry. Is this used after repositioning the stock in the collet? Or for positioning for second and subsequent passes? Bit lost I'm afraid.

It definitely helps a lot. Can't be more definitive really. I was just looking for general guidance on the relationship between 2 choices I want to make - deciding to model in a tiny scale, and buying a lathe to, amongst other things, assist in the modelling. Which I have received.

Chas

Ridiculous.

There's no reason why any should get wound up by the positioning of a reply.

Surely it is the content of the reply which counts?

Ridiculous.

There's no reason why any should get wound up by the positioning of a reply.

Surely it is the content of the reply which counts?

In article , Chas writes

You can get similar things from UK suppliers.

Some have it (Myford S7, Unimat, the Sieg C0 and C1) but many don't (Myford ML7, Sieg C3, lots of other Oriental lathes, my Harrison M300). It is extremely useful for moving the carriage in precisely controlled increments to apply a cut of known length. See the top picture:

It's the handwheel at the bottom right.

Otherwise, you have to use the topslide (which may or may not be set to turn parallel, depending on what you last did with it) or use power feed with a stop, having measured the length previously by some other means. Whatever this means is, it is unlikely to be more precise than the large

1 thou graduations on the big handwheel.

You can buy add-ons, for example

but you would perhaps have to work out for yourself how to fit it. You could also buy a blank handwheel, eg

...but then you would need to graduate it yourself. (Make a graduating head and you will learn more about precision machining than you could imagine.)

One feature of lathes with fitted leadscrew handwheels is that they (usually) have left-hand leadscrews so that the direction of turning the handle is the natural one. Lathes without often have right-hand leadscrews, which means that the wheel (if you fit one) turns the wrong way. One can get used to pretty well anything, but it helps if all the handles work in the same way. I have been contemplating fitting a handwheel to my M300 with a sun/planet gear to reverse direction, but I doubt I'll ever do it.

I suspect that if you buy a tiny lathe to do tiny bits, you will soon be frustrated. I started out with a Unimat 3, but found it fairly feeble and soon got pissed off with it. (It also got through drive belts with distressing frequency, usually breaking my last one on a Sunday.) Consider buying something second-hand that's got more capability. A few years ago, the common advice would have been "buy a Myford" but today it's hard to justify that if you are not seriously keen - the far east stuff has got so much better and is much cheaper than a decent second hand Myford. Of course, Dave Sanderson had a nice looking Harrison L5 on homeworkshop.org.uk on Monday at a good price, but that might be a bit big for you.... (He was too much of a gent to mention it here so I'll do it for him. Of course it may be sold by now.)

Another question you should ask yourself is "am I ever going to want to cut screw threads (much superior to using a die). If so, be sure it can do this (the C0 can't, AFAICS). Are you likely to need imperial and metric (the C3 is only one or the other, depending on which you buy). Some (eg

seem to be able to do both.

I started out using dies, but once I had experienced the delight of a well made screwcut thread I was hooked.

BTW, you may have had trouble with the Chronos link because the last letter wrapped to the next line. Sometimes you need to copy/paste these things.

David

I wouldn't disagree with any of the advice you have been given, but maybe I can add a few comments from the point of view of one who uses lathes of 3.5" (Myford ML7), 2" (clockmaker's), and 1.75" (watchmaker's) centre heights.

The 3.5" lathe is fine for general small scale engineering work involving a compound slide taking sizeable cuts where finish does not need to be the best, but would be awkward to use a graver on because all that cast iron gets in the way. It can be done of course, but why make things more difficult than they need be. There is also the difficulty of maintaining concentricity unless you invest in collets.

I use the clockmaker's and watchmaker's lathes exclusively with collets, turning sometimes with a compound slide and sometimes with a graver and T rest. The graver gives a finer finish because there is more feel than a screw fed tool, though it requires more skill in its use. If made exceptionally sharp and held at the correct angle the graver can take off two tenths of a thou, even from fairly tough blue steel, and leave a surface that only needs a bit of Simichrome for a mirror finish. Naturally these lathes run faster than the Myford, 5000 rpm on my smallest machine, though I rarely use top speed. The other advantage is the alignment of the tailstock is generally much better than the larger machines. I drill 0.5mm holes with carbide bits and only rarely break them. That would be impossible unless the tailstock is spot on.

Cliff Coggin.

In article , Phil O. Sopher writes

Content is only of full value if people can follow it. It is always helpful to make it easy for people to see (1) question and (2) answer, or (1) assertion and (2) response, especially as threads can get quite complicated.

Of course, if this doesn't bother you, or you have nothing of value to say*, go ahead, no-one is likely to shoot you.

*I find there is a fairly strong correlation between this and posting under a fake identity.

David

Chas was thinking very hard :

You will no doubt develop those after lots of practise.

Hugh or Harry(something) as he calls himself on ebay? That was who I bought mine from several months back. He is good to deal with and very helpful if you do find problems. Be warned that these are just as they come from the Chinese factory and need some time spent on them to get the best results.

I'm sure the 7x14 will suit you and it is well supported with information. Look up the 7x12 mini-lathe yahoo group.

Chas used his keyboard to write :

You are starting with a thicker material and even if the lathe centre is a little off, it will turn it down to wherever the centre is. The error (assume 2 thou)only becomes a problem if you take it out of the chuck and reposition it in the chuck 180 degrees from your initial position, where upon the off centre amount will be doubled (4 thou). So you mark piece and chuck, if you intend taking it out and putting it back.

Another way is to use an independent 4 jaw chuck which allows you to centre the piece - each jaw can be independently adjusted.

I think you are confusing tool center height with spindle center. You are correct that stock set off from the spindle center will behave as you describe, and as you say this only matters if you want to remove and reposition the stock. However setting the tool cutting edge on center is a must for thin work. If the tool is not at center height then the stock will either try and climb over the tool, or be forced away from the stock by the non cutting front face.

A tip that an experienced machinist told me once for fine finishing is to grind a *ROUND* tool square on the front edge, half thickness (like a D bit), but with a hook chip breaker and some (5 degrees or so) front clearance. Then make a holder for the round bar so it ends up approximately on center height. Rotate the tool 45 degrees in the direction of travel and use it to take

*very* fine finishing cuts. because the tool presents a flat edge that is perpendicular to the horizontal from the center height it is always going to be on center height. Its harder to describe than to make honest.... if its not clear imagine a stanley knife blade held so the sharp edge is at 45 degrees from vertical, and pointed towards the stock, and towards the headstock (assuming R to L travel).

Dave