|Will Cole||08/09/2019 17:43:46|
|24 forum posts|
Hi. I currently use cnc mills with waxes to create castings.
I am now looking to purchase a lathe but have specific needs, so hope someone on here can help me with some practical advice.
I am looking to create jewellery rings from stainless steel and ideally damascus steel. The melting points of both these metals are way beyond the equipment I have, so I need to machine them out with a lathe.
I will be using 25mm rod and will be boring a centre hole of anything between 15mm and 20mm to match finger size. The outside diameter will be machined down to suit. The rings will typically 6mm to 8mm wide.
I work from home so a 150kg monster of a used lathe is not practical. At moment the size and weight of suitable used machines are things like the Hobbymat MD65 (250 watt motor) and the Clarke 300 (300 watt motor). Do folks think these will be usable long term for my intended use of probably about just ten rings per week, if not can you suggest a practical alternative. Looking for something compact and under 50kgs.
All help, suggestions and advice would be gratefully received, as you guys are the experts in using lathes in small production use.
|Andrew Johnston||08/09/2019 20:42:29|
5111 forum posts
Not many people here work in production quantities. One of the oft repeated mantras is that we're not in production and our time is free so it doesn't matter how long it takes.
While a small lathe will cut stainless steel it's going to get tedious real quick in a production environment. Do you need to pass the 25mm stock through the spindle, or is each ring cut to length beforehand? If you need a 25+mm spindle bore then you're going to need a larger lathe than 50kg. Even 150kg isn't heavy for a production machine.
Whatever lathe you look at a question to ask is can it drill the bore to near size using one or two drills at most. Having to work through a large number of drills in small increments, or take lots of small cuts with a boring bar, is going to get boring.
How long have you allowed in your business plan to machine each ring?
|Michael Gilligan||08/09/2019 21:02:21|
14767 forum posts
Mmm ... If boring-out and machining the rings is the only intended purpose of this lathe; perhaps you should be looking for a 'second operation' machine, with a short bed: For any given weight, this should be more capable than the equivalent general purpose lathe.
Edited By Michael Gilligan on 08/09/2019 21:06:25
|Will Cole||08/09/2019 21:33:32|
|24 forum posts|
Thanks for the replies so far guys.
I am 'estimating' the machining time of around 90 minutes, but stress that is a complete guesstimate not based on any scientific formula.
The 25mm rod will be held in the chuck and be cut off to a sensible length beforehand. The boring out and machining of the rings would be the primary use of the lathe.
|Bob Stevenson||08/09/2019 21:42:41|
|333 forum posts|
if I was going to do this work I don't think a lathe would be my first choice of main kit.....Stainless and damascus are now quite pricey materials and there will be lot of wastage with a lthe. Also, using a lathe will more or less preclude any kind of assymetrical design, for example; any projection from the circumferance will be impossible on a normal lathe....
With all of this in mind it might be better to consider a basic forging set-up as the main fabrication technique...this would allow much more economic use of materials, better control of the shaping process and freer design considerations over details proud of the ring surface. A small forge such as a riveters forge or similar along with the all important small anvil and hammers would probably take up less space than a lathe and is likely to be cheaper to buy as well.
I was recently looking at/admiring the tiny electric forge used by a travelling farrier...the forge is just big enough to take a horse shoe and i would think it wold be ideal for a jewller working in ferous. You can work two or three rings at the same time by replacing them in the forge fro next heat while working the next ring. You could also use the same forge to silver solder additional parts etc.
Edited By Bob Stevenson on 08/09/2019 21:57:55
|37 forum posts|
I think Andrew raises valid points. I can tell you that as far as the Hobbymat goes, I don't think it'll fit the bill - others may disagree, but to my mind it wasn't really designed for repetition drilling of 20mm holes into stainless steel. The standard 3-jaw chuck will only accept material up to 16mm into it's internal bore, and the tailstock only has a 1MT taper to hold tool shanks, which tells one really what the designer and manufacturer envisaged for it.
Parting off tough material will unnecessarily hard work for this small, flexible machine - the "bed" is not much larger in section than the work you are proposing to turn.
Unless someone knows otherwise, the machines haven't been made for (?)some years, and there is no realistic spares back-up other than for the most generic items such as drive belts.
Considering the nature of the work you are proposing, I would make my economies in the bed-length, and be looking for the largest swing/spindle bore capacity coupled with the shortest bed - I too am inclined to think 50kg is likely to be to small to successfully achieve the kind of machining you are considering with much ease.
Could you bore them on your mill?
|350 forum posts|
I have made several finger rings from titanium using a lathe, the final sizing cuts are done using boring bars rather than drills.
There is a lot of waste but you can collect the swarf to scrap easily if you're only using the one metal.
A Raglan Loughborough would be my choice if I was only making rings on it.
17061 forum posts
My Unimat 3 would bore out a bit of 25mm stainless in less than 90 mins but unless you have a high hourly rate something a bit larger would get the time down. Even a mini lathe or SC4 will drill it out to 13mm in say 3 steps and then a few passes with a boring bar will take care of the rest.
If you are allowing machining of 90mins they you are only looking to produce a few a day so don't see the need for anything larger unless you want to knock out a batch of blanks. Spend the money you save on a half decent bandsaw to chop up the raw stock and saw off the part machined rings.
|37 forum posts|
..Having just seen your second post, if you are only planning to bore and finish the rings on the Hobbymat, you could certainly do it, but only if you enjoy the time you spend at the machine and are confident of recovering the costs of the processing involved.
You'd need to step up drill sizes from, say, 6mm to 10 (possibly visiting 8 in between), and then use a boring bar to finish to size. If you can find one cheap, it'd get you started, but I certainly wouldn't spend too much money on one if I could buy a larger machine with a warranty and spares support for very little more..
Have you rejected the idea of a new Far-eastern machine? ..the 180mm-sized machines have a 20mm spindle bore, weigh about 40kg (as a short-bed), and have about 500w, depending on the supplier..
|Andrew Johnston||09/09/2019 08:46:25|
5111 forum posts
Ninety minutes seems a long time to make a simple ring?
Would we be correct in assuming the ring is just that, a plain ring? Are the edges rounded to stop them digging into the finger? Before looking at specific lathes the machining sequence needs to be worked out. Assume we're starting with a short blank. Is that almost the correct length or longer to allow for holding the work?
If it's longer then the ID, OD and one edge can be machined in one setting. Then the part turned round and the excees length machined off. Be aware that it is difficult to hold thin rings securely without distortion - it's why 6 jaw chucks are made. There is quite a lot wasted material as well.
If the blank is almost to length then the ID and one edge can be machined in one setting. What sort of fixture are you going to use to hold the rings to machine the OD and other side? One for each ID value or one that will cover the range?
I'm curious as to your value proposition. Ninety minutes to machine a ring, plus material and double direct coststo give for gross profit, plus overhead seems like quite a lot for a ring. What added value means I should buy your ring rather than someone elses?
If you look at industrial setups there's a reason large, heavy machines are used to produce quite small parts. Business is very different from hobby machining.
|Andrew Evans||09/09/2019 08:52:49|
|286 forum posts|
I think if you are doing it on a regular basis using a very small lathe would be slow and get tedious very fast. You would be spending 90 minutes doing a job that should take 2 minutes. Do you have any space to have a larger machine at all? Do you have a garage or shed to put a lathe in?
1 option is a smaller CNC lathe like a Denford Starturn. It would be slow but at least you could do something else while it worked away.
|Will Cole||09/09/2019 09:45:27|
|24 forum posts|
Thanks for all the detailed responses I have received, this is really helpful to me.
To quickly explain my current setup, will probably help clarify things, why I am looking at these materials in particular and why I would need to machine them.
Currently I have CNC four axis prototyping machines. Essentially small mills that work with light materials,working to a very high degree of accuracy. The fourth axis means I can create rings with high levels of details and complexity, essentially leaving the machine to do its thing to create a usable master.
All good to this point, but the problem then comes with casting. Getting up to the temperatures to cast stainless would take some serious kit as most commercial metal furnaces only go up to 1250C. Similarly burnout kilns need to take flasks up close to the pouring temperature to prevent premature cooling of castings, but commercial investment flasks are themselves made of stainless steel. In practical terms just not doable. Damascus steel adds the further complication that casting would completely destroy the symmetrical pattern as the metals fuse into one mass. To create in the materials on a simpler scale points to machining on a lathe.
At the moment this is essentially a costing exercise to assess its viability. This is in response to an enquiry from an existing customer. Whilst they may seem strange materials for jewellery, they are considerably tougher than either gold or silver, do not require the hassles with hall marking and are becoming very popular now, as indeed is tungsten.
|Andy Carruthers||09/09/2019 09:57:56|
262 forum posts
In view of the number of operations to be carried out you might consider a capstan lathe - one that has several tools mounted on a rotating capstan in the tail stock. This would greatly simplify tool changes and increase both productivity and repeatabili8ty but at the expense of reducing available bed space which probably isn't of great importance for the work you anticipate carrying out
|Will Cole||09/09/2019 10:02:10|
|24 forum posts|
Forgot to add that this is essentially the ring core I am talking about rather than the finished item. Other materials would be added to machined channels. I obviously wouldn't spend 90 minutes to create a plain stainless steel band.
Edited By Will Cole on 09/09/2019 10:03:17
|David Colwill||09/09/2019 10:02:36|
|598 forum posts|
If you do go down the route of a lathe perhaps look out for an EW lathe. Details can be found on lathes.co.uk.
These are small but have back gear and while you won't get anything of note through the spindle it would at least have some torque at low speed.
Instead of drilling and boring out consider using an annular cutter or rotabroach. These will leave a slug of metal from the centre thus saving work.
If you are anywhere near Nottingham I do have both an EW and a set of rotabroaches that you can look at / play with.
|Will Cole||09/09/2019 10:06:59|
|24 forum posts|
Thanks David. I had looked at the possibility of diamond coated core drills, but must admit that rotabroaches are not something I had ever heard of, so thanks for that idea. Something else to look at.
|Mick B1||09/09/2019 10:12:45|
|1355 forum posts|
I've made finger rings for friends and family from ironwoods and titanium on a Myford Speed 10, and more recently on my Warco WM250V.
They were plain rings, and I found it easiest to turn, drill and bore from barstock and part off, sometimes mounting the ring on an expanding spigot made from a bit of scrap brass to clean up the part off side where necessary.
I think almost any lathe from mini-lathe size and up would make your 90 minute time criterion very easily (with time for a cuppa and a sandwich), and so long as the hole in the chuck will take your stock size you probably don't need a big spindle bore unless you're doing much bigger quantities than your projected 10 per week.
|Neil Wyatt||09/09/2019 11:15:15|
17070 forum posts
If looking at a Mini lathe I would go for one of the brushless motor ones if it was going to be something I relied on.
They will happily work the materials you want, I would suggest using carbide insert tools for stainless steel.
|Neil Wyatt||09/09/2019 11:16:18|
17070 forum posts
If you have four-axis CNC can't you machine the blanks on that?
17061 forum posts
Sound more like the OP has something like a 6040 spindle router so that would be pushing it to bore out the bar, OK for light engraving etc around the edge.
Does it have to be a specific grade of stainless? could just go and buy a bag of M16 nuts which would reduce the amount of metal that needs to be removed and save having to part/saw up longer bar.
Edited By JasonB on 09/09/2019 11:26:38
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