AWGB Woodturning Forum
General Category => General Discussion => Topic started by: edbanger on May 26, 2014, 07:49:32 AM
-
Hi All
I've been reading a post in the gallery posted by Sergio on his mirrors, he had a couple of faults which have been pointed out and he replied, he states that he normally turns at under 1000rpm and keeps a sharp tool and a steady hand.
I turn mostly larger items and in the main my lathe is spinning at 500rpm once the wood is roughly shaped and in balance, I think that I get a good finish with the gouge so not to much sanding is required, I have read post on here where people use different sanding methods because they think that there turned finished work needs it, do people spin their lathes to fast so they have not got full control of the tool in their hands?
This has prompted me to ask this question. What speed do you spin your work at and why?
Ed
-
How long is a piece of string? Simple answer is the fastest speed that is safe. As you can imagine, some of the things I turn with cracks splits voids etc not to mention potentially loose bark are turned as low as 200 or 300 rpm at first but when I am say doing small spindles for drop spindles it can go up to as much as 3000 rpm. Sanding on the lathe I do at lower speeds as it generates less heat. As a sort of average I would guesstimate that I am turning at around 1000 rpm or less most of the time though on the variable speed lathe. the old Tyme Avon I use has belt change and is used for smaller stuff and is more or less permanently on 1000.
-
Hi Ed,
I turn at the correct speed for the piece I am turning, slower for large pieces and faster (but not always) for smaller pieces. The speeds range from just going round ie.about 5 rpm to 3000 rpm.
-
John & Pete have summed it all up,
As you get better the speed you turn at increases but it's still only at a 'Safe Speed' for the item you are turning.
-
How long is a piece of string? Simple answer is the fastest speed that is safe. As you can imagine, some of the things I turn with cracks splits voids etc not to mention potentially loose bark are turned as low as 200 or 300 rpm at first but when I am say doing small spindles for drop spindles it can go up to as much as 3000 rpm. Sanding on the lathe I do at lower speeds as it generates less heat. As a sort of average I would guesstimate that I am turning at around 1000 rpm or less most of the time though on the variable speed lathe. the old Tyme Avon I use has belt change and is used for smaller stuff and is more or less permanently on 1000.
i total agree i personaly turn as fast as a piece will go and still be safe and that i feel safe doing so but its all personal just because turning a bowl at 1500rpm is ok for me dose not mean its the right speed for some one else
-
Lowest speed I can go is 200 so there are times when I have decided not to turn something as even that is too fast. The speed that you use can also depend on the lathe. There are some lathes where the lowest speed is 700 rpm and to be honest that is far too fast IMHO for some off centre work. Remember that the faster you are going, the faster things happen and so if a piece breaks off or the work gets detached it stops being painful and becomes downright dangerous. With experience it is all too easy to become base and think it's OK to go faster. It isn't.
Pete
-
Hi All
thanks for your answers, I agree that you should turn at a safe speed for the work you are turning, part the reason for asking was we purchased our son a Axminster lathe for his birthday as he quite like the idea of turning but the slowest speed his lathe runs at is 500rpm which seems a bit fast when your turning something to shape, this is designed to be a beginners lathe.
Ed
-
I'm so glad nobody has linked to some table showing lathe speed against dimension of timber. IMHO these are so dangerous as there are so many variables to consider when selecting the appropriate speed.
It's noticeable that everyone has referred to a speed suitable for the piece being turned but no-one has mentioned the lathe set up being used, though Ed has kind of hinted at it with the beginner lathe for his son. A bench lathe on a weighted bolted down bench would allow more use of the speeds available than one on a flimsy bench used for storage and not bolted to the floor.
-
You're right mark. In fact some of the legs that come with lathes such as the one I was using at Yandles are IMHO not worth having. have two old lathes on a a single big workbench. I have to dismantle everything to move it and yet there have been times when I can feel it vibrating if I have the speed up too much. One thing I learnt the hard way (not getting hurt fortunately) was to check the speed before putting the work on. Even with variable speed, turning it down after mounting isn't the best or safest way. Even small pieces that are off balance (and that can be for a number of reasons, not just the shape of the wood) can set up a surprising amount of vibration and potential hazard.
Pete
-
it really depends on what each turner is comfortable with, i have recently turned some large walnut bowls and was down at the 4-5 hundreds but yesterday and today i've been turning 2 and 3" spindle work which was at 3000rpm.
when i make skittles i turn them at 2000rpm and they are usually 5" diameter. if it's balanced you can up the speed a bit if you want but if its too unbalanced then you need to keep it down.
-
Ed
Lots of good advice already given above. On a recent course, we were told to turn at the speed we felt safest with. Turning 8" bowls at circa 2100 rpm didn't feel safe at first but after a few hours, felt OK.
Add a good sharp tool to the speed and you get a really good clean cut. We were using 180 down to 320 grit only as the finish off the tool was excellent.
The Axminster lathe does run fast for a beginner but with some careful supervision at first, should be OK for your son. It's amazing how quickly youngsters get the hang of things these days!
David
-
A question for Mark - without some sort of speed guide or method for calculation, how do you explain to beginners what a safe speed is and what is a realistic maximum speed for a given diameter workpiece?
One observation possibly worth bearing in mind when considering turning speeds is that if you double the speed, the centrifrugal forces multiply by four because it's an exponential relationship. It's the centrifrugal force that will cause the workpiece to separate, particularly if there are flaws in it. Having a well balanced workpiece may not be enough to prevent an accident if it's running much faster than it should be.
-
We all seem to have learnt that the safe speed is dictated by the piece of wood that your turning, but many people who start turning use pre-cut blanks could there not be a speed guide for this type of turning? It might make it a bit safer for those starting out who have little common scene.
Just an idea
-
We all seem to have learnt that the safe speed is dictated by the piece of wood that your turning, but many people who start turning use pre-cut blanks could there not be a speed guide for this type of turning? It might make it a bit safer for those starting out who have little common scene.
Just an idea
Ed you have very nearly answered your own question here re:" those with common sense". It is not, as has been pointed out, the size of the wood that dictates the turning speed, there are many factors that can affect it. Some timbers have a marked weight difference from one side of the "plank" to the other. Weigh the light coloured wood from Laburnam and then weigh the darker wood and there will be a differential in weight between them. This will affect the lathe speed (or could affect it). If the wood you are using is damp the side nearest the floor when stacked will be heavier than the top. There are all sorts of variables that should be factored in. Those with common sense will realise this and work accordingly, those with little common sense will either hurt themselves or someone else and/or give up, I favour them giving up.
-
A question for Mark - without some sort of speed guide or method for calculation, how do you explain to beginners what a safe speed is and what is a realistic maximum speed for a given diameter workpiece?
One observation possibly worth bearing in mind when considering turning speeds is that if you double the speed, the centrifrugal forces multiply by four because it's an exponential relationship. It's the centrifrugal force that will cause the workpiece to separate, particularly if there are flaws in it. Having a well balanced workpiece may not be enough to prevent an accident if it's running much faster than it should be.
I asked for that Paul ;D but a good question. I simply get my students to feel the lathe as they increase and decrease the speed along with explaining that consideration has to be made for both the timber blank and the tools that are being used i.e. faults/imperfections in the blank and it also has to be an appropriate speed to allow the tool to do it's job.
-
More on the centrifrugal force - an 8 inch bowl at the "optimum" speed of 750 rpm (based on that approximation that Mark doesn't like! ;D) would have a force of approx 65G on it's periphery. the same bowl turning at 2000 rpm would have a force of approx 450G. It's easy to see how choosing the wrong speed could end in disaster if the piece of wood had any flaws in it.
-
More on the centrifrugal force - an 8 inch bowl at the "optimum" speed of 750 rpm (based on that approximation that Mark doesn't like! ;D) would have a force of approx 65G on it's periphery. the same bowl turning at 2000 rpm would have a force of approx 450G. It's easy to see how choosing the wrong speed could end in disaster if the piece of wood had any flaws in it.
Yuk. I hadn't realised it would be anything like that.
-
I explain it slightly differently;
The circumference of a circle is calculated as πd,
So for a 2” spindle for a candlestick, rotating at 1000rpm
= π x 2 x 1000 = (approx) 6¼” x 1000 = 6250” or 525’ per minute past your tool.
And for a 8” bowl blank, rotating at 1000rpm
= π x 8 x 1000 = (approx) 25” x 1000 = 25,000” or 2100’ per minute past your tool.
Also useful for explaining why you need to cut slower as your tool moves in towards the centre of a bowl blank, the rotational speed is the same, but the speed of the wood over the tool is less.
(π = Pi, but does not show very well in this font)
-
I suspect a lot of turners, experienced and new are unaware of the speeds, the forces and the velocity of a piece that breaks off. Using D'fly's calculations a bowl that breaks off at 1000 rpm will hut you at just under 30mph. Not good.
pete
-
to complicated for me, never was any good at maths. I will stick to seat of the pants turning, start slow and wind up until I lose my nerve ;D ;D ;D ;D
-
A few years ago when I was unable to do any turning I put together a spread sheet to work out the speed of wood on a lathe. Belwo is a screen capture of it if anyone wants a PDF of it drop me a PM with your email and I will send you one.
Here I must insert a warning I did this for fun and not for it to be used as a guide to safe turning speeds.
john
(http://i73.photobucket.com/albums/i237/jptaylor_photos/Workshop/speed_zpse386db74.jpg)[/URL]
-
Thanks for all the reply's to this thread it make interesting reading and the speed at which the wood could hit you should it come off the lathe call for full body armour :) :)
Ed
-
I a uncomfortable with the table and feel the best advice is to ignore items such as this as they can be misleading,
I would personally recommend only turning sound timber and to work at a speed at which you feel comfortable and safe.
This statement was in most of the articles I wrote for GMC publications.
Nick Arnull. RPT.
-
My lathe doesn't have a digital readout of speed but it does have a chart stuck on it giving the speeds for different dial settings on each of the pulley combinations. I usually find I am turning at much slower speeds than I thought I was. :)
-
I a uncomfortable with the table and feel the best advice is to ignore items such as this as they can be misleading,
I would personally recommend only turning sound timber and to work at a speed at which you feel comfortable and safe.
This statement was in most of the articles I wrote for GMC publications.
Nick Arnull. RPT.
I agree 100% with this.
As I said it was done mainly for fun and to show the difference in speed between near the centre and the outside.
I turn at a speed that I, the lathe and the wood all feel comfortable at, which quite often varies even with blanks of the same wood and size turning the same thing. Another important thing to mention here is to always wear a full face shield of the highest impact resistance just in case.
john
-
All of my wood is in the form of chainsaw cut " blanks " so are invariably out of balance so I start off slow ,and gradually build as it becomes more balanced but rarely do I turn fast , except for small pieces , lids, knobs etc ,but I really have no idea what the speed is as I do not have a speed gauge on my lathe . I have a short bed lathe and most of the time I stand at the end so am out of harms way if something comes off, which does happen on occasion ,mostly loose bark .
-
just started turning a 30"x 6" chainsaw cut walnut that weighs 70kg and started it down at the 60's. just got up to 250 near round.
-
The most common answer to the speed question seems to be: turn at the highest speed you feel confortable/safe. I have a problem with this because it does not rest on any logical bases. Can a subjective feeling be use for a safety issue? I do not believe so.
In my opinion the answer could be reversed. The turning speed is the lowest speed that allows a good finish. For this of course one needs a sharp tool, practice and a steady hand. Increasing the speed increases the amount of wood that touches the edge for a unit of time thus one can increase the speed of the tool travel. But the same result can be achieved with a lower lathe speed lowering the feeding rate of the tool. More difficult because it involves a better technique and probably not good for a professional for which time can be money.
There are two other points I would like to address. Radial speed is, as explained in another post, proportional to the diameter of the wood, and diminishes going from the periphery to the center (zero diameter, zero speed). But for a safe speed one must consider also the way in which the wood is hold. Spindle turning is the safest, chuck is the least safe. Also, when turning a bowl on a chuck it is important to consider the hight of the bowl since the high bowl means more overhang and stress on the tenon.
For one example I attach goblets, the tallest is exactly 17 high (just measured) with a stem that starts at less than 3/16 inch and turned at less than 1,250 rpm.
-
Sergio, you've added some well founded considerations, there are so many compounding factors which we all need to know, may encounter and hopeful not within our turning life time, I consider it calls for a common bases on speed, I was given a list, read much the same in many books when I started all those years ago, it was deemed wise, let alone safe then, what has changed today, it's very much like there are speed limits on most roads/within towns .. how many still consider to drive at a greater speed ... we all have done it ... what of safety though, throw it out the window as not relevant.
The point has already been raised with the differences with lathes, vari speed/vari matic or set pulley sizes, in the latter case the given speed could well be very slow until the piece is balanced, I know only to well with both my lathes... then where you've mentioned it's not economical to the professional, as such we read as to the advocating of higher speeds, fine, yet not advisable for the novice until you've not only got more experience: but greater understanding and awareness of risk assessment.
At the end of the day each and every turner has a differing opinion on not only speeds: but most aspects of turning, ranging from the best type of tools, bevels, grinds, work holding to finishes etc.
I'll end with that's a fine display of goblets there. Thank you for your valid input. David
-
I believe most turn at a speed that is too high and rely on the speed to provide a good finish rather than good technique.I know this is somewhat controversial but it is my opinion.
if you have ever seen me turn I rarely run the lathe at any speed but use sharp tools technique and control to achieve the end result.
When teaching more experienced students they often have trouble with spiral chatter on bowl work, this is caused simply by high speed and differential grain density the answer is simple, drop your speed and sharpen the tool problem solved,for Bowl turning any speed over about 1000 rpm is simply not needed in my opinion.( these comments relate to Bowl work and not other areas of turning)
Nick Arnull.
-
Since this thread started I have been looking at my speed to see what I tend to use and find that like Nick I am rarely if ever over 1000 on faceplate work and spindle work depends a lot on the wood as well as the size. As a lot of the wood I use is potentially likely to split etc I use even lower speeds. Yesterday I was roughing out at 300 for one piece. The top speed on both my lathes is only about 2000 anyway and it is rare that I go the flat out speeds.
Pete
-
Sergio
I think that you are correct, people should be taught to run the lathe as slow as possible and to have sharp tools and master good tooling techniques. Since I started this post I've been checking my turning speeds and I find that I work well under 500rpm once the wood is balanced, dependent on the size of the piece the range is from 200rpm to 400rpm. I only use the faster speed for buffing.
We should all promote turning at the lowest speed possible this would make things much safer should something decide to depart from the lathe unexpectedly.
This has turned out to be an interesting post and the feedback from everybody has been first class.
Ed
-
I find that I work well under 500rpm once the wood is balanced, dependent on the size of the piece the range is from 200rpm to 400rpm. I only use the faster speed for buffing.
That does seem VERY slow. I must give it a try and see.
-
that sounds too slow for many purposes.
my skittle production at that speed would take ages. one set might be finished in a days work at that speed rather than the 1500-2000 i currently make them at and one set takes 2-3 hours.
as many people have already stated it's probably what were are comfortable (or used to) turning at which is best. diameter does have an impact and will slow it down immensely.
the walnut i have on the lathe at the moment is running at 250 and is 28" across. i'll be turning the speed up as fast as the lathe and balance of the blank will let me when i start again as it is simply what i like to do. others will feel differently and have a slower or higher speed that they use.
-
"We should all promote turning at the lowest speed possible this would make things much safer."
DEFINITELY NOT !! There are too many people making up rules and regulations and making spurious claims about the safety of this and that. I do not usually use the term amateur regarding woodturning, preferring to say hobby turners as not all hobby turners are amateur but it should be remembered that there are 2 types of turner. Hobby and professional. But some of the claims here are obviously amateur. We all have different ways of doing or achieving an end product, sometimes the professional turners differ in their opinions but that is no reason to promote a method. I was taught to turn at the highest speed I can comfortably work at and as a production turner you will not last in your job long by turning at slower speeds. At the moment there is no chart available that can properly tell you safe turning speeds, think why this is for a moment, bearing in mind that if H&S feel there is a need one would have been produced before now. Turning speed is subjective, in as much as each and every piece of wood is different therefore each and every piece of wood that is mounted on the lathe should be......wait for it..........risk assessed. This does not mean rheams of paper with different gradings and hollow sounding results, what this means is you mount the piece on the machine, whilst you are doing this you are looking at it, feeling the weight and looking for defects you are looking to see which side is heavier as this will affect balance you are touching it to feel the moisture present and how loose the bark is. You are doing all this in a split second or two when first handling the wood. This is called experience, it is not something that you can read from a chart, to some extent can be taught but the best way of learning all about it is to ......experience it. This experience will take the form of things like reducing speed to prevent chatter on a bowl or thin spindle but it must be weighed up with, in my case, the need to earn a living in a reasonable time for each job.
There is no easy answer to this all I will say is what we used to say in the forces.....get some in!
-
just started turning a 30"x 6" chainsaw cut walnut that weighs 70kg and started it down at the 60's. just got up to 250 near round.
How did you get that to the lathe and mounted ? I have access to very large wood and it is always tempting to go BIG but my lathe can cope with what I can get to it and mount ( 30kg max ) and this is plenty I find and do not make large bowls very often ,as I find they do not sell that well , and do not intend to change lathe just to go big . I have seen articles where turners have a chain hoist system over their lathes , but this would also require special tooling and a big shed !! Would be nice to see some pics of a bowl that size though !
-
Plucking figures out of the air for maximum or minimum speeds for any particular object doesn't really convey any meaningful information because, as we all know, the speed of rotation is a function of diameter.
To give an example, I haven't turned anything at below 3000 rpm today tells you very little but if I add I was turning pens with a maximum diameter of 3/4" it then means something.
The chart that everyone seems to be avoiding like the plague is based on the arbitrary cutting speed for wood being around 25 feet per second. Obviously that is going to vary a little depending on what is being worked but as a rule of thumb, at least it gives a baseline and if the proviso of balance, vibration and security of mount is added I don't see a problem with using it as a rule of thumb. Where things go wrong is when only half the information is passed on or the safety factors are ignored.
-
I thought everyone might be interested in a web page I came across some years ago. I think it covers the topic of lathe speeds very well, covering many of the aspects already mentioned but conveniently on one 'page'.
http://www.docgreenwoodturner.com/lathespeed.html (http://www.docgreenwoodturner.com/lathespeed.html)
-
I've just come in from hollowing a couple of vessels from a log of Eucalyptus (still don't like the stuff but a neighbour took his tree down and asked 'Could you... ' - so I'm turning it.)
Anyway it was fairly ovate and well out of balance, so I started at under 200 RPM, well below any vibration level, 400 ish to finish rounding it and once well balanced about 800 to shape the outer and hollow it. No great speeds for a bit of timber only 5" finished diameter but it was all I needed to do the job on green wood. And I had some wonderful ribbons flying.
One thing I have noticed about speed. I have a very acutely sharpened Skew (well several of them), I measured one at a 23º included angle and kept at a razors edge. I find at high speeds it cuts very poorly, in fact it prefers to skate over the wood. It's much happier around 2000 even on small diameters (lace bobbin sizes).
Any Idea why it skates at high RPMs?
-
just started turning a 30"x 6" chainsaw cut walnut that weighs 70kg and started it down at the 60's. just got up to 250 near round.
How did you get that to the lathe and mounted ? I have access to very large wood and it is always tempting to go BIG but my lathe can cope with what I can get to it and mount ( 30kg max ) and this is plenty I find and do not make large bowls very often ,as I find they do not sell that well , and do not intend to change lathe just to go big . I have seen articles where turners have a chain hoist system over their lathes , but this would also require special tooling and a big shed !! Would be nice to see some pics of a bowl that size though !
how did i get it on the lathe, i lifted it on...
i've no huge shed for engine hoists and other pulleys or lifting devices, it's a 20'x14' shop that is chock full of wood and machinery so no space left for fancy lifting gear.
what can i say i'm 6'3" and 17stone of mostly muscle but i don't think i could lift a heavier weight.
the roughing out is finished and the bowl at the moment though admittedly sopping wet still weighs 23kg i've cored it and should get another 2 from that.
i'll see about getting pictures on here but last time i tried nothing happened.
-
what can i say i'm 6'3" and 17stone of mostly muscle but i don't think i could lift a heavier weight.
Ah that explains how then !! Still it is probably not easy getting the face plate and headstock threads to marry up though !! I do not know if like me you cut the blank with a chainsaw as accurately as you can and shape the outside a bit as well ... saves time !! My shed is only 7x6 so you would not fit in it !!..ha ha ..... Terry...
-
Paul H a point well made a statement needs facts, I did not know that the arbitrary cutting speed for wood was around 25 feet per second so that something that I've learnt, and give me something tangible to work with
Paul (DWC) thank you for the link that also helps, how to explain to someone turning speeds.
Bowler - Your right also once you have learnt the skills required go as fast as you like and if your production turning a slow speed would be a waste of time. But if when we started driving we just got in a car and put our foot to the floor without learning any control .......only one thing is likely too happen :) but if your a professional racing car driver that a different matter and I think that wood turning is the same except you have not got the steel safety cage around you :) :)
-
what can i say i'm 6'3" and 17stone of mostly muscle but i don't think i could lift a heavier weight.
Ah that explains how then !! Still it is probably not easy getting the face plate and headstock threads to marry up though !! I do not know if like me you cut the blank with a chainsaw as accurately as you can and shape the outside a bit as well ... saves time !! My shed is only 7x6 so you would not fit in it !!..ha ha ..... Terry...
i did use a lever to get it on to the spindle and it was about seven sided with a chainsaw when i mounted it..
7x6 is about the space i have to use in the workshop that isn't cluttered with wood or machinery.
-
I feel , 7x6 is small but mine is dedicated uncluttered turning space though , however it soon gets knee deep in shavings though ! Most of my work is fairly large hollow forms and I may start with a 20 kg lump , but end up with something that only weighs a kilo or 2 so lots to clear up ,but green wood so cuts nice and very little dust .
-
Ed, back to your question, on reflection of the automatic ... pulley the belt is on, the most average 8" flatwork and 2>3" spindle the Mystro normally remains at the middle range, on checking I'm most surprised at it being 916rpm, much like Pete found under the 1000, my next increment is 1483rpm... the other speed are used to reflect the varied shapes and sizes.
I do wonder as why when this post related to lathe speed, with all of us being a singular body as Turners, that the distinction of 2 types ... Hobby and Professional has been raised ... just which is it that is being Amateur.
David
-
I believe most turn at a speed that is too high and rely on the speed to provide a good finish rather than good technique.I know this is somewhat controversial but it is my opinion.
if you have ever seen me turn I rarely run the lathe at any speed but use sharp tools technique and control to achieve the end result.
When teaching more experienced students they often have trouble with spiral chatter on bowl work, this is caused simply by high speed and differential grain density the answer is simple, drop your speed and sharpen the tool problem solved,for Bowl turning any speed over about 1000 rpm is simply not needed in my opinion.( these comments relate to Bowl work and not other areas of turning)
Nick Arnull.
true words there nick a sharp tool will always win over brute force
-
David let me try to explain what I meant by "amateur". Both professional and hobby turners will turn out(no pun intended) work of a high standard, if not straight away then eventually. They will all serve, whether they like it or not a period akin to an apprenticeship during which they will learn "the rules" for instance "don't cut uphill"etc. These rules have been unchanged for 100's of years and only changed or adjusted by innovative new tools or devices that are developed over a period of time and have been proven to work. I am well aware that pole turners turn at a lower speed than those using an electric powered machine (and their work is no less of a quality for it) but we have over the years developed tools and steels for those tools to cut at higher speeds and it is my opinion that the call for turning at slower speeds was made by an amateur turner, an amateur being a non professional and non specialist turner as opposed to a professional or hobby turner that can specialise due to experience.
-
David let me try to explain what I meant by "amateur". Both professional and hobby turners will turn out(no pun intended) work of a high standard, if not straight away then eventually. They will all serve, whether they like it or not a period akin to an apprenticeship during which they will learn "the rules" for instance "don't cut uphill"etc. These rules have been unchanged for 100's of years and only changed or adjusted by innovative new tools or devices that are developed over a period of time and have been proven to work. I am well aware that pole turners turn at a lower speed than those using an electric powered machine (and their work is no less of a quality for it) but we have over the years developed tools and steels for those tools to cut at higher speeds and it is my opinion that the call for turning at slower speeds was made by an amateur turner, an amateur being a non professional and non specialist turner as opposed to a professional or hobby turner that can specialise due to experience.
What's to explain ... if one's not time served ... make a living from turning ... then you're an "amateur" .... how will we ever encourage anybody into turning.
-
Here Here David
I guess that my comment about turning at slower speeds for safety gave me the title of "amateur" allow I've only been turning for 5 months I'm a pretty good turner and I would like other people to find what I have found in woodturning.
I'm a member at my local club and chatting to other members find that many don't turn, one old boy had one go and in his words "it didn't go well" so he never returned to his lathe. If he had a lathe with a starting speed of 500rpm I guess it might not have gone well dependent on what he was trying to do.
If you have a lathe that can spin at 3000rpm and you know what your doing all well and good but if your new to woodturning and your told the faster you spin the lathe the better the finish you might think you know what your doing and wick-it-up BANG a piece leaving the lathe spinning at 3000rpm hitting you will be a bit different from a piece hitting you on a lathe spinning at 300rpm but you you still get a very good finish spinning at 300rpm.
Ed
-
A short story about my first turning experience.
I’d gotten into woodworking from buying our first home and doing a lot of DIY. The tool collection grew and the DIY became maintenance level. Free time meant I could and did, pick up where I’d left off at school and make things out of wood.
Then one day the wife saw an advert for a ‘Woodwork machine’, as it happens a Coronet Major. Complete with Table Saw, Planer Thicknesser, Morticer, oh and a lathe. Well we looked, I liked it and so bought it.
Getting it home in pieces (the only way to lift and carry it) I built it back up and decided to play with my new toy. There were some saw blades with it but also some turning tools. So I put a bit of wood on the lathe (thankfully just a small bit between centres) and turned it on!
0 to 5000 rpm in nothing flat – I hit the stop button and walked away terrified while muttering rude expletives under my breath!
Thankfully my Ever-Loving bought me a course at the local adult education centre, night school, in Great Malvern, the first thing the nice man (I do wish I could remember his name) showed me was the pulley system and how to ‘lower the speed’, I’d put it together and set the pulleys for the table saw, not the lathe.
That lathe and my next were both pulley driven so the speed ranges were preset, I learnt to turn at the lower of the available (pulley) speeds for the wood size as it ‘felt’ safer.
Variable speed now means I (and I think most of us) have better control of the speed but I still prefer to work on the slower side. And from reading this thread, I think it is safe to say that the majority of us turn slower than we thought we did, having now had cause to stop and look at the speed indicator.
-
I am very new to turning and try to remember to turn the speed down before stopping the lathe ( my speed dial does not go all the way to stop ) On the odd occasion I have forgotten I find it quite disturbing to see the wood go from zero to 1000. I would not want to be learning on an older lathe.
-
I am very new to turning and try to remember to turn the speed down before stopping the lathe ( my speed dial does not go all the way to stop ) On the odd occasion I have forgotten I find it quite disturbing to see the wood go from zero to 1000. I would not want to be learning on an older lathe.
Far more important to make sure the lathe is at a lower speed when starting up. I suspect many of us have thoughtlessly not done this and put a heavy piece on with the speed up after a smaller job. Especially likely if we have lathes that don't have variable speed.
Pete
-
That was my point :)
-
that's very important when turning large diameter like i have recently been doing up to 28". i had to remember to turn the lathe down to 250 max before i turned it off or a kill switch cut the power and the blank just runs down.
there is too much inertia in a blank that weighs 50kg plus for the jet 3520b to handle but as long as i remembered then i was ok or i have to turn the whole thing off and on again.
-
there is too much inertia in a blank that weighs 50kg plus for the jet 3520b to handle but as long as i remembered then i was ok or i have to turn the whole thing off and on again.
Sorry, could you explain that ?
-
there must be some sort of kill switch on my lathe, a jet 3520b. if i hit the nvr switch on the lathe whilst i have a large bit of wood spinning it appears to be too much for the lathe to stop with all that inertia so it cuts the power and to reset i must turn the lathe off at the plug, listen till the thermal switches have clicked and then i can turn the lathe on again. if i don't do this i am unable to start the lathe to continue turning.
i don't know if it is a safety device for the user or the lathe but it just means i must slow the speed down to about 200rpm and then i can hit the stop button.
the 28" i recently turned was going round at about 50 rpm and this would have cut the power turning it of at that speed so i've had to get in to the habit of slowing work down before i turn the lathe off.
-
Ahh. Not sure I would like that.
-
it only seems to happen when working on bits over 24" (not sure what weight) but most of what i turn is under that sort of size and weight band that affects it.
the jet 3520b handles most stuff very well and is a good machine. i've another 6 blanks from this walnut left to turn ranging from 10"-18" all 6-7" thick and would not expect to have that problem with any of them.
-
The inverter drive acceleration / deceleration rates are generally set for an "average" sized piece of wood. If you are turning something much larger / heavier you need to change the parameters so the acceleration / deceleration time is much longer. Otherwise the inverter drive detects an overload condition and trips out.
Check your user manuals for how to do this.
-
there must be some sort of kill switch on my lathe, a jet 3520b. if i hit the nvr switch on the lathe whilst i have a large bit of wood spinning it appears to be too much for the lathe to stop with all that inertia so it cuts the power and to reset i must turn the lathe off at the plug, listen till the thermal switches have clicked and then i can turn the lathe on again. if i don't do this i am unable to start the lathe to continue turning.
i don't know if it is a safety device for the user or the lathe but it just means i must slow the speed down to about 200rpm and then i can hit the stop button.
the 28" i recently turned was going round at about 50 rpm and this would have cut the power turning it of at that speed so i've had to get in to the habit of slowing work down before i turn the lathe off.
Hi Steve,
I may have an answer to your 'problem' but I may be wrong as I don't know the Jet 3520 spec in detail.
Most big, variable speed lathes use a 3phase motor driven by an inverter. This means you still have good power at low speeds, as the speed is controlled by modification of the frequency, not the voltage/current.
All these inverters have a host of settings, as they are used in all sorts of applications, but the one that could be relevant to yourself is usually specified as 'Coast to stop or Ramp to Stop'. If it is set at Ramp to stop, the inverter will use DC braking to try and stop the motor in a set time. For many that is 10sec but it can be set at any value. The shorter the time, obviously the more braking is required. However, the braking puts a load on the inverter. If the load is too high, which I guess is what is happening in your case with large lumps of wood, the inverter will overload and cut out. You then have to power off and on to reset it. The inverter can cope with smaller (lighter) bits of wood, as it won't require so much braking.
The alternative of 'Coast to stop' means that when you stop the lathe, the inverter just removes any drive to the motor. There isn't any braking applied and it will just slow down of its own accord. Obviously a large lump of wood, with a lot of momentum, will take longer than a small piece.
It is easy to find out what setting you've got, but be very careful with what I am about to suggest. Put a piece of wood on the lathe. Turn it to a nice, smooth cylinder that you are happy to put your hands round. Now remove the toolrest and switch off the lathe. If you can slow the lathe by holding the wood, it is set to Coast to stop, but if you can feel the lathe trying to keep going, it is set to Ramped or Braked to stop.
Unfortunately if it is the latter, you would need to find and change the settings of the inverter. You may prefer to contact Jet for help doing that.
All my lathes are set to Coast to stop, for another good reason. Some of my chucks cannot be locked onto the headstock. If the inverter was set to Brake to stop, and I am turning very large, heavy pieces, the inverter can stop the motor but the momentum of the piece keeps it spinning, thereby unscrewing the chuck off the lathe :o
Sorry for the rather extended reply but hope that helps.
-
i had the 6" face plate unscrew because the motor braked and the work didn't stop just nearly came off.
i think you are right about what causes it but i don't perceive it to be a problem as such because in general i do so little at that size needed to create this situation and i'm not going to go fiddle with the settings on the inverter.
i can stop the work by hand any way to make sure it doesn't cut out in the first place.
-
I take it back, I do like that. Clever stuff.