This is an idea I'm thinking about but because I have no real engineering experience I thought I'd reality-check it here. If its a rubbish idea, please tell me before I expend any more precious thinking-time on it.
Anyway, a few years ago I bought an inexpensive lathe and got into wood turning. I did turning for about 6 months before giving it up - making some quite nice things - but ultimately deciding there were enough dog-bowls in the world already. The one thing I remained interested in however, which I would still like to pursue, was making some really large bowls - I guess I'm meaning 500+ millimetres across, maybe up to 800mm.
I have all sorts of ideas about large bowls which look good in my mind (probably not in practise but we will see and thats the fun of it).
Obviously you cant make something that big on an inexpensive lathe - the distance from bed to centre would stop you if nothing else.
So I'm thinking of perhaps making my own lathe.
Most of my mega-bowl ideas are not what you would call finely-featured forms. Thats good, because it steers me away from a high-precision engineering solution.
Thinking about making a lathe means going back to scratch. As I'm only interested in making a lathe suitable for very large bowls (no turning between centres stuff) I have wondered if the best solution is a vertical lathe. I did a search for vertical lathes for home-oriented wood turning on the internet with no success. This seems odd as I doubt I'm the first person to think of it.
So I guess its a lathe like a potters wheel - but larger and very much more robust as its turning very large bits of wood.
The advantages I can see are that:
1. You would be able to turn a very heavy object (subject to motor size) without gravity playing a negative role. This means you have more tolerance in terms of engineering precision, bearing quality etc. Thus it should be easier to make.
2. You could have a very wide, flat platen (the wide horizontal plate which I see the blank sitting on), which would enable you to have all sorts of holding mechanisms for these large blanks. The blank would sit on the platen with great stability.
3. There could be a safety angle. There is little risk of the blank coming loose and hurting you because its already (in a sense) fallen as far as it can.
4. There would be no limits on the size of the object you could turn, except perhaps motor power.
Out of these, point 1 is the main one. It seems to me that building a lathe to turn heavy object with a horizontal shaft is wrong, because the object is putting immense downward, and therefore lateral, pressure on the shaft.
So what I'm thinking about is making something with:
1. A low robust and rigid table made out of angle iron.
2. a metal top to the table.
3. a 2hp motor bolted to the legs of the table.
4. a central spindle, mounted to the table top, piercing it vertically, and with a pulley on the bottom.
5. a belt between the motor and the spindle, preferable with gearing for different speeds.
6. a big wide platen on the top of the spindle - say 600mm wide. This is the bit the blank sits on.
7. a bearing race towards the outside of the table, directly supporting the platen. Probably a dozen or so bearings - maybe these : http://www.amazon.com/Bearing-6201RS.../dp/B002BBJSO0 .
The bearing race would take most of the downward force. They would need to be on adjustable shafts, so they could be raised or lowered a tiny bit to make sure all bearings are in contact with the platen. They would need to be in a circular arrangement - so the platen rides smoothly on them. They would need to be somewhere towards the perimeter of the platen - but basically at the point where they provide the most support with the least platen flex. These take most of the downward pressure, so the shaft takes very little pressure and is basically just providing turning force.
So is this idea any good, or is it rubbish ?
Arron
Anyway, a few years ago I bought an inexpensive lathe and got into wood turning. I did turning for about 6 months before giving it up - making some quite nice things - but ultimately deciding there were enough dog-bowls in the world already. The one thing I remained interested in however, which I would still like to pursue, was making some really large bowls - I guess I'm meaning 500+ millimetres across, maybe up to 800mm.
I have all sorts of ideas about large bowls which look good in my mind (probably not in practise but we will see and thats the fun of it).
Obviously you cant make something that big on an inexpensive lathe - the distance from bed to centre would stop you if nothing else.
So I'm thinking of perhaps making my own lathe.
Most of my mega-bowl ideas are not what you would call finely-featured forms. Thats good, because it steers me away from a high-precision engineering solution.
Thinking about making a lathe means going back to scratch. As I'm only interested in making a lathe suitable for very large bowls (no turning between centres stuff) I have wondered if the best solution is a vertical lathe. I did a search for vertical lathes for home-oriented wood turning on the internet with no success. This seems odd as I doubt I'm the first person to think of it.
So I guess its a lathe like a potters wheel - but larger and very much more robust as its turning very large bits of wood.
The advantages I can see are that:
1. You would be able to turn a very heavy object (subject to motor size) without gravity playing a negative role. This means you have more tolerance in terms of engineering precision, bearing quality etc. Thus it should be easier to make.
2. You could have a very wide, flat platen (the wide horizontal plate which I see the blank sitting on), which would enable you to have all sorts of holding mechanisms for these large blanks. The blank would sit on the platen with great stability.
3. There could be a safety angle. There is little risk of the blank coming loose and hurting you because its already (in a sense) fallen as far as it can.
4. There would be no limits on the size of the object you could turn, except perhaps motor power.
Out of these, point 1 is the main one. It seems to me that building a lathe to turn heavy object with a horizontal shaft is wrong, because the object is putting immense downward, and therefore lateral, pressure on the shaft.
So what I'm thinking about is making something with:
1. A low robust and rigid table made out of angle iron.
2. a metal top to the table.
3. a 2hp motor bolted to the legs of the table.
4. a central spindle, mounted to the table top, piercing it vertically, and with a pulley on the bottom.
5. a belt between the motor and the spindle, preferable with gearing for different speeds.
6. a big wide platen on the top of the spindle - say 600mm wide. This is the bit the blank sits on.
7. a bearing race towards the outside of the table, directly supporting the platen. Probably a dozen or so bearings - maybe these : http://www.amazon.com/Bearing-6201RS.../dp/B002BBJSO0 .
The bearing race would take most of the downward force. They would need to be on adjustable shafts, so they could be raised or lowered a tiny bit to make sure all bearings are in contact with the platen. They would need to be in a circular arrangement - so the platen rides smoothly on them. They would need to be somewhere towards the perimeter of the platen - but basically at the point where they provide the most support with the least platen flex. These take most of the downward pressure, so the shaft takes very little pressure and is basically just providing turning force.
So is this idea any good, or is it rubbish ?
Arron
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