Is this too big for my lathe?

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Wood&StuffLtd

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Morning. I've just cut up a sizable piece of chestnut with the 'hope' of making a shallow bowl/plate/platter for the other half as she's got a birthday soon.
The diameter is 400mm/16" & 80mm/3 1/4" thick. It weighs in at 12kgs with face plate attached or 8kgs alone.
My lathe is 1 hp and will attach by 6 screws. It's still green so would you suggest I wait for it to dry or give it a shot now?
Some pics of the set up.

Cheers Shan View attachment 132630 View attachment 132631 View attachment 132632
Your faceplate is 4kgs?
If I had time I would rough turn it round seal the end grain and let it dry for a few months at least, a moisture meter would be useful, you can bake it in the oven or even microwave to speed the drying process but you have to be careful. You could also turn it thin and hope it doesn't warp too much. I'm sure someone more knowledgeable will be along soon to tell me I'm an silly person 😁😁😁
Hi Shan
Some good idea being suggested. Can I suggest that you trim the blank round on a bank saw or a jig saw before turning. The shape you show is not balanced and is likely to assist in greater vibration until it gets to a balanced round. I would then start at say 400rpm and take it from there. You could then turn the bowl to finish and then leave it to see if a distorted shape develops as the wood dries. You can get interesting distortions which may turn the bowl into an Object D’Art! Good luck.
 

Yorkieguy

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A useful 'rule of thumb' formula to bear in mind is that the diameter of the timber ('D') x RPM should not exceed 6,000 - 9,000:

So for example: A bowl blank is 8 inches in diameter.
8" X 750rpm = 6,000
8" X 1,125rpm = 9,000

Or to transpose the formula, 6,000 / diameter = RPM. So in this example, 6,000 / 8" = 750 RPM, 9,000 / 8" = 1125 RPM.

If the lathe is a step pulley drive system, choose a setting around 750 RPM to 1100 RPM, staying lowe,r around 750 RPM if you can.

In the case of your 16" diameter blank, 6,000 / 16" = 375 RPM.

But this assumes that the blank has been cut to the diameter, is accurately centred , and is of even thickness, so is well balanced and will need little truing up, after which - when running smoothly - you could up the turning speed . Your blank ticks none of those boxes so at 375 RPM will I think it will be a challenge to true up and get into balance. For each rev, about 48 inches of timber will pass the tool, so at 375 RPM, that's 18,000 inches = 1,500 feet. (25 ft per second). I'm not saying don't do it, and when you start the lathe, you'll soon know whether or not you feel happy to true it up.

Dave Regester, a pro, who used to turn hundreds of large salad and fruit bowls for the likes of Harrods, (maybe still does), turned the blanks down to about 1" wall thickness to get rid of as much moisture as possible, then put them in sacks in a cool dry place for a few months to let they dry out, by which time they'd have warped. He then put them back on the lathe and trued them up.

As I said, it's a 'rule of thumb' - more experienced turners instinctively know how far they can push the boundaries. As Ray jones said many years ago in his video 'Bowls for Beginners': "Novices come at the hobby with a dangerous cocktail of enthusiasm and inexperience". Over the years, I learnt to temper my enthusiasm with discretion, avoiding the temptation to prove 'Darwin's theory of the non-survival of the stupidest'.

Just my thoughts, which I hope are of interest.

Every good wish with it.

David.
 

Blister

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Hi Shan
Some good idea being suggested. Can I suggest that you trim the blank round on a bank saw or a jig saw before turning. The shape you show is not balanced and is likely to assist in greater vibration until it gets to a balanced round. I would then start at say 400rpm and take it from there. You could then turn the bowl to finish and then leave it to see if a distorted shape develops as the wood dries. You can get interesting distortions which may turn the bowl into an Object D’Art! Good luck.

The above is good advice , I would turn the bowl but leave it at least 1" thicker the the desired finished size , then let it dry naturally , or even put it in a plastic bag , then every 2 or 3 days take it out of the bag , Turn the bag inside out the put it into the dry bag , Also weigh the bowl and note the weight reduction , When it stops loosing weight and moving finish to the desired form .
 

Owd Jockey

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Hi Shan, I don't see any real problems here. You could do with trimming up the excess around the outside of the circle abit to get it close to balance by sawing, planing or chiselling. As with the other advice as above, adequate PPE and if the lathe starts to 'walk' try and remove more of the excesss. I would'nt bother drying at this stage, do that after you have rough turned. Use all of the screws on the face plate and ensure you use the tail-stock until you get balance.
 

Shan

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Take the power in through a switched cable outlet. I have two, one for when I'm long hole boring and one in the middle that you can just see here - it's between the two rows of tools - for when the headstock is turned.

View attachment 132673
Phil. I like your set up. When I wired mine in due to logistics I put a mains switch on the wall at the head stock end. I'll send you a foto to show it. Probably would have been a better idea at the other end but hey, hindsight!
I do have a saint watching proceedings! 😇😇😇
20220329_100314.jpg
 

Shan

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A useful 'rule of thumb' formula to bear in mind is that the diameter of the timber ('D') x RPM should not exceed 6,000 - 9,000:

So for example: A bowl blank is 8 inches in diameter.
8" X 750rpm = 6,000
8" X 1,125rpm = 9,000

Or to transpose the formula, 6,000 / diameter = RPM. So in this example, 6,000 / 8" = 750 RPM, 9,000 / 8" = 1125 RPM.

If the lathe is a step pulley drive system, choose a setting around 750 RPM to 1100 RPM, staying lowe,r around 750 RPM if you can.

In the case of your 16" diameter blank, 6,000 / 16" = 375 RPM.

But this assumes that the blank has been cut to the diameter, is accurately centred , and is of even thickness, so is well balanced and will need little truing up, after which - when running smoothly - you could up the turning speed . Your blank ticks none of those boxes so at 375 RPM will I think it will be a challenge to true up and get into balance. For each rev, about 48 inches of timber will pass the tool, so at 375 RPM, that's 18,000 inches = 1,500 feet. (25 ft per second). I'm not saying don't do it, and when you start the lathe, you'll soon know whether or not you feel happy to true it up.

Dave Regester, a pro, who used to turn hundreds of large salad and fruit bowls for the likes of Harrods, (maybe still does), turned the blanks down to about 1" wall thickness to get rid of as much moisture as possible, then put them in sacks in a cool dry place for a few months to let they dry out, by which time they'd have warped. He then put them back on the lathe and trued them up.

As I said, it's a 'rule of thumb' - more experienced turners instinctively know how far they can push the boundaries. As Ray jones said many years ago in his video 'Bowls for Beginners': "Novices come at the hobby with a dangerous cocktail of enthusiasm and inexperience". Over the years, I learnt to temper my enthusiasm with discretion, avoiding the temptation to prove 'Darwin's theory of the non-survival of the stupidest'.

Just my thoughts, which I hope are of interest.

Every good wish with it.

David.
David. Thanks for this but unfortunately your assumption is way off the mark. Blank is way off centre in thickness and circumference. I plan to true it up but haven't got a bandsaw yet. Hopefully get one soon.
Cheers
 

Lefley

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Yep, screw on. But only tightens when turning so no problem with it detaching.

How about mounting a router where your tool rest would go and turning your blank by hand slowly using the router to true up blank to round state. Then using same procedure to take some face cuts to true up the blank the other way. Then you have a round blank. Off to the races!
 

Shan

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How about mounting a router where your tool rest would go and turning your blank by hand slowly using the router to true up blank to round state. Then using same procedure to take some face cuts to true up the blank the other way. Then you have a round blank. Off to the races!
Lefley, that's a novel idea. Cheers. I don't have a router but looking for a bandsaw at the moment. In the meantime I'm leaving the blank to dry out a bit and then once I've got the bandsaw can sort it out. Regards Shan
 

Lazurus

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Look up Lyle Jamieson on you tube he shows a method of starting with any blank between centres and balanced, he never uses a chuck and is a great demonstrator. I have used his method several times and it really does work on out of balance blanks, I use a VB36 so size is not an issues but i feel more in control when a big out of balance blank is between centres
 

sawtooth-9

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The lathe will handle this ok. IF ....
Centre your blank, determine thy OD of the bowl and bandsaw the OD + a machining allowance.
If you don't have a bandsaw, find someone who does.
If you can't centre / balance your blank - don't turn it. It's amazing just how bits can "fly" around - and stand aside !
Once a piece is way out of balance you need serious "holding" and serious machine weight and slow initial speed until you can turn the piece into balance.
Speed can be an issue, but if you are running a little fast, just take finer cuts.
 

Duncan A

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Another option is to reduce the imbalance forces by adding counterweights very securely to the blank, or even drilling out material that may be particularly dense and will be lost when turning to a bowl.
Duncan
 

Richard_C

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Yep, screw on. But only tightens when turning so no problem with it detaching.
Until you press the stop button. Then the momentum in the spinning workpiece can loosen it. I always keep the tailstock up as much as I can.

I've dealt with an out of balance blank, too thick for jig saw and before I got a Bandsaw, like this. Get as good as you can with bowsaw or chainsaw, drill a shallow hole in the centre at the mounting end (in your case the midpoint of the faceplate), put a rod or screwdriver sticking up in a vice, balance blank on your little hole and use chalk to mark the heavy point. Use a small axe or whatever you have to hack some wood off there. Repeat, repeat.... Hard work but eventually get something enough in balance to be able to spin at low speed without the lathe wandering across the floor. But only if you really really need to and have plenty of time and energy.
 

Shan

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If you can get the lathe speed below 300 rpm (maybe less if a long way out of balance) you should be ok turning the blank as it is.
Paul, unfortunately I don't have the option to slow down the speed. It's an old lathe with a 3 phase motor and have tried a VFD which didn't work. Kept cutting out all the time, so just got the pulley system. Don't know what the rpm's are but I know it's way too fast for what I had in mind. Cheers
 

Shan

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Did you risk trying it in the end?
Not as yet. Leaving it to dry out a bit and have noticed a small crack developing. Still haven't managed to get it centred as yet. Tried out a potential band saw recently but it kept tripping out so didn't purchase same.
Some of the smaller bowls I've made from the same trunk have started to warp so I don't think this will be a good look on a large size plate, could be wrong tho.
Thinking to buy a wood carving disc for an angle grinder or even a chain disc. Still looking for a bandsaw but few and far between here. Even contemplating if I can use a smaller bar, say 6" or 8" on my chainsaw. Would be easier to cut/carve away excess wood. Cheers Shan
 
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