weighing down a lathe

[boysie39]

Hiya all, I have come across a forum in which someone said it is better to put the extra weight such as sand above the lathe as 1 bag of sand over the bed is = to 4/5 bags on a bench under the Bed or ways.
He suggests that a metal frame attached to the end of the bed Headstock end and raised 2' above the head has a better dampening affect on vibration on the lathe. anyone any views or experience of this.
This is NOT my theory in case you think it is. Maybe someone could do the maths on this WAY above my head If you pardon the Pun. REgards Boysie.

 

[TEP]

Hi Eugene.

I remember reading that also somewhere, but never gave it much thought. It may be true, but someone better than me better try to explain it.

IMO if your lathe is secured properly, and used well within its capabilities you shouldn't have too much vibration.

Of course this all depends on you not attaching this great big piece of unbalanced timber your mate Fred passed on to you. :lol:

 

[boysie39]

Tam , Your in for a surprise one of these days in the not too distant future, Did you see the picture on the TV news with the truck hanging out the back, of the ferry Bog Oak And BOG YEW are very heavy :lol: :lol:
Will say nomore :wink: :wink:

 

[TEP]

Oh! my god! :shock: [-o< Is the bog wood OK? :twisted:

 

[Vulthoom]

Boysie,

I did see a website where this was proposed and some pictures of the bloke's setup (using a bucket of rocks as this was to be a portable).

I think that the idea was that the weight leans out from the attachment point and acts like a couterpoise exerting more force down than if the weight was sitting on the lathe stand. (I think...)

I was going to try it, but I am very limited for space around the headstock.

I'll try and dig up the link.

*edit - have scoured my bookmarks and can't now find it. Doh!

 

[BMac]

There could be a problem with this theory, I think. If the equivalence is correct - that 1 bag of sand above is equal to 4 or 5 below and you go for that option, then, if the piece you are turning starts to vibrate the lathe you have the equivalence of 4 or 5 bags of sand being waved about with no support below (unless you put 20-25 bags of sand below which seems to defeat the purpose). I would love to see the link to this set-up.

Brendan

 

[cambournepete]

The theory makes sense, but is outweighed by the practicalities.

With an off-balance piece of wood the lathe will try to pivot about where the foot of the stand meets the floor. The wood acts like a lever. With the weight in the stand the wood is outside the weight and can move it more easily than if the weight is outside (ie above) the wood.
I think

 

[Vulthoom]

Took some searching, but I found it again....

http://www3.sympatico.ca/3jdw8/antivibration.htm

 

[BMac]

Excellent hunting Vulthoom, well done and thank you.

Now that I see it and how the theory is explained I have to admit that it does seem to do what it says on the tin.

Brendan

 

[chipchaser]

I don't think this makes sense, at least not to me! Why does it matter whether the weight is above, below or to one or both sides of the headstock? Turning the explanation upside down I would suggest that the weight in the base is also benefiting from the lever effect that John Williams claims.

However, for this to be true the mounting must be stiff enough for the lever arm and inertia of the weight to work. If the base, or equally the pole that JW would mount the weight on, are flexible another, sympathetic, vibration could be induced by an out of balance object spinning in the headstock. The frequency and magnitude of this secondary vibration just might be a problem at certain turning speeds although presumably JW would have said so if this was his experience.

You may recall the Tacoma bridge disaster when the deck of the bridge started to oscillate and this gradually built up until it failed. See the film here:

http://uk.youtube.com/watch?v=3mclp9QmCGs

The Millennium Bridge over the Thames also had vibration problems which were corrected by addition of two viscous dampers and one tuned mass damper paid for by the design engineers Ove Arup.

I am not qualified to advise but would myself ensure the base is stiff, by plenty of bracing, well fixed to the floor and add mass as near the lathe bed as possible. If anyone tries JW's solution please make sure that bucket of rocks above head height is well fixed or wear a hard hat :lol: I would love to see some proper tests of this theory.

Regards

Graham

 

[boysie39]

Vultroom , thanks for the search some times I think my imagination is running away with me. If that theory is correct isuppose it would make sense to make a frame which would run the lenght of the bedand with a shelf attached more storage and more rubbish can be had.
If any of you folk have ever travelled on a Horse drawn cart to pick up a load,this in the time when there wre no Springs attached you would have found that the journey back was a lot smoother with the load on top. Think about it . The Ford model Y was the same if you had a couple of passengers it wasent too bad. Go to the musume and see one I used to own one!! I think the theory might work. REgards Boysie

 

[BMac]

Boysie reminded me of a similar situation. My father bought a Lada (yes, he regretted it on the way home) and for the eight months he had it comfort was a word seldom used.....except....the holiday trip from Armagh to Mayo when the car drove like a limo. The difference - there was a heavily laden roof rack for the journey. When the roof rack was removed on return the car went back to being the big, awkward, bouncy thing it was, despite still carrying 4 people

Makes you think!

 

[cambournepete]

I don't think this makes sense, at least not to me! Why does it matter whether the weight is above, below or to one or both sides of the headstock? Turning the explanation upside down I would suggest that the weight in the base is also benefiting from the lever effect that John Williams claims.

If we just simplify it to a horizontal bar with static vertical forces (not what happens in reality, but enough to explain the principle):

A-------------H-------------B-------------P

A - position of weight if above Headstock
H - position of headstock
B - position of weight below Headstock
P - position of pivot point - i.e. floor.

IF AH=HB=BP then to counteract a force F acting downwards at H (the headstock) you need a force of 2F acting upwards at B (the base) but only 2F/3 at A (above your head)– i.e. a third as much force (weight).

I'm sure the maths teachers will be along soon to tell me where I've gone wrong...

However, for this to be true the mounting must be stiff enough for the lever arm and inertia of the weight to work. If the base, or equally the pole that JW would mount the weight on, are flexible another, sympathetic, vibration could be induced by an out of balance object spinning in the headstock.

I quite agree, which is why I'd never try it - sand is cheap

 

[Vulthoom]

sand is cheap

I think this really says it all.

Sand it is for me.

 

[boysie39]

thanks to everyone who had an imput to the post. On reading mr williams post again he asks that anyone who tried it to let him know what they thought. I wonder is he looking for guinea pigs, or has he tried it himself.
They are gritting the roads here and they have stockpiled some loads round the corner arent they very helpful people over here.
Regards Boysie.
SHE,stedfastedly refuses to go out with the bucket in the snow!!!
:shock: :shock: It's hard to get good help these days. :lol: :lol:

 

[John. B]

For goodness sake Eugene, don't use that!
Half of it is made up of rock salt that is hungrily waiting for a big chunk of metal to attack. :tongue9: :tongue9: :tongue9: :tongue9:rust,rust,rust,rust!rustRUST

 

[boysie39]

Settle down John B its me that has the metal pins SHE is all clear :lol: :lol: .


REgards Boysie