G'Day,

I don't know what the correct property is I need to look for here... Basically
I have a tabletop which supports a small lathe, and the tabletop is made
of wood, and I'm replacing it with sheet steel.
I'm sure there's a property that I can look up for the wood, and then use
the number from that to compare to the sheet steel to make sure the thinner
sheet steel will support the lathe in the same way without flexing. All other
aspects of the design will be the same - spacing of support beams, size of
tabletop, maounting location, etc.

The lathe is a cantilevered design (Taig)

If someone who is more familiar with the strength properties of materials
can tell me what the property is I need to look for, I'd appreciate it.

Thanks,
Des

In the spirit of RCM, I'll ignore your question and suggest an
alternative: why not just put the sheet steel on top of the wood?

Bob

Hello Bob,

Basically I'm trying to remove the timber, and reduce the weight - the "tabletop"
is actually the top of a small shelf/ cabinet which holds the lathe.

By making the tabletop steel, I can weld things to the top, and drill and
tap fixtures as required - things I'd be less comfortable doing with wood
underlay.

I've got 4mm (just over 1/8") thick galvanised sheet that I plan on using
to replace the 12mm MDF.

If the properties says the 4mm isn't as "stiff" then I'll be putting some
braces or something in - but I'm trying to reduce the weight since I'm adding
other accessories such as VSD, taper turner, etc to the system.

Des




In the spirit of RCM, I'll ignore your question and suggest an
alternative: why not just put the sheet steel on top of the wood?

Bob

On Sun, 25 Jul 2010 12:25:58 +0000 (UTC), des bromilow
wrote:

Hello Bob,

Basically I'm trying to remove the timber, and reduce the weight - the "tabletop"
is actually the top of a small shelf/ cabinet which holds the lathe.

By making the tabletop steel, I can weld things to the top, and drill and
tap fixtures as required - things I'd be less comfortable doing with wood
underlay.

I've got 4mm (just over 1/8") thick galvanised sheet that I plan on using
to replace the 12mm MDF.

If the properties says the 4mm isn't as "stiff" then I'll be putting some
braces or something in - but I'm trying to reduce the weight since I'm adding
other accessories such as VSD, taper turner, etc to the system.


You're looking for the modulus of elasticity of the materials, AKA
Young's modulus. All other variables held equal, deflection varies
inversely with the cube of the thickness. So the modulus of the steel
would have to be 27x (3x3x3) that of the MDF for equal stiffness.

Damping is also something to consider. You may get more vibration with
a thin steel sheet than with the MDF, even if the stiffness is the
same.

--
Ned Simmons

On Jul 25, 5:02*am, des bromilow wrote:

I don't know what the correct property is I need to look for here... Basically
I have a tabletop which supports a small lathe, and the tabletop is made
of wood, and I'm replacing it with sheet steel.

The lathe support is a substructure under the sheet, the sheet itself
just has to hold random tools and swarf and capture any dripping
coolant?

A thin sheet won't be less 'floppy' than wood (will sag if loaded in
the center). That's why corrugated, not flat, steel is used for
roofing
and such.

Bending the edges of the sheet to form a lip will stiffen them a lot.
That's how steel shelving gets its stiffness.

Hello whit3rd,

I was hoping that with a substantial thickness sheet, I could support the
lathe, and taper turning attachment, motor bracket, and then still be able
to support DTI bases, etc plus the swarf, tooling, etc

I will be folding the edges for the drop tray aspect of it, and once I check
the Young's modulus, I'll know if I need to add anything else under the tray.

I figure the Taig and the motor way less than a chuck for a larger lathe,
and the drip trays,e tc on them are thinner than my proposal, but I do like
to understand what I'm doing...


Thanks to you and Ned for the replies... Bob's question is certainly valid
if all I was chasing was drip protection - it's the need to weld, drill and
tap the tray which is forcing this change from timber to steel.

Thanks all,
Des




On Jul 25, 5:02 am, des bromilow wrote:

I don't know what the correct property is I need to look for here...
Basically
I have a tabletop which supports a small lathe, and the tabletop is
made
of wood, and I'm replacing it with sheet steel.
The lathe support is a substructure under the sheet, the sheet itself
just has to hold random tools and swarf and capture any dripping
coolant?

A thin sheet won't be less 'floppy' than wood (will sag if loaded in
the center). That's why corrugated, not flat, steel is used for
roofing
and such.
Bending the edges of the sheet to form a lip will stiffen them a lot.
That's how steel shelving gets its stiffness.

On Sun, 25 Jul 2010 22:24:56 +0000 (UTC), des bromilow
wrote:

Hello whit3rd,

I was hoping that with a substantial thickness sheet, I could support the
lathe, and taper turning attachment, motor bracket, and then still be able
to support DTI bases, etc plus the swarf, tooling, etc

Then I would suggest at minumum, a nice sheet of 1/2" plate, if you cant
find any 5/8" " plate.



I will be folding the edges for the drop tray aspect of it, and once I check
the Young's modulus, I'll know if I need to add anything else under the tray.

I figure the Taig and the motor way less than a chuck for a larger lathe,
and the drip trays,e tc on them are thinner than my proposal, but I do like
to understand what I'm doing...


Thanks to you and Ned for the replies... Bob's question is certainly valid
if all I was chasing was drip protection - it's the need to weld, drill and
tap the tray which is forcing this change from timber to steel.

Thanks all,
Des




On Jul 25, 5:02 am, des bromilow wrote:

I don't know what the correct property is I need to look for here...
Basically
I have a tabletop which supports a small lathe, and the tabletop is
made
of wood, and I'm replacing it with sheet steel.
The lathe support is a substructure under the sheet, the sheet itself
just has to hold random tools and swarf and capture any dripping
coolant?

A thin sheet won't be less 'floppy' than wood (will sag if loaded in
the center). That's why corrugated, not flat, steel is used for
roofing
and such.
Bending the edges of the sheet to form a lip will stiffen them a lot.
That's how steel shelving gets its stiffness.



One could not be a successful Leftwinger without realizing that,
in contrast to the popular conception supported by newspapers
and mothers of Leftwingers, a goodly number of Leftwingers are
not only narrow-minded and dull, but also just stupid.
Gunner Asch

On Sun, 25 Jul 2010 15:50:31 -0700, Gunner Asch wrote:
On Sun, 25 Jul 2010 22:24:56 +0000 (UTC), des bromilow wrote:
I was hoping that with a substantial thickness sheet, I could support
the lathe, and taper turning attachment, motor bracket, and then still
be able to support DTI bases, etc plus the swarf, tooling, etc

Then I would suggest at minimum, a nice sheet of 1/2" plate, if you
can't find any 5/8" plate.

0.5" steel plate would weigh about 20#/sq ft, so for example a
2' x 4' top would weigh 160#. Some 1"-thick composites like at the
following links would be plenty stiff and weigh only 1.2# per sq ft.
This stuff isn't expensive, it costs less than $10 per sq ft.

http://www.portafab.com/aluminum_honeycomb_panels/alum_on_alum.shtml
http://www.pacificpanels.com/GPpanel.html
http://www.panelteccorp.com/html/stockpanels.html

....
On Jul 25, 5:02 am, des bromilow wrote:
....
I have a tabletop which supports a small lathe, and the tabletop
is made of wood, and I'm replacing it with sheet steel.
The lathe support is a substructure under the sheet, the sheet itself
just has to hold random tools and swarf and capture any dripping
coolant?
....

If the tabletop is just holding tools as you suggest, I think 1/8"
steel is thick enough for unsupported spans of a few inches -- eg
could be supported by welded-on rails at 8"-12" intervals. If you
are going to use the table for any heavy hammering, or if it's
bigger than say 3'x4', go on up to 1/2" or 5/8" steel sheet like
Gunner recommends, and put crossbars along the bottoms of the legs
so you can move the table around with a $250 pallet jack.

--
jiw

On 2010-07-25, des bromilow wrote:

G'Day,

I don't know what the correct property is I need to look for here... Basically
I have a tabletop which supports a small lathe, and the tabletop is made
of wood, and I'm replacing it with sheet steel.

[ ... ]

The lathe is a cantilevered design (Taig)

With that (the cantilevered mounting) -- I doubt that you will
have to worry about flex as long as it is thick enough to support the
lathe's weight without moving as you turn the cranks.

Part of the question is how large is the table beyond the area
of the lathe. The larger the area -- the thicker you need it to be.

Another is whether the metal will be formed at the edge to make
a large rim. If this is done, it adds to the stiffness significantly --
and you don't have to worry about cutting yourself or your clothes by
rubbing against the edge.

Or -- you could weld it to a steel frame all the way around.

With other lathe designs (separate feet under the headstock and
the tailstock) flexing of the top will twist the bed of the lathe and
introduce errors, so you need to keep considering rigidity until you get
down to a poured concrete floor. But a Taig is very forgiving.

Good Luck,
DoN.

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