Pounds/foot (and other nonsense) MEW 226

Advert

New Replies

Report Bug

Help/FAQs

Pounds/foot (and other nonsense) MEW 226

This topic has 60 replies, 22 voices, and was last updated 4 March 2015 at 05:45 by Hopper.

Viewing 25 posts - 1 through 25 (of 61 total)

1 2 3 →

Author

Posts
1 March 2015 at 23:17 #181801
Frank.N Storm
Participant
@frank-nstorm18349
So I stumbled over that article about recondition of a drilling machine, and especially on the new physics on page 13. Well I admit my lessons were a long time ago, but about one thing I'm absolutely sure: torque is measured in foot-pounds (if it must be imperial) and not pounds/foot. Let's look what Wikipedia says:

"A pound-foot (lb·ft or lbf·ft) is a unit of torque…. One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point. "

So it has the same dimension as for work.

A bit further down, the dimensioning of horsepower lacks the time part.

(Wiki) " (1) Mechanical horsepower = 33,000 ft-lbf/min "

I'm not fluent enough (as I said above) to comment on the other formulas, but I hope I did threw the stone in the pond and am awaiting the waves (and answers from the wise men)…

And, btw, would it be expecting too much from a asserted serious magazine to check contributions for blatant errors? (Neil?)

Regards, Frank
Advert

1 March 2015 at 23:17 #38284
Frank.N Storm
Participant
@frank-nstorm18349
1 March 2015 at 23:53 #181802
jason udall
Participant
@jasonudall57142
Ignoring SI vs imperial for the moment.

Torque is as stated in wiki etal..force acting at a perpendicular distance…
Double the distance with same force..double the torque…thats why long spanners help…
..thus T = F x D..
Now units.

Si…Newtons x meters…Nm
Imperial. ..say pounds ( are pounds the unit in imperial? )..x feet
..pound foot…more commonly foot pounds
But..
As you say in SI..newtonsx metres ..could also be joules…a unit of work..
Torque seems to be equivalent to work…well in most ways it is but you need in all..cases to multiply the revolutions..a dimensionless value. ..thus 10 Nm for 10000 revolutions does 100 kilo Joules of work…
And if machine is doing say 600 rpm…
It would be developing 10 Nm x600/60 watts ..100 watts ( joules/S…

Edited By jason udall on 01/03/2015 23:57:53
2 March 2015 at 00:03 #181803
jason udall
Participant
@jasonudall57142
It seems
.
Force[ ft-lb]
Torque [ ft-lb ]x[ ft]
Work [ft -lb] x [ft].
So work per minute…..seems to be..
Ft-lb.ft/minute…so with the right factor
Hp = ft-lb.ft/min
2 March 2015 at 06:48 #181807
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Frank.N Storm on 01/03/2015 23:17:58:

And, btw, would it be expecting too much from a asserted serious magazine to check contributions for blatant errors? (Neil?)

.

"a asserted"

Let he who is without typographical sin cast the first stone !

MichaelG.
2 March 2015 at 07:30 #181811
JasonB
Moderator
@jasonb
Posted by Frank.N Storm on 01/03/2015 23:17:58:

And, btw, would ……………………………

Regards, Frank

Missed that one Michael
2 March 2015 at 07:39 #181813
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Frank.N Storm on 01/03/2015 23:17:58:

I'm absolutely sure: torque is measured in foot-pounds (if it must be imperial) and not pounds/foot.

.

Frank,

For what it's worth:
1. I do agree that the 'slash' is incorrect, because it was traditionally used as division symbol, to mean 'per'
2. I think the preferred typography is to use a dot [as seen in this useful conversion calculator], not a hyphen.
3. Guidance on the conventions for use of those new-fangled SI units is available from NPL
MichaelG.

Edited By Michael Gilligan on 02/03/2015 07:41:15
2 March 2015 at 08:47 #181819
Jesse Hancock 1
Participant
@jessehancock1
For the record or not it's not going to change the power output, that is the power is still the same it's just people messing (as they seemingly love to do) with the way things are written down. Calling it foot pounds denotes your method of measurement and leave it at that.

Not that I don't find it annoying when people keep meddling for no apparent reason.

It seems to me that there are people out there who have to justify their existence and that's all it is.

No wonder school kids haven't got a clue anymore.

For the record the most common spelling or typing error I see is hte or similar for the. I've always struggled with spelling but never was it called dyslexia, however I think I am mildly dyslexic. I keep a dictionary close by in case of the dreaded squiggle. Plus I try and read things through before posting. It's still not 100% though.
2 March 2015 at 08:50 #181820
Michael Gilligan
Participant
@michaelgilligan61133
For your further entertainment:

**LINK**

MichaelG.
2 March 2015 at 09:19 #181822
Harold Hall 1
Participant
@haroldhall1
As there appears to be some confusion at the start of this thread readers may like to hear about the method I used at collage to remember, regarding work and torque, which was which in terms of their unit of measurement. Very many years later I still remember it.

The statement is, I go to work for pounds(foot-pounds). Work, as in earning a living, pounds as in money. Knowing one makes it easy to realise that Torque is pounds-feet.

Harold
2 March 2015 at 09:30 #181824
Neil Wyatt
Moderator
@neilwyatt
Hi Frank,

I spent along time on that article, and tried to follow the logic of the calculations (I checked all the maths and reduced the precision to 3 decimal points, but I accepted the various formulae at face value) as the final results all appeared to make sense. I can make calculations of power, torque etc.. in metric units, but have no experience of imperial beyond simple conversions.

As far as I can see the issue is that pound/s/foot should have been written pound-feet, noting that it is used as an alternative to foot-pounds to distinguish torque from work, although they are dimensionally the same unit.

If anyone an edit a magazine like MEW in ( notional) two and a half days a week and achieve perfection in articles dealing with equations you have no previous experience of with no technical backup, they are welcome to take over!

Neil
2 March 2015 at 10:00 #181826
john jennings 1
Participant
@johnjennings1
I read this article and wondered why all this "theory" was needed since the solution relied on an experimental test rig on a fail / not fail basis. I didn't therefore start thinking about the precise syntax , The solution for the editor is not to accept that such items are probably OK but is anything lost by omission . Gives a bit more space to fill You cant win them all!

John
2 March 2015 at 11:02 #181837
Capstan Speaking
Participant
@capstanspeaking95294
Foot pounds is a measure of force in a radial direction aka torque.

0.5 pound at 2 feet is still 1 footpound. It is a multiplication sum and represents a fixed overall value. It often has a dot between them.
Anything with a division implies a ratio and so cannot be relevant.

Horsepower equaling to ft.lbs/min or torque applied for a period of time is a rate of energy transfer (work done) as is always the way with power.

Now then footpounds is also an old term for a quantity of kinetic energy and is still used accross the pond in relation to ballistics.

One pound travelling at a speed of one foot per second has 1 "foot pound" of kinetic energy.

Have I made it clearer or murkier? ;o)
2 March 2015 at 11:12 #181841
Bikepete
Participant
@bikepete
Hi Neil, while we're on the subject of 226 and the drill restoration article – unless I'm mistaken the figure numbering seems to have gone awry – worth perhaps checking it's all back in synch when it continues in 227. Interesting article anyway and a good issue IMO. Cheers Pete

Edited By Bikepete on 02/03/2015 11:12:59
2 March 2015 at 11:44 #181844
Jesse Hancock 1
Participant
@jessehancock1
Frank, Wiki's, I believe are produced by the public free of charge, so if I'm wrong for gods sake tell me. They are also free to use, that is no charge. You can donate money to the cause if you like and I'm sure the wiki people running the site will thank you.

In the mean time wikis are open for addition and editing if you know better or more on the subject . When I say open you have to apply to wikipedia for permission to alter or edit the said wiki, that's a given other wise it would be complete carnage.

I just been over to reassure my bad memory on wikipedia and I notice we have professionals offering to write them for you at a price of course. It really makes my blood boil. Rather than do that see a local librarian or some such who will proof read it for you.

Edited By Jesse Hancock 1 on 02/03/2015 12:26:12
2 March 2015 at 12:47 #181848
Jesse Hancock 1
Participant
@jessehancock1
Neil, I sympathise with you on the point of spelling, grammar and so on. In deed I have just edited the above and now I see a couple of errors. I think I already said you do a sterling job mate. Chin up the suns out, well down here it is.

Any way what does it matter as long as people understand what you are saying.

Edited By Jesse Hancock 1 on 02/03/2015 12:49:02
2 March 2015 at 14:24 #181858
Harold Hall 1
Participant
@haroldhall1
Having read Capstan's comments I am confused. For me, foot-pounds relates to Work and pounds-feet to Torque, if I have got it wrong then I will be happy to be told. However, I will have been wrong for a very long time.

Harold
2 March 2015 at 14:52 #181859
Capstan Speaking
Participant
@capstanspeaking95294
Posted by Harold Hall 1 on 02/03/2015 14:24:35:

Having read Capstan's comments I am confused. For me, foot-pounds relates to Work and pounds-feet to Torque, if I have got it wrong then I will be happy to be told. However, I will have been wrong for a very long time.

Harold

Since it's a multiplication there is absolutely no difference which way it is written or pronounced.

A x B = C and B x A = C so footpounds or poundsfeet are the same.

footpounds is a quantity of force.
footpounds per minute is power.

1 foot pound per minute =0.0225969658 watts

As I said it can also be a unit of energy. It is sometimes written as foot-poundal and can be converted to Joules.

Force, energy and power are the basic principles of mechanics and electrics

Edited By Capstan Speaking on 02/03/2015 14:53:49
2 March 2015 at 15:28 #181861
Harold Hall 1
Participant
@haroldhall1
I am sorry Capstan but I was happy to be told I had got them the wrong way round but cannot accept that both torque and power have the same term for the unit of measure.

If I were to tell you that the result of experiment was 15 pound-feet can you tell me what that answer means?

Surely torque and power need differing units of measure, that is the way I was always taught, still it was a very long time ago.

Harold

Edited By Harold Hall 1 on 02/03/2015 15:31:08
2 March 2015 at 15:46 #181863
jason udall
Participant
@jasonudall57142
Ok working in si.

Newton..unit of force…
Equivalent to..
Kg. m./ S.S
…ie mass.distance /( t.t)

Now thats obviously cumbersome so the unit Newton is used

Now foot pounds of various kinds are used..and unfortunately this ” woolly ness” leads to confusion and the consideration that these “old fashioned” units to be error prone.

For me ..deal with the dimensions. .then worry over the units…
Btw HH..There are seperate units for torque and work in SI…Nm and J ( oules)…

Edited By jason udall on 02/03/2015 15:47:06

Edited By jason udall on 02/03/2015 15:48:13
2 March 2015 at 15:53 #181864
blowlamp
Participant
@blowlamp
Neil.

Please don't ever be tempted to publish any articles discussing the conversion of Poncelets to Lusecs.

Martin.

Edited By blowlamp on 02/03/2015 15:57:31
2 March 2015 at 15:53 #181865
Harold Hall 1
Participant
@haroldhall1
I have now looked at Wikipedia which states

The foot-pound force (symbol: ft·lb_f or ft·lbf), or simply foot-pound (symbol: ft·lb) is a unit of work or energy

Also says Not to be confused with Pound-foot (torque) or Foot-poundal.

Then on another page

A pound-foot (lb·ft or lb_f·ft) is a unit of torque

I have to admit that it goes on to say

However, the torque unit is often still referred to as the foot-pound

To me that is a very risky thing to do and easily open to errors. Would be like using the term voltage for both pressure and power

Harold
2 March 2015 at 15:53 #181866
Gordon W
Participant
@gordonw
Harold is correct.
2 March 2015 at 16:08 #181867
jason udall
Participant
@jasonudall57142
Quite…the use of foot pounds OUT OF CONTEXT is potentially ambiguous.
( simular to mass vs weight..though in that case its usage not fact..like I say simular)
I mean.. we use pounds ( force) in psi fairly safely
2 March 2015 at 16:29 #181871
The Merry Miller
Participant
@themerrymiller
I would always taught to remember "torque" as a "pound" at one "foot" as if using a force of one pound at the end of a lever one foot long. not a "foot at one pound" or ft-lb.

thus "pound-feet" is lb-ft is "Torque"

Len.
Author

Posts