Greetings.
I am making a lamp for my living room. I will use a 45 pound plate for the
base and some 1/2" rebar for the lamp itself. Base will be on one wall an
d light bulb will be about 7' away. I need to bend an 11' piece of rebar i
nto a perfect arc. It would be 180 degrees of a circle. I am thinking to ma
ke a fixture out of plywood. Fixture would be similar to what an electrici
an would use to bend conduit. I don't intend on heating rebar. Just bend
on fixture. Other way would be to create a fixture using a coomplete sheet
of plywood. I think that is overkill.
Any thoughts?
thanks
Bob
There's many with a lot of practical experience on here.
However, none have replied - so my little thought, for what it's
worth...
I don't think the template will work, because of spring-back in the
bar. Steel is very elastic.
Accurate template yes I believe in your skills - but it won't impose
an outcome on the steel.
I suspect
- use a string and chalk to mark-off the radius on a flat floor
- find and object with a smaller radius to bend the bar a sector at a
time - where it springs-back to the radius you want
- laws of the universe coming through metallurgy mean you can "unwind"
a radius quite easily in the minutes after making the bend
- in metal-forming, some craftspersons over-bend, then get the corrent
radius on the "unbend"
Something for you to look up also - see "yield drop" and "Luder's
bands". Mantras like "Perfect Planning Prevents Poor Performance"
only work in limited deterministic situations often with
already-existing commodities. You will realise that even with a
perfect method you might get a "jagged" outcome with local tighter
bends.
Rebar is cheap (ish!) and if you don't get what you want first time,
you will be usefully experienced the second time :-)
Hope this is helpful.
Best wishes,
Rich Smith
There's many with a lot of practical experience on here.
However, none have replied - so my little thought, for what it's
worth...
I don't think the template will work, because of spring-back in the
bar. Steel is very elastic.
Accurate template yes I believe in your skills - but it won't impose
an outcome on the steel.
I suspect
- use a string and chalk to mark-off the radius on a flat floor
- find and object with a smaller radius to bend the bar a sector at a
time - where it springs-back to the radius you want
- laws of the universe coming through metallurgy mean you can "unwind"
a radius quite easily in the minutes after making the bend
- in metal-forming, some craftspersons over-bend, then get the corrent
radius on the "unbend"
Something for you to look up also - see "yield drop" and "Luder's
bands". Mantras like "Perfect Planning Prevents Poor Performance"
only work in limited deterministic situations often with
already-existing commodities. You will realise that even with a
perfect method you might get a "jagged" outcome with local tighter
bends.
Rebar is cheap (ish!) and if you don't get what you want first time,
you will be usefully experienced the second time :-)
Hope this is helpful.
Best wishes,
Rich Smith
*******************
I tend to shy away from job requests the include the words perfect,
precisely, exactly, just, or only. Certainly not as part of the job title
without a tolerance in the description. The word "just" along with "only"
has its own special hell. "make it just like" lumps it in with the other
three (and their synonyms), but its also often used to denigrate the value
of the job as a pre-negotiation technique. "Its just a simple job." "You
only have to push a few buttons."
Anyway: I wanted to help, but I would hack and slash my way towards an
acceptable tolerance. I don't have a clue how to JUST make it PERFECT.
LOL. I guess my first choice would be a ring roller as it does just that.
Work slowly towards the acceptable tolerance.
A fixture to bend conduit? Hmmmm. I bent a lot of conduit in 23 years as a
licensed contractor and if anything I used the application itself as a
"fixture." I think it might be more accurate to call it a gage than a
fixture. I bent the conduit with a tool called a conduit bender.
Occasionally I used a tool called a pipe bender to make slight offsets in
larger conduit. Often to save time I'd get the bend or bends right and
leave the ends long, then cut to fit. Especially if working with a helper.
Like wire, conduit is cheaper than time. Rebar would fall in the same class
I think. Rebar is cheaper than time, so get it close and then cut the ends
off to fit.
********************
Rich, Since Ernie quit participating in this group there is a lot less
activity than there once was. He was our "resident expert" so to speak.
I've had fun winding-up people about the word "just" and resulting in
them having to think what they are about to say, inspecting it for
that word.
In engineering design jobs...
Tee-hee... :-)
Rich Smith
On 11/18/2018 12:07 PM, Richard Smith wrote:
>
>> ...
>> title without a tolerance in the description. The word "just" along
>> with "only" has its own special hell. "make it just like" lumps it in
>> with the other three (and their synonyms), but its also often used to
>> denigrate the value of the job as a pre-negotiation technique. "Its
>> just a simple job." "You only have to push a few buttons."
>> ...
>
> I've had fun winding-up people about the word "just" and resulting in
> them having to think what they are about to say, inspecting it for
> that word.
> In engineering design jobs...
> Tee-hee...
>
> Rich Smith
>
As a contractor those words would "just" make me automatically increase
the price of the job, because I "only" wanted to deal with that if I was
going to get paid for the headache.
"It's a simple job, it just take you a few minutes". Every time a
potential customer says that to me I know the job is really going to
take much longer. When they say that to me I ask them if they are a
machinist or a welder. The answer is always no. But they can tell JUST
by looking the job will go fast.
Eric
I think TeeNut had posted this years ago. I don't remember
exactly
the wording but it went something like this:
We only do three kinds of work here.
Quick Cheap and Accurate
If you want it Quick and Accurate it won't be Cheap..
If you want it Cheap and Quick it won't be Accurate.
If you want it Accurate and Cheap it won't be Quick.
Take your pick and wait your turn.
One thing I won't do is crappy work. And not just because it rankles
me. You know if you do a quick and dirty joib that looks crappy but
that the customer insists is OK the customer will then blame you for
the crappy job when it doesn't work or when someone sees the job and
comments on how crappy the work is.
Eric
That was my view - but I would make theatrical inrushes of breath and
interject with things like "Ooooo, that doesn't sound promising - this
is all going to be more costly".
Etc.
On Sunday, November 18, 2018 at 11:59:55 AM UTC-5, Bob La Londe wrote:
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Thank you Bob.
I said, "Fixture would be similar to what an electrician would use to bend
conduit." Yes, the fixture I am thinking to cobble up would be like I sai
d, what an electrician would use to bend conduit. I was more wordy while y
ou got right to the point with - a conduit bender :)
On Saturday, November 17, 2018 at 7:50:25 AM UTC-5, Richard Smith wrote:
the base and some 1/2" rebar for the lamp itself. Base will be on one wal
l and light bulb will be about 7' away. I need to bend an 11' piece of reb
ar into a perfect arc. It would be 180 degrees of a circle. I am thinking t
o make a fixture out of plywood. Fixture would be similar to what an elect
rician would use to bend conduit. I don't intend on heating rebar. Just b
end on fixture. Other way would be to create a fixture using a coomplete s
heet of plywood. I think that is overkill.
Thank you Rich. I think it was answered last week. I think 'perfect lookin
g' was the phrase I was after. Perfect is a strong word. I am going to us
e a piece of 2'x4'x1/2" plywood to bend the rebar around. I can attach it t
o the side of my workbench and just bent a small arc at a time. Eventually
I will put 20 or so larger lamps down my driveway. I will have local shop
do the bending for those. I will use full 20 feet lengths for driveway.
Not sure if I will use rebar for that tho. While lamps will be lightweight
, and rather small, I am not sure how rebar will take the wind load. Ther
e will be some dancing of the lamps in the wind. Should be pretty cool with
motion detectors on each lamp.
Thank you Rich. I think it was answered last week. I think 'perfect
looking' was the phrase I was after. Perfect is a strong word. ...
============================
To those of us who built custom equipment "perfect" was a red flag
that indicated the customer didn't know what he really needed or what
was involved in making it, and could be difficult to deal with.
For example I helped build a test station for [a device] that detected
and reacted to a fault condition. The Ph.D. who designed the device
specified the stimulus level at the fault threshhold to the 8 digits
of precision his calculator gave him. He didn't know that the
resistors in his op amp circuit would have tolerance bands.
Fortunately he was willing to listen to us and agreed on a sensible
and economically achievable value. Later we heard that the production
version had an overall error window of 40%.
On Saturday, November 17, 2018 at 7:50:25 AM UTC-5, Richard Smith wrote:
the base and some 1/2" rebar for the lamp itself. Base will be on one wal
l and light bulb will be about 7' away. I need to bend an 11' piece of reb
ar into a perfect arc. It would be 180 degrees of a circle. I am thinking t
o make a fixture out of plywood. Fixture would be similar to what an elect
rician would use to bend conduit. I don't intend on heating rebar. Just b
end on fixture. Other way would be to create a fixture using a coomplete s
heet of plywood. I think that is overkill.
Good call Rich. Was considerably less than perfect with the spring back.
I am going to make radius a tad smaller and give it another go. When I eve
ntually get to the 18 or so street lamps for my driveway I will have them b
ent at my supplier's shop. Will have to figure out how to get them here af
ter they are bent up tho. May need a special curved trailer ;)
On Saturday, November 17, 2018 at 7:50:25 AM UTC-5, Richard Smith
wrote:
.....
Good call Rich. Was considerably less than perfect with the spring
back. I am going to make radius a tad smaller and give it another go.
When I eventually get to the 18 or so street lamps for my driveway I
will have them bent at my supplier's shop. Will have to figure out
how to get them here after they are bent up tho. May need a special
curved trailer ;)
====================
https://www.harborfreight.com/tubing-roller-99736.html
https://www.garagejournal.com/forum/showthread.php?t15729
-jsw
Take a guess and make a former smaller than you want and bend round it
past the angle you want,then it is easy to bring back to where you want
it, if you get it right first go you are lucky, if not you then have an
idea for second try
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