Ignoramus26696 wrote:
I made this boat trailer guide base:

http://igor.chudov.com/projects/Trailer-Guide/

To it, I planned to attach a short 1 foot 1.5" pipe nipple, and to it,
another 5-6 or so feet of same pipe using a rigid union.

A person mentioned that pipe is seriously weakened by threading, and
that I should reconsider. I am now seriously considering NOT using the
1 foot section, and instead to use a solid piece of pipe. The nice
thing about using the union is that the big pipe sections could be
removed for storage easily, and the thing could be a little more
easily assembled and drilled in a small basement shop.

Anyway, now I think that the latter consideration is BS as I could
always unbolt them etc.

My question is, is this an important issue? The objective for the
guides is to hold the boat in relatively strong (to me) current.

I can't put a figure on it, but my instinct is that the pipe will be
weakened quite a lot by this joint. The threaded collar is pretty short
and will therefore not offer much support when the pipe is flexed. It
might fail suddenly under load if the thread is stripped, or if the iron
coupler isn't ductile enough and cracks. As someone else here pointed
out, a plain mild steel pipe wouldn't fail in this manner. You could
strengthen the joint by using a longer threaded coupler, or even better
a slightly larger mild steel pipe which is bolted to your trailer which
the long mild steel pipe slots into (secure it with a pin). The most
important question is how serious the consequences of a failure will be.

Hope this helps,

Chris

Iggy
Your strength in part comes from wall thickness of the pipe. As you thread
you reduce the wall thickness at the root of the thread and this being
tapered threads your wall thickness is reduced further. I'm not sure what
the stress is on this but if it a bending stress I would not rely on it.
I've seen to many pipes break in the threads.
lg
no neat sig line

"Ignoramus26696" wrote in message
.. .
I made this boat trailer guide base:

http://igor.chudov.com/projects/Trailer-Guide/

To it, I planned to attach a short 1 foot 1.5" pipe nipple, and to it,
another 5-6 or so feet of same pipe using a rigid union.

A person mentioned that pipe is seriously weakened by threading, and
that I should reconsider. I am now seriously considering NOT using the
1 foot section, and instead to use a solid piece of pipe. The nice
thing about using the union is that the big pipe sections could be
removed for storage easily, and the thing could be a little more
easily assembled and drilled in a small basement shop.

Anyway, now I think that the latter consideration is BS as I could
always unbolt them etc.

My question is, is this an important issue? The objective for the
guides is to hold the boat in relatively strong (to me) current.

My last outing was great, but pulling the boat was embarrassingly
difficult as it just would not stay where it should be.

i

If you're worried about it, go get some schedule 80 pipe and make it out of
that, the wall thickness is about double. - GWE

Ignoramus26696 wrote:

I made this boat trailer guide base:

http://igor.chudov.com/projects/Trailer-Guide/

To it, I planned to attach a short 1 foot 1.5" pipe nipple, and to it,
another 5-6 or so feet of same pipe using a rigid union.

A person mentioned that pipe is seriously weakened by threading, and
that I should reconsider. I am now seriously considering NOT using the
1 foot section, and instead to use a solid piece of pipe. The nice
thing about using the union is that the big pipe sections could be
removed for storage easily, and the thing could be a little more
easily assembled and drilled in a small basement shop.

Anyway, now I think that the latter consideration is BS as I could
always unbolt them etc.

My question is, is this an important issue? The objective for the
guides is to hold the boat in relatively strong (to me) current.

My last outing was great, but pulling the boat was embarrassingly
difficult as it just would not stay where it should be.

i

I regularly use 3/4 inch pipe with PONY clamps. They are common for
clamping applications in woodwork. We use them in a steel shop of pulling
frames and the like into alignment. The threaded ends often fracture and
twist.
On my personal clamps I use one inch round bar welded to the pipe so
that I have about two to three inches of bar threaded on the outside joined
to the pipe. the best arrangement is to put the bar on the lathe and turn
half of it down to fit inside the pipe. This makes welding easier and moves
the stress point away from the weld.
If you have a lathe and a pipe die you are in business. You could rough
grind the bar down if you did not have a lathe.
Randy

"Ignoramus26696" wrote in message
.. .
I made this boat trailer guide base:

http://igor.chudov.com/projects/Trailer-Guide/

To it, I planned to attach a short 1 foot 1.5" pipe nipple, and to it,
another 5-6 or so feet of same pipe using a rigid union.

A person mentioned that pipe is seriously weakened by threading, and
that I should reconsider. I am now seriously considering NOT using the
1 foot section, and instead to use a solid piece of pipe. The nice
thing about using the union is that the big pipe sections could be
removed for storage easily, and the thing could be a little more
easily assembled and drilled in a small basement shop.

Anyway, now I think that the latter consideration is BS as I could
always unbolt them etc.

My question is, is this an important issue? The objective for the
guides is to hold the boat in relatively strong (to me) current.

My last outing was great, but pulling the boat was embarrassingly
difficult as it just would not stay where it should be.

i

1-1/2" schedule 40 (the normal stuff) pipe has an OD of 1.900" and an ID
of 1.610. standard thread depth diameter is 1.727 So the standard wall
thickness of .145" is reduced to (1.727-1.610)/2 = .058" Your strength
at the threaded portion is 43% of the original. Worse yet, the sharp
corner gives you a nice stess riser, it will always break at the first
exposed thread outside of the coupling.

Ignoramus26696 wrote:
I made this boat trailer guide base:

http://igor.chudov.com/projects/Trailer-Guide/

To it, I planned to attach a short 1 foot 1.5" pipe nipple, and to it,
another 5-6 or so feet of same pipe using a rigid union.

A person mentioned that pipe is seriously weakened by threading, and
that I should reconsider. I am now seriously considering NOT using the
1 foot section, and instead to use a solid piece of pipe. The nice
thing about using the union is that the big pipe sections could be
removed for storage easily, and the thing could be a little more
easily assembled and drilled in a small basement shop.

Anyway, now I think that the latter consideration is BS as I could
always unbolt them etc.

My question is, is this an important issue? The objective for the
guides is to hold the boat in relatively strong (to me) current.

My last outing was great, but pulling the boat was embarrassingly
difficult as it just would not stay where it should be.

i