heat sinks

[quasi]

i need to make a couple of heat sinks for use inside round cro-moly tubing. i plan on taking round bar and split it in half long ways then use a couple of wedges to hold it securely against the ID of the tube. my question is what should i make them out of? aluminum is my first choice as it is cheap and readily available. but bronze and brass are also thoughts? any reason to use these more expensive materials? material is <.045 so not a ton of heat will be put into them but controlling distortion is paramount

[dave powelson]

Originally Posted by quasi

i need to make a couple of heat sinks for use inside round cro-moly tubing. i plan on taking round bar and split it in half long ways then use a couple of wedges to hold it securely against the ID of the tube. my question is what should i make them out of? aluminum is my first choice as it is cheap and readily available. but bronze and brass are also thoughts? any reason to use these more expensive materials? material is <.045 so not a ton of heat will be put into them but controlling distortion is paramount

Since 'controlling distortion is paramount'.....then the weld joint design is the place to
address this anticipated distortion, by changing the design---possibly to a curved doubler plate.

[quasi]

no can do, joint is the way it is. two thin wall cromo tubes intersecting at ~60* what is important is the ID of the non-mitered tube stays round and does not ovalize

[dave powelson]

Originally Posted by quasi

no can do, joint is the way it is. two thin wall cromo tubes intersecting at ~60* what is important is the ID of the non-mitered tube stays round and does not ovalize

Your requirement above is exactly 'why' a doubler plate is used.

??Do you understand what a doubler plate is??

[quasi]

um no

[dave powelson]

Originally Posted by quasi

um no

Depending on the joint/structure design/requirements,
a curved double plate is the same tube wall thickness, cut in half, spread to fit the o.d. of
the existing tube, long enough to span the 60 degree mitered tube mouth + at least 1/2 the tube's
dia. extending out in each direction from the fishmouth.

The doubler is closely fit and clamped to the tube o.d., then a weld ran along
each 'long' edge, with NO weld--around the curved ends.

In any case from the little I've seen of your posts and questions, getting really dialed in on welding
techniques, machine settings, etc. ---to avoid excessive heat, melt thru, etc.--by you doing some
samples is going to help you, but the key to distortion control in what you've described is
to change the joint design.....I've been there, dun' that---what you're trying.

You'll see curved doubler plates (not as often as you should!) on bike and cycle frames.

[quasi]

you just described what i have always known as a gusset. as it coincidence would have it this is for a bike frame, but i don't think your solution is the right one for my application. my goal is to control heat input without adding any extra material. i have never seen a failure of the head tube joint that was not due to crash damage so i think the joint design is fine the way it is i just want to make it a little easier to weld.

so any ideas as to what is the best material for my heat sinks

[DesertRider33]

I'm guessing you'll end up machining the inside ends of the head tube after welding so they're just the right diameter, round and lined up with eachother for the bearing cups to press in each end, like align-boring an engine block for the crankshaft main bearings.

You can add gussets under the down tube and between the down tube and top tube to strengthen the head tube joint.

[quasi]

i am going to face and ream the head tube, pretty standard practice.

i don't need to strengthen the head tube, just control heat. bicycles design hasn't changed much in over 100 years the design is pretty solid and for traditional road bikes for riders of less than obese proportions that joint and every other one on a bike is fine. when you get into MTB applications where you are putting suspension and heavier tires then gussets are a good idea. in the 5 years that i have worked in the bike industry (and the 5 in the welding industry) i have never seen or heard of a bike fail at the head tube, unless it was in a nasty crash.

so any idea what material will be best for my heat sinks???

[dave powelson]

Originally Posted by quasi

i am going to face and ream the head tube, pretty standard practice.

.<snip>

so any idea what material will be best for my heat sinks???

Use the aluminum
Some suggestions on this:
-the heat/melt from the steel welding thru the tube wall can produce adhesion to whatever material is used for these mandrels; plus you'll may have the aluminum expanding greater than the tube's I.D.
This can be alleviated by:

-polishing the aluminum round halves

-cleaning, then spraying a dry graphite or moly spray on the tube ID and the mandrel O.D.--this
really helps to prevent sticking

[ed mac]

eastwood has a heat sink puddy
you can form around the area you want to weld