View Full Version : Securing Round Head tube to Square Alum. Tubing

09-19-2014, 08:13 PM
Thinking about aluminum instead of steel for my delta trike build, and I have an idea of how to secure the head tube to the aluminum tubing.

Someone else probably had this idea before so Iíd like to run it by the more experienced home builders to see if this will work, and if perhaps you have some ideas for improving on my design.

Instead of flat steel for the fins should I use round bar stock, or perhaps some other shape? If the flat steel is okay, what thickness do you recommend ?

Its quite some time since I last used Photobucket but hopefully my diagram will be displayed here:


09-19-2014, 09:14 PM
I don't really see how that will help you in anyway as you still have to attach the square tube to something. Aluminum does not just stick together.
Maybe a drawing of what you hope to accomplish. Aluminum will still need to be cut and welded unless you plan to bolt it all together such as the N55 the Hillary placed in another post.

09-19-2014, 10:59 PM
I donít have a place to weld so Iím looking at material other than steel for my trike build. One material under consideration is aluminum assembled with stainless steel bolts.

I already have on hand pillow block bearings, hub flanges welded to axles, wheels laced to those flanges, and freewheel adapters.

I can see how to attach those parts to an aluminum frame but the round head-tube was a bit more challenging. I think it will be easier to attach a square head-tube to a square or rectangular aluminum frame, so I decided to design one.

Not only will my HT have a square exterior shell, that shell will be aluminum. Once the trike is fully assembled, I can bring it to a weld shop to have some critical frame joints reinforced, including the aluminum HT.

09-20-2014, 12:13 AM
I under stood the no welding issue. The problem I see is attachment of the square tube to the rest of the frame. Just stuffing the round steering tube in to a square would not help you.

Might I suggest leave the top tube See figure H: http://www.atomiczombie.com/Tutorial%20-%20Bicycle%20Autopsy%20-%20Page%201.aspx attached to the steering tube off the bike your getting it from. Then stuff the top tube into the Aluminum square tube boom. Drill a couple holes to bolt the top tube inside the aluminum boom.
Stuffing the steering tube into a square tube does not attach it to the frame. That is what I mean by I don't see how it would help you. Stuffing the top tube into the boom would attach the front forks anyways. Especially for a Delta trike configuration. Could be used in a Tadpole as well.

Hope that makes the meaning clearer.

You could use steel as well as Aluminum to do that.

09-20-2014, 05:04 AM
Your suggestion to stuff the top tube into the aluminum square tube boom is a very good one, except that you are not aware that my top tube has already been separated from my head tube.

I started out building this trike with a steel frame in mind, thus both the top and down tube were removed from the head tube so as to allow the new square steel down tube to be welded to it.

Now that I am contemplating the use of aluminum for the frame instead of steel, I had to go back to the drawing board.

As poet Robert Burns once wrote: ď The best laid schemes o' mice an' men
Gang aft a-gley ď,

09-20-2014, 06:58 AM
As you are starting from Square 1 then a new steering tube is in order with top tube attached. What size is your Steering tube? I may have one still attached to cycle I could maybe chop off and ship to you. Then you stuff your fork, bearing into it. Just need the size so it will match up.

09-20-2014, 11:36 AM
DTD: Thanks for your generous offer, but I think Iíll stick with my plans for the head-tube. To date, Iíve only done minimal research on available aluminum shapes and sizes so will only make a final decision once I have more information under my belt.

09-20-2014, 01:39 PM
Might I suggest, if you wish to go this route, you drill and tap the head tube and use bolts through the outer aluminium(aloominum) :) tube with spacers in between to avoid compression of the square tube,8 bolts will give you a rigid mount
P.S. I only think outside the box because I lost the box

09-20-2014, 10:21 PM
John: Thanks for your suggestion. Several months ago, when I was planning to build a steel frame trike, I wanted the head-tube to pass through the down tube as in the LoadRunner plans.

My head-tube has an O.D. of 1-3/8 Inches or almost 35 mm and the steel tubing in my plans was smaller than is used for the LR, so I had to scrap that idea and think about fish-mouthing the down tube to the head-tube.

However, with the larger dimension tubing of my current aluminum frame plans, it will now be possible to have the ď square ď head-tube pass through the down tube, and fixed in place as per your suggestion.

Having said this, I will probably get rid of the down tube, put the head-tube through the one piece main boom, and have one less joint to worry about.

09-21-2014, 04:25 AM
Aluminium and steel have different expansion rates for temperature changes which needs to be kept in mind.

If you were going to weld fins onto head tube you could also use the fins drilled to bolt to the aluminium.
I'd have a good root around (google) bamboo bicycle stuff for info on attaching aluminium and steel bits to the bamboo frame using epoxy and hemp or carbon fibre etc.

Same applies to attaching the metal bits to carbon fibre frames.
It is also suitable for joining steel and aluminium bits together, or aluminium to aluminium I suppose.

I would vote for the having one bit inserted into another then wrapped and epoxied as per DTDs to tube suggestion or your drill a hole and insert tube through option.

Epoxy is not too difficult to work with in the house (built myself a wee boat last year).

09-21-2014, 12:17 PM
HHJJ: You bring up some very good points about necessary precautions when working with different metals. I am aware of the potential for problems, and have recently been doing much research on this subject.

OTOH, I can forgo the steel head-tube completely, and just buy or make one of aluminum.!