ovalising tube

[naughtyboy]

looking at using mountain bike frame for chopper as want to use rear suspension on it.

frame is made of oval tube and need to extend it.
i want to make one end of tube oval to fit to frame and other end rd where it fits head stock.

whats best way to do it?
havent got press only vice.
also how do i work out what size rd i need?

cheers

 

[chunkolini]

You have got this diesease pretty bad.
Apologies to your family.
You are not butt welding your tubes are you?

 

[anjum]

Can't answer the rest but to work out what diameter tube you need measure the existing tube circumference with a piece of string, measure the length and divide by pi (3.1416). This will give you the external diameter of the round pipe.

 

[chunkolini]

I have heard of people using two round tubes and putting flat sheet up the sides.

 

[naughtyboy]

You have got this diesease pretty bad.
Apologies to your family.
You are not butt welding your tubes are you?

was going to make smaller oval to act as internal sleeve and plug weld to and leave 1-2mm gap between outer tubes then seam weld it for extra strength.

and yes got it bad put pics in brew room of another frame ive done, and at mo working on converting old racer frame to trike for eldest girl.

 

[MrFluffy]

Can't answer the rest but to work out what diameter tube you need measure the existing tube circumference with a piece of string, measure the length and divide by pi (3.1416). This will give you the external diameter of the round pipe.

Thats spot on, theres actually a super accurate way of doing the same thing, but overkill for this using something called a Pi tape.
http://www.pitape.com/

 

[graffian]

Thats spot on, theres actually a super accurate way of doing the same thing, but overkill for this using something called a Pi tape.
http://www.pitape.com/

It's more accurate than a tape and calculator;-)

 

[KemppiFrog]

Making the tube oval is your biggest problem. Squeezing it in the vice will flatten the sides. You need formers, could be hardwood, but shaping them is going to be tricky, esp if trying to match an existing tube. Vice needs to be biggish too.

Example: I wanted to form some 'D' section copper tube for solar panels. Put the round tube in a square bar with the half circle machined along it's length. Ran it through under a roller in a simple jig, easy. No, the roller has to be concave by a small amount or it actually forms a hollow in the flat.

 

[DrNik]

how about some hardwood bobbins made to the profile of your oval, easy to make and then have a small frame with one bobbin on a bearing and the other bobbin on slots on the frame with a thread so you can wind it slowly down till the bobbins touch and then wind/pull it in and out , that shouldnt take long at all

 

[chunkolini]

How about chop out the oval tube and replace it with round.
This is chopper tech, measuring and formers? what are they?

 

[the snooper]

chunko has the best idea get rid of the oval

 

[KemppiFrog]

I was asuming he wanted a nice finish

 

[chunkolini]

Nice finish?
What is that?

 

[outofthefire]

If its as rough as Chunko's alluding to use a piece of round tube thats a nice tight fit inside the oval then build up the round tube with weld to match the oval then grind it so it flows nicely.