MJT etched brass emu sides forming the Tumblehome help.

[piranha230]

I Have tried to form the curve on the etched brass MJT emu sides with a wooden rolling pin but the thick brass sides are staying flat.

Can anyone give me some advice please on the best and easiest way of forming the curve.

The brass sides are quite strong and thick.

Thanks.

[macgeordie]

As you haven't said which EMU you are trying to build, I will assume you are trying to form a tumblehome at the bottom edge. If you are simply trying to form a gentle curve on the side then rolling a metal bar across the etch  while it is lying on a pad of kitchen roll should do the trick easily. You do need to use a bar of diameter significantly less than the  curve you are trying to form as the metal will tend to spring back after rolling the component.

 

To form the tumblehome I would suggest putting a round bar in a vice with a layer of kitchen roll wrapped around it, put the etch in place with the point of the start of the radius on the centre line of the bar. Take a 12" steel rule and press it against the etch and then roll it towards the bar, keeping the ruler pressed hard against the etch. This usually works and if you put in too much tumblehome it is easy to press this out again on a flat surface. If that fails, you will need to find someone who has a set of rolling bars and is prepared to help you but forming a tumblehome is not easy with rollers.

 

Ian

[piranha230]

Hi Ian,

I am building several mk1 based emu,s , so it would be a gentle continuous  curve, I have noticed now that MJT say to use a metal dowel between 15-30 mm diameter.

I just need to find out what diameter would work the easiest, the thing that's concerning me the most is that the etched brass sides are quite thick brass, so I am assuming they will be a to bend.

[macgeordie]

Forming the gentle curve of the sides should be easy enough if you do what I suggested above. How thick is the material the sides are made from? The most usual size is 12 thou (0.3mm) or 15 thou (0.38mm). If they have used 18 thou (0.47mm) then you will indeed struggle to bend it. I usually use a bit of either 15mm or 22mmm copper water pipe myself depending upon how much curve needs to be introduced. You could also try rolling on the back of a mouse mat as they are usually made of a fairly hard sponge rubber type material.

 

Ian

[billbedford]

If the metal is hard, rather than just thick, rubbing the inside face of the sides with some coarse (80 grit) emery will make the sides curve the way you want. You will have to be careful that the sanding is even and parallel to the long edges of the sides, so it is a good idea to mount the emery onto a block of wood. 

 

Sanding works because the faces of rolled brass work harden more than the centre, by piercing through one hardened face the stress in the other unbent face will bend the whole thickness. It would be a good idea to test this out on some spare etch as if the metal is soft it won't bend as well, but then it will be easier to to roll it to shape.