concur with Johns suggestion that hand bending the rib
profiles by hand is possible. I did this last year to make a
2m diameter dish.
didn’t worry about using any timber, each rib went straight
in the vice and was bend bit by bit by hand. The first rib
takes ages, and it’s a bit of an art getting used to the
spring-back of the material.
can’t see that a rolling machine would be helpful, because
the nature of a parabolic curve is it ever changing radius.
spend lots of time getting the template right, because you
never know when the desire for a higher band might come
an aside, I’ll shortly be replacing the mesh on my dish, and
have just received some sheets of expanded aluminium mesh
from the Expended Metal Company. They were easy to deal with
and the material looks good.
[mailto:UKMicrowaves@groups.io] On Behalf Of John
Sent: 27 August 2020 10:05
Subject: Re: [UKMicrowaves] Bending dish ribs any
tips or tricks?
You can hand form the box section .
Find a 1m length of good solid hardwood
- something like 35-50mm thick and cut a square hole
through the thickness such that the section to be formed
will just pass .
Clamp wood into a solid bench vice or
one mounted on a solid pillar drill stand , with the
square hole set to have its sides vertical and horizontal
Pass the section through the hole and
apply a gentle downwards force at around 1 metre from the
hole .You will be able to "feel" the required effort
needed to bend the section .
Remove section and offer up to your rib
template to determine if bend is conforming to the shape -
reverse thrust if required or try bending more if needed.
It is better to underbend at this stage
as work hardening will occur with each applied effort
When happy push section approx 100mm
further through hole than the first bend point and repeat
the bending stage - remove and test each time you perform
a bend and progress along full rib length ,testing
against template as you go .
Ensure the hole does not move from its
initial set point and that the applied force is vertically
downwards , to avoid any tendency to spiral the formed
Although a slow process you should
finish up with the full rib following the template and it
should be plenty good enough into the mid microwave area .
On Wed, 26 Aug 2020 at 16:22, David Law
Hi, I'm on Mk2 of my 4m 0.38f/d dish
project this time using traditional square tube and
The material will be 18mm x 1.6mm square tube.
I've made a template from wood sheet.
I wondered if anyone has any tips or tricks in how to form
a nice smooth accurate reproduceable parabola.
Or indeed what not to do! Roll bending machines are not
really in the budget for a one off project.
It will be attached to the stiffening rib via trusses and
riveted plates which will avoid using a welder.
It's for 23cm at this time and likely to stay that way so
points of mm accuracy isn't too important.
I touched base with Howard, g4cch a while ago who gave me
some tips, but the more advice based on experience the
PS Mk 1 used 1/2" round tube on a hub but it was too
floppy (probably only good up to a 2m dish)
If anyone wants any bent 1/2" round tube let me know!