I have been avoiding this for ages. I have been scared of bending the tubes for my frame. Why have I been scared though?
1. I was concerned that the pipe-bender wouldn't be up to it.
2. I was worried that I'd get it wrong and have to scrap some of that expensive pipe.
3. I didn't really have a fixed frame design
And so I simply kept avoiding the issue - and the trike project has stayed dormant
However, following through with my holiday resolution and bolstered by a renewed motivation and energy (that comes with a sunny Sunday morning) yesterday I bent some pipe :-)
I now see why so many trikes are made out of angle iron - bending pipe is not as simple as you'd like it to be.
I still didn't really have a fixed design for the frame, but I took an intuitive stab at what I thought 'looked nice' for the lower rails, plotted the curve on a piece of cardboard and just went for it. The pipe bender (12 tonnes) works a treat. I remember someone telling me that the secret was to bend the pipe in little bites, working round the curve - as opposed to simply pumping away in one bend.
I had spent some time a few months ago filing out one of the cast dies to suit my specific diameter of tube, So I was all set..... or so I thought.
You will see from the photos that although the pipe will bend, the pressure is such that the rollers are marking the tube (i don't think this is a 'dent' as such - ie not a significant structural weakness - it just looks horrid)
And so I made up a couple of wooden formers to spread the load a bit - and these worked well until they broke up (as you'd expect under 12 tonnes).
By this time it was "Happy Hour" (another bring-back from holiday) and so I packed up for the day.
And so I'm left with another predicament that if I'm not careful will turn into another barrier to making progress..... what to do about bending tubes? As I see it I have 4 options...
1. Just get on and bend the buggers - it might not look lovely but what the heck - you can probably linish out those marks - this is not my preferred option
2. Get some big rollers turned up that will suit my tube - expensive?
3. Get someone else to bend the pipe for me - but could i specify the design? this is something that I'm inventing on the fly
4. Get someone else to bend the curvy parts for me and then I weld them in between the straight bits - this seems like a bit of a fag and a risk to the integral strength of the frame, but my welding experience with CWB shows that I can make a good enough weld both structurally and cosmetically that this might be the simplest way to go - and it might give me more flexibility when it comes to working things out on tube that need to bend in more than one plane. I shall phone a bender this afternoon
2 comments:
I agree, I don't think the "dents" will detract from the strength of the frame and cause any problems considering how you will be using it.
It might be an idea to replace the rollers with a pair of "slippers" (one for each roller). These are streight pieces of steel into which a groove has been machined. The rad of the groove is the same as your tube. These spread the load and follow the tube round as it is bent thus avoiding the dents. You find them on some copper pipe benders.
Lets see what price your pipe bending people come up with. Good luck.
I like the idea of creating some 'slippers' - my only reservations being 1. that will cost me time and/or money, and 2. I'm still stuck with the difficulty of calculating/creating symmetrical and even bends myself.
Ive heard back from Accurate-Sections (the tube benders), and they can do the job.
Price is about what I expected - though I could have done with it being cheaper. Quote....
2 off sections - 90 deg, 300mm rad @ £21.00 each
2 off sections - 80 deg, 125mm rad @ £14.00 each (we offer 150 centreline rad)
1 off section - 180 deg, 200mm rad @ £18.00 each (we offer 150 centreline rad)
And they add a note of warning... "Our formers are 48.3 o/d so the tube will distort and ovality will be visible"
Hmmm - I think i need to go and balance some rocks to work out what to do
Post a Comment