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Bending 5mm brass rods to make driveshaft

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Who Boot31/01/2021 16:11:13
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49 forum posts
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Hi,

Can anybody advice me on how to bend brass rods to make a crankshaft for a model boat? I have two 5mm brass rods of 12 inch length and I wish to bend them so that they are identical. Previous efforts to bend metal rods of this size using only my hands when the rod is held in a vice are error prone. Whilst I managed to get similar shaped crankshafts it was obvious they weren't identically shaped and getting them to be so is important. There has to be an industrial way with all its accuracy to enable modellers to bend brass rods which might mean using some special tool or other. Can anybody advise me please?

P.S. the crankshafts are to go in a model canoe as per plan in Model Boats October 2016 called Waddler and built by Glynn Guest. There is a wooden paddle fitted on each crankshaft. Guest used metal knitting needles for the crankshafts which are great materials to use but if you can't bend them to be identical or near to identical the first time, like happened to me, the needles won't stand too much bending and shaping before they snap.

ashley needham31/01/2021 18:37:57
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7150 forum posts
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WB. I would think some sort of tool to use as a press, in a vice might do. Also, the brass needs to be annealed by a blowtorch regularly to keep it malleable. Or you could try bending two pieces at the same time....a vice is a must here of course.

Alternatively could you make a crank by fabrication....using brass side webs and drilling holes and soldering perhaps?

Ashley

Richard Simpson31/01/2021 19:22:38
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341 forum posts
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I definitely think you need to bend them at the same time so both cranks go through exactly the same process. I would make up some sort of jig that holds the two cranks simultaneously. Something along the lines of a piece of wood with two close fitting holes drilled through it that will hold the rods then, when put into a vice will actually grip them. The rods can then be bent together by applying a force through another piece of wood or a bar.

You are going to have to think the process through for yourself but I would tend to suspect that bending the offset might be done first. At the end of the day the main shaft has to remain perfectly aligned, which is far from easy with bending. I also suspect though that, for what you need it for, absolute perfection isn't necessary so trial and error may be required. Perhaps a few practise runs with some cut up coat hangers might help you think it through and practise. Knitting needles are usually aluminium so you will only get one chance at bending them.

David Marks 131/01/2021 20:31:14
255 forum posts
44 photos

Firstly the brass needs to be annealed (softened). This will make the bending easier, provide a sharper bend radius and greatly reduce the risk of the material fracturing whilst producing the bend. You will need a small butane powered torch to heat the brass to a very dull red. To produce the bend (as previously stated) you need to make a bending tool. If you have a lathe or know someone that has, drill a couple of pieces of 10 mm bar with a 5mm dia hole through each, One bar is held in a bench vice and the other used to bend the brass into the correct angle.

Who Boot01/02/2021 17:28:37
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49 forum posts
21 photos
Posted by ashley needham on 31/01/2021 18:37:57:

WB. I would think some sort of tool to use as a press, in a vice might do. Also, the brass needs to be annealed by a blowtorch regularly to keep it malleable. Or you could try bending two pieces at the same time....a vice is a must here of course.

Alternatively could you make a crank by fabrication....using brass side webs and drilling holes and soldering perhaps?

Ashley

Thank you Ashley. I like the idea of using heat to soften the brass to make bending easier.

Unfortunately, I don't understand what you mean by making a crank by fabrication nor what is side webs. My fault as I'm not an engineer. If you tell me though then I will learn. I'm learning more all the time about building model boats, the tools and electronics thanks to the kind guys on this site who are so generous of their time and sharing their knowledge.

Who Boot01/02/2021 17:36:33
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49 forum posts
21 photos
Posted by Richard Simpson on 31/01/2021 19:22:38:

I definitely think you need to bend them at the same time so both cranks go through exactly the same process. I would make up some sort of jig that holds the two cranks simultaneously. Something along the lines of a piece of wood with two close fitting holes drilled through it that will hold the rods then, when put into a vice will actually grip them. The rods can then be bent together by applying a force through another piece of wood or a bar.

You are going to have to think the process through for yourself but I would tend to suspect that bending the offset might be done first. At the end of the day the main shaft has to remain perfectly aligned, which is far from easy with bending. I also suspect though that, for what you need it for, absolute perfection isn't necessary so trial and error may be required. Perhaps a few practise runs with some cut up coat hangers might help you think it through and practise. Knitting needles are usually aluminium so you will only get one chance at bending them.

Hi Richard

Thank you for your reply. Yeh, using a jig in the way you have described sounds good. I'll try that. I'll also add to that a suggestion from other members of the forum which is to soften the brass with a blow torch to make it easier to bend. You're right in that absolute perfection is not a requirement but in my previous effort I thought my two rods weren't close enough in shape. I'm sure with the jig they will come out very satisfactory.

Who Boot01/02/2021 22:14:14
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49 forum posts
21 photos
Posted by David Marks 1 on 31/01/2021 20:31:14:

Firstly the brass needs to be annealed (softened). This will make the bending easier, provide a sharper bend radius and greatly reduce the risk of the material fracturing whilst producing the bend. You will need a small butane powered torch to heat the brass to a very dull red. To produce the bend (as previously stated) you need to make a bending tool. If you have a lathe or know someone that has, drill a couple of pieces of 10 mm bar with a 5mm dia hole through each, One bar is held in a bench vice and the other used to bend the brass into the correct angle.

Hi David

Thank you for going to the trouble of explaining quite a detailed procedure. Because it is something I've not done before I don't quite follow what to do ; is it the bending tool that gets drilled with a 5mm hole? How deep would the hole be? I'm sorry you're going to have to explain that a bit further to me please before the message gets through to my lack of understanding. I've no doubt the explanation is clear to somebody who knows the subject better than me.

neil howard-pritchard19/03/2021 00:15:14
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1775 forum posts
1432 photos

Are you sure that you need them to be of that large diameter..........that is one chunk of brass to bend, whether anealed or not.

because every time you bend the brass one way or another to get conformity, you loose the anealed advantage as the brass reverts back to a semi solid state again and then you have to go through the process of annealing it again to cherry red which eventually weakens it.

if i were you i would try with 3mm brass, as i am sure that would still be strong enough for you.

Edited By neil howard-pritchard on 19/03/2021 00:15:40

Malcolm Frary24/03/2021 10:23:47
996 forum posts

If the original used 5mm brass, fair enough. I would be tempted to look at stainless bike spokes. About 2mm diameter, much easier to get a 90 degree bend in, probably as durable as 5mm brass. They come in packs of 10, but unused ones tend to find uses very easily.

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