Straightening a section of Nitronic 50 rod

[Ian_Edwards]

Hi, I have short section of 10mmn Nitronic 50 rod with a slight bend in it, near the end and only about 5 degrees over a 100 mm section.
Nitronic 50 rod is really hard and very difficult to bend.
It's been suggested that a 2 pronged leaver would work, and I can see how I could ease the bend out bit by bit.
Does anyone know where I could buy such a beast?
I know I could make one, but at the moment i don't have the time or the facilities to do that.

Cheers Ian

 

[Spirit (of Glenans)]

I dont know what nitronic rod is, but to straighten rod with limited resources, what comes into my mind would be perhaps a bench vise, or a heavy plank with a suitable sized hole drilled in it, combined with a length of tubing of the appropriate strength and internal diameter.

 

[RichardS]

I could straighten it with my hydraulic press but, even then, there's a difference between it looking straight and actually being straight over its entire length.

Richard

 

[Norman_E]

Nitronic 50 is used for rod rigging, but I'm not sure what a short length would be used for.

 

[Graham_Wright]

How straight is straight? Do you have access to a lathe?

 

[dom]

Hi, I have short section of 10mmn Nitronic 50 rod with a slight bend in it, near the end and only about 5 degrees over a 100 mm section.
Nitronic 50 rod is really hard and very difficult to bend.
It's been suggested that a 2 pronged leaver would work, and I can see how I could ease the bend out bit by bit.
Does anyone know where I could buy such a beast?
I know I could make one, but at the moment i don't have the time or the facilities to do that.

Cheers Ian

Is this short section serving a critical role? If so, might be best to just replace. Else ask Navtec, but suspect they’ll say the same.

 

[Zing]

If it goes back into your rigging, the loads of the rigging will straighten it. My forestay curls up when off the boat. On it, it’s straight.

 

[rogerthebodger]

What you need is a pair of Vee block to rotate the rod in to check any offset with a dial gauge.

Use a hydraulic press to put pressure pressure on the offset.

I have straightened a propshaft using this method.

 

[rotrax]

I could straighten it with my hydraulic press but, even then, there's a difference between it looking straight and actually being straight over its entire length.

Richard

Over the last 55 years I have successfully straightened hundreds of motorcycle fork tubes. I can, by experience, tell instantly whether it is worth bothering with, or to just order a new one.

I use my big hydraulic press - about 7 feet tall, gauge redlined at 50 tons, a Churchill from a tank repair depot. Vee blocks, alloy shaped pads and a dial gauge.

A 5 degree bend should be little problem.

Experience tells me it is sometimes required to 'judge' how far past straight to go as when relaxed again it springs back.

That is where the " Black Art " bit comes in, not science!

As to it being straight against lookinging straight, you are bang on the money. A couple of thou, no problem, Half a mm/20 thou perhaps so.

I am not familiar with the material or its loads, as opposed to what I know. I suspect stretching and compression loads as opposed to bending/twisting loads on motorcycle forks.

 

[Ian_Edwards]

Thanks for the replies, but unfortunately non of them really help.
I was pushed for time when I wrote the initial question. Here's some more detail. It is rod rigging, the bend is at the top of the forestay, just short of the termination. The bend was introduced when the mast was last professionally rigged in April 2018. The bend has caused a slight eccentricity in the forestay furling system. I could feel a slight "high spot" once per rev. After 2 season of use like that it has more or less destroyed the top section of the plastic insert inside the foil.
The tension in the rigging hasn't straighten it, despite using a 2 ton hydraulic back stay tensioner, which is capable of put a significant bend in 22+ m carbon fibre mast.
The forestay is currently horizontal supported by a series of tressels, it's about 20m long and not that easy to move.
I have removed the top section of foil and plastic insert.
It's not that practical to get it near a hydraulic press or a big vice, and I don't really want to heat it to cherry red, I'm not sure what that would do to the Nitronic 50 rod.
I'll try and post a photo when I can get to my PC.

 

[Ian_Edwards]

I'm in Australia at the moment, the boat is in Scotland, I'm trying to "get the ducks in a row", so that when I get back I have a clear plan, so I can get the boat back in the water at the end of March.
I've just re-sizes the photo's which were on a micro SD card.

 

[rotrax]

It was bent by the rigger installing it then?

You could make - or have made - two pieces of thickwall soft alloy tube split lengthwise that will slide into the foil, install them down the foil as support and bend it by hand by sliding another tube over the end fitting.

Have a collar on the top so you can get them out! You will have to judge the length, I would suggest 1 metre.

Looking at the second photo, perhaps only one half would be needed as it might well be impossible to slide two into place. Something will be required so as to not damage the foil.

Or, prefered option upon reflection, remove the end fitting pull the rod completely out of the foil and deal with it. Two pieces of tube, protect the rod where the pressure points are to avoid local damage. Or, a big vice with soft jaws.

IMHO, pretty straight will be OK, not required to be within a few thou, but straight enough so as to give the upper bearing an easy time.

Otherwise by a new one and use a different rigger.

 

[vyv_cox]

I understand from the literature of various manufacturers that rod rigging is most likely to be supplied in a cold rolled condition. This will be considerably stronger than annealed material, as with cold drawn 316 wire for rigging. Heating your Nitronic 50 to red heat will reduce its strength considerably, whereas cold bending will have little effect on strength, provided no cracks or surface damage are introduced.

 

[Ian_Edwards]

Thanks for the replies.
I already have a simple top bearing being made, taking a aluminium joining section, which is extruded to fit inside the foil, with a clearance hole drilled through the centre. The machine shop is going to cut it axially, and then drill and tap it to so that it can be fitted back together, with a shim plates to make up for the saw cut. I can't just slide a section over the rod, the top nut is retained by a cold formed "elephant's foot". This will fit inside the top section of the foil and act as a bearing. As Rotrax suggested, it I can take most of the bend out, so that it's straight to a 1mm or 2, that'll be good enough, it doesn't have to be as straight as a prop shaft.

I already have a new rigger helping, I wouldn't let the original rigger anywhere near may boat again, he made a real mess of so many things. The rod rigging was renewed in 2014, but it would be very expensive to replace just the forestay, there's a very high transport cost to get the big coil of wire up from the South Coast of England.

Vyv, thanks for the info' on Nitronic 50, it's as I suspected, heating it would make the rod significantly weaker, and taking a small bend out of the wire wouldn't make much difference.

I've taken the top section of foil off, as noted in my original post, so I have 1m or so of rod to play with. I still need a practical way of straightening the bend.

Having not made any progress on sourcing a 2 pronged leaver, I may just have to order some steel bar and some 12mm bolts and make one when I return to Scotland.

 

[Ian_Edwards]

Update.
I couldn't get anyone to straighten the rod for me, and I didn't find any 2 pronged leavers I could buy, and the guy who said he could make me a top bearing, didn't follow through. So I set too and did it myself.
The rod was bent like this;


I stripped off the top section of foil, to discover that the internal plastic spacer was badly damaged by being rotated on the bent wire.
I contacted Andy Postel at All Spars, who was very helpful, and suggested that top bearing would help, but first I had the straighten the rod.
I made two 2 pronged leavers, with different spacing between the prongs one 35mm the other 28mm, from 6mm x 25mm flat bar each 1m long.

I tapped the center of each bar with two M12 thread and fitted 2, 12mm high tensile bolts with locking nuts.
By gently working the bend out the rod by slowly working my way down the rod, putting very small bends into the rod every 5 to 10mm, I managed to straighten the rod, not completely, but good enough.
I can't get the photo to load, so I'll continue with another post.

 

[penberth3]

Well done!

 

[GregOddity]

Yeah, you did well.

 

[Ian_Edwards]

To Continue;


Straightened Rod.

I then used a 100mm length of a joining piece to make a bearing.
I couldn't just slip this onto the rod because it wouldn't slide over the "elephant's foot" and securing nut.
I hacksawed to 100mm length axially, to make a split bearing,


And then drilled and tapped 4 @ M3 holes in the new bearing to hold the bearing in place at the top of the foil.
I also split the plastic lining tube axially.

I then dry fitted the new bearing onto the rod.
I dry fitted the new bearing into the top foil section with a new internal spacer, several time, making slight adjustment to improve the fit.


M3 CS set screws to hold the bearing in place.





The finished top bearing, as far as I can tell the foil now rotated freely, and the slight bend in the rod will straighten out when the rig is in and the forestay tensioned.
I hope that other will find this post useful if they are ever faced with a bent bit of rod rigging.

Cheers Ian

 

[rotrax]

Well done - good fix.