How much will I weaken steel bar, by drilling through it?

[Greenheart]

My launching trolley is low-tech, but has given solid service for eight years, and was far from new when I acquired it.

The steel bar that acts as an axle is 35mm thick, but the outside 100mm at each end are 25mm, to fit the holes in the wheels. The thickness of the central section has holes drilled through it, to bolt it to the wood cross-member that supports the boat. The trolley is upside down in the photo below.

The bar is severely corroded and I want to replace it. The wheels barely turn because the rust is so bad.

I would much prefer to pay for a 25mm bar, than a 35mm bar with custom-milled/machined narrower ends to carry the wheels...

...but if I drill 8mm holes through a 25mm bar to attach it to the timber cross-member, how much strength will it lose?

Are 8mm bolts strong enough? Could I get away with a higher number of 6mm, perhaps?

Is there a practical alternative way to secure a 25mm steel bar to a 60mm thick piece of hardwood, other than by drilling?

And am I right, thinking that a 25mm bar will be easily strong enough (and remain straight) to carry a 160kg boat?

Thanks!

 

[sarabande]

U bolts ?

Amazon.co.uk : u bolts

 

[PaulRainbow]

I'd use 25mm tube, it'll be stiffer than solid bar and some clamps, perhaps something like this Kiowa Ltd. - 25mm C4 Std PP Pipe Clamp Jaws - | Kiowa Ltd | Industrial Components Online Store

 

[Greenheart]

U-bolts are a good idea, thanks...although they will need to be very long ones to reach through the thickness of the hardwood support...which would also have to be thicker, otherwise the U-bolt pins would be very close to the outside of the timber.

How is 25mm tube, stiffer than 25mm bar? I don't disbelieve it, I just don't understand it.

Wouldn't I pay a lot more for tube of strong enough grade, than for the same size bar?

 

[NormanS]

Why not just take the whole thing apart, then using a small angle grinder or similar, thoroughly clean up the existing steel bar, paint, and reassemble? Also, it doesn't matter what size of steel that you use, if you don't grease the wheels they will always seize up.

 

[Gary Fox]

Remove the wheels and clean the stub axles, grease, reassemble, bob's your uncle.

 

[Greenheart]

This sounds wise. Especially now I have a cordless grinder and not much employment for it. I'll have a go, thank you.

I'm afraid the ends of the bar may be too far gone to restore, because several years ago I made the ridiculous mistake of using split pins of a superior grade of steel. The washer and the bar are now crusted like deep-sea wreckage; the pin is strong as new.

 

[TernVI]

The 'bar' in the middle will be tube, I'm sure.

Galv steel conduit is cheap to buy from toolstation or Screwfix.
As are some heavy duty angle strap brackets.

I bodged one trolley by cutting off the corroded end of the cross member and inserting a length of conduit to serve as stub axle,
Worked fine forseveral years.

 

[LadyInBed]

You can drill as many holes as you like, as the strength is provided by the wood, but I agree that U bolts are a better solution.

 

[LadyInBed]

There must be a better solution than to use Pop Bottles tied on with string presumably to cushion the boat!

 

[Topcat47]

If it is 35mm bar stock, allowing for rust to be 2 or 3 times the volume of steel, cleaning and painting the original won't do it any harm. Similarly, cleaning up the outside ends won't do any harm as there's no load on them. The stubs will need to be cleaned to allow the wheels to run free. Shame on whoever used it and didn't grease the axles. A bit of Elbow grease and hammerite is a lot cheaper than a new axle. Waterproof grease the axles, preferably using a polymer grease.

 

[Greenheart]

Thanks for the good advice here gentlemen, I'll post a photo after the clean-up.

There must be a better solution than to use Pop Bottles tied on with string presumably to cushion the boat!

I'm very confident you're mistaken. The bottles are re-pressurized by freezing to fill them with dense cold air...

...then the bottles are carefully roped onto the cross-member. They provide a smooth, air-cushioned rest for the hull, far broader and better than the narrow hardwood beam with a bit of lifeless soggy foam on it, as when I bought it.

The bottles are good for about five years. Then they can be recycled. It works, brilliantly.

 

[Gary Fox]

There must be a better solution than to use Pop Bottles tied on with string presumably to cushion the boat!

Is there still a PBO book of Useful Tips?
It's basically British Leyland Hydrolastic suspension, for sailing dinghies, ideal as the OP's trailer has no suspension.
The spring rate is controlled by residual pepsi volume: more pepsi for harder springs; damping force is controlled by air flow: to increase damping, tighten the lid clockwise.
The bladders found in wine boxes are also ideal for jobs like this, especially if you have a lot of empties..

 

[LadyInBed]

Not as cheap as Pop bottles but a padded roof rack would do a job.

 

[sgr143]

How is 25mm tube, stiffer than 25mm bar? I don't disbelieve it, I just don't understand it.

A 25mm tube won't be stiffer than a 25mm bar, but there won't be very much difference, for a tube of reasonable wall thickness. That's because the controlling parameter is the "second moment of area", which is (Pi/4)r^4 for a rod, or (Pi/4).(r1^4 - r2^4) for a tube with OD = 2.r1 and ID = 2.r2. That fourth power of radius tells you that it's the outer skin that does most of the bending resistance. Also the tube will be a lot lighter for a given stiffness. And yes, U bolts.

 

[Daydream believer]

But we might not mention that tube sometimes tends to collect water & corrode from the inside outwards Thus reducing the life span a little. But in the words spoken by many in our village " that'l see you out"

 

[sgr143]

But in the words spoken by many in our village " that'll see you out"

As find, as I get older, that phrases like "That'll see me out", spoken in cheerful self-mocking jest in my youth, are now becoming rather depressing statements of fact.

 

[vyv_cox]

I'm afraid the ends of the bar may be too far gone to restore, because several years ago I made the ridiculous mistake of using split pins of a superior grade of steel. The washer and the bar are now crusted like deep-sea wreckage; the pin is strong as new.

The corrosion shown has nothing whatsoever to do with the stainless split pin. Even if the whole thing was permanently immersed the relative sizes of the anode(the trolley) and the cathode (the pin) would lead to minimal corrosion of the former. If it was a stainless trolley and a mild steel pin it would be a totally different matter.

As it is normally standing in marine air (presumably) the cause is simply neglect. As suggested, a good dose of angle grinder will clean it up and a smear of grease will help it to last.

 

[Greenheart]

6th June

I'm grateful for the advice regarding the size of hole I could safely drill in steel bar - the U-clamp solution is fine. So I no longer need to drill steel bar, although that question remains an interesting one.

Yesterday I went to remove the wheels in order to sand/grind the rust off the axle, then Hammerite it, grease it generously and hopefully have many more years without bother. Unfortunately, nothing I could do would remove the wheels from the axle.

At that point I remembered that these wheels had a larger bore than fitted my 25mm axle, and that they were supplied with a central 25mm 'bore-reducer', which fitted my axles perfectly - a little too perfectly, because now these are stuck hard to the axle.

So in fact, the reluctance of the wheels to spin, is a failure of lubrication between the inside of the plastic wheels, and the 'bore-reducer', because the bore-reducer never rotated on the axle, and was never designed to. Unfortunately there is no way to usefully apply lubricant without first separating the wheel from the bore-reducer, which first requires removing both from the axle.

They are only plastic so can't be rusted on, but when I used a bottle-jack to apply a lot of lateral force between the wheel's centre and a strong-point on the axle, they began to deform without actually sliding along - they're immovable.

So...I am still inclined to build myself a new trolley, meanwhile making do with the old one in its reduced state, and since you gents understand more than I'll ever know about wheel-bearings, I have a couple of questions.

Do the insides of the bores of trolley wheels just rub against a fixed steel axle? Or is it normal to have some kind of fixed smooth lining? I can't see what would hold the grease onto the slender gap between axle and wheel under load, if it isn't somehow enclosed.

My boat is around 150kg, so possibly I need a cleverer or tougher design than metal rubbing on plastic. I do have plenty of ordinary automotive grease - but is that effective for such purposes? I don't want to pollute the sea by regular applications that could be avoided.

Thanks!

 

[penfold]

The steel axle has corroded and rust occupies several times the volume of the steel it is made from; the extra volume has expanded the plastic sleeve, jamming it on the axle and expanding it in turn, creating extra drag on the wheel. In order to avoid this in future grease the axles regularly. If you have a big enough bucket you could dunk each wheel in turn in vinegar, it will eventually dissolve the rust and free the wheel and spacer.