Thread: Log Splitter Repair

Evening All,
I am half owner of a RedGum log splitter. Today the co-owner was using it and the cast iron “knuckle” that screws onto the end of the hydraulic ram broke. Hopefully we can buy a replacement part.

Worryingly, the thread on the end of the ram is also damaged. I’m hopeful I can clean it up with a suitable die. The machine is at his place, so I can’t measure it, but I’m guessing the thread is around 7/8”. Even if I can repair the thread it’s going to be weakened and I expect it won’t be long before it fails again.

I’d appreciate any advice on how to proceed. I don’t want to spend money on a die and new knuckle only to have the joint fail again. What would you guys do?

Hi Jack,

In my ttravels on the web in search of ideas for my own splitter, I have seen several occasions where the cast clevis (is that the correct name) has cracked. One occasion was when they used a stroke limiting ring which puts tensils stress on the part.

Anyway, I think the cheapest and easiest place to start is to see if you can clean up the thread with a thread file. As for the clevis, I would fabricate one out of MS. It does not have to be exactly the same. Just need to realise that the major force in use is a compressive force. This makes the design of the fabricated parts pretty simple.

Edit: as long as the clevis is designed so that it threads right up to that shoulder then the force is transfered straight to the shaft and not on the actual thread. In fact I'm wondering if the grub screw that holds the clevis tight in the thread has come loose. That would allow the clevis to partially unscrew and then all the splitting forces would be on the thread. This is a sure fire way to destroy that cast clevis.

Cheers,

Simon

G'day Simon,
Thanks for the prompt reply. "Clevis". I knew there had to be a proper name!

Originally Posted by simonl

as long as the clevis is designed so that it threads right up to that shoulder then the force is transfered straight to the shaft and not on the actual thread.

That's what I figured. I wonder if the clevis on my machine wasn't hard up against the shoulder? Making one from MS is a possibility if the threads are metric, because that's all my lathe will cut.

Originally Posted by jack620

G'day Simon,
Thanks for the prompt reply. "Clevis". I knew there had to be a proper name!



That's what I figured. I wonder if the clevis on my machine wasn't hard up against the shoulder? Making one from MS is a possibility if the threads are metric, because that's all my lathe will cut.

No worries Jack. I actually edited my last post while you were reading it suggesting exactly what you said. I think theres a good chance it's metric.

Simon

Originally Posted by simonl

In fact I'm wondering if the grub screw that holds the clevis tight in the thread has come loose. That would allow the clevis to partially unscrew and then all the splitting forces would be on the thread.

Maybe. For that to happen the hydraulic ram would to need to rotate, since the clevis is prevented from rotating by the splitter head. Is it possible for the ram to rotate? If so, the direction of force should cause the ram to tighten on the clevis, not loosen (I think?).

I hope you're right about it being metric.

WRT the ram, it is possible for the piston and rod to rotate in use. It's only the friction from the rod seals that make it difficult to rotate when static but while it's moving in and out, it does not take must effort to rotate it. However, as you point out the splitting wedge (and clevis) cannot rotate because it's located in a slide and the rod and piston should not rotate because it should be screwed tight on the clevis and retained with that grub screw. Unless the grub screw came loose. It does seem unlikely but I'm trying to understand why the thread on the rod would be damaged.

You would think that the compressive forces would keep the clevis tight on the rod but if you consider it's only experiencing that compressive force for a small fraction of that total cycling time, so maybe not.

Just looking at your pics again. Looking at the clevis I notice that the first part of the thread is clean and undamaged. It's the last half of the thread that is damaged. Looking at the smaller of the two broken parts, you can see that the inner lip is rounded over, indicating that maybe the clevis was half unscrewed when it failed. This small part is the underneath part (as the grub screw would be facing up)

The splitter has been extended out to split a piece of would and with the clevis only half screwed in, the splitting force has forced the clevis to go skew wiff, producing that rounding over on the edge.

I may be wrong but similarly, if you look at the rod, the last half of the thread is not all that damaged as it was not engaged when it failed. The only other thing that comes to mind is to check that your ram does not have a small bend. From memory, the red-gum splitter has a flange mounted ram which means it cannot pivot. If the clevis was forced up on breakage then the cylinder cannot pivot to allow for it.

Simon

Originally Posted by simonl

Looking at the clevis I notice that the first part of the thread is clean and undamaged. It's the last half of the thread that is damaged. Looking at the smaller of the two broken parts, you can see that the inner lip is rounded over, indicating that maybe the clevis was half unscrewed when it failed.

You're right. The inner half of the clevis thread is pristine. It certainly does look like the rod wasn't fully engaged in the clevis when the clevis broke. I suspect the grub screw had come loose.

I hope the ram isn't bent. That would really spoil my day.

Hi Chris, that's the trouble being part owner of things, you don't know how the other half treat things!!!!! DAMHIKT
Just tell him that your part of the machine is OK, it's his part that broke
Kryn

Agree Kryn, especially when it's people with no mechanical sympathy who use your stuff and just drive it into the ground.

Simon

Agree Kryn, it's always a risk. My biggest beef is when a part-owner loans the machine to one of his friends. That hasn't happened with our splitter because I made it very clear it wasn't to happen before I agreed to the deal. To be fair, the ram may have been unscrewing itself from the clevis when I used it last time. I've never thought to check it.

Yea, in fairness I reckon if I bought a log splitter similar to yours, I would never take any notice if the clevis became slightly unscrewed or maybe not considered the consequence of it happening. It's only because I had to design and make my own from scratch that it made me aware of potential issues and weaknesses.


Simon

This just a thought.....is this part pushing the block of firewood onto the "spear point" of the splitter? If it is, I think that the threaded part would fail again due to the part being moved "off line" by the firewood. I would make the part a sloppy fit (agricultural) so it is able to conform to the attitude of the firewood block

Rod,
The clevis attaches to the splitting wedge with a thick bolt. The wedge's base plate captures the I-beam rail, so it can't really move much laterally.

Yes I can see what you mean. I was thinking the "push came straight from the ram's piston. The way it is set up, makes you wonder how it became a problem