Jump to content
I Forge Iron

Cylinder rod keeps backing out of ram

Recommended Posts

My hammer has a 1" rod which screws into a 'bung' style nut welded to the ram. I have a jam nut on top of this as well. Even though I clean the threads and use locktite, it still loosens. I thought about drilling through the nut and rod and putting in a rolled pin but was worried about weakening the rod and having a stress fracture . Another idea that I used years ago was to drill and tap a hole, place a short piece of brass rod in the hole to protect the rod threads and then use a set screw to pinch the rod. But I think that there is just to much vibration for that to work well.

Link to comment
Share on other sites

When I worked at a Hydraulic and Pnuematic cylinder manufacturer about 30 years ago, many cylinders had the piston right hand threaded to the rod, then a left handed lock nut, we used red Loctite with the primer and in severe service drilled the jamb nut for a small roll pin. We still ocasionally got one back from the oil fields with the piston off the rod. Those oil field roughnecks could break anything.

Link to comment
Share on other sites

Having watched *4* roughnecks standing on a dozen feet of cheater and bouncing up and down trying to unfasten a mud pump fitting they had run way past it's maintenance period I could well believe that!

Or like the old saying "your basic marine should be able to break an anvil with a rubber mallet"!

Link to comment
Share on other sites

The basic problem is that the piston is like a flywheel on the upper end of the cylinder rod and there is usually an inherent twisting motion as the piston moves up and dow. Because of the flywheel effect, the tendency is for the rod to keep rotating a smidgeon each stroke so that eventually it will unscrew if not impaired from doing so. This is especially true if the piston and rod are pinned. That is the option I use in my Norgren cylinders. Before that I had some pistons and rods come unscrewed inside the cylinder. And I have had some problems like you are experiencing. Maddening.

If you have good tight fitting threads that are clean, the red Loctite provides good service. Any loss of thread quality as well as lack of cleanliness prior to application of the red Loctite impairs its holding power. I believe you know this already, but others reading this may not.

Because the rod's threads are about 1" long and you are using a jam nut, there may not be adequate threads for red Loctite to work at its best.

I believe you are correct that drilling a hole through the rod for a pin will possibly create a location for the rod to break. Note how axle spindles place the cotter key hole at the outer end of the spindle shaft and you may have never seen that end of a spindle fractured, I sure haven't.

So where does this leave you? One approach is to use one of those alignment couplers so that the shaft and piston can "free wheel" relative to the hammer head. It can be red Loctited to the shaft and the housing for the free wheeling end can be bolted to the hammer head.

Another approach, of possibly many, is to tig weld the jam nut exterior to the nut already welded to the hammer head. (After all the loctite is cleared away!)

A better approach and the one I would use, and have used, is to use the flats on the cylinder rod as a basis for a piece that is shaped like an open end wrench and weld that piece to the hammer head to lock everything so that the rod cannot unscrew. I believe such pieces are used on some hydraulic cylinders. Big Blue uses such a piece and bolts it in place with an auxilliary bolt. I'm sure that the open end wrench idea gives you the picture. With a 1" diameter rod the flats are likely to want a 13/16" wrench. If you make the "wrench" make the fit snug on the flats.

Good luck.

Link to comment
Share on other sites

If you’re pretty good at drilling and tapping small screw holes, you might consider what I did. I don’t care for locktite because if the connection ever needs to come apart, you can bet the stuff works real well.

I constructed my shaft/ram threaded connection to be held tight by an “off center” locking screw. Drilling and tapping the offset screw hole in the nut was done carefully since the drill and tap will be side loading upon breakthrough.

I ground a small flat on the shaft thread for a pivot surface so as this screw is tightened, the shaft connection is rotated tighter and harder towards bottom out. The flat also prevents goobering up the threads should this connection ever need to come apart.

Installing a locking screw “dead center” on a threaded connection will neither allow the male thread to go tighter or looser. However, offsetting the locking screw on the correct side will actually allow/make the male shaft screw in tighter. So if there is any wear or peening inside this threaded connection, the locking screw can actually make it go tighter and tighter.

This method has worked real well for me and the locking screw is real easy to check for tightness.

Good luck, Spears.

post-9545-0-66425000-1318339133_thumb.jp post-9545-0-73226900-1318339145_thumb.jp

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...