With the lathe cutting properly and demonstrating that I can cut M24-1.5 threads I could move on to making a retainer to bolt the frame to the jack. Dropping into engineering design mode I defined several requirements for this part:
- Secure the frame to the jack without wobbling and able to take off-center loads.
- Attach using the M24-1.5 threads in the jack.
- Able to screw the retainer into the jack.
At one level these requirements are pretty straightforward. But there are many ways to implement them.
The first requirement involves torsional loads. The best way to do this is by providing support as far away from the bolting point as possible. The easiest way to do the is drill a hole through the top and bottom of the frame and bolt it in place. But this would leave a bolt head sticking up on top of the frame where it could hit whatever I was lifting.
Another approach is to just bolt through the bottom of the frame and make the bold as wide as possible. After allowing for the thickness of the tubing and the corners of the tubing the widest this could be is 1-3/8″. And I have some 1-3/8″ steel rod.
But wait – there is a raised lip around the threaded hole in the jack. This provides more material for the threads but means I can’t have a flat bottom on the retainer. The retainer has to have a 0.080″ recess a little over 1-1/8″ in diameter. This could complicate making the retainer.
The threaded hole in the jack is close to moving parts, so the retainer can’t stick out below the bottom of the mounting plate. The threaded hole in the jack is about 0.25″ thick, so the threads on the retainer can’t stick out more than about 0.30″.
When cutting threads on a lathe you need a runout area for the cutter that extends at least 1/4″ past the threads. Cutting threads up to a shoulder is difficult – especially at my skill level!
The easiest way to screw in the retainer would be to have a hexagonal head on it like a bolt head. They make hexagonal fixtures to use on a milling machine for applications like this. But it would be easier if I could just use a bolt head.
After sketching up several ideas I finally decided that, although elegant, it would be too hard to make this as a single piece.
I moved on to looking at ways to make two or three piece designs and weld them together. I came up with several approaches that looked like they would work. But the all involved a lot of work. And welding a thin threaded part to the body was giving me lots of heartburn.
Then inspiration hit – use an actual bolt! Specifically, use a standard 1/2″ bolt. Drill a 1/2″ hole through the body of the retainer. Cut a recess in the face of the retainer to clear the lip on the jack. Cut the body of the retainer to length so that the head of the bolt would be just below the top of the crossmember of the frame.
The threaded piece became simple: Make an adapter with M24-1.5 threads on the outside of a rod. Drill and tap the inside of the rod to 1/2″-13. Cut off a 0.30″ length that is threaded on both the inside and the outside.
Run the bolt through the body of the retainer. Thread the adapter onto the bolt until it sticks out the bottom of the retainer the needed amount. Cut off the part of the bolt that extends past the adapter. Weld the adapter to the end of the bolt. Viola! – you have a ready to use retainer!
Take the retainer over to the jack, drop it into the frame, and screw it into place. Strangely, it actually fits. Snug it down with a ratchet and socket and check to see how sturdy it is.
Sturdy enough! I wouldn’t try lifting the entire car balanced on one side of the frame, but for loads like a gas tank it should work great.
