I don't know what your bolt suppliers are like, but here in the Antipodes if you want six inch Whitworth bolts with square heads, you have to make them yourself. I've not made steel bolts before, just tiny brass ones.
So, get some one inch square steel and turn it down to half an inch like this:
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'll make the bolts in pairs and chop them apart later. The old bolts are way past their prime after 109 years.
Here's the lathe at work. There's a lot of metal to get rid of:
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used a hand die for cutting the thread. I suppose one day I'll learn how to do the threading on the lathe. I have no idea how that is done. I have a horror of the tool winding itself into the chuck. Not that I've ever done that.
First 6 weeks in the apprentice school 50 years ago and not used since! AFAIR you obviously need a cutting tool ground to the correct thread form. The lead screw is mechanically synchronised with the chuck but you have to work out the correct gear ratio for your chosen thread pitch. After that things get a bit hazy.... an expert will be along shortly:-)
I suspect I could get the size from my local supplier, but with hex heads rather than square. However, he has surprised me before with what he has in stock.
There are three main ways to thread on the lathe.
First, buy a lathe with a threading function. The crosslide is driven at the right speed to give the number of threads per inch (or mm) you want. When it runs up against a stop, the drive disengages. You do end up with a groove at the end of the thread this way. As you will probably need to take multiple cuts, there is a small clock device that shows you when to engange the drive again to follow the same cuts.
Second, use a button die holder in the tailstock. This has two parts - a fixed part that goes in the tailstock (or capstan if applicable) and a part that holds the die. The die holder part is free to rotate unless pressed up close to the fixed part, when it is held stationary by dogs. It needs a steady feed to keep the two parts together. When you reach the end of the thread, stop feeding and the die holder part will pull forward and rotate freely. The disadvantage here is that you have to back the die off the thread, as you would with a hand die.
Third, use a Coventry die head. These have a set of three of more cutting dies that move in and out radially. Again, this is fed in using the tailstock or capstan but, at the end of the cut, when the die pulls forward the dies snap open, coming clear of the thread. The holder can then be pulled straight back off the workpiece without having to reverse the lathe. You can also get Coventry die heads that open on striking a stop, rather than on pulling off. Coventry die heads are expensive, but completely worth the cost for repetitive machining with a capstan lathe.
You also need one with a leadscrew that's either metric or imperial, as needed. It's awkward to convert from one to the other (although it can be done, it can usually only be done on larger lathes, on account of needing a 127 tooth changewheel for the conversion).
If you have access to one, a die box is the best practical way to cut threads on a lathe.
If you're making "bolts", then a normal hand die stock is a perfectly adequate way to do it - there's a small tendency for the thread to wobble, but if you're only using short nuts on it, then that's no problem. Supporting the die stock with the tailstock from behind is normally a help.
Thread cutting with a point tool on the lathe is a specialist task. Even when you're tooled up and experienced in doing it, it's unusual to do it if you're merely making a thread for a threaded fastener.
What grade of material did you use? It looks as if it might be ordinary mild steel. Is that strong enough, given that almost any bolt you purchase these days will be a high-tensile grade?
Not criticising, just wondering. You've certainly got a nice finish on them.
I think it was mild steel, bought for that job by a qualified person. I need to match 109 year old bolts, which are not high tensile. They are merely holding pieces of wood together.
I will thread all these bolts by hand. There are other jobs involving two inch threads with unusual pitches, that will have to be done with a point tool on the lathe. I shall watch someone else do it with interest.
So why would you need a high-tensile bolt if it's going into CI? The threads will fail long before the bolt. If it's a bolt with this much force on it, you'd use a stonger thread than Whitworth.
I've got stashes of BSF bolts from the '30s & '40s that are high tensile, but none of the Whit are.
Can I be a complete Philistine and ask why the thread matters at all if these bolts are just being used to hold bits of wood together? Why not just buy a nut and bolt set off the shelf? So what if it's metric?
I was surprised to see you proposing a replacement for that. Put a bunch of nuts on it and you can whack it back straight too, I dont think I'd replace it. Wire brush the head clean.
I wouldn't really count a Myford CL7 as a 'larger lathe', unless you are comparing it to a Pultra. One lathe I had you could set the thread pitch with a gearbox, rather than having to change gearwheels, although the range was fairly limited and Imperial only.
The best way to form threads on most materials is to roll them. It may not be the most practical way for the home worker though.
It is cheaper and easier than having a lot of dies you don't use very often.
I did make a couple of long bolts a few years ago simply because I was unable to buy stock ones long enough. I cheated and puddle welded a second nut onto the end of a length of rod, then hand threaded the other end. I first cut a short thread for the nut that made the head, about two thirds the depth of the nut, puddle welded the remaining hole and ground it off smooth. The finished article looked just like a bolt head.
Any with a head marking of 8.8 or H are high tensile. I would also be surprised if you could buy anything other than high tensile bolts off the shelf today.
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