Replacing compound lock down bolts

JR49

JR49

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I need to replace, or make, some new swivel lock bolts for the compound of my Logan 12"X35" lathe. They seem to be common 5/16"nc threaded bolts but with square heads. I'm sure I can "make" the square heads easily (build up round headed bolt with weld then grind it square), BUT, my question is, are the original bolts made out of something special like high grade, or hardened steel, or ?? The originals are stripped, and no, I didn't strip them lol, I'm still a few months away from "firing it up" for the first time. Thanks, JR49
 
McMaster has square headed bolts in a grade 5.
 
I would just use socket head bolts. Alot easer to adjust things. That is what I did on my atlas. But mine is a tool not a show piece.
 
Any steel will work. You can harden them yourself with a torch and oil quench. Gives a nice period looking patina as well.


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I had to replace one of the compound hold down bolts on my Logan about two weeks ago. An unknown previous owner had repaired this before by making an uneven thickness square, drilling a hole through the square and then plug welding it to a headless 5/16 threaded bolt. The weld eventually failed and I thought the bolt was stripped but found a separate square head and a threaded headless 5/16 bolt. I repaired it by getting a mild steel hex bolt of the same size and using a mill, thinned it to appropriate thickness and also changed the hex to a square. I bought the hex bolt a little long and cut it to the correct size. I didn't use a grade 5 or grade 8 bolt because of unforeseen unintended consequences, such as the cast iron of the compound cracking because I put too much force on the hardened bolt. Also, I'd have to heat the hardened bolt prior to milling it and then re harden it. The new bolt works great and holds the compound solidly.
 
1040 gives a strength close to grade 5 bolts. I made new bolts from hot rolled MS several years ago. Mild steel is strong enough for the job. The bolts do not need to be tightened up that much, a good firm nip is enough. The head does not need to be square, round with a couple of flats is lots good. The flats can be put on quickly with a bastard file. A file is probably quicker than messing with a mill (if the mill is not already set up). I would recommend a grade 8 nut so the nut does not get the corners rounded. The other thing I would advise is making thick flat washers that will not deform or at the very least use hardened washers.
 
I have a Logan 820, and the carriage lock bolt had been lost by a previous owner and replaced with a socket head bolt. I wanted a more original look, and also wanted to use my OEM carriage lock wrench. I bought a 5/16" square head bolt at Menards, and milled the 1/2" square head down to 3/8" square. The bolt head is not as tall as the OEM, but it didn't cost $25 that the OEM does either. I thought of building up weld material on the head to make it taller, but the wrench seems to stay on it just fine the way it is. Someday maybe I'll make a whole new bolt out of some 1/2" square bar stock.

GG
 
TOOLMASTER said:
fine thread tightens better
Click to expand...

But coarse threads tighten enough and tend to last longer. And fine threads have a tendency to strip and coarse threads not so much, that's why we use coarse threads in soft metals where there is a low tensile (and thus shear) strength.

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kd4gij said:
I would just use socket head bolts. A lot easier to adjust things. That is what I did on my atlas. But mine is a tool not a show piece.
Click to expand...

The problem with socket head bolts in this application is the socket fills with chips and that becomes a PIA.
 
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