Sedgwick MB rise and fall damage

[jetsetwilly]

This would be easy to identify as the threaded portion will be larger than the smooth portion of the shaft as the metal deforms during the rolling process it becomes larger.

You must remember that Sedgwick is a very small artisanal manufacturer of woodworking machinery, there are no special processes or expensive machinery involved in the production of these machines, in fact it's very archaic and they almost always go for the cheapest possible way of manufacture whilst keeping the quality somewhat acceptable. I can say without a doubt that they cut all their in-house threads with dies or single-point cut in the lathe, because when you examine their threads you will often see the burr left behind by the dies or the steps in the thread at the end where they've pulled the cross-slide back and the tolerances vary massively from machine to machine, particularly spindle moulder shafts where one nut will thread on very loosely and another will be so tight to thread on that you need a spanner just to wind it on.

Hmm, interesting, thanks - I'll get a better look at the lifting bar when I get it out, but I expect even a small manufacturer might use rolled threads in something like this as it's potentially just a length of standard stock. I don't know a lot about Sedgwick, this is the first of theirs that I've had my hands on, but I like the simplicity, and I've always thought their castings look lovely.

 

[J-G]

@J-G it's probably rolled as you said which does harden it - point was just that it's a lot harder than the cast iron lifting foot

Thread Rolling doesn't 'Harden' the steel in any way. It does make a stronger thread (compared to a 'cut' thread) - not harder as in an increase in the Rockwell, Brinell (etc.) number - as long as it is done properly, such that the 'crest' does not have a cavity which can be due to the blank bar being marginally too small.

'Cast Iron' is a blanket term with variants having a Brinell Hardness range of 130 to 450 - non heat treated Mild steel has a Brinell range of 95 - 126 and I cannot envisage any 'manipulation' of a mild steel bar - other than specific heat treatment - making a mild steel bar harder than Cast Iron. By 'Harder' I mean in the accepted metallurgical sence.

 

[Fergie 307]

As with many things it comes down to the use of the machine, and the facilities available to the OP.
If the machine is only in occasional use then an insert has the advantage that it is quick and easy to do with minimal tools necessary. It will give a stainless thread which might be better at coping with the damaged screw. But relatively expensive.
If the machine is in regular use then a proper repair as suggested by Deema is definitely the way to go. But IMO you can't go half way, if you are going to fit a threaded bush then you really need to change the screw as well, as I suspect the damage on it would quickly chew up your new bush.
New screw and bush would not only be a better repair, probably better than new, but potentially cheaper too if you can find someone who will machine it for you for beer money. If you have to pay the going rate then overall probably going to cost more than the insert, but will last.