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.
Sedgwick MB rise and fall damage
- Thread starter jetsetwilly
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J-G
Established Member
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.
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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.
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.
Always my understanding that rolled threads had higher tensile strength, never really thought about hardness as such. Interesting.
http://sedgwick-machinery.co.uk/
contact them, I am sure they will sell you a new part.
screw pitch gauge a fiver. as the part is out run a file over, that will clear up if its hardened!
bog standard studding on my sedgwick tenenor cost no more than tenner.
still of the opinion the gear cog is pinned, studding machined or ground.
simple fix
Surprising how much mild steel will harden either by heat or by work hardening. We were told as apprentices that m/s couldn't be hardened, except by case hardening, but fairly recently I used heat to bend some steel bar, quenched it to cool it, and then tried to cut it with a hacksaw. No joy.
Bright drawn is harder than black ms bar.
J-G
Established Member
I'm not convinced that these figures are related to THREAD Rolling. Mild steel bar is 'rolled' as part of the manufacturing process and yes that does affect the Brinell hardness but not in the way that I'm considering which is by case hardening via a Cyanide or nitriding process - it's too long ago that I spent a short while in the hardening shop at Matrix for me to recall which particular materials went through which process
Thanks I already did that, and they will - for £329. If in a commercial workshop the machine would already be back up and running with whatever new parts it needed, and I wouldn't have bothered posting. But this is a hobby for me, and part of the fun is making and fixing things myself, learning (and buying more tools!) along the way.
I have limited metalworking skills or equipment but I recently acquired a nice old Boxford lathe that I haven't set up yet - might be time to finally dust it off...
The gear cog is pinned and grubscrewed if it's the same as the MB that @deema restored here https://www.ukworkshop.co.uk/threads/sedgwick-mb-planer-thicknesser-full-refurbishment.136008/page-2. I'll let you know.
as i said, a simple fix.
Plus whatever they want for the screw. So simple I grant you, but rather pricey.
OP has a metal lathe, so I would say go for it. Get some mild bar to practice on first, but should be pretty straightforward.
Against_The_Grain
Established Member
Just remember that you may replace the thread but not actually solve the problem, binding in one spot rather than a constant tightness throughout a rotation is usually an indicator of a bend somewhere in the mechanism. I would've thought it's most likely that one of the shafts is bent slightly which is causing the meshing of the gears at the end to get tighter together and bind.
Current plan is to fit a new leadscrew and bronze nut; the other shaft is v short. And actually, I was unclear before - although it did appear at first to bind in one spot I later realised it was consistently binding up after about a half-turn, regardless of where it started, which is more like a galled thread than a bent gear shaft.
The only vaguely similar process I am familiar with is gun barrels.I'm not convinced that these figures are related to THREAD Rolling. Mild steel bar is 'rolled' as part of the manufacturing process and yes that does affect the Brinell hardness but not in the way that I'm considering which is by case hardening via a Cyanide or nitriding process - it's too long ago that I spent a short while in the hardening shop at Matrix for me to recall which particular materials went through which process
One traditional method for rifling was to have a hardened mandrel machined as the male profile of the rifling. The barrel was then passed over this and essentially squashed onto it thereby forming the rifling on the inside, and at the same time reducing the diameter of the barrel blank, and increasing it's length. It would start off being considerably larger in diameter and shorter than the finished size. But be reduced in diameter and increase in length much like rolling a piece of dough. In the old days this would be done by heating and beating the steel onto the mandrel, so very much forged.
Nowadays I believe it is done cold using hydraulic rollers, a process not dissimilar to rolling a thread?
Barrels made in this way are always much longer lasting than those made by cutting the rifling, and tend to have a better finish with smoother lands.
They are of course also much more expensive.
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So, current threaded bar is M20x2.5mm, and has an unthreaded portion which passes through the bottom planer casting and receives the retaining collar above and driven gear below. It's not bent but it is worn, major diam varies from 19.97mm in the virgin section to 19.30 in the middle, and the thread is a little deformed with some rough bits.
Looking at leadscrews, 20mm would typically have a 4mm lead, meaning a significant increase in the gearing of the thicknesser lift. Also, I'm not finding any stock leadscrews with an unthreaded portion. I could turn down one end of a larger leadscrew but then the gearing would be even higher. Am I missing something?
Looking at leadscrews, 20mm would typically have a 4mm lead, meaning a significant increase in the gearing of the thicknesser lift. Also, I'm not finding any stock leadscrews with an unthreaded portion. I could turn down one end of a larger leadscrew but then the gearing would be even higher. Am I missing something?
Several options.
Your existing thread doesn't appear to be trapezoidal. You could use a length of threaded rod in M20x2.5. To get your smooth end turn down the end to say 13mm. Make a sleeve nominally13 ID and 20 OD and fit it to the end, press, glue, weld loads of ways to attach it.
Then make your own bush to suit, a 20x2.5 tap not that expensive, or better still turn it and thread it on your lathe. That way you can fine tune it to fit snugly.
Does the lathe have screwcutting facilities? If it does then you would just need to buy a suitable internal threading tool, cheaper than a tap.
Does the gearing have any relationship to the indicator for the degree of rise or fall, or is it just a pointer that moves with the bed to show it has moved by a certain amount?
If the latter then the only concern with a 4mm pitch versus 2.5 is it will require a little more effort to turn and it will be slightly more difficult to achieve a fine adjustment. If you can put up with that then use the combination screw and flanged nut in trapezoidal you have found. The smooth end can be achieved exactly as outlined above. Might be worth a call to the supplier and see if they can point you in the direction of a supplier of finer threaded leadscrews/nuts.
Alternatively have you looked at an imperial option Maybe 3/4 x 10 tip. That will give similar gearing. If you are changing both nut and thread then it doesn't really matter if it's metric or imperial.
Your existing thread doesn't appear to be trapezoidal. You could use a length of threaded rod in M20x2.5. To get your smooth end turn down the end to say 13mm. Make a sleeve nominally13 ID and 20 OD and fit it to the end, press, glue, weld loads of ways to attach it.
Then make your own bush to suit, a 20x2.5 tap not that expensive, or better still turn it and thread it on your lathe. That way you can fine tune it to fit snugly.
Does the lathe have screwcutting facilities? If it does then you would just need to buy a suitable internal threading tool, cheaper than a tap.
Does the gearing have any relationship to the indicator for the degree of rise or fall, or is it just a pointer that moves with the bed to show it has moved by a certain amount?
If the latter then the only concern with a 4mm pitch versus 2.5 is it will require a little more effort to turn and it will be slightly more difficult to achieve a fine adjustment. If you can put up with that then use the combination screw and flanged nut in trapezoidal you have found. The smooth end can be achieved exactly as outlined above. Might be worth a call to the supplier and see if they can point you in the direction of a supplier of finer threaded leadscrews/nuts.
Alternatively have you looked at an imperial option Maybe 3/4 x 10 tip. That will give similar gearing. If you are changing both nut and thread then it doesn't really matter if it's metric or imperial.
Thanks, hadn't thought of looking at imperial sizes.
Yes the indicator is just a pointer, and yes it was the effort I was concerned with - that and the rather flimsy-feeling plastic crank. The lathe does screwcutting, though it remains to be seen whether I can...
Right, I now have several workable solutions, thanks - enough analysis paralysis! My next post will probably be about lathe problems
Yes the indicator is just a pointer, and yes it was the effort I was concerned with - that and the rather flimsy-feeling plastic crank. The lathe does screwcutting, though it remains to be seen whether I can...
Right, I now have several workable solutions, thanks - enough analysis paralysis! My next post will probably be about lathe problems
You should find the basic turning fairly straightforward. Screwcutting is a bit more complicated, but still not that difficult if you approach it methodically.
