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Silver steel or stainless?

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Chris R 125/01/2019 14:42:17
29 forum posts
18 photos

The rod doesn't touch the casting, so alignment isn't hurting. A flexible rod would do, though.

SillyOldDuffer25/01/2019 14:53:02
4719 forum posts
1010 photos

As Nikon aren't noted for bad design, perhaps this is an assembly defect?

Could it be that the rod breaks because it isn't being screwed firmly flat against the prism? Perhaps the thread is too long and bottoms out preventing full insertion? Or the rod's shoulders are rounded such that the end can't sit flat? Or a washer is missing?

If the rod isn't screwed hard in, any bending stress will concentrate on the thin part which is further weakened by having a thread cut into it. In a tight assembly of the same parts I think the bending stress would be taken by the thick rod instead. Perhaps it's essential the rod is torqued in hard so as to pull the whole assembly firmly together with no tendency to rock?

I wonder if the design is analogous to the way rivets work. The strength of a riveted joint depends more on the friction between the two plates as pulled together by tight rivets than it does on the side shear strength of the rivets alone. Red hot rivets make especially strong joints because of the enormous force generated as the metal shrinks during cooling.

Dave

Edited By SillyOldDuffer on 25/01/2019 14:54:18

Michael Gilligan25/01/2019 16:35:56
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14023 forum posts
609 photos
Posted by Chris R 1 on 25/01/2019 12:39:09:

I see why it looked like there was stub - it was a reflection. Here it is unscrewed a bit.

Trying a bigger pic..scru.jpg

.

Thanks, Chris ... That makes it clear yes

Simon Williams makes an excellent point ... definitely worth a try.

A quick&dirty 'proof of concept' would be to fit a 3mm screw into a short length of nylon tube.

MichaelG.

Michael Gilligan25/01/2019 17:42:52
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14023 forum posts
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Posted by Michael Gilligan on 25/01/2019 16:35:56:

Simon Williams makes an excellent point ... definitely worth a try.

A quick&dirty 'proof of concept' would be to fit a 3mm screw into a short length of nylon tube.

.

Note: I do realise that the rod does not contact the hole in the casting ... but a lightweight, flexible, rod would better accommodate the accidental side-loads generated by handling.

MichaelG.

Howard Lewis25/01/2019 18:16:44
2341 forum posts
2 photos

The casing would provide for an outrigger bearing, IF it was concentric with the rod.

How about making up a short slave screwed rod, to fit inside the casing and bored to act as a bearing for a counterbore, so that the hole in the casing can be made concentric with the rod? With a suitable bush, with an external flange, either screwed or "glued" into place, the rod would be supported so that it is subjected to minimal bending stresses.

I know that this sounds like making a big production of it, but once done, the chances of breaking the new rod would be reduced.

Howard.

Chris R 126/01/2019 13:59:17
29 forum posts
18 photos

I don't think there's a manufacturing defect, it works the way it's designed to.

There may be a washer - or perhaps one flat oand one spring washer - missing, but there's precious little thread to put them on as you can see from the close-up.

IF the shiny part into which the rod is screwed happens to be parallel to the outside of the box (there's no reason why it should be, with any precision) then I guess I could recentre the hole in the box, drill and tap it maybe 10mm and make a bush, for each rod (there's one each side).

But if that shiny surface is angled then the rod wouldn't stay in the centre of any hole, so things would bend inside when the rod is pulled/pushed. Can't have that.

My foot of 303 has arrived so I'll go that way for now. A slight annoyance is that the rod is not quite straight. Perhaps silver steel would have been ground, I don't know?

One significant contributor to the trauma is the nature of the dried up grease on the cubes' track, which makes them jerky. A dot of WD40 has helped but it'll evaporate.

Microscope greases ("Nye" tend to be very specific and expensive.

This isn't critical but what type of grease would be light, clean, and long-lasting?

Ta.

Douglas Johnston26/01/2019 15:19:13
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613 forum posts
32 photos

Let me be the fourth person to advocate the grub screw idea, must be the easiest and best method.

Doug

Michael Gilligan26/01/2019 16:09:51
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14023 forum posts
609 photos
Posted by Chris R 1 on 26/01/2019 13:59:17:

[ ... ]

Microscope greases ("Nye" tend to be very specific and expensive.

This isn't critical but what type of grease would be light, clean, and long-lasting?

.

PlusGas Formula A 'dismantling fluid' [mostly kerosene] seems to thin greases very well.

... much better than WD40, in my opinion.

White Lithium Grease, by 'Weldtite' [they couldn't have a less appropriate name] is good enough for me

... it's available cheaply from 'Chain Reaction Cycles'.

https://www.chainreactioncycles.com/s?q=weldtite+tf2+lithium+grease&cat=product

MichaelG.

.

P.S.

I am disappointed to see that you didn't use the lightweight, non-rigid rod sad

... Sometimes it's just better to re-think the 'engineering'

Edited By Michael Gilligan on 26/01/2019 16:24:46

duncan webster26/01/2019 20:36:38
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2234 forum posts
32 photos
Posted by Chris R 1 on 26/01/2019 13:59:17:

.... My foot of 303 has arrived so I'll go that way for now. A slight annoyance is that the rod is not quite straight. Perhaps silver steel would have been ground, I don't know?....

Ta.

Roll it along a flat surface with a bright light behind to find where the bend is, then nip it in a vice with the bend at the edge and treat it to some light abuse with a soft faced hammer. You can get it pretty good if you're patient. Did the same with my motorbike front forks once, although we used a flypress and vee blocks

Chris R 131/01/2019 21:40:51
29 forum posts
18 photos

Well you wanted a picture - it doesn't look much after 3 pages20190130_165512.jpg

Those screws are para/weakly magnetic so A2/304 stainless perhaps, I've some HT ones coming.

I managed to break a plug tapsad, then discovered I could have held the tap in the tailstock and hand turned the bar in the head chuck to pull/push the tailstock along. Not sure of my terms here.

Is that a normal way to do it?

 

Hardest part was parting off the bar. Tool too high and it just reduced it then rubbed, too low and it pushed the tool down and the tool went under the bit that was left. It's a cheap lathe, and I don't know what I'm doing.

 

Edited By Chris R 1 on 31/01/2019 21:43:05

Clive Hartland31/01/2019 22:46:41
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2473 forum posts
40 photos

Microscope grease are very specific to task, they tend to be a bit, 'Tacky' in use and they also tend to creep.

If you can afford the real stuff contact the Microscope division of Leica in Milton keynes, it is sold in 25 gram. pots.

Dont ask the price of a Kilo tin, you will fall off your chair.

Clive

Simon Williams 331/01/2019 23:18:14
412 forum posts
67 photos

Hi Chris, looks like you've got the hang of this.

If you are tapping a hole in the end of a rod, there is a down and dirty short cut you can try. Instead of asking the tap to drag the tailstock along the bed of the lathe, just catch the tap in a drill chuck in the tailstock, then release the taper so the drill chuck spins in the tail stock. Start the lathe ( low speed is good) and grab the drill chuck with your hand so you stop it from rotating. Press the tap against the hole in the rod being tapped, it will feed itself until it meets the bottom of the hole. You can hold the chuck just enough that the tap when it bottoms out takes the chuck out of your hand. Maybe try this first with something a bit more robust than M3!

Needless to say you need a chuck with no scags or sharp edges or you cut your hand, and not too heavy as the snatch as you meet the bottom of the hole mustn't break the tap. You also need a key operated chuck as the internal mechanism of the chuck mustn't let go of the tap shank as you now stop the lathe and back the tap out of the finished hole by hand. Rumour has it that keyless chucks do exist which will hold on in both directions - none of mine do.

The Stealth and Pastry Police would have conniptions at this suggestion - but give it a go, it's very quick and effective.

So are your newly completed operating rods the magic fix?

Best rgds Simon

Chris R 131/01/2019 23:24:08
29 forum posts
18 photos

Clive - yes, £30 /10g is a figure I remember. Nye make a range.

These rods will do the job, but I've found another, or perhaps the original, problem, The carriers the cubes are on, are way too tight..... "Sliders too tight"

I'll post another thread.

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