Forgotten engineering techniques

[David ColwillParticipant @davidcolwill19261]

Ian T

I suspect the tapping compound you are after is trefolex and is available from Cromwell **LINK** amongst others.

Regards.

David

[Larry Coleman 1Participant @larrycoleman1]

Hey fella's

Yes tapping of small threads are scarey but I learned somthing about taps in a sheet metal shop when I was an apprentise.

There are taps and then there are taps. The tap to buy is called a gun tap and only has two flutes. These taps are made to be used in a power driven tapping head in a drill press.

Try and get a gun tap and with the right tapping compound it is chalk and cheese compared to the three & four flute taps.

Also the best oil if there is no other try 80 grade diff gear oil.

Larry

[Larry Coleman 1Participant @larrycoleman1]

Jason

Yes the hot spot is very small in relation to the shaft dia. With smaller dia shafts eg 2"dia it would be about a quarter of an inch.

On the big lathes we used in the ship yards they had an inch button. It turned very slowly and was quite controllable because of the automatic brake on the spindle.

If you turned the shaft to fast it would brake loose because there was to much pressure on the centre.

What I have described takes a bit of practice so don't be to wild with the heat. When you apply the heat you will see the shaft rise and when you hit it with the coolant it flys back quite suddenly.

I have done some small shafts and it will work but you have to be quick.

Larry

[Larry Coleman 1Participant @larrycoleman1]

Jason

When we did the long shafts we checked it evry foot to identify where the bend actually is and we would straiten it. Then we would machine the end tapers remove the steady and do a second straitning. After that we would replace the steady and do the finish cuts on the ends. the drive flange face would be fitted and machined on the shaft

And that days work would cost the customer $6000.

Then the propellor would be scraped on.

Larry

[JasonBModerator @jasonb]

Not with you there Larry.

You say you straighten it, turn a taper on the end and then have to straighten it again

What is causing it to bend that it needs to be done again?

If its that delicate then whats to stop it bending again between being taken out of the lathe and fitted to the boat?

[Larry Coleman 1Participant @larrycoleman1]

Jason

When you machine the tapers you remove a lot of metal and it releases tensions on the end of the shaft. The reason they where straitened twice was to ensure the tapers run true to the shaft.

And yes they were that delicate due to there weight we used special lifting spreader bars and delivery jigs.

The patrol boat shafts had to be inserted into the boats by Navy approved fitters.

Now have you ever been on a large ship and felt a distinct thump while under way.

There can be two reasons for that: The shaft is bent or the propeller has not been scraped in properly.

When the prop is scrapped it is fitted to the shaft in a special jig and rotated to check that each blade tip tracks on the same radius. The pitch is measured in roughly for sections of each blade.

It is then balanced and all the exposed shaft not in the bearings were wrapped in fibre glass matting and sprayed with resin and hardener.

The shafts were rated for 900 revs. The diesels reved out to about 1500 rpm with gear reduction to the shaft.

The biggest ship I fitted was 25,000 ton and the prop was 12 ton.

The patrol boats were 2000 ton.

Larry

[Larry Coleman 1Participant @larrycoleman1]

Typo error. 220 Tons not 2000.

Larry

Edited By Larry Coleman 1 on 18/01/2015 15:38:20

[Bob Brown 1Participant @bobbrown1]

Posted by Larry Coleman 1 on 18/01/2015 14:09:45

Now have you ever been on a large ship and felt a distinct thump while under way.

Yes and no, large ships, one 264,000 ton twin screw diesel, no thump but then prop speeds only 120rpm max.

Do not think the heating method applies on prop shafts that are 400mm plus diameter with propellers that are over 25ft diameter and over 25tons.

Bob

[JasonBModerator @jasonb]

Posted by Larry Coleman 1 on 18/01/2015 14:09:45:

Jason

Now have you ever been on a large ship and felt a distinct thump while under way.

Larry

No, Luckily I was not on the Titanic

[Bob Brown 1Participant @bobbrown1]

**LINK** thump

[Larry Coleman 1Participant @larrycoleman1]

Well I have only done one real big shaft when I was working at Garden Island for the HMAS Supply. It was straitened with heat as I described. It was twelve inch in dia and Sixteen feet long. The heat applied was proportional to the dia of the shaft. That is common sence.

If you didn't use that process how do you think you would do it? Remember a big shaft could weigh in at 3 to 4 ton.

By the way Bob where did you do your trade.

Jason would't they let you on board, maybe stowage was full.

Larry

[IanTParticipant @iant]

Mike/David (and Murray)

Trefolex does seem to ring a bell – and the little man (who lives under the bench in my shed) hasn't returned my old 'tapping' pot yet – so I will order a new one. Thank you for your advice everyone.

Regards,

IanT

[julian atkinsParticipant @julianatkins58923]

hi ian,

i dont want to put you off but 'trefolex' was called 'snot' in my younger days! it is awful stuff! Rocol products are far nicer and superior, and dont have that awful smell or green sickly look.

i am not sure if much of what ive read on here could be described as useful in the amateur home workshop!

i have picked up lots of hints and tips over the years from old hands but all pretty well known and very useful in miniature loco building.

in respect of Larry's prop shaft anecdotes, i knew very well sid hendicott who was responsible for turning J.S. White's (of Cowes) prop shafts in WW2 and subsequently. he was a senior and much respected member of my first MES club and gave us a talk once. all he had was a set of calipers and a bit of chalk to turn prop shafts for destroyers etc.

cheers,

julian

[Bill PudneyParticipant @billpudney37759]

At one stage I worked at Vosper Thornycrofts ship yard in Southampton. The yard was gearing up for it's 100th Birthday when I was there. In the machine shop they had a huge lathe that was designed "in house" and built/erected in situ (in the late 1800s) solely for machining destroyer prop shafts. This thing was an absolute monster, and the whole yard knew when it was being used. There was a low frequency vibration that could be just felt at the other end of the yard, some 400 or 500 metres away.

Sadly the shipyard closed about 10 years ago, and is now "up for development".

cheers

Bill

[Larry Coleman 1Participant @larrycoleman1]

Julian

In regards to my prop shaft anecdotes I would like to talk to Sid and find out how they did it in the WW2 days. I do know that some shafts were put into the big lathes and were trued up using a type of tool post grinder. Have a think about what we were dealing with. A long heavy shaft which could sag due to its weight. Now I am only talking about twenty thou sag. So you put one end in a four jaw chuck and get it true. The other end needs a centre hole put in it so you place that end in a roller fixed steady and put in the centre hole. Now you have a problem.

You have a long shaft with one end in the four jaw chuck and the other end supported by the tail stock. When you rotate the shaft SLOWLY it runs out of true.

The problem: You have a four inch solid shaft between a chuck and centre that is running out by about twenty thou and you have to get it within .002 to meet Navy specs.

Ok my critics tell me how you would do it?

All I can tell you is how it was done at NQEA and thats a fact.

Also those Fremantle class patrol boats were designed in the UK and were twelve ton to heavy in the stern and were redesigned by the NQEA owner Don Fry a very experianced engineer. The last time I spoke to Don he was working on the scram jet project.

Any way if you dought that the process I discribed does not work tell me how you would do it.

Larry

Edited By Larry Coleman 1 on 19/01/2015 10:36:10

[Thomas GudeParticipant @thomasgude37285]

Posted by Speedy Builder5 on 10/01/2015 15:38:51:

It seems sacrilege, but I have a few old engineering books which I have advertised here and elsewhere some which are over 100 years old with no interest. Such as Reed's Engineers handbook All about marine steam) – available USA for 4$ UK, £8. , Model Power Boats 1940. By the time you add on postage, nobody is interested. Should I just dump them in the bin ??

BobH

Bob,

I've got the Model Power Boats book, apart from the section on motors which is a bit out of date now it is really comprehensive on how to design a boat – model or otherwise. Really interesting read and I cannot wait to put the theory into practice.

[Larry Coleman 1Participant @larrycoleman1]

Bob

Those old books you have should be delivered to your local library or museum if you have no use for them so please do not dump them.

At least if you ever want to read them you can get access to them.

Larry

[Nigel McBurney 1Participant @nigelmcburney1]

I find Trefalex is better than rocol when tapping steel,its very similar to the home brewed tallow and flowers of sulphur used at my first job,I also have Rocol paste and liquid ,the paste is very good on small taps i.e. 10 BA , for small drills i.e. 60 to 80 spit works wonders .Rocol tends to be expensive but I was lucky a chap at an auto jumble had boxes of rocol products and I bought two plastic containers of liquid and a tin of paste for £2 each and he was doing a roaring trade.

[Larry Coleman 1Participant @larrycoleman1]

Well said John

But I think you have to understand whats happening here. Its called "Intellectual Jousting".

This is sometimes practised to belittle people thus protecting their superority and is very previlent in clubs which I avoid.

I'm not affended.

Larry

[Neil WyattModerator @neilwyatt]

I think we have to accept that a forum like this is a 'virtual club', and that if there wasn't space for the banter and digression, it would all become rather dry and the 'really useful postings' would probably not be made either.

Neil

[Bob Brown 1Participant @bobbrown1]

I doubt you will find any forum on line stay "on topic" they all wander off topic it is the nature of the beast!

Bob

[Russell EberhardtParticipant @russelleberhardt48058]

Agreed trolls and bullsh**ers exist on all forums. However some forums have a means of allowing a user to block his view of posts from people he considers to fall into that category. Could that facility be added here?

Russell.

[Larry Coleman 1Participant @larrycoleman1]

Bob

Personally Bob your the one who has deemed conversation and interjection Banter which I believe is human nature.

Now heres a bit more banter for you. If you don't like what you are reading don't read it.

Your the one that needs to apologize.

See you!!!!!

Larry

[Neil WyattModerator @neilwyatt]

> Agreed trolls and bullsh**ers exist on all forums. However some forums have a means of allowing a user to block his view of posts from people he considers to fall into that category. Could that facility be added here?

It always has been, there's an 'ignore member' button below every post.

Experience suggests that most forum members would rather complain about people than ignore them

 

Now can we all calm down a bit please?

Neil

Edited By Neil Wyatt on 22/01/2015 15:00:15

[Bob Brown 1Participant @bobbrown1]

Larry

If you want me to apologise my second word is off.

Bob

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