Forgotten engineering techniques

[Martin KyteParticipant @martinkyte99762]

I always thought that fettling was to remove the sand,flash and risers from castings prior to machining and has a general application to mean improve the quality of something.

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Kyte on 15/01/2015 08:22:44:

I always thought that fettling was to remove the sand,flash and risers from castings prior to machining and has a general application to mean improve the quality of something.

.

Agreed, Martin … That's consistent with the etymology that I linked earlier.

MichaelG.

[JasonBModerator @jasonb]

Agreed John but some of us have propper jobs to do in the day not like those who spend it in the armchair not including yourself.

I seem to remember you did a very good write up on making a cylindrical square, Is it still on line somewhere? it may prompt a few people to get out and make something heaven forbid

 

J

Edited By JasonB on 15/01/2015 13:24:16

[Larry Coleman 1Participant @larrycoleman1]

Well I really think the discussions are suffering from TMI.

The purpose of this thread is to assist the introduction of unskilled people into the hobby. That does not mean people are uneducated and it really means that some people are inexperienced in the field of Machining. As an engineer and toolmaker I have no knowledge of foundry work because that is a field I have never tried or had any experience in.

I like the mention of using coconut oil and I am going to try that.

Andrew I like you cylindrical grinder.

I suggested buying screw presses and that was to encourage new people setting up there workshop to consider what can be done with them. No reply !

I have been getting some good laughs at some of the comments but with all the TMI we may be scaring away the very people we are trying to encourage.

I still think Mr Gates has a lot to answer for, I have no hair because of him.

One thing worth mentioning is I believe Garden Island dock yard has been shut down and I think Cockatoo is also. Most of the big industry in Australia like AWA, WRE ( Weapons Research Establishment in SA ) Phillips and a lot of Hawker factories have vanished.

One thing that is worth noting is, In the seventies I visited a plywood factory in the Sydney western suburbs called Ralph Simons Plywood and inside the factory tucked up into the roof was the molds for the WW2 Mosquito which was manufactured in Aust for the war. A complete ply aircraft.

My how things have changed.

Larry

Edited By Larry Coleman 1 on 15/01/2015 14:39:04

[John CParticipant @johnc47954]

John B

I will put myself forward as 'anyone', as over the years I have spent many enjoyable hours reading your posts, and learning from them. So please do make them available.

Best wishes,

(another) John

[EdHParticipant @edh]

Incase someone is interested in why the end of a cylindrical square is finished at an angle there is a description on the use of a cylindrical square on this site along with a picture showing the etched parabolic lines and how to use them by turning the cylinder end for end and sitting it on the angled end.

Look for figure 15

http://its.foxvalleytech.com/MachShop1/Inspection/AngleMeas.htm

[jason udallParticipant @jasonudall57142]

The intent of this thread is good.
Like many threads there are nuggets of wisdom..
Much dross also.
For such a thread to ” work”..can I suggest two threads..one open..in effect ” for submission”..the other being the edited version. …where the distilled wisdom is reposted..Credit as due but edited ..

One of the things that frustrates me with this forum..isn’t the “off topic” but that frequently posts are ON some other topic. .
I normally ignor thread about specific loco models…but might thus miss something of intrest( to me)….but who could tell?
But again the intent of this thread is valuable enough to get some serious treatment/edit..

[jason udallParticipant @jasonudall57142]

Re bogstandards links…
Bogstandard.etal…

Thats the sort of thing I ment.

[Bill PudneyParticipant @billpudney37759]

Talking about stonemasons chalking details of Cathedrals on the floor…..

In the mid 70s I had to go to Devonport Dockyard on a course. As part of the introduction we had a tour of the place, really interesting. However, for me as a draftsman the most interesting part was in the place where they lofted all the frames for a ship. Basically they were drawn on the floor, from a set of offsets (co-ordinates). All the frames for any given ship were drawn, initially faintly, then when all the frames were drawn, they could be faired and the offsets reset. Finally the accurate frames were painted to make them permanent. The boilermakers, or whoever was responsible for forming the frames would make a template of the actual frame he was responsible for and get stuck in.

When a new ship was being built a new floor was laid, using something like 1/2" thick timber, straight over the old frame lofting (drawing on the floor). This obviously has the effect of reducing the height available. In the 60s with a new ship to build (those were the days!!) the vertical clearance from the "floor" to the ceiling was reduced to the extent that it was impractical. So the decision was made to remove all the old floors or frame layouts. As each layout had the name of the ship or class of ship, the date that it was finalised the floor removal became something of a voyage of discovery. Apparently they were all recorded, how I don't know, but the interesting thing was that the first ship built at Devonport using this technique, turned out to be a small frigate (I think it was anyway) in the late 1700s.

They also had what we were told was the only working gallows in the UK. It was kept because hanging was still the ultimate penalty for treason…..

cheers

Bill

[John OlsenParticipant @johnolsen79199]

Boats are still built using offsets. For my steam launch, all I had from the designer was a set of offsets, a sketch section through the keel and a longitudinal section sketch showing the deadwood. Oh, and a carved half model. All the information fitted on the back of an old chart, about A3 size. I didn't try to loft it all on the floor. The offsets were used to make the temporary frames, the frames were set up on a strongback and aligned and adjusted to be fair, and then she was planked.

Speaking of forgotten techniques, a bunch of us from the Steam Engine Society here in Auckland NZ have built a replica Newcomen engine, nominally about half scale, although since the original information was not to scale I would not be dogmatic about that. It first ran a couple of years back, having been built to mark the tricentenary. Since then a waterwheel has been built for it to operate, by pumping the water. So if you want to learn to operate a Newcomen engine, Auckland is the place to come…bring a few bags of coal. I understand there is a German group interested in making one too. They wanted a copy of our drawings, which is a little difficult since nothing very formal exists.

John

[V8EngParticipant @v8eng]

There is a working Newcomen replica (full size) at the Blck Country Museum, near Dudley in the UK.

The engine is run regularly and is rather impressive to watch.

Edited By V8Eng on 16/01/2015 07:34:13

[pgk pgkParticipant @pgkpgk17461]

<<They also had what we were told was the only working gallows in the UK. It was kept because hanging was still the ultimate penalty for treason…..>>

I have some vague recollection that even after hanging for murder was repealed it was still on the books for 'arson in his/her majesty's dockyards' – unless that's an urban myth…

( a bit like the quaint but prbaby untrue story of the Cambridge student who discovered an old college rule allowing him to take a pint of ale into an exam – And was punished for not wearing his sword.)

[Harry WilkesParticipant @harrywilkes58467]

Posted by pgk pgk on 16/01/2015 07:19:34:

<<They also had what we were told was the only working gallows in the UK. It was kept because hanging was still the ultimate penalty for treason…..>>

I have some vague recollection that even after hanging for murder was repealed it was still on the books for 'arson in his/her majesty's dockyards' – unless that's an urban myth…

"the death penalty was abolished in all circumstances in 1998."

H

[jason udallParticipant @jasonudall57142]

probably not forgotten.. but at least long used

**LINK**

[Larry Coleman 1Participant @larrycoleman1]

Can any one tell me how to straiten a four inch solid shaft ten feet long. Tolerance .002"

Larry

Edited By Larry Coleman 1 on 17/01/2015 11:03:03

[Speedy Builder5Participant @speedybuilder5]

Lines, offsets, stations, butts – When I was an apprentice at Vickers Weybridge, becoming BAC etc, I was lofting lines for Concord(e) on 8' x 4' aluminium sheets using red striping lacquer (Cellulose paint). Our mold loft was contained within a building constructed from the frames of one of the R100 airship sheds. Note, we spelt Concord without the (e) until the government capitulated with the French and added the (e) in about 1968.

BobH

[Anonymous]

Posted by Larry Coleman 1 on 17/01/2015 11:01:56:

Can any one tell me how to straiten a four inch solid shaft ten feet long. Tolerance .002"

Tell the bar that it owes £10k in tax and demand immediate cash payment.

Andrew

Hint: Look at what was actually written

[Larry Coleman 1Participant @larrycoleman1]

Well Andrew.

Don't look at what was written try reading it

So you have a propeller shaft ten feet long and you set it up in the lathe between a chuck and live tail stock centre but it tends to sag. You have to get it running with less than two thou run out. You carefully dial the run out every foot and find the place the run out is highest. Then you carefully turn the shaft to the high point is up to the dial.

Now here you may think a big hydraulic press may come into play…. Wrong" the shaft never leaves the lathe until complete.

You get an oxy cutting torch and heat a small spot about one inch dia to cherry red and then hit it with as much coolant as you can. The shaft cooling happens that fast it bends the shaft past its original point. This process is a bit of a hit and miss process but it works. After a bit of experience you get good at it. When I worked in the ship yards we did shafts up to fifteen feet long and eight inches in diameter. Although we had a two hundred ton hydraulic press it was never used to straighten prop shafts.

Now the point I am making here is it can be applied to small shafts as well and it works but you will have to experiment to get good at it.

Once the shaft run true the sag was then lifted with a fixed steady to machine the taper at the ends for the coupling and propeller. Now in this case we were using a thirty foot Pareeba lathe but the same principle can apply to a small shaft as well.

Once the tapers were finished and the shaft checked for straitness they were wrapped in fibre glass matting to prevent oscillation and corrosion at high revs.

If you try this out the heat must be applied quickly and you don't heat the whole area and if you try it on small shafts you must redce the size of the spot on top of the shaft and only heat the top. The shaft will react by bending up when heated but it will return very quickly.

All Navy patrol boat shafts we made were constructed this way.

Let the scepics begin.!!!!

Larry

[pgk pgkParticipant @pgkpgk17461]

Am I right in guessing that this technique depends on rotating the stock slowly enough that the sage is consistent at the measuring point?

[JasonBModerator @jasonb]

I think you would just rotate by hand.

The sag should be constant so not show up on the dti and if there were a 0.010" bend then you would see 0.020" movement in your dti as the shaft is rotated, so just turn the shaft until the highpoint is at the top and then shrink the metal.

Larry how deep does the heat have to penitrate the shaft, I would assume a 1" hotspot is only about 1/2" deep so you are putting the tension into teh surface as it would not go all teh way to the core.

Sounds like the same method used to remove dents where the metal has become stretched due to teh impact or over hammering, just heat and rapidly cool small areas until it shrinks the metal back to original.

[Anonymous]

Posted by Larry Coleman 1 on 18/01/2015 07:04:56:

Don't look at what was written try reading it

So I should ignore what you actually wrote? I'll give that a try.

Andrew

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Andrew Johnston on 18/01/2015 09:37:50:

Posted by Larry Coleman 1 on 18/01/2015 07:04:56:

Don't look at what was written try reading it

So I should ignore what you actually wrote? I'll give that a try.

Andrew

I think it went over his head Andrew.

Russell.

[IanTParticipant @iant]

Mislaid my little pot of green tapping paste last week (filled from a much larger tub at college many years ago).

I needed to tap some 20+ 6BA holes in mild steel and wanting to "get on" decided to 'dry' tap and of course (sods law) broke a tap – fortunately outside the hole, so could remove it. I suspended operations for that night and the next day still couldn't find the pot so thought of this post.

The foil under the breakfast bacon in the grill was retrieved (with Domestic permission) and the white fat that had solidified in the "wrinkles" was carefully scraped away – about a spoonful.

I'm pleased to report that bacon fat works very well when tapping – although it does of course smell a bit of bacon. The difference in tapping by the way was not in the 'screwing in' but with the back turns – even 'dry' I could tap inwards OK but I was getting 'snagging' on reversing the tap. The bacon fat seemed to eliminate this problem and certainly made tapping much easier.

As a footnote, I wandered around Alexandra Palace yesterday and on my shopping list was tapping 'paste'. None of the Traders seemed to stock it – all they had were more liquid solutions (cutting oils). One guy asked my why I wanted a paste – well for small taps I like to dip the tap into it, wipe off the surplus (and into the threads) and then (on withdrawal) use a tooth pick to sweep the paste (and metal cuttings) out of the flutes.

So, I will continue the search for my 'tapping' pot and hope the bacon fat doesn't turn rancid too quickly!

Regards,

IanT

[MuzzerParticipant @muzzer]

Use the word "compound" instead of "paste" (or fluid) and you will find some. I have a small tub of Rocol RTD myself but there seem to be a few alternatives.

Murray

[Mike pParticipant @mikep]

Hi, If looking for the" green compound" for tapping just look for Trefolex a brand name and widely available. I have used this stuff for 40 odd years.

Mike p

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