Member postings for Andrew Johnston

Personally I wouldn't buy basic stock material from Ebay. A free cutting steel is almost certainly a low carbon steel and may also contain lead. Low carbon steels cannot be hardened in the same way as silver steel or gauge plate. They can be case hardened, which increases the carbon content of a thin layer on the surface. Case hardening can give a very hard wear surface while leaving the core softer and more ductile. However, that's not really what you want for a centre punch. One regrind of the tip and you'll lose the hardened surface.

The 24 is tpi - threads per inch. A 5/16-24 thread is UNF, a US standard, UNified Fine. I'd use an M8 bolt instead. The M8 fine thread has a pitch of 1mm, so 25.4tpi which is a good match. However, metric fine screws are less widely available than metric coarse. If coarse or fine is not specified assume coarse. So I'd stick with M8 coarse which has a pitch of 1.25mm.

Andrew

I think JasonB needs to edit the above reply again to correct an unfortunate spelling error.

Andrew

That's correct; same on the front wheels as well:

We can safely say that my wheels aren't pretty, but they're not going to come apart.

Andrew

Correct, like this:

The sheet steel template and follower can be seen bottom right. Given that the follower needs to be the same shape as the tool bit it is simple to make a follower for a circular tool.

Andrew

That might be roughly true of a silicon diode but it ain't so for an LED, as they don't use silicon as the semiconductor. As a rough guide forward voltage drops of LEDs are as follows:

Red ~2V

Yellow ~2V

Green ~2.1V

Blue ~3.3V

White ~3.6V

Like silicon diodes the forward voltage drop of a given LED is dependent upon the exact type, manufacturer, forward current and probably the phase of the moon.

Andrew

+1

I'd be tempted to donate the project book to a charity shop. Then I'd make a centre punch from silver steel, hardened and tempered as required. I can't see any real need for it to be hexagon, other than to stop it rolling away. In which case file a flat on it before hardening.

Andrew

Rollocks, I've just lost what I was typing. I'm not going to retype as SoD seems to have covered most of what I'd said. We can summarise as follows:

• Steel specifications are a mess and different systems have no exact equivalence
• For the purposes of making a clock it doesn't really matter if the exact steel isn't used, a rough equivalent wiil be fine
• Silver steel and gauge plate are sold in the UK as such and are roughly equivalent to W1 and O1

To be pedantic EN19 is not a high carbon steel; it's a medium carbon high tensile alloy steel. The principal alloying elements are manganese, chromium and molybdenum. The steel is also easily welded and the original 4130 specification is know as moly-chrome steel. In tube form it is widely used for welded tubular structures for aircarft and racing cars.

These people have useful datasheets on steel:

**LINK**

Andrew

When I made the rivet snaps for my traction engine wheel spokes I used silver steel. Hardening was done by soaking at 800°C and quenching in brine. It is critical to vigorously agitate the part when quenching. Otherwise you don't get anything like full hardness. I tempered at around 240°C. The snaps have been used to close 3/16" steel rivets using a flypress, so they have a fairly hard life:

After 150+ rivets the upper snap has a slightly mushroomed head, but it should last the remaining 100 or so rivets. If I was making the snaps again I'd reduce the tempering temperature by ten degrees or so. The flypress is probably less of a shock load, but the forces are much higher, than using a hammer. My initial riveting trials with a lump hammer failed to close the snap head properly, whereas a few good swings on the flypress did the job:

Andrew

Known as 'maggot' racing. It keeps the crews amused during competitions, and allows them to snigger at the other crew if a rival is seen to be scrabbling in the weeds.

The official name of the system is Flarm and is an anti-collision system. Each glider has a unit which takes GPS data and communicates with a ground station. I'm not sure where the computations take place but the unit in the glider has a clock face. If there's another equipped aircraft close by you get a green LED around the clock face and one for above or below. If the LEDs go red then that means a potential collision if you don't do something. One problem is that the circle provides information on track, so the glider isn't necessarily where the LED indicates. That can result in a lot of head swivelling, and it's not unusual to never see the other glider. If the LEDs are red then I can safely say that causes a LOT of frantic head swivelling!

I wouldn't be surprised if Flarm became mandatory in the UK. It's already mandatory in the Alps.

Andrew

Thanks for the welcome back one and all.

Man, I miss the Pawnee - really liked flying it. I much prefer to fly tailwheel. But sadly it had to go for cost reasons. One, there are ADs out on the wing fittings meaning the wings have to be taken off and the fittings crack tested at regular intervals. The initial problems were caused by the nasty chemicals used in spraying. But even if you don't spray you still have to do the ADs. Two was fuel consumption. Being a flat six rather than four all things being equal it drank 50% more fuel than the other tug. I flew the Robin DR400 on Saturday as duty tug pilot. There was a local club competition, so I did eleven tows on the trot before refuelling. Most tows were to 2000ft, one to 3000ft and couple of chancers went to 2400ft, giving a total of almost 24000ft. On refueling I put in 13.5 gallons. That's just over half a gallon per thousand feet. Nio way the Pawnee could compete with that.

Andrew

Interesting, but probably not. Today was the last day of the Cloud Rally at Gransden Lodge; an informal non-rated competition primarily for club members. I'm not sure what the task was, but when I looked online this afternoon there were a lot of Gransden gliders out west around the Bedford area. So it was almost certainly a **** it moment, start the engine or land in a field. Of course once the engine is started your flight is over as far as the competition is concerned. But at least you get back in time to drink beer in the clubhouse rather than sit in a field and wait for the retrieve.

I flew the number one tug at Gransden yesterday, another very windy competition day. Quite a tiring day, eleven tows one after the other for a total of two hours flying. The weather ranged from good lift wherever you went to where the hell am I going to tow to? Upwind of course; it's embarrassing if the glider lands out direct off tow.

DrDave: You are of course welcome at any time at Gransden Lodge to fly.

Andrew

After my interregnum I have decided to return to the forum.

As before I intend to mostly steer clear of electronics and signal processing threads, as those are my areas of professional interest. Apart from my CNC mill all my machine tools are ex-industrial and I make no apology for that. Mind you I don't know of any material or cutter than is self-aware and can distinguish between industrial and hobby equipment. So the basic cutting process is exactly the same irrespective of the machine heritage. If anybody disagrees with that then too bad.

Not so much TTFN as ITMA.

Andrew

Read your PMs.

Good grief, I'm stunned by the responses. I thought i may get a few "that's a shame" and a couple of "thank gawd for that" replies, but not the flood that has happened. What can I say, other than thank you, very much appreciated. It's really good to know that people find my posts helpful.

Truth be told I'd be really sad to leave the forum permanently. Over the next few weeks I have a fair bit of paid for work to do and I have some family care commitments. So I plan to step back for a few weeks, and then I'll be back, like it or lump it.

It would be iniquitous to pick up on only one of the responses, but I'm going to do it anyway. A special thanks to MartinM for reminding me of the project we did together way back in 1975 at SETC (Student Engineers Training Centre) at RAE Farnborough. I've still got copies of my original reports and sure enough the report I produced with Martin was in my handwriting. It is correct that we failed to achieve a working 100MHz amplifier, although I think the logic for the counter itself worked. Of the three projects i did at SETC only the mechanical one worked; may be that should have told me something.

Once again, thank you for the supportive replies.

Andrew

A few days ago there was a thread (now closed) started about abuse and intolerance within posts. Rather ironically there were a couple of derogatory posts made, one of which was directly aimed at me, apparently because I use, and talk about, ex-industrial machinery rather than "hobby" machines. I suppose I should at least be grateful that I wasn't excoriated for having a CNC mill.

I understand that the offending post has been removed, but I can't be doing with the attitudes expressed. Consequently I have decided to leave the forum. Time will tell whether my absence is temporary or permanent. If it does turn out to be permanent I will not be deleting albums and asking for my account to be deleted as that will mess up many posts in which other people have posted in good faith.

In the short term at least I will be reading and responding to PMs.

Andrew

PS: The title of this thread is an appropriate acronym, although I'm not old enough to have experienced its birth first hand in WW2.

Further investigation shows that the end with the spanner flats is screwed in, and is a very tight fit:

On "calibration" against an external micrometer and gauge blocks the internal micrometer reads about 1 thou under with the end screwed fully home, So it can be adjusted to be exact.

However, I do nor believe that to be the correct means of calibration. The knurled ring is definitely screwed onto the plain shaft that fits into the micrometer thimble. I expect that shaft to also be screwed into the extension rod, so the knurled ring can be used to set calibration. However, the knurled ring is very tight, and I don't feel like fudging an extension piece just to prove a point.

As new M&W are claiming an accuracy of 0.0001", I find it difficult to believe that they are machining extension rods to that accuracy as a matter of course in production. Much easier, and cheaper, to machine to a looser tolerance and calibrate.

Andrew

Nigel: Thanks for that, no doubt you're correct. In the only picture I have of fullsize frost spikes they're so rusty it's impossible to tell how they were manufactured. You're also correct about quantities, I've made 36 and that's only for one engine.

It's not clear how the frost spikes and anchor bolts were held in place. A straight tapered key wouldn't fit properly if perpendicular to the axle due to the curvature of the wheel rim, and if parallel to the axle there wouldn't be room to fit it. In the picture referred to there is a partially hidden tapered key; so that's what I've gone for. It's designed, a 1:1 card model made to check the fit, and the next step is to make one from metal strip. which arrived yesterday..

Andrew

The spikes are resting on two lengths of nominally 1/8" keysteel, held in place with double-sided tape. Keysteel is normally a few thou over nominal size so gives just enough clearance as the stock material was 5/8" and the machined shank is 3/8".

The spikes were hand held during broaching. Once pressure was applied the down force kept everything in place. The biggest problem I had was maintaining the broach vertical. The relatively small diameter of the shank meant that at best only two teeth were engaged at a time. Sometimes the broach went straight through with ease, other times it jammed. A jam simply required the broach to be twisted slightly back towards vertical and then it went as normal.

Not ideal, but I suspect the original spikes and rectangular holes would have been made by the blacksmith, so at least I'm better than that.

Andrew

I have now finished forming the rectangular slots in the anchor bolts and frost spikes for my traction engines. To summarise the sequence:

Three holes drilled and then the slot milled to size with a slotdrill, both on the CNC mill. Finally the square ends were done with a keyway broach, thinned on the surface grinder to be a snug fit, using an arbor press, with a drill and shims as required:

Andrew

On my Moore & Wright 2" to 12" internal micrometer I'm pretty sure the additional rods are adjustable:

The shortest rod (bottom left) doesn't appear to be adjustable. In that case I assume the micrometer head is adjusted. I think all the other rods are adjustable. Looking at the shortest of the other rods (top left) there are spanner flats on the left hand end and the knurled nut at the right is a separate item, and can therefore be loosened. I don't know what the exact method of adjustment would be, but no doubt it would be clear once the knurled nut is loose.

Andrew

Edited By Andrew Johnston on 17/07/2019 22:00:54