Member postings for Tim Stevens

In my experience Roman roads are straight where you can see from end to end, but only straight-ish elsewhere. Much straighter than the rolling English road made by a rolling English drunkard, though. One fa\ctor was the freedom that the invaders had to put the road where they wanted, in a countryside which was, effectively, empty of roads.

And have you considered why the straightness was needed? In flat country, it does give the 'quickest' or shortest route, but was that the only reason? One question is 'How were Roman vehicles steered?, or Have you ever seen a picture of a Roman Wagon with any steerring scheme at all?'

I await your answers ...

Cheers, Tim

Sorry, got distracted, and wrote about two cams (which is actually easier to design) - but the same principle applies if one cam is used, and the different timings are achieved by varying the shapes of the followers. Remember, too, that if you use one pivot for both followers, one follower will be backwards in appearance. In other words, one will lead the cam, and the other will trail - like the shoes in an old-fashioned drum brake.

One problem you might find with the 'one pivot' design is that if you wish to change the timing, you will be limited to changing the dwell (open period) for both valves by the same amount. And you won't be able to change the valve overlap usefully without a lot of compliaction, because both followers use the same pivot.

Books have been written on valve timing, so a paragraph or two can only hint at the complications - sorry.

Cheers, Tim

The two valves need to open at a given rotation, one after the other, x degrees apart. Once your timing is selected, mark out on the cam gear the two opening positions, and arrange the two bell-cranks so that the followers start to rise on the cam, one for the first angle, and then x degrees later the other follower starts.

If I was designing from scratch I would make a cardboard (etc) disc to represent the half-speed gear, centred on a drawing pin, and mark on it the required opening and closing positions. Then I would play with various options (eg one pivot or two, etc) until I arrived at a pair of followers which give the desired timing. It would help, as you are starting from scratch, to make the gear with a keyway, and a spindle with a matchning longer keyway to fit, and then the two cams to the same profile to fit the spindle, but no keyway yet. Then you can position each cam where you think it should go, and turn the engine slowly to check where the valves lift and close. You can do each cam separately to avoid confusion, but be sure to mark each cam so that you always get them in the desired position and the desired way round. When you are sure you have it right, mark each keyway position and cut the slots.

As regards the 'best' timing for your engine, it depends a lot on what you want to use it for. Look at the timing details for a range of full-size engines, and you will find a big difference between lawn mowers, designed to slog all day, and racing machines, designed to go flat out for short periods. And the further back in time you go, the slower and steadier the engines are, with smaller angles of 'overlap'.

Hope this gets you going

Cheers, Tim

There are many more suitable plastics now than there were in the 'good old days' - but butter knives are not made using it. Using ivory is frowned on, so anything that imitates ivory is frowned on just as hard.

But hope may be at hand. There is a 'hobby' which can help - making fancy pens. Axminster is one supplier that comes to mind - they are likely to have something that will meet your needs.

Cheers, Tim

There is a way I have used which does not require a lathe or column drill - an ordinary electric hand-drill, and an ordinary bench vice was all I had access to. But I did have a selection of hole 'drills' - the sort which has a central boss carrying a twist drill of 6mm (or 1/4 inch). Around the boss is a thread onto which can be screwed steel tubes in various sizes, with the end of the tube formed into saw teeth. One name for such things is 'Hole Saws' - and plumbers use them to bore the holes in the sides of your kitchen fittings.

You will need two of the saws themselves, one to fit inside the required shim, and one to go outside it. Now you need two oddments of plywood, one fairly thin (8mm +/-) and the other rather thicker, both a bit larger than the finished shim should be. Use the twist drill to bore a hole in the middle of the thin plywood, and clear off the splintery edges to leave smooth surfaces. Clamp a piece of shim material between the two plywood offcuts, and clamp one edge of this bundle in the vice, leaviung the whole surface area of the desired shim visible. If you have a small G-clamp or a similar tool, add it to the free edge to hold the two sheets of ply tight against the shimstock. Set the hand drill to a slow speed, and fit to it the smaller of the two hole saws. Guide the twist drill into the prepared hole, and drill slowly through the thin ply and the shim behind it. A squirt of oil will help. Lift out the disc of ply, and the inner off-cut of shim - carefully as the edges will not be nice and smooth. Now fit the larger hole saw, and repeat the operation, relying on the hole in the thick plywood to maintain concentricity.

This should produce a reasonable shim, which is likely to need trimming to neaten the edges, and it can be held in vice between the remains of the plywood to do this. If the shim material is thin (as they often need to be to take up clearance) you could trim the outer edge using tin-snips or a reject pair of scissors (when no-one is looking).

Don't be tempted to hold the assembly in your 'spare' hand as you do the drilling. If things start to go wrong you need to keep all your organs well away from spinning sharp edges ... And if you are not sure, don't try and hope for the best. Gambling is never worthwhile.

Regards, Tim

The compositor idea suggests to me that it was a holder for the type masters for a machine engraver. The slots could accommodate master letters of different sizes, or two or more rows, and the big slots (as Rob suggests above) could hold movable end stops to keep everything centred.

That seems much more likely than a hand-compositor's tool, as they need to be light for holding in one hand all day, and don't need the ability to set more than one line at once. But I'm guessing, like we all are.

Cheers, Tim

Many of the larger UK towns have an engineering supplier of some sort, where the 'everyday' basics can be bought - aluminium and its alloys, steel in various grades and finishes, but in my experience the most variable factor is their helpfulness, so be prepared to shop around.

You can use the internet to search if you are 'out in the sticks' - Feed in a local big town and an idea of what you are looking for, and let the search engine do the work. Something such as 'Doncaster - stainless steel rod' should prove helpful.

And if it is a specialised product (such as a 22mm reamer, or a model boat ventilator) then a question on this form will be helpful, as long as you also say where you are in the world.

And don't forget the suppliers who advertise in ME and MEW, and alongside this forum - their adverts help to pay for the forum itself.

Cheers, Tim

Yes, this is a way to find how far the C of G is from the front of the Locomotive. But it does not fully locate the C of G, as you also need to know the height and whether it is bang on the centre line or how far to which side. And the figures will all change when fuel or water is added or used. The device which measures the applied load needs to be zero-ed, and it helps to fix a fulcrum below the beam so that no errors can be added when the relative positions are changed (but I expect you knew that).

The C ofG position will also change whenever the locomotive accelerates or slows down, and also when it is on a gradient up or down, or going round a bend, because of the effect these changes have on the fluid levels and fuel position, so there is very little benefit from a calculation to three places of decimals.

Hope this helps

Regards, Tim

Eric says: I was in and wasn't expecting a parcel also schedule was spelt incorectly

You need to be careful - we might start to think your message was itself suspect ... !

cheers, Tim (nit-picking runs in the family)

It is a shame that magnets don't work on photographs

Cheers, Tim

I am not encouraged by a detailed peer at the drawing. In particular - the bolts in question are drawn with a sharp corner where the head meets the shaft. Really?

Tim

This problem can be boiled down to three questions:

1. What tensile strength is required to resist the radial force from the rotating weight at max rpm, times the relevant safety factor?

2. What shear strength is required in the square heads to resist the required tightening torque? Bearing in mind that an increase in torque (to meet the need in 1) means a reduction in tensile reserve.

3. Does it matter what the bolts look like in detail? ie: would a hex socket serve? Or could the square heads be a bit bigger?

Which all depends on - for 1 - what the max rpm is, and how accurately and how permanently controlled this is, and what is the proper factor? And for 2 - What size spanners are carried with the vehicle, and is there a way to check torque with the size selected?

And a further factor: Off the shelf high tensile bolts tend to be much more reliable than home made fittings.

My guess is that at the rpm at which small steam engines run, the answers are not super-critical. But it also depends on what (if anything) surrounds the rotating crank, and how strong it might be to stop a flying bolt should the worst happen.

Cheers, Tim

Edited By Tim Stevens on 27/12/2022 12:14:00

I agree with Ady 1 that Neo magnets from a well known web source are both fragile and rust prone once they are cracked. And some of them arrive like that - but they still work for attaching important (but temporary) papers to a tool box lid or the top of a mill column.

I suspect that as the Neo mix is chosen solely for its magnetic properties, it is not easy to form into shape by old-style methods. My guess is that sintering is used, and a quick flash of zinc is a good way to stop the rust while not affecting the dimensions significantly.

I await news from Michael G about what his magnets comprise when they arrive. If they arrive.

Cheers, Tim

The mention of reinforcing steel in concrete is a further clue to the problem. the reinforcing adds two new causes of condensation - first it allows the concrete to be thinner so less insulating, and the steel conducts heat through it so even less insulating.

I now realise that although the Welsh Marches is not always a very good place to enjoy a garage hobby, it has one major advantage. We are only about five miles from a Kingspan factory. And they have off-cuts and rejects ...

Cheers, Tim

I may have found a product in a smaller tube - but with the same properties;

Everbuild Stixall. This is described as having properties of silicone and polyurethane, and includes two chemicals which I can neither pronounce or spell.

Knowing a little about the way inductry works, my guess is that there are three or four firms which supply the UK building trade with stuff in tubes, and Everbuild is one of them which serves the Welsh Border.

And it says it sticks 'virtually everything' - so maybe it is CT1 in disguise. But if you know different ...

Regards, Tim

The question does not relate to a modern car with windows that are fitted from the outside. To replace the glass (as I am doing) requires the removal of two leather panels, held in place by tin-tacks, and covered by a leather strip, as well as the removal of a wooden upright from the hood mechanism. Then the wooden panel which holds the lift device has to be destroyed because it cannot be removed, and a new one made. So, you will understand that I do not wish to do the job again because
a) a joint designed for a pressed steel car is not in use, and for which there is no evidence that it will last in a 1928 body made of worm-eaten forestry products, and
b) because it is a seriously long job.
The steel-rubber-glass joint in question is about 5 inches long, (127mm) and the glass it holds is about 12 x 20 inches (300 x 500mm), so any comparison with a complete windscreen which actually fits all the way round is not reasonable, either.
But thanks to those of you who suggested that a polyurethane adhesive should serve well - as used for sticking mirror brackets to the backs of modern windscreens. All being well, I will report on progress, but ...

I will not be able to report on the strength of the finished job, as the recent failure was caused when the closed touring hood lifted from its catches on the screen as a truck passed me rather close. And Ii was doing about 60 mph into a head wind. As far I am am able, I intend that to be a once-in-a-lifetime experience.

Off to the Builder's Merchants tomorrow to see if anything useful comes in a smaller tube than is needed to reglaze a row of houses.

Thanks again - Tim

I am repairing a wind-up window in an old car. The bottom edge of the glass is trapped in a thin folded strip of steel*, with a thin moulding of synthetic rubber between them. The glue used by the previous owner was black silicone, and it had worked fairly well, except that there was rusting between the rubber and the steel - which I guess was caused by the acetic acid from the sealant as it cured.

There are lots of more modern versions of 'glue' now, and I wonder if a polyurethane product would be better? Or a Loctite might be better still? Perhaps superglue might cause problems, as the glass has to be pushed carefully into its rubber-lined slot, and so a slow-ish cure would be best.
If you have experience which worked well, or didn't, please tell us - thanks.

* the steel strip is welded to a thicker strip, slotted for the lifter chain, in case that helps work out what is going on. And the chain is a 'block chain', and nothing to do with fancy ways of losing money.

Seasonal greetings to you all

Regards, Tim

Edited By Tim Stevens on 16/12/2022 15:44:42

Can I suggest that crimping is for factory work - with accurately controlled presses and precision dies. And the same size wire and connectors every time. Our workshops are quite different. Not only that, the best crimped connection still has holes between the wires, which can fill with water (which is often not pure water). This can cause corrosion inside the fitting, and this is very awkward to rectify.

Soldered joints, with a manual crimp first to hold everything firmly in place, are better in our varied environments (and sometimes out in the snow.)

Only my views, after about 40 years of doing it successfully.

Cheers, Tim

Two memories from my (too brief) time at BSA in the late 1960s:

Their twins, and Triumph equivalents, had through big-end bolts in light alloy conrods, that were measured for length and tightened to a specified increase in length. The nuts were all-metal stiff nuts, (which vary a lot in initial stiffness) so this ensured that the applied stress was independent of nut-stiffness.

The big-end nuts (on the ends of the taper-ended crankpin) on the BSA Gold-star singles were tightened to 180 foot-pounds. This required a special crank-holding jig, bolted to a bench, which bolted to the wall - and a 4 foot tube over the end of the spanner.

Happy days

Cheers, Tim

There is a simple way to check - in the shop - how flat a tile is. Hold it about horizontal and look at the reflected view through a bright window. Move the tile around a bit and look for wiggles in the reflection. With no wiggles, and a view that in all respects stays constant - no distortion - you can be fairly sure that the surface is flat*. Ceramics will only be flat, though, if they are ground, like granite always is. That doesn't mean, though, that granite tiles are always flat, they still need to be checked by the same method. It is more difficult to do this test with a surface plate, whether granite or iron, as holding them up at arms length is jolly hard work.

*It could, though, be part-spherical, domed or hollow, but this is not likely with normal surface grinding.

Cheers, Tim

Edited By Tim Stevens on 24/11/2022 17:51:28

Edited By Tim Stevens on 24/11/2022 17:52:31