Monthly Archives: June 2024

David Andrews Princess Royal – Pressure Turned Washers

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Then I connected the loco and tender together and it immediately tripped out the controller and so I started a further round of troubleshooting. First I removed the bogie and after coffee I went back into our cloakroom where I have temporarily set up my test board. This room is west facing so gets sunlight mostly in an afternoon but it’s below ground level as the path outside the window is cut into the embankment and so doesn’t get quite as much natural light unless the sun is really high in the sky and it’s late afternoon.

Now one of the suggestions from Thursday nights meeting besides dig out the multimeter was to try hunting for shorts in the dark as sparks are easier to see. As I went in for further testing I forgot to turn the light on and so the room was a little gloomy. This proved to be a benefit, because as soon as I moved the bogie on it’s own, I noted a spark which I wouldn’t have seen with the light on. I noted that the guard irons were quite close to the rails and may have caused shorts on curves so they were adjusted and then further examination showed that I had fallen foul of the etched washer/hub insulation again. A further check of the trailing tuck revealed the same issue. I had a few spare insulated washers that I had turned when working on the tender but they proved to be too thick even after turning/milling down the axle bushes.

I was initially going to make some up by using a hole punch to cut holes in some styrene sheet and then snip of /file them into circles. By good fortune a video that I had seen some time ago that was lurking in my memory surfaced on my Youtube feed. After rewatching it I decided to have a go at pressure turning a number of washers all at once.

Now unless you want really big washers the process is a little wasteful because you need enough stock to hold onto to drill the centre hole. I chose to cut some 0.5mm styrene sheet into 20mm x 20mm squares aiming for a finished size of 10mm diameter. You also need some scrap to hold the parts and one of them becomes almost sacrificial.

The first step is to grip the styrene squares between the two pieces of scrap material.

Drilling blanks

I used a 1″ G clamp and a small engineers clamp to hold them all together to drill a 5mm hole through all the parts. This was to allow clearance on the 3/16 (4.7mm) axles. At this point you transfer the whole set up to the lathe before releasing the clamps.

Setting up for pressure turning
Pressure Turning Parts

I created the above set up which consists of a 22mm piece of Delrin in the collet (I had to turn a stub down to fit in a 16mm collet which is the largest ER25 collet that I have). This had a 5mm hole drill partially through it. At the tailstock end is another piece of 22mm Delrin which has had a 60 degree cone turned in the back so that it fits on a live centre then a short section turned down to 10mm to allow the tool to clear the workpiece(s) again it has a 5mm hole through it. Then a length of 3/6 rod was passed into the hole in the mandrel in the collet chuck and the parts fed onto it, before removing the clamps. Lastly the live centre is wound tightly against the parts which squash and grip all the parts for turning and locked.

The next step was to turn down the sacrificial scrap support until all the parts start to be turned. My sacrificial scrap was plastic which has a layer of aluminium either side of it and I found that the most depth of cut I could manage was 0.25mm per pass otherwise the parts started to slip. I started turning with a carbide tipped bit until it would no longer fit, then I changed to high speed steel grooving tool that I had ground for another job some time ago.

Washers well on their way.
Finished Washers

One piece of advice given in the video was to make sure that you were using a sharp tool for the final pass to help prevent the tool from rolling the edges of one part over onto the next.

Finished Washers

These are the finished parts and they are all really crisp, aside from the one that was nearest the left hand piece of scrap which had a small burr around the edge (visible at the corner of the ruler). This burr was easily scraped off with a scalpel blade.

David Andrews Princess Royal – Tender Shorts Sorted

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Since my last post I have been beavering away identifying and curing the shorts on the tender which I am happy to say that I have done.

As with many things in life getting there required at least one side project. During last Thursday’s GOG online modellers meeting the consensus was that I really needed to dig my multimeter out of the depths of the shed. On friday morning I bit the bullet and started to pull out plastic stacking boxes (having first removed the lawn mower, petrols cans, oak kitchen cabinet doors and finally my router table). An hour and a half later I had retrieved one of my two multimeters and put everything back.

Sadly the one that I found was the one with the missing probe, the wire was there but the common probe which had broken off in the dim and distant wasn’t with it. Before embarking on making a new probe I fitted a new battery to test that it still worked which thankfully it did. The metal section of the probe was made from a length of brass rod which sat atop my useful bits box on the workbench and I quickly drilled one end to accept the wire and turned a step onto the other to fit snugly into the yet to be made insulated delrin handle.

I didn’t take photos along the way but this is the finished article alongside the original ‘live’ probe.

New Probe for multimeter

Once I had it I reassembled the tender chassis test along the way without find any further shorts.

David Andrews Princess – Tracing the Elusive Short Circuit

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The last week and a bit of modelling time has been spent tracking down shorts on the tender and isolating them. This has required me making a number of additional bushes and delrin/acetal washers.

Insulated washers and bushes

I also had to rethink the way that I had mounted the two U shaped brackets which fit across under the tender. Unthinkingly I had mounted them in the same way as on the MOK Stanier tender using small pieces of brass angle drilled and tapped for 14ba screws. Sadly when assembled these frames touch the brakes which although the shoes are insulated the hangers are not and between the two breached the insulation between tender chassis and body.

I made up some wire supports and then shortened the brackets to clear the outer frames. Below are a couple of shots of the sets that I used to get them soldered vertical to the brackets and then cut them off to the right size. I read recently on one of the forums someone say that you cannot have too many engineers clamps. I agree wholeheartedly although when used as soldering aids they do have a tendency to rust. I do have a cunning plan to get around that, I have a length of brass bar that I have had for about 10 years which will be just enough to make a pair of brass jawed clamps which shouldn’t rust.

Jig for soldering legs

I used the Expo pliers that I recommended recently to bend the corners pretty uniformly.

Jig for trimming legs

I also had a feeling that the washers which I had used to reduce the side play in the axles, might have been bigger than the insulation gaps in the wheel hubs thus creating a short, hence my making the delrin washers.

Highly Recommended for modelling tasks – Expo 75611 Half Round/Concave Combination Plier

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I bought these at Thirsk show last year or the year before and I hadn’t really used them much until recently.

I have absolutely no affiliation with Expo aside from a satisfied user of these pliers. Which I can highly recommend.

The curve of the jaws is slightly offset and I thought that this might be an issue initially but it has proved to be a design feature that has been very useful for bending wire to complex shapes.

Expo Curved Pliers
Expo Curved Pliers

David Andrews Princess Royal Return Crank Shenanigans

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Those who are observant, will have noted the jaunty angle that the return crank is sat at, in the top photo of the post with the sand pipes fitted. Having had this pointed out by someone this came back to bite me.

Initially I just thought that in lifting the loco up I had dislodged it causing it to unscrew and come loose. However no matter how much I tried I couldn’t get it to tighten back up in the right place. I tried shortening the bush but realised too late that the crank pin itself must have shifted in the wheel. Then having shortened it I found that when tight it was nipping the conrod and coupling rods so that they wouldn’t move.

Making a replacement bush was the order of the day.

Replacement return crank bush

Shop Made BA Tapping Guide Bush

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Following my posting of the Joe Pie tap wrench on the Guild forum there was a bit of discussion on the types of tap wrenches in use and one member shared a BA tapping guide that he had bought commercially. Which I thought was a great idea for tapping holes that are too inconvenient to fit in a vice

Having been given the idea, I couldn’t resist having a go at making one this morning.

BA Tap Guide
BA Tap Guide

I even managed to use the reject first attempt at making a drawbar for the Princess which I broke during machining due to me doing the wrong order of operations. I keep one of those square plastic trays that Slaters pack their small items like plunger pick-ups horn guides etc. on my workbench and all my small offcuts of brass and nickel go into it. Once I had machined each end off it was perfect for the guide bush.

I probably over engineered it in so much as I turned the end of the bush down to 5mm for 1.6mm and drilled a 5mm hole in the flat bar which is 1.6mm thick. It was a nice tight fit but I realised that due to the bar being drawn, it wasn’t exactly flat on top and the guide sat at a slight angle. still having the coordinates in the mill from drilling the hole I used a 6mm end mill to mill a recessed flat to accommodate the bush. I checked for squareness with a 1-2-3 block and then soldered the bush in.

The hole in the bush is 3.3mm and will take my 6 -12ba taps freely but with virtually no sideplay. I also have a 14ba tap and I might at some point add another guide bush at the other end of the ‘handle’ with a smaller hole to take that.