0.2mm from Success

I am never ever ever ever making wheels again. As you can probably guess the next step in the long running saga of building Ivor didn't go entirely as planned.

Having remembered from last time that it was hard work profiling the wheels I set everything up carefully and then turned the first wheel. Just as last time it was a slow process. I'm not sure if that's because the tool isn't as sharp as it might be, or if the brass Shapeways uses isn't ideal for turning, or if the Unimat 3 is a little underpowered for the job, but you have to take very very light cuts and I stopped frequently things cool slightly (otherwise the cutting tool gets so hot the oil smokes). Anway slow and steady got me to a nicely profiled 20mm wheel.

After the success of the first wheel, I made a coffee, and then profiled the second wheel. Then I made another coffee and profiled the third wheel. Then I made another coffee and started on the fourth and final wheel.

I took the final wheel nice and slowly and was just 0.2mm away from a completed wheel (i.e. I needed to advance the cross slide by just 0.1mm) when the threaded rod of the wheel holding tool sheared off and the knurled knob when flying across the room; fortunately away from me. So that's the second time I've had that tool fail now and I've no idea if it's just a bad design or something I'm doing wrong. Either way I was now just 0.2mm shy of four completed wheels which was rather frustrating.

The rod had snapped very close to the wheel so there wasn't enough left to try and screw anything on to the remaining stub. In the end I used the live centre to push the fixing against the wheel. It wasn't pretty and the wheel did slip a couple of times but it stayed straight and allowed me to reduce the diameter by the final 0.2mm.

Fortunately I think none of the remaining work to use the wheels would need the wheel holding tool (they just need holding in the step chucks) so hopefully I can continue on with the build of Ivor, but I don't think I'll ever try making my own wheels again.

Signs of Life

Given how sporadic, or none existant, posts have been over the last year or so I've no idea if anyone is still reading this blog, but believe it or not there are signs of some modelling happening!

Some of you may remember that for Christmas all the way back in 2016 I was bought a kit for building an OO guage model of Ivor the Engine. This was a nice present and the first from my then newly born son, Toby. Well Toby, is now five and a half, and I now have a second son, Thomas, who is 14 months old. What I don't have though is a completed model of Ivor the Engine.

The last time I blogged about the kit was almost four years ago in August of 2018 when everything had gone horribly wrong: I'd broken the wheel holding tool for my lathe and the wheels I had made, although correct to the instructions, didn't fit in the model. At that point I put the kit away in a box, never expecting it to be four years before it would appear again.

So where are we know? Well, fohrmann-WERKZEUGE were very helpful and sold me replacement parts for the wheel holding tool which saved me quite a bit of money over buying a complete replacement. Of course any money saved was then spent on having new set of wheels produced. These are essentially they same as last time (lost wax brass castings using 3D printed waxes all done through Shapeways) albeit slightly smaller to solve the main issue that arose with the originals.

So far all I've done is separate the wheels and drill out the axle hole to 2mm, but as you can see roughly placing them against the chassis suggests that they will fit this time, especially given they will be fractionally smaller once I've turned them on the lathe to properly profile the edge and add the flange.

I've no idea when I'll get to do more work on the wheels but hopefully it won't take four years before there is more to report.

Ivor is Going on Hiatus

So unfortunately work on Ivor is going on indefinite hiatus.

After doing the maths this morning I thought I'd go ahead and turn the wheels down to 20mm from their original 21mm diameter. If you remember when I originally turned the wheels I said it was hard work to get them down to 21mm, well getting down to 20mm seemed nigh on impossible. I continued to take it very very slowly but the work involved looked like being too much for my lathe without substantial extra work to the wheel (thinning the depth and reducing the width with a normal cutting tool first etc.) but with perseverance I got the first wheel to 20.5mm and so decided to split the difference and stop there. All (reasonably) good so far.

Having let the wheel cool (they get quite hot during profiling) I went to undo the wheel holding fixture only to find it was quite tight. I gently used a pair of pliers to start loosening it (I did this last time when it was too hot to touch) only for the threaded rod to snap in half! This means that the wheel holding fixture is now useless. More to the point I now have one 20.5mm diameter wheel and three 21mm diameter wheels so Ivor is going nowhere anytime soon.

I think the best thing to do is simply put the kit away for a while and focus on something else. This will give me time to rethink the wheels (I'll redo the 3D model for a smaller diameter and to make them easier to profile) and probably to save up to replace the wheel holding fixture. I could continue on with the body, but I think I'd just get frustrated knowing I couldn't fit it to a working chassis (plus it might need modifying to fit the gearbox etc.) so will probably turn to something else entirely. Not sure what yet, but I'll be sure to post when I've done something new.

RP25-110

Next up in the sage of making wheels for Ivor is the bit I've been dreading the most; profiling the wheels to add the flange. In theory this should be easy as in essence all it involves is reducing the diameter of the casting using a profiling tool, but that glosses over a whole bunch of issues.

Let's start by defining exactly what we mean by "to profile" a wheel. Put simply it's to shape the tread and flange of the wheel to a specific shape. There are lots of different profiles all defined by different guidelines and associations. For Ivor I've settled on using wheels profiled to match RP25-110. This means I'm using the RP25 profile, as defined by the NMRA, with code 110 wheels, i.e. wheels that are 0.110" in depth (or for those who prefer metric, 2.794mm). Now a lot of the work of making the wheels fit this profile was done during the design of the 3D model as it set the depth etc. but it is impossible to 3D print thin enough and accurately enough to produce the flange.

To add the flange (and to ensure a nice smooth turned tread) I'm going to finish the wheel profile on the lathe, using a specific profiling tool. You can get profiling tools from numerous places but I picked up this one from Carbide Solutions as it had a square shank which made mounting it in the lathe easy.

Even with a sharp profiling tool (I'd not used mine before) this is actually quite hard work for the lathe and involved taking very very tiny cuts and quite a few breaks even during each wheel to ensure I didn't over heat the lathe or the wheel (it got exceptionally hot).

As you can see I've held the wheel in the lathe using a tool designed specifically for the job (another purchase from fohrmann-WERKSEUGE). The tool ensures the wheel is perpendicular to the lathe bed and clamped tight, although I did manage to over tighten the clamp on two out of the four wheels which unfortunately opened out the axle hole in the wheels slightly -- not a problem as I'll fit insulating bushes to these two wheels so will need to open the hole further anyway.

You'll also notice that I've left as little of the profiling tool hanging out of the toolpost as possible to try and reduce chatter, and I clamped the crossslide tight so as to remove as many sources of movement as possible. On the first wheel I started with the lathe on a slow speed but that was a disaster as the tool tended to dig in and bounce around, even with the lathe locked as solid as possible. I reconfigured the belts to run the lathe on it's fastest setting (4000 rpm) and with very very tiny cuts this worked a lot better, and fortunately I figured this out before destroying the first wheel. Once I'd reduced the first wheel to the correct diameter (21mm for 5' 3" wheels at 4mm to the foot) I took a note of the position on the cross slide, and then repeated the process for the other three wheels.

It took me all morning (in blocks of a couple of minutes here and there) but I've managed to profile all four wheels. While I'm not going to claim any of the four as perfect, I'm happy enough with them all to try and assemble the loco. All four have a difference of no more than 0.02mm when measured and all are slightly above 21mm rather than below, so they are close enough that I think they should sit level. The main issue with them is that when I removed them from the sprue, and filed the excess away, I didn't take into account that the edge of the flange was the edge of the casting (something I'll change if I produce any more) and so in a couple of places there is a slight straight edge on the flange, but hopefully not enough to cause a problem, if it is I can always order another set and replace them but fingers crossed...

Axle Hole

Having separated all four wheels for Ivor from the sprue they were attached to during printing the first step is to drill out the central hole to take the axle. Normally if I was trying to make a hole to fit an axle I'd drill it slightly undersize and then open it out slowly with a reamer to get a tight push fit. In this case though I'm going to turn the axle as well, so I can make the axle fit the hole. This means I can use a cheap drill to make the hole and not have to worry about buying an expensive reamer. That isn't to say this step doesn't include expensive tools as not only did I do the drilling using my lathe but I bought a set of step chucks specifically for the task.

Specifically I bought the 20.00mm to 24.50mm step chucks from fohrmann-WERKZEUGE. As you can see these allow me to hold the wheel (or any other appropriately sized cylindrical object) in the lathe for accurate centre drilling. In this case I've used them to widen out the axle hole to 2mm in each of the four wheels.

Visually the wheels all look good and the hole appears to be nice and central so hopefully that's the first step successfully achieved, and now they all have an identical sized axle hole I should be able to mount each in turn in the same position in the lathe which should make turning the flanges on each in turn a little easier.