Author: Woody

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Rosebud Fire Grate on a Silvercrest BR Class 4

A variation on a theme

I received a blog enquiry asking if I could make a fire grate for a Silvercrest 5″ BR Class 4. The owner had inherited the locomotive but it was missing the fire grate. Given the age of the model Silvercrest were unable to help. I gamely said I would ‘have a go’ but on the basis of making a rosebud rather than a conventional bar grate.

What I didn’t realise was that the grate on this model is made up of 3 separate long sections which are shuffled into place via the firebox door …

I asked the owner to first of all make a template of the grate size based on three equally wide sections of hardboard. This resulted in an overall grate size of 57mm x 209mm. From this I used my Excel spreadsheet to derive a grate with 15% hole area occupancy from a matrix of 25 x 6 holes each of 4mm diameter counterbored with a BS4 centre drill.

I thought it might be a good idea to have a draft angle on the inner edges of the grates. Don’t ask my why – it just seemed like it would make it easier when dropping the middle section into place and perhaps reduce air leakage through the joint .. and of course this makes the design more complicated than necessary and added to my machining woes. This can be seen on the image above.

The design was created as a single grate and then extrude cut into the three sections so the middle and outside grates could have their own CAM program. Here is the Fusion model view looking from the under side.

Having grasped the basis of the design I sent the owner a set of 3D printed grate sections which he cross checked and confirmed would fit correctly. (Could these be the ultimate chocolate fireguard I wonder ?)

The next step was to think about the CNC CAM operations and the stock holding. I find holding the stock and the order of doing things to be the most challenging part of the machining process. As the three sections of grate were all under 25mm I opted to use 6mm x 25mm BMS as the base stock material. I had the Fusion 360 model reference the stock at the centre point. This is easy to probe using the Tormach PathPilot inbuilt routines. I cut three pieces of the BMS to 215 mm lengths and mounted each in turn on parallels in the machine vice. I had a vice stop set up to make the process repeatable. Each section was then drilled for the 4mm through holes (50 off in each) and then counter bored with the BS4 centre drill such that the taper on the drill finished flush with the stock top. This just left the outer profile of the model to be cut on the residual stock.

This was accomplished by using a piece of 30mm wide BMS as the sacrificial backing jig mounted on parallels. This was centre referenced and a number of the 4mm hole locations were drilled at 3.2mm and then tapped 4mm. These holes were then used to bolt down the three grates in turn so they could be profiled to size. The profiled width had to be the maximum width ignoring the intended draft profile (i.e. 19.10mm + 20.916mm). Here is the end view (upside down) showing the three grates with their draft angle .

The machining process was then transferred to my Myford VMB manual mill. This was set up with a tilting vice set to 10 degrees. The two bright edges of the centre grate and one edge of each of the outside grates were then blackened with a Sharpie before each being placed in the tilted vice and skimmed at 10 degrees such as to just remove the blackened surface.

The resulting grates all butted up together nicely and the job was complete. Here is the bottom side view.

These were shipped off to the owner for trials and he later confirmed that they fitted nicely into the firebox. I am not sure if anyone has made a rosebud for a Silvercrest with split grates so it should be interesting to see how well this configuration steams out on the track.

I think the above should give you enough to think about but there is one other spin off that resulted. While drawing up the grate in Fusion 360 I decided it would be much more convenient if the rosebud grate design could be automated using Fusion’s parametric functionality.

This resulted in the Excel spreadsheet being modified and the Fusion model also being updated. The result is the ability to get all the factors needed for the Fusion parameters from the Excel sheet (but you have to manually copy them between Excel and Fusion).

Here is a ZIP file with both these files included.

Update : the user has reported back that the grate performs well. Like other installations of a Rosebud grate, he has found a need to keep the blower slightly open.

Rosebud calculator with Fusion FxDownload

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A Very Old Burgess Bandsaw

A version that I have never seen before

I had a contact through my blog from a gentleman who had inherited a Burgess Bandsaw. I have published various support details for the BK3 so he was curious about the model in his possession and he sent me some pictures as shown below.

I have never seen this model before. The BK1 through BK3 all have a belt drive from the motor but this one has a chain drive. The shape of the housing is much more curved and both the blade wheels look to be cast and perforated rather than being plastic. It is clearly a very early model, probably before the design went through a manufacturing cost reduction.

The manufacturers plate suggests this is Serial #225.

If anyone knows the likely history of this version I would be interested to know more details.

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Three axis stepper controller PCB in stock

Due to popular demand

Some while ago I described how I had fitted stepper motors to my Myford VMB milling machine. It was not the intention to convert the mill to CNC but simply to give my arms a rest winding handles back and forth. This was particularly so with the Z axis. The secondary advantage is that the motor driven movement leaves a much smoother finish than my hit and miss erratic winding of the hand wheels.

The design is Arduino based and allows selection of a single axis at a time with variable speed control in forward or reverse direction together with the option to fit limit switches/emergency stop facilities. The PCB, with appropriate stepper hardware, could be applied to any other machine needing motorised movement.

You can read the full article here.

Following some recent publicity of the conversion, I received a number of requests for the unpopulated printed circuit board. I now have a few of these left in stock if anyone is feeling adventurous. Here is a view of the external connections needed.

This conversion started off as a ‘I wonder if I can’ and is now probably one of my favourite projects in terms of its impact on my day to day use of the VMB.

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Simple Water Level Sensor for Live Steam Locos

Avoid a panic half way round the track

While coming to the end of a running session of my 5″ loco at the club raised level track I suddenly realised the axle pump was not making its normal rattling noise. Water level was likely very low and there appeared very little in the glass sight gauge. My state of panic endured until I reached the filler hose.

On returning home to the workshop I resolved to try to make this alarm situation more readily visible. The common solution is to add a second sight glass feeding from the water tank and visible in the ‘cab’. My engine did not have a great deal of room for this addition.

Sacrilegiously I began to consider an electronic solution which probably wouldn’t make me popular with the mechanical diehards but the challenge appealed.

The electronic solution turned out to be a multi faceted activity. An initial bird’s nest lash up was followed by a PCB designed in Fusion 360 Electrical. The PCB was milled on my vacuum table fitted to the Tormach 440 with the Gerber and Epsilon files converted to GCode using FlatCAM. Having completed the PCB board this led to a customised enclosure designed in Fusion 360 and 3D printed in the Qidi X Smart 3.

The circuit is a NPN transistor that is turned on by water conduction between two sensor probes which in turn drives a second NPN to illuminate a flashing LED. The module is powered by a CR2025 button cell.

The enclosure consists of three parts, the base, a snap on lid and a round boss that matches the diameter of the water filling hole on the engine side tank. The two water sensing probes are made from 16 swg wire protruding from the boss.

The round boss is held in place with a M2.5 countersink screw and could be dimensioned to suit different sized filler holes. Having it as a separately printed item is also useful in that it allows the enclosure base to be 3D printed without support.

Here is are some views of the completed assembly.

It seems to work quite well and is surprising sensitive down to the last few millimetres of the probe rods. Time will tell.

If you want more details then please send me a message.

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Dry lining wall fastener fixing aid

Simple jig that makes DIY easier

In my experience there is only one fixing style that works with plasterboard lined walls. These are shown in the image below and are supplied in various mounting thread sizes. The image below shows the 4mm and 5mm versions. Also shown is an example of how they expand out when you clamp them inside the cavity behind the plasterboard. Note that while intended for dry lined walls, these can also be used on thin walled surface such as a modern ‘hollow’ door (good for bathroom towel hooks). The fasteners are available in various lengths to suit the mounting surface thickness.

In use you drill the appropriate clearance hole for the body (6.8mm for the 4mm version and 8.8mm for the 5mm version) and push the fastener into the hole so it is flush with the outer surface of the plasterboard. You tighten the screw to cause the ‘wings’ to expand in the cavity.

There are a few issues with this. To cause the expansion process to start you have to apply a lot of pressure downwards on the screw head. Once you feel the screw beginning to turn easier you are on the way to crushing the wings against the wall inside surface. The next test is judging when you have reached optimum expansion of the wings. This comes with experience. The screw rotation will go from relatively easy to increased pressure.

When used on plasterboard the two triangular prongs on the fastener are supposed to grab into the plasterboard surface and stop the fastener rotating as you tighten the screw to initiate the wing expansion. My experience is that you need to apply heavy downward pressure on the screw head to stop the prongs just rotating free and cutting a nice circular vee groove in the plasterboard surface. This is slightly less likely to happen if you are fitting one to a hardboard surface such as a hollow door as the hardboard will give greater resistance to the rotation.

This tightening process can be helped if you put a washer under the screw head with some grease. This eases the possibility of the whole fixing rotating.

You can buy a tool for mounting these fixings. My version is a 3D printed double pronged restraining jig. So far I have created two sizes, one for 4mm and one for 5mm threads. It is simply a disc with two 1.6mm panel pins embedded in it that mate with the notches in the fitting. The tool is offered up over the fastener with the pins in the V grooves and then pushed home into the plasterboard. The pins embed deeper in the wall surface than the prongs on the fastener and stop it rotating.

A couple of other comments. Once you have the fastening in place on the wall the screw thread will likely be longer than you will need to hold the object being fastened to the wall. You can therefore substitute a shorter screw as needed so long as it is long enough to mate with the fastener thread. You can also change the screw head style. When fitting curtain battens I use a number of these fittings along the batten length and replace the dome head screws with countersink heads into which I fix the commercially available small plastic star head covers (see below).

Here is an image of the fasteners, the two jigs sizes I use, a view from the rear of how a fastener expands in the cavity and the small coloured plastic covers that can be used to cover countersink screws.

Depending on the technique that has been used to fix the plasterboard, you can sometimes have a reduced depth of cavity for the fixing. This can be overcome by drilling the mounting hole for the fastening not just through the plasterboard but as deep as need to match the fixing’s length into the solid wall behind. This allows you to get the fastener in place and the expansion of the wings will not be inhibited. Clearly this is not so easy with a steel lintel behind the plasterboard …..

The STL files for the two sizes can be downloaded on the link below. I used PLA with a 4 perimeter print and 0.25mm layer depth. Once printed, clean out the two panel pin mounting holes with a 1.6mm drill. Cut the panel pins to around 6-8mm length and push home into the drilled holes. The small counterbore on the print surface will match the fastener flange but not to full depth so there is a pressure exerted from the jig as you push it against the wall.

cavity-fastener-jigsDownload

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