An international forum for garden railway modellers in all scales and gauges. It is free to join and is funded through voluntary contributions by its members. Many thanks to all those who keep it going.
Next I removed the false floor from the body by scoring around it with a scalpel run along the inside faces of the body which then allows the floor to be flexed and snapped out. The ‘ears’ were removed in the same way and the lower edges were then filed smooth to remove any remnants of the false floor, ears and the lip around the bottom edge (referred to as the ‘elephant foot’ effect). The ‘elephant foot’ is caused by the need to overexpose the first few layers of the resin print causing the surrounding resin to cure and leaving a small lip where the body was adhered to the build plate of the printer.
I then removed the supports from the printed bufferplates and cleaned up the rear face with a wet sanding stick.
IMG_4831.jpeg (3.67 MiB) Viewed 3067 times
Note the printed bufferplates represent the side extensions to the iron strip that wrapped around each headstock on the prototype. They are handed pairs, oriented with the 4 bolts in the inboard top corner.
Next I cut a strip on black 30 thou platicard using the printed bufferplates as guides for the thickness. Black plasticard was used to avoid coloured resin showing through if the paint was worn off the buffer strip face when the wagon was coupled to other stock.
IMG_4832.jpeg (3.34 MiB) Viewed 3067 times
This strip was left over length then glued to the headstock with superglue. I found it best to glue one end first, with the body flat on the bench, before bending the strip around the headstock and holding whilst the glue cured. Applying the glue to one face and accelerator to the other face before bringing them together makes this a quick process.
I then glued on the bufferplates which could be butted up against the over length plasticard strip. I deliberately allowed the superglue to ooze out at the joint, filling any gap between the strip and plate. Once the glue was dry, the strip was trimmed back and the joint sanded smooth, with a slight radius on the corner to represent the continuous iron plate of the prototype.
Next stage is the floor. The floor is 154mm x 74mm which I have cut from 3mm Perspex. I use Perspex in preference to ply or MDF so I can easily wash the model before painting. I also cut a 145mm x 13mm rectangle that acts as a jig/spacer for the two longitudinal in the centre of the vehicle.
I cut my Perspex on my CNC milling machine. This is a Genmitsu 3020 Pro Max V2 (https://www.sainsmart.com/products/3020 ... RlZ1mOTwIX) and is a really useful machine that is capable of high precision cutting, carving, boring in a variety of materials. It’ll cut softer metals up to and including mild steel, but I mostly use it for brass and aluminium where cuts of up to 1mm per pass are possible, allowing complex shapes to be cut in reasonable time.
Here’s the CNC machine in action, it helps to have a vacuum cleaner on hand to remove the chips/swarf.
IMG_4851.jpeg (3.34 MiB) Viewed 2875 times
After cutting the parts are held in the sheet by tabs that can easily be cut with a knife and the part tidied up with a file or sanding stick.
IMG_4852.jpeg (3.22 MiB) Viewed 2875 times
The two parts are screwed together and then glued to the body from above using superglue.
I also used the CNC machine to cut the bearing holders/solebars from a piece of 15x25x1.5mm aluminium angle.
I first cut two pieces of angle slightly over length on my Proxxon mitre/chop saw. These pieces are then clamped to the CNC machine using a pair of bending bars as a rudimentary vice.
IMG_4853.jpeg (3.19 MiB) Viewed 2874 times
I cut the two pieces at the same time, first cutting the top that includes mounting slots through which they can be screwed to the underside of the floor. The crescent shapes are to provide clearance for the wheel flanges, I should have raised the floor mount in the body print a few mm higher and then would have had sufficient clearance! I then unclamp the pieces and flip them over to cut the sides with the 6mm holes for the bearings to mount in. Using the CNC machine ensures the pair perfectly match and will mount the wheels level and square.
IMG_4827.jpeg (2.91 MiB) Viewed 2874 times
I then glue in the bearings, the Axleboxes and screw in the brakegear using M2 screws tapped into the aluminium.
A bit more progress. The two longitudinal are glued to the floor. The spacer helps to align them and also helps straighten them out as printing them flat on the build plate resulted in them taking on a slight curve after curing. I also added the bottom of the door posts using some 60thou plasticard trimmed to size.
IMG_4855.jpeg (1.94 MiB) Viewed 2702 times
Binnie wheels and axles are prepared. I have used 65mm axles and set the back to back to 40mm for 45mm gauge track. The 3mm id bearings are from Houstoun Gate Loco Works https://www.hglw.co.uk/misc_accessories.html
IMG_4828.jpeg (2.78 MiB) Viewed 2702 times
Next the solebars are screwed to the floor. The slots allow some fine adjustment on the side play to optimise running.
A little late to catching up with last month's developments, but I am fascinated by your clear and persuasive description of a CNC machine. The way you've used the 3D printed parts together with the acrylic and aluminium parts milled on the CNC machine is impressive. I hadn't really I understood CNC routers at all previously, or how they might be used in constructing models.
Most, require you to build (at the least, partially) the machine, then spend some considerable time 'tweaking' things, to get it to perform well. - As with 3D printers..
I think they can be a 'hobby' in themselves, and take the stated capabilities, with a pinch of salt.
SimonWood wrote: ↑Wed Mar 12, 2025 9:54 am
A little late to catching up with last month's developments, but I am fascinated by your clear and persuasive description of a CNC machine. The way you've used the 3D printed parts together with the acrylic and aluminium parts milled on the CNC machine is impressive. I hadn't really I understood CNC routers at all previously, or how they might be used in constructing models.
I am now very very tempted by a CNC machine!
I have been really impressed by my CNC machine. There are a lot of 3020 type machines on the market but the Genmitsu is definitely one of the better ones, being rigid enough to cope with metal milling and accurate to better than 0.1mm which is plenty accurate for most tasks. Other than needing to bolt the two main parts of the machine together, fit the spindle motor and wire in the controller (about 30mins work) it is pretty much ready to go, I’ve not needed to adjust anything since I got the machine 2 years ago.
I use the free version of Fusion360 for CAD which produces the G-Code programmes that the CNC uses. The files are transferred via an SD card.
Establishing what combination of settings (cutting speed and depth of cut) to use on different materials has been the main learning point but I now have my own rules of thumb that work well enough. I use single flute endmills for non-ferrous metals and Perspex, purchased from here: https://www.shop-apt.co.uk/1-flute-carb ... inium.html
My most used bit is the 1/8” which I run at the same 300mm/min in all materials, changing the cutting depth to 0.1mm for brass/nickel silver, 0.5mm for aluminium and 1mm for Perspex.
To show what the CNC is capable of, here are some examples of parts I cut for an O gauge loco chassis which used 0.7mm brass sheet for the frames, 1.5mm nickel sheet for the coupling rods and 2mm aluminium stock for the fly cranks. The chassis is sprung with hornguides cut into the chassis frames to mount the slaters hornblocks. This chassis ran perfectly with no fettling needed to any of the machined parts, which is testament to the CNC accuracy.
IMG_4128.jpeg (3.66 MiB) Viewed 1914 times
IMG_4130.jpeg (2.57 MiB) Viewed 1914 times
IMG_4166.jpeg (568.41 KiB) Viewed 1914 times
And a video cutting some smaller parts using a 2mm bit
That chassis is really impressive. Are you sure you haven't slowed down the video .....
I found the video of the machine in action mesmerising. My wife looked over my shoulder whilst I was watching it. Her only comment was "That looks thrilling...."
ge_rik wrote: ↑Thu Mar 13, 2025 8:21 am
"That looks thrilling...."
Mmmm, it does! I've already looked up the m/c and found that it isn't as expensive as I imagined it might be. I only have two problems ( well 3, if you include the cash!), one is space and the other is software. Fusion360 is a black art as far as I'm concerned, but of course Sketchup has the major drawback that it doesn't do true curves.
That chassis looks superb. I'm a bit smitten by this machine.
As a result of you posting these explanations and wonderful example videos, for which many thanks, I'm going to take the liberty to ask some more daft/very basic questions: what is going on with in the cutting video with repeatedly cutting around the piece - is this cutting a little deeper each time? And what is holding the workpiece in place - is there some sort of adhesion with the surface beneath it?
Once you start watching CNC videos on YouTube, be prepared for your feed to fill up with CNC crash videos, they really are properly thrilling!
For learning Fusion360, there is a series of videos called Learn Fusion360 in 30 days. I found these really good to pick up the basics, you only need the first 10 or so lessons to cover most of the common operations.
I see announced as of today there is a new version of the Genmitsu machine I have, with a few changes including a more powerful variable speed spindle motor (possibly allowing deeper and/or faster cuts). It also appears to include covers over the limit switches which was a suggestion I sent to the manufacturer as I did find metal chips can get into the open switches and short them, causing the machine to stop mid operation. https://www.sainsmart.com/products/3020 ... T78.M42MAU
To answer Simon’s questions, the parts are cut out using multiple passes, each deeper into the material by whatever depth of cut you set. For harder metals like brass and nickel silver, I use 0.1mm depth of cut so it takes 10 passes to cut through a 1mm sheet. In practice, you’ll need more passes as, unless you are using ground flat stock, you’ll need a few passes above the top surface of the stock to cut through any high points and a few passes below the bottom of the stock to make sure it is cut right through. In aluminium which is a lot softer than brass, I work with a depth of cut of 0.5mm so it needs fewer passes to cut through and is therefore quicker to complete the operation. Aluminium is also a lot cheaper than brass! To get a really nice finish on the cut edge, you can choose to do a finishing pass at full depth, which then means the preceding passes (roughing cuts) leave some stock material around the part so the the finishing cut has something to cut into. All these are settings in the manufacturing module of Fusion360, that can be altered to suit.
In the video I used the masking tape and superglue method to hold the parts on the machine bed. This just involves sticking masking tape to the entire bottom surface of the stock material and all over the top surface of the machine bed. I then use medium superglue on the non-sticky masking taped surfaces to glue the stock material to the bed, holding the stock flat on the bed. Once machining is finished, the machined parts can be removed by peeling off the masking tape to release the parts. Clamping stock to the bed using screw clamps provided with the machine or in a separate vice are also options, but the superglue and masking tape approach is generally easier for sheet stock.
I am still amazed at the capabilities of my machine when combined with Fusion360given the relatively affordable costs involved. Not many years ago, the only CNC machines available then would cost £1000s or even £10,000s and CAD software to use with it would also be expensive. The Genmitsu machine is around £400 and Fusion360 is free for hobby use.
