D869's Workbench Thread

[D869]

I haven't posted much on my blog recently so thought I would try creating a workbench thread and see how that goes... so here goes...

 

As some of you may know MinerChris is building a cameo layout based on Callington in Cornwall for the Diamond Jubilee challenge. I'm calling it 'Cameo Callington' (he isn't).

 

He's making good progress but I can't see him having time to finish any appropriate steam locos before June so I thought I would take a break from Hayle North Quay and make a contribution.

 

The original plan was to build an N Brass LSWR G6 kit and put it onto an 0-4-4 chassis to make an O2 class suitable for the layout. It hasn't quite worked out that way but there will still be some N Brass bits on the loco.

 

For the last few weeks I've been concentrating on the chassis. Some words and pictures in somewhat backwards order...

 

All put together.

 

The bits. In spite of appearances here, the frames are 0.5mm phosphor bronze. I'm trying out the Dave Holland 'keeper' style of chassis and so far it's proving very handy during the mechanical fettling stage. The front spacer is solid brass to get the weight forward with a PCB insulating layer. The rear one is Tufnol.

 

The main frames straight off the milling machine. I must thank Mr Brummitt for his kind advice on the subject of CNC converting the Proxxon.

 

Some actual milling in progress. You may notice that this is not a chassis component.

 

It didn't all go right - it took me some trial and error to get the milling parameters sorted. The top one has too much depth of cut.

 

Bang up to date - after two rounds of fettling the bogie pivot and wheel arches, it finally managed to get through the horrible curves of South Yard's pointwork. The O2 will also be my first South Yard appropriate steam loco.

 

The body is rather more advanced than shown here but I will save that for another posting when I get back onto that part of the build.

Edited September 28, 2023 by D869
photos AWOL

[-missy-]

Fantastic work Andy.

 

Those CNC mills come in very handy don't they! Invest in a replacement spindle, it gives you far more flexibility when selecting cutters.

 

J

[D869]

Thanks Julia, I think it was your blog that first put the idea of a CNC Proxxon into my head. It's just taken me quite a few years to make it happen.

 

I will probably keep the mf70 as is for a while. My tooling improvement  'to do' list is already long and distinguished.

[-missy-]

There are lots of mods possible on the MF70. I'm currently looking into the possibilities of a motor swap to try and get the spindle speeds down a bit.

 

The only other suggestion worth mentioning, especially with the Proxxon, is backlash on the table. Backlash on a CNC is bad news.

 

Julia. 

[richbrummitt]

Good to see this come to fruition. Looks like you've already done as much with yours as I have with mine. I'm interested to know what cutters you are using, software, speeds and feeds &c. I could PM you but the information will be useful to others I'm sure.

 

The usovo spindle upgrade is the one I went for. Easy to fit but about €100 so not impulse purchase, plus you have to get some collets too. Mine was a christmas present last year. It does open up the market for cutters, as Julia stated, where many are 4 or 6 millimetre shanks. If you need the more expensive one let me know. I bought the one with the extra adapter part because the serial number on my machine was high enough to require it according to the website but I actually didn't so it is spare.

 

[D869]

Cheers Rich.

 

(non techies look away now)

 

Speeds and feeds... mostly 40mm per minute when cutting. About 14K RPM for the 1mm cutter, slower for a 2mm cutter. I stick to about 0.2mm depth of cut which means 2 passes for 10 thou... takes maybe 5 minutes per pass for a typical part but when you consider the overall planning and setup time then it's not that big a deal.

 

My 1mm cutters are from eBay - there is a chap selling a brand called Cobra Carbide made in the US. They have a 3mm shank. No idea if it's a good brand or not really but I tend to think that the US is probably better than some unknown stuff from China. So far since I've had the MF70 I've snapped one Proxxon and two Cobra 1mm cutters (including non CNC work). The 2mm cutter is from the Proxxon set. I used that on the spacers.

 

Controller - I started with an Arduino Uno and a cheapo (and quite suspect) clone of the Protoneer CNC shield and A4988 stepper drivers. This was running GRBL and got me up and running but I wanted backlash compensation and as you know it can't do that.

 

I looked at running GRBL on an Arduino Mega - this has a version with backlash compensation but it can't use the same pins used by the CNC shield so that was no good unless I ditched the CNC shield.

 

Then I found the Marlin firmware and put this on the Mega. It can do backlash compensation and can be set up to use the pins required by the CNC shield. I'd need to dig around a bit to find exactly what I needed to change to make that happen. It's more focussed on 3d printing than CNC milling and its G code is a bit odd but it does the job. It also has the possibility to use an LCD display and keypad and run jobs from an SD card but I don't do that.

 

There is an rough version of UGS that I use to send G code to Marlin from the PC. See here https://github.com/winder/Universal-G-Code-Sender/issues/1080

 

Upstream of that I use QCAD for the drawings and dxf2gcode to produce the G code. The latter does the job, at least for simple profiling and drilling work but documentation is very sketchy so figuring out how to get it right is tricky. It is free though.

[D869]

15 hours ago, -missy- said:

There are lots of mods possible on the MF70. I'm currently looking into the possibilities of a motor swap to try and get the spindle speeds down a bit.

 

Yes the Proxxon spindle speeds don't go down far enough for my liking especially when using 2 and 3mm drills. I haven't looked into changing this myself. I did find a thread elsewhere about the MF70 motor and speed controller. It won't answer your question but it will give you at least some idea about what you are dealing with. https://www.model-engineer.co.uk/forums/postings.asp?th=140490

 

I must admit that the Model Engineer thread and some info from Rich rather made me doubt the long term robustness of the MF70 and this doubt has probably influenced my thinking somewhat.

 

One of the reasons for my lack of postings on here recently was the acquisition last August of a bigger lathe to live in my shed. I can now run bigger milling cutters and generally chew more metal off things by doing the heavier grade milling on there. I was also running into the height limit on the MF70 for some jobs (drilling mainly) so moving to the lathe has sorted that too. The Proxxon is now 'CNCed up' so I can keep it for jobs like milling 2FS loco bits which is what I intended it to do in the first place.

 

The only other suggestion worth mentioning, especially with the Proxxon, is backlash on the table. Backlash on a CNC is bad news.

 

I found some CNC controller firmware that does backlash correction (see my posting above) and it seems to work pretty well. I found about 0.08mm of backlash on both the X and Y axis on mine, some of which is from the axis leadscrew and some probably from the shaft couplers that hook up the stepper motors.

 

One thing that I forgot to mention last night is that I've also found that the size of cut tends to be a bit more than the cutter size. I first found this when manually milling the frames for the shunting tractor. I don't know if this is down to vibration, the cutter flexing or being slightly off axis but it does happen and it's not down to backlash. After doing the O2 bogie frames and measuring how they came out I added a fudge factor to the cutter diameter that I told dxf2gcode and the main frames came out pretty spot on.

[Izzy]

6 hours ago, D869 said:

 

One thing that I forgot to mention last night is that I've also found that the size of cut tends to be a bit more than the cutter size. I first found this when manually milling the frames for the shunting tractor. I don't know if this is down to vibration, the cutter flexing or being slightly off axis but it does happen and it's not down to backlash. After doing the O2 bogie frames and measuring how they came out I added a fudge factor to the cutter diameter that I told dxf2gcode and the main frames came out pretty spot on.

 

There will be a tendency for a slot/end mill to cut oversize depending on the depth of cut, and the flexibility and length of the cutter. This is especially so when facing the cutters into the cut ( which of course is the recommended direction to avoid backlash grab/jump) - the action will 'pull' it sideways into the material. So the deeper the cut and the longer the cutter the more it will tend to flex. The rate of cut relative to these will also have a bearing.

 

Izzy

[D869]

Thanks Izzy. so paraphrasing a lot, there are many variables involved so doing a test piece with the same speeds, feeds etc and then finding the 'fudge factor' by measuring it seems like the right thing to do.

 

The metal being cut is another variable I think - I found different levels of 'fudge' with brass and phosphor bronze. A bit less with brass IIRC although I wasn't being 100% methodical when I did the brass.

[Izzy]

Yes, and softer material can grab the cutting edge more than harder. As with a lot of lathe work, roughing cuts and a finish one , or just several light cuts, are often best for optimum and repeatable sizing ( where multiples are being produced). Obviously a lot depends on the size of the machinery being used. 
 

Izzy

[justin1985]

I'm really intrigued by the discussion of the CNC conversion of the MF70. I recently got one of these mills with similar kinds of things in mind for loco frames etc. But in practice so far all I've made are PCB webs of sleepers for board joints etc. 

 

I had taken a look at the Arduino CNC conversion options for the mill - if nothing else because they seem much simpler to set up given the way most other reasonably priced options involve parallel ports. Have you used commercial stepper conversion mounts like the ones that seem widely available from China on ALiExpress? 

 

Justin

[richbrummitt]

I used some that I found on eBay from a seller in German who I think was making them or sourcing locally.  Andy made his own along the same lines. 

 

10 hours ago, justin1985 said:

Have you used commercial stepper conversion mounts like the ones that seem widely available from China on ALiExpress? 

 

Justin

 

[D869]

Hi Both,

 

Yes Rich is correct. I made my own mounts from aluminium, very much along the lines of the ones available from China/eBay etc. The available ones seem to come and go.

 

I didn't particularly want to make my own but I did want my mounts to allow me to revert to manual operation quickly and easily and I couldn't find anything else to fit the bill.

 

If you don't need to be able to swap and change like me then there really isn't much reason to make your own but if you do want more details of the ones that I made then drop me a PM and I will be happy to share the details.

 

My steppers are NEMA17 45Ncm 2A jobs from eBay. I was uncertain whether these would have enough torque but they seem fine. I'm feeding them 24V and in practice the whole drive system draws about 0.5A in total when running (I only have two axes powered so far).

 

Regards, Andy

[D869]

Thoughts are now turning back to the O2 body. I'd assembled enough of this to check clearances around the motor etc but then left it to one side while I got the chassis built and running.

 

Making use of the hard-won lessons from building 2mm scale track and reading about other people's efforts, the obvious next step was to deploy the 80W iron and start taking the body apart again...

 

 

Seriously, one side was very slightly further back than the other. We're talking about a few thou but it was noticeable when looking at the overlaps at the end where the bunker rear and the tank fronts will join. Having thought it wasn't too bad when I first assembled the body it has been bugging me so I decided to bite the bullet now before the misalignment is replicated in the cab front and rear panels.

 

The photo above also shows the N-Brass bits used so far - the two layer footplate and valance etch and the inner carcass for the side tanks and bunker. The tank inner etch had solid sides which didn't seem like the best idea either for soldering or for weight distribution (most of the tank sides are aft of the rear driving axle) so the CNC miller was used to turn most of it into holes. I changed my mind a bit between one side and the other...

 

 

The bottom edges were also filed down to reduce the overall height - the N-Brass kit seems to have the tank tops more or less flush with the top of the sides but photos of the O2 show the tops being a little lower with the sides extending up to form a slight lip.

 

As seen in the previous post, the outer tank and bunker sides were milled to the outline traced from the GA drawing in the Wild Swan book on Adams locos. Here is a side next to the N-Brass G6 etch for comparison...

 

 

The O2 is a tad longer and the cab (at least on the Callington locos) is 6 inches lower than the G6. Some O2s had taller cabs.

 

The observant may have spotted a problem here - how can I build a longer loco using the N Brass G6 footplate etch? Answers on a postcard

 

At the close of play the body is back together although I decided not to refit the rear spectacle plate for now.

 

 

Next step is to get the front spectacle plate done... which also needs to match up with the top of the boiler so that will also mean getting the boiler pitch sorted and probably deleting that cross-piece between the two tank tops.

Edited October 1, 2023 by D869
pics AWOL

[D869]

A bit more progress. On Friday I cut out the front spectacle plate and a few other odds and sods and tack soldered them to the body. Now the boiler (brass tube) can be tried in place and the thing starts to look a bit more locomotive like.

 

At the moment the back end of the boiler is held up with Blu Tack. I intend to make the boiler removeable for painting so I need to come up with a proper arrangement to keep this in place - not something I've ever really 'registered' when reading about other people's loco builds. How do other people stop the boiler from dropping onto the motor?

 

I might still have another go at the spectacle plate to get a closer fit to the boiler top.

 

I think the next job is to tackle the smokebox. This is complicated by the presence of rivets on the real thing, the front ones following a sort of horseshoe shape around the boiler and smokebox saddle. The starting point for my plan was to steal Ian Smith's rivet press idea...

 

But whereas Ian made his to fit his Peatol lathe, I wanted mine to go on the MF70 which meant making the punch, limit adjuster and return spring concentric so that's what I did. The punch has a hole down the middle so that a piece of 2mm steel rod can be held in the MF70 spindle to keep the thing in one place while the workpiece is moved around by the XY table... which means... CNC rivet embossing... well, CNC assisted anyway.

 

Here is the thing in use. Mine has no lever - pressing down on the adjuster with a couple of fingers seems to be sufficient pressure. My workholding arrangement could be neater.

 

 

... and without any brass or digits to impede the view...

 

 

The press is smaller than I intended because that was the only bit of 1/2 inch aluminium (or any other metal) that I had to hand. It's just big enough for the O2 bits but I will need to make a new 'block' if I want to do any bigger panels in future.

 

Below is my first go at the smokebox front rivets in 5 thou brass. My plan is to solder another 5 thou layer behind this and then cut around the outside manually. There are a few dummy rivets at the bottom to show me where the bottom corners should be plus one right in the middle. I'm still a little uncertain whether my first attempt will get used - the rivets do tend to make a slight crease in the metal - probably not a big deal on the smokebox front but maybe more of an issue for join lines on otherwise flat surfaces.

 

That's another place where I could use some advice - how do other people avoid getting creases along the line of rivets?

 

 

Edited October 1, 2023 by D869
pics AWOL

[Caley Jim]

56 minutes ago, D869 said:

At the moment the back end of the boiler is held up with Blu Tack. I intend to make the boiler removeable for painting so I need to come up with a proper arrangement to keep this in place - not something I've ever really 'registered' when reading about other people's loco builds. How do other people stop the boiler from dropping onto the motor?

Have you room to put a strap across somewhere under the tank tops to support the boiler?  Either that or fit a narrow 'shelf' on either side, under the top of the tanks, for the boiler to sit on.

 

As far as the spectacle plate is concerned, I always make it project below the level of the boiler with the rear of the boiler butting up to it.

 

Can't help with the crease problem with rivets, In CR days everything was flush!

 

Jim

[D869]

Thanks Jim. Yes I think that some sort of bracketry attached to the inside of the tanks is the most likely answer but I'm open to other ideas - it's just one of those things that has never occurred to me as a question that needs to be answered when scratchbuilding a loco... which is probably because I haven't scratchbuilt a loco until now.

[richbrummitt]

The pannier tank I'm building atm has removable tanks and boiler. There are pegs on the back of the tanks that fit in holes on the front of the cab; one each side. This removable portion is the only bit that is original Farish and the front fixing screw has been retained to hold all in place at the front end. 

[D869]

The smokebox on the O2 is now together. This proved to be a tricky job with lots of starting over - 2 inner wrappers, 2 outer wrappers and 3 fronts. Getting it all lined up on the boiler and then cleaning up the join around the front was also very tricky but it's done now. The door was turned up on the lathe, finishing off with a hand graver.  At the moment it's not fixed into place.

 

 

Here is my dodge for holding the front still while getting the thing aligned and then soldering into place. This was front No 2, which wound up being removed because I'd put the rivets a tad too far out and they wound up right on the edge once I'd filed the edge flush.

 

 

To finish the topic started by my question from the previous episode, I added a couple of brackets from phosphor bronze inside the tanks. They are not very elegant but they are out of sight and it has been handy to be able to adjust them to get the boiler to sit upright. Here's a pic of the body upside down to show how the brackets support the rear of the boiler. I think I need to add a positive 'back stop' to prevent the boiler from being pushed too far back and possibly damaging the paintwork.

 

 

The front splashers are looking like being the next job.

 

Thoughts are also turning to the cab roof. This has a rib all around the edge plus another that goes across the centre from one side to the other. At the moment I havent figured out a good way to do do this, so suggestions would be welcome.

Edited February 17, 2020 by D869
photos went AWOL

[Caley Jim]

17 minutes ago, D869 said:

Thoughts are also turning to the cab roof. This has a rib all around the edge plus another that goes across the centre from one side to the other. At the moment I havent figured out a good way to do do this, so suggestions would be welcome.

I've done this by cutting thin strips of 5thou brass shim with a craft knife, then tack soldering one end to a corner of the cab roof, hold the strip taught along the side of the roof and solder the other end, then solder the rest, finally cutting the excess of.  For the curved front and rear edges you can gently curve the strip ti fit and repeat the process.  The centre strip need to be pre-curved and cut to length then held in tweezers while soldering in place, again tacking it at one end first, then the other and adjusting each end to get it in the right place.  Solder paint is your friend for making a quick joint, otherwise you need to tin everything first.  Don't expect to get it right first time!

 

HTH

 

Jim

[bécasse]

In 2FS I would seriously consider using straightened out staples to form each rib, they would need preforming in the case of the three crosswise ribs.

[Izzy]

There is a very good thread in the 7mm section about building an 02 from a Connoisseur kit. Page 15 deals with the cab roof and it seems some gained sliding hatches. I’d also use cut brass shim strip flooded with solder then scraped away to finish to suit. At the edges this may need to be edge on to appear correct looking at photos.

 

Izzy

[D869]

2 hours ago, Izzy said:

There is a very good thread in the 7mm section about building an 02 from a Connoisseur kit. Page 15 deals with the cab roof and it seems some gained sliding hatches. I’d also use cut brass shim strip flooded with solder then scraped away to finish to suit. At the edges this may need to be edge on to appear correct looking at photos.

 

Izzy

Thanks. I think that Calbourne on the IoW has the hatch but as far as I can tell 30225 did not... although shots of the roof without steam obscuring the view are not exactly commonplace.

[D869]

Is it just me? Can anyone else see the photos I posted yesterday or are they gone for everyone?

 

The posting last night went very slowly and two copies appeared when it eventually finished. I deleted the second one and all seemed OK, but today the pics have vanished for me.

[Ian Smith]

21 minutes ago, D869 said:

Is it just me? Can anyone else see the photos I posted yesterday or are they gone for everyone?

 

The posting last night went very slowly and two copies appeared when it eventually finished. I deleted the second one and all seemed OK, but today the pics have vanished for me.

I can't see the photos Andy.

Ian