Tom Mallard’s Workbench L&B in 7mm scale, CR 828 in 7mm, GWR Saints in 4mm

[adrian]

The castings are made directly from 3D printed waxes and are largely as hoped for, though I was expected a less matte finish. I am particularly pleased with the motion brackets which are nice and flat, and the coupling pockets.

They are very nice and crisp. Did you 3D print them or was that all handled by the casting company? As you mention I'd have expected a slightly more glossy finish based on other work I've seen. Is this a subtly different brass composition or have they been finished post casting. I'm aware many jewellery casters use various surface treatment processes after casting.

 

[Tom Mallard]

They are very nice and crisp. Did you 3D print them or was that all handled by the casting company? As you mention I'd have expected a slightly more glossy finish based on other work I've seen. Is this a subtly different brass composition or have they been finished post casting. I'm aware many jewellery casters use various surface treatment processes after casting.

They are certainly nice and crisp, and so they should be based on the cost of the prints. It is also of course a function of eliminating the mould making step and the subsequent small loss in resolution and chance of wax deformation during handling. It’s an expensive approach but in my opinion for small duplicated and handed parts is very worthwhile.

The prints are by Precision Wax, the casting by Slaters if that’s of any use.

Investment castings seem to show highly variable surface finish depending on the investment selected by the company, brass composition and post processing. Slaters assured me that a gentle process is used to remove the investment.

I’ve used 5 or 6 different casting companies over the years. Slaters are close to the best so far and nice to deal with. Sanspareil had the best finish by far but are much too opaque for me to be happy dealing with on a regular basis. They are also the only two companies who seem to understand the importance of the work we send them, and our expectations of the results.

I didn’t have an opportunity to view the waxes prior to casting as I had them sent direct to the caster, but their resolution capabilities didn’t give cause for concern about surface finish. However there does seem to be seem creep or wander evident in the castings which can only be a result of the prints not being totally consistent left to right.

It’s my first set of finished castings following an unsuccessful test enquiry with a Scottish firm, but based on results so far should work successfully. The learning curve is steep, if including learning to use a new piece of solid modelling software, but I got there in the end. It’s quite likely this process will be used again...

Tom

 

[Tom Mallard]

Substantial effort has been placed on modelling these cab fittings for the SR condition Manning Wardles. They are critical to the appearance of the cab after all. Some information has been from the works drawings of the Southern LEW engine, and observation of on line resources that suit the condition that YEO and EXE ended up in.

In terms of the time taken to model these patterns, it is possible that it has been equialent to making physical patterns, though the quality and dimensional conformity is likely higher.

I understand that not all of the detail will cast at the resolution modelled, but if it does, then so much the better. For practical reasons, several of the finer features (such as the lubractor tap handles) will be left off and added later. These fittings come out fairly small at under 10mm in any direction and assuming I have them printed in wax this will be undertaken at the highest available resolution in an effort to maintain surface finish.

I will doubtless need to clean and refine the surfaces here and there where the castings are unpainted.

Hopefully the outcome demostrates the viability of using 3D printed waxes as an alternative to handmade patterns.

Lately I have cleaned up some of my early castings from the first batch to use as masters for some parts. These are with the caster along with some 3D prints of the pony truck wheels which were omitted from the first run. We can then see if the shrinkage allowance was about right, and where degradation of surface finish or dimensional stability might occur.

Best regards

Tom

 

[AdeMoore]

Majorly impressed by the attention to detail and the time and effort going into this build.
Amazing looking forward to more.
Cheers
Ade

 

[Giles]

Quite remarkable workmanship! Beautiful!.......

 

[Tom Mallard]

Thanks for the very kind remarks.

The models are looking much more recognisable with the addition of tanks and a rear spectacle plate. Much careful fitting ensured that the tanks were aligned properly, with the cab sides, boiler and smokebox saddle. The saddle fitting was quite nerve wracking as the saddle edges sit on the frames (or will do) so setting the level of the boiler and tanks.

I realised too late that I have yet to attach boiler bands located fore and aft of the dome. The tank tops aren't attached yet as some detailing is better done without them in position.

A lot of tiny bolthead details were machined up as the Southern had chosen to replace the more easily modelled rivets attaching the cabside to the tanks with bolts... Likewise with the rear of the cab, more little boltheads represented for the lamp bracket fixings and so on.

The duckboards for the cab floor should be resolved soon, or fitment could be troublesome later on if it isn't already.

Best regards

Tom

 

[Tom Mallard]

Hi again, it's been a while.

Working on TAW to bring it up to YEO and EXE development position. It will be a case of spot the difference to really tell at the moment, but I can say that there are no valance reinforcement plates beneath the cab opening, a square edged smokebox front and a unique arrangment of ventilation holes on the cab rear by which each engine can be readily identified (or not)... It will be modelled as running circa grouping/early 1920's.

Some constructional features are visible in this view of the uncovered tanks. These are all etched parts so I was able to include very conventiently positioned recesses and bend lines to aid assembly. The pin prick holes on the inside of the tanks are for locating oil pots and on the right hand one, the sanding operating linkage.

I'm pleased with the boiler fittings so far, but some more detail is to be added to the domes and a lot more polishing and removal of abrasive marks.

All are turned from brass which in this case was nicer to work with than nickel silver and I am told that the cap of the chimney should be brass in any case, so this is correct. As usual, boiler fitting are extremely distinctive things, and these are perhaps the most characteristic I've modelled, particularly the gently tapering dome and the Manning Wardle pattern of chimney cap.

Best regards

Tom

 

[Tom Mallard]

It is difficult to convey the time it takes to make valvegear properly, but from the last post to this, it's more or less been the main task. All the valvegear is machined in two planes to reproduce as much of the relief as possible. None of it is finished yet - theres lots of finishing of the surfaces to come. The naming of all the parts is most peculiar compared to Walschaerts' type, yet the parts occupy more or less the same location.

The connecting rods are being kept mounted on their workplates as there's still some final work to do. With the coupling rods, they will need their oil pot tops adding.

The domes have crept in again, as I've added the rolled edge to these three, and some partially machined wheel castings have been included too.

I am unsure (what a surprise!) whether to use free machining stainless steel, or nickel silver for the tyres. Answers on the proverbial if you have any insights.

If I remember, I'll refer back to this post when there's a rolling chassis and we can see where everything went.

Best regards

Tom

 

[Hobbyhorse]

Lovely work Tom, with the tyres not a lot of difference between machining the two materials. I've got stainless steel tyres on one of my locos and reports from a few customers that those are a bit light footed with them, my preference is Nickel Silver which I was very lucky to obtain a quantity of very free cutting years ago.

Simon

 

[Mikemill]

Tom

Your domes are impressive, I assume they are turned on the lathe could you explain how you form the curves where the dome meet the boiler barrel.

Thanks


Mike

 

[Tom Mallard]

Lovely work Tom, with the tyres not a lot of difference between machining the two materials. I've got stainless steel tyres on one of my locos and reports from a few customers that those are a bit light footed with them, my preference is Nickel Silver which I was very lucky to obtain a quantity of very free cutting years ago.

Simon

Thanks Simon, that's just the kind of information I was looking for.

Tom

Your domes are impressive, I assume they are turned on the lathe could you explain how you form the curves where the dome meet the boiler barrel.

Thanks


Mike

Mike, it is done by hand though I know of at least one other who has a fixture where much of this is machined off.

The profile is turned into the dome down to the top of the boiler, then I remove a lot of material from the sides using a burr mounted in the lathe, and hold the dome and arbour against this. I find fine control is easier with the burr completely static axially. So, the bulk of the material is ground off until close to the right shape, then files of elliptical section are used to blend the surfaces and remove tools marks. I work at it until it looks right, so having a little extra material on the diameter to work with is useful. The most useful tool is light as I use the reflections coming off the dome to see where there are disruptions in the blending of the surface. You get a feel for it in the end.

I hope this makes a bit of sense; the image shows stages of some partially completed work.

Tom

 

[Hobbyhorse]

Tom, this is probably the fixture you are referring to. The cutter goes into the lathe with the bit to be machined mounted onto the spinning fixture.

Simon.

 

[Tom Mallard]

Tom, this is probably the fixture you are referring to. The cutter goes into the lathe with the bit to be machined mounted onto the spinning fixture.

Simon.
View attachment 146241

That's pretty much what I had in mind. Richard Hersey has an adapted version which allows for a variation in the position of the follower and a corresponding change to the displacement of the cut relative to the skirt. These devices take a lot of guess work, worry and possibly time out of forming the skirt of chimneys and domes.

 

[Overseer]

That's pretty much what I had in mind. Richard Hersey has an adapted version which allows for a variation in the position of the follower and a corresponding change to the displacement of the cut relative to the skirt. These devices take a lot of guess work, worry and possibly time out of forming the skirt of chimneys and domes.

While they can speed up the removal of metal there are very few domes or chimneys with a constant radius around the base. I thought about making one when described in MRJ years ago but decided that it couldn’t replicate the prototypes I want to make. Finishing with files doesn’t take very long but care is needed.

 

[Susie]

Dear Tom,
Beautiful and inspiring work as usual. Could you please explain your method for pantograph milling when machining items (such as the vibrating links) in two planes? Do you machine in one plane and file the other profile, or machine one plane first and then turn the part machined item 90 degrees to work the second plane - if so, how do you support the material and keep it in registration with the patterns? Sometime I might be making a NSWGR 55 Class with Southern valve gear which has a plethora of items like this.

 

[Tom Mallard]

Dear Tom,
Beautiful and inspiring work as usual. Could you please explain your method for pantograph milling when machining items (such as the vibrating links) in two planes? Do you machine in one plane and file the other profile, or machine one plane first and then turn the part machined item 90 degrees to work the second plane - if so, how do you support the material and keep it in registration with the patterns? Sometime I might be making a NSWGR 55 Class with Southern valve gear which has a plethora of items like this.

Susie, thanks for the kind comment.

I machine a blank in the vertical plane to include the curves and blending of the bosses or forks, using an appropriately small milling cutter between the 'prongs' if practical. It is made close to the correct overall length. The blanks are then mounted, using solder, in the second plane to a work plate and packed with suitable scrap material to provide support as necessary. I thought for a while about how to hold work in position, and eventually realised solder would work best for me.

The work plate also means I can cut past the back face of the part and not mark the table.

The work plate is mounted on the work table of the pantograph milling machine and the blank to be machined is aligned with the template on the other table, albeit rotated through 180 degrees of course. A datum is selected, usually at an extremity, and the work table positioned to begin the cut. Hole centres are located from the template during the process, since each time I must reset the datum of the next blank to be machined.

That's it! sort of...

It is a bit of an overview as I am 'writing something' for eventual publication on my approach to model making.

Best regards

Tom

 

[Susie]

Thanks Tom. I thought that solder would come into it, and is what I have been considering. The difference is that I just think about it and you do it!

 

[Tom Mallard]

Some harsh pictures of recent work. I've made a lot of tyres lately (over 40 including spares), and they're a bit more straightforward than expected though still not simple to do. The castings for the drivers weren't to the standard I expected from direct to cast brass 3D prints (a different supplier) but the carrying wheels are much better.

The tyres are of 306 grade stainless steel, which turns very nicely if a slow enough spindle speed is used. The bulk of the turning was undertaken on a friends much larger toolroom lathe or I think I'd still be drilling out the middles.

The blanks were finished off at home, with attention paid to the correct face appearance with the little bevel on the corner. After removing most of the material, the tread profile started with a form tool, but I found that this chattered a great deal, so ended up grinding a simple version with just the angle of the outside face of the flange ground in and traversed at 2.5 degrees on my compound slide at slow rpm. This was much better. I bonded the centres in with araldite (the full strength type) and wondered about electrical insulation for a while. I will be using paxolin centres on the driving wheels and for the carrying wheels an insulated axlebox with a split axle since I would like the face of the wheels to not have evidence of the insulation material visible.

The rods have had various oil pot tops added and cotter pins for the connecting rods which are all turned and machined with the hex flats represented. Just as an exercise, the fillet around the base of the hole in the middle of the connecting rod is trepanned using a ball ended cutter. There's not much to say about the curved link in the last picture other than it will be a working representation with the vibrating link (short forked link) being able to slide up and down on trunions right through the groove in it. There is still final finishing to do on most of these parts.

Onwards and upwards with the axles and axleboxes...

Best regards

Tom

 

[Podartist79]

Incredible work Tom.
A great pleasure to watch the build through these pages!
Neil.

 

[Tom Mallard]

Thankyou Neil.

What a palaver. The hornblocks are finally in, but not without some work to machine appropriate axleboxes from ColPhos phosphor bronze. This is likely overkill, but in terms of machining is much more amenable material than the usual pinkish stuff that is the opposite.

The hornguides are a casting directly from a 3D printed wax, as using an adapted casting as a pattern for subsequent casting introduced a deformed casting which I wasn't keen on working with in what is always a fraught exercise in any case. The plan in the end is have sprung suspension, using Exactoscale hollow grub screws through the hole in the top and little coil springs set into the axleboxes. I hope the springs I get are going to be stiff enough.

Taw's bogies (as they are called by Manning Wardle) follow the shape of the prototype with cast front, rear and axle keeps. The axleboxes (not shown) have been machined from Paxolin for insulation purposes and utilise a Phosphor bronze insert for the bearing.

I noted with significant interest the announcement from Lionheart!

Best regards

Tom