Rebuilt Bulleid West Country 3D CAD designed & mft in 3.5 in

[twombo]

Excellent point Roger, regarding machining difficulty! I am wondering if some form of grinding process or. Possibly, diamond, tooling, would be possible. If only for the bearing surfaces of points to achieve a. ‘flat’ surface! New processes demand, yet, more new technologies!

On a positive note. Once. The proper Mechanical. Fit is achieved the only wear factor of immediate concern is that of associated parts. Here, being, union links, slidebars , etc! Combination levers, Etc.

My dentist uses a lot of diamond tooling! I suspect expensive based on those prices! Such beautiful parts, fortunately require, but a few areas to be fettled into shape.

Mick

[Roger]

May 3, 2020 19:48:48 GMT twombo said:

Excellent point Roger, regarding machining difficulty! I am wondering if some form of grinding process or. Possibly, diamond, tooling, would be possible. If only for the bearing surfaces of points to achieve a. ‘flat’ surface! New processes demand, yet, more new technologies!

On a positive note. Once. The proper Mechanical. Fit is achieved the only wear factor of immediate concern is that of associated parts. Here, being, union links, slidebars , etc! Combination levers, Etc.

My dentist uses a lot of diamond tooling! I suspect expensive based on those prices! Such beautiful parts, fortunately require, but a few areas to be fettled into shape.

Mick

Hi Mick,
I'd be surprised if Carbide tools wouldn't cut it, I've only found one hardened Stainless Steel ball that I couldn't drill with carbide PCB drills. That doesn't mean it's necessarily easy though, just possible.
Grinding will cut anything, but you really don't want to do that unless absolutely necessary unless you've got the kit.
However, 3D printing loses some of its appeal if it's a complete pain to machine. Casting might be preferable if it's really painful to machine the prints.

[Oily Rag]

All this  is fascinating, model engineering with new applications and techniques.  I look forward to seeing these parts machined/ground etc  and how this is done and fitted up in the frames and on-wards to steam tests and then operations.

I can recall over the past 35 years reading letters to the editor in  ME mag the  expressions of  disgust regards LASER parts, even investment casting being the decent into evil. Let alone DRO and even Metric was evil. Crikey there was some ignorant sods with lazy thinking.

Keep the updates rolling in.

[masahiraoka]

thanks Roger et all for your comments and questions and my apologies for the delay in responding

the crossheads were printed in 316 in a layer thickness of 0.1mm if i recall correctly and cost approx. 50 UK pounds each.

and yes stainless steel is difficult to machine but not impossible as Roger indicates. the following article from the British Stainless Steel Assoc. clearly sets out the requirements for successfully machining stainless steel and interestingly it states that the light weight machines tools that are typically found in our hobby are not robust enough.

That said all will be revealed when Andrew begins machining these components. if this proves to be too difficult we will have to revert to the lost was casting process that Adam Cro utilises.  What we're trying to achieve is eliminate the 3D print in wax required for casting. If we can use 3D stainless steel prints it will, as Darrell notes, take us truly into the 21st century with regard to manufacturing processes. 

some model engineers may disagree with this philosophy but as a professional engineer i'm very excited by the possibilities offered by 3D CAD and 3D printing with regard to reproducing the detail of the full size locomotive and at any model scale we care to choose.

ciao MArtyn



General principles of machining stainless steels

www.bssa.org.uk/topics.php?article=192

Introduction

The most common and hence most frequently machined stainless steels are the austenitic types, such as grades 304 (1.4301) and 316 (1.4401). These are characterised by their high work hardening rates and poor chip breaking properties during machining. This article covers the important issues that influence the successful machining of these steels.

Machine and tooling rigidity

When machining stainless steels it important to ensure that there is no dwell or rubbing caused by machine vibration or tool chatter. Machines must be 'substantial' and capable of making the deep cuts needed in machining austenitic stainless steel without slowing down the set feed or surface speeds. Small training or 'hobbies' lathes and milling machines intended for machining mild steel, brasses etc. are unlikely to be substantial enough for the successful machining of stainless steels.

Machines should not be prone to excessive vibration in the machine bed, drives and gear boxes or at the cutting tool or its mountings. Large overhangs of tool shank out of the tool box should be avoided. The distance between the cutting tip and toolbox support should be as short as practicable and the shank cross section as substantial as possible. This can also help in dissipating heat away from the cutting faces. Arbours for supporting barrel milling cutters should be stout as short as possible. The arbour supports should be as close as possible to the ends of the cutter to provide maximum support.

Some 'squealing' as the metal is being cut is not unusual, but can indicate that the tool may be wearing and need replacing.

Tool materials

Either high speed steel (HSS) (wrought or sintered) or cemented carbide tools can be used for machining stainless steels.

High speed steels

Either tungsten or molybdenum HSS can be used. These are particularly useful in machining operations involving high feed and low speed machining operations where there are variable cutting edge stresses induced from complex tool shapes.

The tungsten types (eg T15) can be useful for their good abrasion resistance and red hardness. The molybdenum HSS are more widely used, M42 being useful for applications such as milling cutters where a good combination of hardness and strength are required at lower cutting speeds. M42 has better hardness than grades like the more common M2, but may not be as tough however.

If the tools are prone to edge chipping, use a tougher grade, eg M2, M10 If tools are burning, use a higher red hardness grade, eg M42, T15 If the tools are wearing, use a more abrasion resistant grade, eg T15

Cemented carbides

Cemented carbides are normally used for machining stainless steels where higher speeds or higher feeds than those that can be produced using HSS are required. Either disposable insert or brazed-on tips (where lower cutting speeds can be tolerated) can be used and are composed of either tungsten carbides or a blend of tungsten and other metal carbides, including titanium, niobium, and chromium. The carbides are bonded with cobalt. The 'straight' tungsten carbides grades are used for machining austenitic and duplex stainless steels and the 'complex' carbides are used for machining martensitic and ferritic family grades.

Coated carbides have the additional benefit of improved wear resistance and resistance to breakage. Consequently they are capable of higher cutting speeds compared to un-coated carbide tools.

The wide range of carbide tools available usually means that machining trials are needed to get the optimum machining characteristics for specific situations.

Tool geometry and sharpness

It is essential to keep the cutting tools sharp when machining stainless steels. Careful grinding and honing of the tool faces to give accurate and sharp face angles is important. This helps optimise:

    tool life

    finish, accuracy and tolerances

    productivity between regrinds

and reduce:

    tool breakages

    power requirements

Re-sharpening should be done as soon as the quality of the cut has deteriorated.

Machine grinding using properly dressed wheels, free from glazing, is preferable to hand grinding to get the necessary accuracy of tool geometry.

Correct tool geometry is important for minimising swarf build up on the tool faces.

Swarf build up can also result in increased machine power requirements and poor surface finish on the machined surfaces.

Tool relief angles must be flat. Concave relief faces can result in tool chipping or breakage due to the reduced support of the cutting edge.

Where possible the tool faces should incorporate chip curlers or breakers as austenitic stainless steels are prone to forming long spiralling turnings that can easily wrap around the tool and tool post. These can easily become entangled around the tooling and are difficult and time consuming to remove. In extreme cases the tool can become jammed by entangled turnings.

Lubrication and cooling

It is essential that cutting fluids are used when stainless steels are machined. This is due to the combination effects of the deep cuts and high feed rates needed to overcome the effects of work hardening, and the low thermal conductivity of the austenitic stainless steels, restricting the flow of heat away from the machined faces. Overheating stainless steel surfaces, characterised by the formation of heat tinting colours, during machining can impair corrosion resistance and so must be avoided. If formed pickling the surface can be used to restore corrosion resistance on the finished part. Overheating can also result in distortion that can be difficult to compensate for or correct.

The lubrication provided by cutting fluids also helps reduce tool wear and wash away the machining swarf.

Generally cooling is more important than lubrication with faster the cutting speeds and so high cutting fluid flow rates are normally used when machining stainless steels.

Either mineral oils or water soluble emulsifiable oils can be used. Minerial oils are more suited to severe machining operations with heavy loads at low speeds or where HSS tools are being used. Emulsifiable oils are used for machining at higher speeds with carbide tooling.

Mineral oils

Sulphurized, chlorinated or sulpho-chlorinated mineral oils can be used with additions of up to 10% fatty oils for machining non-free machining grades. Paraffin is used to dilute these oils, in oil/paraffin ratios between 1/5 for high speeds and light feed work to 1/1 for slower speed and heavier feed machining.

If excessive wear is being experienced, consider using greater dilutions. If the cutting edge is tending to burn, consider reducing the dilution.

Emulsifiable oils

These oils are diluted with water and provide better cooling than the paraffin diluted mineral oils. If extreme pressure (EP) emulsifiable oils are used, more sever machining operations can be supported. It is important that dilution is done by adding oil to water, not water to oil so that the correct form of emulsion, with the right lubrication and cooling properties, is formed.

After machining all traces of the cutting fluid should be removed from the surface so that the stainless steel surfaces can self-passivate. Under certain circumstances acid passivation should be considered.

Further information on the selection of cutting fluids for machining is available in the BSSA Training Note No9 'Machining Stainless Steels'

[masahiraoka]

Roger

correction to my earlier post - the layer thickness in the 3D print is 0.05mm not 0.1

regards Martyn

[Roger]

Hi Martyn,
Thanks for the additional information, the layer thickness is very impressive.

It sounds like you're using the same material that our other Forum member had, that fits the description of the machining difficulties exactly.

I'd strongly suggest that you attempt to machine something before going any further, this is not an easy thing to do. I doubt if you'd ever cut a full depth thread in one of the parts, in fact I'd avoid threads altogether if you can do that. If not, you will almost certainly have to go considerably over size on the tapping size to avoid breaking the tap. However, you don't need much thread depth in the part, although that might cause the bolt to strip if you go too far.

I'll be very interested to see how you get on. It's a great process, it's just a pity it results in something that's so hard to machine. I'm sure they will find better materials in the fullness of time.

[masahiraoka]

Roger
we're avoiding tapping the stainless steel absolutely wherever we can.
regards Martyn

[92220]

May 4, 2020 3:41:18 GMT masahiraoka said:

t
ciao MArtyn



General principles of machining stainless steels

www.bssa.org.uk/topics.php?article=192



Machine and tooling rigidity

When machining stainless steels it important to ensure that there is no dwell or rubbing caused by machine vibration or tool chatter. Machines must be 'substantial' and capable of making the deep cuts needed in machining austenitic stainless steel without slowing down the set feed or surface speeds. Small training or 'hobbies' lathes and milling machines intended for machining mild steel, brasses etc. are unlikely to be substantial enough for the successful machining of stainless steels.



Hi Martyn



That is a very interesting statement in that text you got off that website. However, I would have to strongly disagree with their statement that "Small training and 'hobbies' lathes and milling machines ...... are unlikely to be substantial enough. When I was an apprentice draughtsman at Wynstruments Ltd., 90% of our work was in EN58B stainless steel, which equates to today's 316 stainless. The only machines we had were Myford Super 7s and one ML7. The milling machines were Senior M1 and a Senior Major......typical hobbies machines(!). We had absolutely no trouble machining stainless. It's just a case of having a VERY sharp tool. When I machined my loco wheel castings, which were investment cast in 316J stainless steel because I needed the strength for the scale section spokes, I tried using carbide tools but couldn't get them sharp enough at home, so I reverted to HSS. It machined the wheels perfectly, and very easily. My lathe is a Myford S7, so I would take what they print with a very big pinch of salt!! I must admit that if I had read that before I had machined my wheels, I would have been very worried though!! With properly sharpened HSS tools, it is perfectly possible to machine 316J stainless steel to tolerances of +/- 0.0005". I've done it, quite easily. Printed stainless would almost certainly be a totally different matter though. Carbide tools can be extremely sharp, these days, so as Roger suggests, they should be able to be used. 

By the way....VERY interesting thread. Keep it coming!!! Some lovely draughting to.

Bob.

[masahiraoka]

Bob
thanks for your comments regarding matching stainless steel, they give me great confidence we’re on the right track, (excuse the pun!)
regards martyn 

[John Baguley]

I was on the Home Machinist forum last night and someone has just started a thread regarding their experiences of machining 3D printed stainless. It may be of interest:

Machining printed stainless steel

John

[Roger]

The post John has posted is a most interesting useful document. I don't think you can use experience of machining 316 Stainless to machining these printed parts. Machining and tapping 316 isn't as much of a problem as this.

I'd suggest getting some polished Carbide Inserts for the turning operations, those have much sharper edges than General Purpose inserts which will probably rub and need a lot more force to begin cutting. That makes machining something to an accurate size much more difficult.

[92220]

Hi Roger.

I fully agree with you about machining printed stainless. I wasn't referring to machining that. It was the fact that the article was saying that stainless, in general, couldn't be machined on a 'hobby' lathe, which, frankly, was just not true. The article wasn't referring to printed stainless. it was referring to generally machining stainless steels. It also says, quite correctly, that HSS can be used on stainless. It was just the fact that they said 'hobby' lathes couldn't be used, that I had issues with. They also say that deep cuts are necessary when machining stainless. That is also not true. With a newly sharpened HSS tool, you CAN take a 0.001" deep cut on a 316 stainless bar. I've done it many times when I worked at Wynstruments. As I said, 90% of our machining was in EN58B (316 stainless), done on Myford S7 lathes.

About the polished carbide inserts you mention....can you point me towards a supplier, and what should I look for? I can find tips advertised, that are polished, but they are noted to be for machining aluminium, so I'm guessing the have a much greater top rake than for steels.

Bob.

[simplyloco]

May 5, 2020 8:11:57 GMT 92220 said:

Hi Roger.

I fully agree with you about machining printed stainless. I wasn't referring to machining that. It was the fact that the article was saying that stainless, in general, couldn't be machined on a 'hobby' lathe, which, frankly, was just not true. The article wasn't referring to printed stainless. it was referring to generally machining stainless steels. It also says, quite correctly, that HSS can be used on stainless. It was just the fact that they said 'hobby' lathes couldn't be used, that I had issues with. They also say that deep cuts are necessary when machining stainless. That is also not true. With a newly sharpened HSS tool, you CAN take a 0.001" deep cut on a 316 stainless bar. I've done it many times when I worked at Wynstruments. As I said, 90% of our machining was in EN58B (316 stainless), done on Myford S7 lathes.

About the polished carbide inserts you mention....can you point me towards a supplier, and what should I look for? I can find tips advertised, that are polished, but they are noted to be for machining aluminium, so I'm guessing the have a much greater top rake than for steels.

Bob.

Hi Bob
I got mine from JB Tools. I haven't used HSS for months...
John

[92220]

Hi John.

Thanks for that info. I'll follow that up.

Bob.

[Roger]

May 5, 2020 8:11:57 GMT 92220 said:

Hi Roger.

I fully agree with you about machining printed stainless. I wasn't referring to machining that. It was the fact that the article was saying that stainless, in general, couldn't be machined on a 'hobby' lathe, which, frankly, was just not true. The article wasn't referring to printed stainless. it was referring to generally machining stainless steels. It also says, quite correctly, that HSS can be used on stainless. It was just the fact that they said 'hobby' lathes couldn't be used, that I had issues with. They also say that deep cuts are necessary when machining stainless. That is also not true. With a newly sharpened HSS tool, you CAN take a 0.001" deep cut on a 316 stainless bar. I've done it many times when I worked at Wynstruments. As I said, 90% of our machining was in EN58B (316 stainless), done on Myford S7 lathes.

About the polished carbide inserts you mention....can you point me towards a supplier, and what should I look for? I can find tips advertised, that are polished, but they are noted to be for machining aluminium, so I'm guessing the have a much greater top rake than for steels.

Bob.

Hi Bob,
Ah, I see what you were getting at now. Agreed, small lathes are certainly capable of machining  Stainless Steels or pretty much any thing else really. Rigidity is always a help, so parting off Silver Steel with a wide blade on a Myford is going to be a struggle.

I use the ones they sell for Aluminium if nothing else is listed, they don't seem to have excessive top rake. Clearly the edge is more fragile due to its sharpness, but they work well on Stainless Steel, Phosphor Bronze, Bronzes, Aluminium and Plastics. In fact any situation where a razor sharp edge is an advantage. I keep one pair of facing and turning tools with general purpose inserts, and an identical pair with the polished inserts ready to go in the rack, they're so useful.

[uuu]

I have "aluminium" grade inserts, which do have an aggressive top rake. But they're fine for other metals, if used gently. I'm a bit nervous with brass - not usually a problem just taking a shaving off, but any kind of deep cut is asking for the tool to be pulled in.

Wilf

[92220]

Hi Roger.

Thanks for the explanation. JB Tools, that John mentioned, do the polished carbide bits, so I will get on to them for a selection. Maybe I will be hooked on carbide turning tips. You certainly changed my mind on carbide milling cutters. I hardly ever use my HSS cutters now!!

Bob.

[Roger]

May 5, 2020 9:16:16 GMT uuu said:

I have "aluminium" grade inserts, which do have an aggressive top rake. But they're fine for other metals, if used gently. I'm a bit nervous with brass - not usually a problem just taking a shaving off, but any kind of deep cut is asking for the tool to be pulled in.

Wilf    

I don't suppose there's any benefit from using them on Brass in any case, that turns fine with general purpose inserts.

[masahiraoka]

Thanks Roger, Bob, John and others for your useful comments on the joys of machining stainless steel, I'll pass these onto Phil and Andrew. I believe that we will be able to successfully machine the 3D printed parts but time will tell.

I thought I'd get back to the topic of the thread this time regarding the boiler.

Boiler

• The conventional drawing is a "mirrored" extract of SR drawing number W5190 of the boiler for the West Country.



• I purchased this almost certainly professionally made boiler which quite closely follows the full-size design from a UK dealer in 2009.  The boiler came with a boiler hydraulic test certificate stating a working pressure of 90 lb/sq in. but no information as to the manufacturer of the boiler.



• The serial number stamped on the boiler is "LL-DW 4311". I'd very much appreciate any help anyone can give me with identifying who might have made this boiler. Knowing which boiler maker made it would greatly assist in me securing approval for the boiler from the Australian boiler inspectors.

• At the moment the scale boiler design is simply a 3D CAD "copy" of this existing boiler .



• In due course we'll design a 100 lb/sq. in. AMBSC (Aussie code) / CE approved boiler with tapered barrel, Belpaire fire box, combustion chamber with water tubes and 3 element radiant superheater.

• The current boiler doesn't incorporate a combustion chamber as can be seen in the sectioned screen shots below

[Roger]

Just a thought.... do you need a combustion chamber if you have three radiant superheaters?