Member postings for Will Robertson

Hi David,

Thank you very much for all the information - very interesting and helpful. I hadn't thought of using a Swiss file on a bore. Have you any advice on how to choose a file fine enough and good enough?

Does this work with both ferous and non-ferous metals?

Edited By Will Robertson on 09/08/2012 21:53:04

Hi Mike,

Thanks for correcting the link.

Edited By Will Robertson on 09/08/2012 21:50:57

Hi Clive,

It's good that Cobalt actually refers to the composition of the steel in this case.

Thanks for your advice about sharpening - am I right in thinking that tools like this should never be allowed anywhere near the dark grey carborundum grinding wheels used to shape HSS tools? Are white grinding wheels always a finer grain?

When you say 'diamond stick' what should I look for in buying one? I've a set of diamond stones but the manufacturer didn't specify the grain and they don't seem to hone to a very fine finish.

The fiberoptic job sounds difficult - small and fine alignment!

I was having a look at some of the suppliers AES had mentioned and trying to work out where to get materials to make the piston and valve spools. Looking through the 40 page catalogue of one at the moment - wish they'd state composition as well as code numbers for the steels.

Will

Wow. I have to admit that I've never seen such a large collection of boring tools. I'd thougth that most folk just had a handful or two to cover different sises.

For the detachable head boring tools, what are the different heads for? I'm guessing there are heads for screw cutting, finishing, roughing and internal shoulders but I'm not sure.

I've found Ifanger - I think I missed them because they're "internal machining" not "boring". They list Internal machining ASB, ECS, DK, GWS, TRG, etc. but I'm not sure how to work out what those codes mean (some are clearly specialised but I'm not sure which are just simple boring and bore finishing).

Are they easy enough to sharpen?

Will

Hi Clive,

That would be interresting to see a photo of your boring tool collection. I've seen the toolholders before but it would be very interresting to see the boring tools you use - there are a lot out there so knowing which are good would be a big help in chosing one.

Sorry to hear about the flanges. It gives the rest of us encouragement though knowing that even experts get things wrong sometimes so we're not alone when things don't go according to plan.

The same climatic changes seem to have messed things up for ice climbers and beekeepers alike.

I'd never understood that the mechanisms for supercedeing a queen were so sensitive.

Will

Hi Clive,

Thank you very much again - am I right in understanding that you're very particular in choosing the best quality boring tools?

I had a look at the Brütsch Rüegger catalogue - are your tools from the Coromant series (sorry - I didn't see tools marked as Cobalt - maybe I'm misunderstanding)?

Very good to heat that you finished the bore with an indexable carbide tipped tool -

Have you ever built a Stirling engine? I remember the cryogenics engineer at Sheffield a Stirling Engine he had made at the end of his training and I was always in awe of how a gas-tight seal could be made with such low friction.

Great that the bees are doing well despite the volatile weather.

Will

Hi Clive,

Did you bore the cylinders of your engine using an HSS boring bar or a boring bar with an indexable carbide or fixed carbide tip? Am I right in guessing that a normal boring bar would be fine for cylinders of this sise and that a between centres boring bar only becomes necessary for longer cylinders?

Will

An enormous amount to reply to... I'll try my best to reply to a few mounts now and a few tomorrow.

Great that there's such strong interest in cylinder boring.

A reason given to the move to lighter 5.56mm ammunition was that it was intended to injure not to kill - an injured soldier caused a lot more problems for the enemy than a dead one. I've never had any interest in boring rifles - I think they were part of my life for long enough that I was happy to leave them behind. As Clive said, it all comes down to the effect you want the weapon to have.

Hi Pailo,

be good to hear a bit about your boring machine. I think boring machine is beyond the means of most folk on here so we have to do what we can with lathe and milling machine. Some of the boring heads for milling machines do look fairly substantial though.

Hi Nathan.

My ice screws have seen good service and hopefully will see more in the future. They're mostly bought form one or two high quality manufacturers now (poor quality screws are a big problem on steep ice) but in the early days they were home made from mild steel then heat treated to improve hardness. I once had 3 men hanging from one of them on a route on Ben Nevis but I dread to think what might have happened under shock load... thankfully nylon dynamic ropes have a lot of dynamic...

Hi AES,

The names of some Swiss suppliers would be very useful - I'm in canton Schwytz - I am finding it difficult here and I don't want to take up fiends' time putting small orders through their businesses. When buying anything of any sis from the UK I ask UK suppliers to supply it ex. VAT (exports outside the EU are exempt from VAT). Maybe once I've recovered enough to use a lathe again I can have a look at some of the some of the things that are causing you problems.

Ni Neil,

Interested to hear about your use of a vacuum cleaner - may help a lot of folk for whom flood coolant isn't available.

Hi Clive,

Thank you very much again for all your help. I thought I was the only person who counted and categorised bumble bees in my childhood - good that other people find it fascinating and I'm learning a lot from you. In Scotland it was fairly common to have hives up in the mountains over the summer to make Heather Honey then bring them down to the valleys for the winter so that the bees didn't die in the mountain winters. Thanks for the photos of the engines.

Will

Yup - that's a good idea - I'll try to do that - this topic has gone a bit off-topic.

Back on topic - did you drill then ream or drill then bore before lapping the cylinders? What did you use for the piston? (Would I be right in guessing a cast iron piston for a bronze bore?)

Let me know how the drilling goes with some water based coolant squirted liberally into the hole during drilling with the cobalt drills. My theory is that water based coolants have a much higher specific heat capacity and thermal conductivity than cutting oil and so should hopefully help to carry heat away and reduce local heating, reducing work hardening - not sure how strongly this works in practice though. We used to adjust the bottle so that the coolant came out as a jet rather than as a spray.

Will

What are people's favourite finishing tools for doing final turning, facing or boring cuts?

Pretty much anything will do for hacking off metal but different authors seem to suggest different shapes of HSS tool to get a good finish on the final cut. Harold Hall's books suggest one shape of finishing tool while the articles in Model Engineer by Tubal Cain (I'm not sure who this is an alias for in Model Englineer) suggest a different shape of shaving tool to give a good finish. It may vary depending on the material - I'm not sure.

Other people seem to use indexable carbide tips for the final finishing cut.

Would be great so see what people's favourite finishing tools are. Photos welcome!

Hi Clive,

Sorry to hear about the two hives you lost over the winter. I've often wondered if some form of small low-power thermostatically controlled electric or gas heater could be used to warm the inside of the hives at the coldest times and help the hives survive over the winter. Do you give them fondant over the winter (very popular in Scotland)?

Am I understanding "1000 grade" correctly - is that ISO/FEPA grit P1000 with particle diamiter 18.3 micron? (I'm having to improve my understanding of this sort of thing.) Is bronze hard enough that there's no need to worry about the abrasive embedding itself in the metal surface?

http://www.pts-uk.com look great - wide range, metric and they supply small quantities. Many thanks.

You'll know much more about drilling stainless than me. One thought did come to mind though - in the first shop I worked in we didn't have flood coolant on the pedestal drill so used to squirt on coolant from a bottle sold to spray water onto plants. It seemed to help a fair bit when drilling harder metals.

Re. me I'm due to be allowed to drive again next week. Will be on crutches for a while longer. Typical to survive over 10 years ice climbing without injury then to have all this trouble as the result of a simple everyday lifting accident!

Will

Very interesting to learn more about the bees. I share your doubt that the bees in Northumbria could have lived in genetic isolation for a hundred years. There's a lot of interest in 'pure' Scotts Pine seed - a notion of limited validity since there haven't actually been that many generations of Scotts pine since the last ice age.

The cocking handle on the SA80 thankfully got replaced in the SA80 A2 - a big relief for my ribs. I remember a lot of nostalgia for the SLR... before my time.

I couldn't find www.pts.uk.com - maybe there's a typo in the URL? Really interested because most model suppliers are only imperial but I see metric as the way forward for new engines.

When you lapped the bores of your two cylinder engine did you use a set of cylinder laps/break laps?

Hope the swarms are under control for now.

Will

Hi Clive,

How are things going with the double expansion engine? It sounds great.

Let me know where you got the hex head M2 screws - I've been trying to find some M2 or M2.5.

Apologies for my silence - I was kept in hospital a little longer than I'd expected and I'm banned from working or driving for 2 weeks - only allowed to sit or stand for max. 2 hours per day. The internal damage turned out to be fairly bad. I'm using the pause to do some background reading and watch some YouTube videos on techniques.

Thanks for mentioning Mullermachines.com - I'll keep an eye on them  and pass them on to some friends who are sometimes in the market for second hand equipment.

Hope the bees are coping OK with the weather.

One mystery I never worked out in the military was how they designed the cocking handle for the original SA80 - it always looked like some chunk of scrap that someone had pulled out of the bin to temporarily use on a prototype. Used to keep getting caught on webbing and accidentally cocking the weapon...

Will

Edited By Will Robertson on 19/07/2012 19:08:03

Hi Clive,

Unfortunately, the situation's turned out to be fairly bad so I've been preoccupied trying to find the right surgeon (a very good specialist arthroscopic knee surgeon) to give me the best chance of a good outcome and avoiding arthritis in 5 to 10 years.

My attempts to secure the use of a suitable lathe have stalled - there is one but getting hold of the busy owner is difficult. In absence of a suitable lathe I'm pushing ahead with buying some of the small bits and pieces needed.

Hope your engine goes well - is it two cylinder single expansion or a double-expansion animal?

Will

Hi Clive,

Sorry to be slow to reply. Unfortunately an accident (not machine tool or mountaineering related!) has meant I've been in and out of hospital over the last few days.

I live in the German speaking part and I struggle away in German (my French is better...). A friend has a small but busy factory so I think he'd be willing to put my small orders for steel together with his much larger orders. For other metals I've no idea what to do yet apart from getting help from a friend's garage.

Great to hear about your work in instrument making - my first job was as a junior technician at a university helping making mountings for equipment for laser optics. (Not much precision involved there because all the precision alignment was done using the lasers.)

I might have a go at restoring an existing engine before starting work building my own - I've got a Stuart S50 where someone made a real mess of the machining - I bought it on Ebay and I reckon if I re-bore the cylinder and replace the damaged parts I can get it running (I'll use Tubal Cain's set of articles for guidance).

I haven't tried that trial cut on the big chunk of mystery brass yet - I need to get access to a better lathe (the small lathe could turn it but I don't think it would be safe).

In one interview I remember being thrown a lump of metal and told to identify it. It took me a while to work it out but when I eventually did they seemed impressed - Monel alloy.

Will

I did manage to get my paws on a 25mm and a 50mm standard ( both labeled +- 0 μ ) yesterday and - sure enough - it turns out that in ideal conditions my cheap digital calipers do give a better than advertised accuracy

(PS - I remember using military compasses marked out in Mils - a special drill if you broke one of them - the glowing paint was radioactive. Microchips can never match the magic of the Strowger exchange.)

Edited By Will Robertson on 09/06/2012 21:22:00

Hi Clive,

Thank you for your advice. The idea of the steel bore was because of the scrap metal I've got at the moment - thanks for confirming that it's inside-out. Terryd's advice about how metals wear also suggests bronze cylinder and steel piston.

I've no idea what brass scrap I've got (or even if it is brass) - just that it looks and feels like brass and has a similar weight - I'll hopefully get use of a large enough lathe to do some trial cuts on it in the next few days. Is using scrap in this way a good idea or should I concentrate on getting the correct sort fo bronze from a supplier? (I'm over in Switzerland because of work so finding suppliers is more difficult than in the UK.)

The advice from you and from others has been very valuable - much more valuable than what I've found in books - are there any books you'd recommend? (I've bought several books but they all seem limited and I'm running short of cash and space for them!)

Will

Hi Clive,

Sorry about the delay.

My present steam supply is 1.2 bar saturated steam (low pressure but I hope it'll do for now - I'll maybe try higher pressure and/or superheating in future). If I say a maximum force on the piston of 30 Newtons (working expansively the average will be less) that gives a piston radius of 8.92 mm - so I thought a piston radius of around about 10mm would be OK. I'm not sure about how to work out the most appropriate stroke so I guessed based on other models - maybe 20 to 40mm to give a cylinder and crank of manageable sise?

For my first attempt at the cylinder I'll start with an unknown piece of scrap stainless steel tube 27mm bore and 3.7mm wall thickness or another of unknown not-so-stainless steel of 20mm bore and 5.2mm wall thickness. Rough cuts with carbide and finishing cuts with better quality carbide or HSS honed with diamond stone. For the piston a lump of unknown scrap brass. If my attempts to machine the unknown scrap steel fail I'll try to get the SAE 303 and 316 steel you recommended in another thread. For the piston seal a grove packed with plumbers' PTFE tape (to be upgraded to the PTFE yarn or graphite yarn from Reeves you mentioned or the woven square section PTFE you recommended - I think Sealrite Limited might supply this) or a ring machined from solid PTFE.

That's the initial plan...

Will

Thank you for such carefully thought out advice - much better than what I've found in books.

Hi Clive,
Thank you very much for your advice again. I'd originally thought about i) Machine a cylinder. ii) Machine a piston with grove to fit the cylinder. iii) Machine then split a piston ring from a block of PTFE (or similar) to fit both. - is this a suitable approach?

I can't get my paws on a face plate but I can get use of a 4 jaw chuck. I hadn't considered using the milling machine for boring - I'll give it more thought. Where did you get your lapping stones and mandrel / honing tool? What specification of bronze and cast iron do you use?

Hi NJH,
The sise will depend on the stock I can get (no casting skills or facilities). I'll choose materials based on advice from more experienced people. I haven't used machine tools for 10 years so I'll make and test prototypes of all components using scrap for practice.
Have access to a fairly good lathe and milling machine owned by a friend. An enormous challenge is to design the engine myself based on ideas from John's series on puddleducks and existing engines and bearing in mind thermodynamics and reading about André Chapelon's and Corliss's principles.

Hi Ian,
Thank you for your advice about the low coefficient of friction of cast iron. Is there any particular grade of cast iron you'd recommend (I'm not sure what would give the best balance of machinability, corrosion resistance, etc.)?

Hi Terryd,
Thank you for your advice about about the hard metal wearing more than the soft - I hadn't realised that - it changes my understanding of things a lot. (Makes sense as well when you think about someone cutting class with abrasive paste and a coper wheel.) Thank you also for your advice about not honing/laping the piston and cylinder together - I've seen this recommended in several books but your advice seems better. Thank you for helping me to understand things with such clearly explained advice.

Hi mgj
How many piston rings would you generally use in a model steam engine (guessing 2 or 3)? I don't know if the lathe I'm borrowing turns parallel but I should be able to calibrate it so that it does. Thanks for advice about using coolant and mentioning a floating reamer - I didn't know about them. Thanks also for advice about using a milling machine for boring - I've never done that before - any more advice would be interesting. Please could you explain "and to the size specified by the ring gap is what is needed." a little more. Unfortunately, I don't have a good enough knowledge to understand this.

Three other general questions that have been confusing me:

Am I right in thinking that there are two fundamentally different approaches: i) Make piston precisely fit bore with an oil grove in the piston to help it seal. and ii) Make piston a looser fit and rely on piston rings or packing to achieve the seal.?

Dissimilar metals for piston and cylinder seem to be essential (ex. cast iron) - but - different metals have different coefficients of thermal expansion - what should I do to avoid making an engine which turns smoothly at room temperature but ceases up under steam due to different components expanding by different amounts when heated by the steam?

What is best for piston rings - graphite tape, plumbers' PTFE tape, a ring machined from PTFE stock or something else?

Thank you very much again!

To add to what Ian said: stainless steel is also used extensively in medical autoclaves - here the temperatures and pressures required aren't anything like as high as in a power station but large changes in temperature and high temperature gradients are very frequent. Stainless steel seems to cope with this fine - biggest clinical autoclave I've seen had a 4 cubic meter capacity with a steam supply from an oil fired steam plant and it ran for decades.

I suspect that in the past stainless steel was avoided because of limitations in welding technology in smaller workshops - modern TIG technology has changed things a lot.