A bit of time in the shed

[-steves-]

Firstly I have been about on here now and again, but mainly reading and catching up on threads, a couple of blinding threads that have had me very interested. I will hopefully post up on those later if I get the chance, but I have been very very busy with one thing and another,

I came up with an idea part way through my wild rose project and wondered now I have DRO's on my mill and lathe, would I be any better at getting things any more accurate. So I took the stock below and started tinkering.

But what will it be???

[-steves-]

I will be interested to see what this does turn out to be. Besides all the workshop stuff I have added another little project to my list as well. There has been a short series in Model Engineer about a simple and realatively crude "Dairy Engine". An oscillater with a vertical boiler, meths fired on a little trolley. I found a Unit Engine kit lurking as you do, ideal for a bit of fun. So I don't have to make the engine, just a pulley and a pot boiler. I even found some old raw Mamod flywheel castings I bought from them years ago. These will make the wheels I hope once fettled and machined.

Have fun!!!

I will be interested to see how you get on with the DROs, i have no plans myself but will look forward to seeing how you progress.

Sounds like a fun project you have on there, looking forward to seeing some pictures on the forum?

The DRO's I can confirm worked perfectly, life has never been so easy. The little project is in fact finished and I am posting up the finished article

[-steves-]

So here it is, a couple of days in the shed and I have come up with a working chassis. Total cost of a chassis will stand me at around £50 for parts. I showed it to my step father and his first comment was "how much will I sell it for", lol. It's somewhere between a GRS chassis and an Essel chassis, based on neither but has similarities to both. It seems to be a success, so with that in mind, I will probably try an 0-6-0 chassis at some point with a drive crank, aim high hey, lol If that's a success then I guess I can build myself any size electric chassis depending on what body I want to build it for.

A quick thanks to those that have given engineering advice in the past as this was all invaluable during this build. I could not have done this without your advice and guidance with simple little things like centering a circular piece of metal under a mill, simple yes, but without it, all sorts of mistakes.



The wheels are all the exact same size despite how they may look in the picture


I will mill the next lot of motor bolt holes as I bodged this one by using an electric drill and expending the holes, they do need a slot for adjustment, but not a problem and I will know to add them next time while I am making the chassis sides.


Motor mount and gifted motor from my step father


Axles milled at the ends to make quatering so so easy and it works very well. The gear was adapted with the nylon cut off and a brass insert knurled to go inside to make it fit under the motor giving me the option to run the chassis as either 32mm or 45mm.


Phosphor bronze axles bearings with steel cranks and con rods. the bolts were also made made as I needed a plain shaft for 2mm and threaded for another 2.5mm, works perfect


The chassis up and working, but with round cranks, which were hack sawed down to give them some shape. Set at 45mm gauge



Chassis now sprayed up and set to 32mm gauge.

[FWLR]

Thats actually a very nice job Steve. Like the way you have done the wheels to be gauge adjustable. Well done mate. Now waiting for the body to be built episode....

[-steves-]

Thats actually a very nice job Steve. Like the way you have done the wheels to be gauge adjustable. Well done mate. Now waiting for the body to be built episode....

LOL, thanks Rod. The body for this one will likely be a Whisbech style tram as I have always fancied one of those. I part done the plans for one a while back, I just need to finish the plans off and then start a build, but in wood, now that will be interesting as it's quite some time since I worked in wood, I think the last time was when I was into RC boats in my teenage years, lol

I am considering making some more of these and taking them to the local club and seeing if anyone wants to buy one, it might give me some hobby money, not a lot, but every little helps

[ge_rik]

Anything ex Great Eastern will certainly float my boat - even a shed on wheels! Looking forward to seeing it develop....

Rik

[GTB]

So here it is, a couple of days in the shed and I have come up with a working chassis.

Well done. I've been wondering how long it would take you to realise that the skills to build a rolling steam chassis were the same as those to build one that runs on elektrickery.........

You aren't the first and won't be the last model engineer to have to move a hole. Welcome to the club.

I took a night course in machining many years ago and the teacher was quite definite that drilling holes by opening them up with successively larger drills was not the way to ensure accurate placement.

I found out quickly when I built my first chassis that he was right, but I still see articles in the model press advocating drilling rods and sideframe bearing holes together and then opening up the bearing holes.

I fitted a DRO to the mill last year and have found it works much better than counting turns on the handwheels. I always drill rods and sideframes separately, but the ones for my current loco build were the first drilled with the DRO and required the least amount of work to get a smooth running chassis of any locomotive I've built. Probably because I couldn't lose track of the handwheel count this time.......

Regards,
Graeme

[tom_tom_go]

Interesting this, so even large holes in metal should only be drilled once rather than successive smaller holes first?

[tom_tom_go]

I always drill pilot holes but Graeme mentioned he has been taught otherwise?

[FWLR]

It all depends Tom. Pilot holes are just that, a pilot hole, to help with locating a bigger bit. But mostly I would use engineers blue and then a centre punch when ever I drilled holes, there was no danger of the bit wondering off then.

[-steves-]

I used to centre punch all the time, but found that can be inaccurate when very fine tolerances are required, such as chassis side frames and con rods. If absolute accuracy is not required, then I use a centre punch and then final drill size up to about 7 to 8mm, after that, as much as I loathe to do it, then I will use a step drill to get there, however I have found the more drill bits you use, the more inaccurate the centre of the hole can be, not every time, but sometimes it can be monumentally out if you have used a number of drill bits. If it's for a chassis side or con rod, then holes up to 5mm I just use the appropriate size spot drill in the mill and go straight through as it's generally just sheet metal, all set up on the DRO's, now that is accurate! After 5mm, I pilot the hole with a 5mm slocombe drill and then use the final drill as I have not had to drill anything much larger than that so far.

Since doing these last few projects I am learning very fast that accuracy in some scenarios is absolutely essential, not just close or even really close, but "absolute perfection is required" [Edit: Close enough to be right first time with no fettling]. For this reason I can understand why people use laser cutting, sure, it takes away one type of manual skill and the satisfaction that brings of doing it by hand, but brings another skill through computers and the satisfaction of a dead accurate piece of work. Me personally, I am more happy with the manual way of doing things, I am enjoying the skills I am learning and the gratification that brings, kinda had enough of computers to last me a life time (he says, tapping away on the keyboard, lol )

The 0-6-0 chassis has now had plans drawn up so I may make a start on that in the next few days, time dependant as we have quite a bit of family time planned too.

[-steves-]

Hi Steve,
I would like to point that there is no such thing as "absolute perfection". ALL engineering works within tolerance band widths. For example take computer disc drives, the read/write heads actually fly, they are aerodynamic and even when hard disc drive discs were 14" (356MM) diameter the heads flew nanometres above the surface of the disc. The Queens Award for Technological Achievement citation for that project read something along the lines of: " this has achieved the equivalent of flying Concorde at Mach 2 some 12" (300MM) above a ploughed field". Every component in that drive had a tolerance bandwidth. I know I was there and have the gold cufflinks as testament. I spent much of my time as did every other designer and engineer on the project checking what were called tolerance stacks for each sub assembly and assembly. Machining of base castings was done under extreme controlled conditions down to a temperature (within a small bandwidth) and that had to be accounted for. Humans were not allowed inside the controlled area once a machine programme had started yet they still had tolerances!

It has been said over many years in the model engineering field that the worst steam engine builders are toolmakers, not a derogatory comment at all. Because these guys always strived for perfection and that was never the intention of the original masters of the art.

Its a contentious issue but it all comes down in the end to experience, gathered in depth knowledge of the subject and most of all designing out the problems at the paper stage and making allownces for adjustment as the model comes together. Stan Bray a well known author and builder actually uses and advocates eccentric bushes in his motion rods so that adjustments can be made. He is certainly no slouch look at his portfolio from the simple to the complex. You can chnge your "absolute perfection" by picking the thing up with your warm hands or moving from shed to central heated lounge and its enough to seize a mechanism.

Ian. I think you have taken my words a little too literally, I am of course aware that even a 4mm drill bit does not drill a 4mm hole, and that under a microscope actually looks nothing like a round hole, perfection really doesn't exist, however the word does. I think the point I was trying to make that making a drilled chassis side, drilling corresponding con rods and cranks drilled right, takes small tolerances between working and not working. I have tried by hand to dot punch and drill on a pillar drill having marked everything out and to say it needed "some fettling" afterwards is an understatement, big files were required all over the place, that much that the bearing actually moved inside the hole I have to open it up so much. Suffice to say that attempt actually went in the bin, but that was quite some time ago that I tried that. The chassis that I made above required no fettling of con rods, wheels, bearing, cranks etc, it all ran when just bolted together, I was as surprised as anyone, but also very pleased

[GTB]

I always drill pilot holes but Graeme mentioned he has been taught otherwise?

The operative phrase is 'if you want accurate location'...... Which is what the teacher was getting at.

A normal jobbing twist drill makes a hole, but it won't be round in thin material and not necessarily in the place you want it. Especially small drills which are the most flexible.

Ever noticed that a normal drill bit often produces a wide spiral of swarf and a narrow one? That is because it is cutting more on one side of the hole than the other. If it has just started cutting it be moving off line, if the hole is deeper it will probably be generating a curved hole.

I use pilot holes when drilling large holes and I may open up the hole in several steps, but I don't do it where the hole has to be placed with any accuracy.

I'm building a steam loco at present and I recently drilled a hole that way in the cab floor to mount the lubricator. It could be half a mm out and it wouldn't matter.


Moving on.........

The coupling rod holes were another matter and they were located, spotted, drilled with a single drill to minimise the drill wandering off line, then the DRO was used to move to the next location.

I like my wheelsets to be removable, so the frames were milled for axleboxes using the spacing of the holes in the rods for reference. The crankpins and their mounting holes are another source of error that has to be controlled and I use a drilling jig for crankpin holes.

The sources of variation in all of this are in the cutting tool runout for each operation (drills, milling cutters, taps and dies), and measurement error in the quartering jig, DRO, digital calipers and micrometer.

Given all that, I consider I did well to only need to ease the leading crankpin bushes by 0.02mm or so to get the chassis rolling smoothly.


All physical processes are statistical and accuracy and precision are two different things. The commonly used example is to think of an archery target. Accuracy is how close an arrow is to the centre of the target. Precision is how close an arrow is to the other arrows. Just to make life even more interesting, the smaller a measurement is, the greater the spread in the precision.

I don't think I've ever seen tolerances quoted on a model engineering drawing. From my perspective, the measurement on a drawing is analogous to accuracy, tolerances if quoted, are a form of precision.

Regards,
Graeme

[FWLR]

Just carry on Steve with how you are doing things. I think you're doing an absolutely brilliant job and it just shows what you can achieve without all the modern stuff, though they do have there place, skills like your's are disappearing fast....

[GTB]

The chassis that I made above required no fettling of con rods, wheels, bearing, cranks etc, it all ran when just bolted together, I was as surprised as anyone, but also very pleased

One can't ask for better results than that......

I forgot to ask earlier. You mentioned you milled flats on the axles to set the quartering on the cranks. How did you machine those?

Regards,
Graeme

[-steves-]

The chassis that I made above required no fettling of con rods, wheels, bearing, cranks etc, it all ran when just bolted together, I was as surprised as anyone, but also very pleased

One can't ask for better results than that......

I forgot to ask earlier. You mentioned you milled flats on the axles to set the quartering on the cranks. How did you machine those?

Regards,
Graeme

As Ian said, a very good question. I spent ages trying to work this one out, I thought about rotary tables and the like, then realised that a simple solution was best. I took a square bit of brass, drill through it from one end to the other at the thickness of the axle, then on the side drilled a hole and tapped it for a grub screw. Simple pop the axle in sticking out of both ends, mill one end, take it out, turn it around 90 degrees and mill the other end, simple and works perfectly every time. The only down side is you need one tool for each size of axle, but no real biggy.

[-steves-]

That's an interesting question Graeme. I have often wondered about milling grub screw flats for flycranks. I drew the conclusion that under the circumstance of them NOT having to be exactly 90 deg (R.H. by convention leading), one axle could be milled both ends using the rotary table, accurate enough I would think but only mill one flat on the other axle leaving the remaining flycrank to be set to give best running. The other conclusion I came to was that in future all flycranks and the like mrequiring securing to round shafting of any sort would have two grub screws set about 90deg apart unless there was suitability for a roll pin.

The other way is to leave the axles over long, centre the outer end and mill the flats indexing along, then machining the axle to length.

I hope the post above clarifies how I have been doing it, really simple but it works

[-steves-]

A bit more time on the shed, the pictures do not show the con rods, but I made those as well and tried it as just the 6 wheels and again, works perfectly, no fettling required. Spot drills and DRO's are a massive improvement on the accuracy I used to get. The flycranks will be filed as before so they are not round and resemble something with a fly weight.

I have not tried the motor drive side of things as I ran out of 4mm stainless steel so I am waiting for my local metal shop to get that in so I can build the 4th axle for the dummy motor drive. The actual motor drive will be the same as the 0-4-0 chassis previously made.

[GTB]

A bit more time on the shed, the pictures do not show the con rods, but I made those as well and tried it as just the 6 wheels and again, works perfectly, no fettling required.

You're on a roll.........

I wondered if you'd used that sort of jig for milling the axles, as I made one recently while I was waiting for some parts to turn up in the mail. Not an original design in my case, as a friend who works in the ride-on scales made one a while ago for milling keyways.

Now the $64 question, how are you keeping the tapped holes for the grub screw and the crankpin in line from one crank to the next?

I was thinking of making a jig based on the one I use for drilling crankpin holes in wheel castings, to hold the cranks in a fixed position while drilling for the grub screw.

Regards,
Graeme

[-steves-]

First a bit of an update. The dual gauge 0-6-0 chassis is now working, all be it with the con rods in their raw state that still need a good fettling down to take the proper shape, however the theory was all good and the thought became a working reality. Very happy with both the 0-4-0 and the 0-6-0 chassis, I already have an order for couple so that should cover some of the initial outlay costs.






32mm gauge


45mm gauge