Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 51967 times)

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #240 on: April 08, 2020, 10:12:59 PM »
Hi Andrew,hope you are well.  Re your bushing query......Due to lockdown I have to rely on memory :headscratch:  On our recent rebuild of our SCC roller (since sold :'() the slot was filled with a cast block fitted from one side and a bolt from the other, the block was tapered. I do have some pics but only one vaguely shows it. (you will have to zoom the pic) There is no snifter on the roller but the block allows for a second rod.  I have no pics to hand of our SCC tractor but if I rcall correctly it is the same.  Sorry I can't be more help.       Terry

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #241 on: April 10, 2020, 11:05:46 AM »
..........hope you are well.

So far so good, although I'm not overly worried about the virus. I'm obeying the rules to the letter, but if I do get it the chances are I'll survive. If I don't I won't be in a position to worry about it. Anyway, I've been here before; when I was a few months old I had Asian flu, which killed 1 to 2 million worldwide.

I wonder why Burrell would have gone to the trouble to fill in a recess? I suspect we'll never know. Thanks for the picture, very useful. I've just finished the cylinder front cover and trim covers. The front cover in the picture looks like the casting I had for the front cover, but I've modelled mine on another engine where the front cover appears to be in two parts. Fortunately I've modified the design of the trim covers to look like the picture. I note yours are painted, as they are on the SCC in the Burrell museum. Other pictures I have show them shiny. I've made them from stainless steel, so won't be painting them. I guess originally they were cast iron?
I've reached the tentative conclusion that every SCC engine that Burrell built was different.  :thinking:

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #242 on: April 10, 2020, 07:50:38 PM »
Following on from my notes in the previous post on the front cylinder cover I've made same and the trim covers that are bolted to it. Here are the finished trim covers:



These were machined from sawn blanks of 303 stainless steel. A sectional drawing of the cylinder in a book shows the trim covers to be plain cups and hollow. That makes sense as the air gap will provide some insulation of the cylinder cover. So I ignored the solid, and flanged, covers shown on the drawings. The sections are thin (1/16") and I had trouble with some parts dishing. I should have stress relieved them before machining. Stainless steel bolts were also made:



The bolts were made from 9/16" diameter 303 stainless that I also used for the piston rods. When machining the piston rods I had problems with poor finish. But this time around the bolt shank was reduced to 1/4" in one pass with a HSS steel toolbit and it left nice finish. I don't know what the feedrate was as the repetition lathe only has a hydraulic power feed which is uncalibrated. When I turned the piston rods I was using insert tooling, so may be that was the problem.

The cylinder front cover is modelled on pictures I have of a fullsize engine where it appears to be in two parts with a straight join between the bores. I didn't go that far but have redesigned the front cover to look more like the fullsize engine and to have the correct number of studs. The front covers were made from simple castings.  It wasn't clear where to start when marking out. So I stuck a 1:1 drawing of the cover onto the casting making it as central as I could. I then centre popped the rough location of the cylinder bore centres. These were lined up on the manual mill using a  tapered pin in the drill chuck and zero set on the centre of the LP bore. From then on it's simply a case of co-ordinate drilling. I made a simple fixture to hold the cover in it's correct orientation for drilling the stud holes and profiling the outside:



Here's the cylinder front cover and trim covers assembled:



Time to start preparing a batch of artichoke and carrot soup. The artichokes were dug out of the compost heap this morning and it seems a shame to just put them back on the compost.

Andrew

Online Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #243 on: April 10, 2020, 07:58:04 PM »
Hi Andrew,
Nice looking cover & trim parts!   Glad the stainless worked better for you this time around.  I've only used stainless a little bit and have had good luck with it. Plan to use it more going forward!
Kim
« Last Edit: April 11, 2020, 05:55:47 PM by Kim »

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #244 on: April 11, 2020, 10:38:08 AM »
I've turned a lot of 303 and 316 stainless and in general they machine beautifully with insert tooling. So I'm still not sure why I had problems with the piston rods. Even odder, having  turned the spigot I then screwcut a 32tpi thread with no issue. Still, if it was easy it'd be boring - not.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #245 on: April 12, 2020, 10:36:22 AM »
I'm working my way around the cylinder; this time with the valve chest covers. Sooner or later I'll have to bite the bullet and start on the cylinder itself.  :)  They have been altered from the drawings to have the correct number and layout of studs as per fullsize. The covers were machined from hot rolled steel. Size and thickness were done on the manual mill while stud holes and recesses for the nameplates were done on the CNC mill:



I program my CNC mill in metric, irrespective of whether the part was designed in metric or imperial. Although the valve chest cover was programmed in metric I generated an imperial G-code program to cross check that the holes were where they should be. One was a tenth of a thou out, but that's less than the resolution of the CNC mill so I elected to leave it as was. The stud holes were drilled 6.4mm, so that should give me a couple of thou play on the 1/4" studs.

The cast nameplates were milled to overall size and the backs machined flat and to thickness. The nameplates are fixed to the covers using 8BA brass roundhead screws in blind tapped holes:



The assembly is not quite as fullsize. But I'd like to finish the engines before I kick the bucket. So I've left the design as it is. I will clean up the lettering on the cast nameplates but they will not be painted as per fullsize.

Andrew

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #246 on: April 12, 2020, 10:57:31 AM »
Andrew, I have found a better? photo of the reg rod bush.  If you zoom in you can see the insert is "wine glass" shaped , inserted from the rear. I assume it's to stop the rods flexing??
Re your observation on the cylinder covers painted........as I understand all early scc engines were black and that includes the valve cover which was cast iron including the name plates, not brass as the model folk supply.  As you can see mine are painted black and include forcing screws that you mentioned earlier.  Your engines continue to impress, I long to see one running.  Compared to your accuracy mine was "thrown" together but drives beautifully with plenty of power. yours will be outstanding.       Regards            Terry

ps why have I got ally cylinder covers? :facepalm2:  will make steel/black ones soon.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #247 on: April 12, 2020, 07:41:13 PM »
Terry: Thanks for the additional pictures. I see the wine glass shaped insert; could well be to steady the rod. I have some pictures of fullsize engines where the cast valve chest cover has cast rims into which fit fairly thin brass nameplates. I reckon I can approximate that by painting the outer edges of my brass nameplates black while leaving the centre plain.

Just before the lockdown I went up north to retrieve my glider. On the way up I dropped in to see John Rex in Pontefract. The main purpose was to return some castings that I'm never going to use, including lots of light alloy ones. If I'd had the wit to realise they were light alloy I wouldn't have bought them in the first place!

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #248 on: April 12, 2020, 08:58:54 PM »
Working my round the cylinder I've also recently machined the cylinder rear cover. Although deceptively simple it has a number of features associated with the pistons and slidebars that need to be accurately aligned for the engine to run. I started off by skimming the back face and then bringing the bosses for the piston rods and the pillars for the slidebars to the correct height. One of the issues was lining up the casting in its slanted position, as in this picture:



Note the two round pillars each side of the casting. These are clamped in a T-slot and were cylindrically ground to better than a tenth of a thou relative to each other. A length of silver steel (aka drill rod) was trapped between these pillars and the square pillars on the casting to get the correct orientation. Both sides of the square pillars, and the outside edges, were then machined to size. I could then indicate off these pillars to set a zero on the centreline of the pistons in two dimensions. Using the DRO I then drilled and reamed the piston rod holes, which were opened up for the glands with a 7/8" endmill plunged straight down. Holes in the gland bosses were also drilled and tapped for studs using the DRO. The cover could then be set vertical for locating and drilling the holes in the pillars for the studs and bolts that hold the slidebars:



I also drilled and tapped some holes in the outer edges of the pillars of which more later. Some of the fillets on the casting were over-generous so I thinned them down by eye using a 10mm ballnose cutter. Holes for the studs to hold the cover on the cylinder were co-ordinate drilled, with the DRO, and counterbored with a 1/2" slotdrill to provide a seat for the nuts. The number and rough location of the stud holes has been copied from fullsize. At this stage of the machining it is simple to hold the cover to profile the outer edge on the CNC mill:



A final skim on the back side was done on the manual mill as the covers had a couple of thou rock when placed on the surface plate. Here's the finished cover:



The additional holes in the sides of the slidebar support pillars are for side clamps which would be used to clamp the slidebars side to side once shimmed upon assembly. On my engines these are intended for show only. However on another forum I have been informed that the fullsize engines, and one model one, definitely needed shimming and clamping to get everthing snug. Any difference in the forces on the two piston rods translates into torque acting on the crosshead. The slidebar side clamps are modelled directly from pictures of fullsize engines. I roughed out U shapes from a length of hot rolled steel on the manual mill. Each clamp was then bolted to a fixture on the CNC mill to form the ends - fullsize they would have been cast:



Here are the finished batch of sidebar side clamps:



Having made the above parts, plus a load of 1/4" BSF studs and a new batch of nuts, I could assemble the crosshead, slidebars, cylinder rear cover and the pistons:



I'm pleased to say that with everything nipped up the crosshead and piston rods slide smoothly the full length of the slidebars with no shake or misalignment. That bodes well for a smooth running engine. Here's a close up of the cover, slidebars and slidebar side clamps:



The studs with plain ends and cross drilled holes are as per fullsize, although there is some variation engine to engine, especially on the use, or not, of lock nuts. Note the relief on the bottom slidebar to clear the spigot on the piston rod gland.

Andrew

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #249 on: April 20, 2020, 08:21:28 PM »
Very nice Andrew :ThumbsUp:          Terry

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #250 on: May 04, 2020, 01:36:49 PM »
After some faffing about I've finally finished making the blowdown plugs for my traction engines in LG2 gunmetal:



At the top of the picture are two fusible plugs for a member of another forum, whose lathe will not cut 19 tpi threads. The interesting part is that the threads are 3/8" BSPT, in other words a tapered thread, which I haven't screwcut before. The standard BSP taper is 3/4" per foot on diameter, or 1.79 per side. The challenge was how to screwcut a tapered thread while still being able to use the Ainjest high speed threading unit on my lathe, with it's automatic trip at the end of each pass. I have one of these:



For those not familiar it's a Coventry diehead, but one specifically for cutting tapered threads. In operation a template gradually opens the diehead until the trip point is reached. There were two issues in using this; one it would be a lot of work making a mounting bracket for the lathe and two, while readily available the die chaser tapered thread sets are expensive. So instead I went for the hydraulic copy attachment:



The full form threading insert is at the back, but is upside down, so all the lathe controls work as normal and the thread cut is still right hand. The tapered template was marked out and filed by hand from sheet steel. The blowdown plugs mate with a parallel BSP thread so the exact angle isn't that critical to two decimal places. A trial run in brass proved the concept, but I had trouble getting the gauge line for the thread correct. The taper on the thread is shallow so any errors in diameter result in the position of the plug moving by a lot more. I've had trouble with this before when using the copy attachment. Time to investigate! First I measured the movement I was getting from the toolpost adjustment knob (centre towards the top). Turns out to be calibrated in thou on the radius. So one tick is two thou off the diameter. Secondly at the back of the copy attachment is a silver knob (centre right) which the manual says is a finish cut micrometer adjustment. I've never used this, and in a quick test it didn't seem to work. Having posted about this on another forum someone kindly posted a link to the appropriate patent, which enabled me to work out how to use the feature. In the event the smallest increment is 0.1mm which is much too coarse in this application. So I stuck with using the toolpost adjuster. The toolpost has a slide lock operated by the bent spanner in the centre. The locking pin is a daft design and it broke some months ago. I took a time out to make a new one in EN8 alloy steel. Once I'd done all that I found that I was much more repeatable on diameters. The position of the gauge line is pretty consistent across the plugs, so I estimate I've held the diameters to better than a thou. One other thing to mention is that I didn't bother turning a taper before cutting the thread. I just turned a parallel cylinder of the maximum diameter (found from the 3D CAD model) and let the threading insert form the taper.

Here's the square on the end of the plug being milled before parting off:



To index the dividing head for the square I used the direct indexing plate behind the chuck. Apart from one plug where I misread the numbers and used the wrong slot. That plug is now in the recycle bin.  :embarassed:  Although these are simple parts it's been an interesting learning exercise.

Andrew


Offline yogi

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #251 on: May 04, 2020, 05:35:08 PM »
Very interesting Andrew!  :popcorn:

A hydraulic tracer attachment is a piece of equipment I never got to use. I definitely can see its potential.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #252 on: May 30, 2020, 05:01:33 PM »
Recently I've been working on the regulator for my traction engines, to my own design, but based on fullsize:



The horizontal steel handle operates the regulator. The brass button operates what I call a 'singling' valve. The valve admits full pressure steam to the low pressure valve chest. It's not a simpling valve as that diverts the high pressure exhaust to the chimney and allows an engine to operate as two singles in parallel. Neither is it a starting valve as both pistons are on dead centre at the same time. So unlike a double crank compound admitting steam to the low pressure cylinder doesn't help to start when the high pressure piston is on dead centre. What the valve does do is enable the engine to operate as a single using the low pressure cylinder. Being larger in diameter this should produce more short term torque, if not long term power. I'm told this is how the valve was used fullsize, a quick push to give more oooomph for a short period. The operating shaft will be spring loaded. This has been a lot of work making lots of parts for not much to show.  :(

Some time ago, while I had the CNC mill set up with a 10mm cutter, I couldn't resist starting on the two main parts of the body from hot rolled steel:



I used the repetition lathe to knock out 1/4" BSF nuts, bolts and studs and 4BA studs. I bought 4BA nuts and the one 4BA countersunk screw needed. After CNC milling the body parts most of the machining was manual turning and milling with two exceptions. The outline of the regulator handle was CNC milled from a length of hot rolled steel, which fortuitously was just wide enough, by about 20 thou:



The rectangular slot in the brass button was CNC milled with a 6mm cutter and the corners re-machined with a 3mm cutter to sharpen them up. The final square corners were formed with fine, and needle, files. Thinning the ends of the regulator handle was done on the vertical mill, in two stages on the longer side to avoid chatter:



The last part to make is a cover for the stop bar which has recessed lettering showing which end is OPEN and which is STOP. The part is designed, but CNC milling the recess and lettering will require a 0.5mm end mill. I've made several parts using 1mm cutters but haven't gone down to 0.5mm yet. It should be an interesting learning exercise. I just hope the wallet isn't too exercised as well buying replacement cutters.

I've been diverted recently as a couple of weeks ago the UK government unexpectedly decided to allow limited private flying to restart. So I've been inundated with people wanting gliders certified and signed off for flight.

Andrew