Mill Engine

I have started work on a new project, a horizontal steam engine designed by Mr Harold E Benson. The plans are free, metric and have been well drawn by J.A.M. DeWaal of New Zealand. Here is the link http://www.vapeuretmodelesavapeur.com/telechargements4/.
The engine is quite large, nearly 700mm in length. This will be a bit of a relief over the last engine as it required a lot of M2 tapping and I felt more like a watchmaker than a hacker machinist. These plans call for a twin flywheel arrangement but mine will have to make do with one as that is all I have at the moment and funds are tight, plus I'm in the doghouse for a bit of an overspend on tooling so it behooves me to keep a low fiscal profile and let the storm clouds blow over.
My cast iron flywheel is quite a bit different from the one in the drawings, in a previous life it was probably a flat belt drive pulley in a shearing shed, I got it for a few dollars from an Op shop a while back. It just fitted into my lathe, I made a stub axle and press fitted it into the hub. This was later drilled and bored to the correct diameter and machined off in the mill. Most of the turning was done with a boring bar turned upside down and the lathe run in reverse as that was the only way I could get at it. I expected that the cast would be diamond hard because of the age, in truth it turned like butter silk and was an absolute joy except for the MESS! In the end it turned out quite well and I was pleased with the result. The pics tell the story better than I can. More later. Cheers, Peter.

Next to the crankshaft. These are not my favourite thing to make, over the years I've tried various methods, all of which ended up with a case of the wobbles that required a bit of discipline to bring into line. The plans called for this one to be fabricated, Loctited and pinned but if I had had the material on hand I would have preferred to cut it from solid as I have had more success that way than any other. One thing for sure, I was not going to silver solder it together. To those who can do it that way, I salute you. My attempt was so distorted as to be unusable. To make the cranks I had a small piece of 25 x 25 mild steel, not the preferred material but this is on a tight budget so it would have to do, the shafts would be cut from 15mm round bar. For once, everything went reasonably well, after press fit assembly with Loctite and left to cure overnight, I pinned the shafts and cranks using 4mm nails press fitted in with Loctite and machined off. The final result was about 200 microns off and some persuasion was needed to improve on that. So far, so good. Next the main bearings. Cheers, Peter

Before going on to make the main bearings for the crankshaft, I decided to construct the base of the model. I used a piece of 6mm aluminium plate 767mm x 260mm, a seriously large piece of metal to handle in my small shed. There is only limited work to be done on it, mainly the cutting out of the sump for the crank to turn in. The cutting was done using a 16mm ruffer milling cutter and proved fairly easy to do but it took a long time to set up in the machine. The next problem was the edge of the plate, this needed to be 20mm. Firstly I tried epoxying 20mm x 6mm bar to the sheet, total failure. Next brilliant idea was to fasten through with 3mm countersunk screws. This looked dreadful so in the end I used 20mm x 20mm x6mm angle and bolted this to the plate and radiused the edge using a router trimmer and CT wood bit. Much filling with bog and sanding produced a reasonable base in the end and I think it will look OK when painted, it was a lot more messing around than I anticipated, furthermore, because the piece of aluminium had been guillotined from plate it has a slight curve across its width, I'm sure that will come to haunt me in the coming weeks. The plans call for the base to be elevated on a timber stand. I made this from some Spotted Gum hardwood flooring that I had lying around. The two pieces were dowelled together but not glued, then screwed down onto two cross pieces forming the feet. Four coats of varnish and this was finished. The supporting posts in the plans are simply round pipe but I think that they can be made to look a bit better than this, I'll have a think about it and show the results in the next post, Cheers, Peter.

To make the posts for the base, I decided that because the Mill engine was from the Victorian era I would try to add that flavour to the model. I cut six pieces of 20 x 20 x 1.6 mm square tube to length and set up my mill. I firstly wanted to put some stopped chamfers on the posts and this is quite easy on my machine as I have adjustable electric stops added to the X axis of the table. Once the distance is set, each post is placed in the vice and the 45 degree radius bit traversed back and forth on each edge. Next I decided to "vein" the posts as this adds a lot of charm, I think so anyway. The process is similar to stopped chamfering but this time using a 3 mm bull nose bit. Two veins were added to each side of each post, this sounds quite time consuming, in fact it is very quick if electric stops are used on the traverse, additionally I have used a dynamic braking circuit on the X axis DC motor, this ensures that the motor stops almost instantly when the power is removed and ensures good accuracy. When the posts were finished, the most laborious part was the cleaning up and polishing. I used 600 grit wet and dry paper on the surface plate with a spray of kerosene and oil to remove any surface scratches, then polish on the wheel. They are a bugger of a thing to hold but I got the job done in the end. I think they look quite good. In the next post I will show the making of the brass and teak bases for the posts and the fitting to the base. Cheers, Peter

This looks very interesting. I’ll have to try the reverse trick if I’m forced to use my Enco 9” lathe in the future!

I like your solution to the standoff posts as well. Very nice!

As for silver soldering, if you don’t need high temperature resistance, buy the lower temp silver solder instead. When higher operating temps are expected, just make sure and use plenty of the correct flux on the cleanest surfaces you can produce. If possible, a clearance of .001” to .002” will allow a better flow, at least that’s what I was taught in high pressure gas school in the Navy, and relieving a channel to place a piece of solder between the pieces to be joined ensures an even flow after temperature is achieved.

Looks like a nice project, and I'll be following along!

John

Thanks for the comments John. To finish the supporting posts I thought they needed a plinth to stand on. I cut some 3 mm brass bar into squares, milled the edges and drilled a 8 mm hole in the centre. I ran around each one with a radius mill then polished them. Squares of Teak timber the same size but 10 mm thick were cut to place under the brass plate. I used 8 mm threaded rod for the bolts going through the posts. It is easier to see the results from the pictures than me describe the assembly. The top nuts on the engine bed plate will be changed for brass at a later date. The whole became very rigid and strong when the nuts were tightened which it will need to as I am starting to realize that this will be a very heavy model when finished. I'm sorry the photos are a bit out of sequence with the text, I am having all sorts of difficulties with this site that has never happened before, possibly it is because I'm getting older but not wiser. More later, Cheers, Peter.

Wow, very decorative! This’ll be a beautiful piece when you’re done Peter.

I’m still a newbie after about 20 years with my equipment, and you’d think I’d be better at prettying things up with my years of woodworking and cabinetry. The plain and simple truth of the matter is that I build my metal projects for function more than beauty and I can’t quite break that habit. I’m just starting on building Henry Ford’s “Kitchen Sink” engine, and I can’t think of a more cosmetically ugly engine. I guess I just love the beauty of the engineering!

John W

Good to see the crank did not cause you any grief, it looks like a reasonable sized engine which will need a reasonable sized boiler or is it going to run on compressed air.

Hi retailer, this engine has a 76 mm piston (three inch) and a stroke of 100 mm (four inches), I haven't done any calculations but I think it would be a real steam hog and certainly too big for my tiny air compressor. My immediate aim is just to finish it, then it will probably sit alongside the beam engine (pictured) I made a while back. It is also a very large model, so I'm hoping they will complement each other. Historically they were two very important styles of steam engine during the Industrial Revolution.

That beam engine looks fabulous it must be very satisfying to complete something to that standard.

Thanks retailer, I really appreciate your comments. I made the Beam engine not long after starting out with this hobby and I sure learned a lot when I was building it. I got a lot of help from the members of this forum which is why it is my favourite. I put up quite a few posts during the build and if you would like to know more, you can find them here. https://www.homemodelenginemachinist.com/threads/bolton-12-beam-engine-from-scratch.26462/ Cheers, Peter

Now that the base and engine bed has been sorted I could turn my attention to the main crankshaft bearings. There are three of these, one either side of the crank and one near the flywheel. My model will only have one flywheel. The bearing housings were cut from 25 mm thick aluminium bar to a finished size of 75 x 50 mm. I glued all three blocks together with super glue and machined, drilled and reamed all as one piece, then broke them apart. The bushes I made from brass and these were press fitted with Loctite into the bearing blocks, then an oil gallery drilled down from the top of the block through the bearing. These will be fitted with little brass spring ball bearing feeders after painting. The underside of the blocks were drilled and tapped with two 10 mm holes each and then the whole assembly, bearings and crankshaft, was aligned and bolted to the engine bed. I attached the flywheel and would like to report that everything spun like a delicately balanced gyroscope, but of course it didn't. Not really tight but certainly stiff, I connected a battery drill to the other end of the shaft and after 20 minutes or so, with lots of oil, everything freed up and I was reasonably pleased. If I was to do these again I would bore the bearing holes rather than drilling and reaming, I think the result would have been better. Here are the pics, hope you enjoy. Cheers, Peter View attachment 110116 View attachment 110116

The big end journal bearing is the split type. I made the bushing from brass and press fitted it into a 25 x 25 block of aluminium which was then machined to size. A couple of saw cuts with the slitting saw on the mill and the piece was made. I drilled an oil gallery through the cap and bearing in the same fashion as the main bearings.and will shim the bearing to the correct tolerance on the final assembly of the engine. The plans call for 14 mm bar fro the connecting rod, but as I only had 12 mm on hand this would have to do. I threaded this M12 into the bearing block and left the rod slightly longer than called for, this will be cut to the correct length when the crosshead yoke is fitted to the other end. Polished the bearing and fitted. Looked pretty good, starting to get a feel for the model now and think that it might possibly be one that I finish. Cheers, Peter

The little end of the connecting rod connects to the crosshead through the crosshead yoke. The little end is a block of aluminium with a bearing. It is attached to the connecting rod by press fitting into a 12 mm hole and pinning. Two things were important during the making of this, firstly that the distance between the main bearing journal and the crosshead pin be accurately established and that the crosshead bearing and the main bearing be aligned in the same plane before drilling the little end pin. The pictures explain it better.

The design of the crosshead on the plans, I thought it looked a bit ordinary and could do with some improvement. I kept the basic idea of the crosshead slide, made out of brass, but changed the style of the supporting pillars and slides. The finished result looked terrible, I sure hadn't improved anything looks wise and I wasn't convinced it was going to work all that well. I bit the bullet and started again. I decided that the crosshead slide should be steel with proper bearings and these would slide on 12 mm bright steel bars, this being the best that I had lying around. The supports for the slides I made from 12 mm aluminium bar with the end being larger and bored to later support the stuffing gland end of the cylinder. This time everything came together, at least to my mind, and with things in place I thought it looked quite good. The bearings were a little stiff on the slides and I think this is due to the overall alignment and height of the various parts. I will wait until the cylinder and the piston rod have all been made before checking and shimming as necessary. I hope these pictures compliment the text and things are made a little clearer, Cheers, Peter.

Well, onward and upward as they say. This model is starting to occupy nearly all my free time and mutterings can be heard about leaking shower taps and a retaining wall that needs repair. Possibly tomorrow, more important things first. The cylinder for this engine has a 76 mm bore and the plans suggest using steel pipe, however 76 mm ID x 88.9 mm OD is a standard size in aluminium round tube and by using this I would not need to bore the cylinder, something I was not looking forward to, it would really push the limits of my machines. The internal walls of the tube are very smooth and seamless. The roundness I just had to accept, when the piston is made I will lap as necessary. Setting the over 160 mm long cylinder up in my lathe took quite a while as I do not have any means of supporting it. Taking extremely light cuts I managed to machine the end to size but I set it up in the mill to square off the ends and bring the overall length to specifications. The milling of the inlet and outlet ports was straight forward, all in all there wasn't a whole lot of work required. The cylinder end was a different matter. Made from a chunk of 100 mm round bar it took all morning of boring and turning with endless checking of the measurements. This item is a press fit and I almost never seem to get these quite right, either too sloppy or the opposite. This time I left the cylinder 0.02 mm oversize, popped it in the freezer for 30 minutes, added Loctite to the end cap, brought the two together under the press, and gently pressed away. Perfect. So, things are starting to take shape. Ratting around in the junk box has revealed a piece of bronze cored bar that might be good for the piston, we'll see. Turning a blind eye to the retaining wall, I went inside for a drink. Cheers, Peter

Time to work on the opposite end of the cylinder, two flanges need to be constructed, one bored and press fitted to the cylinder body, the other becomes the head of the steam engine. I cut two pieces of aluminium, bonded them together with super glue and marked out the bore hole. Using this centre I then marked the radius of the top and cut away the waste on the band saw. Next I drilled a 10 mm hole through the centre of both and using this hole as a pivot, carved the radius slowly against a spinning 12 mm long series end mill. I saw this technique on Youtube some time back and it works well, just remember to work against the rotation of the mill. The two flanges were still bonded when the holes were drilled for the head bolts but then separated so that one was tapped for M12 and the other enlarged to 12.5 mm. Both received a quick facing skim, then the flange with the tapped holes was bored to be a press fit on the cylinder using Loctite. Everything went well, so now the cylinder is complete with only the stuffing box at the other end to make. Photo's, as always will help with the explanation. If anybody is reading these posts, please feel free to add any comments. Cheers, Peter.

Looking good!

John

You're a braver man than me to do that radius like that! I've done similar to shape conrods and small bits, generally with some hard stops so it can't completely spin the part if it grabs, and I've had it grab on occasion. Maybe it's easier to control with a larger part but I'm just too scared to try it. Nice job on it though - turned out great.

I too am impressed with you pulling off that radius cut on the mill! I may have to give that a try, but like Cogsy says, with some type of a hard stop so it doesn’t get away from me.

I’m really liking what I’m seeing on this engine. I especially like the treatment on the con rod big end!

Looking good engine, and being BIG I’m doubly impressed!!!

John W