Author Topic: Hick Crank Overhead engine  (Read 2887 times)

Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #30 on: December 18, 2019, 07:48:53 PM »
It has been some time since I reported my progress on the model. Cold weather forced me out of the workshop and other persons set my priorities. However I have made some progress.

The Caps for the Plummer Blocks are gunmetal castings, or to be more correct, one casting. This immediately leads to a question: Should I use the casting and try to copy it when machining the second cap or should I make two identical caps and ignore the casting? Thinking I would not be able to produce a good copy the casting I chose the latter option. Two simple caps were made from round bronze bar, what type of bronze I do not know but it was not aluminium bronze. I think I will put slopes on them, like the casting, when it is warmer.

The bearing Brasses were made from bronze bar. The usual way to make these is to solder pairs of partially machined blocks together just as Andy (Chipmaster) on his Stuart Major Beam Engine. My attempts to do this in the past have failed completely, I even considered silver soldering. Thinking about it I decided using a fixture to hold the two halves together was the answer particularly when there are a lot of brasses to make. Before going ahead with the first fixture I had a chat with a former work colleague who makes large model locomotives and such like. He sort of laughed: “As an apprentice, the first day on the shop floor I had to machine and match large bearing brasses. We did not use solder, a ****** large fixture instead.” I made a nice set of fixtures (photograph of one attached) and job became easy – just mount the two halves of the brass in the fixture, put fixture in a lathe collet chuck, drill and ream the bore, face the front face, turn the clamping plate round and face the rear face.

I sat down and started drawing out such a fixture but, since the Brasses were about twice the size of any I had made before, it was quite large – too large to take advantage of a collet chuck. Also was it worth making a fancy fixture for just two sets of Brasses? Previously I had a stupid idea of using the Plummer Block and Cap as the fixture and doing the machining in the milling machine. This had the obvious advantage that the Brasses would match the Blocks and the Caps. I re-visited the idea and decided that if the structure was supported by a plate to take the vertical machining loads while a machine vice clamped everything together it was not stupid. It was also very simple.

During the preparation of the Brasses prior to facing, drilling/reaming and matching I hit a problem – I just could not understand drawing and wasted a day trying to do so. I sat there not understanding what Geoffrey King had drawn and dimensioned. It was a mess unlike his drawings for the smaller sets of brasses. It was nothing like the drawing I would have produced. I then realised that a dimension was missing – problem solved. I puzzled over the mistake and decided he was trying to draw too many parts on one sheet of paper. This seems to be a common failing in model engineering. I was trained to draw one part, however small or large, on one or more sheets of paper with plenty of room. The drawing started with three or more views using the favoured projection. Then additional views, sections, dimensions, notes etc would be added without crowding the drawing. Rant over.

A simple support plate with a hole in it to give a passage for the drills and reamer was made. With the assembly clamped and tapped down on to the plate, and having taken lots of measurements to ensure the bearing hole would be in the centre and of the split of the Brasses, the bearing was drilled, reamed and faced. The drilling was done with increasing diameter steps prior to being machine reamed with an H7 reamer to hopefully give a bore between 0.3125” and 0.3129”. The assembly was turned over, re-clamped and the reverse face faced. Before the assembly was taken apart for marking the entrances to the bore were well chamfered.

After the excitement of the bearings, the Crankshaft (I would call it the main shaft) was easy. The bearing surfaces were done first. A parting off tool was used for the rough machining which was followed up with a freshly sharpened left hand knife for the final cuts. The top slide was set at an angle of 2.5° to facilitate very fine cuts. The shaft was turned round in the collet chuck to cut the surfaces in the reverse direction. The journal adjacent to the crank has an axial float of about 0.002” and a diameter of about 0.3122” (a bit tight, a bit more polishing required). The flywheel journal has an intended generous axial float and a diameter of about 0.3110” (a bit free running, the brasses may need to be closed very slightly). The nose which carries the Crank is a good push fit. The keyways for the Crank and Flywheel have been machined. For good reasons I have not provided a flat for the governor bevel gear grub screw.

I have just started on the Flywheel (diameter 7.5”). An update will follow in a few days.

AVTUR
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Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #31 on: December 30, 2019, 08:01:13 PM »
The Flywheel has been machined and now, or more likely in a few months time, needs finishing with a file. There were no problems but it took a little time, I don’t really like machining cast iron. I had hoped to machine the faces with the wheel in my big four jaw chuck before finishing the rim using the face plate but everything was too large for the lathe gap. Therefore everything was done using the faceplate. I recessed the rim of the wheel which Geoffrey King left as an option. As far as I could see there were three ways doing this:
1.   Mount the wheel on a rotary table and milling out the recesses, one face then remount the wheel to do the other face, with slot cutter – this sort of made sense.
2.   Keep the wheel on the faceplate and drive a square faced tool, like a parting off tool, square in to the face. This is rather like trepanning which I have done on brass plate. I consider this much more frightening than parting off.
3.   Keeping the wheel on the face plate and cutting into the face at an angle of about 20° to the surface with a knife tool, to a depth of about 0.015”. The cut is the opened out using the lathe cross feed, and so on. This takes time and requires left and right hand knife tools but is much easier and gentler than the other methods. I have the time.

I broached the keyway. I had not done such work before and I knew it would be difficult. I ground the end of a short length of square high speed steel to what I thought was a sensible shape and mounted it in a quick change tool holder. By manually advancing the carriage I found I could shave off around 0.001” each in each pass. It took quite some effort, both hands, and however tight I did the nut up the tool post eventually rotated requiring the tool to be reset. I managed to cut a slot 1/32” deep. I feel that this job was at the margin of the lathe’s ability. Both my hands suffered but the arthritis in my left wrist seems to be less now. If I had to broach a number of keyways I think I would make a lever system as shown in Ian Bradley’s book Myford Series 7 Manual.

After all that I made the associated key by filing.

I am now going on to make some of the small governor and control items. Quite a few are fiddly and need to be thought about. So it is going to be a few days producing planning sheets.

The more I think about the Standards the more I believe that they are not fit for purpose. Whether this is my fault I do not know. However I have bought some 5/8” aluminium plate with the idea of machining a pair.

AVTUR

There is no such thing as a stupid question.

Offline MJM460

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Re: Hick Crank Overhead engine
« Reply #32 on: December 30, 2019, 08:49:00 PM »
Hi Avtur,

Coming along pretty well.  It is always good to see another update.

I do like that detailing on the flywheel.

What is the problem with the standards?

MJM460

The more I learn, the more I find that I still have to learn!

Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #33 on: January 04, 2020, 06:52:22 PM »
Earlier this week I wrote that I was not happy with the Standards. After doing the running trial assembly with the finished crankshaft and bearings I found that the shaft is about 5° to the model centre line. In other words the top of one standard is out by about 0.22”. Not very clever and all my fault.

The two options are:
1.   To try to correct the existing standards. This, I feel, is trying “to make a silk purse out of a sow’s ear”.
2.   Or to make a new set which will take some time but is quite achievable.
In both cases a lot of thought is required.

I do not intend to rush in to this work. I am still writing job sheets for the small parts between migrations to the workshop. I have discovered I need more metal but I do have enough Φ3/32” mild steel rod to make 12BA nuts and bolts!

AVTUR

There is no such thing as a stupid question.

Offline Jasonb

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Re: Hick Crank Overhead engine
« Reply #34 on: January 04, 2020, 07:24:45 PM »
You could try some over size holes in the bottoms of the bearing pedestals which may just give you enough movement to swing them into line. Bit more involved would be to solder plugs into a frame sand pedestals then redrill and tap, if you tak ethis option then best to drill it as an assembly rather than individual parts, I did similar with the Allman A frames.


Offline AVTUR

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Re: Hick Crank Overhead engine
« Reply #35 on: February 19, 2020, 08:49:36 PM »
I have not posted a progress report for some time. This does not mean I have not been busy. When it has been warm enough I have been in the workshop making governor parts. Most of these are half finished, in most cases waiting for a calm day so that I can silver solder and harden silver steel outdoors. When it has been cold I have been producing lots of planning sheets (wasting a lot of paper and ink).

Making the six (actually seven because I made a spare pair) 12BA Nuts and Bolts was fun! The governor assembly nuts and bolt heads are cylindrical, diameter 3/32”, with a set of flats, 5/64” across the flats, and are mild steel. I started with two sets of taps and dies expecting to break at least one tap. I did a trial manufacture of one bolt without difficulty but ran into a problem with the nut. I just could not drill the hole up the rod for tapping. In the end I used a length of 3/16” diameter bar which was turned down after drilling and tapping. The parting off was done using a cutting disc in a Dremel mounted on the cross slide of the lathe. I had used this arrangement for parting off square headed screws and nuts in the past. I started on the bolts only to have a bolt break off in the die [see the thread I posted last month under “Mistakes, muckups, and dangerous behaviour”]. Still, I had a new second die only to find it had a broken tooth. After ordering two replacement dies I sat down and had a think: Everything would be easier if I cut the heads off 12BA screws, of which I had quite a few, make a second set of nuts and glue them together to make the screws. This was done, using 222 Loctite (I don’t think Loctite grades mean very much with very small screws) and filing the tops flat. The spanner flats were filed using a small piece of hardened gauge plate with a 12BA clearance hole as a stop. The bolts will be filed to length after a trail assembly of the governor. Happy, except that one, the spare, nut has gone walkabout. Now I have to make two nut runners.

Geoffrey King’s drive to the governor spindle was through two bevel gears, the pinion on the crankshaft had 20 teeth and the wheel on the spindle 24. The overall diameter of the pinion was 0.643”. I have only cut simple cycloid clock gears. Small bevel gears are a completely different matter. Looking at various books (Ivan Law’s “Gears and Gear Cutting” and “Gears for Small Mechanisms” by W.O.Davis) it seems that making a good set of bevel gears is possible without hobbing but the whole method/result appeared to me to be a bodge. Anyway I decided that the gears I required were too small for me to make. Fortunately a set of gears, about the right size, were included in the kit. However they
1.   were the same size, a ratio of 1:1 compared with 5:6. This was considered acceptable
2.   had a bore of 3/16”. The diameters of the crankshaft and spindle are 3/8” and 3/32” respectively
3.   The boss diameter was 7/16”, far too close to the crankshaft diameter.
A quick look at the catalogue of a leading supplier showed that bevel gears are expensive and I was unlikely to find a set with a ratio of 5:6. So the supplied gears had to be modified.
1.   A plug would be silver soldered into the bore of the wheel, the plug drilled and reamed to suit the spindle and the dead end of the bore faced to length. The required hole for the 10BA grub screw would be drilled and tapped with a short counter bore to locate the screw during assembly.
2.   A sleeve would be silver soldered over the existing pinion boss to bring its diameter up Geoffrey King’s of 9/16”. Again the boss faced to length and the bore drill out and reamed to suit the crankshaft. Geoffrey King used a key to locate the pinion, however I opted for a grub screw.

I have to admit I was worried that silver soldering might mess-up the gears. Prior to any silver soldering I calculate the amount of solder required for the joint and add on about 25% for the fillets. The solder is then placed so that it finds its own way into the joint during heating. Finally I add a little extra using the rod of solder. I used typewriter correction fluid to keep the solder away from the teeth etc, vulnerable areas received three coats. After running out of Tippex I found that the local supermarket sold Snopake (who buys such stuff these days?) which gave a far thicker coating. I managed to do the soldering, along with some hardening, on what seems to have been the only calm day this year. I was pleasantly surprised with the results. The gears have been finished except for one solder fillet which I will admire for some time before tidying up.

The one other finished part is the Governor Sleeve that did not give any problems. One thing it taught me was that a lot of the small parts can be made from one end of a bar/rod which allows one to have a good holding spigot.

I have started looking at the alternative Standards, more about that later.

AVTUR
There is no such thing as a stupid question.

Offline MJM460

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Re: Hick Crank Overhead engine
« Reply #36 on: February 19, 2020, 10:24:56 PM »
Hi Avtur, good to see another update.  Those small parts do take a lot of time to make.

MJM460
The more I learn, the more I find that I still have to learn!