crankshaft's for Seal engines

Construction diary

[Note: to help some readers (who have asked where they can buy an item) I have placed links in the write up which are sources on eBay for the relevant item]

Menu of sessions.

Session 1 8th October 2010          -         Problems with materials
Session 2 9th October 2010          -        More Problems with materials
Session 3 6th February 2011         -         'Normailsing' the steel bar
Session 4 10th February 2011         -        Marking out
Session 5 20th February 2011         -         Machining waste areas of the crankshaft
Session 6 21st February 2011         -         Roughing out the journals
Various sessions April - May 2011          -        Turning both crankshaft ends

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Session 1 8th October 2010

Because of the cost of the bar of high tensile steel I decided to try and make two crankshafts out of the one bar. To get both blanks to the correct size I need to cut the bar in half. This should just about give me the correct size blanks.

My chosen methodology is to tap the end of the bar and secure two 'ears' to the end of the bar and these ears then clamped to the saw table (see picture). Hopefully this will allow both halves to stay securely when the final cut is made.

Session 2 9th October 2010        More Problems with materials

I set everything up last night ready to make a start on cutting the 1.5" diameter round bar of high tensile steel, in half. I was full of hope that with the carbide tipped saw blade that cuts wood and metal, this would be a successful. However two issues quickly arose, firstly the width of cut was increasing beyond the width of the blade, and secondly, it was very brutal and I suppose to a degree I chickened out!

So I decided to see whether a 4" slitting saw with side cutting teeth would do the job. I hadn't tried this previously due to how to hold the work and secondly, all the handle work on the mill. These issues were resolved because the power feed was working well and I now had a method to hold the work (the use of tapped holes in one end to secure plates too). Well it worked to a degree, after adding additional table clamps to stop some lateral movement. However it was again very slow going and I was not convinced that this would be successful in a reasonable amount of time (and blades!!).

So I have decided to approach the problem in a different way. 1, search out a local engineering firm to see if they can help cut the bar. 2, research whether the need for High Tensile steel is still valid bearing on mind how much materials have changed over the last 63 years since Westbury designed the Seal. and finally 3, look to take on another element of the build such as con rods or pistons while I sort out 1 and 2 above.

Session 3 6th February 2011        'Normailsing' the steel bar

I knew I shouldn't have gone out to the workshop, feeling a little under the weather after being brutalised by my younger brother Stephen (he maliciously tripped me up when I was already wobbling - my life is spent being 'wobbly' all the time). However he also suffered some damage to his ribs, from laughing so much!!!

I have to make excuses for a very poor couple of hours at the milling machine somehow. Those who have been following the build of a pair of Westbury Seals here (or on my main website) will know I made a fixture for making the con rods and that the methodology for machining was in development. Well the radius turning for the ends worked well, and I shall keep that, but profiling the rest of the con rod didn't achieve either consistent, or satisfactory results, so it is going to be left until after the crankshafts now.

Another reason to stop is the revelation (to me after 4 years or so) that always using my scrap box (I call it recycling to be politically correct) for all my parts is not really the way to go for critical parts. Hugh, my nearest model engineering neighbor, supplied me with a link to his metals supplier. So I am going to order some aluminum flat, with known properties for the con-rods. That allows me to put them to one side, waiting for the metal to arrive (smart excuse eh!). I am simplifying my procedures as well. Milling to shape using 'normal' techniques is the best way to go only using my fixture to radius the small end and mill the indentation in the centre of the con rod body.

I tried to be to clever really, and use the rotary table in the same way I made the 4 chess knights. So when the correct stock arrives, at a known grade, and closer size, I am sure it won't take long to get them done.

Now over the the crankshafts. I got myself tied up in a knot over the requirement of HT steel for the crankshafts as described in Westbury's article and plans. This brought no end of trouble in cutting a bar of HT steel in half (again being to clever for my own good bought a bar of sufficient diameter to get two cranks from). In the end I went back to Hemingway's site (supply plans and a kit of castings as well as bar stock) and ordered two crankshaft blanks from them.

They arrived quickly enough and I put them to one side to concentrate on the con rods, however as you know from above this has now changed. A couple of years ago now I machined a piece of flat steel bar and was amazed when releasing it from its clamps, to see it bend like a banana! HMEM (the forum I use) members explained how cold rolled steel (that was what I was using at the time) had so many stresses when rolled that before use the metal should be 'normalised'. This is achieved by heating it to a cherry red colour, then letting it cool naturally, so releasing all the stress. Whether the steel as bought was normalised or not, ( knowing my recent luck, or rubbish working....) being bent like a banana, is not good for an engine.

Since I had never carried out the simple procedure before, it seemed sensible to heat it up so that's what I did. Whether my cherry was dark enough I don't know, but its been done. So when I next go out to my home from heaven I will face off the ends of both bars so they are square, then drill 3 holes for the lathe centres to run in. One for the two central end shafts and the others for each throw.

I never seem to learn that the body is a better teller of my potential workmanship than my head!

Session 4 20th February 2011         Layout of measurements

After converting all the plans dimensions to decimal using a excel spreadsheet, they were transferred to both steel blanks. To ensure they were as accurate as possible a small angle plate combined with an engineer's square clamped in position ensured the markings were at right angles to the longest side. Allowing any errors in end squareness to be eliminated.

Whilst they will not be needed initially because of the use of digital readouts on both lathe and Mill, they do provide a constant check whilst machining.

Session 5 20th February 2011        Machining waste material prior to turning

After quite a bit of work on laptop the produced a set of dimensions were transferred to my master build notebook and also the white board alongside the Milling machine. I first tried using my dividing head but because it meant using a chuck I decided that my Vertex Rotary Table would be easier. It also meant using my as yet un-used, tail-stock, as the first method of securing the blank. I took good care to make sure the blank was level in both planes and then added an angle plate with vertical flat bar to secure part of the blank with an engineers clamp. Finally, a small jack was secured under the blank allowing a very stiff fix to take place.

Once the top side was completed the bar was revolved 180 deg. and the remainder of the blank milled to shape (see photo alongside). This was then transferred to the lathe for the next stage in the process of producing the two crankshafts.

Session 6 21st February 2011        Roughing out the journals

Quite a bit of time was spent setting up the lathe. I decided to tackle the turning by fixing a driving dog (to be made up) to the face plate. Using a new large centre at the head stock end and a live centre at the tail stock meant a smooth turn could be achieved. The final task was to ensure the tail stock and head stock were in line before turning the whole face plate one complete revolution to ensure nothing caught.

I have a Glanze replaceable carbide tipped parting tool and thought I would try to use the parting tool to machine the crankshaft. The carbide insert hadn't been changed for some time but I thought it would be best to turn all down before finishing cuts would be made using a brand new insert.

The surface finish gained so far though shows promise for final cuts. So far I have turned one end to just round before turning down the three different sizes required of that end. So far , so good.................

Various sessions April - May 2011

Managed to get into the model engineering workshop (I now have a separate wood workshop which is great if I am not feeling well enough for the more demanding (for me)metal work) to continue with machining the Seal crankshaft. My now established methodology is very slow, but it also seems to be giving accurate results. The part I am turning now has a seating for one bearing which is (according to my micrometer) dead on 0.375" with the second part 0.0005 undersized and the nut end dead on.

Of course this only adds to the pressure of not *&^%$%& it up! The finish I am achieving is also very good and will need little final polishing, if any. Basically I am using a carbide tipped parting off tool for cutting and only cut 5 thou at a time and at only 100 rpm with the finest feed rate on my lathe. There more than likely are many better and even more professional methods, but it works for me!

After bringing two parts of the taper end of the crankshaft to size I set the top slide over to 5 deg to get the required 10 deg inclusive angle. Beforehand however I sightly scored the finish position to gauge if everything was all right and was relieved to see the taper completed to the mark exactly.

Once the both ends of the crankshaft are completed I will make spacers to fit between flanges to help maintain the shape and add support when turning the journals. At present its not a problem because I am turning on the central crankshaft.