Engines > From Kits/Castings
Hick Crank Overhead engine
AVTUR:
It is over four months since I posted an update. This one covers the crosshead and connecting rod.
The Crosshead was started months ago as part of a silver soldering session. About 1 1/2 long length of mild steel 3/8 square bar was cross-drilled towards one end and a similar length of ϕ3/16 mild steel bar silver soldered in place. The piston end face was faced and the rod hole was drilled and reamed. The square bar was turned to a diameter for about 1/16 from the face and the hole well chamfered, at 45°, to butt on the shoulder of the piston rod. After the cross drilling of the crosshead and the Piston Rod, in situ, the rod was removed and the slot for the cotter pin and pad finished. The part was mounted in the four jaw chuck and the trunnions machined. The dead end with the tapped hole to take the clamping screw (described previously) was cut off and the part glued to a short length of ϕ5/32 mild steel rod. The top, crank end, of the crosshead was then carefully faced to length. The rod was then removed by a sharp, light, tap with a hammer and the crosshead re-glued to turn the final chamfer.
I did a lot of thinking about how to make the Connecting Rod which is forked and looks very flexible (I attach the drawing of the part). Prior to starting I solid modelled a number of machining options.
Two ϕ10mm holes were drilled at the ends of a 4 length of 1 3/4 x 3/8 mild steel plate for bolting the plate directly on to the milling machine table. In addition two ϕ3mm datum holes were drilled so that the part could be quickly re-positioned after being moved. With the plate sitting on a similar aluminium plate the top surfaces of the connecting rod were machined with a slot drill. The rod was the removed and the aluminium plate machined to give a mirror surface so that rod had a good base to sit upon. The rod was turned over, sat on the aluminium plate and the bottom machined in the similar manner.
ϕ3mm holes were drilled at every internal corner and at the ends of cutter runs. Prior to cutting the part out with a ϕ3mm slot drill end holes for the cotter pin and pad slots (two 3/64 wide and one 1/16 wide) were drilled. These slots were then cut to just over half depth followed by the edges, again to just over half depth. The part was turned over and the slots and edges cut through. I now had successfully produced the rod without breaking any small drills. Because it was thin and forked I decided it could easily be damaged. Therefore, before any further work, two small brass blocks were glued in the fork (these have been removed a number of times, just rest a long face on a flat metal block and give the brass a sharp tap). An attachment shows the connecting rod after tidying using a selection of small files.
The progress on the model is way ahead of this blog. Since the weather is too cold for the workshop the next posting could be quite soon.
AVTUR
Jo:
Well done. You have made a good job of that connecting rod 8)
Jo
Admiral_dk:
That is a rather complex shape for 'a simple conrod' :o - but very nice result, that you can be happy about :cheers:
Per
AVTUR:
--- Quote from: Admiral_dk on November 27, 2021, 08:05:12 PM ---That is a rather complex shape for 'a simple conrod' :o - but very nice result, that you can be happy about :cheers:
Per
--- End quote ---
Per
Everything about the engine is complex.
AVTUR
AVTUR:
Autumn has come and gone. During that time I have been occupied making and trying to fit small fiddly bits.
The connecting rod has two little end bushes (Geoffery King calls them brasses, a name I have not seen before and not quite in my Collins English Dictionary) and a single big end bush. Each is held in place by a strap with a cotter pin and pad.
The straps were produced from rectangular bar with the outside dimensions matching the width and thickness of the strap. I cut the bar to a length far longer than required for one strap and the drill the ends of the eventual slot to easy slot cutter access and to locate to filing buttons. The buttons were used to facilitate the shaping of the end with a file. The two small straps have rounded end while the large, big end, strap includes a boss for an oil hole. I did not make too much of a mess of this filing exercise. After the slot that holds the bush was cut the slots in the sides for the cotter pin and pad were produce using a slot cutter cutting from pre-drilled holes. The cotter slots on the small straps are 3/64 wide while those on the larger strap are a 1/16. The ends were filed squarish with a modified needle file. I discovered that I could buy a 1mm across the faces file that only cut on the edge. I bought two knowing that one edge would have to be ground back to get into the slot. In the end I also had the grind back one of the faces. The surplus end of the part was then removed with care using a slitting saw. And I have yet to break a 3/64 slot drill.
I have made cotter pins and pads before. Then there were ten sets required so I cut a length of rectangular bar on the milling machine with the head set at a slight angle to give the correct profile and then sliced the bar like bacon using a slitting saw. While this worked the control of the cotter angle was poor and I felt I could do better. A short strip of 1/2 plate had the profile of the seat of the pad cut in one end and the other left square. Slots were then cut with a slitting saw on both ends so the remaining strips of metal were the correct thickness, 3/64 and 1/16, for the cotters. The plate was transferred to a vertical slide set at 7° mounted on the lathe cross slide and the pins and pads cut off with a slitting saw. Sharp edges were then removed with a small file.
The production of the 3/64 thick cotter pin and pad for the crosshead was included in this work. Geoffery King only used a pin in his design but I opted for a pin and pad.
I have more photographs covering the making of the cotters and bushes than allowed for a single posting. Therefore details for the bushes will follow shortly.
AVTUR
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