| Gallery, Projects and General > Project Logs |
| New Project Started! |
| << < (6/28) > >> |
| NickG:
This instalment covers the pistons, or piston and valve. I started off in the same way as the cylinder and trued up the cast iron: Turned it around in chuck and started whittling it away nearly down to size: Now taking finishing cuts of 0.0005” and trying in cylinder: I got so far and thought right, it’s time to start lapping. I just did that with some wet & dry wrapped around a bit of square tool steel. But it still didn’t fit after lapping so I took another ½ thou cut off and it slid in – DOH! It was a good surface finish so need minimal lapping and I didn’t want to reduce the size any further. Also turned the spigot: Parted off: Am not that confident it’s a good enough fit, feels a bit loose so am thinking I’m probably going to have to re-make it. Here’s a video of the piston sliding down with the cylinder resting on the surface plate, trouble is, the surface plate isn’t that flat so air will leak around the cylinder. If I put my thumb in the end and form a tight seal the piston stays pretty much where it is until I remove my thumb. So it might work, I’ll give it a try but I’ll know the first place to look if it doesn’t! I also made the valve for the back end of the cylinder. I thought with this one I won’t make the same mistake twice, I’ll measure the bore and aim for maybe 0.1mm over then lap the rest until it fits nicely. Only got down to 0.1mm oversize, it wasn’t – it slid in again so I had to do minimal lapping to avoid making it much smaller. I have about the same fit on both pieces now. Just need to drill the cross hole in the valve for the valve rod (slightly different design to Jan’s, I just incorporated it into 1 turned bit). Interestingly, Jan calls for a 2.3mm hole with 2mm rod. Wonder if this somewhat sloppy fit is just to stop things binding? On the piston, I am going to do it the same way as my hot air engine. Mill a slot into the cast iron and cross drill right through. The pin will be a nice sliding fit in the cross-hole but a tight fit in the rod, thus will be held in the middle to prevent scoring of the cylinder walls. So I’ll finish those off, make the little bushes, valve rod, adjuster and pillars then that’s the cylinder and pistons complete. Still have the base plate, crankshaft, conrod and bearings to do. Who was I trying to kid doing this in a week?! Nick |
| bogstandard:
Nick, That 2.3 mm hole is necessary, it allows for the transition going in and out and stops vibration from the rod affecting it. John |
| NickG:
Thanks, thought he must have specified that for a reason! |
| NickG:
Due to the bedroom obstacle and a cold starting on Sunday the only thing I've managed to do on this was 1/2 a cylinder pillar ... wasn't even worth taking a pic of. Just realised I'm taking lots of pics of straightforward turning which is pretty pointless after the first one! I am machining these from 303 or 304 stainless (can't remember which the guy said, but it is free cutting which ever that is!) It machines really nicely and leaves a superb finish. The good news is, the bedroom should be finished by Friday and my cold should have eased off so I should be able to restart this project. Have been thinking about what I need to do and wondered if it's worth getting a length of 6mm silver steel for the crankshaft and 3mm for the crankpin because it's usually a nice ground finish. got a couple of questions on this though a. Will 6mm rod be a good fit in the bearings? I would have thought if size for size I'd have a job getting it through! b. does silver steel silver solder ok or would I be best going for mild. Nick |
| CrewCab:
--- Quote from: NickG on November 06, 2009, 02:53:02 PM ---I was always taught to go 1 turn forward ½ turn back anyway. --- End quote --- You and me both Nick ............. and I suspect ½ the collective at least :dremel: CC |
| Navigation |
| Message Index |
| Next page |
| Previous page |