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| bogstandard:
--- Quote ---I can fine tune that length if it runs! --- End quote --- And what does that mean Nick!!!!! You have no reason to think failure, IT WILL RUN, we will not allow to not run. :poke: :wack: Just a little note about some of your holding techniques. You have been very lucky in some of your machining. When you are cutting two or more pieces, say side by side or on top of each other like for your end milling, the thickness or width of the two parts can cause one to be held tighter than the other, it only requires a minute amount of difference between the two for one to be sent flying out of the vice or move and have the cutter bury itself into the job. If you can, stick them together some way (I use superglue or good quality double sided tape) or drill holes in areas you are later going to machine away, and bolt them together. I don't know why people get such a rough finish when using an end mill. So here is how I do it, and it gives me mirror like results. You really need a new or little used cutter for doing this job, one that has been used a fair amount will have dull side flutes. Or use an area of the cutter towards the shank, that is liable to be the sharpest. Get the cutter speed well up with a very slow feed, and keep away from climb milling if you can, plenty of lube (for ali, a squirt of WD40) and if you have an air blower, keep the shavings from being dragged around by the cutter and so getting embedded into the cut face (DON'T use a brush, it is liable to get snatched into the cut). The finishing cut should only be something like 0.002" (0.05mm). John |
| AdeV:
--- Quote from: bogstandard on November 29, 2009, 03:49:57 AM --- I don't know why people get such a rough finish when using an end mill. So here is how I do it, and it gives me mirror like results. You really need a new or little used cutter for doing this job, one that has been used a fair amount will have dull side flutes. Or use an area of the cutter towards the shank, that is liable to be the sharpest. Get the cutter speed well up with a very slow feed, and keep away from climb milling if you can, plenty of lube (for ali, a squirt of WD40) and if you have an air blower, keep the shavings from being dragged around by the cutter and so getting embedded into the cut face (DON'T use a brush, it is liable to get snatched into the cut). The finishing cut should only be something like 0.002" (0.05mm). --- End quote --- I concur with all of that; in particular the sharpness of the cutter has a particularly marked effect on the final finish. I have one truly excellent end mill which I reserve for these final cuts. One thing, and maybe it's because I have a big heavy mill, I find I can get away with a 0.002" climbing cut, which is a little smoother than the equivalent conventional cut. |
| NickG:
Bogs, Thanks for the tips. I did use a new cutter but guessed on the speed and didn't use any lube. I used a 12mm cutter with the max in the lower gear which is meant to be 1000rpm. I'm not sure whether I mentioned in the text but you're right, I was lucky. When I took the skim off the base with both clamped 1 on top of the other, it was only a tiny skim to make sure it was square after cutting the sides. but when I tried to do the same on the other end taking the bigger cuts to get down to size, as you pointed out, 1 of them kept moving. It must be a minute amount as you said because I'd previously milled them together to make sure they were exactly the same size. Probably the only reason I got away with it when I turned them around was because I hadn't touched the thickness. Will certainly remember this in future. On my rocking engine when I used that poor quality aluminium from the shelf it gave really bad pick up, sort of tearing the soft metal and I did have to take a small climb cut to get an acceptable finish. I will try the lube, still not sure whether the speed is right. Also, they were cheapo end mills from China - £12 for a set of 7! Nick |
| NickG:
Here is tonight’s instalment. It’s quite hard to get motivated to get out there initially after being at work all day but once I get out there I don’t want to come back in! Came in at about 11:20 tonight, got a reasonable bit done. First I thought I’d measure the 12mm end mill to see if it was actually a 12mm – it was! So I decided to put it in the vice and try opening the bearing housings by hand: To my surprise it worked a treat – nice push fit: I decided to put a dab of loctite on them; they will never be coming back out. So with that bit quickly done, I was feeling quite good and made a start on the crankshaft. I decided I would do it my old way, but with more care and attention – threaded shaft, disc and pin. Started by facing off the stock (think this is either 32mm stainless or some sort of chromium steel I was given at work) it seems to machine quite nicely whatever it is. I then drilled and tapped 3/16” x 40 tpi. I didn’t fancy my chances of parting off – am a bit nervous about doing steel for some reason, it starts to make squeaking noises then I get the hacksaw out! Anyway, it was sticking way to far out of the chuck for parting off. Getting it closer to the chuck would have meant another saw cut since it didn't fit through the chuck body. So this time I just skipped a step and went for the hacksaw – which is now pretty blunt! About 10 mins later I had this: I was pretty happy with that straight cut and the finish was ok, so I thought I’d just leave it! Lol, just checking you’re awake, of course it would be screwed to the shaft and faced off later! Started machining down some 10mm stainless for the shaft. It cuts really nicely, think it’s 303 or 304. The metal comes of in long spirals: In fact on one of the cuts it was one continuous piece of swarf Taking finishing cuts and lots of passes at the same setting. I had a bit of a flexing issue so the end furthest from the chuck was always larger – this makes it hard to test fit in the bearings. Consequently it is a marginally looser fit on the end near the chuck that I would have liked, no play but just a sliding fit rather than a push fit. I contemplated buying some 6mm bar but I think it would have needed reducing marginally to fit the bearings anyway. I turned the shoulder for the thread and gave it an undercut with the hack saw – dodgy I know but a parting tool wouldn’t work that far out from the chuck. Then I put the 3/16” x 40 Tpi thread on. This engine is a bit mix & match on the sizes. It was originally designed in metric so for the first time I am trying to stick to that, but all my taps and dies are imperial or BA and some of my metal was imperial! Oh, and my machines, so there’s been a bit of conversion going on! I used to always use imperial but I think I actually prefer metric now – if I had DRO’s I definitely would. Crankdisc screwed on and loctited in place. Facing disc down to thickness. This also gets it square to the shaft if there is any misalignment in the threads. The back face doesn’t matter as long as it doesn’t catch on anything but there doesn’t appear to be much misalignment anyway. Bit of a polish with some wet & dry and here is the crankshaft / disc. Next I turned the crankpin which is 3mm. I decided to use some 1/8” silver steel for this, it didn’t need to be silver steel, just about anything would do, it was just the nearest size I had. Turned the slightly smaller shoulder and threaded 6ba, don’t think I took a photo of that. I set the crankshaft / disc up in the milling machine to drill & tap the hole for the crank pin. To do this I just aligned the centre drill by eye to the centre pip then wound the table out 13.5mm which is the throw. Centre drilled, then drilled and tapped 6ba. Screwed and loctited the pin in place: Some of you will notice I’ve deviated from the drawings here. I’ve just got a pin sticking out rather than a special shoulder and screw that clamps together. The cylinder / bearing housings will be arranged on the baseplate such that the big end bearing is positioned in the centre of the crank pin (1.5mm space either side) but it is free to slide which should allow it to account for any out of squareness without binding. As John (Bogs) said it would be better practice to do it the way he has and Jan has in his drawings but this is the same method I used on my stirling engine and it seemed to work on that so I’ll give it a go here. If not, I can easily make up a spacer and a screw to make it rigid. Then I'll get :poke: and :wack: I'm also not bothering with any balancing. I think the pin / big end is light enough and the flywheel sufficiently heavy not to make a difference on this design. Quick test assembly: I still need to machine the slot and hole in the piston, make the conrod, make the base plate, a base from brown stuff and now I think a burner. I was planning to use the glass burner from my chemistry set I had when I was about 10 but it’s a sort of bulb shape and interferes with the cylinder columns so I don’t think I will be able to manoeuvre the flame into the correct position with that one. Not sure whether to solder a burner or machine one from solid alloy as I did with my stirling. This will need a lot more fuel though so think I may solder it to save time boring stuff out! Got one eye on the finishing line but am determined not to attempt any start up until it’s completely finished! Nick |
| Darren:
Very nice Nick, very nice ..... looks like a bit of mill finish steel .... get yourself a magnet to test Stainless. Though you will be able to "see" it in time as it has it's own look colour usually. Also it's the one with no rust on it after you've had it for a while :lol: |
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