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| Arnold building the "Little Blazer" |
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| shoey51:
very enjoyable read :thumbup: :clap: |
| madjackghengis:
Hi Arnold, I finally read your post beginning to end and have a couple of comments which are appropriate. First off, you are doing a very fine job, both in the machine work, and in the posting, like so many others have said, I'm not a bit bored, I just feel like maybe you should have more friends to present gifts for the improvement and expansion of your "kit". The one I built is the same size, I made an assumption, having read other builds that were done "by the book" rather than out of the magazine, as I did, and they were twice the size I, and now you, are building. Mine is essentially identical, except not metrificated. The plans called for aluminum for the cylinder, and you did very well to ignore that and use iron, I suspect you will have far better an engine for that choice. I would suggest you look at the thermal expansion factors of cast iron and compare it to the bronze you are using, and multiply the approximately half a thousandth clearance necessary, by the difference, to ensure the piston does not expand beyond that clearance. In Machinery's Handbook, it lists cast iron at .0000065 unit length expansion per degree, with bronze listed at .00001, making just short of twice the rate of expansion. I suspect a full thousandth of clearance will give a working clearance of less than half a thou when up to temperature, which is plenty with graphite as lubricant. If you have any problem with the piston sticking, it could just as well be made of cast iron from the same source, and would not be significantly heavier if you keep the walls thin, as well as the top, of the piston, that is. I don't believe you will need to use graphite for a piston as the iron won't gall the way aluminum does. Having read through your post, I'm half tempted to turn an iron cylinder and a piston to go with it, and be done with the aluminum cylinder altogether. I think you have eliminated all the problem factors I've already been frustrated with over a period of twenty years since I built mine, and since I got it running, only a few short months ago. I don't wish to impose on your log, but as you, I did not have much in the way of tooling when I built mine, and I used a four jaw chuck instead of the rotary table I didn't have, to turn the cam, and I used Mr. Duclos' numbers, forgetting I was in a different position, and my cam came out with a substantially wrong profile, because I used a radius distance from center, rather than diametral, it seemed to be the same thing at the time, but gave a profile very much wrong, and kept the engine from running, along with other issues. If you use a four jaw to form the cam, make sure your indicator is showing the full diameter offset, and not just the radial offset, as I did. I expect you will have a very good running little engine in the very near future, and I'm looking forward to the video, the one with your piston and cylinder is good and shows a very good clearance and fit and should work very well. I have a cheap tachometer off e-bay, put a tab of reflective tape on the flywheel, and was getting about 2500 rpm easily with fresh pistons and cylinders, and I expect you will get similar results without the galling, just needing cleaning on occasion as the drop of oil for the crankpin will end up in the cylinder. I am very pleased to see this engine being built again, with differing thoughts, and in my opinion, better materials than I used. I have seen it built and run with the engine half sized, with a bore of a quarter inch, on u-tube sometime in the recent past, so they will run even smaller, as well as seeing many made in double size, with about an inch bore. Looking forward to seeing it run soon, great build and fine build log :poke: mad jack |
| arnoldb:
:) Thank you very much Eric! :beer: Olli. I'm not sure if this is the way it should be done either; I'm just doing it. And having seen your Stirlings, you should have no problems at all getting a flame licker going :thumbup: Stew, Thanks very much mate :D Thanks Trion :beer: Cheers David D :beer: - I hope you had a full English :thumbup: - nothing like lots of eggs and bacon ! Thanks for checking in you Shoey51! Thanks Jack - I don't like to call you Mad Jack by the way ;). There are many members here on MadModder who have helped me a LOT - not through giving me "kit" but through sharing knowledge and supporting me - and that's something all the kit in the world can not make up for. A load of fancy kit without knowing the basics of how to use it is just that - a load of kit. I'm striving to use the bits I have, and with the generous help received, learn to use them well. Then, as I'm expanding my available bits, I'd just be in a position to use it even better. Thanks; I did consider the materials I have available for this build - that's why I settled on the CI cylinder. I'll give the bronze piston a go - if it does not work, then I'll re-do it in cast iron. The influences of heat in an engine is an entirely new experience for me, so I have a lot to learn from it :) I didn't get as much done today; which makes for a shorter post for a change - saves you chaps from eye strain :lol: Following Mr Duclos's instructions I turned a piece of aluminium stock down to the outer and core diameters for the combined crank web/cam: This was followed by drilling the center 2.9mm and reaming it out to 3mm for a fit on the crankshaft. Reading through the steps required to machine the cam on the mill and rotary table, it seemed (and was!) a good idea to make up something that I could clamp in the mill chuck for centering purposes. Seeing as the crank shaft would be ideal, I cut that off from some 3mm music wire I have. The Dremel and a cutting disc works great for this; the music wire instantly blunts the junior hacksaw blades I have ::) : I then centered the rotary table to the mill spindle, clamped up the workpiece in the small Myford milling vise, and used the shaft chucked up in the small drill adapter to center the workpiece-with-vise combination on the RT - with the RT set to 0 degrees. When I built the RT I took great pains to make sure that the T-slots were exactly on 90 degrees apart and the one on 0 degrees was just that. So I used the edged square shown in a previous post with the edge located in a T slot to set the vise square, and clamped a bit of flat iron down against the top of the vise to keep the reference Phil mentions in his write-up: Then I just followed Phil's instructions and dialled in the offset needed on the Y axis, moved the vise against the clamped down reference bar, and used the shaft-in-chuck to locate the final spot to clamp down the vise. Then milling the cam profile was easy - though I did get the milling depth slightly too deep and ended up scarring the lower workpiece face :doh:: Fortunately the scar is not as bad as it looks; it's mostly a burr... That 6mm milling bit is getting a bit blunt! It was easy to set everything back to "0" after milling the cam, and then to dial in the 43 degrees counter clockwise on the RT needed, and then dial in Y to depth to locate, drill and tap the connecting rod screw-hole: The workpiece was then removed from the RT, and parted off from the parent stock on the lathe. I wish I'd read the instructions trough to the end again before doing this, as I could have saved myself a lot of work later :Doh:. Phil mentions at this stage of his instructions that you have to leave "sufficient" extra stock on the back of the workpiece to later clean up... So I left 1mm extra and parted off... A bit of a diversion followed; the parted off workpiece had to be clamped to the RT again to mill out the webs. I do not yet have a good selection of bits 'n bobs for clamping to the RT; my mill's clamping kit is waaay too big. The RT's T slots are the same size as my lathe's, and I always just used 6mm cap screws of appropriate length and home-made T nuts to clamp things on the lathe's vertical slide. I couldn't find a suitable length cap screw today, so I had to use a bit of high-tensile threaded rod. One thing I did not do in my more inexperienced making of said home-made T nuts, was to prevent anything screwing right through them - as an arbitrary length of threaded rod would do, so a quick-fix was called for. A chisel, a hammer, a T-nut clamped upside-down in the big bench vise, four quick blows, and the result: Now a rod or bolt won't screw through past the end :ddb: I laid out the back of the workpiece, and an odds 'n ends clamping session on the RT followed, using the shaft-in-chuck to make sure the shaft-hole was on center: No super-accuracy was needed for this step, but parts do look better if accurately made, so I took a bit of time getting it just right. Then I milled out the web; 6 degrees offset On the RT for each side, and to the lines: To drill and tap the web for an M2 set screw, I clamped it in the mill vise, and used a bit of 2mm brazing rod chucked in the small chuck to locate the hole: There was not enough clearance for a center drill to get in there, so I used the 1.6mm tapping drill to make a little dent to act as starting point. With the mill stopped, lightly press it down on the workpiece, lift of, turn the chuck 180 degrees by hand, press down slightly harder, lift off, turn the chuck 90 degrees, lightly press down again, turn another 180 and press down slightly harder again. Lift off and start the mill, and drill the hole; the small drill bit will hit the correct spot using this method most of the time without wandering, as the light dent in the workpiece serves as a center mark. I drilled the 1.6mm threading hole using this method, and then tapped it M2 for a set screw. Phil notes at this point to chuck up a suitable rod (or turn one down) to 1/8" (3mm in my case) and make a flat on it, and then mount the workpiece on it, locking it down with a set screw through the threaded hole made in the previous step, and to face off the the back of the workpiece to get it to an overall thickness of 1/4" (6.35mm). I tried that and it was no fun at all... This is on an interrupted cut with a puny screw trying to hold on... And remember I left 1mm extra to face off :Doh:. When the workpiece came loose from the shaft the second time, I went to plan B - which was to wrap a bit of paper around the cam, chuck it up in the 4-jaw chuck by the cam; just roughly on center, and face it off to thickness: . Had I read the instructions up to this point, I would have parted off to just 0.01mm over size initially, and just removed the toolmarks on a bit of emery; that would have left the workpiece perfectly on size without a lot of additional faffing around. After a bit of filing to round corners and some work with emery to clean up, I ended up with this: The crank/cam took quite a while to make, as I expected, so shop time was running out for today. I did manage to get some additional small bits made though. The crank pin bushing - 2mm ID, 2.48mm OD and 4.35mm long: Followed by a 2mm bolt from some 1/8" brazing rod, and a little retaining washer: I will most likely re-make the bolt from silver steel; it just occurred to me that it will experience quite big forces on it when the engine is running! At least, things are starting to resemble an engine now :D: Regards, Arnold |
| Dean W:
Very nice work, Arnold! The crank/cam is deceptively complicated, and you went right at it, just like a machinist. : ) I've read all your writing from the beginning, though some days don't have time to post. This is another fine write-up with you as the author. Entertaining and educational. Something for later, (next time you make T-nuts), if you use an old ball bearing or 60 deg center, you can flatten the bottom thread in the nuts with a good whack of a hammer. Works well, and leaves the bottom of the nut smooth. Dean |
| NickG:
Hi Arnold, just found this, not read it yet but posting a quick reply to remind myself and say well done - your work looks great so far, I love these engines. :thumbup: Nick |
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