I am finally getting around to sorting out out my Faircut Junior lathe. It’s currently fixed on to a rather battered MDF board, and it’s really difficult to adjust the belt tension,and/or change which drive pulleys are used.
Plan is to make a proper stand, which is the correct height for myself, and to use an arrangement somewhat like the following sketch to tension the belts…
Am still doing work on the free body diagrams to determine the correct relationships between belt length, belt tensions, strut length/angles, and hinge positions.
Lots being going on here, but once again not much in workshop 😦
Inspired somewhat by Mekanizmalar’s you-tube animations I’ve been looking again at an old idea…
My mechanism uses epicyclic gears, as that is a compact way of introducing a phasing angle to a shaft and/or cranks. As I’ve drawn the mechanism power is sent in via a drive gear, and it ends up exiting at the ball joints on the planet carriers. With the drive gear, and one lever fixed in place, I hope it can be seen how moving the free lever, results in the planet carrier nearest it rotating. That’s altered the phasing between the planet carriers, and similar happens when the drive gear is rotated.
If mechanism is powered and neither lever is moving, driving a ram from the eccentric mounted ball joints, will result in output from the rams that is a sine wave. The only difference between the motion of the rams is one might lag between the other.
Possibly to “sum” the motion of the rams using a bar as per Mekanizmalar’s animation here. It also possible to sum the motion of the rams hydrologically, if the rams act as a pair of pistons working a single common chamber as a pump. When both rams are moving into the chamber together (0 deg phase) the effective stroke is twice that of a single ram. If the rams are 180 deg out of phase, (their motion is mirrored, ie one ram “up”, other “down”) then the effective stroke is 0.
After a busy/stressful month, back to working on projects.
snapped a drill bit drilling axially in to the end of oil pump drive shaft using lathe, but lucky it didn’t get stuck in the hole. hole taped, and now have 35 tooth gear mounted on oil pump. I’ll probably just add glue if it does slip under power. Waiting for the RTV liquid gasket to set again.
Used paper to “shim” the gap between motor shaft and the worm- it’s not a tight fit so will need to add glue. Now on to making the frame to mount the DC motor to the oil pump.
Motorbike oil pump turned up last week, and I had a little time to work with it this weekend. Before going to all the hassle of making a proper cover plate- made a temporary cover out of mild steel sheet and epoxied pipe elbows in place for the oil ports. Hoping RTV flexible gasket will provide some sealing, but oil will probably leak oil all over the place. So long as some goes where it’s supposed to ie over the atomising tube, I really don’t mind. Any spillage will go back into a sump, just the same as the overflow from the atomizing tube. After a bit of struggle managed to get the gear removed from the drive shaft, so for initial test runs, motive power will be via an electric drill chucked on the drive shaft.
If that goes well I’ll then have an idea what kind of revs will be needed for the pump, and can calculate some pulley ratios. A final cover plate should really hold the driving motor too. That ratio will be needed to set the approximate distance between pump shaft and motor shaft.
Been working at Kicad. Think I’m getting the hang of how to create component footprints, and convert schematics into PCB layouts. Seems the relaxation oscillator can be constructed on a single layer PCB, so looking for surface mount PUTs. The optocoupler is surface mount so if possible I may as well save the time/effort/cost of drilling holes.
Mulling over ideas for how to adapt my milling machine to CNC. First thought is to get a digital readout for each axis and then use an “elastic band” pulley between shaft of a DC motor and the handwheel. Feedback from the digital readouts goes to a controller, which then powers the motor in the appropriate direction. Problem for me is the scales for accurate digital readouts seem to have their own proprietary interfaces. and most aren’t cheep. I might have a shot at adapting a digital calliper for this. Failing that it’s gonna be position encoders driven directly by the axis motor, and reduction gears onto the handwheel shafts to a) increase torque b) increase effective resolution of the position encoder. eg if there’s 30:1 speed reduction between motor and output, the encoder will turn 30 times for each rev of the output. a really simple way to improve the effective resolution of an encoder. If the rpm weren’t too high, it would be possible to drive the gear off “speed up” gears – the encoder itself will have a low inertia. Should work well to use the antibacklash technique where one gears pair is locked to their shafts , and another identical pair of gears is in parallel to the first, but only one gear of 2nd pair is locked to it’s shaft, the other gear is sprung loaded against it’s matching gear. the spring takes up the backlash. Of course there’ll be extra backlash introduced by the gearing, between motor and axis, but I think that can easily be programmed out, by mimicking the antibacklash technique used in manual machining. It’s only a problem when the direction along an axis changes sign. When backlash might occur, following is way to reduce it’s effects …
- the tool withdrawn from work.
- tool moved a short distance, 180 degrees against the direction it will move in after anti-backlash routine.
- Tool then moved back to where it was before it was withdrawn.
- machining continues.
Enough of ideas for now, so back to practical. Have an engine oil pump from a small 4 stroke motorbike on it’s way to me. Should turn up early next week, and when it does, it’ll be driven with an electric motor (or drill), for another attempt at getting my Babington waste oil burner design running . The last experiment certainly proved that the principle worked, even if the burner casing needs work to avoid flames outside of it, and had to be aborted when the automotive washer pump used to pump oil over the atomizing tube, cut out. After letting everything cool down, the washer pump began worked again as if nothing had happened to it. The veg oil had got pretty hot, so I’m guessing that the components of the gear pump heated up and expanded, and the extra friction then stalled the pump’s motor. Must have shut the motor down before it burnt its windings out. Should have more success with a pump that’s intended for moving hot oil around, and with a pulley so the motor can run faster without needing PWM to reduce the oil flow.
1st project nearing completion and as I’d hoped output from photocouplers can charge capacitors at low constant current
optocoupler relaxation oscillator with 5nF cap
perfect as uCurrent current sources perhaps?
Thought it to be about time I got my head around blogging, and began documenting some of my projects