I'm looking at the possibility of making a gearwheel from scratch. With no pattern to cast it from and complex teeth shape, I'm thinking of using wood for speed of manufacture. Either holly or walnut.
But... here's the trouble. I've got no gear cutting equipment and no experience making gearwheels. Its not a simple wheel, as the teeth will be angled in 2 axes. And I cant fit my calipers in there to take measurements, its far too compact.
This gear will engage with a (misaligned) small diameter worm drive,, so you pretty much know the teeth geometry.
Initial plan is to use a drill as a lathe, an angle grinder for roughing and a die grinder for teeth cutting. Central hole will probably be nothing fancier than an auger drill.
The gear will be roughly 1.5" dia, 0.5" central hole, 0.25" thick.
Oh, and the mechanism is all fixed together with slotted head screws that are so tight or well glued that none budge, even with a screwdriver bending. All the existing gears are steel, and the case cast ali.
The only gearwheels that you have much of a hope of cutting are worm wheels, as you can hob them using the same worm (actually a matching spare one, with teeth cut and then hardened). Otherwise forget it and buy a matching pair from Cogs 'R Us.
Make them out of Delrin or Tufnol. Holly (ivy, box or apple too) would be OK in large sizes, but not that small. Walnut is far too soft.
Try Camden Miniature Steam for books - MAP, Argus or TAB have little cheap guides.
BTW the motor running the system is 55w, and the gearwheel in question takes a fairly small percentage of the mechanical power. At under 1 rpm it sees a fair bit of torque.
snipped-for-privacy@gglz.com:
I won't know till I get the machine apart and get more precise measurements
No trace of it remains in the machine unfortunately. Would be a lot easier if it did.
Andy Dingley:
I dont know how to make a copy of the worm drive gearwheel And even with one, I dont have the equipment to use it to make the driven wheel.
I really dont want to take the whole mechanism apart to replace the existing worm drive gearwheel. And since the driven wheel is offcentre from the worm drive, is there really much chance of finding something that matches?
Synchronous operation is necessary here, so close sizes are no use, and there's no way to adjust the positions of the wheels.
mark:
will do :)
harry:
most centre lathes.
Well, I dont have any such equipment.
That's basically the approach I'm looking at, just using the die grinder as a powered file. Gearwheel speed will be under 1 rpm, hence I'm expecting to get away with some degree of filing imperfection.
In which case, the gear should follow the form of the worm, and the profile of the cog should be concave as well as gear-cut.
I've got a better idea - I think...
Soak in diseasel^h^h^diesel oil.
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Good.
If you can get the worm drive out, you might be able to find a plastic (in the proper sense of the word) medium which can be moulded to the right form, and then hardened.
Make it into a strip, and with guides either side to ensure uniformity of thickness, roll the worm down it several times to start the teeth (at the correct angle) and before it hardens, cut and fix to the outside of a plain wheel of the right diameter, then impress the worm again using the same principles.
Or, make the gearwheel in similar fashion out of Plasticene, make from it a plaster of Paris mould, bake the mould dry (otherwise it will spit) and pour in molten 'white metal'.
You could use a resin for the casting - but I don't know the mechanical properties of resin. You *CAN* get a resin which uses cast-iron as a filler - that would probably do nicely.
I like the idea of moulding it, sounds a lot more doable. Would ali from food cans be an adequate metal? I also have lots of epoxy, and could fill it with glass fibre, if its tough enough.
Hi I msay be able to help you by making a worm and wheel to match, I have suitable hobbing kit, however I am rather buisy and will need a lot of data from what yoy have to make an exact fit, if you wish to go this way get in touch Peter snipped-for-privacy@hotmail.com
No - the aluminium would need to be powdered - or very finely granulated. Glass fibre should be unnecessary, as you'd use a lot more ally (filler) than epoxy. I don't know what resin you'd use, but the cast-iron stuff I had was far tougher than GRP resin.
If you were thinking of melting it and poring it in, a light metal like aluminium would need considerable pressure as it is poured - this is usually accomplished in a sand mould with several inches height of sprue, added to that, I'm not sure that plaster would take the heat without it driving off the water of crystallisation.
If it did, it might go off like a grenade...
Your best bet if you want to use ally, (and it's not a bad choice from the bearing-surface point of view), is to approach a firm which does thermit welding. (Mixture of aluminium powder and iron oxide, with trace elements for adjusting composition, ignited with a big plump sparkler, and the aluminium reduces the iron oxide to iron or steel, depending n additives, which is tapped at the right temperature and runs between the two surfaces to be joined, fusing the ends.)
Ask Railtrack whom they use for track maintenance these days - not sure if Jarvis is in that business after Potters Bar. (And you don't want to file a bit of ally to get it. If you do, Dural is better than plain ally)
'White metal' is a good bearing metal and is heavy enough to be poured into an open mould, and being an alloy of tin, lead and sometimes other metals, the melting temperature isn't high. Plumbers' solder might do the job, but a touch of antimony would help with hardness. (Use type metal or auto wheelweights. 50-50 lead and wheelweight metal makes the right hardness for casting bullets, so I'd guess that 75% plumbers' solder, 25% wheelweight should make a satisfactory mix. Melting it with MAZAK will produce a hardness that rings if you hit it.)
It's sufficiently cheap to suck-it-and-see - just be sure everything is centred - you will have to make a jig.
Cutting the teeth would require proper machinery, as the profile of the teeth on your cog would be dished. It *CAN* be done, but you would need something like a lathe with a good tight milling slide, a dividing-head and a properly-formed milling cutter. (Years ago I had the machinery, and could have modified a milling cutter, but alas...)
If you want to make it to occupy many hours of your time and then have it break within a few seconds of putting it into service then bodge it up with melted drinks can, thermite or whatever has been suggested here. There is no shortcut or a cheap and easy way to make gears. If you want it to last and you don't have the necessary equipment then either buy the necessary equipment or buy the gears ready made.
I'm hoping you're wrong :) I know how much force it needs to bear and am fairly confident white metal can do that. Buying the gearmaking kit isnt really a practical option, nor is buying the gear ready made, so white metal it is, as soon as i get one of those tuits.
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