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PostPosted: 19 Dec 2017, 22:24 
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I've drawn up a (quite longstanding now) project that has lots of gears; 60-odd.

Originally I got them laser-cut in 3mm acrylic... but the laser cutting service produced a bevel rather than cutting vertically, which on the bore made them run off-true on the shaft and so miss-mesh (parallelograms in cross section not rectangles) even if the teeth might have tolerated the inaccuracy.

Because some of the gears run on nested tubes concentrically, the bores need to be different sizes.

Ideally I'd find a source of cheap nylon (or similar) modulus 1 or, better, modulus 2 gears, where I can drill my own bore from a, say, 1mm pilot (it's just a fun project, I don't want to throw a ton of cash at my prototype), and select gears from c.12 to c. 104 teeth. I need to stack them so flat is good. Modulus 0.5 I can find but are too small to accomodate the larger nested shafts. Any sources?

Failing that, I'd pay a bit more for metal ones and, failing *that*, I'd cut my own.... which brings me to second question: what's the best sheet material for this if my available tool is a scroll saw (I have a band saw but I think it won'y like to do even modulus 2 teeth)? Aluminium 2mm sheet? I have to both cut teeth and drill the bore. I also need to fix (CYA) some to the shafts (which are nested brass tubes). Brass sheet seems pretty expensive.

Advice very much welcomed.


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PostPosted: 19 Dec 2017, 22:51 
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A scroll saw with a metal cutting blade would do 2mm aluminium.

http://www.axminster.co.uk/pegas-metal- ... s-ax877557 ... these will cut up to 3mm

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PostPosted: 19 Dec 2017, 23:16 
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[quote="NazNomad"]A scroll saw with a metal cutting blade would do 2mm aluminium.

That's helpful - thank you


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PostPosted: 19 Dec 2017, 23:29 
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Cutting 104 teeth is going to be very tedious!
An expensive but accurate way is to buy gear wheel cutters

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I use a scroll saw to cut out the spokes.

Rod


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PostPosted: 19 Dec 2017, 23:32 
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I'd suggest getting them laser cut without the centre holeand then drilling them yourself for the axle.
alternately a hobby sized cnc machine would do you for machining acrylic... or aluminium.


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PostPosted: 20 Dec 2017, 10:51 
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I suggest 'Tufnol' - as shown in harbo's picture - and yes, making your own is undoubtedly the cheapest and most efficient way to go - you'll never find 'off the shelf' gears with variable bores and re-boring stock items would likely be difficult to maintain concentricity.

As long as you have a dividing head, a milling machine (you might get away with a pillar drill) and a lathe,

A set of Involute gear cutters for MOD 1 or 2 is easily available though you might like to look out for a Jacob's Gear Hobber - not the cheapest route but by far the best. I have one, but only have hobs up to MOD 0.7.

My guess is that you are making an Orrery - in which case you should be looking at cycloidal form gears rather than involute, and fixing them to the shaft with a key would be better than 'gluing' them.

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PostPosted: 20 Dec 2017, 11:32 
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J-G wrote:
I suggest 'Tufnol' - as shown in harbo's picture - and yes, making your own is undoubtedly the cheapest and most efficient way to go - you'll never find 'off the shelf' gears with variable bores and re-boring stock items would likely be difficult to maintain concentricity.

Reboring using a hand drill or drill press might pipper up concentricity, but it's pretty easy to do accurately in a lathe, or mill.

it just comes down to accurate centreing, which is a standard procedure.

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PostPosted: 20 Dec 2017, 11:37 
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Deadeye, do you know anyone with a 3D printer? once you have a basic gear routine changing diameters, teeth numbers etc. is fairly straightforward.

See the wealth of OpenScad Scripts that can be manipulated.

Some images and explanation

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PostPosted: 21 Dec 2017, 19:35 
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@deadeye:

This is a VERY long shot, but I've just spent a couple of days+ stripping 3 old inkjet printers and a small photocopier (MUCH to my good Lady's disgust)!

I must say that when I answered her question about "Why are you making yourself all dirty messing about like that?" I had to answer that I had no particular project in mind but just had to keep hold of lots of "good" stuff like precision ground steel rods (many look like silver steel), springs of all sorts, various small can motors of 12 and 24V, and Yes, lots and lots of gears of all sizes, most but not all moulded in a "plastic" of some sort (very nicely moulded too I must say).

As said, at present I have nothing particular in mind, so if you send me a PM with your postal address I'll send you a Jiffy bag full of those gears.

The "deal" would be that, after Xmas now, I'll send the gears to you by post at my cost, you take out whatever gears you can use - they're not all on the same size centres - and whatever is left (doesn't matter if it's 10 or 100 (I guess there's about 100 or so in total, I haven't counted them), then you post the rest back to me at your cost.

As said, I have no idea whether or not a single one or all of them (I very much doubt it!) will fit your needs, but if you want to try that, we can do it.

The only other thing I can suggest off hand is that on the net I've seen various suppliers of gears (and related stuff) of all sorts, used by hobbyists in the model car and small robotics areas. That COULD be a source??

Other than that, cut your own, get them CNC'd, or 3D printed (though I guess those last 2 options may probably be as expensive as buying gear cutters and cutting them yourself).

HTH

AES


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PostPosted: 21 Dec 2017, 20:23 
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Many thanks all.

This forum is amazing for someone like me who's just starting.

I don't have a metal mill/lathe, so I think gear cutters may be "too hard".
Tufnol, scroll saw and patience seem like the answers.


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PostPosted: 21 Dec 2017, 22:38 
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A clockmaker's gear cutting mill should be made for the job.
I saw one recently for sale...... I think he asked for something like 200 euros for the whole rig. An old hand cranked version. Should cutt brass gear wheels easily.

I know the oldtimers did cut gear wheels in a metal shaper using a dividing head though I have never seen it done in reality. I have a shaper and a dividing head but neither is ready for use in the near future. They are both mothballed awaiting more space. This is how it's done though they show a bevel gear not a straight one: https://www.youtube.com/watch?v=d6RmNSiTMwg
If you can find a small metal shaper cheap this may be a route forward. Shapers generally went out of use in industry in the 1950-ies so those that survive often turn up cheap. This is a 7" Atlas: https://www.youtube.com/watch?v=5ToNsP8EMbk

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PostPosted: 22 Dec 2017, 08:21 
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Deadeye wrote:
Many thanks all.

This forum is amazing for someone like me who's just starting.

I don't have a metal mill/lathe, so I think gear cutters may be "too hard".
Tufnol, scroll saw and patience seem like the answers.

Do you have a drill press?

If you add a cross vice AKA XY table (and some metrology) you might be able to re-bore accurately.

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PostPosted: 22 Dec 2017, 10:06 
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Hi

Yes - I do have a smallish drill press and a 4" vice. I think I can do the bores pretty accurately. The issue is the teeth

If I could buy blanks with the right numbers of teeth I'd be sorted.


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PostPosted: 22 Dec 2017, 10:31 
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Deadeye wrote:
Hi

Yes - I do have a smallish drill press and a 4" vice. I think I can do the bores pretty accurately. The issue is the teeth

If I could buy blanks with the right numbers of teeth I'd be sorted.

Indeed. The process I was working towards was getting a fresh batch of laser cut plexiglass gears, with no more than a centre-dot
made by the laser, and you could create the various central bores yourself.

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PostPosted: 22 Dec 2017, 10:45 
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Hi

Yes - the perspex was looking good other than the beveling issue. It affected the bores most but meant that the teeth were also slanted (talking c. 10 degrees off perpendicular). If the bores are cut square then the teeth will mesh, although not as well as I'd like. I don't know if that's an inevitable outcome of heat cutting a melt-able material or my provider just did an inept job?

If I could find a source of 2mm or 3mm thick, Mod 2 or 3, toothed nylon cogs with no bore (or a teeny pilot) I'd be laughing. I can get Mod 0.5, but they're too small and fiddly and won't take the larger tubes as axles.

Thanks again everyone


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