Gear wheel 45mm in diameter with 70 teeth

[Former MemberParticipant @formermember19781]

[Former MemberParticipant @formermember19781]

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[Tom S.Participant @toms]

You could do worse than checking out ClickSpring on YouTube, I think. He has a few videos on dividing with nothing more than manual tools on brass sheet.

**LINK**

Although, if you want to use a lathe instead, you may want to make a simple dividing head – if you measure the circumference of your lathe chuck, and print a template that divides that exactly, you can stick it to your chuck, and create a simple 'finger' sticking out from the headstock – all you'd need then is some way to lock the spindle (and a toolpost mounted grinder or tool).

That said, I'm not sure how accurate that would be, nor what lathe you have, but there are various modifications you can make to a lathe for simple dividing without paper – Steve Jordan on YouTube has a number of options.

I suspect the main problem will be the thickness of the material – you might want to put it in a confined arbor of some kind to stop deflection.

Anyway, some amateur ideas from me

[Pete RimmerParticipant @peterimmer30576]

What's the application Bill? Can you suffer a slightly modified diameter or gear form? What does the gear have to mate with?

[roy entwistleParticipant @royentwistle24699]

Bill can I ask how did you calculate the blank diameter ?

Roy

[SillyOldDufferModerator @sillyoldduffer]

A bit more information would help Bill.

• What tools do you have?
• How many teeth on what diameter? (Edit Doh! this info is in the title…)
• What does the gear mesh with? (Presumably a clock?)
• How much time and money are you prepared to spend?

Making a one-off gear with nothing but hand-tools is possible. It will take a long time, requires filing skills, and will test your powers of concentration! Many CAD packages can draw gears for you and there are also online gear designers like this example (involute), or this one (cycloidal). You draw and print the gear at 1:1 scale, glue it to the blank as a template, stick it in a vice and painstakingly file each tooth to shape and depth. How painstaking depends on the gear's purpose: clock teeth need to be good but gears for other purposes can often be crude, even mere gashes. In the good old days, water and wind-mill gears were cut roughly to shape and then assembled. After fettling to get the mechanism to turn, running the gears together for a while would cause a reasonable tooth fit to emerge from the mayhem. Yuk.

There are better ways of making accurate gears if you have the facilities or are prepared to make, lash-up, or buy them.

Dave

 

 

 

 

Edited By SillyOldDuffer on 09/10/2018 12:09:20

[Former MemberParticipant @formermember19781]

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[Simon Williams 3Participant @simonwilliams3]

Dividing a circle into 70 shouldn't be beyond the wit of a man with a sharp pair of spring dividers and good eyesight (or a magnifying glass). Oh, and a steel rule.

Assuming the gear blank face can be marked, first divide it into seven. The key here is that if you set the dividers to 0.439 times the diameter of the blank you will divide the circle into seven chords. Mark off the seven chords, making sure that the last chord steps back exactly to the starting point of the first.

Incidentally the figure of 0.439 comes from this:

Seven chords in a circle each subtend 51.42 degrees at the centre. Length of a chord of a circle = 2 sin a/2 where a is the angle subtended by the chord.

(Or you can look it up in Machinerys Handbook under Circles – lengths of chords for dividing))

So back at our gear blank, divide each seventh in half. You could divide the original circle into 14, but the bigger the starting sector the more accurate it will be. Examine each halfway – seventh to make sure they are all equal. At this point mark the fourteen divisions on the periphery of the gear blank with a couple of strokes of a three square needle file.

You could guess what happens next. With the needle file, mark five subdivisions in each fourteenth of the periphery of the gear blank. I reckon a practiced eye could get these evenly spaced around the periphery to an acceptable accuracy, whatever that means.

You've now got the position of the teeth – all 70 of 'em – marked on the blank. File to shape. Easily said!

However I'm not entirely sure about the original dimensions, but for the sake of keeping this post to a reasonable length I'll post that separately.

[Former MemberParticipant @formermember19781]

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[Former MemberParticipant @formermember19781]

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[JasonBModerator @jasonb]

Looks like a German model from what I can see so metric gears

A 0.5MOD 18T gear is 10mm OD which ties in with your sketch

To get a gear to suit the 26mm ctrs you actually need a 0.5MOD 86T which has an OD of 44mm

[Simon Williams 3Participant @simonwilliams3]

Let's do a bit of arithmetic.

45 mm is 1.772 ins. DP of a gear = (n+2)/OD, so DP = 72/1.772 = 40.64.

That's a bit fishy not to come out (closer to) to a recognisably whole number, so convert to module and see if the answer is more comfortable.

Module = 25.4/DP so mod = 25.4/40.64 = 0.625 which isn't a "standard" number either.

Since I started this the picture above arrived, given the age I'd rather believe in DP science than module. 40 DP would be a recognisably standard number, would you like to check the OD of the blank carefully and see if 45 mm could be comfortably 1.800 inches/45.7 mm? I'd hate to think you went to all that trouble to make a gear which turned out to be a little bit too small!

And while we're at it, could you please advise why 70 teeth? If the 45 mm blank carried 69 teeth it would be 40.07 DP which I could believe was as close to 40 DP as one might expect to measure. Mind, dividing the circle up into 69 by eye is going to be more difficult!

Best rgds Simon

Edit – Jason's beaten me to it (again!)

Edited By Simon Williams 3 on 09/10/2018 15:51:16

[Former MemberParticipant @formermember19781]

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[JasonBModerator @jasonb]

Posted by Bill Chugg on 09/10/2018 16:09:57:

Jason thanks for calculation – you are correct so it is metric as you say.

I will now turn up a 45.7 mm blank and report back.

Why?

Simple maths you have 26mm gear ctrs, valley to valley of the small gear is 8mm so 4mm radius. 26mm less 4mm = 22mm so max diameter you could fit in is 44mm. which just so happens to be what I suggested

 

Edited By JasonB on 09/10/2018 16:20:41

[Simon Williams 3Participant @simonwilliams3]

'ang on ang on ang on!

If Jason has it right, and I'm pretty sure he has, then the gear you are aiming for is 86 teeth at 0.5 module, the OD of the blank is 44 mm. My calculation was based around the number of teeth being fixed, but now we have a dimension for the centre to centre distance that changes everything.

Centre to centre distance = mod x (n1 + n2)/2 where n1 and n2 are the tooth counts of the two gears. I take it that Jason has used this to calculate n2.

I suggest we need to be sure of the centre distance – everything depends on that.

edit – Jason can draw pictures faster 'n I can type

Edited By Simon Williams 3 on 09/10/2018 16:23:27

[Neil WyattModerator @neilwyatt]

Bill,

0.5 module gears are everywere. If you can find a plastic one about 1 1/2" – 2" diameter anywhere you can make a flycutter by filing a slightly hollow faced wedge shape to fit the gaps in the plastic gear. You can then use this to cut your gear (possibly backed up with a bit of MDF or plywood.

For dividing, make up a simple spindle to fit the embryo gear, I'll let you decide how to clamp it in place, but I would use a threaded spigot on the end of a thicker bar.

Get a block about 2" high you can clamp to the bed of your mill. Put a suitable hole to clamp the spindle close to one edge of the block and split through with a hacksaw from the far side. Drill and tap for a simple clamp screw.

Print out a disk about 3 1/2" diameter with 86 marks around the edge and fit it to a wooden backing board. You can glue this to the back of the spindle and use it to index it around against a fixed pointer attached to the mill bed.

If you cut your gears just a touch over-depth, I bet your gear will work first time.

Neil

[Simon Williams 3Participant @simonwilliams3]

So the problem becomes "how to mark out 86 divisions around the circumference of a 44 mm gear blank".

My Boys Own Dividers method wont work, because half of 86 is 43, which is a prime number. So resort to the paper and triangle method. You've mentioned "turning up a blank" so I assume you have a lathe, therefore a chuck, though any disc of known diameter will do.

Assume for the sake of simplicity that the OD of the chuck is 100 mm. Then the circumference will be 314.2 mm. This doesn't divide neatly into 86 equal portions of any simple size, so take a piece of A3 paper and draw a line 315 mm long. This allows a smidgeon for the thickness of the paper. At one end draw a line 292.7 mm long at right angles to the first. Make the right angle as accurate as you can. Now join the two ends to make a hypotenuse 430 mm long.

430 mm divides nicely into 86 times 5 mm. Mark these divisions along the hypotenuse.

Now drop parallel lines from each mark on the hypotenuse to the 315 mm line. There will be 86 lines marking out the length of the circumference of the chuck. Cut out the 315 mm line, now divided into 86 equal increments, and stick it to the periphery of the chuck. Rig up a pointer as an index, mark out the 86 teeth on the gear blank.

I'm betting Jason's drawn a drawing to explain in the time I've tried to explain.

HTH Simon

Bit of an OOPS!.  You need 87 divisions because the first and the last will be overlapping.  Otherwise the arithmetic is valid in principle, though wrong in practice.  Sounds like the comments I got in my last maths exam!

Edited By Simon Williams 3 on 09/10/2018 16:58:39

[JasonBModerator @jasonb]

Posted by Simon Williams 3 on 09/10/2018 16:53:28:

So the problem becomes "how to mark out 86 divisions around the circumference of a 44 mm gear blank".

You find a nice man to produce a PDF of a 66mm dia disc that will fit nicely on the spindle pully of your Unimat 3 plus a 1:1 outline of the gear so you can also try the stick it and file method

[Former MemberParticipant @formermember19781]

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[JasonBModerator @jasonb]

Check your home e-mail.

[Pete RimmerParticipant @peterimmer30576]

Where are you Bill? I'm in North Kent and I could hob those teeth onto your blank in very short order.

[Simon Williams 3Participant @simonwilliams3]

I held off offering to make a gear for you as I read it that the "I fixed it" factor was part of the entertainment value here. But I'm W Gloucestershire if that helps, and although I haven't checked there is a 43 tooth circle on my dividing head I'm pretty sure there is. If it helps to rattle one out I'm game.

Simon

Edited By Simon Williams 3 on 09/10/2018 18:00:10

[Dick HParticipant @dickh]

Looks a bit like this set up from Doll & Co. or Carl Doll (**LINK** You can probably count the teeth from the photos.

[SillyOldDufferModerator @sillyoldduffer]

Not sure we've got the full story yet. Looking at the photo, I see the big gear wheel rotates freely on an axle, and the the axle is quite long, ie able to accommodate something wider. Could it be that the original was a compound gear, with the drive taken off the smaller wheel?

Anyone know what the original engine looked like? The engine appears to have various practical ways of taking off power and a single gear in that position would be an idler. Unless it was only ornamental?

Oh dear, I shall be counting rivets next.

Edit:  Dick H got in as I was typing with a photo.  All is revealed.  I guessed a compound gear, actually it's a gear plus  pulley!

Dave

 

Edited By SillyOldDuffer on 09/10/2018 18:45:18

[Former MemberParticipant @formermember19781]

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