Author Topic: Mandrels, Gearcutter & Gears  (Read 23832 times)

Offline arnoldb

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Mandrels, Gearcutter & Gears
« on: July 22, 2012, 08:28:58 PM »
This will be a fairly lengthy post, so please bear with me  :)

I offered to make the metric conversion and some missing gears, as well as a leadscrew handwheel for a fellow member's Myford lathe.  A package containing some lumps of cast iron and a lump of aluminium arrived yesterday; accompanied by another package containing 6 bottles of very nice high quality fermented red grape juice  ;D - Thanks W!

There were also five very nice bits of tungsten included; perfect for making up an indexable grooving tool.  I added a couple of sections of printer shafting that will be needed for the project:


The longer section of printer shafting volunteered first, and was turned down over it's length to 16mm to fit my ER25 mill collets, with an accurate 24.5mm long 10mm diameter section at the end:

It was then drilled and tapped for an M6 screw at the end. (and Yes - it's a 24.5mm long section; not a 1" (25.4mm) section  :P

Then I flipped it in the chuck, and turned and drilled the back section to make a thick matching washer to the front, before parting things off; I'm a lazy rotter, so the washer and the removal of the last thick section were done one-after-the-other:


A quick trip to the mill, and the end had a 2mm thick x 1mm deep slotted section added:


Mandrel done - this one will be used to mount the gear "hob" on - and I took the bit of extra effort to make it well, as it can be used for many future projects:


As I'll be making five gears in total, I made up a mandrel for these as well.  I just carefully clocked up the other bit of printer shaft in the 4-jaw (less than 0.005mm run-out), and turned the end down to 5/8" for a close fit for Myford change gears:

I did this so that I can remove and re-install the mandrel at will; It takes me less than two minutes to center up a shaft in the 4-jaw to this accuracy.  The bit of shafting was also drilled and tapped M6 at the end.

Next bit - a 25mm long slug of 20mm diameter silver steel (drill rod) - that was drilled and reamed 10mm to fit the first mandrel I made:


Off to the mill with that, and a "keyway" section milled into it; the keyway may be round, but will work with a bit of 2mm rod on the first mandrel:


Myford change wheels use a 14.5o pressure angle.  Dang - the first (and only) set of gears I made were 20o, so some tool grinding required.
I grabbed a fresh good quality HSS-Co8 tool blank from my stock, and used my precision protractor to mark it out for the necessary tip:

The scribe marks literally are just as deep as the permanent marker ink; my scriber won't touch HSS!

Off to the bench grinder, and after a couple or ten minutes, one side was ground down.  I don't know how fast other home-shoppers grind down tool bits; for me it takes a while and especially on a bit like this, I do a lot of dunking in water while grinding it up.  My own rule of thumb is that the HSS should never reach a temperature where it starts to colour.
I took a break and a photo:


The next side took a bit longer to grind down.  As the tip gets thinner, more frequent cooling is needed, as the thin sections are the first to start overheating.  HSS is actually a pretty poor conductor of heat, so the thin tip section of the toolbit can overheat in a jiffy.
Lazybones that I am, I just ground the toolbit down till the tip fit the root of one of my own changewheels properly - I do have all the calculations and measurements to calculate out the correct tip dimensions, but this was easier  ::):


After a final honing on the fine side of an oilstone, the toolbit was sharp enough to make a neat and clean cut in paper:

It will also do that to skin  ;)

Back to the lathe, and the silver steel section I'd reamed earlier was mounted on the mandrel that was made - I just used a short section of 2mm brazing rod as the key - and lightly skimmed off to true up the outside:


Then I set up the toolbit that was ground up. As the toolbit was marked out relative to the parallel sides, I could just use a small square to make sure things were set up properly.  I don't know of many people who own 29o fishtail gauges:


I plonked the long-travel DI on the bed - I needed to get accurate 3.99mm spacings for the gear hob (well, 3.9898mm to be more accurate, but 1.2 microns are a bit hard to measure in my shop  ::)):


Cutting commenced; this was a fairly big job, as it was done without tailstock support and each groove had to be plunged 2.85mm deep.  That's the reason why I honed the toolbit up that sharp, and for this operation I used the Myford's lowest high-range speed (200RPM) with LOTs of cutting fluid.  A plain HSS cutting bit will keep a keen edge even machining one of the tougher steels like silver steel - as long as it's not pushed to the point where it heats up too much.  And it mustn't be allowed to "rub" either - one needs to see the chips coming off all the time; if things rub, the silver steel will work-harden and take the edge of the cutting tool near-instantly:


Once all the grooves were done, I tested it against a gear - Looks OK to me:


I left off there for today - I don't think I'll be able to do more on this project till next weekend.

Regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline lazylathe

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Re: Mandrels, Gearcutter & Gears
« Reply #1 on: July 22, 2012, 10:08:59 PM »
Great work as usual Arnold!
You make it all look so easy...

Will be following along with you on this adventure.

Andrew

PS what was the name of the fermented red juice?
We don't get the good stuff here in Canada...
A new place to hide my swarf!

Offline tel

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Re: Mandrels, Gearcutter & Gears
« Reply #2 on: July 22, 2012, 11:10:57 PM »
Good start to an interesting project Arnold, I'll be watching.
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Offline John S

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Re: Mandrels, Gearcutter & Gears
« Reply #3 on: July 22, 2012, 11:17:08 PM »
Nice work and a good choice on using the 6 bottles of red as cutting fluid, lets face it it's not much use for anything else.   :-*
John Stevenson, Nottingham , England

Offline Millwright

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Re: Mandrels, Gearcutter & Gears
« Reply #4 on: July 22, 2012, 11:25:16 PM »
Watching this one with great interest Arnold.
John

Offline Dave G

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Re: Mandrels, Gearcutter & Gears
« Reply #5 on: July 23, 2012, 01:05:19 AM »
Yeap, I'm watching too, Dave

Offline EmanMyford

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Re: Mandrels, Gearcutter & Gears
« Reply #6 on: July 23, 2012, 06:32:41 AM »
As usual very nicely executed  :). Looking forward to see more.

Kind Regards,
Ewald

Offline swilliams

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Re: Mandrels, Gearcutter & Gears
« Reply #7 on: July 23, 2012, 11:19:15 AM »
I'm also watching with interest

Steve

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #8 on: July 23, 2012, 05:31:20 PM »
Many thanks Gents  :cheers:

Andrew, I can't reveal the name of the juice  ;)

John S, it hides blood as well - so has to be used with care  :)

Regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Online steamer

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Re: Mandrels, Gearcutter & Gears
« Reply #9 on: July 23, 2012, 05:36:07 PM »
Im watching Arnold!

Dave
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Damned ijjit!

Offline pwasbury

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Re: Mandrels, Gearcutter & Gears
« Reply #10 on: July 24, 2012, 07:26:04 AM »

My kind of interest, looking forward to the next post!

Paul

Offline WagnerJ

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Re: Mandrels, Gearcutter & Gears
« Reply #11 on: July 24, 2012, 08:09:56 AM »
Great Stuff Arnold!  :bandrock:
I'll be watching over your shoulder ..... and keep that red stuff for your burfday!  :DrinkPint:
Wow ... and look at all this smileys!!!  O0

Groetnis
Wagner

Bogstandard

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Re: Mandrels, Gearcutter & Gears
« Reply #12 on: July 24, 2012, 09:24:37 AM »
Arnold,

A few years back, I purchased sets of commercially made hobs, and was going to follow a DVD about gear cutting to hob gears out.

Unfortunately, illness got into me, and the project had to be put onto the back burner.

Very soon, when I get back into the shop, the second item on the agenda will be that project, so your post about it will come in very handy indeed.

BTW, in the next issue of Model Engineers Workshop, as far as I know, will be showing exactly what I will be attempting to do. Freewheel hobbing.

John

Offline jonesie

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Re: Mandrels, Gearcutter & Gears
« Reply #13 on: July 24, 2012, 03:54:20 PM »
 arnold i to will be watching this one real close :LickLips: jonesie

Offline John S

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Re: Mandrels, Gearcutter & Gears
« Reply #14 on: July 24, 2012, 08:26:54 PM »
Go to you tube and look at a series of gear cutting video's by a user called hobbynut. There are quite a few to the set and IMHO these are very good at getting across the easy way to hob gears.

IMHO that video mentioned by John on gear cutting by Jose Rodregius is a waste of money, it's not clear enough on quality and he make mistakes all the way thru, Pi is not 3.416
John Stevenson, Nottingham , England

Offline Woodguy

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Re: Mandrels, Gearcutter & Gears
« Reply #15 on: July 24, 2012, 08:35:17 PM »
Apparently those videos were removed, but were compiled into a single movie available here: http://leatherwoodplayground.com/Gears%20and%20Hobs%20Joined.wmv

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #16 on: July 24, 2012, 09:08:04 PM »
Many thanks for the responses Gents  :NotWorthy: ; I didn't think there would be this much interest!

Wagner, I only tested one bottle  :NotWorthy: - the rest will be kept for that day - and some saved for future as well!  ;D

John, I recall your purchase of those gear hobs.  I can't remember if they were straight-cut though   :facepalm:  There's also been quite a bit of discussion about this method on the 'net and it seems to work.  I'll try and keep a look-out for the next MEW - its delivery here in Windhoek is totally sporadic and non-guaranteed  :rant:
The only free-wheel hobbing I've tried was when I made the worm wheel for my rotary table - that worked a treat, even in the hands of a complete newbie like me.

I first tried this straight-hob method when I made the 0.5 module gears for my Cracker locomotive - and this was the results after the second try (hob, gears and grooving tool shown):

For those who do not know about my Cracker build and are interested in small live-steam locos, you can have a look at this thread on MadModder

Kind regards, Arnold

Edit:
John S & Woodguy, I'm not sure precisely which video Bogs was referring to; videos are a bit scarce in my neck of the woods, and the link Woodguy posted to would take a lot of time downloading; Internet bandwidth here is a bit slow.
« Last Edit: July 24, 2012, 09:12:51 PM by arnoldb »
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Bogstandard

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Re: Mandrels, Gearcutter & Gears
« Reply #17 on: July 25, 2012, 06:59:04 AM »
Arnold,

It is this sort of post that will help many of our members.

If they can follow your instructions, they too can make their own gears for their little engines. It could save them lots of pennies in the long run.

You keep showing, we'll keep avidly reading. :ThumbsUp:

John

Offline IanR

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Re: Mandrels, Gearcutter & Gears
« Reply #18 on: July 25, 2012, 02:39:18 PM »
There was an article in ME years ago by the late J A Radford, on cutting gears this way. It saves making several B & S type cutters, but I suspect indexing the blank is slower. Awaiting the next instalment with interest.

Offline grayone

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Re: Mandrels, Gearcutter & Gears
« Reply #19 on: July 25, 2012, 07:17:51 PM »
OK for a complete idiot like me can some one explain what gear hobbing is as opposed to cutting gears with a cutter which I understand needs a different cutter for different numbers of teeth.   While I wait for an answer  :DrinkPint:

Graham
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Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #20 on: July 25, 2012, 08:19:57 PM »
John, Ian & Graham - many thanks for your input Gents  :)

Ian, I don't think indexing the blank is  slower; the small gears I showed were done to full tooth depth for each of the index positions - exactly the same as what would have been done with a B&S cutter.  The only slow cut was the very first one, as it had to remove a significant amount of stock on that cut; the rest of the cuts actually became lighter.  I'll try and show that when I cut the gears.   
For this set of change wheels, I'll have to see if I can go in at full tooth depth; that will depend on how sharp I can get the cutter, as well as my mill.  I'll see when I get there  ;)

Cheers Graham  :cheers: - I hope you enjoy your libation  ;D
The term "hobbing" might be confusing - it's also just a way of cutting a spur gear.  In many industrial gear-cutting operations, they use a helical "hob" that is a cutter that basically resembles an Acme thread, and by synchronised rotation of the gear blank against the turning cutter, presented at the correct angle to it, the gear is cut - hence the term "hobbing". 
The cutters you were referring to is what has already been referred to in this post as B&S cutters - there you need a different cutter for gears with different ranges of tooth counts.  A complete B&S cutter set comprises, if I recall correctly, 8 cutters in total for the whole range of gears from 12 tooth to rack - for one specific DP or Module. 
What I'm showing, while loosely called hobbing, is more akin to cutting the way you thought of it.  The "hob" I'm busy making is basically a multi-point cutter, and will cut an approximate tooth profile with facets on it.  This method produces less accurate tooth profiles than either "hobbing" or using the correct B&S type cutter - but produces entirely satisfactory gears for home/hobby use.  In fact, I think it will produce a better resulting gear than the spur gears that came with my small Cheap 'n Cheerful Asian Import lathe.

Please note; failure IS an option here; If the results are not satisfactory, I'll resort to making gear cutters using the "button" method to get a more accurate tooth profile - these basically work like B&S cutters.  I'm trying the "hob" method first, as I have to make a 60, 35, 30, and two 21 tooth gears.  I haven't checked yet, but that lot would require 3 different B&S type cutters at a quick thumbsuckguesstimate.

At least the weekend's getting closer  ;D

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline Alan Haisley

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Re: Mandrels, Gearcutter & Gears
« Reply #21 on: July 27, 2012, 02:00:33 AM »
Arnold,


I see how, for 14.5o you ground your tool to that angle on each side. I assume for a 20o pressure angle that each side would be ground to that. What is the geometry of how deep to cut with the tool and how far apart to space the individual cuts?


Assuming that this method turns out satisfactorily, a little table of the math/geometry involved would be useful to us aspiring gear cutters.


Alan

Near Raleigh, NC, USA

Offline Dan Rowe

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Re: Mandrels, Gearcutter & Gears
« Reply #22 on: July 27, 2012, 03:05:42 AM »
Arnold,
I always like to read and watch gear cutting threads. Gears are just fun.

Alan,
One of the best books on hobby gear cutting is "Gears and Gear Cutting" by Ivan Law. It has the math and explains the set ups with a chapter on grinding cutters.

One of these days I hope to cut true scale bevel gears for a Shay.

Dan
ShaylocoDan

Offline RMO

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Re: Mandrels, Gearcutter & Gears
« Reply #23 on: July 27, 2012, 07:00:54 PM »
This is fasinating, one of these days I want to try this.  Until then I watch and hopefully learn.

Mike O

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #24 on: July 28, 2012, 08:30:27 PM »
Alan, Dan & Mike, Thanks for looking in.

Alan, yes, for a 20o pressure angle, it would be exactly the same method; just set at the correct angle.  I cheated and used Marv's GEARSPUR program - it gives all the necessary figures.
Like Dan mentioned, Ivan Law's book is very good about explaining all the theory involved.
This method does work - at least for small gears; the brass gears I posted earlier runs a treat in the little locomotive they are installed in  :) .  It works best for higher tooth-count gears.  I'll try and post close-up photos of the results on these bigger gear tooth profiles once done.

Dan, if I recall correctly, Chuck (cfellows) showed an excellent method to cut bevel gears a while ago.  That might make interesting reading if you haven't read that yet.  I seem to recall reading somewhere that the Shay's bevel gears are kind of "offset" as well...  - I do hope you'll show when you cut them :) .

Mike, I hope there's something useful for you  :)


On to today's shop session; not as much as I wanted, but progress at least.

First order of the day was to form the teeth on the cutter.  I used a 6mm mill to mill them out - I put the bottom of the milling bit about 1mm below the centerline of the workpiece, to try and get some rake on the teeth.  It's minimal, but it's there.  By a quick eyeball after cutting the first profile, and cranking the dividing head while counting turns, I saw that I could form six teeth on the circumference:


As a last step, I used a file to add a bit of rake to the short "round" sections on the perimeter behind the tooth tops.  Just a shallow angle to nearly meet up with the tooth tips. 
After removing the workpiece from the mandrel:

You can click on the photo to see a bigger image.

It looks a bit of a dog's breakfast as I didn't de-burr it, and overshot some of the milling cuts  :-[ .  The no-de-burring is on purpose - and based purely on one of my own pet theories:
If the cutter is de-burred before hardening, the cutting edges can already be slightly blunted.  During the hardening process, the high temperature needed and the resulting oxidation of the metal will also blunt the cutting edges further.  By leaving the burrs attached, these protect the cutting edges during hardening, and it is thus easier to sharpen the cutter after hardening. 

I don't have photos of the hardening process - I'm not yet comfortable about wielding around a camera while playing with a torch and extremely hot metal  :disagree:
Before hardening it, I coated it lavishly with dish-washing soap; this also protects it from oxidation during hardening.  Then I heated it to orange-red with a butane torch, grabbed it with a pair of pliers and dunked it vertically into a bucket of water (the workpiece is made of water-hardening silver steel) 

Proper hardening was just tested with an old file on one of the edges; it skidded right off without removing any metal.  I gave the workpiece a quick brush-off with a small stainless steel wire brush - that removed a couple of the bigger burrs - as they were very hard they just broke off, and then started removing the rest of the burrs with some diamond files.  Here the front bottom set of teeth has been cleaned up a bit, while you can see burrs left on the rest:


After more time spent carefully de-burring it further, it's pretty sharp already, and just needs a light hone.  In the past, I've mostly worked with cutters hardened up like this as-is, but that was in soft metals like brass and aluminium.  As the gears will be made from cast iron, I decided to rather temper the hob, as I could feel that it was extremely hard and thus very brittle while de-burring it.  I didn't want to loose the hardness on the teeth edges though; just toughen up the "inside" of the hob.  That meant raising the inside of the hob to a high enough temperature to turn it blue again, while not allowing the flame to touch the outside...  My solution - slip it over a 10mm bolt, and heat the bolt alternately on both sides of the workpiece while checking for the colour to flow:


The result - I took the photo on a piece of paper to show up the colour contrast a bit better.  You'll notice it's darker on either side and in the middle, and what I'd like to think of resembles the "straw" colour described in tempering guides towards the tips of the teeth:

All it needs now is a final hone  :)

As I'm supposed to be making gears here, I set the bandsaw to work:


While waiting for the saw to do its business, a thought broached my mind...  I'll need to cut keyways in the gears!
A quick grinding job on some virgin 4mm round HSS stock, and I have a match to the keyway in one of my Myford's gears:


It was easier to use the new piece of HSS, as it is 80mm long and gives some better control while holding it for grinding.  It's still a bit tight in the keyway in the gear, but that's fine, as it also needs a final hone on the oilstone.  After cutting off the necessary length, it was mounted on an arbor I've had for a couple or three years (actually it's an inside turning tool!).  A bit light-weight, but I'll be cheating a bit while broaching the keyways  ;)


The last thing I did in the shop today was to face the first gear blank to thickness.  The Myford gear specifications are for a 3/8" (9.53mm) thickness, but testing the gear from my lathe, they range from 9.4mm to 9.6mm - so, as I thought, not a critical thickness:

I must say, this is very nice cast iron indeed; there's a small chilled spot close to the skin that runs in towards the center for about one mm, but I did expect that and specified the material slightly-oversize.

 :whoohoo: - there's nothing like the smell and taste of machining cast iron for me - I love the stuff !

More tomorrow  :)

Regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline vcutajar

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Re: Mandrels, Gearcutter & Gears
« Reply #25 on: July 28, 2012, 10:07:30 PM »
Making gears is something I need to learn, so Arnrold, I will be looking over your shoulder.

Vince

Offline zeeprogrammer

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Re: Mandrels, Gearcutter & Gears
« Reply #26 on: July 28, 2012, 10:59:18 PM »
Making gears is something I need to learn, so Arnrold, I will be looking over your shoulder.

Vince

Same here.
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Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #27 on: July 29, 2012, 08:05:50 PM »
Thanks Vince & Carl  :)

The next installment...

I drilled out the center of the gear blank to 13mm, and bored it out to the required 15.86mm.  Seeing as I'd be making 5 gears, I'd turned up a plug gauge beforehand to test the hole size.  Then I moved the chuck over to the rotary table on the mill (purely because it's convenient to mount it like that), and drilled two 1mm holes on the inside of where the keyway corners will be:


Next I used  a 2mm drill to drill out most of the excess stock - the drill broke through slightly into the hub hole, but stayed nicely on course:


Next I used a 2mm end mill to clean out most of the rest of the stock - to leave a minimum for broaching out:


Then I mounted the chuck back on the lathe, honed up the broach I made yesterday, and mounted it on center on the toolpost.  Then I had at it using the apron to feed the broach longitudinally, and after each in-feed and retraction, the cross-slide was moved out about 5 thou before the next pass.  After it was done, the Myford's change-wheel mounting bush easily, but accurately fits into the gear blank hub:


The broaching went so easy, that for some subsequent gear blanks, I didn't bother to drill & mill the excess stock out first.  I just jumped in and slotted the keyways right from the start; much quicker than the palaver explained above...  Just lighter feeds on the cross slide required; .0025" (0.05mm) per pass worked a treat - making for light cuts but it goes quite quickly once one gets the sequence right of feeding the apron and the cross-slide  :D
I forgot to take a photo of the broaching setup; so just before I stopped shop today, I took a photo where I'd broached the keyway slot in the 60 tooth gear's blank:


The last photo was out of sequence; the rest of the photos to come are the continued work on the first lot. 
As you may have noticed, that gear blank (it's the 30 tooth one) was just faced and bored, but not turned down to size yet.  For that, I mounted it on the mandrel I'd turned up for the gears, and turned it down:

Lazy me  ;D - the mandrel was still centered up in the four-jaw, so it was quick to mount!

A final hone on the gear cutter, and it was sharp enough to shave some grooves into a bit of brass plate by hand:


Back to the mill, and with the dividing head mounted and the 4-jaw chuck screwed on, I used my height gauge to find the top of the gear blank:


Then it was easy to deduct half of the blank diameter and mark the center line:

The black ink mark on the front was made to "remember" the starting position for the machining to come.

I mounted the cutter, and aligned one of the teeth on center with the mark made:


The first cut was made in three passes; two of 1mm deep each, and the last the additional 0.85mm required to reach full depth.  I kept spindle speed well down; just 280rpm as the cutter will be doomed the moment it heats up too much, and a gentle rate of feed:


If you like to watch paint dry, here's a video clip  :) :
<a href="http://www.youtube.com/watch?v=ZpE60v1RvPE" target="_blank">http://www.youtube.com/watch?v=ZpE60v1RvPE</a>

From the first cut to the last pass took about 45 minutes - and that includes time in between monkeying around to set up for the video and so on.  Not fast, but OK considering I was really taking my time  :) :


So, how does it measure up to the real thing ? - well, the tooth profiles are slightly thinner than the real deal.  If you did look at the video clip, you'll see that the cutter is running slightly eccentric... I'd grabbed my "wonky" 16mm collet, and the wobble on the cutter will cause it to remove more metal.  Overall it's a result - far from perfect, but serviceable:




Nobody wants to count teeth every time a gear is picked up - so I swung the hammer a bit:


I've already turned up the blank for the 35 tooth gear; I'll switch the rummy collet out for the good one, and see if the result improves.  If so, I'll re-make this gear as well. 
The cutter really stood up well, and still feels as sharp as when I last honed it, so that's some good news at least  :)

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline chucketn

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Re: Mandrels, Gearcutter & Gears
« Reply #28 on: July 29, 2012, 10:18:53 PM »
Beautiful work, Arnold. And, great photos and explanaton. I do have one question. After the first cut is to full depth, how far do you index for the next cut. Is the 2nd and subsequent cuts to full depth?

Chuck

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #29 on: July 30, 2012, 08:24:33 AM »
Thanks Chuck.

Indexing is to the next required tooth position each time.  I did all the subsequent cuts to full depth, as there is less material to be removed after the initial cut.  That will depend on your milling machine though; if its a bit light, you might have to make two or three passes as needed.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline swilliams

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Re: Mandrels, Gearcutter & Gears
« Reply #30 on: July 30, 2012, 09:38:05 AM »
That's great Arnold. I've never done it that way, but feel much more confident about using that method in the future now.

Steve

Offline Dan Rowe

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Re: Mandrels, Gearcutter & Gears
« Reply #31 on: July 30, 2012, 12:42:24 PM »
Very interesting stuff Arnold. I do remember Chucks gear cutting work and there were several discussions of bevel gears that made me pick up my key board.

No worries I will post my attempt to cut a Shay bevel gear no matter what the out come is. The loco with the offset bevel is a Climax.

Dan
ShaylocoDan

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #32 on: July 30, 2012, 06:06:03 PM »
Thanks Steve & Dan  :)

Ahh - yes Dan it's the Climax.  Those should be fun to try one day.  Next up for me - after finishing these gears and an engine build - I'd like to try my hand at an internal gear...

Kind regards, Anold


Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline Firebird

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Re: Mandrels, Gearcutter & Gears
« Reply #33 on: July 30, 2012, 09:17:47 PM »
Hi Arnold

Very nice  :ThumbsUp:

Its satisfying to see a gear emerge from the blank isn't it. Do you remember me making some timing belt gears. The first one I cut put a smile on my face.

Well done and thanks for the write up, its been very interesting.

Cheers

Rich

Online steamer

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Re: Mandrels, Gearcutter & Gears
« Reply #34 on: July 31, 2012, 09:27:39 AM »
Nice one Arnold!   Is there a minimum number of teeth that is viable with this method?


Dave
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Damned ijjit!

Offline dsquire

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Re: Mandrels, Gearcutter & Gears
« Reply #35 on: July 31, 2012, 01:14:25 PM »
Arnold

You make it look so easy. Thanks for letting us watch over your shoulder.

Cheers  :cheers:

Don
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Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #36 on: July 31, 2012, 06:27:48 PM »
Thanks Rich  :) - yes, it's actually very therapeutic - just like screw cutting on the lathe.  Requires slightly more attention though...  This one was easy as it was a full two turns per tooth, but the 35 and 21 tooth gears I have to cut will have the dividing head's sector arms and hole plates come into play.
Just a quick note for others reading this; my dividing head has a 60 tooth worm wheel, hence the two turns per tooth for this 30 tooth gear.  I think many of the commercial DHs have 40 tooth worm wheels - so check yours before cutting a gear  :ThumbsUp:

Dave, thank you  :) .  I'm not sure of the minimum - the 10 tooth 0.5 module gear I showed in an earlier photo cut OK, though there is some under-cutting visible on the teeth.  So I'd say that's about as low a tooth count one can go  :shrug:

Thanks Don - it's really not hard to do.  Just a bit of planning, work and time involved - but that goes for any tool or engine building process anyway  :)

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline ref1ection

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Re: Mandrels, Gearcutter & Gears
« Reply #37 on: August 01, 2012, 04:41:19 AM »
This was a great tutorial Arnold. Enjoyed every minute of it.

Ray
Indecision... the key to flexibility!

Offline chucketn

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Re: Mandrels, Gearcutter & Gears
« Reply #38 on: August 02, 2012, 05:32:13 PM »
I want to use this method to make change gears for my Micromark. Will I have to make different hobbs, as in involute cutters, depending on tooth count?

Chuck

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #39 on: August 02, 2012, 06:16:17 PM »
Thanks Ray  :)

Hi Chuck.  No, that's why I chose this method; one can use the same hob for the full range of gears.  For gears with a high tooth count, you just have to make sure that the mandrel holding the hob can extend far enough out of the chuck to give adequate clearance for the gear rim. 
If you look at the hob I made, you'll see that the roots of the teeth are below the mandrel outside diameter.  In my case this places a restriction on the maximum tooth count I can make on a gear with it; it will be just sufficient to make the 60 tooth gear I have to make.  The ideal would have been to make the hob out of thicker drill rod, but I didn't have any...  I could have made it longer and added more teeth to it to compensate as well, but that would have made hardening and tempering it the way I did slightly more difficult, as well as adding more of a risk of deformation during the hardening and tempering process.
Hope all this makes sense  :)

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline chucketn

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Re: Mandrels, Gearcutter & Gears
« Reply #40 on: August 02, 2012, 07:15:32 PM »
Thanks for the explanation, Arnold.

Chuck

Offline WagnerJ

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Re: Mandrels, Gearcutter & Gears
« Reply #41 on: August 02, 2012, 07:26:18 PM »
O goody! It's almost weekend and time for our next installment!  :smokin2:

Good going Arnold  :cheers:

Regards
Wagner

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #42 on: August 04, 2012, 09:32:31 PM »
Pleasure Chuck  :) - I included a photo in today's post that might show a bit more clearly what I meant.

 :) Here you go Wagner - not much of an installment, as it's all a bit similar.

 :whoohoo: Today was the first warm day here in quite a while - meaning no jacket and pretty much Spring weather.  Shrek the parrot barely bode me "morning" before asking for a bath; it's been quite a while since he did that.  So, he got his bath, and I gave the canine furballs a bath as well - but I stopped short of washing the car  :Lol:

Everything was set up for cutting the 35 tooth gear - except for the correct hole plate on the dividing head.  Seeing as I'd be cutting 35 and 21 tooth gears, they share a common divisor of 7 and would most likely be able to share the same set of hole rings on one of my dividing plates, so I ran Marv's DIVHEAD program to check:
Code: [Select]
DH Worm gear ratio = 60:1
No rapid indexing plate available
Divisions of workpiece = 21
Ratio/Divisions = 60/21 = 2.85714285714286
Turns required = 20/7 = 2 & 6/7

2 full turns of crank
and 36 holes on 42 hole plate
or  42 holes on 49 hole plate
or  66 holes on 77 hole plate
or  78 holes on 91 hole plate

For the 35 tooth one (abbreviated):
Code: [Select]
1 full turns of crank
and 30 holes on 42 hole plate
or  35 holes on 49 hole plate
or  55 holes on 77 hole plate
or  65 holes on 91 hole plate

Well, that was easy - my plate with both the 49 and 77 hole rings was already mounted, so I set up on the 49 hole ring (less hole counting involved), and set the sector arms on the dividing head (DH) to starting hole and 14 additional holes - thus 15 holes.
This might sound counter-intuitive, but it actually makes perfect sense (I just hope I can explain it clearly  :shrug: )
  * The sector arms on my DH cannot include an angle of more than about 240o, and the 35+1=36 holes needed in the included section is about 265o.  (36/49*360o ~= 265o)
  * The "normal" solution as was shown from the calculations in the quoted text above (35 holes on 49 plate) is for the case where the sector arms are moved in the same direction as the DH crank for the next position.
  * As the sector arms can't open wide enough to accommodate this included angle, one can set them to use the "excluded" angle, and use them in the reverse direction of cranking the DH.
  * The "excluded" angle is the total number of holes in the dividing plate minus the holes needed from the calculation:  49-35=14.
  * The "+1" hole is the starting hole; that's not counted when one counts the holes to the next position for the sector arms - or - alternatively, one counts it as 0.  That means the sector arms must encompass the starting hole, and the additional holes required to the next position, hence the "+1" - this goes for using both the "included" or "excluded" method of using the sector arms.

Counting the holes can be a bit tedious and error prone; I keep a permanent marker (sharpie) handy, and mark every tenth hole counted on the dividing plate.  Then I mark the final hole with it as well.  It's easy to clean up with some solvent later on, and helps if count was lost somewhere.  ALWAYS count a second or third time as well - it follows the old adage of "measure twice; cut once".

Here's the photo I took after setting the position; you can click on it for a larger image - the "sharpie" marks shows up very faintly - but if you use your mouse to count the holes from the pin in the third set of rings from the outside, you should just be able to discern them - count "one" as the hole to the right of the pin:

If anybody's interested in a video of setting up the dividing head and operation while cutting, please shout up; I have to go through similar motions for the 21 tooth gears, so I'll be happy to oblige.  Just note, I'd have to talk on the video, and if someone laughs at my Namibian/Afrikaans/English accent, I'd be forced to come on a surreptitious visit to your shop and inject diamond paste into your machines' moving parts  :LittleDevil:

Last week I mentioned the cutter was running "wonky" - I addressed that by using my better ER25 collet, and then cut the gear.  It turned out slightly better - but not much... The cutter most definitely was happier for running more true,  and after 45 minutes  - taking things slowly and methodically, this was the result (original Myford gear on the left):


The next photo is for Chuck (chucketn) - to add to the explanation I gave earlier in this thread.  It shows how the hob I made is just barely large enough for the 60 tooth gear when set at full depth of cut:


Cutting the 60 tooth gear was pretty much a no-brainer; with my DH having a 60 tooth worm wheel, it was one turn per tooth, so no sector arms involved  ;D.  One thing I did differently was to run the RT counter-clockwise this time, so that the major amount of cutting (and hence larger cutting forces applied) would be done closer toward the mill's spindle - (the top of the cutter) - for improved rigidity.  That helped a bit, and the gear turned out quite well:


Then I started off on the two 21 tooth gear blanks - and engineered the first serious booboo of this escapade... While boring out the hub of the one blank, I forgot to halve the calculated feed measurement, and bored it over-size.  I only realised that 1/3rd of the way through what should have been the finishing pass  :-[ .  One very good quality bit of cast-iron ruined - for this job at least.  I turned up another blank, and that one is ready and rearing to go, already mounted on the milling machine for tomorrow's shop session.  I ended the shop day with this measly crew; a couple of finished gears, a 21 tooth blank ready to be turned down to size (like stated, the other one is already done and set up on the mill) and the booboo blank.  Hey, "stuff" happens, so it's only fair to show that as well  :) :


Regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline chucketn

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Re: Mandrels, Gearcutter & Gears
« Reply #43 on: August 04, 2012, 09:47:03 PM »
Thanks, so much Arnold. Great thread, great pictures, and great explanation.

Chuck

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #44 on: August 05, 2012, 08:08:18 PM »
Pleasure Chuck, and thank you  :)

The last installment of this thread...

During today's shop session I finished off the two 21 tooth gears  Unfortunately I cannot stamp numbers on them as I don't have a small enough punch set:


Then I just randomly assembled a gear train on my Myford using original gears for all except one of the gears I'd made during this thread and with a strip of paper to set the appropriate gear tooth spacing:


Then I swapped the original gears for the home-made ones, and dropped some oil on each gear:


Rotating the gear train by hand, nothing jammed, and it ran just as smoothly as with the stock gears.  I engaged the gear train to the spindle, and fired up the lathe.  Under power, they run just slightly noisier than the originals - but they need to bed in a bit still.  The original gears for my lathe have had 40+ years of bedding in  ;) :
<a href="http://www.youtube.com/watch?v=gfXlS9vW8U0" target="_blank">http://www.youtube.com/watch?v=gfXlS9vW8U0</a>

The final family photo of all the bits 'n bobs that went into the process; there's even some stock left  ;) :



Some final comments


I'm really surprised at how well the silver steel (drill rod) cutter lasted; it's still as sharp as when I first sharpened it.  I must admit that I nursed it along though.  The good quality of the supplied cast iron could also have had an effect on this, but at higher speeds while turning the gear blanks on the lathe, it was quite easy to toast the tip of my HSS turning tool, so speed does matter.  Sometimes slower works faster!

It was a bit time-consuming making the gears this way.  Not everyone enjoys this type of machining challenge, but I found it relaxing, fascinating and extremely rewarding.  I must be weird  ;)

One always have the option to buy gears online, but having checked what these specific gears would cost to procure and import, and given the state of the local currency against international ones, it's actually significantly cheaper to make them this way for us here in the southern parts of Africa. 

The method shown does not make perfect gears, but they are entirely suitable for hobby use.  While I'd shown how to make the gears for a lathe, this same method can be used to make custom fitting gears for traction engines, geared locomotives, and timing gears for IC model engines - and pretty much any other modelling need.  In fact, at some point in future I'll make up additional change gears for my small lathe using this same method; it's supplied gears can not go below 0.5mm pitch, nor imperial.  One of the reasons I bought the small lathe was to make tiny screws on it, and I need well below 0.5mm pitch!

It allows one to easily make application-specific gears for which commercial cutters are hard to find - need a, let's say 20.3DP  gear set ? - Easily done. this way.
(Well, 20.3DP = 1.251 Module, so you might get away with a 1.25 module commercial cutter  :) - sometimes it helps to check both metric and imperial systems for something that would work...)

And last but not least:  While I have cut small gears using this method, I learnt some new things along the way.  I've never tried broaching before, and this was completely new to me.  It was not at all difficult even using the primitive broach I'd made up for the gear keyways.  The main thing appears to be to just hone up those cutters.

All in all, I had lots of good fun in the shop, and I hope the gears will help their new owner along his way in model engineering  :)

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline chucketn

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Re: Mandrels, Gearcutter & Gears
« Reply #45 on: August 05, 2012, 08:49:52 PM »
Again Arnold, I thank you for a great presentation. Well documented. As soon as I can get some silver steel big enough I intend to follow your methods.
I need a 55 tooth gear to repair a lift chair, some more change gears for my lathe, and am working on a gear reduction for a leadscrew drive.

Chuck

Offline EmanMyford

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Re: Mandrels, Gearcutter & Gears
« Reply #46 on: August 06, 2012, 06:35:31 AM »
Hi Arnold,

I echo Chuck, thanks for a great detailed thread.

Kind Regards.
Ewald

Offline jonesie

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Re: Mandrels, Gearcutter & Gears
« Reply #47 on: August 06, 2012, 02:30:29 PM »
thanks arnold ,nice post.  ihave some gear cutters but not all so will be making some like you did. thanks again jonesie

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #48 on: August 07, 2012, 12:29:37 PM »
Chuck, Ewald & Jonesie, thanks gents  :cheers:

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline mklotz

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Re: Mandrels, Gearcutter & Gears
« Reply #49 on: August 07, 2012, 04:17:16 PM »
Your thread has the honor of being my first bookmarked thread in my MEM folder.  Well done.
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Offline Alan Haisley

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Re: Mandrels, Gearcutter & Gears
« Reply #50 on: August 07, 2012, 05:19:33 PM »
Great thread, Arnold.


Seems like I always have "one last question" though:


Early on you mentioned that the tooth profile was faceted by this method. My question is do the number of facets, and hence the degree of imperfection, depend upon the number of passes and the depth of feed for each?


Thanks for a ton of good info in this thread.


Alan

Near Raleigh, NC, USA

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #51 on: August 07, 2012, 07:16:22 PM »
Thanks Marv & Alan  :)

Alan and anybody else reading this - please do ask questions if you want to; it's for everyone's benefit.

The number of facets depends on the number of the teeth on the gear - not at all on the amount of infeed or number of cuts taken on the same tooth spacing.

With reference to the following photo.
I set things to cut the tooth gaps - and the third-from-bottom tooth on the cutter is bang on center line to cut the gap.  The teeth on the cutter immediately above and below the center line one cuts the first facet, and the ones further out from those cuts the second facet.  This is because the cutter actually looks like a rack gear to the gear blank when presented this way. 


With a low tooth count for the gear, one can get to the point where it will only cut the tooth root and one facet because of the tighter curvature on the gear blank.  I tried to draw up a quick C-o-C of what I mean with that:


One thing one could try to get more facets, and hence a closer-to-form tooth profile, would be to cut the gears like I had done on the "gap", and then offset the dividing head/rotary table by one half of the offset used for each tooth.  Then by raising or lowering the cutter by half of the tooth spacing as well and taking another pass through the gear, the amount of facets will be doubled.  Such a second pass could be done quite quickly as well; there will only be a minimum of material removed to form the extra facets.   :facepalm: Now, why didn't I think of that a bit earlier! - I'll have to test that out - unless someone beats me to it  :)

So thank you Alan for asking the question :NotWorthy: ; it's good to make one think a bit  :ThumbsUp:

Kind regards, Arnold
 
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline IanR

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Re: Mandrels, Gearcutter & Gears
« Reply #52 on: August 07, 2012, 08:52:58 PM »
I thought you'd have 7 facets per tooth flank, as that seems to be the number of cutter or rack teeth that will engage with a gear with an ordinary number of teeth. If I'm right, each facet would be about 16 thou wide on a 20 DP gear.
I've just reread the article by J A Radford, he made things more difficult for himself by cutting the hob from a dirty great lump of HSS, and did the indexing round half a tooth and along half the pitch, partly to get the necessary undercutting on a 25 tooth gear.
He said his 20DP gears were a little noisy until they'd had about an hour's running, so I'm not sure that his results were any better than yours. So I'll be trying it your way when I get round to making timing gears, instead of making 3 different cutters.

Offline JohnC

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Re: Mandrels, Gearcutter & Gears
« Reply #53 on: August 12, 2012, 07:45:16 PM »
Hi Arnold,
A bit late to the party, but you did say:
'If anybody's interested in a video of setting up the dividing head and operation while cutting, please shout up; I have to go through similar motions for the 21 tooth gears, so I'll be happy to oblige'.....


Well, I'd be very interested - if you haven't already done the job without the camera present! 

Thanks for a very informative post.
Rgds,
John
John
York, UK

Offline arnoldb

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Re: Mandrels, Gearcutter & Gears
« Reply #54 on: August 12, 2012, 08:44:40 PM »
Thanks Ian & John  :)

Ian, sorry; I thought I'd replied to your post  :-[
The number of facets depends on the amount of teeth on the gear; for smaller tooth-count gears, less teeth would be engaged with rack teeth. 
Well, technically this is not quite correct either; in the case of a straight-cut rack and pinion gearing setup, or with two straight-cut spur gears running together, there is only one tooth from each of the gears in contact at any point, with a momentary double-contact during operation as the gears move.  Strictly speaking, the spacing between the teeth of a gear must leave adequate clearance for the non-engaged teeth - otherwise the drive train would just lock up.
The width of the facets will depend on the DP/Module of the gear in question, and also on which part of the cutter actually cut it.  The widest facet is closest to the root of the tooth, and the narrowest facet closest to the tip of the tooth.

John, I've finished cutting the gears, but I will do some more work using the dividing head this coming weekend or the next.  I'll take a video then and post it up  :ThumbsUp: - When I first used it, it seemed a daunting thing to do, but is actually quite simple to use.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!