Author Topic: Mandrels, Gearcutter & Gears  (Read 23739 times)

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

Online 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

Offline 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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and your better best

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!