Author Topic: when you have to cut an odd numbered gear  (Read 9131 times)

Offline madjackghengis

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when you have to cut an odd numbered gear
« on: April 07, 2010, 11:18:27 AM »
While cutting the old valve seats out of a set of heads, the portable power unit for my portable valve re-seating machine stripped out its worm gear, the first gear in the train that gives me fifty rpm, and about two hundred foot pounds of torque to turn the spindle.  A quick check with Boston gear showed they don't carry a fifty one tooth gear, checking with the company that took over, when K.O. Lee went out of business gave me the answer they could give me an estimate on the cost of having the gear made, however they did not have one and would job it out to a machine shop.  Looking at my dividing head, I quickly discover I don't have differential indexing either, so I'm out of luck there too.  Since I've been using my DRO on my mill for lots of holes, it suddenly occurs to me, I can make an index plate for my dividing head using the DRO, and by drilling fifty one holes in it, I can make it possible to use my simple index head provide fifty one holes for the cost of making a plate, and with this and a twenty dollar gear cutter, or a fifty cent tool bit and my shaper, I can cut that gear and make that motor just as good as it was when I bought it, twenty years ago.  The next step is deciding whether to grind a cutter to fit the shaper, and save the money and shipping, or do the gear cutting on the mill, and wait till a proper #3 cutter arrives, and then set the angle and cut the gear.  Unfortunately, this "worm gear" was not cut as a worm gear at all, but as a spur gear, cut with the angle of the worm matched by the teeth of the "worm gear", which gives strictly line contact between the worm and the gear, while a true "worm wheel" cut with a "worm hob" would give a plane of contact, and thus a place for lubrication to interact with the worm and gear, and not just get pushed out of the way.  The index plate has been drilled, I just have to fit it to the dividing head, and find some material suitable for a "worm gear" or better named bevel spur gear.  Pictures are forthcoming, the repair will be shown and joy and happiness restored after weeks of muted anger and hostility.  I thought the machine was supposed to last a lifetime, and I'm only half dead yet!!! :bang: Mad Jack

Offline madjackghengis

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Re: when you have to cut an odd numbered gear
« Reply #1 on: April 08, 2010, 11:15:04 AM »
This gear has presented about three different ways to make a replacement, and I have finally settled on using a dividing head, even having made tooling for another method.  Having already turned an index plate, and drilled the fifty one holes using my DRO function, here is the plate in the lathe, being turned to size

Taking a cut, this is a piece of scrap, and its hard cast iron, part of a lathe scrapped out almost thirty years ago, the feed clutch plate for the apron.  It has cost lots of time getting to this point.  This is recycling at its most efficient :thumbup:

The center hole was too large, so I bored it to put on a stub arbor to turn the o.d., with a tight press fit and locktite, and now am boring the arbor to fit the arbor on the dividing head, as the "stub" will end up part of the index plate when it is finished.  After this, three mount holes, drilled and counterbored, and it is done.

index plate mounted and tested on the dividing head, now I just need to make a blank and an arbor to hold it on, and buy a cutter.  Mad Jack :beer:

Offline Darren

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Re: when you have to cut an odd numbered gear
« Reply #2 on: April 08, 2010, 12:03:46 PM »
Excellent, I like the way you used the dro on the mill  :clap:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Bernd

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Re: when you have to cut an odd numbered gear
« Reply #3 on: April 09, 2010, 10:13:39 AM »
Mad jack,

I have to say the light bulb went on after you said use the DRO on the mill to make an index plate. Can't believe the answer to making index plates was sitting right there in front of of me.  :clap:

Seems like I'm forgetting stuff I learned years ago. :scratch:

Bernd
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Rob.Wilson

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Re: when you have to cut an odd numbered gear
« Reply #4 on: April 09, 2010, 10:33:45 AM »
hi Mad Jack

if you have 51 holes in the index plate , and are using the 40:1 reduction on the dividing head , how will you get 51,  am i missing some thing ? ( i probably am )

would it have not been better to make the index plate fit the front of the dividing head ,were you can do direct indexing, just a thought .


cheers Rob

Offline madjackghengis

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Re: when you have to cut an odd numbered gear
« Reply #5 on: April 09, 2010, 11:15:40 AM »
Hi Rob, Bernd, when I bought the DRO for my mill, I thought I was doing it primarily to be able to accurately machine with it, drilling holes where they are supposed to be, and putting slots right on target and the like.  My first experience was with bolt circles, and I thought, "what a great extra", and went on.  It was only when I stripped a fifty one tooth gear in a valve reseating machine, and realised I needed to be able to do differential indexing to get fifty one, and of course don't have a differential indexing setup, that it occured to me I could do a fifty one hole bolt circle.  Rob, when you are using your indirect indexing, meaning not using the indexing plate, but using the worm, the index plates, and a hole circle, in the case of a forty to one dividing head, you divide the number of holes by forty, and you then select an index plate with holes sufficient to account for any "carry over".  Since the smallest plate with fifty one as a factor is a fifty one hole plate, one must have it, or a multiple of it to do the indexing indirectly.  With the fifty one hole plate, one completes the circle by moving the pin forty holes in the fifty one hole circle, not counting the hole the pin is in as one of those holes.  Most indexing books use examples that are almost useless, such as twelve divisions, or sixteen, where there is no challenge in finding an answer.  Think of it this way:  forty fifty oneths, turned fifty one times will bring the indexing pin around fifty one times, and will equate to the full circle, and account for forty teeth being used to get all the way around.  By the way, I did make a direct indexing plate before the light bulb lit, but didn't use it as my mill power down feed chose to keep feeding long after the lever popped out, and gave me one hole three times as deep as the other fifty, and I didn't trust it's accuracy.  I see this as opening the way to transposition gears for doing metric gears on my American lathe, and getting the gears as accurate as the ones you can buy at highly inflated prices.  It struck me that it is even more accurate than "differential indexing", which actually only provides an approximation for most counts between fifty and a thousand.  One can put an hundred line plate on an indexing head, with a cursor line, and calculate the divisions on the plate to make any count, and with a hundred division plate, and a forty tooth worm, this is accurate to one part in four thousand, and with a simple vernier on the cursor plate, bring it to one in forty thousand, however that is extremely tedious and very easy to lose track of exactly where you are at, and would best be left to a stepper motor setup, than done by hand, although many people have done good work with such a setup.  mad jack

Rob.Wilson

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Re: when you have to cut an odd numbered gear
« Reply #6 on: April 09, 2010, 12:26:15 PM »
Hi Mad Jack

I new i was missing some thing  :doh:  , i get it now , your way is much better  :thumbup:

Thanks Rob

Offline madjackghengis

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Re: when you have to cut an odd numbered gear
« Reply #7 on: April 15, 2010, 12:21:35 PM »
Hi Rob, I could have made the plate for direct indexing, but running it through a forty to one head makes the accuracy much greater.  Here's the gear
it may look like all the teeth are there, but the worm has worn the center out of each tooth and it is only the ends still showing.

here's a side view of the gear and the flycutter which will cut the new gear.

A close look at the fly cutter will show the ground tooth which will cut the groove in the new blank

The chuck will come off the lathe, go on the indexing engine, set at the worm's helix angle, and the fifty one teeth cut for a new gear.  More pictures will come, when the gear is cut, and when it is back in the drive motor, and working. :headbang:  mad jack

Offline madjackghengis

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Re: when you have to cut an odd numbered gear
« Reply #8 on: April 17, 2010, 11:34:41 AM »

with the chuck, stub arbor and gear blank mounted on the mill, making the first cuts

a closer look at the mill, cutting with a fly cutter, ground to match the old gear teeth

another close look at the cut

teeth finished, gear ready for cutting a keyway, note the groove worn in the teeth of the old gear

new and old gear lying side by side

setting up the shaper to cut the keyway

cutting the keyway, ten minutes to set up, two minutes to cut it.

gear pressed on shaft of the driver, and fit in its place in the machine, perfect fit.
Just have to reassemble the driver motor, and test it out.

Drive motor completed, assembled, and tested, works great.

another view of the drive motor, complete.

Rob.Wilson

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Re: when you have to cut an odd numbered gear
« Reply #9 on: April 24, 2010, 09:53:15 AM »
Hi MAD  :wave:


Top job  :bow: :bow: :bow:, thats a great fix  :clap: :clap: :clap: :clap: :clap: :clap:

Regards Rob

Offline TriHonu

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Re: when you have to cut an odd numbered gear
« Reply #10 on: June 20, 2010, 09:39:37 PM »
  I see this as opening the way to transposition gears for doing metric gears on my American lathe, and getting the gears as accurate as the ones you can buy at highly inflated prices.

If you can find a 127 division plate to make a metric transposing gear...

If you want to really go cross-eyed and brain numb make that plate.  It took me over 3 hours to drill the 127 holes using a Bridgeport with a DRO.  I'm slowly working on making a set of metric change gears for my LeBlond.

Offline John Stevenson

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Re: when you have to cut an odd numbered gear
« Reply #11 on: June 21, 2010, 03:08:21 AM »
Marypoppinsbag on Ebay sells division plates with 127 holes.

Also available at www.metoolsonline.com

Might not have any on sale at the moment as i have a shed load to make for them  :doh:

John S.
John Stevenson

Offline Stilldrillin

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Re: when you have to cut an odd numbered gear
« Reply #12 on: June 21, 2010, 03:28:15 AM »
VERY nicely fixed, (and explained) Jack!  :clap:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!