Making Gear Cutters (Ivan Laws Book)

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Making Gear Cutters (Ivan Laws Book) Steve 06-15-2008
Posted by Steve on June 15, 2008, 6:30 am
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 I've been reading Ivan Law's book on making gear cutters and he described
the design and build of a "button cutter" to generate an approimation of the
involute profile.

Mr. Law sets out two tables of design information for the cutters, one
20deg pressure angle and the other is at 30deg pressure angle. The design
data is normalised at one diametrical pitch.

The puzzle I have is that the two buttons are of diameter "D" and the
distance between the button centres is "C".

The thing I'm struggling with is that in both tables "C" is less than "D".
How can this be?

Too be honest it's a bit of an armchair question as I've had a kind offer
from one of the guys on the group to cut the two gears I'm after, but can't
abide leaving things I don't understand to one side!

Steve



Posted by houstonceng on June 15, 2008, 3:36 pm
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> I've been reading Ivan Law's book on making gear cutters and he described
> the design and build of a "button cutter" to generate an approimation of t=
he
> involute profile.
>
> Mr. Law sets out two tables of design information for the cutters, =A0one
> 20deg pressure angle and the other is at 30deg pressure angle. =A0 The des=
ign
> data is normalised at one diametrical pitch.
>
> The puzzle I have is that the two buttons are of diameter "D" and the
> distance between the button centres is "C".
>
> The thing I'm struggling with is that in both tables "C" =A0is less than "=
D".
> How can this be?
>
> Too be honest it's a bit of an armchair question as I've had a kind offer
> from one of the guys on the group to cut the two gears I'm after, =A0but c=
an't
> abide leaving things I don't understand to one side!
>
> Steve

Yes !

C is less than D to make cutters to cut gears with the smaller number
of teeth. In those cases, you have to grind flats on the buttons in
order to get the required distance apart. It's all to do with the
geometry of involute gear teeth.

Andy

Posted by houstonceng on June 15, 2008, 4:27 pm
Please log in for more thread options
>
>
>
>
>
> > I've been reading Ivan Law's book on making gear cutters and he describe=
d
> > the design and build of a "button cutter" to generate an approimation of=
the
> > involute profile.
>
> > Mr. Law sets out two tables of design information for the cutters, =A0on=
e
> > 20deg pressure angle and the other is at 30deg pressure angle. =A0 The d=
esign
> > data is normalised at one diametrical pitch.
>
> > The puzzle I have is that the two buttons are of diameter "D" and the
> > distance between the button centres is "C".
>
> > The thing I'm struggling with is that in both tables "C" =A0is less than=
"D".
> > How can this be?
>
> > Too be honest it's a bit of an armchair question as I've had a kind offe=
r
> > from one of the guys on the group to cut the two gears I'm after, =A0but=
can't
> > abide leaving things I don't understand to one side!
>
> > Steve
>
> Yes !
>
> C is less than D to make cutters to cut gears with the smaller number
> of teeth. =A0In those cases, you have to grind flats on the buttons in
> order to get the required distance apart. =A0It's all to do with the
> geometry of involute gear teeth.
>
> Andy- Hide quoted text -
>
> - Show quoted text -

Sorry. Got my "Cs" and "Ds" mixed up Should have said "C is less
than D to make cutters to cut gears with the larger number
of teeth"

Andy

Posted by John Blakeley on June 15, 2008, 6:24 pm
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Steve wrote:
> I've been reading Ivan Law's book on making gear cutters and he
> described the design and build of a "button cutter" to generate an
> approimation of the involute profile.
>
> Mr. Law sets out two tables of design information for the cutters, one
> 20deg pressure angle and the other is at 30deg pressure angle. The
> design data is normalised at one diametrical pitch.
>
> The puzzle I have is that the two buttons are of diameter "D" and the
> distance between the button centres is "C".
>
> The thing I'm struggling with is that in both tables "C" is less than
> "D". How can this be?
>
> Too be honest it's a bit of an armchair question as I've had a kind
> offer from one of the guys on the group to cut the two gears I'm after,
> but can't abide leaving things I don't understand to one side!
>
> Steve
>
>
I have a pencilled note in my copy saying that there is an error in the
table/tables on P114/5 and that there was an amendment published in
Model Engineer, P744 15th June 1990.

I remember copying it and placing it carefully in the book - but damned
if I can find it now. Maybe some kind soul has that issue handy?

John

Posted by Cheshire Steve on June 16, 2008, 4:04 am
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> Steve wrote:
> > I've been reading Ivan Law's book on making gear cutters and he
> > described the design and build of a "button cutter" to generate an
> > approimation of the involute profile.
>
> > Mr. Law sets out two tables of design information for the cutters, one
> > 20deg pressure angle and the other is at 30deg pressure angle. The
> > design data is normalised at one diametrical pitch.
>
> > The puzzle I have is that the two buttons are of diameter "D" and the
> > distance between the button centres is "C".
>
> > The thing I'm struggling with is that in both tables "C" is less than
> > "D". How can this be?
>
> > Too be honest it's a bit of an armchair question as I've had a kind
> > offer from one of the guys on the group to cut the two gears I'm after,
> > but can't abide leaving things I don't understand to one side!
>
> > Steve
>
> I have a pencilled note in my copy saying that there is an error in the
> table/tables on P114/5 and that there was an amendment published in
> Model Engineer, P744 15th June 1990.
>
> I remember copying it and placing it carefully in the book - but damned
> if I can find it now. Maybe some kind soul has that issue handy?
>
> John

Search the newsgroup for "Ivan Laws" and you will find a couple of
threads on this topic and one contains a link to a spreadsheet written
by Duncan Munroe. I ended up concluding that there is an error in the
tables in my 2006 copy of this book, but as I was after 14.5 degree PA
then I had to resort to my own calculations anyway. It is a shame that
Ivan Law didn't spell out how he calculated the numbers in his tables
so we could check his workings - but on the other hand it is important
to realise that circular cutters are only an approximation to the
involute, and even pre-made cutters cover a range of gears. So there
is a fair bit of tolerance.

Steve (yes, another Steve)

Steve

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