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Posted by PG1D/PA-11Ø12 on June 16, 2008, 7:24 am
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> John Blakeley wrote:
>> 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?
>
> --
> Lester Caine - G8HFL
> -----------------------------
> Contact - http://lsces.co.uk/lsces/wiki/?page=contact
> L.S.Caine Electronic Services - http://lsces.co.uk
> EnquirySolve - http://enquirysolve.com/
> Model Engineers Digital Workshop - http://medw.co.uk//
> Firebird - http://www.firebirdsql.org/index.php
>
If the attachment is the revised table, then THANKS...!!!
Best regards,
Dirk
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Posted by Peter Harrison on June 16, 2008, 3:34 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 spreadsheet that will calculate these values. You can see it here:
http://www.helicron.net/files/involutecuttercalcs.xls
It calculates the button diameter, pitch and infeed for the form tool
described by Ivan Law in his book "Gears and Gear Cutting". To obtain
actual sizes then either divide by the DP of the actual gear to get
sizes in inches or multiply by the module to get sizes in millimeters.
The table in the book is acknowledged as being in error and other tables
exist on the 'net. One of these can be found here:
http://www.metalwebnews.com/howto/gear/gear1.html
(written by John Stevenson)
An article in Engineering in Miniature (Oct 1998) by D A G Brown
describes the process and gives a set of formulae for calculating the
relevant dimensions. I have used those calculations in this spreadsheet.
The calculations are a bit scruffy but accurate in as much as they
replicate the results of DAG Brown. Where those results differ from
other published tables there are a couple of reasons. One is rounding
errors. Another is that the tables often give dimensions for a cutter
intended to cover a range of gears. The compiler of the table may have
chosen any particular number of teeth for that cutter in the range quoted.
In general it seems that close enough will do. For example, take the No4
cutter (26-34 teeth). For this, the range of button sizes is 8.89 to
11.63. Any button size you pick will be an approximation for the other
tooth numbers.
A related discussion I came across had the following suggestion from
Jerry Kieffer: He makes single point form tool by using an end-mill to
cut the profile out of a suitable blank. He says that for any given
gear, there will probably be a standard size end mill of a diameter
close enough for the task in hand. So for example, to make a 48 tooth,
0.5module gear, the button diameter would be 16.42 * 0.5 = 8.21mm. An
8mm end mill would be quite close enough using Jerry's method.
Please note that I have never had to make my own cutters but expect to
one day which is why have taken the trouble to keep track of these bits
and pieces.
Peter Harrison
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Posted by Tony Jeffree on June 16, 2008, 4:27 pm
Please log in for more thread options On Mon, 16 Jun 2008 20:34:20 +0100, Peter Harrison
>A related discussion I came across had the following suggestion from
>Jerry Kieffer: He makes single point form tool by using an end-mill to
>cut the profile out of a suitable blank. He says that for any given
>gear, there will probably be a standard size end mill of a diameter
>close enough for the task in hand. So for example, to make a 48 tooth,
>0.5module gear, the button diameter would be 16.42 * 0.5 = 8.21mm. An
>8mm end mill would be quite close enough using Jerry's method.
Peter -
I described yet another approach in MEW #131 - ther article is also on
my website here:
http://www.jeffree.co.uk/Pages/multi-tooth-gear-cutter.htm
Regards,
Tony
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Posted by Peter Harrison on June 16, 2008, 5:05 pm
Please log in for more thread options Tony Jeffree wrote:
> On Mon, 16 Jun 2008 20:34:20 +0100, Peter Harrison
>
>> A related discussion I came across had the following suggestion from
>> Jerry Kieffer: He makes single point form tool by using an end-mill to
>> cut the profile out of a suitable blank. He says that for any given
>> gear, there will probably be a standard size end mill of a diameter
>> close enough for the task in hand. So for example, to make a 48 tooth,
>> 0.5module gear, the button diameter would be 16.42 * 0.5 = 8.21mm. An
>> 8mm end mill would be quite close enough using Jerry's method.
>
> Peter -
>
> I described yet another approach in MEW #131 - ther article is also on
> my website here:
>
> http://www.jeffree.co.uk/Pages/multi-tooth-gear-cutter.htm
>
> Regards,
> Tony
So you did! I remember now. I have a similar, but less thorough, page here:
http://www.helicron.net/workshop/gearcutting/
But didn't you, or soeone, do a further piece about using CNC on the
cutter position to get a much better generated shape?
As an aside, seeing your page prompts me to haul out my Peatol lathe and
make it into a tool sharpener. It was going to go on Ebay but I don't
think they fetch much.
Pete
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Posted by Tony Jeffree on June 16, 2008, 5:50 pm
Please log in for more thread options On Mon, 16 Jun 2008 22:05:49 +0100, Peter Harrison
>> Peter -
>>
>> I described yet another approach in MEW #131 - ther article is also on
>> my website here:
>>
>> http://www.jeffree.co.uk/Pages/multi-tooth-gear-cutter.htm
>>
>> Regards,
>> Tony
>
>So you did! I remember now. I have a similar, but less thorough, page here:
>
>http://www.helicron.net/workshop/gearcutting/
>
>But didn't you, or soeone, do a further piece about using CNC on the
>cutter position to get a much better generated shape?
That would be a straightforward thing to do - I made a passing comment
in the article that it would be simple enough to do if you had a CNC
mill to hand, but haven't actually don it (yet).
The great thing about that technique is the simplicity of the cutters
- it doesn't get much simpler to make than a rack form cutter.
>
>As an aside, seeing your page prompts me to haul out my Peatol lathe and
>make it into a tool sharpener. It was going to go on Ebay but I don't
>think they fetch much.
Yep - good plan.
Regards,
Tony
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