CVA Lathe Metric Change Gears

This topic has 5 replies, 4 voices, and was last updated 4 November 2019 at 22:59 by Michael Gilligan.

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29 November 2011 at 17:16 #11858
Nigel Parkinson
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@nigelparkinson39932
Pressure angle wanted
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29 November 2011 at 17:16 #78855
Nigel Parkinson
Participant
@nigelparkinson39932
I have a CVA series III with some of the 32DP metric set of change gears, including the 127 tooth one. Does anyone know what Pressure Angle is for these, so I can set out to make (some of) the missing ones? If not how does one measure the PA easily?

I thought of rolling the gears through plasticine to make a “rack”, but I don’t have access to a projector to measure the angle if I do t6hat and I think that at 32 DP it might be a bit difficult to discriminate between 20deg and 14 1/2 deg without some form of magnification.

Regards

N
1 December 2011 at 10:42 #78993
edward brown 1
Participant
@edwardbrown1
On larger gears it is quite possible to determine the pressure angle by a series measurements over the flanks of several teeth by means of a vernier or digital caliper then refferring to a table of base pitches. I am not sure if the normal digital caper in the home workshop will get into the tooth spaces of a 32DP gear and give a sufficiently accurate result.

However the procedure is as follows. Select any one of the gears you have and open the caliper to span across the flanks of several teeth (for example for a fifty tooth gear span 5 or 7 teeth). Take the measurement as accurrately as possible and note the dimension, then another measurement over one less number of teeth than the first reading and note this dimension. then subtract the second size from the first and note the result,

For 32DP 14,5 degree PA the measurent should be 0.0950 inches

For 32 DP 20 degree PA the measurement should be 0.0923 inches.

As the difference is only 0.0027 inches it may be necessary to take a few readings to come to a conclusion.

Regards

Ted Brown
2 December 2011 at 10:12 #79064
Nigel Parkinson
Participant
@nigelparkinson39932
Ted,

Thank you. I shall give that a try. My calipers may not fit, but I’ve got a few other things that might be good enough.

Regards

N
4 November 2019 at 19:38 #436011
George Maclean
Participant
@georgemaclean24517
Not sure this should go here BUT!

Hi need some help on a CVA seris 3 1A I have a travelling steady but there are no studs/ holes on my carriage to

fit it. Well there is one threaded hole on the back of the carriage on the chuckside (where itcould posible fit) but

the other three fixings/holes are not there. Also on the steady I have the fixing position at the front if fitted there

would foul the front gib wiper. Hope this makes sense I think I have an series 3 steady and not aseries 3 1A?.

any comments welcome or a photo of one fitted would help. While I can maket it fit ,it would be nice to know what I have an /or a photo of the correct one,

Thanks

George.//
4 November 2019 at 22:59 #436048
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Nigel Parkinson on 29/11/2011 17:16:58:

[…]

I think that at 32 DP it might be a bit difficult to discriminate between 20deg and 14 1/2 deg without some form of magnification.

.

Scan one of your gears on a flat-bed scanner at [say] 600dpi then zoom in
… this is the poor man’s Shadowgraph !

[ transparency acetate is useful for protection ]

It is very easy to see the difference between 14.5 and 20 degree pressure angles.

Have a look at the animation in post 20 here: **LINK**

https://www.chiefdelphi.com/t/turning-down-the-od-of-a-gear/137417/20

14.5 is not shown, but I’m sure you will get the idea.

MichaelG.
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