# Measuring Gears

• posted

My Kerry lathe, whilst it has a gearbox, needs a pair of gears changed to convert from imperial screw threads to metric. Of course the lathe came without those gears so I need to meaurse the imperial ones and either buy or make some new ones. My problem is how do I measure acurately the current gears to know what DP to get? I don't have a gear vernier so can someone tell me what t do to?

Many Thanks

Charles

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Charles, getting the DP should not take too long. There are two things that you need to do:

(1) Measure the diameter of the gear over the tips of the teeth.

(2) Count the number of teeth.

You then have to do the working out, specifically add two to the number of teeth and divide the "revised" number of teeth by the overall diameter in inches. This will give you the DP.

This works for gears with an addendum of 0.5, I know that dedendums vary between gear systems, but the addendum seems fairly consistent. Maybe JS can advise on this one?

• posted

Count the number of teeth on one gear, add two to that number and divide by the OD. e.g. 28 tooth gear + 2 = 30, divide by OD of 1.500" will give a DP of 20

Can you post the result here as I'd be interested in knowing. If by any chance they are 20 DP then I have a machine setup at the moment that can do any size.

-- Regards,

John Stevenson Nottingham, England.

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Printed in the HPC gear catalogue are silhouettes of gear sizes that are very useful for comparison purposes. In fact surprisingly accurate !

It is a freaby and they are on 01246268080 or

Andrew Mawson

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The measurements are 40 tooth at 2.5935 inch which gives 16.19 DP The other gear is 32 tooth at 2.1190 which gives 16.05 DP

So I guess I'm after 16DP gears of 36 and 34 teeth about 5/8" thick.

Unless anyone has anything the I suppose it's either HPC or get a

16DP gear cutter and have a go!

Thanks to all

Charles

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I'll have a look tomorrow, I may have some but you will probably have to sleeve the bore. HPC are no good for change gears. They only do 20 degree pressure angle gears as standard. Most lathes use 14.5 degree as they are a throwback to when the lathe was first produced and they can't change because of interchangeability problems. I don't know of any of the older British lathes that use 20 degree angle gears. A lot of the newer import stuff uses 20 as they don't have this grandfather problems.

-- Regards,

John Stevenson Nottingham, England.

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Thanks John. Sleeving bores isn't a problem.

I'm happy to accept that since it's an early seventies British lathe, at the end of a family line that can be traced back to the early fifties, it's almost certainly 14.5 degree pa anyway. As a matter of interest how could I measure the gear to find out whether it's 14.5 degree pa or 20 degree pa?

Thanks

Charles

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Charles, Just had a dive in the pile and I have two gears.

34T with 0.690" bore and 3/16" keyway, 0.500" wide 36T with shallow 8 spline a' la Colchester 0.880" Mj D, 0.814 Mi D, 0.550" wide

Measuring PA is quite hard. Usual method is to use a set of pitch gauges similar to thread gauges, second method is to 'run' the gear with a two known ones, 20 and 14.5, and look for fit.

-- Regards,

John Stevenson Nottingham, England.

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Charles,what model of Kerry do you have?I`ve got one lying in a container with a stripped feedbox.I`ve always been looking for a copy of the feeds and threads chart of the end cover.Mine is about 5.5" CH x 23/24" ctrs. Regards,Mark.

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Mark

Quite possibly the same machine: Mine's an "1124" as per this:

I've emailed you a zip file with the screwcutting charts from the gearbox. I've also got the manual if you need a copy.

Regards

Charles

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Mark, I have a Kerry AG24 mark 2, so if yours isn't a mark 3 , I can help with the chart you require -( I did a spreadsheet with all the info on)

----------------------------------------------------------------------------------------------------- snipped-for-privacy@boltblue.com John Lloyd - Cymru/Wales

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Charles,it`s an 11" AG model I`ve got.Bought it several years ago.Someone had dismantled the apron and on rebuilding had replaced the interlock between feed and screwcutting levers wrongly.Then they had engaged both levers at once under power and stripped a few gears in the feed gearbox.I needed a small lathe at the time so I bought it but the next week the CVA turned up so the Kerry was stuffed in a container and has remained there ever since.It`s next move will be the skip. When I bought it,it was in an old church,in the corner of a field in the middle of nowhere up in Perthshire.Belonged to someone who had emigrated to Canada. Regards,Mark.

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