Henry Milnes Screw Cutting

[Bob AstillParticipant @bobastill76884]

Hi all i want to do metric threads and am trying to learn screw cutting on my Henry Milnes lathe according to lathes.co.uk they did several change gears for my lathe but i can not find any i have emailed loads of companies who do used machinery to no avail can anyone point me in the right direction to find some do they do machine breakers like scrap yards for cars? or will i have to have some made?

Many thanks Bob

[Bob AstillParticipant @bobastill76884]

change gears

[Chris Evans 6Participant @chrisevans6]

It would help if you give the lead screw pitch, then a grown up will be along to advise.

[Bob AstillParticipant @bobastill76884]

ohh ark at err

on lathes.co.uk it says

with a conventional "Norton" pattern quick-change gearbox, the lathe could generate 27 pitches and feeds with a further 27 available by the simple expedient of swapping over two gears on the drive arm. A range of other changewheels (with a 20-degree pressure angle) was supplied to allow a wide range of metric pitches to be generated, these included: 30t, 45t, 55t, 60t, 65t, 70t, 75t, 120t and 127t. The 11/8-inch diameter 4 t.p.i Acme-thread leadscrew was fitted with a dog-clutch at its headstock end and was normally left disengaged.

[Keith LongParticipant @keithlong89920]

Bob before anyone can really give suggestions for finding gears you'll need to tell us the diameter of the studs and shafts that the wheels have to fit as well as what diametral pitch (dp) they need to be, to mesh with any other gears on the lathe. If you don't know the dp then tooth number and outside diameter of a gear that they must mesh with will help. Also any details of key-ways or other means of driving the gears. If the gears are 20 degree pressure angle then most gears for British common lathes won't mesh properly as they are mainly 14.5 degrees, but 20 degree is the more "modern" angle for gears now, so the good news is that gears from the likes of HPC, Davall et al will be the correct tooth form if you can identify the dp. Bores and key-ways can be modified relatively easily – you've got a lathe after all. Tooth width will also be important to make sure that the gears are strong enough and will line up correctly especially if you have to compound two wheels, Gears that are narrower than ideal will still work, just be abit more tender but you'll need spacers to get the correct alingment. Gears that are too wide would more than likely need to be machined down to the correct width to make fitting possible.

[Bob AstillParticipant @bobastill76884]

thank you for the reply i will take a gear off and have a good measure and come back to you a friend who is a turner is also coming to look for me

[Bob AstillParticipant @bobastill76884]

I now know my lathe is missing several change gears for screw cutting for standard and metric threads it comes with 30, 45, 55, 60, 65, 70,75,120 and 127 I only have 30.60,65 and 120 the 60 has one tooth missing so I need to replace that one as well they are 20° pressure angle gear.

The 6 gears I need are 45,55,60, 70,75, 127

The gear measures the best i can with a vernier 16mm (0.63) thick the hole is 19.04mm (0.7500) and the keyway is 6.3mm(0.2490) widw and 2.82mm (0.1110).

[Brian WoodParticipant @brianwood45127]

Hello Bob,

The information still missing is the DP value for the gears you have. You can determine that yourself by measuring the across tooth diameter, in inches, of any gear and counting the teeth on that gear.

The DP is given by (n+2) divided by the diameter, where 'n' is the tooth count. I am assuming here that the gears will be DP and not module, it would be odd to have a 4 tpi lead screw with module gearing for the change wheels. The value you get will always be whole even numbers, so if you get a result like 13.92 that will be 14 DP

With that information you can then search for change wheels to suit. Are you sure the pressure angle is 20 degrees and not the older standard of 14.5 degrees? It does matter as meshing will not be correct.

Regards Brian

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Brian Wood on 15/01/2016 17:59:22:

Are you sure the pressure angle is 20 degrees and not the older standard of 14.5 degrees? It does matter as meshing will not be correct.

.

Brian,

You raise a very valid point, but [simply for reference] here is the page from which Bob's information is quoted.

MichaelG.

.

P.S. … For general interest:

Post #21 on this thread has a good animation of Pressure Angles.

Edited By Michael Gilligan on 15/01/2016 18:25:00

[Bob AstillParticipant @bobastill76884]

Thank you Brian i am unsure now after speaking to a friend who is a gear cutter and might be making me my missing gears has said it can be 14.5 i am taking a gear to him later this week for him to measure up as i am having no luck finding any i will keep you posted.

Thank you Michael the animation explains it easier than trying to read how the differences work.

[Bob AstillParticipant @bobastill76884]

right the gears are 20 degree pressure angle and 1.5 module (pitch) 5/8 thick and 3/4 hole with a key slot does anyone know the best place to start looking for the ones that are missing out my set

regards Bob

[Brian WoodParticipant @brianwood45127]

Hello Bob,

Why not try eBay? Cutters for 20 degree 1.5 Mod are also readily available so if you know how you could make your own, it is quite satisfying if you can guarantee interruption free working

Regards Brian

[Bob AstillParticipant @bobastill76884]

i will have a look thank you

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