Worm gear

[Franco ConvertiniParticipant @francoconvertini28916]

Hello, I want to make a worm gear for this gear. Could you tell me what pitch I need to set? Thanks, Franco.

[DC31kParticipant @dc31k]

The gear specification is given in GHT’s book, in connection with the headstock dividing attachment. See:

https://www.hemingwaykits.com/HK149X

If you wish to learn fishing instead of just being thrown a fish finger, you can upskill to answer the question yourself.

Gears have three specifying parameters: no. of teeth, diametral pitch and pressure angle. You do not need any further skills to identify the first of these. If you read Ivan Law’s excellent book, you will learn how to calculate the second of these.

Download GearDXF software and print out on paper gears using those two parameters and guessing at the pressure angle. You only have two choices. Offer the print out up to the gear  and see which of the two fits best.

[old martParticipant @oldmart]

The gear showed is not intended to mesh with a worm gear, however it can be done although not able to carry power as the meshing is not exactly correct. You need to measure the diameter of the bull gear and count the number of teeth to use an online gear module calculator which will give you the tooth pitch. The worm will have to be tilted to mesh with the straight teeth on the wheel. You will also have to choose the number of starts on the wheel you make.

We were given an Atlas 12 x 24 lathe which did not have its threading dial which works like a worm wheel on the leadscrew which is simply a straight worm of infinite diameter. I knew the number of teeth that the worm wheel should have and the TPI of the leadscrew and bought a gear that meshed correctly. The axis of the gear had to be tilted to match the leadscrew thread and the housing made to suit. The threading indicator works perfectly since it does not transmit more power than needed to turn it.

[JasonBModerator @jasonb]

Circumference of a 1″ circle is 1 x pi = 3.142″

Divide 3.142″ by the DP of the gear which I think is 20DP on a Myford

3.142/20 = 0.1571″ pitch

If you want tpi then 1/0.1571 = 6.365tpi

But may be easier to select 4mm pitch as that is very close

[John PParticipant @johnp77052]

The bull gear on a Myford   is 16 DP   ,well it is on mine  checked against  16 DP hob   fits

perfect ,  Ivan law’s  book list the pitch as.1963 inch    5 mm = .1968 inch  so that would

do .Depth of cut =.135 inch.

20 deg  PA.

John

[Nigel Graham 2Participant @nigelgraham2]

Presumably this for a dividing-attachment.

Note that a worm meshed with a spur-wheel is fine for such purposes as it’s not transmitting any power, but in any case it will need its axis angled sideways at the helix angle, not perpendicularly to the axis of the lathe spindle.

[old mart]

On old mart Said:

…as the meshing is not exactly correct.

Please could you expand on this statement and say what is incorrect. When you talk of meshing not being correct, in my head it implies that the required conjugate action does not take place.

We produce spur gears by hobbing and a hob is little different to a worm gear.

To me, the low power capability of the setup is more to do with the “quantity” of meshing (an hourglass worm and fully enveloping wheel is the other end of the scale) rather than some intrinsic geometric problem with the setup.

[MacolmParticipant @macolm]

A “proper” worm wheel will make line contact with the worm. The setup proposed will make point contact, which will be fine for indexing purposes, not so good for power delivery.

[egaParticipant @ega]

When the OP acknowledges the above advice I hope he will say something about his unusual Myford with its gold coloured knobs and flip-top oilers.

[Franco ConvertiniParticipant @francoconvertini28916]

Thanks, I’ll look into your suggestions. Unfortunately, I won’t be able to do that on the MyFord Super 7 (4mm pitch).

[bernard towersParticipant @bernardtowers37738]

Wont be able to do what Franco???

[JasonBModerator @jasonb]

Franco, see John F’s post after mine, I was not sure of the DP but John says it is 16DP not the 20DP I thought so you need 0.1963″ pitch which is approx 5mm not 4mm

Depending what change gears you have it should be possible to get very close. You may have to drive the leadscrew by hand and let the gear train drive the spindle rather than use the motor.

[JasonB]

I’m not as good at doing these things as you are, even though I really enjoy them. I wouldn’t know how to set a 5mm pitch on the lathe.

On JasonB Said:

Franco, see John F’s post after mine, I was not sure of the DP but John says it is 16DP not the 20DP I thought so you need 0.1963″ pitch which is approx 5mm not 4mm

Depending what change gears you have it should be possible to get very close. You may have to drive the leadscrew by hand and let the gear train drive the spindle rather than use the motor.

 

[JasonBModerator @jasonb]

Franco, I do not have a Myford but I’m sure one of the many owners here will suggest how you can get 5mm pitch or 5.094tpi from what looks to be a gearbox equipped Myford.

[JasonB]

On JasonB Said:

Franco, I do not have a Myford but I’m sure one of the many owners here will suggest how you can get 5mm pitch or 5.094tpi from what looks to be a gearbox equipped Myford.

If only it were true.

[JasonBModerator @jasonb]

Where are all the Myford users, surely someone can help with a suitable gear setup for a gearbox machine. I’m thinking it needs the 24T replacing with a 38 but that is not a perfect pitch at .198″, probably do better playing with gears on the metric conversion set.

The slightly coarser 0.198″ pitch would probably work on a dividing attachment as it will just not lower down quite as far as the bull gears pitch circle and as we all know the distance between contact points increases as you move away from the pitch circle.

 

[Charles LamontParticipant @charleslamont71117]

In the book, GHT says that the worm is 0.19707 pitch. The pitch is greater than for a normal 16DP because the worm is skewed at 4.9° to mesh with the bull-wheel. That is for a worm 0.855″ OD. For a different diameter worm, the helix angle would be different too.

He suggests 60 – 55 / 65 – idler – 45 as close enough at 0.19697. But that would be for a change-wheel machine. I don’t know about one with a gearbox. Mine is without.

[Pete RimmerParticipant @peterimmer30576]

For indexing it would not much matter but if I were making this gear i would 3d print it with a keyway and then I could have any pitch, any DP, any helix angle and just key it to a steel shaft. Or even press it onto a straight-knurled shaft.

[John PParticipant @johnp77052]

In Ivan Law’s book on page 96 is a list of gear trains
for DP sizes from 6 DP to 40 DP ,this is for
changewheel machines .125 inch lead screw ,
Myford, for 16 DP only 2 gears and an idler are needed
driving 55 T , idle, driven on leadscrew 35 T.

Found this useful info Myfords g box

https://stevenson-engineers.co.uk/files/s7gbox.pdf

on page 4 at the top set up for cutting 16 DP
looks as if some extra gears are needed.

John

[John P]

On John P Said:

In Ivan Law’s book on page 96 is a list of gear trains
for DP sizes from 6 DP to 40 DP ,this is for
changewheel machines .125 inch lead screw ,

OP Franco seems to be saying he has 4mm lead screw?

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