Worm gear machining

[Memmeddu]

I'm in the process of restoring a BAIER EHS1 hand held cold saw.
It has a worm gear transmission which has been neglected apparently (maybe not enough preload on the bearings)
I've took measurements, made calculations etc but apparently you can't machine this part.
As from the measurements you'll never be able to reproduce it exactly.

Now from the measurements it's impossible to recreate the brass gear on an horizontal milling machine as I was thinking about using my lathe for the purpose (easier than you think)
And that's why

16 teeth 22.5° included angle 11mm pitch
59mm nominal outside diameter
47.05 on the smallest diameter
51.40 on the smaller outside diameter
54.65 in the middle of the edge of the tooth where the screw gear core is rubbing against.

Now to achieve the correct roundness you should use a 16.5mm tool radius
But you won't be able to do that as you have not enough rigidity or space on a driveshaft to drag the tool .
Which has to be 7.2mm square to machine the complete tooth once at 12mm dept of cut .
To do that you'd need a 23mm swing radius.
But the smaller outside diameter would be 2 or 3mm undersized.
It's impossible from what I've been able to see to reproduce the exact shape following a perfectly circular tool path.
Now it would work even with the 23mm circular radius but how they made it originally.
I think it might have been cast or they used some type of off center machining technic
The only option is a 46mm slitting saw spinning on a 9mm shaft which would instantly snap

 

[gaz1]

you can machine that on both a lathe and a milling machine

 

[Memmeddu]

you can machine that on both a lathe and a milling machine

How?
I can't understand, because I can't see a cutter that big held by a 9mm shaft to clear the cutter to go enough deep
I believe I have to sacrifice those 2 mm and go with the 20mm shaft or replicate the screw gear which has a 16mm shaft and maybe use a drill bit as cutter.
Put 2 bearings on the shaft as close as possible to reduce deflection and mount the gear on the cross slide at the helix angle, use a dead stop to set the pitch.
Cut a tooth rotate towards the stop and repeat.
But will this setup be enough strong?

 

[Kram]

I dont see any issue machining that tho I havent done gears before. First you would screwcut the worm on lathe and a spare one which becomes the cutter. Grind teeth into it and then set up the brass blank so that it spins freely. Look up worm wheel hobbing on YT.

 

[Agroshield]

It would be good to learn the terminology surrounding worm and worm wheel pairs.

This book is a gentle introduction:

Workshop Practice Series Volume 17 Gears & Gear Cutting : Free Download, Borrow, and Streaming : Internet Archive

Workshop Practice Series Volume 17 Gears & Gear Cutting

archive.org

The worm wheel is a helical gear. Call Rob Cox and he will make one for you on his shaper.

Your drawing is superb. You might have to re-do it once you understand the critical measurements from reading above.

Measure the worm as well as the wheel and measure the centre distance at which they mesh.

Biggest challenge in worm wheel cutting is not to cut a beautiful right hand wheel when you need an average left hand one.

Is it you on the cover of this one?

MACHINERY' S REFERENCE SERIES NO 1 WORM GEARING 52 PG : Free Download, Borrow, and Streaming : Internet Archive

52 PG

archive.org

 

[minimutly]

You are about to fall into a very deep rabbit hole my friend. The book recommended above is a good start. You will need to make a cutter, but the good news is you can make a worm wheel (the bronze bit) in a lathe by free hobbing. This makes a close approximation. If you want to make an exact copy you are into all kinds of cutting operations on a lathe and mill, involving dividing, plunge cutting etc.

 

[gaz1]

as i have a horizontal milling machine

vertical milling

lathe

 

[Kram]

This video explains the process and details of making and using a hob and he has others that are worth watching.

 

[Memmeddu]

Thank you all for the replies
We do similar jobs at work on a proper horizontal milling machine with the table that can be set at an angle and the space for a proper diving head.
I've asked to my colleagues and they said those gears are enough standard and I can use a single point cutting tool.
I should start to source the material as the off cuts at work were either to small, or they had a very big hole in them
One of my colleagues offered to lend me his Milling machine

 

[minimutly]

as i have a horizontal milling machine

vertical milling

lathe

The first vid is plunge cutting - not so easy to do accurately, the second is free hobbing in the mill - potentially more accurate but you have to make a hob.
Good vids @gaz1...

 

[Agroshield]

As from the measurements you'll never be able to reproduce it exactly.

Do you know anyone else with the same machine? Then, potentially, you could measure an undamaged part.

The other option is to re-make both the worm and wheel as a pair. Then you are only constrained by two things: the worm ratio (which you know, 16:1) and the centre distance (which you also know). You can pick worm OD, worm pitch and hence wheel helix angle as well as pressure angle to suit yourself.

Especially if you are to grind your own cutter, it does not have to confomr to any standards, just fit the space available. Making two parts that match each other is easier than making a single part to match an existing worn part (do not underestimate how worn the worm is and how much it would shorten the life of a new wheel).

 

[zx9]

I have seen discussion on worm gear replacement / reproduction on the 4x6 band saw IO user groups, it was some years ago so I could not point you in the right direction but here is the 'worm' keyword search for that group. https://groups.io/g/4x6bandsaw/search?p=recentpostdate/sticky,,,20,2,0,0&q=worm good luck.

 

[Memmeddu]

I have seen discussion on worm gear replacement / reproduction on the 4x6 band saw IO user groups, it was some years ago so I could not point you in the right direction but here is the 'worm' keyword search for that group. https://groups.io/g/4x6bandsaw/search?p=recentpostdate/sticky,,,20,2,0,0&q=worm good luck.

I'll leave like that right now.
I'll source the material then I'll make it on a proper milling machine maybe at work too.
I've tried to find a replacement but they either have the wrong size or teeth number so that's the only way

 

[iNf]

https://www.mig-welding.co.uk/forum/threads/bandsaw-repair.109669/
Here is a thread where @RobCox made a wormgear for his bandsaw, which might give you some ideas. I found this thread when I was half way through making one similar for mine (but not to the same standard) I can post some photos if you want?
here is a link to a site for working out sizes, you may need Google translate
http://nino.bplaced.net/Schneckengetriebe.php

 

[Memmeddu]

https://www.mig-welding.co.uk/forum/threads/bandsaw-repair.109669/
Here is a thread where @RobCox made a wormgear for his bandsaw, which might give you some ideas. I found this thread when I was half way through making one similar for mine (but not to the same standard) I can post some photos if you want?
here is a link to a site for working out sizes, you may need Google translate
http://nino.bplaced.net/Schneckengetriebe.php

Thanks every input is useful I'm going to have a look at both later