Hobbing a Pulley for driving accessories for Model Steam Engines or Toy Steam Engines

[JimDobson]

Hobbing a Pulley for driving accessories for Model Steam Engines or Toy Steam Engines
This worked out really well for a first attempt, I've been wanting to try this for ages to stop belt slippage on pulleys and drive wheels when running accessories off steam engines under load which can very often be a problem as some engines lack the power to be able to put a lot of tension on a small round drive belt.
It’s a great hobby and pastime working on your metal lathe or metal milling machine making parts for model engines and model or toy steam engines.

 

[timo_gross]

I had more success with spiral flute taps, because the workpiece is transported more reliable. Made a serrated wheel for the 3d printer and it works O.K..

If you calculate the diameter and infeed you can also make small usable worm-wheels. A matching bolt is the worm.

 

[JimDobson]

Thanks Timo, I do have quite some weight in taps if I was to weigh them all together....but I don't own any spiral fluted taps.

 

[Steamchick]

It works - for him. But the use of Vee-pulleys - in Engineering terms relies on the pre-tension to apply the initial friction, but the MAIN work is done by the loading of the belt adding tension on the tension run of the belt and pulling the belt into the VEE... thus creating adequate friction to drive the load, but when the pulley rotates so it "sees" the slack side, it has very little load needed to pull the belt from the groove. The Groove angle is what makes it work - related to the coefficient of friction of the belt-pulley interface.
By Hobbing the groove to make a rough surface, he is relying on the distortion of the belt over the rough surface to introduce some effect of material being in shear (as with a toothed dive) to take the driving load. By lowering the area of initial contact surface, a higher surface pressure is obtained for the same pre-tension, so to get "initial grip" he is reducing the pre-tension. - Useful to him. But I am sure his muscular arms pulling on the belt do not replicate the tiny loads of the model engines and driven machines he enjoys. The belt would not slip in that demo if he had not hobbed the pulley, as the wrapping of the belt into the groove and subsequent pulling has caused the high pressure contact to provide the grip he wanted anyway.
Don't believe all that is presented on U-tube. Some has erroneous information.
But the load to remove the belt from the groove is likely to be significantly increased (elastomer has been squeezed into some shapes from the hobbed vee-surface and needs pulling back out), thus the efficiency of the drive is probably reduced - Considerably? - Which may impact his models with flea-powered engines. And I assume he is not interested in belt wear, for his model use.
The same sized pulleys and glued O-ring belts happily take the machining torque from motor to mainshaft of my Unimat lathe with 200W motor, without slippage, but sometimes break a belt where the glued lap-joint in the O-ring is a bit stiff, and causes fatigue... on a "good load" you can see the belt "slack" on one side, and bar-taught on the driving side to demonstrate how the Vee works. So I am surprised he has needed Hobbing to "improve" the design? Possibly he is using a pulley and belt system that is simply too large for the models? I have seen models (e.g. Mechano clockwork motor powered, and tiny AA cell 1.5V electric motor powered) running with small rubber bands (1mm square section), not 3 or 4mm O-ring material...
I also enjoyed this - which happened to follow!

K2

 

[timo_gross]

It works - for him. But the use of Vee-pulleys - in Engineering terms relies on the pre-tension to apply the initial friction, but the MAIN work is done by the loading of the belt adding tension on the tension run of the belt and pulling the belt into the VEE... thus creating adequate friction to drive the load, but when the pulley rotates so it "sees" the slack side, it has very little load needed to pull the belt from the groove. The Groove angle is what makes it work - related to the coefficient of friction of the belt-pulley interface.
By Hobbing the groove to make a rough surface, he is relying on the distortion of the belt over the rough surface to introduce some effect of material being in shear (as with a toothed dive) to take the driving load. By lowering the area of initial contact surface, a higher surface pressure is obtained for the same pre-tension, so to get "initial grip" he is reducing the pre-tension. - Useful to him. But I am sure his muscular arms pulling on the belt do not replicate the tiny loads of the model engines and driven machines he enjoys. The belt would not slip in that demo if he had not hobbed the pulley, as the wrapping of the belt into the groove and subsequent pulling has caused the high pressure contact to provide the grip he wanted anyway.
Don't believe all that is presented on U-tube. Some has erroneous information.
But the load to remove the belt from the groove is likely to be significantly increased (elastomer has been squeezed into some shapes from the hobbed vee-surface and needs pulling back out), thus the efficiency of the drive is probably reduced - Considerably? - Which may impact his models with flea-powered engines. And I assume he is not interested in belt wear, for his model use.
The same sized pulleys and glued O-ring belts happily take the machining torque from motor to mainshaft of my Unimat lathe with 200W motor, without slippage, but sometimes break a belt where the glued lap-joint in the O-ring is a bit stiff, and causes fatigue... on a "good load" you can see the belt "slack" on one side, and bar-taught on the driving side to demonstrate how the Vee works. So I am surprised he has needed Hobbing to "improve" the design? Possibly he is using a pulley and belt system that is simply too large for the models? I have seen models (e.g. Mechano clockwork motor powered, and tiny AA cell 1.5V electric motor powered) running with small rubber bands (1mm square section), not 3 or 4mm O-ring material...
I also enjoyed this - which happened to follow!

K2

I use a serrated pulley, made with the same approach to push my PLA plastic into the 3d printer. It has a much smaller diameter about 8 mm.
The teeth were hobbed into the wheel with an M3 tap, they really bite into the plastic. Pressure is applied with a plain bearing pressing the plastic against the serrated wheel.
Some steam toys use a long spring with a cone shaped end. The cone end is screwed into the other end to form the loop. (was not able to find a picture), the "wormish" pulley might work very well with those.
Can we use a wormwheel made with that method as a pinion and use a threaded rod as rack?

Small worm drives with low (load) requirements can be made with a tap.
The photo shows the worm made out of an M6 set screw, the shaft is 4 mm. Brass wheel was hobbed, using an M6 tap as hob.

Greetings Timo

 

[JimDobson]

It works - for him. But the use of Vee-pulleys - in Engineering terms relies on the pre-tension to apply the initial friction, but the MAIN work is done by the loading of the belt adding tension on the tension run of the belt and pulling the belt into the VEE... thus creating adequate friction to drive the load, but when the pulley rotates so it "sees" the slack side, it has very little load needed to pull the belt from the groove. The Groove angle is what makes it work - related to the coefficient of friction of the belt-pulley interface.
By Hobbing the groove to make a rough surface, he is relying on the distortion of the belt over the rough surface to introduce some effect of material being in shear (as with a toothed dive) to take the driving load. By lowering the area of initial contact surface, a higher surface pressure is obtained for the same pre-tension, so to get "initial grip" he is reducing the pre-tension. - Useful to him. But I am sure his muscular arms pulling on the belt do not replicate the tiny loads of the model engines and driven machines he enjoys. The belt would not slip in that demo if he had not hobbed the pulley, as the wrapping of the belt into the groove and subsequent pulling has caused the high pressure contact to provide the grip he wanted anyway.
Don't believe all that is presented on U-tube. Some has erroneous information.
But the load to remove the belt from the groove is likely to be significantly increased (elastomer has been squeezed into some shapes from the hobbed vee-surface and needs pulling back out), thus the efficiency of the drive is probably reduced - Considerably? - Which may impact his models with flea-powered engines. And I assume he is not interested in belt wear, for his model use.
The same sized pulleys and glued O-ring belts happily take the machining torque from motor to mainshaft of my Unimat lathe with 200W motor, without slippage, but sometimes break a belt where the glued lap-joint in the O-ring is a bit stiff, and causes fatigue... on a "good load" you can see the belt "slack" on one side, and bar-taught on the driving side to demonstrate how the Vee works. So I am surprised he has needed Hobbing to "improve" the design? Possibly he is using a pulley and belt system that is simply too large for the models? I have seen models (e.g. Mechano clockwork motor powered, and tiny AA cell 1.5V electric motor powered) running with small rubber bands (1mm square section), not 3 or 4mm O-ring material...
I also enjoyed this - which happened to follow!

K2

You totally don't seem to have any understanding of running accessories off toy and model steam engines. You erroneously went off the mark numerous times. LOL belt wear?

The currently largest maker of toy steam engines in the world is the German company wilesco, all of their drive pulleys have always been hobbed and toy steamers enjoy using joined O ring and watchmaker polyurethane belting on their Wilesco drive pulleys. Wilesco also manufactures and sells spring belts that work exceptionally well for some applications on their hobbed drive pulleys.

So I must add to anyone reading your post 'Don't believe all you read on forums'!!! especially by people obviously lost on the actual subject, but feel the need to take down another enthusiast.

I am extremely happy to be able to duplicate now on my DIY drive pulleys what Wilesco has always done.

A Wilesco stock standard drive pulley -

 

[krypto]

Jim, I understand the needs of the toy engines and often wondered what would be an easy way to replicate the Wilesco shiv texture when I make new pulleys for the Jensen fleet. Your technique of hobbing with a tap is quick and easy and should make pulleys that work really well with the spring belts.

 

[JimDobson]

Jim, I understand the needs of the toy engines and often wondered what would be an easy way to replicate the Wilesco shiv texture when I make new pulleys for the Jensen fleet. Your technique of hobbing with a tap is quick and easy and should make pulleys that work really well with the spring belts.

G'day krypo, this method will work great with Jensen spring belts (which I like better than Wilesco spring belts). Here's some photos of a vertical transmission that I made some years ago that I have 'retrohobbed' one side of the drive pulleys on this morning.

 

[JimDobson]

I use a serrated pulley, made with the same approach to push my PLA plastic into the 3d printer. It has a much smaller diameter about 8 mm.
The teeth were hobbed into the wheel with an M3 tap, they really bite into the plastic. Pressure is applied with a plain bearing pressing the plastic against the serrated wheel.
Some steam toys use a long spring with a cone shaped end. The cone end is screwed into the other end to form the loop. (was not able to find a picture), the "wormish" pulley might work very well with those.
Can we use a wormwheel made with that method as a pinion and use a threaded rod as rack?

Small worm drives with low (load) requirements can be made with a tap.
The photo shows the worm made out of an M6 set screw, the shaft is 4 mm. Brass wheel was hobbed, using an M6 tap as hob.
View attachment 158301



Greetings Timo

G'day Timo here's a picture of Wilescos drive belts -

https://www.collectormodels.com.au/...lesco-flexible-drive-belt-50cm-long-pack-of-5

Jensen's are a little thicker than Wilesco's 2mm one and have hooked ends (they are easier to undo than Wilescos) -


https://www.ministeam.com/product/Jensen-Steam-Engine-Model-009b/Toy-Steam-Engine-Parts

 

[timo_gross]

G'day Timo here's a picture of Wilescos drive belts -

https://www.collectormodels.com.au/...lesco-flexible-drive-belt-50cm-long-pack-of-5

View attachment 158315

Jensen's are a little thicker than Wilesco's 2mm one and have hooked ends (they are easier to undo than Wilescos) -


https://www.ministeam.com/product/Jensen-Steam-Engine-Model-009b/Toy-Steam-Engine-Parts

Thank you for the foto. (happy I remembered it correct) Next question pops up. Can we make this in the home shop? It is for sure not worth it, given the price.

 

[Steamchick]

Thanks Jim,
I stand corrected, and apologise for my wrong assumptions/aspirations or whatever. I have not seen or ever heard of such a drive as you are dealing with in my INDUSTRIAL experience, nor with models I have owned in recent years. (As a younger person I spent years using Mechano, and other modelling stuff in the 1960s and found which belts worked - and which didn't - and my Dad would suggest things - akin to the larger O-ring style belts - that were simply too stiff/large/strong for the clockwork motors I was using as the drivers of the models). It did appear that the application of "o-rings"/round belts were being used to transmit loads on models that were large orders smaller than the sizes of belts/pulleys were suited to drive. Maybe a change to smaller pulleys/belts would resolve the issue? - It did for me as a lad. And from what I could see of the "3mm tap" - used for hobbing - a 3mm-belt seemed huge compared with the 1/16th in belts used on my Mechano stuff. (I didn't have the means to acquire Wilesco models etc. when I was a lad).
Talking of wear on belts, I use 4 and 5mm belts on my lathe, - because that is the O-ring material I had - and have had belts that have worn a pair of flats to become Vee-belts. But that was with a 90W electric motor, used for 10s of hours, so perhaps rather larger than the power you are transmitting?
For a steam powered boat, I decided to us a 5mm polyurethane toothed belt drive, as that was much less demanding than Vee-belts of what I considered (by design) to be the equivalent Vee-belt drive. It really feels like a slack belt, but works perfectly without slip as does not consume all the power from the engine. My first attempt with a 3mm belt from O-ring material had slipped when I put the boat in the water (the bath) or took a lot of power if I tightened it further. (Engine slowed as it loaded the belt/bearings as I tightened the belt tension adjuster.).
But I accept your criticism, as I don't really understand what you want or need from your models.
Sorry,
K2

 

[JimDobson]

Thank you for the foto. (happy I remembered it correct) Next question pops up. Can we make this in the home shop? It is for sure not worth it, given the price.

Timo I bought the Tubal Cain spring making book many years ago and must admit to very limited success in my spring making adventures.

 

[JimDobson]

Thanks Jim,
I stand corrected, and apologise for my wrong assumptions/aspirations or whatever. I have not seen or ever heard of such a drive as you are dealing with in my INDUSTRIAL experience, nor with models I have owned in recent years. (As a younger person I spent years using Mechano, and other modelling stuff in the 1960s and found which belts worked - and which didn't - and my Dad would suggest things - akin to the larger O-ring style belts - that were simply too stiff/large/strong for the clockwork motors I was using as the drivers of the models). It did appear that the application of "o-rings"/round belts were being used to transmit loads on models that were large orders smaller than the sizes of belts/pulleys were suited to drive. Maybe a change to smaller pulleys/belts would resolve the issue? - It did for me as a lad. And from what I could see of the "3mm tap" - used for hobbing - a 3mm-belt seemed huge compared with the 1/16th in belts used on my Mechano stuff. (I didn't have the means to acquire Wilesco models etc. when I was a lad).
Talking of wear on belts, I use 4 and 5mm belts on my lathe, - because that is the O-ring material I had - and have had belts that have worn a pair of flats to become Vee-belts. But that was with a 90W electric motor, used for 10s of hours, so perhaps rather larger than the power you are transmitting?
For a steam powered boat, I decided to us a 5mm polyurethane toothed belt drive, as that was much less demanding than Vee-belts of what I considered (by design) to be the equivalent Vee-belt drive. It really feels like a slack belt, but works perfectly without slip as does not consume all the power from the engine. My first attempt with a 3mm belt from O-ring material had slipped when I put the boat in the water (the bath) or took a lot of power if I tightened it further. (Engine slowed as it loaded the belt/bearings as I tightened the belt tension adjuster.).
But I accept your criticism, as I don't really understand what you want or need from your models.
Sorry,
K2

G'day Steam Chick

I have an immense amount of model & toy steam engines in my collection and many of them have hobbed drive wheels from the factory.
Its really handy for me now being able to duplicate the hobbing (though I would guess that they did it much differently) on homemade drive wheels for engines and for accessories.


This is a German Doll, around 120 years old (please excuse the poor phone pics) -

This is a German Märklin 16051, a more modern copy of a limited run of a much earlier older Märklin steam engine -

Thanks for your post and hope you're having a great weekend.

​

 

[JimDobson]

Retro Hobbing.....(Worm Gearing) I've been busy hobbing my vertical and horizontal transmissions I made some years ago plus a few other accessories.
Things I've learned from doing many now - what works for me.

Lathe 400rpm
Use lots of WD40 and a toothbrush to keep clearing away the chips
Very critical is to have the tap centered perfectly in the middle (spend some time eyeballing this) if there's any chatter whatsoever the tap is either trying ride up or down
Don't put too much pressure on the tap, its not needed and just keep going in a couple of thou at a time. When you're at the depth you want, let the piece rotate at least another 4x for a really clean cut.