Cycloidal gear hobs

[Pete RimmerParticipant @peterimmer30576]

Does anybdy even use these any more? I have a bunch of cycloidal gear tooth hobs of 8mm and 10mm bore but after doing a search I don't see any used ones for sale which means they are either undesirable or unobtainable, I suspect that it's a bit of both. I also have a few ratchet cutting hobs.

Having no interest in horology or instrumentation I don't suppose I will ever use them. They don't take up much space so keeping hold of them is not much of an issue but on the other hand I'm conscious of the fact that with the advent of additive machining in metals these hobs might soon become completely obsolete that is if in fact it has not already happened.

If these things are still in common use somewhere I should like to find out where. Alternatively, if there's a common range of gears used I wouldn't be averse to producing cycloidal gear form bar stock for people to part off their own gears from but again I wouldn't know where to start looking.

It just seems such a waste to have them sitting in a box for the next twenty years (hopefully, at least) for them to then end up in a skip.

Looking for ideas, suggestions etc.

[Pete RimmerParticipant @peterimmer30576]

[Bob StevensonParticipant @bobstevenson13909]

" advent of additive machining in metals "…wot dat?

[Michael GilliganParticipant @michaelgilligan61133]

Very intriguing, Pete

What module sizes are they ?

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

Posted by Michael Gilligan on 23/05/2021 10:18:21:

Very intriguing, Pete

What module sizes are they ?

MichaelG.

Ah, now there's a question. Most of them have only numbers so I am laboriously measuring each one and labelling them. I have a nice little measuring microscope which I have fitted with a mount for the hobs and tenth-reading dials so that I can accurately take pitch and form readings. Some are module but most of the numbered ones so far conform to DP sizes. Some are marked with the module or pitch. I will be working through them today so I'll have a good list. I'm using paper tags at the moment whilst I gather the bits to make an etching pen.

 

Edited By Pete Rimmer on 23/05/2021 10:34:11

[Michael GilliganParticipant @michaelgilligan61133]

That’s even more intriguing, Pete

Cycloidal usually implies Horological, and Horological usually implies Module

Mmm

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

I'm (slowly) working through them. I have cycloidal hobs that conform to sensible numbers in DP, module and metric circular pitch so far. For instance the latest one I've measured only makes sense for it to be called a 2.25mm circular pitch. The module would be 0.7163.

I've knocked up a spreadsheet so I can input the normal pitch and it spits out all the conversion numbers. I was using the chart from Davall which is very good but I have loads that just don't appear on it.

Using the microscope shows me that I have not so many cycloidals as I thought, some are all kinds of weird shapes. For instance I have one which is triangular shaped, straight sides 55deg rounded root and crest just like a Whitworth thread (except a straight sided hob will produce involute teeth) and a pitch of 0.0394" or 1mm CP. Somebody somewhere must be chuckling at me.

I would dearly love to get some insight from someone who has hobbed cycloidal gears in the past. Some of my cutters have tooth counts on them too.

[John HaineParticipant @johnhaine32865]

I believe that cycloidal hobs can only cut a limited range of tooth sizes, unlike involute, for which a rack form can cut any pitch provided the tooth doesn't undercut.

[Pete RimmerParticipant @peterimmer30576]

That would make sense John because the shape wuld change on smaller tooth counts.

As I said I have no clue about cutting these types of gear. I do recall being most upset when I found out that my 33DP gear cutter (a very rare involute size) turned out a lovely cycloidal gear

I have catalogued the first twenty cutters and they are a mic of DP, CP and module. Some are actually marked as module but an insensible size (like 0.505 mod) until you realise that it's exactly 1/16"CP. Seems to be no rhyme nor reason and I guess conventions have changed over the years my collections span.

I will continue to catalogue them and see what I end up with. I have about 20-25 ratchet/escapement hobs to measure also. Some are new in the box.

[sjb72Participant @sjb72]

Hi, did you ever sort through these hobbs ? cycloidal ones

I have just come across this post after sorting through a large box of involute hobs I was told came from the a Timex factory some where in Wales in the early 1980s . There’s a few dozen, some have modules on them, some DP, some just numbers I don’t understand. We have used some in the past for cutting change wheels etc on our old MICRON hobbing machine. We have done a limited amount of cutting horological gears on it too, and after milling brass ratchet wheels I was wondering how hard it would be to hob them…..if anyone has had a go i would love to know.

 

Cheers Steve

 

[Phil PParticipant @philp]

Hi Steve

I might be interested in buying some hobs if you have any to sell. I have quite a good selection already but there are a few gaps in my collection.

I also use a Mikron hobbing machine it is a model 112……….What model is yours ?

I have found that when hobbing ratchets, the hob only produces a correct profile for one specific tooth count, that elusive number is often only discovered by trial and error if the hob is not marked with it.

Phil

[bernard towersParticipant @bernardtowers37738]

Yes I am in the same situation as Phil P and I use a Mikron 92.

[Michael GilliganParticipant @michaelgilligan61133]

I am way out of my depth here, but have just put a document into my Gallery which may be of interest … There is brief reference on p22 to the Cycloid form.

MichaelG.

.

https://www.model-engineer.co.uk/wp-content/uploads/sites/4/mediapress/members/79913/678121/hobsgearhobbing00edgarich.pdf

[sjb72]

On sjb72 Said:

Hi, did you ever sort through these hobbs ? cycloidal ones

I have just come across this post after sorting through a large box of involute hobs I was told came from the a Timex factory some where in Wales in the early 1980s . There’s a few dozen, some have modules on them, some DP, some just numbers I don’t understand. We have used some in the past for cutting change wheels etc on our old MICRON hobbing machine. We have done a limited amount of cutting horological gears on it too, and after milling brass ratchet wheels I was wondering how hard it would be to hob them…..if anyone has had a go i would love to know.

 

Cheers Steve

 

Hi Steve,

I still have the hobs and I’d be more than willing to do some horse-trading for involute ones or buy any doubles which would add to my collection. I am particularly interested in any module hobs you might have but also any involute coarser than 48DP. Like Phil P I have a Mikron 112 but I also now have a Dowding & Doll hobber which cuts spur and helical gears. That machine has a removable arbor so can use hobs of any bore size unlike the Mikron which uses only 10mm bore cutters.

Regards

Pete.

 

 

[Phil PParticipant @philp]

Hi Pete

Does your 112 not have removeable hob arbours ?

Mine has a spare spindle that only takes 10mm bore hobs, but it also has one which I use all the time that takes taper shanks which are the same taper as the main work spindle.

I made various new arbours to take the different size hobs I had available.

[Clive SteerParticipant @clivesteer55943]

I believe the hobs that Pete has came from Pullars Instruments in Brighton. Pullars were a division of Smiths Instruments and I believe they made parts for aircraft instruments, possibly altimeters etc, so the hobs could be DP but may also be non-standard MOD sizes.

I have quite a few wheel and pinion cutters that came from the same source. All of these have identification codes rather than DP/MOD sizes. The codes are similar to those on cutters sold by A. Shoot of Clerkenwell. For instance a cutter I have just has the marking K1978 which by measurement may be for an 8 tooth pinion M0.59/DP 50.8. A. Shoot may have only been a supplier rather than the manufacturers and I have a list of their Catalogue numbers with associated cutter info. For instance their Cat No K1007 cutter is listed as M0.32 12 T special cycloidal.  Although we now only have PP Thorntons as a UK manufacturer of cutters there must have been others and does anyone have any info about them.

Clive

[Clive Steer]

On Clive Steer Said:

[…] The codes are similar to those on cutters sold by A. Shoot of Clerkenwell. For instance a cutter I have just has the marking K1978 which by measurement may be for an 8 tooth pinion M0.59/DP 50.8. A. Shoot may have only been a supplier […]

I have a dim and distant memory of visiting Shoot’s emporium and, based only on that, I would think ’supplier’

MichaelG.

.

Edit: __ Ref.  https://clockdoc.org/gs/handler/getmedia.ashx?moid=57294&dt=3&g=1

.

[Michael GilliganParticipant @michaelgilligan61133]

Just in case it might be relevant:

In 1992, when Shoot & Sons Ltd closed after more than thirty years on the corner

MichaelG.

.

Ref.  https://spitalfieldslife.com/2014/08/20/at-the-little-yellow-watch-shop/

 

[bernard towersParticipant @bernardtowers37738]

Terrific story Michael.

[Pete Rimmer]

On Pete Rimmer Said:

Does anybdy even use these any more? I have a bunch of cycloidal gear tooth hobs of 8mm and 10mm bore but after doing a search I don’t see any used ones for sale which means they are either undesirable or unobtainable, I suspect that it’s a bit of both. …

It just seems such a waste to have them sitting in a box for the next twenty years (hopefully, at least) for them to then end up in a skip.

Looking for ideas, suggestions etc.

Cycloidal gears have mostly ‘gear up’ applications, traditionally mechanical clocks, an industry almost obliterated by electronic timekeeping.   Today, almost all gear requirements are for ‘gear down’ power transfer, for which involute gears are more suitable, leaving cycloidal cutters in a distinctly niche position.   Not much call for them.

But!  Clockmaking is a popular hobby, whilst clock and watch-repairers remain busy.   Therefore, although these tools may not be in hot demand at the moment, it can be almost guaranteed that someone will want them in the future, when they may have considerable rarity value.   Even possible that someone is desperate for them now.

I’d be inclined to offer them on ebay, and if there’s no interest, try again in a few years.

There’s an analogue with electronic valves.  I remember when almost all scrap electronics contained a few unwanted ECC81 valves, and millions of them in Good Working Order must have ended up as landfill.   Now they sell for between £15 and £40 each, and get more expensive with every passing year.

Dave

 

 

[Phil P]

On Phil P Said:

Hi Pete

Does your 112 not have removeable hob arbours ?

Mine has a spare spindle that only takes 10mm bore hobs, but it also has one which I use all the time that takes taper shanks which are the same taper as the main work spindle.

I made various new arbours to take the different size hobs I had available.

Phil,

My spindle does look like the bone pictured. If it does take tapered armors I never knew about it. I just moved house and have yet to bring the machines to the new workshop but as soon as I get a chance I will

How are the arbors held in the taper?

[bernard towersParticipant @bernardtowers37738]

I would think by the tailstock

[Phil PParticipant @philp]

My other photo did not load properly, these are the cutter arbours I made for mine and they are held into the spindle with an M6 drawbar.

I also made these workholding arbours, also held in with an M6 drawbar.

[Phil PParticipant @philp]

The cutter on the right hand side of the previous photo was used to produce the worm gear on my model of a Pollit & Wigzell barring engine.

 

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