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Replacement gear required

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J-G

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I said at the start that much more information would be needed before anyone could undertake manufacture and this morning (having little or no commitments) I decided to draw the Gear, taking scale measurements from the photo's posted.

Ridgeway Gear.png

Naturally I have made some assumptions which may be wrong but only the OP can correct those by direct measurement of the failed gear.

I have no idea where the 'Ridgeway' was made so am not hide bound by partial knowledge but by enlarging one of the photo's, I was able to measure the thread at over 10 times true size so imagine my surprise when the 'calculated' pitch came out to be exactly 24tpi. Since there are only 3 'standard' threads 3/8" Dia. & 24 tpi -- Admiralty, UNF & Spark -- more work is needed to correctly determine whether it should be Whit. or Unified form - though, in reality, it may not matter a great deal as the mating screw could be replaced with even a metric equivalent.

As the photo's only show the damaged gear - rather than the gear plus the broken away 'boss' - I cannot determine whether the tapered hole really is a 'hole' or a 'slot'. I've drawn it as a hole but it could just as easily be a slot, in which case dimension F is irrelevant.
 

Doug71

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@baldkev thank you for the photos, really helpful.

I wonder if the springs lose tension over time and need replacing, let me know how the new one works out 👍
 

baldkev

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@Doug71 I can get better ones tomorrow if needed, those were from when i tried to sort it last time. Yep, it looks like the oerson who had yours wound it down the coils to shorten the spring length.

It looks like ive got a long wait, ebay said est delivery 17th march! China i guess.
 

Richardsth

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I said at the start that much more information would be needed before anyone could undertake manufacture and this morning (having little or no commitments) I decided to draw the Gear, taking scale measurements from the photo's posted.

View attachment 127878
Naturally I have made some assumptions which may be wrong but only the OP can correct those by direct measurement of the failed gear.

I have no idea where the 'Ridgeway' was made so am not hide bound by partial knowledge but by enlarging one of the photo's, I was able to measure the thread at over 10 times true size so imagine my surprise when the 'calculated' pitch came out to be exactly 24tpi. Since there are only 3 'standard' threads 3/8" Dia. & 24 tpi -- Admiralty, UNF & Spark -- more work is needed to correctly determine whether it should be Whit. or Unified form - though, in reality, it may not matter a great deal as the mating screw could be replaced with even a metric equivalent.

As the photo's only show the damaged gear - rather than the gear plus the broken away 'boss' - I cannot determine whether the tapered hole really is a 'hole' or a 'slot'. I've drawn it as a hole but it could just as easily be a slot, in which case dimension F is irrelevant.

Finally, Ive got round to to resurrect this thread, as I’m desperate to get this gear replaced. you are correct with most of your measurements the OD is indeed 4.2” and the pitch is 4“. However, I measured it from the inner slot to directly opposite inner slot and that was 3.75”. As for the bore, that was 20mm, with a M10 slotted hole.

Is this enough information to get this gear replaced? If so, where do I go from here?

cheers Rik
 

guineafowl21

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I had some custom gears made up in Delrin for my Boxford lathe by you_engraving on ebay. Might be worth sending him a message. He takes a while to get back to you.
 

Sandyn

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I wonder if a 3D printed gear would work for a while until you sourced a better replacement.
 

guineafowl21

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Actually, I did send him a message back in December, and I’m still waiting for a reply!
Give him gentle chase, as he’s busy at the moment. I’d included gear tooth numbers in my first message, so I sent a second, suggesting the first might have got blocked for containing a ‘phone number’. He did reply quite quickly to that.
 

Bigegg

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I wonder if a 3D printed gear would work for a while until you sourced a better replacement.
If you could 3d print a working replacement, then it's not impossible to cast one from aluminium and fettle it with files.

You'd need to make the print about 10% oversize to account for shrinkage

Either sand cast one using the 3d print as a pattern, or take a silicone mould of it, cast a wax pattern, coat in POP, burn out the wax, and pour in aluminium.
Aluminium can be melted in a hole in the garden, using a tin can, charcoal, and a blower fan (hair dryer, vac, bouncy castle blower)

just to demonstrate:
I did this with alginate rubber to make a POP master, then a latex mould of the master.
Then (several) wax patterns.
Coat in POP slurry, imbed in a 50/50 mix of sand+POP in a bean tin.
Melt/burn out the wax over the BBQ.
Melt aluminium (wheelium) in another bean tin using a "fox hole" furnace + bouncy castle blower.
Pour alloy into the mould.

repeat about 8 times, until I got a decent cast.

Its actually quite detailed, which doesnt show up in the picture - theres even traces of fingerprints

IMG-20180204-WA0002.jpeg
 
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guineafowl21

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This is also the sort of job that youtube’s Doubleboost would enjoy. He turned down a 1 1/4” spindle, from a Cooksley spindle moulder, to 30mm for me. He also re-threaded it and made a new nut. Made two very interesting videos of the job too.

He gives his email out freely, so I’ll give it here: [email protected].
 

Jameshow

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I doubt it would trouble a miniature steam engineer. Or for that matter a full size steam engineer? Any heritage railways nearby?

Cheers James
 

Doug71

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The lad who fitted a new gear on mine finally got back to me, he thinks he got it from a local engineering place


I'm sure if you can find some local engineering company they will be able to supply you one off the shelf or at least order you one in.
 

Sandyn

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Designing the part in CAD is reasonably straightforward, but I would just print the gear wheel on the 3D printer and machine a modified centre part with a flange to mate to the plastic 3D gear. I would machine it in steel or aluminium. I'm not sure how well the PLA gear would withstand the forces of a stubborn mortiser.
Designing and printing gears on the 3D printer is very easy, but the centre part with the orthogonal holes is difficult to do well on the printer.
 

J-G

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Finally, Ive got round to to resurrect this thread, as I’m desperate to get this gear replaced. you are correct with most of your measurements the OD is indeed 4.2” and the pitch is 4“. However, I measured it from the inner slot to directly opposite inner slot and that was 3.75”. As for the bore, that was 20mm, with a M10 slotted hole.

Is this enough information to get this gear replaced? If so, where do I go from here?
Hi Rik,

I was busy with other pressing matters yesterday so didn't see this post 'til this morning so apologies for the delay.

The Root of your Gear should be 3.74" so your 3.75 could mean that the Hob used to cut it was using a smaller dedendum multiplier but is irrelevant as far as a new gear is concerned.

I'm concerned about your measurement of the bore being 20mm it seem somewhat odd that it isn't the imperial 3/4" (19.05mm) and I would suggest that measuring the dia of the spindle would be more important.

There have been many suggestions regarding the easiest method to procure this gear but most simply ignore the fact that the original gear, which was made from either cast or wrought Iron, failed in service due to the enourmous pressure being applied to it. The chance that a Delrin or Aluminium gear will do the job seems most unlikely.

Here is a drawing of what I consider most likely to be a suitable replacement - though I am still working from only partial knowledge. It is drawn at 1 : 1 but due to conversion to .PGN the image you see will not be actual size.
Ridgeway Gear 40T.png


I am not sure that the gear thickness (0.75") or the Boss height ().75") are correct but they are easy enough to change once the original gear has been measured.

I've specified the material as Case Hardened En36 which HPC Gears designate 655M13 since this is has the highest tensile strength.

You mention "M10 slotted hole" which doesn't make engineering sense. Either there is a slot or an M10 threaded hole - I have to assume the later. If the shaft onto which this gear fits has a 10mm hole and what is essentially a shear-pin is to pass through that I would recommend using a modified Cap Screw - not a High Tensile version - so that under potentially fatal stress that pin will shear rather than damage the gear.

It seems that you have not yet confirmed that the Pressure Angle is 20° - ie. that you have measured the rack (or taken an impression of the Rack and measured that).

My recommendation would be to send HPC Gears an enquiry - enclosing my drawing (when you are sure of the bore, width & PA) and get a quote.
 

yetloh

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Try George Lodge & sons in Hull. Very helpful and excellent service.

Jim
 

bansobaby

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Why not replace both the rack and the gear? You can source matching rack and pinions quite easily and just need something approximate to the original. You could shim the rack accordingly to get the correct engagement.....
 

Richardsth

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That’s an idea, I had not thought about changing the rack as well, after all I only need it to travel approximately a few inches.
 
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