Bevel Gear Replacement for Astra L2/L4 Mill – any ideas?

[B TulleyParticipant @btulley]

A friend has an Astra L2/L4 Milling Machine; the nylon(?) bevel gear in the head (which mates with a metal gear) is very worn – when the gear fails completely the machine will become a large lump of scrap.
Searches for a spare have failed – the Manufacturer in Italy still exists but they no longer supply spares for this model. So does anyone have any ideas please? Approximate dimensions are as follows: Overall Diameter 51mm, Plain Boss Diameter 35mm, Shaft Bore Diameter 15.3mm, Length 33mm, 25 Tooth (I think it's a spiral bevel gear – can anyone confirm?)
I'm told that removal of the mating gear would be very difficult, so replacement as a pair isn't really an option. Any ideas please – 3d printing etc. are waaay over our heads and he's naturally very protective of the existing gear and would be very uneasy about sending it away for copying, matching etc. So any supplier would need to be within reasonable travelling distance of M25 J25. Unless of course someone happens to have a decent spare in their shed, or know of a supplier….
Many thanks, Brian

 

 

Edited By BRIAN TULLEY 1 on 22/03/2022 09:07:50

[B TulleyParticipant @btulley]

[Brian WoodParticipant @brianwood45127]

Hello Brian,

I think your best bet, unless someone here is willing and capable of stepping in, is to contact HPC Gears in Chesterfield to arrange to have it copied in metal while there is still enough of it left for measurement and identification..

It won't be cheap but they do a nice job. Phone 01246 268080

Regards Brian

[John HaineParticipant @johnhaine32865]

Is this for power transmission or vertical feed? Does it mate with another nylon gear or a metal one?

[Brian WoodParticipant @brianwood45127]

Metal gear John, the information is in the original post. #

That is why I suggested a metal replacement. Looking at the lathes.co website at the Astra models, the only place I think a bevel gear might be used is for the knee operating leadscrew—in which case I seriously question the combination of the gear pair chosen

Regards   Brian

Edited By Brian Wood on 22/03/2022 10:40:37

[OldironParticipant @oldiron]

You could try Bevel Gears

Link is for Apple Rochester Gears Ltd Wellingborough Northants. Less than 2 hrs from M25 J25. I have used them many times in the past. Always found them very helpful.

regards

[DutchDanParticipant @dutchdan]

You could possibly try contacting the manufacturer. They may have a spare stashed away in storage somewhere, or if not, be able to supply you with spec/drawings of the gear to get a new one manufactured.

[Anonymous]

It's not really a spiral bevel gear, but the teeth do look slightly skew. That seems an odd choice, and makes manufacture more difficult. If possible a picture of the mating gear would be helpful as, presumably, it is less worn.

Andrew

[B TulleyParticipant @btulley]

Thanks for the replies; the manufacturer has been very unhelpful – I did ask about a drawing etc. but got nowhere.

I've not seen the exact position of the gear but am pretty sure it's in the head drive from motor to cutter; the mating gear is metal. I'll be seeing the owner in a couple of hours and will ask him more.

Kind Regards,

Brian

[Jeff DaymanParticipant @jeffdayman43397]

Finding replacement miter gears (for shafts at 90 degrees to each other) is not difficult, several industrial suppliers in North America have a huge variety of them, likely some in UK do as well. But skew (angled tooth) miter gears are much harder to find, especially in plastic.

Food for thought – replace BOTH gears with an available set of metal non skew / straight tooth miter gears to keep your machine running.

[John PParticipant @johnp77052]

Found this photo of the head drive gear on an Astra L2.
Is this the same setup as you have , is the nylon gear
fitted on the shaft of the vertical milling head.

Some other photo's of this machine here
https://www.stationroadsteam.com/astra-milling-machine-stock-code-2977/

John

[B TulleyParticipant @btulley]

Do you know if this is a spiral bevel gear? Or a skew gear? Or something else?

[Anonymous]

The picture posted by JohnP is definitely a spiral bevel gear, as the teeth are curved. The gear set probably is driving the spindle, you wouldn't bother with spiral bevel gears just to move an axis. I agree with a previous post that nylon seems an odd material to choose.

Andrew

[Clive FosterParticipant @clivefoster55965]

Spiral bevel would be the preferable engineering choice for driving a vertical milling spindle from a horizontal shaft as the amount of gear engagement is pretty much constant throughout a revolution. So the load is carried smoothly reducing the chances of marks on the machined surface due to cutter oscillation.

I have seen a similarly seriously chewed up nylon bevel gear that was said to have been forced into contact with a metal gear of different form. No idea what the mating gear was, just shown the chewed up gear as an example of things wot people do accompanied by a plaintive "and it actually worked".

If an ordinary nylon mitre gear had been forced against a metal spiral bevel I'd expect a similar wear pattern with only the outer tips retaining enough engagement to drive whilst the spiral chewed out the rest of the nylon tooth form until clearance was generated. Starting off with the head a bit loose and slowly tightening down as it ran it would work if the perpetuator were sufficiently mechanically unsympathetic.

In a perfect world a pair of matching spiral bevels from one source would be best.

Clive

Clive

[HOWARDTParticipant @howardt]

I agree with Clive a matching pair would be the way to go. It looks like a straight bevel to me, any pair you buy you may have to machine some washers to achieve the correct mating of the gears. We assume the gear shafts are at 90 degrees and inline.

[David George 1Participant @davidgeorge1]

In repairing a large milling machine with a universal head HPC made a new pair for the mill.

David

[John PParticipant @johnp77052]

If your friend has all the parts for this still to be a working
horizontal mill and a dividing head ,all you need is a copy of
Ivan Law's book Gears and gear cutting and make a set of
parallel depth bevels as replacements.
These gears here replaced a steel and nylon gear set that
had gone the same way as your set .In this sander the pinion
runs a 18000 rpm.
Providing that you harden them they will last a lifetime
John

[B TulleyParticipant @btulley]

Hi all,

Firstly, many thanks for all the very helpful replies

Having received numerous recommendations for HPC Gears both on here and also elsewhere I'll suggest to the owner that would be his first starting point – ideally replacing both gears as a matched pair. I'll be seeing him tonight (Model Engineering Evening Class/Group) and it looks like the first job will be to investigate how easy (or not) removal of the other gear will be……

Kind Regards,

Brian

[Andrew TinsleyParticipant @andrewtinsley63637]

I did a similar repair using a matched pair of gears from a large, ancient , burnt out angle grinder. The gear ratio wasn't quite the same as the original, but who cares. It cost nothing.

Andrew.

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