Lathe crash!

[ChrisBParticipant @chrisb35596]

Update, Warco replied, they do stock change gears and related parts. The gears range in price from £15 to £30 +VAT and shipping each, while the keyed bush is at £7,29 + VAT.

I'll order a couple of bushes to have some spares…but ordering a new set of gears would be too expensive. I'd be better off buying a set of gear cutters for €50 and cut the whole range of gears I may need. One more project for the next year! **LINK** I like the concept, but would adapt it for the milling machine.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Will Noble on 24/12/2018 09:20:39:

I'd be surprised at MAZAK. It's not magnetic and has a very fine, silvery appearance if scraped with a sharp blade, like a highly polished aluminium alloy – and very soft. Old carburettors were made from it and had an awful durability on wearing surfaces.

.

Note my 'Ooops!!' edit last night.

Incidentally, however, I don't think your description of MAZAK's appearance and texture is valid for all instances of 'Zinc based alloys' … I have seen many examples with a coarse crystalline structure, liable to brittle fracture.

There are probably too many 'variations on the theme' for us to generalise.

MichaelG.

.

P.S. Myford feed screw nuts seem to do reasonably well for durability.

[BazyleParticipant @bazyle]

Posted by ChrisB on 24/12/2018 09:43:57:

keyed bush is at £7,29 + VAT.

well that solves the metal identity – silver based

Why do people assume it is a good bearing metal as if it was cast or extruded as seems the case it would be selected for that. Think of it from the manufacturer's point of view (not the importer) We only want a few thousand of these so it is a one time buy of a box full, dead cheap. Probably knocked off one Friday afternoon in the diecast washing machine part maker factory.

[Chris TriceParticipant @christrice43267]

Posted by JasonB on 24/12/2018 07:02:47:

Chris, how would you subsequently harden the soldered part?

Suppose it could be wire sparked, I'll did one of mine out later and have a look and tickle it with a file.

I'm really responding to everyone else suggesting silver soldering but changing the order of construction. How much real wear is that bush likely to receive in its lifetime? You could make it from brass or bronze with a steel key or you could always bore the steel version out and press in an Oilite bush. For £7.25 plus VAT, hardly worth the effort of any of that. If you wanted several however you could make one long one and then cut into slices of a suitable length.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 24/12/2018 09:53:33:

Posted by Will Noble on 24/12/2018 09:20:39:

I'd be surprised at MAZAK. It's not magnetic and has a very fine, silvery appearance if scraped with a sharp blade, like a highly polished aluminium alloy – and very soft. Old carburettors were made from it and had an awful durability on wearing surfaces.

.

Note my 'Ooops!!' edit last night.

Incidentally, however, I don't think your description of MAZAK's appearance and texture is valid for all instances of 'Zinc based alloys' … I have seen many examples with a coarse crystalline structure, liable to brittle fracture.

There are probably too many 'variations on the theme' for us to generalise.

MichaelG.

.

P.S. Myford feed screw nuts seem to do reasonably well for durability.

My bad! When I wrote 'they could be non-ferrous, they are dull grey, not dissimilar to Mazak' I was referring to their appearance, not necessarily that they actually are Mazak. My dear old dad used to call the cheaper Zinc casting alloys 'Shit Metal' and they're not made of that, though one of the fancier varieties was a possibility. However, Chris says his are magnetic so they must be iron based.

Now I know they're less than £10 I might order a spare. I have a bad habit of putting things in a safe place and then not being able to find them again…

Dave

[ChrisBParticipant @chrisb35596]

Funny, this thread has become like one on of those "guess what's this or mystery object" threads

I'll ask Warco if they know so they'll spare us the speculation!

True at £10 it's not worth the hassle trying to machine one, but I need the piece delivered to Malta, so it's going to at least double in price…to make it worth while I might as well chuck in a rotary table for the mill – it's been on the wish list far too long and tomorrow is Christmas!!

[I.M. OUTAHEREParticipant @i-m-outahere]

Those keyed bushes are not hardened , i have filed them to clean of any burrs and make fitting the gears easier . The shafts they run on are not hard either . If you make them yourself do the slot cutting and silver soldering before you drill and ream the bore that way ther is no distorsion and you can make a long keyed section then part of many bushes to length. Even better is to bore the gears out and machine to accept a splined bush but that is a bit of work . The keyed bushes on my al 50 lathe were terrible and made it a pia to change gears over .

You could,make them from brass or bronze and they will be ok , mazak is nothing spectacular !

[ChrisBParticipant @chrisb35596]

This morning continued the thread cutting project I was on before the lathe crashed, finished turning a left and right hand M16x1.5mm thread and started preparing the change gears for cutting two M16x2.0mm threads. On taking the gears off I find this :

Another broken bush!

So now I'm left with only one serviceable bush… I 'm not sure if it's me who's doing something wrong or if the material is either too weak or I had a defective batch. I have two spare bushes on order – something tells me I should have ordered more!

[not done it yetParticipant @notdoneityet]

Looks like a spare part money spinner, to me!

I make drive pins from drill bit shanks – if I ever need another. Simple design for a simple application.

[JasonBModerator @jasonb]

Only a money spinner if enough people crash their machines, I've not needed a replacement in 10years of ownership.

I also saw mention of knocking them in and out, far kinder to press them out gently with your bench vice and squeeze back in with same if they are tight.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ChrisB on 27/12/2018 13:34:38:

.

Jason … At first sight ^^^ it looks like ChrisB's bush was loose rather than tight, in that 80 tooth gear.

MichaelG.

 

Edited By Michael Gilligan on 27/12/2018 16:37:34

[Chris TriceParticipant @christrice43267]

Aren't these supposed to be a close sliding fit rather than needing "pressing"? I'm struggling to understand what forces in a jam up would cause this level of destruction in a bush. I imagine teeth would fly from the periphery of the gears before this item disintegrates.

[JasonBModerator @jasonb]

I suppose you have one of the pair of gears being driven and the other is stopped from rotating by the carrage against the headstock there will be a very high twisting force as one gear wants to turn and the other does not. If the teeth are stronger than the bush the bush will fail.

[SillyOldDufferModerator @sillyoldduffer]

I hope I'm imagining it but has the gear cracked too? Enhanced by me and could be wrong:

Original:

I half remember a trick using petrol or other light oil for highlighting genuine cracks. Soak the suspected area in petrol, wipe dry immediately, then watch to see if anything emerges from the crack. Have I got that right or is there a better method?

Having crashed a WM280 lathe myself I can confirm that the forces involved can be considerable. First time was nothing to write home about. Second time was far worse. So violent I replaced my steel shear pin with a brass one to break faster and am neurotic about not doing it again …

Dave

[ChrisBParticipant @chrisb35596]

Nah, the gear is fine, the damaged parts I found so far are two bushes on the change gears and the shear pin on the lead screw. Although the shear pin failed I find it strange the bushes failed as well…I have now replaced the brass pin with an aluminium one.

The bushes fit tight on some gears and slide fit on others, so it's a bit of a mash up honestly. I'm of the opinion that the material for the bushes could be better, but then again, it's a low cost hobby lathe so I cannot expect much better.

[JasonBModerator @jasonb]

And it would probably cost more to replace a gear if you lost a tooth than the bush going bang.

[ChrisBParticipant @chrisb35596]

Posted by JasonB on 27/12/2018 18:18:30:

And it would probably cost more to replace a gear if you lost a tooth than the bush going bang.

That's very much true, got a quote for a set of 6 gears…£150. Got myself an HV6 rotary table instead.

I put an aluminium shear pin on the lead screw as I believe the shear pin should fail before anything else, hopefully I will never need to find out again!

[Will NobleParticipant @willnoble66529]

………… and I'm still going for it being an 'Oilite'-type material which has, as I think I implied/said, the torque transmitting ability of something approaching cast cheese. It's not designed to transmit torque, just soak up a lubricant and then act as a bearing surface.

If Chris is cutting a 16mm thread – and especially if 'going for it' – I'd suggest he's applying quite a lot of torque to the drive to the saddle, especially on a smaller lathe. It's revealed a design expedient (read fault/fudge/cost saving exercise).

The conversion to a suitable shear pin sounds a better bet – but chosen with care. I'd suggest a drill shank might not be appropriate – as in too high a shear rating for the job.

All the above assumes there is no other hidden damage which is causing a lot of 'drag' on the layshaft/feedscrew/saddle side of things.

Will

ps I'm avoiding a discussion of my mention of Mazak. I think that bit is for another time/part of the Forum. Don't need another red herring.

[Anonymous]

Posted by SillyOldDuffer on 27/12/2018 17:06:44:

I half remember a trick using petrol or other light oil for highlighting genuine cracks. Soak the suspected area in petrol, wipe dry immediately, then watch to see if anything emerges from the crack Have I got that right or is there a better method?

A slightly posher way, which I use on aircraft, is Ardrox dye penetrant. A low viscosity red dye is sprayed onto the surface which needs testing. After 20 minutes or so of drying any surplus dye is removed with a solvent. Then a developer white powder is sprayed on. The powder draws out any dye hiding in cracks to give a red line. The system is very eftective, and will highlight cracks which are not easily visible to the naked eye.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

[JasonBModerator @jasonb]

No, I would say it has failed because one gear was turning as indicated by the red arrow while the other was stuck solid due to the carrage being jammed up against something solid. Think of twisting an Oreo in half

Edited By JasonB on 27/12/2018 19:35:58

[Michael GilliganParticipant @michaelgilligan61133]

So … how does the gap appear ?

[ChrisBParticipant @chrisb35596]

I get where Michael's coming from, it got me puzzled as well, the bush fits tight on both shaft and gear…but…when I put the bush on the gear and the shaft on the bush, there seems to be a piece missing – almost as if the material has shrunk or collapsed into itself ! There are no missing fragments and the split ends match perfectly together. Have a look at the photos below and try to decipher what happened because I cant!

[Howard LewisParticipant @howardlewis46836]

Looks to me that S O D is right, and the gear is cracked, from the corner of the keyway.

Either you are in the market for a 80T gear, or a Rotary Table, a set of Division Plates and a No 2 Gear Cutter to suit the gears on your lathe, (either DP or Module).

Howard.

[ChrisBParticipant @chrisb35596]

I'm 99.9% sure it's not cracked. For peace of mind I'll do a penetrant test when I'm back at work next week as described by Andrew above – I'm sure it will be negative.

That said, rotary table and plates are on the way, as well as a set of mod  2  1.5 gear cutters

 

Edit 1: what you're seeing at the key slot corner is a scratch on the surface – in the photo it may lead you to believe its a crack.

Edit 2: As Jason correctly pointed out Mod1.5 cutters are what I need and what I indeed ordered

Edited By ChrisB on 27/12/2018 20:29:04

Edited By ChrisB on 27/12/2018 20:45:04

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