Real Bull CJ18, metal spindle drive gear (Pulley)

[GazzParticipant @gazz]

I think i might have found out why i broke the drive pulley, or at least one of the reasons.

Blooming lump of steel i'm using has screws embedded in it that i didn't notice Doh!
I didnt make that thread BTW, it was already there in these lumps of steel,
i doubt this lathe would be able to produce a thread that large in this kind of steel,

I'm going to weld this bit (once cut off) onto the another piece, this will give me a threaded end to a slug that will fit down the tube of a bar stool, the female threaded bit is already up the other tube and welded in place.

The side view shows it bulging out at a screw location, that bulging happened when i was reducing the diameter of the steel, if i ran my parting tool into this slot like that i'd expect it to break the blade in half…

I'm not even going to try parting it again, when the cold cut saw arrives, this will be the first thing it cuts.

i tried 3D printing a drive pulley or the lathe over the weekend, with the plan to print a standard sized one with a solid infill and see how long it lasted, but also print some larger ones to see how big i could go before the belt started rubbing on the spindle nuts.
But all the bloomin openScad parametric gear makers i tried produced them all too big… a 31T XL tooth pattern pulley should be ~45mm, but they were making them 50mm, so the belt only fits on 3 teeth then it's out of whack.

So i spent the weekend trying to calibrate the 3D printer and getting nowhere, all calibration pieces came out on size, it was me being too thick to look at the printed size display in the slicer software, once i noticed the size was off, i scaled it down by 5mm and it printed a perfect on size pulley slice (but of course with a centre hole too small now)

I was only printing 1mm thick pulley slices for speed, but if i can find a 3D gear making program that makes them the right diameter i might try again, but i don't want to keep this lathe running a timing belt for it's motor drive, i want to get it running on a poly V belt so i can get some slip in the system when i dig a tool in next time,

Wonder if there's any poly vee belt 3D programs out there… i found one for normal v belts, but not for the multi ribbed belts (or serpentine belts as they are known in the motor trade)

[Andy_GParticipant @andy_g]

Posted by Gazz on 12/01/2021 20:03:42:

But all the bloomin openScad parametric gear makers i tried produced them all too big… a 31T XL tooth pattern pulley should be ~45mm, but they were making them 50mm, so the belt only fits on 3 teeth then it's out of whack.

A 31T XL pulley should be ~50mm OD according to this

However – Are you sure it is XL profile (5.08mm pitch)? My mini lathe, and many others, seem to use 5mm pitch belts (T5 ??).

[Iain DownsParticipant @iaindowns78295]

I use OnShape which has a gear generation module associated with iit. It's free to use if you're OK with your designs being public. I've printed gears for my CMD10 mill which worked for a while.

Iain

[JasonBModerator @jasonb]

Amadeal also list a 1.5X belt for the CJ18 which is 4.713mm pitch which is more lilely to be giving you that diameter difference than a 5mm vs 0.2" difference would.

As yours is an older machine 1.5X is more likely.

Edited By JasonB on 13/01/2021 08:53:36

[SillyOldDufferModerator @sillyoldduffer]

Posted by Gazz on 12/01/2021 20:03:42:

I think i might have found out why i broke the drive pulley, or at least one of the reasons.

Blooming lump of steel i'm using has screws embedded in it that i didn't notice Doh!
…

i doubt this lathe would be able to produce a thread that large in this kind of steel,

…

 

I claim to be the forum's leading expert on machining piss-poor metal on a mini-lathe. Before buying a lathe I built up a collection of scrap metal – all sorts of odd bits and pieces. I thought a metalworking lathe would cut all sorts of metal, right? And if it didn't, the lathe was faulty.

Took a good few months for me to realise that all the metal in my scrap box was unsuitable, and the stuff bought from a DIY store is poor. Metals are chosen by manufacturers for a particular property, and very often machinability isn't on their list! I had several lumps of Aluminium from an old-fashioned greenhouse. It's very soft and sticky, smears rather than cuts and clogs the teeth often by welding itself to the edge. Reason, the alloy is formulated to be extruded and rolled into greenhouse shapes. It's not machined – looking at strips showed they were guillotined and punched, not cut and drilled. Also a nice stainless 10mm steel rod from an office grade printer – looks good except it's harder than HSS. (All the other rods retrieved from printers cut well.) I've got 3 or 4 different stainless steels and they all work-harden in a blink. They can be machined, but a particular technique is needed.

My advice, don't mess about with scrap metal at first, or even at all. The material is as important as the machine and the operator. Parting off is difficult at the best of times, small lathes struggle more than big ones, and then your poor little mini-lathe tried to cut something horrid!

Some lucky chaps live in areas were industry produces machinable scrap. Lucky them! Round here, scrap is a wild mixture. I've found it best to buy new metal where the spec mentions 'good machinability' or 'free-cutting'.

Ordinary mild-steel is machinable, but it's not ideal. Tends to tear making it difficult to get a good finish. Try some EN1A or even better Leaded EN1A. EN1A-Pb is 3 times more machinable than ordinary mild-steel…

Another comment: you don't want a crash-proof mini-lathe. You want a bigger lathe! Guess how I know!

Dave

Edited By SillyOldDuffer on 13/01/2021 09:44:03

[GazzParticipant @gazz]

Ahhh, with the pulleys… user error again i guess,

yes i looked on amadeals site for replacement belts, saw the one listed as XL, and presumed that's what i have, my belt is marked '1.5M-70-9.5' which i believe means it's 9.5mm wide, 70mm long,

I've just rendered a 31 tooth T5 style pulley slice in openScad, and it's produced a pulley that is 48.44mm diameter. It can't do an 'X' pulley,

But i'll look at other pulley makers as mentioned, i'm fine with things being public, i'Ve been printing lots of things others have made and shared on thingiverse and that.

I quickly found out i needed a bigger lathe shortly after buying this one, but that was because my first project was to turn some discs or alli into control levers for a train simulator controller i was making for myself,
i ended up using the myford lathe at my then local hackspace to reduce the discs down to a size i could fit in my lathe at home.

But after that i mostly used delrin, acatel, nylon and aluminium in this little lathe, the odd bit of steel was small so machined ok,

But i'm finding myself wanting to machine more steel now, another project is to turn a piece of EN3B bar for my bus simulator build,
Not knowing much about steel i just went on ebay and bought the first bit of steel the size i needed for a cheap price (if £8.25 is good for a piece 40mm by 200mm)

But i already know that when it comes to parting that EN3 steel off i will be using the cold cut saw which is on the delivery van to my place right now.

One day i will buy a bigger lathe, one of the warck's i think, it'll have powered cross feed and a quick change gearbox as a minimum,

But i want a small (as in about WM14 size) milling machine too, and really want to get one of them before i upgrade the lathe,

[not done it yetParticipant @notdoneityet]

Gazz,

I made sure it was as close to centre height as i could get it (i still need to get a QCTP for this lathe) but i had read that it's better to be a little under than over centre height,

Just caught up with this thread (my machines are hobby but not tiny, like yours). My tip is to face off with the tool and if it is on centre height there will be no nib left at the centre – but this will not entirely help you because with the frailty and overhangs, the tool tip will be depressed as soon as it is under load.  You need the absolute minimum cutter overhang and ideally cutting on the centre line of the compound and cross slides – probably not possible with your lathe. Parting in reverse, with an inverted cutter, may be preferable – unless your chuck is of the screw-on variety.

Edited By not done it yet on 13/01/2021 15:04:51

[Andy_GParticipant @andy_g]

Posted by Gazz on 13/01/2021 12:44:24:

my belt is marked '1.5M-70-9.5' which i believe means it's 9.5mm wide, 70mm long,

I believe that's a 1.5 module, 70 tooth belt, 9.5mm wide.

1.5 module = 4.71mm pitch

[GazzParticipant @gazz]

REalised it may be time to upgrade this mini lathe to something a little more capable, needs to be a benchtop model, and it WILL have power cross feed
i started a new topic about seeing what i should upgrade to.

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