Real Bull CJ18, metal spindle drive gear (Pulley)

On the belt pulley - if you are ordering a commercial pulley, check the profile required carefully. Some of the mini lathes use an obscure pitch (maybe not yours) - timing pulleys are available relatively cheaply, so it might make sense to replace both motor and driven pulleys with something more readily available.

On the rigidity issue, I believe that a fundamental weakness of the generic "Mini Lathe" design is the torsional stiffness of the bed - even with the slideways working properly and the gib strips snugged up, the bed can twist in response to cutting forces, allowing the depth of cut to vary.

Once can demonstrate this by putting a DTI between the bed and the work and applying force somewhere that doesn't involve the carriage, compound slide or toolpost .

I have bolted my (similar design) lathe to a substantial beam which greatly reduces this. movement.

Can't remember if I've posted this here before or not.

(Tin hat on)

Edited to add:

This is 42mm dia. leaded mild steel with eccentric holes in it (in fast forward). I don't pretend that it's a masterclass, but it proves that it can be done. Two hands on the cross slide to try and keep an even feed.

Edited By Andy_G on 10/01/2021 13:01:35

Don't be embarrassed to use a saw. No point in persisting with a dodgy method and ruining material which is irreplaceable, or expensive or both, possibly combined with damage to the tooling and/or lathe.

Recently had to part off two pieces of 4 inch diameter x 2 inch long Aluminium.

Went as far as felt comfortable with, and then finished off with a saw and then Often this is the safest, most parctical means.faced the parted / sawn surfaces.

Quite often use the bandsaw to produce a blank which is then faced back to finished length.

Having a small pot magnet with a screw in column, made up a tap and nozzle and with the aid of some monkey blocks, to make up a gravity feed of soluble oil for parting off. The bottle sits above the lathe and feeds through windscreen washer tubing to the tap/nozzle . The nozzle is positioned to drip soluble oil onto the parting blade.

Works so well that often parting off is now with power fine feed!

Howard

Dang, i was hoping i could buy those pulleys, a serpentine belt and have a crash proof set up on my lathe.

I guess i have the tool to produce most of that tho once i get the lathe up and running again, i don't have a mill or own any keyway broaches, but i do have a little 1 ton arbour press, so i could be half way there for that part (depends how much a broach kit would be for the size i need)

I also recently finished building my 3D printer kit, and i could do a proof of concept thing on that for the pulleys, to see how big i can go on the spindle pulley and if it makes enough of a difference to bother with,

You don't need a broaching kit for the keyway, Jason put me onto using a piece of tool steel (picture below), I used the mill as a press I know you don't have a mill but you have your press. Jason also explained doing the same in the lathe with the pulley in the chuck, tool steel cutter in the tool post and use the carriage back and forth to make the cuts.

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)

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 ??).

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

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

H'mmm? I have read through the thread and there is a lot of useful and commendable information. However having owned 2 mini lathes of differing pedigrees over long years, there are two modifications which dramatically improve successful parting. One was sort of OK the other was a complete dog. Both initially impossible to part off with.

The first. Is to change the shears to solid bolt up types properly shimmed. May entail carefully lapping of the underside faces of the bed.

The second. Change the mandrel bearings back to the original Russian design and that is quality taper roller bearings and adjust them and grease them properly.

I never use a rear toolpost and have regularly parted off 32mm diameter EN3 in quantity with HSS blades for rolling stock wheels.

I have never smashed any standard plastic gear.

I know an awful lot has been written about angular contact bearings as replacements but I took the view that the original designers actually knew what they were doing and have proved it in practice even with a very difficult Friday afternoon car machine.

These are not costly in terms of finance but may require investment in time and patience and then practice.

With Real Bull machines as the CJ18 be very careful of the alignments of the motor pulleys and change wheels. There often is tweking of bracketry to be done and the leadscrew shaft end is not really long enough on the 14 inch bed machines.

Regards

Ian

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

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,

Gazz I can recommend the WM14 mill. Had mine 2 years now having had to downsize from industrial stuff.

Very happy with mine. My other lathe is a WM180. Long story and that worked straight out of the box as well. Clean, oil, start work. I have made a few changes but nothing significant. Purely to suit me as nice to haves.

Ian

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

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

1.5 module = 4.71mm pitch

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.