What size lathe would I need ?

Hello all ,

Im new here and new to engineering, I’m looking to

machine some centre lock wheel hubs for a car project of mine,

just wondered what size lathe I would need to be able to machine 150mm dia round solid steel bar

I’d need to be able to cut an m42 thread on to the hub as well .

thanks

Hello Natham,

Welcome to the Forum.

You are likely to need something pretty substantial, a lathe having at least a six inch clearance over the bed [12 inch swing in North American parlance] is the sort of thing I am talking about, together with chucks big enough to safely hold billets of that diameter. This puts the job firmly into the category of heavy industrial sized machinery.

It will also need a hefty motor, say 5-8 HP, to cope with the bulk of metal shifting that will be needed, along with flood cooling to help with the machining. This is NOT a job for small machines.

Without trying to dampen your enthusiasm in any way, and in the light of your stated lack of experience, would it be more cost effective for you to put the work out to a local organisation having the machinery to handle it and prepared to take on one offs of this kind?

Regards Brian

I do not have a lathe that has 5-8 horse power. It does not have the ability to turn 12" diameters but I can certainly work on 150mm diameter bar. If you could sketch what you are describing and photograph it you can create an album and put the photo in it. You will then get a sensible answer to your question.

Martin C

Edited By Martin Connelly on 28/05/2020 09:57:21

Nanthan

+1 for what Brian says about needing a large industrial size machine to do the job.

In the UK the obvious choice would be a Colchester Triumph 2000. Well up to the job, all the modern conveniences and common enough for there to be a reasonable selection out on the market. Considerable range of prices and condition too. Harrison M300 would be another common machine. Plenty of other breeds around but support and special knowledge may be patchy.

However as a first timer wanting a lathe that just works so you can do things, not a project to do things to, expect to have around £5,000 invested by the time its safely in your workshop, up'n running with all the bits to hand to do a proper job. Folk in the know can manage for less, lots less given a bit of luck and patience, but if not in the know its easy to end up with a boat anchor if you innocently try for economy in the wrong places.

Don't neglect to factor in the time and effort needed to build up the skills needed to do a workmanlike job. A centre lock coming adrift is less than amusing. If its for a modern race type centre lock there are material issues too and they need to stand very high tightening torque loads.

Realistically its a farm out job to an industrial shop or a bloke with a big lathe in his backyard. Industrial shop will cost more but delivery date should be certain. Bloke in the shed cheaper but delivery times may be an issue. (I can do that sort of thing but generally don't after one too many guys got aggressive over not understanding the difference between sometime late next month and by this weekend.)

Clive

Hi Nathan,

As you don't want to do shafts (i'm assuming by hub you mean a hunk of steel 150mm long) that size there are plenty of 5" lathes to choose from. spend some time here look for extras ebay this one has a margarine tub full of change gears.

The killer for you is the M42, metric machines are more modern and metric conversion gears for imperial machines are hard to find.

Martin,

I was trying to read ahead a bit and anticipate the series of questions that might follow on in the light of Nathan being a beginner at this kind of work, should he decide to attempt to take it on, while at the same time giving him a straight answer to his question.

I'm not sure that a sketch will help matters a lot for him other than "how do I make 4 of these?".

I don't think I would have the strength now to hump a length of 6 inch bar into a big lathe chuck without standing on the lathe bed to do it safely and comfortably.

Brian

It really comes down to how quickly you want to make the part, with a 150mm dia billet 3-4 inches long you need sufficient for the chuck jaws not to hit the bed so 200-225 swing (100-112 ctr height) would be the minimum. It will not remove metal as quickly as a big machine but will get it done. If you want to buy new then one of the "250" size machines would be a starting point.

I did some alterations to the drive studs for a set of knock on converters late last year for a local racer and from what I remember it is a fairly fine thread in relation to diameter maybe 2mm pitch? so with the right gearing not too much grunt needed from the lathe.

The reason I think a sketch would help is that when i read wheel hub out of 150mm diameter bar with M42 thread I immediately thought of a chuck backplate type of design. Who needs an 8hp lathe to do a backplate?

Martin C

If it's for a Rudge-Whitworth centre lock fitting then they have imperial threads. 8TPI. Oviously if you are going to make everything then the thread can be of your choosing.

Cheers

John

6" diameter bar mounted in my 6" chuck on my 8" machine. This is aluminium alloy as the only 6" diameter iron I have is another chuck.

Martin C

Probably something like this, you use modified bolts/nuts to fix to an existing hub, the bolts/nuts have extended heads that transmit the drive so no splines needed, nut just stops the wheel falling off and takes sideways loads. Alternative is CSK allen heads and separate drive pins.

Edited By JasonB on 28/05/2020 12:59:23

Nice picture Martin.

A superb illustration of how to set up a larger billet job on a relatively small machine. Especially when it comes to showing the "maximum safe" overhang of the chuck jaws and why you dont try to hold a billet of larger diameter than the chuck from the outside.

One for the "1,000 pictures of machining set ups" book that someone really ought to compile for the guidance of newbies.

Entirely agree that the job can be done on a smaller machine. Just like you I could happily do so.

But with an inexperienced driver I think the larger chucks associated with bigger machines will give a much more secure and safer grip.

New guy probably won't realise why you need that centre there with a smaller machine.

On a Triumph 2000 or M300 you can safely just have at it. The greater power at the spindle is dangerous but I feel that newbie will be apprehensive at the quantity of chips coming off long before crash time. I know I was ahem "worried" the first time I was shown what a Triumph 2000 can do when in the mood. Major step up from a Pools Special!

Of course there is an element of "persuasion to take the job seriously" in recommending a bigger and expensive machine. I've picked up the bits atime or three from folk with expectations wya beyond the capbilities of a bargain.

From an engineering viewpoint I dislike the sort of adapters shown by Jason. To easy to think of as a bolt on rather than something that needs engineering into the application.

Clive

I wonder if Jason's example is made from an upset forging or investment casting. It's going to waste a lot of time and material machining a commercial product from a solid billet. Due to the stresses involved I would bet on forging. I also would not make one myself without full access to NDT facilities to check for cracks in the finished part, too much stress in use and nasty failure modes for my liking.

Martin C

To do what you want to do in a hobby setting rather than industrially, 1 1/2 hp will get the job done, it just takes more time. It would be best to get the material cut to length rather than trying to part off that diameter. Turning round the stock to machine the other side would be better done in an independent 4 jaw chuck. They do take more effort learning how to set them up, but it will all be worth it in the long run.

You need to get a lot of practice in before cutting metal for the hubs, especially the threading. A metric lathe not an imperial one is what you need.

Edited By old mart on 28/05/2020 14:20:17

Link does say they are made from billet and they will make to order so would be a lot off tooling for a set of 4 if forged or cast.

Would cracks show on a finished part just from machining?

Edited By JasonB on 28/05/2020 16:39:41

Cracks would only show to the naked eye in a machined part if they were very big. Everything my firm made for aircraft was tested, usually non ferrous was dye penetrant checked, and ferrous was magnetically tested. Dye penetrant can be used at home, but the magnetic is much more involved and the kit costs thousands. Polishing or buffing of the surface will tend to disguise any cracks present and should be carried out after crack testing.

https://www.johnsonandallen.co.uk/product/dye-penetrant-inspection-consumables-kit

Edited By old mart on 28/05/2020 16:55:03

The problem with large round billets is that there can be internal stress cracks from initial casting of the bar stock due to the interior being hot for a tine after the outer shell has cooled. Most of the time there will be no cracks or they have no effect on the part made. For a critical part such as this you would want to be 100% sure it was crack free.

Martin C

Random thoughts.

How many do you need?

Buying a lathe and setting up a to make just one set is a very expensive way of going about it.

Getting the work done by a professional would seem to the better way of going about it, probably a better quality job, with liability resting with the machinist rather than you.

If for just one car, then you will need two with Right Hand threads, and two with Left Hand threads.

They are intended to retain the the wheels. The quality needs to be be good. Having a wheel come off at 30 mph would b, at least, frightening. At 70 mph, it might be fatal!

Since it is a safety critical item, it doesn't seem the sort of job for a newbie to take on.

You need to be certain of the quality of the material, and of the workmanship.

Most certainly not, if quantity production is envisaged. You are taking responsibility for someone else's life.

I doubt if any Insurance company would cover an amateur for such work

If your work fails!!!!!!!!!!!!!

Howard