How strong is a mini lathe spindle

[lee hawkins 1Participant @leehawkins1]

[lee hawkins 1Participant @leehawkins1]

Hello all,

I know this may be a unusual question to be asking. but what I would like to know is, how strong, if this is the right word to use, is a Chinese made mini lathe spindle? Myford lathe spindles are rated at 40-50 tons high-tensile steel according to tony's lathe website.

lee

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Lee, "rated at 40-50 tons high-tensile steel" is a little abiguous, However such a referal is often a measure of tensile strength per sqaure inch, that is, the area of the cross section when subjected to a tensile load.

Given that mild steel is around the 25 tons per square inch mark, should give what you expect the minimum to be.

Regards Nick.

[Sub MandrelParticipant @submandrel]

I found a calculator on the web that worked out a 10" steel pipe with.250" wall and an O/D of 1.250" has a yield load of about a ton if supported at each end.

I reckon a mini-lathe spindle has a bit more meat and much less length between the bearings and is probably better steel than 'pipe'.

I have no idea if that helps, but I'd guess you are talking a load of several tones to permanently deform a mini-lathe spindle – I think the cast headstock would break first.

The bearings are comparable to van-sized wheel bearings too.

I can't see how you could overload the spindle in normal use, even with a huge chuck and workpiece. A bigger risk would be damaging headstock and/or bed in the event of a big jam-up.

Neil

[lee hawkins 1Participant @leehawkins1]

Thanks for the replies,

This is what I wanted to hear, though, I do wonder what they have actualy been tested at, the force before they gave out and buckled.

lee

[Martin KyteParticipant @martinkyte99762]

Maybe the tensile strength figure is more relevant as an indicator of stiffness ?

M

[Brian WoodParticipant @brianwood45127]

Not relevant at all I know, but as a schoolboy I was enormously impressed by the crush strength of an ordinary Fletton house brick on a visit to Stewartby brick works.

It took 70 tons on an Avery machine before crumbling.

I think as the others have said, the headstock castings will fail long before any distortion of the spindle can occur. I doubt if your could even deliiver the power needed from the usual motor size these lathes are equipped with.

Brian

[David JuppParticipant @davidjupp51506]

Posted by Martin Kyte on 09/01/2014 08:54:02:

Maybe the tensile strength figure is more relevant as an indicator of stiffness ?

M

Not really. Stiffness is determined by the shape of the part and the Modulus of the material. To a first approximation the Modulus of all steels is the same regardless of what Yield or Ultimate strength the steel has.

[Anonymous]

I very much doubt the manufacturer wasted any time or money testing the spindle.

Regards,

Andrew

[John Stevenson 1Participant @johnstevenson1]

Advertising hype. Pure and simple

[lee hawkins 1Participant @leehawkins1]

Hello John,

I am not sure, what do you mean by 'Advertising hype. Pure and simple' ?

Regards

lee

[blowlampParticipant @blowlamp]

Why does it make a difference that it's Chinese made?

Am I right in thinking that the Mini-Lathe is based on an eastern european lathe of some description?

Martin.

[jason udallParticipant @jasonudall57142]

Bottom line the stiffness of the spindle is the figure of merit here..
Assume steel ..as said above the youngs modulus is the same sp only the section and over hang matter..and at first guess a 1″ spindle with 1/4″ wall is going to be much stiffer than a 3/4″ with 3/16″ wall ( or even 3/4 and1/4)..but on a scaled down lathe shorter over hang and lighter work will translate to comparable deflection in the work…machines built like brick privies will always win..and last longer.. but if buying a new lathe do you want to pay for the wear that the buyer after you will enjoy?

[lee hawkins 1Participant @leehawkins1]

Ok,

I recently own a 7×14 mini lathe , made in china, Quite frankly they are terrible, I cannot hide from saying this,their just tat, for the amount of work that's needed to bring them up to any sort of good quality, just hold onto your money, , also I found that they could still be described as a mini lathe but just made a bit bigger and they could still be sold at the same price., but then they know this, I could go on.,just so Glad I got a large proportion of my money back

So what I decided was to build my own, based on the concrete lathe but bit more refined.

I already have a practicably brand new mini lathe spindle and taper roller bearings that cost me nothing,also I have two  65 mm diameter hardened chrome Hydraulic shafts each being a meter long.

this is why I started the thread,, as this lathe will be somewhat bigger, I wondered what these mini lathe spindles can Handle.

lee

 

Edited By lee hawkins 1 on 09/01/2014 15:56:36

[Sub MandrelParticipant @submandrel]

As a very happy mini-lathe owner I can only suggest that there are mini-lathes and mini-lathes, and many of the suppliers have greatly improved their quality control. Please don't judge them all by the same standard, though if you had a "bad 'un" I realise you won't risk being caught twice.

> I wondered what these mini lathe spindles can Handle.

Neil

[John Stevenson 1Participant @johnstevenson1]

Posted by lee hawkins 1 on 09/01/2014 15:47:48:

Ok,

I recently own a 7×14 mini lathe , made in china, Quite frankly they are terrible, I cannot hide from saying this,their just tat, for the amount of work that's needed to bring them up to any sort of good quality, just hold onto your money,

Edited By lee hawkins 1 on 09/01/2014 15:56:36

I think you are getting "Fit for purpose" mixed up with "Fit for Purse"

Why is it that all the people who moan about these lathes buy one when for bit more money they can get a far better machine, but no they buy these are wonder why they don't perform the same as a more expensive one.

There is a reason a Ford costs 10K and a BMW costs 50K.

I know one guy who has 4 of these mini lathes, all converted to CNC, two even have bar feeders on them to take the material in 1 metre lengths. He has a niche product, I won't mention it as he likes to keep his product quiet but Ketan knows who I mean.

With these 4 machines he produces 13,000 to 16,000 parts per month, no typo per month.

He goes on at least 3 cruises a year, in fact he's away at the moment as I have parts to one of his machines to alter. So if they were that bad why does he bother ?

And wouldn't he have sourced some better machines ?

Let us know the breakdown cost of your concrete machine when you are done and were we can all source 65mm hardened hydraulic rods cheaply to build our own better machine at a comparable price to a mini lathe.

John S who frankly gets pee'd off by cheap customers buying even cheaper goods and then whinging.

[lee hawkins 1Participant @leehawkins1]

Thanks for posting picture and replies

Thats looks like a quite heavy lump of metal, what rpm have you span up at?

Over the years I have had a couple of Myfords a Dalton and a Cromwell, all old Vintage lathes that some would call clunkers with all the years of use, they all still had that silky smooth quality feel., no way of getting this with the mini lathe I had., Fitted taper bearings metal gears that made it sound like a marble in a tin can, had to mess about with the circuit board ,it would keep hunting, I just got fed up with the thing.

lee

[Sub MandrelParticipant @submandrel]

I must be honest, Lee,

i faced that lump on all 6 surfaces to make a T-slotted table (which I milled the slideways and t-slots for on the mini-lathe too) but I only ran teh lathe at about 60 rpm because of vibration (not attached to bench).

Taking too deep cuts at such slowspeed guess what happened … yes I had to buy a new motor. But I think this was my inexperience, not a problem with the lathe. Just because you CAN make a deep cut t 7"diameter at 60rpm doesn't mean you SHOULD!

No problem these days though – I've fitted a 0.4kw three-phase motor and I suspect the lathe would take a full 1kw.

My concern with a bigger motor though is that a jam up could crack the headstock or twist the bed.

Neil

[jason udallParticipant @jasonudall57142]

Neil…if motor too big then you need to run faster when it gets angry with the abuse
But a larger motor still has useful hp at low rpm.. ( always when you need it most) …

[lee hawkins 1Participant @leehawkins1]

I know one guy who has 4 of these mini lathes, all converted to CNC, two even have bar feeders on them to take the material in 1 metre lengths. He has a niche product, I won't mention it as he likes to keep his product quiet but Ketan knows who I mean

And wouldn't he have sourced some better machines ?

John

He owns 4 of them, bought them for how inexpensive they are, standard quality of the lathe did not matter, he bought them for the sole reason for converting to CNC . he built the quality into them,

If I were converting a mini lathe to CNC the problems these mini lathes have would not of mattered.

John S, Do you own a mini lathe?

I am not a Cheap customer, who buys cheap goods, for 500 quid you can expect something that is worth 500 quid

having owned one of these mini lathes, to me they are not worth 500 quid,most probably, they are only worth what the dealer importer pays for them

John

I did not want to get on this subject of Bashing the Mini Lathe.

[jason udallParticipant @jasonudall57142]

Lee..few of the “things wrong” with a mini lathe would be fixed by converting to cnc..it doesn’t add center height or bed length and probably not fix spindle drive..it ( if you are replacing lead screws) will add consistency but not stiffness..the head stock for a production machine would in my opinion need attention and slideways would need pressure lube…these machines will have been chosen as agood starting point and probably done one then another then another. …… the chap isn’t doing this for fun..and if he runs one into the ground ..buy another carcass and convert that ..treat them as expendible..I’ve seen myford s7 used that way…

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

For a lathe spindle to be stiff enough to be problem free it has to be large in diameter compared to the general dimensions of the lathe .

What steel the spindle is made of is largely irrelevant as far as simple stiffness goes .

Better specification steels are used in practice so that the spindles survive all the knocks they will see in service and in case of plain bearing lathes to provide durable journals for the bearings .

Generally speaking case hardening steels used in the hardened condition are satisfactory for most machine spindles .

Some makers do use very exotic steels for spindles but not always obvious why .

The arrangement of bearings contributes greatly to the stiffness of machine spindles .

The ‘ one bearing each end ‘ so commonly used is a very poor set up really and there are much better arrangements possible .

Machine spindles have to be stiff in another sense – not just the actual spindle but the whole spindle and drive have to be designed so that they don’t vibrate or work in a spongy manner in the torsionwise (rotary) sense .

Basically spindle should just run at set speed independent of any load variations both within a single spindle turn and over many spindle turns .

Can’t always be achieved to perfection but the better the lathe the less likely there are to be problems with poor finish and broken parting tools .

The Moire silk pattern seen on some work is mostly down to torsionwise vibration .

When turning much of the heat produced goes away in the swarf .

Purpose of coolant is primarily to cool and lubricate both the tool tip and the immediate cutting zone in the work .

With heat going away in the swarf quite a small coolant flow is sufficient to keep work cool unless turning very difficult materials .

MikeW

Edited By MICHAEL WILLIAMS on 09/01/2014 19:07:10

[lee hawkins 1Participant @leehawkins1]

Mike,

Thanks for posting that up, most appreciated,

The Mini lathe head casting is very light weight , I will be backing it up with good thickness steel plate, which will also add weight, I am going to use taper roller bearings on the spindle, these are quite heavy duty, I have no problem with these, .

lee

[Ian S CParticipant @iansc]

I don't have a mini lathe (not counting a "Super Adept&quot, I would like a small lathe/mini, but I would like multy speed drive, belt or gear, and back gear. Lack of low speed limits what I would be able to do. Ian S C

[Author]

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