Mini lathe shaft/spindle Bearings

Hello

I have recently purchased a mini lathe, just waiting for delivery, I checked out all the suppliers, and settled on the Amadeal version CJ18A , 7X14 mini lathe, When checking through the dealers websites, I noticed on Arceurotrade they had published a article regarding changing the standard fitted Shaft Bearings for Angular contact bearings, so I started searching the web for information,,as I have been led to understand it, is that the standard 6206-ZZ ball bearings of which are (deep grooved variety) are not up to the job, So to me, what they are saying then is that these standard 6206-ZZ do not take Axial loads? also various people who have changed the bearings on their mini lathes are also saying that their work is more Accurate and better finish and the lathe is now easier to work with.?

Having done some studying on all the various bearings the 6206-ZZ being deep grooved should be/work perfectly fine on the mini lathe. they were designed to take Axial and radial loads

I have not got my Lathe yet but I am looking forward to finding out if this is all true?, and it's not just being put out by people who just like tinkering and stripping things apart or maybe money is being made somewhere along the line

Appreciate anyone thoughts on this

Regards

lee

Also have the same lathe and as Arc is just down the road Ketan also told me about changing the bearings. This lathe is now 2 years old and still has the original bearings and I've encountered no problems with finish or tolerence. I should wait and see how you get on before stipping down and fitting new ones.

regards,

Bob

Hi Lee

i have the same lathe.

i thought about doing the bearings on mine, but Simon at SPG Hinkley told me it was a waste of time and money,( he doesn't sell the real bull lathe or should I say he sell the same lathe but different name and colour lol ) and that he's never encountered a problem with them.

Dave

Stick to the advice above. My lathe is similar construction and have no bothers. Maybe after some practice and use you may feel the need to upgrade and it is not difficult, but probably will not need it in normal turning.

Hi, the ball bearings as fitted will no doubt be up to the job and you should have no major trouble with them in normal use as specified by the the lathe manufacturer.

Apart from the cost, one main differance between ball bearings and angular contact bearings, is that with angular contact bearings all freeplay can be eliminated when they are configured correctly as a slight preload can be applied. This allows a constant preloading of the bearings throughout changes in temperature without any freeplay.

Ball bearings have to have a clearance in them to allow expansion and contraction during temperature changes and also for the lubrication medium, this is not very detectable to the feel on a new bearing but it is there. This is the main reason that the consesus makes angular contact bearings being able to produce a better finish ect.

Regards Nick.

Edited By Nicholas Farr on 15/09/2013 14:25:05

I am obsessive about taking my mini lathe to its limits. For example, it now has 0.5HP 3-phase variable frequency drive.

I changed the bearings on my mini lathe long ago. It was satisfactory before, but afterwards it was excellent.

I recently parted off 2" mild steel, using a 1/16" blade in a quick-change toolholder, no lubricant, just to prove it can be done. I credit the taper roller bearings with allowing me to make cuts like that.

I fitted angular contact bearings to my X2 mill (the taper rollers are too long for this application) and a noticeable difference in surface finish and smoothness of operation was apparent.

Neil

Thank you for the replies,

It's good to hear these bearings fitted as standard,are still running fine after a couple of years, even in that I did expect nothing else really, It do give me a bit of cheer though not having to strip the spindle out.

I rebuilt a Cromwell lathe going back a couple of years ago, total strip down and rebuild, I had a hard job trying to get that lathe running as true as it did before the rebuild, the bronze bush bearings were in spot on condition, so all I need to do, so I thought, was to give it all a good clean and reassemble, so easy! preload those bearings, ha ha,I know this is a different sort of bearing.over tightening by just a little will heat those bearings up and you might not even realize you have a tight spindle/shaft, could end up forever fiddling about trying to get them just right

I do know there are lots of variables involved in how we can decide/judge if this modification is at all worth doing,, things like how often the lathe is actually working under load?, the skill of the operator! what material the lathe is being made to work with, Is it mostly Brass or mostly steel, Stainless would most definitely give it a bit of hard work, also not forgetting the condition of the tool cutting edges.

I keep my finders cross and hope all stays fine

Regards

lee

Nick,

Wouldn't you say there could be a Question mark over this statement below, that in being the Skill of the machinist operating the lathe.

Ball bearings have to have a clearance in them to allow expansion and contraction during temperature changes and also for the lubrication medium, this is not very detectable to the feel on a new bearing but it is there. This is the main reason that the consensus makes angular contact bearings being able to produce a better finish etc.

Regards Nick

Hi Lee, there could well be a question mark in what you say, but I haven't said that I agree to the general consesus. However any freeplay will allow microscopic movments both axially and radially under varying load conditions. The angular contact bearings normally refered to are the taper roller bearings, which have more contact in thier elements and are less prone to the same distortions as ball bearings have under the same load conditions.

You can get angular contact ball bearings of course, but they are a differentrent ball game (excuse the pun) they are often refered to as thrust bearings which can withstand large axial loads but not so good radially. When angular contact ball bearings are used which also have a large radial load involved, a paralel roller bearing is also used on the outer side where the radial load is.

One has to draw thier own conclusions as to whether changing the bearings is viable or not. As I said the ball bearings sould cope within the limits of the machine and its design and the level of accuracy one is looking for. It is nearly always a matter of cost.

Regards Nick.

P.S. I will say that I would choose taper roller bearing in a lathe spindel over ball bearings, for a few reasons.

Edited By Nicholas Farr on 15/09/2013 22:58:40

I think Neil answered this question quite well.

Personally i have the same machine but mine is still on standard bearings and does me for what I want it for, small light work that the other machines are not suited for.

Now if this was my only machine of choice I'd do the bearing swap in a heartbeat because it makes sense. I don't need to part off 2" material on mine, I have other machines that will do this far better.

End of the day it accepted that these machines are built to a price and corners are cut in materials and labour so it makes economic sense to use semi skilled labour to assemble a spindle with two standard off the shelf ball races.

If they swap to taper roller or angular contacts then this puts the price up on material costs and having to use more skilled labour to set them up.

Majority of punters buy on price and this is where some of the box shifters score and say they are fine just to get a sale. Yes they are fine but they could be better however no one will pay for the better machine when it's look alike partner is £xx less. However because your time is your own and not chargeable then a simple bearing change will make a big difference at not much cost.

My lathe is sixty years old and still has the original tapered roller bearings - that's the difference

Russell.

Hi Russell,

obviously not of chinese origin. Horses for courses

Hello all

Lathe delivered today to my door, unpacked everything and alls looking good, everything working as it should, But there was just one thing has got me a bit stumped, turn the lathe on got the Chuck spinning up,, it spins as straight as an arrow, but I noticed looking at the end of the Crank directly behind the Chuck, you can actually see it is not running true! it's like the crank could have a wobble, but the Chuck run dead true, I put a known straight machined rod in the chuck and span it up, it runs perfectly straight and true,

Can anybody explain to me what could be going on with this, something has got to be wrong here, surely this could wear the bearings out if the whole crank is like this

Regards

lee

Hi Oh Mule,

The taper bearings I fitted to my mini lathe are bigger than those fitted as wheelbearings on many cars. As the latter can do 300,000 miles without adjustment or additional lubrication, I expect my chinese bearings to last the course.

Neil

Can anyone comment on how noisy/quiet this machine is please?

Hi Brian,

They are very quiet machines, as a rule, partly because they don't have any metal to metal gears. Bear in mind that most of the time you will be using it at much less than top speeds as well.

Many people do a swap of metal gears for the nylon ones inside the headstock. After 15 years my headstock gears are still fine*.

Neil

*Those on my X2 mill went eventually (the old style X2 mills have the same gear arrangement), but this is probably because milling produces a lot more shock loads on the gears.

Thanks Neil,

The reason I asked was really with the motor in mind. I understand they have brush motors and I thought brush motors were noisy (compared to induction motors).

regards

Brian

Mine runs very quiet, I did have a problem with the circuit board but thanks to a very good friend who tweaked it with a lot of new parts the speed increased to 3500 max ,not that I use it but it shows how much can be done to these machines just by changing standard parts to upgraded. I would suggest putting a stopper in the front of the lathe where you access the front bush on the motor, just to keep out all the swarf out.

The brushed motors are not noisy enough to cause any irritation.

I lost the circuit board on mine to a very long ribbon of swarf that reached in along the lead screw

So now I have a VFD

Neil

Interesting Neil. I understood that a VFD could only be used with a three phase induction motor. Is this correct or are you using it with a single phase brush motor?

regards

Brian

Hi Brian,

I replaced the motor with a layshaft and a pulley turned on my mill, then added a single phase Hoover fractional motor. Once I'd got pulleys for six speed made, plus another six with back gear I found I could do everything I could before, but had more power.

Sadly, I'm an improvement freak and wanted real slow speeds back, so i fitted a 0.4kW 3-ohase motor and a Jaguar Cub inverter, still with the layshaft, but now with a poly-v belt.

Neil