spindle bearings

And use the bearing manufacturer’s advice on lubrication - not the machine supplier. The latter would likely be inferior and more expensive! (I did note the supplier was not Arc, before making that comment)

I'm sure he does, like a lot of people. I served my time as an apprentice with the Timken Tapered Roller Bearing company so I'm a little bit biased. Sadly the company moved out of England and relocated in India. I'm not familiar with this machine, so I don't know what would be involved in changing the bearing arrangement.

With bearings, like a lot of things, you only get what you pay for. In the case of the hobbyist, and if the machine will be idle most of the time, it might be better to go cheaper, just depends how much and what type of work the machine will be doing in the future.

Definitely!

Surprised that Chester did not stock bearings for the machine they sold you.

I wouldn't have thought they would stock them. Bearings usually last for year's (almost ever if looked after). To stock spares, would in my opinion, tell the customer to expect them to wear out quick. A good bearing stockist will usually have what you're looking for on the shelf. My advice....don't skimp on them.

The bearings in my KX3 are I believe are a cartridge type. The markings on the bearings indicate they are a matched pair (7007C). In the first instant I am going to fit a cheap pair of angular contact bearings and try and find a way to apply a preload. They are back to back bearings so preload is not guaranteed. Thinking of dropping a shim in between the bearings, press it all back together again then do a spin test, tweek the adjuster nut until there is slight drag then lock up the nuts and test. Otherwise its £170+ for a matched precision pair!

Cheers Michael.

I had to replace the bottom taper roller bearing for an R8 mill spindle, the wait was a week for SKF, so I chanced it and bought Chinese, and it has been running fine for 5 years.

Hi old mart

Thanks for that.

Cheers Michael.

There are various issues on this thread which are open to confusion..

1. Generally, bearings should be replaced like for like. i.e. angular contact bearings to be replaced with angular contact bearings. Taper roller bearings to be replaced with taper roller bearings and so on.

2. The OP has a manual Chester machine with maximum speed upto around 3000 rpm. The SIEG KX3 CNC... depending on vintage had a maximum speed of around 3500rpm in the early years and the newer versions I think around 5000 ~ 6000 rpm. The bearings in the SIEG KX3 CNC spindle assembly (size and type) have also changed over time.

With manual machines, in place of higher precision bearings, due to low maximum speed, you can probably get away with using general purpose like for like type and size replacement bearings for hobby use, until you start considering bigger industrial machines.

The SIEG KX3 CNCs have always been fitted with higher precision bearings. Where match pair angular contact ball bearings are fitted, they should be replaced with equivalent size/type match pair angular contact ball bearings. This also helps to get better runout accuracy. If one doesn't use match pairs in such cases, the accuracy can be open to question. It will still work, depending on if the user is happy with the result achieved after replacement.

pm sent to Michael.

Ketan at ARC.

Yes I would generally agree with that, but the OP suggested two options including changing to tapers. Personally, if I was going to use the machine a lot and hard, I would change to tapers if the castings allowed for the mod.

Cost is another concern the OP has, but again it depends what the machine will be used for.

I understand, and after re-reading the OP, I also get where you are coming from. In that respect, you are right.

So, I need to clarify my earlier position. This is my opinion... Most machine designers have taken various factors into consideration, and reached a balance/compromise for the type of bearings they have used in the spindle of their machine. For this reason, I have gone along the line of changing like for like... where possible.

So, if one still wants to change the type of bearings which are in their spindle assembly, here are some of the points to consider...

For example, changing from general 'ball raced bearings' to 'angular contact (ball raced) bearings, will allow for a good improvement in accuracy. Similarly, going from angular contact bearings to Taper roller bearings will give a further improvement in accuracy.

The pre-load on bearings is one of the factors. All other things being equal, if you change from ball raced bearings to angular contact bearings, the max speed will reduce based on contact angle and pre-load, and the max speed will further reduce if you change to taper roller bearings, mainly due to the surface area of the rollers in contact with the inner ring, and how much pre-load is applied.

Another factor is the electronics. If changing from one type of bearing to another, one needs to consider the following: With more pre-load facility available for Angular contact bearings, the motor 'may' have to work harder to turn the spindle, and it may have to work even harder for taper roller bearings. The question then arises, is the motor up to it?, is the belt drive or gear train up to it? So, one has to consider the balance of pre-load to motor load to forces on the gear train/belt drive, to get the accuracy required. Are the electronics up to it?

Another factor is heat generation.. are the new bearings lubricated correctly with the right type of grease?, and is the quantity of grease put inside the bearings correct (usually roughly less than 20% of internal volume of the bearing). If this is correct, how will the pre-load on such assembly behave in terms of heat generation, if you change from Angular Contact bearings to taper roller bearings (TRB), when running the spindle at 6000 rpm?, combined with the load on the motor... correct running in procedure - short term high heat generation before settlement, etc...

In our experience, going from ball raced bearings to angular contact bearings is a reasonable change one may wish to consider. However, going from ball raced bearings, or angular contact ball raced bearings to TRB, especially where higher speeds are involved, is something one should be more careful about, keeping in mind the points raised above. For manual hobby machines upto 3000 rpm, this may be a small issue.... subject to control board overload protection/or not.

There are various other points, relating to the cutting tools used before and after such changes, and their effects on the tool - HSS or Carbide (which need higher speeds). As carbide seems to be a new fashion thing, reduction in speed could have deferent effects on the cutter, as well as the results.

So, really up to the person making the change to consider many factors before making a change.

You also made a good point with reference to TRB: 'if the castings allowed for the mod' and/or the inner spindle assembly allowed for it.

These are just observations ( I am not trying to create an argument).

Ketan at ARC.

If modifications to the spindle are required, then the use of another lathe big enough to do the job is required.

As Ketan advises, the original type of bearings would be good candidates, especially as the original bearings had a long life.

Yep, agree, especially about the regard to lubrication. I'm going back many year's now, but I had to investigate several bearing failures and most were due to incorrect lubrication. A lot of technicians/mechanics thought that if the bearing and cavity wasn't full of grease, it wasn't lubricated properly. Fact was the bearings churn the grease and increase the temperature so much that failure is inevitable.

Have to agree with the bit in bold. Whilst playing I filled up the knackard bearings with grease and couldn't believe the increase in temperature at 3000 RPM, burning hand temp . As expected the bearings were growling. I stripped it back down and washed out the grease and just used a sticky oil and it then ran barely warm.

Cheers Michael

The cheapy bearings arrived today. I spoke to Ketan and he gave me some advice on fitting the bearings so will see how it goes. Probably fit them at the weekend.

Cheers Michael.

I got chance to fit the bearings today. It's not good.

Spun up the spindle in the lathe so only the ACB's were spinning, you can hear a noise and feel a vibration.

If you let go of the hub the noise and vibration disappear.

So it looks like I will have to dig deep and buy a pair of matched bearings.

Cheers Michael.