C3 Mini-Lathe bearing options.

[Danny M2ZParticipant @dannym2z]

G'day all.

I decided to tweak my C3 Mini-lathe.

For the headstock bearings I found 3 options.

1. Tapered roller bearings (SKF 30206)

2. Angular contact bearings ( SKF 7206 BWG)

3. Single row cylindrical roller ( (SKF 206 NF)

I discounted #1 as it meant modification of the shaft spacers.

#2 is what ARC are offering (nice).

#3 intrigued me as an engineer friend told me that it is similar to what are fitted to humungous mining crushers (but they use double row). The 'NF' means that the bearings handle axial loads

#2 & #3 both are available in the required C3 size ( 62 x 30 x 16).

For the cross & topslides I found Needle Roller Thrust Bearings – 12x26x4 on the ARC site (prompted by the Myford upgrade thread).

Prices here in Oz are pretty horrific (eg; $66 ea for #2 (+ $15 'handling&#39, even though I am not a cashed up mining company.

What I am mainly interested to find out, is #2 or # 3 better for a lathe headstock, and why? It boils down what are the axial loads on a lathe I suppose, and that depends on what one is making. Most of my work is conventional turning with a bit of occasional single point threading .

Regards from the land of the kangaroo

* Danny M *

[Danny M2ZParticipant @dannym2z]

I want to upgrade my C3 Mini-Lathe

[jonathan heppelParticipant @jonathanheppel43280]

You need to cope with axial clearance (end float) also. Cylindrical rollers aren't adjustable for radial preload either, so angular contacts are really the only choice. I'm not sure why you need C3 clearance- could be that they are the most common cheap bearings. Best choice anyway is precision grade but it looks like they're out of your price range . Check the contact angle you need cos they vary. You may well find that just better quality deep grooves do the job, though they have fewer balls.

[Danny M2ZParticipant @dannym2z]

Hi Jonathon. Thanks for the reply. C3 refers to the Mini-lathe model. C2 bearing clearance is adequate

* Danny M *

[jonathan heppelParticipant @jonathanheppel43280]

No worries mate. I should say that I've no personal experience with mini lathes, just some with bearings. Providing it's not too conflicting, perhaps the info on a dedicated site may help more.

[Ketan SwaliParticipant @ketanswali79440]

Posted by Danny M2Z on 10/10/2013 08:00:51:

Hi Jonathon. Thanks for the reply. C3 refers to the Mini-lathe model. C2 bearing clearance is adequate

* Danny M *

Danny,

C2 clearance bearing is actually tighter than C0, and as a result not recommended/fitted to any mini-lathe.

C3 clearance bearing is looser fit than a C0 clearance, on radial ball bearings.

Usually, mini-lathes are supposed to be fitted with C0 clearance radial ball bearings, which should 'run-in' over time. However, during assembly, there usually is not a real control in place to ascertain if C0 or C3 clearance bearings have been fitted. The C3 clearance bearings give a more run-in feel.

30206 – Taper Rollers will give the most rigidity/accuracy, best pre-load, but the max speed will be more reduced in comparison to the standard radial ball bearings fitted.

7206s – Angular Contact ball bearings will allow greater speed than the 30206, but still lower than the standard ball bearings. Still, will give high rigidity/accuracy due to pre-load ability. Additionally, if with rubber seals '2RS' better protection from dirt ingress, and as dimentionally, as they are the same size as 6206-ZZ/2RS radial ball bearings currently in place, there is no need to make/modify spacers, as will be the case with the 30206s.

6206-2RS/ZZ – Standard ball raced bearings fitted to mini-lathes. They are fine for general purpose use, and they provide the highest speed range, becasue of lowest pre-load ability.

Ketan at ARC.

Edited By Ketan Swali on 10/10/2013 10:02:41

[Danny M2ZParticipant @dannym2z]

Thank you for clarifying my bearing dilemma Ketan. The angular contact bearings seem like the way to go. I read your helpful installation guide on the ARC website. The (local) bearings that I was quoted on are SKF 6206 (2RS).

A few questions if you don't mind.

How does one determine the correct pre-load torque?

Given the price differential (8 quid vs 66 bucks) are your bearings of similar quality?

Are the needle roller thrust bearings worth trying for the C3 slides?

I ask these questions because I suspect that I am not the only C3 Mini-lathe owner on this forum, or even in Australia.

Regards from the land of the kangaroo

* Danny M *

[Ex contributorParticipant @mgnbuk]

Cylindrical rollers aren't adjustable for radial preload either

Not correct. Many CNC lathes use NNU type roller bearings front & rear, with ball thrust bearings to take the end thrust. The NNU range is available with a tapered bore – the spindle has a corresponding taper bearing seat, rather than a parallel seat, with a fine pitch locknut thread behind it. The bearing is driven up the taper by the locknut to expand the inner race & take up the clearance & set a pre-load on assembly.

See here It is unlikely, however, that they are available in the sizes used on a mini lathe – the machines I have worked on have had bearings with bores of 24" and larger. German builders seem to favour this arrangement (Gildemeister, for example), though I have also come across them in American Jones & Lamson lathes.

Regards,

[Sub MandrelParticipant @submandrel]

I did the old taper roller mod to my mini lathe (using bearings from Arc). They continue to give every satisfaction, but note that I don't normally run my lathe above 1000rpm. I had to modify the bearing covers – I turned them in the lathe itself. Note that these are BIG roller bearing races, van wheel sized rather than car sized, so they could potentially take quite a pounding!

Although the apparent overhang is increased by about 4mm, it isn't really as the bearings have a longer contact patch. The real benefit is that you get a little more room for fitting the chuck mounting nuts behind the spindle flange!

Neil

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi all,

I went off on a tangent as usual

Ended up fitting tapered roller bearings , modified the spindle to crop the overhang down as far as possible , made a set of aluminium bearing covers up that are fitted with lip seals to keep the junk out of the bearings then converted it to 3 phase running off an inverter, it also has the drive belts converted to M section V belts and stepped pulleys .

i actually found that the reduced clearance for the chuck retaining nuts made it easier to fit as I can trap them between the mounting stud and headstock and give them a turn with a spanner and they thread straight on.

i picked up some thrust bearings for the cross and compound slides and maybe the leads crew on E bay that I will fit later on and a lot cheaper than you may think .

Just about finished the bench for it and I can fire it up and use it to do some mods on my other lathe.

Ian

[Ketan SwaliParticipant @ketanswali79440]

Posted by Danny M2Z on 10/10/2013 13:45:30:

Thank you for clarifying my bearing dilemma Ketan. The angular contact bearings seem like the way to go. I read your helpful installation guide on the ARC website. The (local) bearings that I was quoted on are SKF 6206 (2RS).

A few questions if you don't mind.

How does one determine the correct pre-load torque?

Given the price differential (8 quid vs 66 bucks) are your bearings of similar quality?

Are the needle roller thrust bearings worth trying for the C3 slides?

I ask these questions because I suspect that I am not the only C3 Mini-lathe owner on this forum, or even in Australia.

Regards from the land of the kangaroo

* Danny M *

Pre-load torque – trial and error. There are two lock nuts. Loosen the two nuts. Hand tight the inside nut, followed by a further quarter turn. Lock it in place with outside nut. Turn on the C3. Bring up the speed slowly without load to max. If the overload doesn't kick in, put in some bar stock and perform test cuts. Again, if overload doesn't kick in and you are happy with the finish, then all is well. If you are not happy with the finish, tighten the inner lock nut and repeat the process. If the overload kicks in at any time, loosen the inner lock nut. Hope you get the idea.

Currently, the bearings we supply are of Chinese origin, sourced from reputed factories. To make a bearing of 30mm inside diameter/bore, the factory which makes the bearing cannot be a small fly by night operation. Usually, such factories are a large scale operation with serious financial investment. Originally, such factories had large Russian machines, and over the last fifteen years, many have changed over to Japanese production machinery. In the case of Angular Contact ball bearings and Taper Roller bearings, the factories are more specialised then the makers of general radial ball bearings. So, the comparison of a like to like for a 30mm bore like to like in quality will result is a possible variation of 10% at best between branded and un-branded product. Traditionalists may disagree, but this is my opinion, having been a bearing dealer before becoming a machines/tools supplier.

Keep in mind that these bearings are designed to deal with greater loads and speeds than the speed a mini-lathe is capable of reaching. So, the 10% quality difference is really of little relevance when applied with the price difference. 66 bucks sounds like a lot of money. What is this price for – branded or unbranded 7206B-2RS? Unfortunately there is a big delay on delivery for these bearings from our supplier.

The needle roller bearings are worth trying if you can machine a recess and mount into the slides. However, it is not something we have tried out. We are aware that some of our customer have, but I cannot recall what they used. However with a thickness of about 4mm including the needle roller cage assembly and hardened washers, they are probably the lowest profile you could use provided you can accomodate them into the slide assembly.

Ketan at ARC

[Neil LickfoldParticipant @neillickfold44316]

Ketan, I know this is an old thread, but where do you get high precision and concentric tapered needle roller bearings from ? I had a project recently and the best concentricity I was getting from the Timken Tapered needle roller bearings, 40 ID X 68 OD was 0.01mm , and was not as close as the 0.003mm that was obtained with Angular contact bearings . Both setups used wavy washers to keep a constant pressure with an 0.04mm expansion allowance. Preloading without the wavy washers did not change the concentricity of either setup. Granted these were not brought or ordered to be spindle rated precision bearings. In the Timken range , i was given a ballpark figure of 600-700 dollars each, but needed to be an indent and ordered item. I did not get a price on the AC bearings as the 0.003mm was good enough for what I was doing with it.

Neil

[Ketan SwaliParticipant @ketanswali79440]

Neil,

The price for Timken bearing seems a little high, and if you want high precision Taper Roller Bearing, then Timken is probably one of the best choices. There are a combination of comments I would make:

In terms of bearing terminology, I would remove the word 'needle' from Tapered 'needle' roller bearings. It would be correct to say 'Taper Roller Bearing', especially when asking a bearing dealer for a quote. The less you know, the higher the quote . The more you know, the more reasonable the quote, before you check on the Internet for the price.

Next, it helps to know the bearings 'generic' number, before introducing the prefix or suffix for precision to this generic number. So again, if you just give the size, price could be higher then if you quote the generic number.

So, in your case, 40 x 68 x 19 or 22mm – so, generic taper roller bearing (TRB) numbers: 32008 if 19mm width or 33008 if 22mm width.

If Angular Contact Ball Bearing, then the generic Angular Contact Bearing (ACB) number for 40 x 68 x 15mm is 7008. You will notice that the width is narrower than TRB 32008 or 33008.

Chances are, you are comparing TRB 32008 with ACB 7008, because the width of the outer ring of 32008 is 14.5mm, even though the stack width is 19mm.

Precision/Accuracy:

A. What is your application – lathe or mill. How are the bearings fitted? Was there any contamination present during the fitting process?…for example I know of situations with lathe headstocks where the outer ring of a TRB has not seated correctly against the shoulder in the housing because there was dirt/swarf present in-between the outer ring and the shoulder.

B. Provided it isn't anything special, and most of the time it isn't with TRB, they have a suffix E sometimes, so lets say E32008, which suggests an extra roller has been fitted to the bearing, to handle extra load capacity. This should not really effect the accuracy for lathe/mill applications significantly in the hobby environment, other than reduction of maximum speed vs the ACBs. It is very rare for me to have come across a special requirement for TRBs. However, ACBs are a different story. Generally greater speeds are achieved vs the TRB to start with. Accuracy with ACBs depends on application and various suffixes after the bearing number, such as suffixed A, B, C. So, A = 30 Deg. contact angle of the balls to the inner and outer ring inside the raceway, B = 40 Deg., C = 15 Deg…so, the ACB 7008 with be stated as 7008 A, 7008 B, or 7008 C. Super Precision Match Pair ACB = GOLD have additional suffixes, and they are normally used in High Precision High Speed spindles. So, they would have a number with suffix similar to 7008 CD UP4, where C = contact angle, D = duplex, U = universal which means that the pair can be fitted back to back or face to face, P4 = High Precision.

So, all of the above factors can effect the price and the accuracy/precision you get, but there is no need for super precision ACB with most hobby lathes and mills, other then for personal satisfaction or requirements. For these reasons, I do not have a clear answer for your specific situation.

Ketan at ARC.

[Ketan SwaliParticipant @ketanswali79440]

Posted by Ketan Swali on 02/04/2015 12:59:06:

B. Provided it isn't anything special, and most of the time it isn't with TRB, they have a suffix E sometimes, so lets say E32008,

Ketan at ARC.

I meant to say prefix E in the above.

[Neil LickfoldParticipant @neillickfold44316]

Thanks for the informative reply.

I have since learnt that the radial run out was due to the class of bearings I brought. It seems there are general, spindle bearings, and a lot better spindle bearings. In my case they were part of a headstock spindle cartridge I made. To get better concentricity will require a better class of bearing with a higher manufactured accuracy. There are other ways of improving the assembled accuracy, like measuring where the high versus low on the shaft are and then aligning it with the high/low on the bearing to compensate . Then there is the final grind/turn of the important faces/surfaces once assembled. I liked the idea of using TRB, but have since found out that the precision spindle class is like gold to buy. The ACB is a new can of worms for me to figure though with the various contact angles and precision.

It appears that the more accurate ones are made to the same tolerance as the cheaper ones, about 0.001 to 0.002 mm but have been measured for their concentricity and marked accordingly .Is this correct?

My goal with all of this is to eventually make a super precision spindle that rotates concentric to 0.001mm or better for another little project I am working on.

Thanks , Neil Lickfold

[Ketan SwaliParticipant @ketanswali79440]

Posted by Neil Lickfold on 02/04/2015 22:15:45:

It appears that the more accurate ones are made to the same tolerance as the cheaper ones, about 0.001 to 0.002 mm but have been measured for their concentricity and marked accordingly .Is this correct?

Neil,

It depends on the manufacturer and the age/quality of the machines they are using to manufacture the components. Some adopt the process you suggest because the machines they use are advanced or correct for the components they are making. Thereafter, it is just a process of selecting and grading as you have suggested. Some have dedicated machines to carry out the specialist manufacture and assembly of specific components. Without going into detail….for reasons of confidentiality, some components are even bought in from other bearing manufacturers who can produce the specific component to better accuracy at a specific price. Bearing sub-factories – assembly and production, around the world change hands – swapping from being under the umbrella of one manufacturer to another all the time…mainly for financial reasons.

I am not entirely familiar with TRB higher precision classes, as I have not yet come across requirement for the same.

If you decide to go down the Super/Ultra Precision Match Pair ACB route, to the best of my knowledge the highest class of precision you will get is Fafnir 2MMV/X or 3MMV/X range. If you can obtain their printed catalogue, study it to get a deeper insight for your application. Fafnir originally stated as just Fafnir. Then came under the following umbrellas to date: Torrington, Ingersoll Rand, TIMKEN, Koyo, JTEC.

Ketan at ARC.

[Author]

Posts