Milling machine choices ......

[Garyrmck]

Hi,

I am waiting on the arrival at a supplier of a Sieg SX2P mill. I have a choice of an MT3 or an R8 spindle.

I had initially thought of getting the R8, but I believe it is possible to upgrade the bearings on the MT3 model but potentially not on the R8 version? Is this an issue regarding choice?

Is there any great advantage of one spindle over the other?

To complicate matters further, another supplier has started stocking the Optimum rage of mills very recently.

The BF16 is similar to the the SX2P in size, would this be a better choice?

I'd love to go up to the BF20, but I couldn't move it due to the weight, and I've seen lots of posts regarding motors dying in them...

Should I consider the Optimum mills? Or just stick with my original choice?

cheers
Gary

[Jonfb64]

Hi Gary,

I would go with R8  ask anybody who has beaten a Mt3 collet to death to release. I believe there are plenty of threads to this on this site. I have the R8  sieg mill and am happy with its performance for the price.

Jon

[vtsteam]

Yup R-8 vs MT in mills has had a long airing of views in other threads. You can find those threads and get the arguments fresher than they would be if repeated here! 

Though the question of whether the bearings can or cannot be renewed for each on your mill of choice is a good new twist, and deserves an answer!

And brand vs brand is less debated, could be interesting......

[Will_D]

According to ARC spares for the super X2P:

http://www.arceurotrade.co.uk/Catalogue/Machine-Spares/Super-X2-Plus-Spares

This implies they MAY have angular contact bearings available.

Why I say MAY is that reading the various texts nits not 100% certain. I would suggest a phone call - they are a very good firm to deal with

[Arbalist]

That's quite interesting about the Angular contact bearings. I'll have to remember this if ever have to replace the bearings on my VMC.

Some of the smaller milling machines have self ejecting draw bars on their Morse Taper machines so no hammer required  Check out the Warco range of mills.

Unlike R8, Morse Tapers are self locking so only need "nipping" up. If you don't over tighten them they only need a sharp tap to eject them.

[Garyrmck]

Hi,

I had read a number of threads regarding R8 vs MT3, with most going for R8.

I had a discussion with a friend who is an engineer and he fully explained the R8 vs MT3, the various angles and why they were the way they were. He suggested that the R8 was the way I should go, not withstanding the angular contact bearing issue. He explained that whilst most mills were fitted with angular contact bearings so that they could plunge mill without issue, he didn't think that on a hobby mill which was going to be used on aluminium mostly and the odd bit of mild steel, that the fitment of standard bearings would be much of an issue. Just use a slower feed when plunging.

He might have accepted the MT3 if there was a slot in the quill that allowed a drift to be used to loosen a stuck collet - but since I didn't know the answer to that I let it pass...

All this from a guy who owns a lathe 10 meters long and a mill that can cut 3/4" of steel on one pass - makes the whole factory vibrate when in use....

cheers
Gary



cheers
Gary

[vtsteam]

Brings up a side issue I sometimes wonder about with tapered or angular rolling bearings of all sorts on lathes mills etc. and the problem of sometimes rare and incredibly expensive spares for older machinery.

Is that just a manufacturing convenience to take up thrust in a single unit? I mean why can't a separate thrust bearing and a straight rotary bearing do the same job of a single tapered bearing, if building your own lathe?

Well I know it can be done (and is done) with plain bearings, because that's what I have in the Gingery lathe -- a flanged plain bearing and a bronze bearing thrust washer behind the spindle flange.

I'm not saying it's preferable in manufacturing, but separating bearing functions in rolling types is an option, isn't it? Or is there some physical advantage (other than space saving) that all-in-one bearings are better for the purpose?

[philf]

Brings up a side issue I sometimes wonder about with tapered or angular rolling bearings of all sorts on lathes mills etc. and the problem of sometimes rare and incredibly expensive spares for older machinery.

Is that just a manufacturing convenience to take up thrust in a single unit? I mean why can't a separate thrust bearing and a straight rotary bearing do the same job of a single tapered bearing, if building your own lathe?

Well I know it can be done (and is done) with plain bearings, because that's what I have in the Gingery lathe -- a flanged plain bearing and a bronze bearing thrust washer behind the spindle flange.

I'm not saying it's preferable in manufacturing, but separating bearing functions in rolling types is an option, isn't it? Or is there some physical advantage (other than space saving) that all-in-one bearings are better for the purpose?

Vtsteam,

The problem with trying to use a thrust race and a "straight rotary bearing" is that straight ball races are made with radial clearance and need to be preloaded to remove that clearance. Two standard ball races can be preloaded together to remove radial play but their ability to take axial loads is somewhat limited because the line of contact through the balls from inner to outer races is almost perpendicular to the spindle axis. The more clearance in the bearing the better the angle is to take axial loads. Angular contact bearings can have different contact angles depending on the required axial/radial load ratio but these angles are huge compared with what can be achieved with a radial bearing.

Using thrust races to oppose each other at the same time as preloading the radial bearings could be achieved but it's too complex when a pair of angular contact or taper rollers would do the job much more simply.

Hope this makes sense.

Cheers.

Phil.

[PekkaNF]

vsteam,

Would this help:
http://www.skf.com/group/products/bearings-units-housings/super-precision-bearings/principles/design-considerations/bearing-arrangements/for-heavy-loads/index.html

That explains it better than I can, there are some other interesting items on "Bearing arrangements". left panel.

At the end of the day it is not the "best" the one that will fullfill requirements, fits in the space available (sometimes on existing or obsolete design), has parts that can be sourced, is possible to manufacture and assemble with resources on hand and fits to company service ideology.

P.S. I never beat up MT3 taper tools. It does not need a key. It is basically a drilling taper and pretty good at it. It can do some hobby milling, but if you need ATC or dogs, then MT or R8 is not the right one on start with. Debate over MT/R8 just indicates that neither of them is really that much better over another. It all depends for which one you have more tools and which one you are used to and like.

Pekka

[Arbalist]

Agreed Pekka, neither are what some folks would call a "proper" milling taper. The R8 is just another Lathe taper like the 5C but with a draw bar in the middle rather than a nut. ISO tapers used in industry are far more robust for milling machines. The R8 is quite well suited to hobby machines though due to its small size although it's interesting to note that some of the smaller mills are now available with an ER collet system. I expect this may become more popular.

I seem to remember reading about bearing replacement on a Tom Senior milling machine some years ago and was surprised at how big the taper roller bearings were on it, far bigger than today's machines of similar size although this was on the Horizontal spindle.

[vtsteam]

Thanks Phil and Pekka. It looks like, in answer to my question of whether a combined rolling and thrust bearing had any functional advantage over a separate roller and thrust bearing, it doesn't sound like it does. (Other than manufacturing ease and simplicity.) In fact the first description and drawing that Pekka linked shows a spindle with separate bi-dirctional thrust bearing and 2 sets of roller bearings.

I asked this because Rob's new lathe apparently would need incredibly expensive proprietary bearing replacements, if they could be found (and if they are actually needed) of about 7 times the lathe's purchase price. It just got me thinking about the whole subject, and what I'd consider if I had a scrap lathe which required special bearings that I couldn't find or afford. And I'm also always thinking about the possibility of building a new lathe from scratch, and just wondering in general about the topic of rolling vs plain bearing practices. (When I say "rolling", I don't mean roller -- I mean all types of rolling contact bearings).

Thanks again for replying!

[awemawson]

Many years ago when my Colchester Student front headstock bearing roller collapsed as previously mentioned, I gave serious consideration to making a bronze plain bearing for it. Fortunately I found the second hand one and didn't have to.

[philf]

Thanks Phil and Pekka. It looks like, in answer to my question of whether a combined rolling and thrust bearing had any functional advantage over a separate roller and thrust bearing, it doesn't sound like it does. (Other than manufacturing ease and simplicity.) In fact the first description and drawing that Pekka linked shows a spindle with separate bi-dirctional thrust bearing and 2 sets of roller bearings.

I asked this because Rob's new lathe apparently would need incredibly expensive proprietary bearing replacements, if they could be found (and if they are actually needed) of about 7 times the lathe's purchase price. It just got me thinking about the whole subject, and what I'd consider if I had a scrap lathe which required special bearings that I couldn't find or afford. And I'm also always thinking about the possibility of building a new lathe from scratch, and just wondering in general about the topic of rolling vs plain bearing practices. (When I say "rolling", I don't mean roller -- I mean all types of rolling contact bearings).

Thanks again for replying!

My own lathe is a Boxford Industrial which were (still are?) available in standard and toolroom versions. The toolroom version used Gamet bearings, the standard used Timken taper rollers. According to the parts diagram the spindle and headstock casting are identical so the bearings must be interchangeable. I'm not saying that is the case with all lathes or if every Gamet bearing has an off the shelf equivalent. I think that a standard taper roller bearing would be adequate for most hobby use.

Another possible option if a specific bearing couldn't be found would be to make sleeves to adapt a smaller section bearing but with risks of reducing the stiffness and accuracy.

Phil.