The Shop > Tools
Milling machine choices ......
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:
--- Quote from: vtsteam on March 08, 2015, 02:11:27 PM ---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?
--- End quote ---
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.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version