[gotis]

Could something like this serve as a spindlehousing for a treadmill motor intended for milling aluminum?

Was thinking of making a spindle with er25 collet

LGN-C d= 25mm

http://www4.rexroth-star.com/INTERNET/WEBDOWNLOAD.NSF/4cacbb0890414ccf41256a0200531057/f8c2452909d79f4041256ba400391ffb/$FILE/RE_83302_2004_06_Ball_Screws_Masch_tools.pdf

[pstockley]

From the document you included it looks like that is a ballscrew assembly. The problem is that they are set up to handle axial loads mainly not radial (ok for drilling but not much use for milling). Also they often have a lot of preload so they will get very hot running much above 2000rpm. Plus they are usually very expensive.

I am currently working on a spindle design which I will post in a couple of weeks. I have a thread here: http://www.cnczone.com/forums/showthread.php?t=16238

I just picked up 8 sets of Fafnir Super Precision ABEC 7, light preload, 15 degree contact, duplex pairs, 30mm ID and 6 10mm ID duplex pairs from a guy in the UK who is getting out of the precision bearing market. I paid less for these 12 sets of bearings than 1 pair of NSK Super precision bearings cost. So I am not afraid to try a few experiments.

[gotis]

From the document you included it looks like that is a ballscrew assembly. The problem is that they are set up to handle axial loads mainly not radial (ok for drilling but not much use for milling). Also they often have a lot of preload so they will get very hot running much above 2000rpm. Plus they are usually very expensive.

well I got one from a discarded custom CNC. preload is suggested to 4Nm.

About the radial load I was thinking of swapping the upper bearings for a set of ordinary ballbearings (dont know the enlish word but I think you get the idea) this setup would make it withstand some more radial load and I could probably back off on the preload, or am i missing something?

Sorry about the Metrics!

[vmax549]

Has anyone though of building a small spindle with built in oil reserve and oil pump to spray the bearings for high speed work? Terry

[pstockley]

VMax, not sure why you would go to the extra complication and potential for bearing contamination. A medium sized spindle can run over 10,000rpm with grease librication. A small spindle with say a 10mm ID bearings could run considerably faster.

Gotis, don't worry about metric, I am orginally from the UK and used to working in imperial and metric. Regarding changing the bearings, it may not be that simple. You need a precision fit on the housing and shaft. The OD/ID and width of angular contact bearings my not be the same as the bearings you have now. Maybe someone with more bearing experience can offer more advice.

[gotis]

The pillowblock is already in my possesion and I am always looking for the cheapest way out, That said, in the end It´s not always the cheapest way, Sometimes I´m wrong.

SKF bearing 6305-2RS1 will fit, and a spacer between the one deep groove single row bearing (found it!) at the top and the two angular bearings in the bottom would have to be made anyway so the thickness of the bearings is not a problem.

Another Idea, use the coolant to cool the spindle on its way to the workpiece.

[vmax549]

Gotis that is a good Idea on the coolant cooling the spindle. Heat is a major player in precision spindles and long lifes.
Pstockley the Idea would allow the spindle to run with less drag less heat and hopefully less dimensional change from spindle expansion and should give a long bearing life. All that would be needed is a seal top and bottom, a small oil reserve and a small elec oil pump very low pressure and volume. The oil could be cooled from coolant as well. It could really be a very small package with coolant cooling, would not have to have cooling fins on the outside. Just a thought. (:~)= Terry

[NC Cams]

The runout potential for an ABEC 1 6305-2RS1 bearing is quite a bit more than that of ANY bearing that is ABEC 7 rated.

Thus, the bearings runout will literally fight each other. I would NEVER suggest or approve mating a 6305 electic motor quality with a precision A/C machine tool bearing (ABEC 5 or 7) of any sort (not without a lot of special, precision matching which is out of the realm of the DIY'er)

I realize that cost is/may be an object BUT when you're making a spindle that will run at any higher speed, you really need to match/select the bearings properly.

You also want/need to know if you're going to run more axial loading (IE: drilling) or radial loading (conventional milliing) in the application. This will help you select the proper contact angles and mounting relationship (DF, DB, DFD,etc). Improper selection leads to the "sometimes I"m wrong" scenario.

Sealed spindles with grease lube have charm in that they are less subject to debris contamination. A 7305 bearing is rated at 9K for grease lube and 13K for oil lube. If you start pumping liquid oi and/or letting it puddle, things can get messy. You especially want to keep from flooding the bearings which will cause overheating with too much oil at high speed.

At higher speeds, oil or oil-air misting becomes mandatory.

The proper way to design a spindle is to determine the loading, the desired life and select/fit bearings accordingly.

Now, when you try to salvage a find, you save money by "using what you've go" and/or "modifying same". BUT you can inadvertently put yourself in to a bind that will cause you lots of problems later on that you often can never figure out why it's happening.

BTW, ball screw bearings are NOT well suited for use in milling spindles - they are designed for absorbing high axial thrust. For milling, you want bearings with an A or C suffix (IE: 7203CTYDULP4 or 7204ATYDUMP4).

In NSK speak
7xxx = bearing size for A/C series bearings (size to suit housing or load life requirements)

C = 15 deg angle or, A = 25 deg

TY = plastic cage

DU denotes universal grind for mix n match mouning (IE: DB, DF or DT)

L, M, H denote light, med or heavy preload (L for high speed, lighter cuts, M for med speed light to moderate cut loads, H for grunt type cutting at lower speed) Probably use L or M in this case.

P4 = ABEC 7