[handlewanker]

My reference as stated was/is the SKF bearing catalogue, perhaps not as recent as your one, probably circa 1990, but neverthe less a valid design for a high speed vertical milling spindle.

If'n I have the inclination to search for it, I will post the relevant page that I photocopied at the time and since my retirement (10 years) still have.

The illustration you posted in the MRC bearing cat on page 11 bears no resemblance to the spindle design I mentioned, and I would venture to say that anyone attempting to make a spindle to that design would be treading in deep water.

I think you, and the illustration in the SKF cat you posted exagerate the "looseness" of the radial bearing, even allowing for the clearance for a lubrication film, and if'n you have a shaft with two radial bearings on it, as I recently dismantled from a cheap junk Chinese wood turning lathe, you will find as I did that it is impossible to measure even with a .0001" dial indicator any deflection of the shaft, at either end, and this is for a very basic shaft layout in the extreme...with no preloading.

BTW, a very basic bearing layout design I made for a lathe as an apprentice has been in operation since 1962, and consists of two tapered roller bearings on a shaft with 19mm bore and spaced at 100mm apart....bearing preload adjusted at the shaft end with lock nuts.

The design was by no means ideal but functional, and if'n there had been a heat problem it would have manifested itself by variation in the preload, but this configuration is very basic indeed and is not the ideal way to have a lathe spindle bearing arrangement, but due to lack of any experience in spindle design it sufficed at the time, and still functions today.....50 years later.

The "silly" statement you refer to was an "if " factor, and that has been used in a design of another machine spindle, but the bearings were in a cartridge form and not preloaded, just spaced apart to give a stiffening effect to the spindle.
Ian.

[Chrisjh]

Guys, Guys,

Please cool down!!!

All have valid technical points and I appreciate the efforts to point out potential pitfalls with my design (which you will note, is completely unproven at this point in time). I for one, am now more aware that my simplistic view of spindle design was lacking knowledge and experience, and I am now in a much better position to come up with something better. I appreciate the references and experience provided by others. It gives me a better platform from which to make design decisions.

My original objective (and still is) was to come up with a low cost design that mere mortals could afford to attempt to make for themselves. That is one of the reasons for a short spindle design, to lower the cost of the material for the 90mm housing. The other reason for the short design was to make the depth of bored holes as small as practical, so that amateurs like me could have a chance of boring accurately without having to resort to exotic solid carbide boring bars with dampeners.

I would like to point out that my present Chinese manufactured Syil X3 Mill has a similar toothed belt driven spindle design using a simple low cost tapered roller bearing at the bottom with preload applied by a thrust nut through a thrust bearing. The top bearing is basically the same as what I proposed to use in the discussion subject.

The Syil X3 mill has given me good results over the last 10 years in terms of accuracy of the finished parts. The spindle has a maximum speed of 3400rpm and is noisy, but gives me, as a hobbyist, satisfactory results. For example, all of the bearing housings for my home made CNC Lathe were done on the X3 Mill. All I had to do to get the bearings fitted into the housings was a light hone using a brake cylinder hone for the smaller bearings and a engine cylinder hone for the large 100 and 110mm bearings for the headstock.

I am still researching and making changes to my design based on the feedback and experience shared by others. For example I am adding a lock nut to the spindle shaft as suggested. I ignorantly thought that friction alone would hold the spindle shaft in place axially.

Regards

Chrisjh

[philbur]

Chris, In the Syil X3 spindle the top bearing is preloaded against the bottom bearings, by the pair of lock nuts. In your design there was no lock-nut to apply the preload. How you mount/preload the top bearing also depends on what bearing type you pick for the bottom end, your current choice is a mismatch.

If the X3 spindle works for you why try to design something different. Are you trying to make a better spindle, a cheaper spindle, or both. Which of these three alternatives will dictate your choice of bearings and their arrangement.

Phil

I would like to point out that my present Chinese manufactured Syil X3 Mill has a similar toothed belt driven spindle design using a simple low cost tapered roller bearing at the bottom with preload applied by a thrust nut through a thrust bearing. The top bearing is basically the same as what I proposed to use in the discussion subject.