Homebrew TS mill spindle

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PekkaNF:

--- Quote from: Steenkamp on June 01, 2015, 01:35:53 PM ---Hi all, thanks for the suggestions. What would the best lubrication be for the angular contact bearings be? I was thinking about auto transmission fluid (ATF). Would that be too thin?

--- End quote ---

First question: Why ATF oil? Do you have excotic coupling/friction materials in it?

Second question: Why oil? You have vertical spindle, right? Oil has tendency to fall down to bottom bearing and drip out. You need some wics, capillaries or something to oil the top bearing and not to drown the bottom bearing.

I would first consider standard grease and seals. If standard grease is marginal, then a little of high speed grease and if you need more rpm than DN factor / temperature allows then you'll need oil.

Somewhat agricultural answer:
http://www.mcnallyinstitute.com/CDweb/d-html/d019.htm

I once calculated and had one mechanical engineer to check them and my conclusion was that on small milling machine is is hard to go too highs speed to warrant oil lubrication, when milling cutter is over 8 mm and taper is under ISO30. Very small milling cutters and large spindle bearings and then you have yourself in funny place quickly, but we are into hobby machines and we don't need the whole "Envelope".

Pekka

lordedmond:
Just had a squint at the chart for some AC bearing that I use

Grease 40000rpm air/oil 63000rpm

That's with the correct pre load as speed in the designation letter on the bearing in question and the correct amount of grease

For that mill I would go for a simple taper roller bearing setup pre loaded with a belvue washer on grease you would be ok to about 5k any higher you need labyrinth seals

Stuart ,s 2cents

Steenkamp:
Hi Guys. Pekka, thought ATF as its the best oil in our roundabouts. I was also concerned with temp increases as it would influence preload on ac bearings. Or am i reading too much into it? But as Stuart just mentioned, highspeed grease will be fine as i only want max RPM of around 3000. For bearing setup i was thinking in order from top to bottom: ac bearing, spindle centre, ac bearing and then deep groove. Deep groove to help with radial loads and ac for axial. Angular contact was what i could get, otherwise it would have been wheelbearings. Do you think my arrangement would be sufficient?

PekkaNF:
What bearings/sizes you are using? I could look aup on tables and then ask trusted oldtimer mechanical designer what does he thinks.

I don't know how you are planning to use those bearings, Probably AC-bearings back to back and preloaded "justa about" or something in that effect on spindle nose and floating deep groove ball bearing in the tail, I vision?

Pekka

philf:
Hi Steenkamp,

I've made two milling spindles.

The first made about 25 years ago was for my Aciera F3 which came with no vertical head and all the drive removed.

This one has a Myford nose and 2MT bore. It uses a preloaded 25mm bore double row a/c bearing at the business end and a floating single shielded deep groove bearing at the pulley end. The pulleys are 4-row J section Poly V. They are 3 step and have ratios of 1:1 (3,000 rpm max), 1:2 (1,500 rpm max) and 1:6 (500 rpm max). The motor is permanent magnet DC. The bearings are grease lubricated.

The most recent was for my CNC mill.

This also used preloaded double row a/c bearing (this time a bigger section - 30mm bore) at the cutter end and two shielded deep groove bearings at the pulley end. The two deep groove bearings are preloaded together with a wavy spring. They are an easy fit in the housing so that they can float as the spindle warms up. The idea of using two deep groove bearings was that they tend to run quieter with preload. The spindle takes ER32 collets directly. The a/c bearings are oil lubricated with an oiler. The seal is a labyrinth with a drain so, in theory, I'm not sprayed with oil. This hasn't been entirely successful and I have a new design in the pipeline. This also has 3 step pulleys from 2:1 to 1:3. The belts are 5 step J section Poly V (easy to get as they are used on lawnmowers). The motor is a 3 phase Inverter rated motor which I run up to 5,000 rpm. This gives me a range of spindle speeds from 450-10,000 rpm. It's surprising how much of the time I use 10,000rpm. 8,000 rpm was the limit for grease lubrication.

Both spindles work very nicely but I have a feeling that the version with 2 deep groove bearings at the top is better.

You say you are considering one a/c at the bottom and one in the middle. Is there a good reason for this? As you run the spindle it will heat up and this will affect any preload on the a/c bearings. The bigger the distance in between, the more the preload decreases.

Hope this helps.

Cheers.

Phil.

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