CNC lathe 5C spindle build

[aarongough]

They are just a disc with a few grooves in the outer edge. The bearing housing bore is the other surface, 0.1mm away... Grease in the grooves keeps the junk out. Make sure any design has has an amospheric relief path. i.e. the inside of the bearings is at the same pressure as outside. If not... they will puke out grease when hot and suck in crap when coolling.

Emco's use tapered bearings front and back with preload applied by a rear nut. Dead simple, robust and works very well... Copied by the Chinese for decades!


This is the spindle from and Emco Compact 10 I'm converting to cnc. It has an MT5 taper and a D1-4 spindle mount. It was unused and in storage for 25 years. Minor surface rust and dried out grease. After these pictures I restored it to "like new".

Awesome! Thanks for taking the time to post pictures!

I was considering going with the 2 bearing arrangement, but I think the simplicity of the design is offset by more difficult and precise setups being required.

It looks like it would be very easy to replicate that seal which is good! I can create a similar seal in 2 places with my current design with very little effort, which works out nicely.

I'll update the draft design tomorrow and post some new drawings!

Thanks again to everyone for all the input! I'm very excited for this thing to become a reality!

[aarongough]

Here's a partially updated drawing. One problem right now is that I'm getting short of room at the heel of the spindle for the drive pulley.

[mactec54]

aarongough

That looks better now, you want a minimum of .5 of thread to lock the front bearing outer race into the housing, & it needs to be a fine thread, like 32tpi or similar in metric

You don't need the breather hole in the body, & can use ( 1 ) nut to lock the centre at the back, this to needs to be a fine thread

The labyrinth seal design you have done is not suitable for your spindle type

[Bubba]

Hi,
Being picky with your drawing, but the "seal/washer" between the pulley and rear bearing seems to have in interference fit with the outer race. You need clearance here as the washer will be rotating and the race static.

[RICHARD ZASTROW]

Ref. grease: We use sealed, lubed for life angular contact bearings.

An additional metal Nilos seal is positioned front of the the first A/C bearing at the spindle nose. This prevents "stuff" from migrating to the seals of the first A/C bearing.

Nilos also has seals for some tapered roller bearings and others as well.

Had some unhappy experience with light air pressure inside the headstock. Moisture condensed in the airlines and ended up in the headstock, even with desiccant line filters. Too much pressure blew out oil seals as well.(old app LOL)

We use sealed precision A/C bearings from GMN; they have small bore pieces. The Nilos seals are an SKF product. I don't push anybody's stuff, just happens to be what we use.

FWIW

Dick Z

[aarongough]

Hi,
Being picky with your drawing, but the "seal/washer" between the pulley and rear bearing seems to have in interference fit with the outer race. You need clearance here as the washer will be rotating and the race static.

I appreciate you taking the time to look over the drawings!

There is actually about 0.010" of relief there, but the drawing doesn't have enough detail to represent that accurately.

I need to work out how I'm going to design/make the labyrinth seals. Seems like one of the more complicated parts of the build.

[aarongough]

aarongough

That looks better now, you want a minimum of .5 of thread to lock the front bearing outer race into the housing, & it needs to be a fine thread, like 32tpi or similar in metric

You don't need the breather hole in the body, & can use ( 1 ) nut to lock the centre at the back, this to needs to be a fine thread

The labyrinth seal design you have done is not suitable for your spindle type

Thanks for having a look Mactec! I'll update the bearing retainer to suit.

I still haven't worked out exactly how I'm going to design/machine the labyrinth seals. With the labyrinth seals that you made for the ER16 spindle, how much clearance was there between the rotating parts?

Will a single nut at the rear not work itself loose? Would it need a setscrew or loctite to retain it? Or would the fine pitch of the thread create enough friction to retain it that way?

[aarongough]

Ref. grease: We use sealed, lubed for life angular contact bearings.

An additional metal Nilos seal is positioned front of the the first A/C bearing at the spindle nose. This prevents "stuff" from migrating to the seals of the first A/C bearing.

Nilos also has seals for some tapered roller bearings and others as well.

Had some unhappy experience with light air pressure inside the headstock. Moisture condensed in the airlines and ended up in the headstock, even with desiccant line filters. Too much pressure blew out oil seals as well.(old app LOL)

We use sealed precision A/C bearings from GMN; they have small bore pieces. The Nilos seals are an SKF product. I don't push anybody's stuff, just happens to be what we use.

FWIW

Dick Z

If I could get my hands on bearings like that for a reasonable price then they would likely be ideal. I would still need to make shields, but they're simple compared to seals.

Mind if I ask what sort of rough price you were paying for those bearings, and what size they were?

Good to know that positive air pressure has it's downfalls too.

[aarongough]

This page: Rotary Seals

Gives clearances in labyrinth seals of between 0.25-1mm...

[aarongough]

It seems that the labyrinth design that Lakeside showed from his Emco headstock is called a 'see-through' labyrinth seal, and is mainly used as a gas seal in turbo equipment.

Not sure how useful that would be in my application.

Source: Seals and Sealing Handbook - Robert K Flitney - Google Books

[ninefinger]

A couple of thoughts...

How fast do you plan to have the spindle turn? Those seals generate alot of heat, especially in the larger diameters and higher speeds (lots of surface velocity for friction). If you're doing the labyrinth seal then skip the seals on the bearings themselves. I was reminded of the heat the seals make as I was running my mil spindle at 3000 rpm and the sealed bearing at the top was hot but the larger tapered roller bearing was not.

Also, though more challenging to do a belt change you could locate the pulley inside the headstock, between the bearings,letting you space the tail bearing out a bit further.

Mike

[mactec54]

RICHARD ZASTROW
Had some unhappy experience with light air pressure inside the headstock. Moisture condensed in the airlines and ended up in the headstock, even with desiccant line filters. Too much pressure blew out oil seals as well.

You would not & should not have any air pressure, in a spindle that has sealed bearing, this would be wrong to start with, Most good lathes have a oil pump that feed the bearings with oil, if they don't have a pump it just gets splash feed oil to the bearings

When you have a correctly designed Labyrinth seals, there is nothing to blow out but used oil which keeps metal chips Etc away from the front of the spindle, if you have air pressure in the spindle for oil mist lub, this is a good thing, If you use grease filled bearings then you don't have air going through the spindle

[mactec54]

aarongough
Not sure how useful that would be in my application.

It's of no use to you at all, and is a bad design for a spinde

When I make the labyrinth seals for general use, they have .010 to .012 clearance, if it is for a grinding spindle I make them with .004 clearance

[aarongough]

A couple of thoughts...

How fast do you plan to have the spindle turn? Those seals generate alot of heat, especially in the larger diameters and higher speeds (lots of surface velocity for friction). If you're doing the labyrinth seal then skip the seals on the bearings themselves. I was reminded of the heat the seals make as I was running my mil spindle at 3000 rpm and the sealed bearing at the top was hot but the larger tapered roller bearing was not.

Also, though more challenging to do a belt change you could locate the pulley inside the headstock, between the bearings,letting you space the tail bearing out a bit further.

Mike

Hey Mike!
The spindle will likely be run up to about 4K RPM so not too fast.... The seals on the bearings have basically been done away with in favor of fabricating labyrinth seals, looks achievable but should be challenging!

Putting the pulley between the bearings would be awesome, but then sealing the headstock would be a nightmare. I think I'm going to have to live with the compromise unfortunately.

[aarongough]

aarongough
Not sure how useful that would be in my application.

It's of no use to you at all, and is a bad design for a spinde

When I make the labyrinth seals for general use, they have .010 to .012 clearance, if it is for a grinding spindle I make them with .004 clearance

Sounds good. I've been going over the pictures of your spindle build and I think I finally saw what I've been missing, I'm updating the design now.

I'll work with 0.010" clearance.

Thanks!

[aarongough]

aarongough
Not sure how useful that would be in my application.

It's of no use to you at all, and is a bad design for a spinde

When I make the labyrinth seals for general use, they have .010 to .012 clearance, if it is for a grinding spindle I make them with .004 clearance

One other question: do you use the same amount of clearance for radial and axial clearance? I'm thinking that the radial clearance probably needs to be higher to account for thermal expansion?

[aarongough]

@Mactec:

I believe this labyrinth arrangement is more like the one you used for the ER16 spindle, is this correct?

It's a little hard to work out how it all fits together from only photos

[mactec54]

aarongough

Same clearance all around, if you have a spindle that is going to move that much with thermal expansion, it would not be any good as a spindle, your spindle design will expand towards the back,or top bearing, the radial expansion is a very small amount

[mactec54]

aarongough

Here is a rough drawing to give you a better idea, they are very simple to make, they can be all done on a lathe, but if you don't have a good way to do the grooves, then you can do that part on a mill, I do other different designs as well but this is just the basic idea

[lakeside53]

It seems that the labyrinth design that Lakeside showed from his Emco headstock is called a 'see-through' labyrinth seal, and is mainly used as a gas seal in turbo equipment.

Not sure how useful that would be in my application.

Source: Seals and Sealing Handbook - Robert K Flitney - Google Books

Emco thinks it's good enough for a lathe There are many paths to success.

BTW.. Not much point in using precision duplex bearings at the front unless you also use a precision bearing on the rear.