SC4 Lathe chuck and Headstock size

What is the max diameter 3 J chuck that can be 'comfortably' used on a SC4 size lathe within its speed range? Would a 125mm chuck (5" ) be unwise? Also, could an owner of an SC4 perhaps measure up the actual headstock width please...I am trying to find out the distance between the bearing outer faces. I know the bearings are not flush with the outer surface of the headstock.

Thank you...

Joe

Edited By Joseph Noci 1 on 03/04/2021 21:41:23

I wish I could help Joe, but my lathe is 150 miles away in a container (not in the Suez canal...)

It's a 4" centre height, a 4" chuck is very comfortable, a 5" slimline chuck would probably be OK.

I use a 4" chuck on my CLM300 (C3-type).

Edited By Neil Wyatt on 03/04/2021 23:25:14

Thanks Neil.

Now there must be a story - A Man and his lathe separated by many miles..

Joe

I've ran a 125mm chuck on mine for years, with no issues.

The hold on things is much better than the standard 100mm one.

Jim

Thanks Jim.

Neil suggested a slimline chuck - is that the type you have? I presume you still have the lathe - could you perhaps do the headstock measurement for me?

Joe

Hi Joseph,

Surprised to see an EMCO aficionado ask a question about an SC4 headstock. I must be dreaming

I am spray painting part of the fence today. If I finish early, I will go over to the warehouse to get you the measurements you seek from the display model.

In the mean time, I am unsure about how many of these links you have seen...

• SC4 125mm Backplate - this allows you to put a 'standard' Chinese 125mm lathe chuck with 72mm lathe chuck onto the SC4, or ER32 125mm lathe collet chuck or ER40 125mm lathe collet chuck onto the SC4.
• the spares page show the spindle along with the front taper roller bearing (TRB) and the back ball bearing currently installed in the SC4 as standard.

Notes:

1. Using above, you can fit a 125mm Chinese chuck to the lathe, and it will be well supported with the TRB on the front. The bore through the spindle is limited to 20mm.
2. the slim chuck which Neil refers to is of Indian origin. you can fit that too after making a new register and mounting holes (PCD) to fit a modified backplate. Register and PCD on an Indian 125mm chuck is different from Chinese.
3. You are correct in asking the information about width of headstock, to check how well the spindle is supported. In my personal opinion, it should be longer to support a 125mm chuck, even though it would be supported by a TRB on the front. The TRB on the front is a 'slim' bearing 32007.... better for speed rather than load, but not a big issue for this size of lathe.
4. The speed and torque are controlled by correct programming of a chip on the circuit board, which in turn controls the brushless motor. So control is more electronic, rather than mechanical (this is the simplest way I can explain the set-up). So the mechanical load on the spindle due to increase in weight of a 125mm chuck will make the set-up perform differently from the standard set-up.

So, although the set-up works, as it does for Jim, and although ARC sell the backplate to enable use of a 125mm chuck of one description or another, and although it is well supported mechanically with a TRB; considering the the headstock width, and electronic control of speed and torque, as far as I am concerned, it would suggest the use of 125mm chucks to be limited to short periods of time.

Ketan at ARC

Hi Ketan!

Thanks for responding, and your opening line did make me laugh! However you probably realise behind my questions lurks an agenda...

What I am trying to do is mechanically unsound, frowned upon and will get me shot on this forum..

You may have seen my 'little' CNC lathe project - well, it has taxed all my abilities, including the brain muscle, which has been found wanting...

As with everything I do here, the solutions are very much driven by what I can obtain, and what is 'importable' within practical limits!

So, the headstock/spindle on this project became a 5C collet setup, with the spindle length dictated by available suitable steel - which ended up being from a section of sheared caterpillar drive shaft...Likewise , the headstock popped out of a chunk of Ali that followed me over the years - no such size material available here! Suppose I could have used a chunk of cast iron from the caterpillar engine..

The collet closer is a 120mm diameter handwheel. There is no space for a tommy bar/spanner hole/flat in the spindle nose or rear to hold the spindle whilst fastening the collet with the handwheel. The spindle motor - a 2KW closed loop brushless servo - has a holding torque of around 40NM, so was banking on that holding the spindle while tightening the collet. It works fine..but the manual effort required on the handwheel is too much. I can replace the handwheel with a torque nut, etc, but there are just too many issues that are now turning into a hack..

So, I want to remake the spindle, to take a 5C collet chuck ( a Bison unit) - that works like a normal 3 jaw chuck -

The chuck is 125mm OD, and 110mm to the collet nose from chuck back. The chuck main body is 125mm OD x 70mm thick. Add the backplate and its space to the headstock and the chuck nose is maybe 125mm from the end of the bearing..

My headstock is only 100mm wide...the bearings used are 100mm OD, 50mm ID, taper rollers, which are also an issue - Headstock is oil filled, but is dribbles from the labyrinth seals, and I have battled enough now! So I want to fit 100MM OD, 50MM ID, 30degree sealed, grease filled Angular Contact bearings instead, with a good preload.

Intended max RPM is 4000 for short periods, but mostly sub 2000RPM.

So, a 125mm OD 5.6kg chuck, 25mm longer than the end to end spacing of the (LARGE) spindle bearings, spinning at 4000RPM....not big loads in the machining, as the stock is limited to what 5C collets can take.

I looked at all the links you provided - I looked also at the Little Machine Shop USA site - they have a dimensioned drawing of a C3 headstock - indicates 106mm bearing outer spacing. Don't think a C3 will take a 125mm chuck..

Now to get into my bomb shelter...

Joe

5C chuck...

The current headstock bits

Lower bit is the spindle encoder

Hi Joseph,

Yes I have been following your project... on and off. Always like to see different approaches.

I have put all the SC4 rough and read pictures with measurements in the album: SC4 HEADSTOCK. Hope the information will help you to decide your direction

Ketan at ARC

From your description Joe, the problem with your existing spindle is mainly the difficulty tightening the 5C nut.

Would not incorporating a spindle lock within the headstock solve that problem?

A 12mm or so hole in the spindle wall between the bearings with well supported plunger would not be difficult to arrange as would a few tommy bar holes in the handwheel.

Just a thought anyway.

Ian P

My 125mm chuck is a standard size one.

Jim

Or coul dyou drill two holes into the end of the spindle for a pin spanner to hold it while tightening the collet.

A sprung lever action closer would be a another option then you don't have to turn anything just unscrew the unloaded collet when changing sizes.

In some sort of order...

Ketan, thank you very much for the photo's - your efforts much appreciated. The C4 headstock is a good 50% wider than my setup. Although the loads and stress calcs indicate the bearings I have are loafing along, somehow I just am uncomfortable putting that 6kg of steel hanging outboard on this narrow headstock..

Ian P and Jason - I think a solution is going to be along your suggested options. The Sprung Lever closer may bear some research...

Sometimes staring at a problem for too long results in solutions that are a bigger problem!

Thank you everyone for your input.

Joe

Joe, maybe something like this that is being used to work the modified R8 collet on a TTS conversion of a SX2.7. The double reduction from the two leavers needs little effort yet the Bellview washer stack gives a lot of pull on the collet

I wish I could come up with a scheme along those lines. It is complicated by the collet itself having to be removed to change size - all kind of reversed..So its not just a pull and push mechanism, but has to 'unscrew' as well. And the stock material must be able to pass through the mechanism too..

Keeps the head muscle working!

Thanks

Joe

About half way through he shows a "box spanner" being used to undo the drawbar and if you make it a hollow drawtube then that solves your stock length. Would probably need some form of forked end to apply the load rather than bearing on the drawtube as that would stop work passing through.

A google for "5C collet closer" will give you a few more ideas

Edited By JasonB on 05/04/2021 07:36:09

Was ER 40 collets an option and why not?

Digging and looking Jason..

Thanks

Niels, ER collets have a shorter contact length, and I have a 0.5mm increment set of 5C's..

Joe