Mikron F75

I have released every screw nut and bolt but there is no lateral movement at all, i have given it several gentle taps with a lead hammer but still no movement

If you have to do it even on a simple drummond then you have to break the spindle key from the pullies with a decent whack, there can be considerable resistance to that first movement because the final fit in a decent lathe is very firm, the key turns the two parts into a single solid unit

So you will probbly have to release the bearings with a c-spanner to get some movement in the spindle and pullies to start with (a bit of jiggle), then figure out which direction to whack it in, the spindle should be slightly bigger at one end compared to the other because of step downs along its length

I wouldn't really be scared of taking it apart, my fears would be about getting it back together

OK chaps after a whole day of poking, pondering and trying different methods I have decided to leave the spindle alone and instead mounted the head on the lathe bed with suitable packing and used the chuck to provide drive to the spindle and polished the pulley, I have heard people say that all information is out there on the internet, you just need to look for it, well that's not true, I spent almost a week contacting the original makers, the import company or whats left of them and many knowledgeable sites in various countries all to no avail but having said that the information I have gleaned has been invaluable and will be retained for future use. The Mikron is nearing completion and will soon be up and running (touch wood). and I will list some pic's of the completed machine. Thanks for all the help and suggestions.

I agree with other Members,let sleeping dogs lie ! They are seldom in good humour when you disturb them,your spindle might be the same !! Why risk it ? Clean it where it is,the belt should soon clean up what,s left.

Never tempt the Gods !! How do I know ? Ask me ! Been there,done that,more than once !

Hi Larry, yes you are right, except the pulley will not be used so the belt will not have the chance to do the polishing, the machine is going to be driven via a pulley on the end of the spindle with power coming from a DC motor giving variable speed control.

Check out this site:

https://www.usinages.com/threads/mikron-t90.21964/

Try translating with google (Site is is French).

You will have to subscribe first to be able to see the pictures, but I think it will help you to solve the problem.

If not, I will try to remember how I did it with my Mikron T90.

I think is is the woodruff key that might block your attempts.

Bill,

Did you see this page?

**LINK**

I can give a little bit of help for the disassembly of the internally geared Mikron T90 and F75 headstocks.

Starting with what you should not do: DO NOT turn those two small screws that seem to go directly into the bearings. They have flat sides at the end that go into slots in the bearings. If you turn them they either break or damage the bearing slots.

You also do not habe to remove the bearings (unless you have to adjust for radial play). Realigning them to the spindle is somewhat time consuming when you put them back.

The spindle comes out at the front. There are two rings around the spindle at the front side. The first is partly hidden and has a small screw. This screw ends in a slot on the spindle and prevents it from rotating. It should not be tightened as it should be moving along the spindle. If it is tightened just loosen it a little (it does not have to be out completely).

The second ring is a nut screwed on the spindle and it is for adjusting the axial play. Remove the screw. Under it appears a small piece of bronze which on the bottom has the same threading as the ring. DO NOT touch this bronze piece - you will never get it back in at the right angle if you move it.

After removing the screw it should be possible to turn the ring somewhat. On the opposite side of the screw there is a hole that is useful if you have to use some force to move the ring in the beginning. But be careful not to insert any rod into the threaded hole to get the ring moving. Also be aware that the ring is rather soft and the also unthreaded hole can be easily ruined with to much force. The ring should move easily - do not use force and stop before it touches the pulley. If the ring is turned to move towards the back of the headstock the hole will be partially covered by the pulley. It is not necessary to screw it that far to the back now. Just leave it where it is for the moment.

Moving to the pulley: You must loosen the screw with the square hole. This screw locks the pulley to the spindle for turning without the internal gearing. If you use the internal gearing the spindle and the pulley turn at different rpm (3:1) and so this screw must be unlocked for this purpose. The other screw on the pulley is for oiling and can stay where it is.

At the backside of the pulley is another ring with two screws on opposite sides. They have pointed ends and fix the ring to the piece underneath. Before you remove those screws check if one of them and the threaded hole in the ring are marked (punched dot or x or similar). If this not the case you really should mark one of the screws, the matching hole, and also the piece under the ring. If you do not you risk that when putting it back together in a wrong combination the internal gearing will block completely (I can tell!). Both screws must be removed. Now the ring should turn freely. Do turn it 90° and look into the threaded hole: underneath has appeared another screw in each of the holes. Unscrew these, too. Now the pulley should be able move a little. You can now can gently turn the second ring at the front to unscrew it from the spindle. It should move to the back along with the pulley and the spindle can be drawn out at the front as soon as the ring reaches the end of the threads on the spindle.

Be careful when you lift the pulley after the spindle is out: The internal gearing drops out very easily if it is not too dirty.

I have two of these internally geared Mikron headstocks. With one this procedure has worked perfectly well without the use of any force - so I can tell it is the way to do it. With the second headstock I followed the same procedure - and the pulley does not move. I think it is stuck because of dirt or hardened oil.

Kind regards, Kaspar

Thank you very much Jan - I've just bought a beautiful Mikron T90 Watchmaker's lathe that's had a very hard life and has a bit over 1 mm play on the headstock bearings so I've been trying to find out how to repair or replace the bearings - I don't think I've got internal gearing so that makes the situation simpler but I am having a lot of difficulty finding documentation on how to adjust, repair or replace the headstock bearings so the article in French that you gave a link to is an enormous help! If you have any other information definitely let me know!

Hi Pete, Thanks for the link - the link is giving an error now but I was able to extract the original URL from it

https://www.usinages.com/threads/petite-fraiseuse-precis.20287

That's very helpful for me - I'm trying to restore a beautiful Mikron T90 lathe that I've just bought - it's had a very difficult life and has a bit over 1 mm play on the headstock bearings so I need to work out how to adjust, repair or replace them.

Hi Kaspar,

Thank you very much for providing such detailed and valuable information - particularly on the things that should be avoided.

I've just bought a Mikron T90 watchmakers' lathe with a bit over 1mm radial play on the headstock bearings and I'm trying to do as much research as I can before attempting to adjust, repair or replace the bearings. I don't think it's got internal gearing though so that makes the situation simpler.

If you've got any other information on repairing the Mikron lathes and milling machines I'd be very interested.

Thank you very much,

Will

The bearings are bronze and adjustable, they are bored with a cylindrical hole and the spindle will have a plain diameter where the bearings run. The spindle definitely is removed to the right. That thrust race is only there to counteract tailstock thrust and ensure the spindle has minimum end float for turning. Not at all scary, of delicate they are very similar to the spindle bearings in a Smart & Brown model A, bulletproof.

Thank you very much.

That's very helpful to me to know about the roles of the bearings and thrust race.

What lubricating oil would be appropriate for the bearings of this sort of lathe? Would a modern low viscosity fully synthetic or part synthetic engine oil be appropriate?

Thanks for mentioning the similarity with the Smart & Brown model A - I hadn't known about that lathe.

Will