Saturday, 10 March 2018

Aaaaw chucks - or when your lathe's spindle tries to take a u-turn (Matra MDR2A)

Lathes are wonderful machines. They literally are the queens of the machine-shop: Of staggering beauty and sometimes with a temper so vile, hell might freeze over. This, is a story of the latter. (Unfortunately!)

When I bought my old Matra MDR2A, almost ten years ago, I put it into service and that was (pretty much) it. I did some maintenance over the years, but nothing overly dramatic to be honest. Unfortunately recently when I did that clutch pressure plate, I had a little crash. On the upside this finally loosened the chuck just that little bit, so I could get it off the spindle nose. What I found was some old damage and the reason, why I couldn't get it off as it was glued on.

In the course of the process even the three M8 screws holding the chuck to the backplate got a bit bent.

I did, what every good machinist would do: I screwed the backplate back on, but the damage was done: I couldn't find the position again. 

Overall runout between highest and lowest registered as 0.70mm and a half of that on the diameter of the backplate.

Get out the old machinist's blue...

and then start turning her back down until it runs true and *JUST* no more blue is left. 

So that's the backplate all cleaned up again. You can also see a scribed mark on the outer circumference, this is where originally there used to be a punchmark for aligning the chuck to the backplate.

Now the runout registers at around 0.03mm on the outside of the backplate and also on the workpiece directly in the chuck and that's realistically speaking as good as she'll ever get again, after all this is a 1946 to 1948 Matra lathe, so she's well in her seventies.

While I had the chuck off, I also took the backplate off and cleaned out the decade-old grease and replaced it with some fresh moly grease and now she's still a bit sloppy, but waaaay smoother. 

Also found some o-rings to prevent the bar of my chuck key from falling out. (Stuff I do, while thinking about how to assess the damage correctly.)

And here's the reason, why I can exactly say, when my lathe was built - because it was already overhauled once in the 1950ies or 1960ies, during her service with the German Bundeswehr.

So what does the future have in stock? Most likely a new spindle or at least a spindle sleeve to step her up one or two sizes to a M39x4 spindle nose instead of the original M33x3.5. As the nose at the root of the threads is only approx. one (!!!) mm in wall thickness.

Alternatively, I shall admit that, if the right lathe comes along, I might be tempted to part with the old girl. But don't worry, at the moment I am not even entirely sure what the "right lathe" could be.

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