I'm only a novice myself, Nige and don't know how an ML4 compares with an ML7 but..did you lock the saddle to the bed first ?
DaveD

Guess before bedtime. Lock the saddle by engaging the half-nut with the leadscrew. With the leadscrew disengaged, ie not turning!

Dave

Edited By SillyOldDuffer on 29/07/2017 21:57:10

Engage the half nuts and use the leadscrew handwheel to move the carriage toward the job so no backlash is present in the cutting direction. Don't tighten your gibs to act as a lock. It's fine if you can push the carriage up and down the bed by hand, that's how it's supposed to be, ideally. But in the real world, you will probably find the section of bed closest to the chuck more worn than the rest. So i fyou set the gibs on the unworn bed section toward the tailstock, it may be too loose on the worn section near the headstock. Trick is to set it at a reasonable compromise, keeping in mind that you rarely move the carriage very far toward the tailstock for most model engineerring sized jobs. So set it so it moves freely but with no slop on the left hand half of the bed.

That said, a saddle lock is a good thing to add down the road sometime. Especially for parting but also for facing. It can be as simple as drilling and tapping an extra screw in between two of the existing gib adjuster screws. The extra one can be nipped up when you want to lock the carriage or slackened off completely for general work. Or you could make something more substantial modelled on the ML7 lock bolt.

Edited By Hopper on 30/07/2017 05:37:32

I am with Andrew, your gib should be a little tighter such that it takes a firm but easy push to move the saddle and the tool geometry, it should be cutting not trying to push its way into the job in hand. I rarely lock a saddle (for facing only), the DRO shows that it does not move away from the job.