Harrison M300 Cross Slide Nut

[Len Morris 2Participant @lenmorris2]

Hi Everybody,

Have a problem and really need some help.

When I took my cross slide apart the backlash adjusting arrangement that separates the nut halves was missing. The manual seems to show a ball, spring and grub screw. Simple enough to replace so didn't give the matter much attention until I came to assemble all the clean bits.

My cross slide is threaded M6 for the grub screw all the way through. With the nuts in position (front doweled, chamfered rear nipped on bolts) an M6 bolt just passes straight between the nuts. Clearly, whatever I put down the M6 hole will not engage the rear nut chamfer and push it back.

Trying to speak 'Harrison', the ball is shown as UB-008 which I think is 8mm diameter. The grub screw is shown as FS-0892 which could be 8×92 mm.

The whole thing makes no sense and it's basically stopped the job as I,d rather not fit the slide and have to remove it later on.

Any advice or information much appreciated.

Len

[Len Morris 2Participant @lenmorris2]

[Clive FosterParticipant @clivefoster55965]

Len

I think you are missing a wedge piece which pushes down between the two haves of the nut acting on the chamfered edge of the back half forcing it away from the fixed and doweled front part. I imagine the spring acts to keep the wedge piece in roughly the right place before adjustment and the ball helps provide a smooth movement for the adjusting screw with no risk of damage to the bearing surface in the wedge.

The M300 manual I have a PDF copy of shows this system, albeit simpler as no spring and ball are shown.

Clive

[Len Morris 2Participant @lenmorris2]

Hi Clive,

Thanks for that, I'm sure you are right. It's the only thing that makes any sense. Not surprised your manual shows no ball and spring as with a wedge of the correct length it can't go anywhere.

With some confidence from your reply set off to make a wedge conscious of the need to keep everything parallel and get the angle right. Lot of work, but then had a 'lightbulb' moment. Simply use a standard 8×40 dowel.

Worked a treat.

Thanks for your help Clive.

Len

[Clive FosterParticipant @clivefoster55965]

Hi Len

Nice job. I'll remember that dowel pin against a wedge trick.

It occurs to me that a spring pushing down on the wedge (or dowel!) might make for better feel when adjusting. A spring loaded wedge would push the two halves of the nut apart to give a basic lightly loaded zero backlash position. The adjuster screw merely follows down to lock that position whilst you are tightening up the fixings for the moving half of the nut. So no actual adjustment with the screw.

My Smart & Brown 1024 backlash adjustment is purely screw driven and was a bit tricky to set just so.

Clive

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