Harrison M300 half nut adjustment

[richard markhamParticipant @richardmarkham58340]

Does anyone know if there is any adjustment in the halfnut on a Harrison M300?

Nothing shown in the rather thin manual…

I have noticed quite a lot of backlash when thread cutting. When I reverse the machine, it takes a while to take up the slack.

[richard markhamParticipant @richardmarkham58340]

[David George 1Participant @davidgeorge1]

Hi Richard what vintage is your M300 the ones I have worked on have no adjustment but if you have that much play it cannot last long. You can make one from phosphor bronze or they are available if not to vintage a lathe.

David

[richard markhamParticipant @richardmarkham58340]

Hi David,

Thanks for the info.

Not sure the year, I'd have to check, but probably 1980's. I bought it used in the 90's.

Surprising that theres adjustment on the cross-slide and not the saddle, but hey ho.

I read about making half nuts in delrin by molding the nut onto the leadscrew which you heat up!

I would assume that when thread cutting, the backlash should be low enough to allow you to run the tool back up while still engaged with the thread? Or is that expecting too much?

[David George 1Participant @davidgeorge1]

Hi again Richard look at the pitch of the leadscrew and look at the amount of backlash which you can measure if the backlash us more than half the pitch you should think if replacing the nut. On all leadscrew type lathes there is a slight backlash and you would have to wind out the cutting tool before reversing the cut. Only on a CNC type lathe with ballscrew leadscrew could you do that. I would think that for your lathe age you can still get the parts from Harrison I would ring the spares department and tell them the lathe serial No stamped on the bed and they can give you a quote.

David

[HopperParticipant @hopper]

I would assume that when thread cutting, the backlash should be low enough to allow you to run the tool back up while still engaged with the thread? Or is that expecting too much?

Oh goodness no. One should always withdraw the tool before returning the carriage . A certain amount of backlash in the gears is inevitable — in fact essential — and will damage your neophyte thread if the tool is not withdrawn.

[richard markhamParticipant @richardmarkham58340]

Posted by Hopper on 18/03/2019 09:45:48:

I would assume that when thread cutting, the backlash should be low enough to allow you to run the tool back up while still engaged with the thread? Or is that expecting too much?

Oh goodness no. One should always withdraw the tool before returning the carriage . A certain amount of backlash in the gears is inevitable — in fact essential — and will damage your neophyte thread if the tool is not withdrawn.

Thought so, but wasn't sure if a new nut/lead screw would mean it wasn't necessary.

[BazyleParticipant @bazyle]

Since the need to retract and return the topslide has been standard practice for ever there are some aids that have been developed. Some lathes have features build in from new to assist this (eg Holbrooke) see this previous thread on the forum.

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