Tool post mods

[David NobleParticipant @davidnoble71990]

This is the tool post on the Mellor lathe I am restoring. The four corners have been opened out to 3/8” from 5/16” I can’t see it being like that from new, so I wondered why it might have been modified.

[David NobleParticipant @davidnoble71990]

[Kiwi BlokeParticipant @kiwibloke62605]

Perhaps the tool clamping screw ends got mushroomed, then some gorilla wound them out, destroying the threads in the toolpost.

[Clive FosterParticipant @clivefoster55965]

Obvious answer is damaged screws.

Toolpost screw heads tend to mushroom under pressure against the the tool. If left too long before pulling out and trimming back down to just under core diameter any attempt to remove them is likely to pull the threads out of the toolpost. Mr Careful will notice and cut the screw before disaster. Mr Not Careful just gets a bigger spanner!

If one or more thread has been so damaged and needs tapping out to next size up it makes sense to do all four corners so only one spanner is needed. I guess the perpetuator didn't use the centre screws or only had four 3/8" ones. When I needed some square head toolpost screws many years ago I had a right old time finding some.

I have a similar one in the might be handy box with just the three on one side operated on and half the rest immobile due to mushrooming.

Clive

(Must type faster)

 

Edited By Clive Foster on 19/01/2023 10:12:55

[HopperParticipant @hopper]

So, when making or fitting your new toolpost screws, it pays to turn the end down to below the root diameter of the thread for a few millimetres and then dome the very end to reduce chances of mushrooming the thread on the end. Readymade dogpoint screws may do the job too if you can get them.

Edited By Hopper on 19/01/2023 10:44:26

[David NobleParticipant @davidnoble71990]

Of course, damaged screws. Simple( when it's pointed out )

Thank you, David

[HopperParticipant @hopper]

Or it could have been the screws overtightened and stripped the threads. Check the base of your toolpost for flatness. The one on my much-abused ML7 was bent like a banana from the previous owners overtightening the toolpost screws repeatedly. They never managed to strip the threads though.

[egaParticipant @ega]

Posted by Hopper on 19/01/2023 10:19:21:

So, when making or fitting your new toolpost screws, it pays to turn the end down to below the root diameter of the thread for a few millimetres and then dome the very end to reduce chances of mushrooming the thread on the end. Readymade dogpoint screws may do the job too if you can get them.

Edited By Hopper on 19/01/2023 10:44:26

Sound advice (and my own practice).

Another suggestion I have seen is to drill the ends for hard steel balls.

And at the other end you can mill squares on hex recess screws so that either a square or hex driver can be used.

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