Gallery, Projects and General > Oooops!
Myford M type safety warning (Dewhurst switch)
lordedmond:
Andrew
It's the screwed on chuck that can get you in trouble. That's why I have a G Meek dog clutch that reverses the lead screw whilst the spindle continues forwards without loosing sync
Stuart
Meldonmech:
I have always used the slow screw cutting speed when reversing to wind back to the thread start position, and have never had any chuck unwinding issues. Some Myford owners have added a grub screw in the back plate to prevent the chuck unwinding in reverse. This of course can happen when using faster spindle speeds.
Cheers David
NormanV:
I had a chuck unscrew and bounce all over the floor from my Littlejohn lathe when using a Dewhurst switch. Why do they fit them on lathes with screw mount?
NormanV:
I am sick and tired of seeing my name attached to a really silly post, I thought that it might be better to tell you a story of a really dangerous situation that I got myself into. I used to be a director of a small packaging company. So small that I used to have to fix the machines that broke down. I was quite good at it, until......
We had a platen press, I don't know how to explain it except that you should imagine a one ton lump moving up and down driven by a crank. One day it seized up, we looked closely at it and decided to remove a key that fixed one of the drive gears to a shaft. As the key came free from the shaft it released the whole mechanism and the one ton platen rolled gently down to its lowest position. In doing so the gears rotated at an enormous speed, inwards, if my finger had been touching that gear it would have sucked me in. I still have shivers from the memory.
Eugene:
Norman,
I'm sorry you see my post as "silly". I don't see any warning of a potentially hazardous situation in that light at all, even from an admitted beginner.
As a follow up, the NVR switch from Axminster blew after about thirty operations, as did it's replacement, so I'm assuming that there is something amiss in the current feed. I have a Triton table saw on the same circuit that sometimes blows it's NVR switches too. I'd put that down to bad luck, but now these ones on the lathe have popped there must be something nasty in the wood(en) shed. I have an NVR reversing switch to hand, but I'm not going to fit it until some further work on the voltage / wiring / motor front. I'll have to get a professional for that, it's not my area of competence.
Eug
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