Gallery, Projects and General > Oooops!

It's the little things that catch you !

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awemawson:
Today's task was to make an adaptor to mount a large wire wheel brush on the spindle of my buffer. Simple turning and threading exercise. Bore of wire wheel brush 38 mm, diameter of shaft of buffer 19 mm so make a bush clampy screwy thing ! Started by turning down a piece of 60 mm bar to the 38 mm required. Then thread the end an arbitrary thread size for which I need to make a nut.

I decided on 2 mm pitch as I had an internal 2 mm threading insert that fits my boring bar, and had just bought various external threading inserts for the Traub including a 2 mm one. OK set the lathe for 2 mm pitch, and decide how to mount the external 2 mm insert, as I don't have the correct threading holder. Well looking at the insert and comparing with a TNMG insert the overall size is the same. Will it fit?

awemawson:
Well they seem to be the same overall shape and fit on the holder

awemawson:
So I fit the tool holder to the lathe, carfully adjust centre height, and try to check that there's clearance under the tip (a clue here !)

And off we go threading. total depth of cut for a 2.0 mm thread is 1.2269 mm, so slice by slice we produce what starts off as a nice thread form, but at about 1.1 mm deep oh heck why's that thread so manky? A very careful look at the holder shows it's rubbing the work below the insert despite my having checked earlier, and we are so close to finished depth it's too late to sort things out. Anyway decide to carry on having truncated the tip of the holder to produce an under diameter thread as after all I'm making the nut to suit.

awemawson:
Then it dawns on me - the DRO is set up for diameter measurements so is only showing HALF depth of cut - we've a further 1.2269 to go - loads of room to clean up the mess.

So one error, compensated by another error ends up with a workable solution

lordedmond:
don't those threading inserts have a carbide shim under them to set up the helix angle ?

the proper ones that I have do have a shim that need to be changed for different thread pitches

it improper ones from the far east nee chronos RDG do not have the shim

Stuart

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