Saturday, May 23, 2015

ER11 drag engraver

This post is a little off topic so I'm sorry about that. It will be relevant to somebody I suppose.
spring loaded ER11 diamond drag engraver
Above is a spring loaded diamond drag engraver. It's 3mm with a 120 degree angle tip. The issue with it is it needs to be spring loaded to allow for uneven surfaces, but there is very little space to build a mechanism inside an ER11 size collet. The commercial ones work externally to the collet. My thinking was if it is in the collet it would be more ridged and more accurate.
CNC spring loaded diamond engraver
Drag engraver apart
So here it is taken apart. An ER11 collet with a 7mm diameter.
A hard brass pipe(Albion Alloys, metric K +S!)
Polished 6mm steel shaft from an inkjet printer with a spring, I'm not sure where that came from!
I chopped the steel shaft with a hacksaw and stuck it in the lathe. I wrapped the shaft in masking tape to protect it from the jaws of the lathe, then drilled the centre to receive the diamond tip bit and trimmed the other end to take the spring. The spring is squeezed on. This is important for a couple of reasons. It ends up >6mm diameter therefor holding the shaft into the brass tube and so the collet.
That's morealess it. The extra lug at the end is just because I cut the main body of the shaft too short. The grey crap is PTFE/graphite dry lube.
To use...(engineers close your ears), I put it onto the spindle as usual then tighten the nut until the collet pinches the brass tube enough to stop the shaft moving, then loosen the nut a smidge. It should return when pushed in. So I'm using the collet slightly loose...

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