DRO system

Hi guy's.

thought I'd got it sorted....BUT....

just ready to order a 3 axis DRO kit for my J head Bridgeport, then they tell me the scales are glass......thought it was Ally.....

major problem ?

help please...

thanks Frank

The actual bit that the head reads is glass but they are encased in an aluminium extrusion which may be whats confusing you.

Who are you ordering them from?

Hi Frank,
Is this thread a continuation of another thread ? If not what was it that you thought you had sorted ? What scales did you think were Ally ? And who does "they" refer to ?

Les.

There are a couple of pics showing the internal construction in one of my albums. The glass scale is laser etched with deadly accuracy and the patterns are picked up by the travelling bogey thing, generating a quadrature output. There's also an "index" mark which is a sort of absolute origin point that allows you a repeatable datum on each scale.

Here are also some pics of my BP clone DRO installation. I actually fitted Z scales to both the quill and the knee but I have almost never used the knee scale. I'd strongly recommend you go for a quill scale - after all you don't tend to feed drills and cutters using the knee crank handle.

Really pleased with the DRO system - probably the best improvement I've made to date in the workshop. It transforms the speed, repeatability and accuracy of your work.

Don't think I've seen any scales in aluminium. The coeff of thermal expansion is quite a bit worse for aluminium than for glass, so not obvious to me what benefit would result.

Murray

Hi Murray,

Just out of curiosity did that scale still work when you put it back together ?

I have often wondered just how fragile they are and what is likely to damage them when installing ?

Ian

Ian

Yes, it was fine. I made sure the section I removed didn't contain the index mark(!), scored the glass with a new carbide insert and snapped it over a cloth covered edge. The Chinese operative who assembled it had thoughtfully left his/her finger prints all over it and I cleaned these off before reassembling it. The glass is held into the extruded channel by several soft plastic slugs, so refitting it was simple.

The trickiest part was actually drilling the 4 holes on the end of the shortened housing that hold the end cap in place. The bogey is guided by something like 5 or 7 miniature ball bearings, biased against the glass by a spring. You can just about make that out in one of the photos.

Unless you are dismantling a full length scale (60-80cm), it's pretty low risk. Mine started out something like 30 cm long and I removed a couple of inches so it was an exact fit for the BP head. It's now sufficiently compact that I will be able to leave it in place when I install the CNC conversion parts, although arguably it would become redundant at that point.

Unless I ever try boring a cylinder block, I'll probably (almost) never use the knee scale, personally. Having said that, I may be fitting a spare power feed to the Z-axis knee at some point in which case you never know, I may make more use of it. Most of my precision (=DRO) work is within the 5" range of the quill.

Murray