Heidenhain DRO advice

[kong]

HI guys, I am planning on buying this lathe in the next couple of weeks, and would like to fit a DRO to it. I've been looking at the chinese import jobs, using the available kit to get the "big screen" DRO, but then I found this Heidenhain DRO kit on ebay. The scale lengths on this one are 270mm 220mm and 120mm, and the lathe has 350mm between centres, and 105mm crossslide travel. Now that's not a lot of info to go on, but what do you reckon? Do I take a chance and buy the Heidenhain and hope I can get it to fit, or go the chinese route, which I know can be cut to the required lengths? I don't know a great deal about DRO's so any advice would be great.

[Swede]

Kong, just eyeballing the H. DRO, it appears to use high-accuracy glass scales, but the scale format appears to be on the "large" size. What I mean by this is that manufacturers of these types of scales have gone a long way towards standardizing scale sizes, from miniature on up, and these appear "large" to me.

My guess is that this particular set of scales would be difficult to mount on that lathe because of their bulk. Miniature and sub-mini glass scales would be ideal if you can find some. Remember that they'd need to be swarf and coolant guarded with shields, which further adds to the bulk.

DRO's generally come in two formats, optical/glass (like these) and capacitative. Glass scales are more accurate, more delicate, and more challenging to mount than capacitative. They are also more expensive.

Capacitative scales (like an LCD caliper) are very reliable, cheap, and easy to mount. They fall short only in the accuracy department, but on a hobby lathe like the one you are considering, they'd be fine. I'd pursue a capacitative scale set for that lathe personally.

Most capacitative systems have an accuracy of +/- 0.001", but that is over the entire length, usually over a short run they are better. Don't confuse accuracy with resolution, just because a scale reads to 0.0005" doesn't mean that the reading is correct.

For lathe work, many guys spring extra cash on a highly accurate X (cross-slide) scale, and live with a cheaper Z axis (longitudinal)scale. Ideally, you'd want a DRO box with a diameter function, which displays the actual diameter of the workpiece as you plunge, rather than the distance moved by the scale.

Also, I'd ignore the top-slide and go with two axes only, a top-slide axis simply isn't used much and isn't worth the money.

All this is opinion, FWIW! I'm open to corrections.

Swede

[kong]

That's sound advice swede, thanks! I will leave those scales to the experts, and go with the chinese route. If anyone is interested, the DRO box I am looking at for the chinese scales is this one. There are a lot of functions in the box, and the guy is regularly adding to it's functionality.

[Al_The_Man]

Kong, being in the UK, It might be better to try and pick up a used Newell DRO http://www.newall.com/Newall_US/6684.cfm (I believe they are made in the UK?).
They have a few superior qualities, inductive pick-up, no glass scale, no head alignment. You pay a bit more for them new, but they seem to outlast most of the others.
Al

[Swede]

Those Newall scales are an interesting technology. What is the accuracy? I wonder if they are prone to interference from masses of iron in proximity.