DRO on lathe cross slide accuracy/resolution

Rubbish.!

The Spitfire I had used rubber bands and 1/4" wooden dowel to hold it's wings on with.

Nick

I already have a DRO on my mill and there the advantage is much more obvious, no more counting handwheel turns and functions like divide by 2 are invaluable. What I am looking for on the lathe is primarily to increase productivity rather than accuracy. I am thinking that it will help on the carriage more than the cross slide. When i did my apprenticeship some 35 years ago we had no DROs then... I am relearning my lathe skills after a 30+year break, productivity is improving (and scrap rates are decreasing), but my thoughts are a DRO will really help.

a couple of things..

the guy martin "bolt" was a between center cylindrical ground pin.

it may have been that close a fit.

the other thing.. adding a dro will make your life easier.

more fun even.

it will even help controlling your TOOLPATH.

.it depending , on wear elsewhere, will not guarantee your parts dimentions..

that said.. more resolution is always nice..but may just serve to make you more unhappy about the machine its attached to..

I would not look for better than tenth of the hand scales....(if say 5 thou scale then 0.5 thou dro)

..unless un upgrade is in the offing......

Edited By jason udall on 30/03/2015 22:17:58

I just fitted a 6' igage on my cross slide. I have a grizzly 14" x 40". I am please with the way it works, But as with any DRO you still have to know how to use a mic Here in Canada it cost me $40.00 well worth it if only to use as a reference with the dial on the machine.

Although the Sinos will read out to five places behind the point when set to imperial, they actually jump in 0.00019 or 0.00020 steps so that is where the 0.0002" resolution comes from.

In Metric they read in 0.005mm steaps

Its worth looking for a readout that combines the carrage and topslide readouts into one line of display as you may find it hard to set that last 2/10ths cut with the carrage handwheel, the topslide being easier to put on a small cut with

The

.

Many years ago when DRO's were mega expensive and very basic one of my customers had machines fitted with Heidenhain DRO's that read to 1/2 a thou. Last digit went 0, 0.5 0, 0.5 etc

When they upgraded to BS 1066 or whatever it was before BS9000 they had to fit all new DRO's to read in tenths

0.0001, 0.0002 etc and I bought a couple of the older two axis ones off them to fit on my round column mill drill, remember paying £400 for a 2 axis second hand setup in those days.

Next time I went into their works ALL the machines had masking tape covering the last digit because the operators were fed up of the dancing numbers. God knows what that operation cost for no outcome.

Edited By John Stevenson on 31/03/2015 09:28:39

I fitted 4 DROs to my Chester machine centre/lathe about 4 years ago. The milling head and tailstock DROs are read directly no problem, however I had to fit two remote head LCD readouts for the lathe saddle.

The main problem I had was reliability of the cables at the DROs, which are non standard rubber 4 contact affairs. In desperation I dismantled one unit and with some difficulty soldered in a miniature USB socket which has been ok so far.

I still found the DROs & head readout units themselves to be unreliable - which is hopeless if undertaking co-ordinate drilling. Replacing the DRO LR44 batteries with 100uf capacitors fixed part of the jitter problem.

Next one of the head LCD readouts switches fell apart - impossible to find a replacement, so I bit the bullet and decided to design and build my own and used nice bright 0.7 " LEDs (Microprocessor based systems is another hobby).

I had always thought the half thou last digit a bit daft so I wrote the software to display in .0001" increments......oh dear, the digits do leap about. I put up with them last year but have changed to half thou to try this year. Hopefully I will now return to producing scrap metal instead of programming bugs!

I only use direct cheapo DROs but I do have a tip for anyone who has live wire weak point issues because my e-cig charger gets heavily used and the wires will soon fail if they are not properly supported

I whipped all the weak points with thread, like a fishing rod whipping, then squirted cheap superglue onto those whippings to strengthen them

Instead of a charger lasting for a few weeks my latest one has been going for months

Just as a FYI, it is about a 30% premium on the scale price to go from 5um to 1um

[Just as a FYI, it is about a 30% premium on the scale price to go from 5um to 1um]

Stuart, that ain't necessarily so. Check out **LINK** I bought a system from this firm at 1um

for my lathe, and one for my miller from M-dro at 5um at virtually the same price!

Would not do with out mine on mini lathe my accuracy as Improved 100 percent no more guessing.

It is not that much more money to have the more accurate scale on the X + Z axis, you can choose if it reads in 2 or 3 decimal places as well, apart from radius or diameter.

Digital readouts have lots of conveniences. Some have the ability to set tool numbers and zero them , so interchanging tools is very easy without having to re zero or reset the tools.

Neil

It is worth remembering that setting , say, 1 thou' on the slide does not mean that the machine will cut 1 thou'.

The capacitative scales (regardless of resolution) work to a code that uses 20,480 positions per inch.

So you can exactly denote any power-of two fraction from 1/1 down to 1/2048.

1 thou = 20.48 units.

0.1 thou = 2.048units

0.01mm = 8.063 units.

0.005mm = 4.031 units

Note these aren't errors and that the rounding required (if done properly) only introduces errors far smaller than the resolution of the units.

The code allows for more sensitive scales than currently made, and you can make a stand alone readout that works to 0.0001" but the jitter will make it unusable like in John's example. My homebrew displays round to the nearest 0.0005".

If the errors in the output follow a genuinely gaussian random distribution (which can't be guaranteed) you could use oversampling to increase the resolution to spuriously high levels.

I don't know if the lower resolution readouts still output every step of the 20480 per inch.

Neil

I feel a metrinch moment coming on...

Hi Neil,
While I suspect all the scales read the data from the scale at 20480 CPI resolution only the original Chinese scales and caliper output it in that format to the data connector. The BIN 6 scales output at 2540 CPI when the display is set to metric and 2000 CPI when the display is set to imperial. The 7 BCD scales output at 2540 when set to metric. I have not made a note of the CPI value when set to imperial. The igaging scales outut data at 2560 CPI. I think there will be some rounding errors generated within the scales for BIN 6 and 7 BCD type scales

Les.

Neil, does this mean the Igaging scales are Metrinch compliant?

.

Neil,

Given the SI definitions of the metre and the second; it's quite likely that the EU will [next April?] ban the use of both decimal and binary, as both systems are incompatible with Cæsium transitions.

.

As you are contemplating tight tolerance scales I am 'presuming' that you are not on a tight budget.

If that is in fact the case I would consider spending those extra coins purchasing magnetic scales.

1) They are a doddle to fit.

2) They are already coolant and swarf proof.

3) They are of a smaller profile. This matters quite a bit on a small lathe so that the amount of capacity reduction is minimised. If a normal (even slim) is fitted by the time a protective cover has been fitted a couple of inches movement / capacity may be lost. This may not be an issue on a large lathe but can easily become a problem on smaller machines that are associated with most model engineers.

Nick

I did look at magnetic, but based on machine DRO's specs, they quote an accuracy of +/ 0.015 mm "typical after installation" even on the 1um resolution, which doesn't compare very favourably with the +/- 0.005mm quoted for optical. The slim optical scale with cover would mean losing about an inch with the tailstock being further way from the chuck.