Will this DRO scale length work for my lathe ?

I am looking at buying a DRO for my gap bed 20X80 lathe . Its one of the magnetic scale type from DRO Pros .
They sell a 14" x 80" scale and a 16" x 110" scale length . Do you think 80" will be enough or will I need to upgrade to the 110" and trim it ? I was going to measure the travel on the lathe but will not be home to do that and I need to get it ordered . Hoping someone can chime in on this .
Also how do I deal with the removal gap ?

Thanks

I doubt that any 80" scale will measure 80". Cutting the scale can be a risk. Contact DRO Pros they should have measuring capacities readily available. That way you will make an informed choice.

Raymond

Safest and simplest to get the 110" one unless you have tape measure, lathe and brochure in front of you.

Hafta go lower than the gap piece if you mount to the main bed which may mean a fairly long bracket reaching down from the saddle. Alternative is to arrange a structure cantilevered out the backside far enough away to clear the swing in gap. No great weight or forces involved so a light structure will do but care will be needed to get it straight and aligned. Some scale suppliers can provide alloy extrusions of suitable size for this sort of thing. Will pay over the odds for the stuff but one stop shopping is is easier and you'd probably spend more than you'd save chasing around for best price. Will almost certainly need to fill the casting where the brackets bolt on. Decent bodyfiller worked for me in a similar application, I cheated forming flat mounting pads in place using a hefty slave assembly aligned and clamped into place before the filler went off. Although its not normal practice there is no inherent reason why the scale shouldn't go on the front of the bed with the reader head fixed to the saddle. Solves the long bracket problem but will need a bit more attention to protective shielding and a bit of creativity to stop the data cable getting in the way. Professional cable protection / control devices are very effective but spendy. Still good inspiration if your budget doesn't stretch tho'. Front is probably way to go if you have a taper turning unit out back.

If you want to do it right it depends to some degree on how the scale (and lathe!) dimensions are defined. Obviously you need the active part of the scale to be long enough for the reader head to safely cover more distance than you have travel on the machine. If you can get a couple of inches more head travel than you need. Its harder than you might think to get the longitudinal positioning right if you only have just enough travel. Getting a scale mounted properly is quite enough futzing about without making life harder by skimping on length. For the (glass scales) I've fitted in the past safe travel is around 6" less than the overall length and the book dimension was the overall length of the scale including the integrated mounts. During market research I found other scales quoted by travel length and by actual glass length sans mounts which got real confusing. Enough to have the order written, check filled out and envelope addressed before I realised I'd got it wrong!

HTH.

Clive

Most brands have around a couple inches more travel than the nominal size.
The only true proper way to do this is to measure the lathe, but reality is that the 80" scale should do it fine. I'm using a 40" scale on my 67" lathe, I never need to go tar far right, and I made a bracket do adjust the head if I ever do have to. But this was just cause I already had the scale and wasn't wasting over 1K on another one the proper length.

Since it has a gap you'll have to make sure you carefully locate the head bracket and scale so that nothing hangs out in the way when the gap is out... ideally anyway, and on some lathes is no issue anyhow.

You most definitely never want to be short on the X axis though.

RDL said:

I doubt that any 80" scale will measure 80". Cutting the scale can be a risk.

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Neither of those statements are correct regarding magnetic scales of the type sold by DRO Pros. The reader head doesn't care about the printed markings on the scale plastic, and will generally work over a range an inch (or three) in excess of the rated length. It's also perfectly safe to shorten magnetic scales with a hacksaw or cut-off wheel.

AG

AlphaGeek said:

Neither of those statements are correct regarding magnetic scales ... AG

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That is the problem with fitting scales especially on the Cross-slide. Their designated 80" scales are much longer than 80".
WARNING: Cutting your scale to “Machine Travel + 4 inches”

Most of the time it is a challenge to find the real length of those scales when attempting to model an installation in cramped quarters.
hd28vsb based his needs on the nominal capacity of his lathe which may induce error.


If a person follows the instructions they should successfully shorten the scales. It is a matter of due care. I shortened my cables because they were annoying and sloppy. Is it recommended? NO! Why?