DRO questions

Suzuki4evr

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I can't afford expensive DRO'S......so are these ok and wich scales are preferable, the normal size or slimline?
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Normal vs. slim is first a matter of glass vs. magnetic. Glass scales (like those pictured) are great at what they do, and offer good resolution for the price. The down side is that they can get dirty from all of the flying chips, oil, and coolant at your machine. Slim scales are now available in resolutions comparable to glass scales, but in a smaller, easier to mount package that is more resistant to chips and crud. Some installs do not allow much room to fit scales, so the extra space afforded by magnetic scales is a boon. Without a big cost or performance difference, today it makes the most sense to go with slim magnetic scales. The head units offer varying functionality and their capabilities are self-explanatory. There are a few common layouts based on whoever originally produced that style of head, i.e. Sony vs. Mitsutoyo. I prefer the Sony style (as a TI user) but people who like HP RPN calculators like Mitsutoyo better (get it?). It's preference at that point, because all heads will give you abs/incr, tool offsets, and bolt patterns, etc. so shop around for what you like. For a knee mill, it's nice to know what your Z axis options are, for instance.
 
I'd agree with the magnetic scales - I had glass opticals on my lathe but replaced them as after a year or so they started getting a little unreliable. Sure, cleaning them with alcohol bought them some new life but I found myself not trusting them as I got caught out a few times costing me a lot of wasted time and material.

Not sure if there's much difference in the displays although when looking for a DRO system for my Bridgeport I did notice some didn't have a huge SDM memory. If you're not familiar with DRO's it stands for Sub Datum Memory - basically you can programme a number of coordinates then when it comes to machining you just travel to 0.000 on the display and make your cut. I use it a lot on the lathe for batch runs of parts. You make the first part and "programme" your DRO as you go then just smash out the rest without having to pay attention to dimensions. On the mill it can be handy for plugging in the coordinates for holes and other features. You'll probably never need as many as 200 but some only offer 20 or so and I think that would limit you a little so in my opinion it's worth going for one with 200 SDM memory, assuming there is negligible cost difference.
 
Glass scales come in both standard and slim line versions but the difference between the two isn't that great. Magnetic scales are considerable smaller than either of the glass scale sizes.
 
I have had a three axis glass scale DRO on my mill for fifteen years and have yet to have it malfunction. IMO, the secret is providing a suitable scale guard. The x and y scale guards are mounted so that any oil, coolant, or chips would have to reverse direction to reach the scale seals. The z axis is more vulnerable but still no problems.
 
I am just asking. How much does one use the z-axis scale? I am contemplating if I must get a 3-axis or 2-axis DRO.
 
With budget in mind go with glass scales if you don't have mounting constraint issues. Glass slimline cost a bit more than standard & then of course magnetic costs the most. Good thing about mag scales is you can cut them if you need a size not offered in glass.

I too have not had any issues with my glass scales. The Z scale on my lathe is constantly getting covered with oil from the ways but it's the cover over the scale that is getting covered with oil. I don't run flood coolant but I do spray on coolant with a spray bottle.

The only slim scale I have is for my cross slide on the lathe. Everything else are just the normal size. Not that it may matter much but the scales on my lathe are Sino, 10 yrs no issues. Scales on my mill are Easson, 8 yrs no issues & all still very accurate. If you aren't familiar with those brands, yes they are China.

I do have a Z axis scale on my mill but it rarely gets used. If you can, get a 3 axis mount the 3rd/Z axis to the quill, still Z. I Never bothered to cause I put a DRO scale on my quill before I got the 3 axis DRO.
 
With BP style mills, some folks run X,Y on the head unit and a smaller battery-powered unit for the quill. This is part because it's not a big deal, but mostly (IMHO) has to do with how bulky a scale mount can be on the BP quill. I reckon this is the most popular setup for home shops.

I just bought a Ditron 4-axis setup with DC10 scales, but haven't installed it yet. That's X,Y, knee and quill. I can sum the knee and quill for a unified Z axis.
 
What type of mill will the DRO be going on?

For my mill, it has a separate (factory) Digital Scale on the Quill. In most cases it's all I need. But the occasions when I've needed to raise or lower the head because quill travel was too short, I was glad I had a Z axis on my DRO. Also on my Medium sized bench mill, I find keeping the quill choked up gives me better accuracy when taking deeper cuts, so in those cases I again use the Z axis DRO and lower head over extending the quill.
 
If you can afford the Z-axis scale, Get it! You can cheat a little by adapting a cheap digital caliper on the spindle, but being able to accurately control the table height is very convenient.

Randy
 
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