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View Full Version : DRO on a lathe , questions



Lu47Dan
01-19-2009, 12:42 PM
Okay , I want to add a DRO to my lathe 14" X 30" . How do I figure out which scales I need for it ? I intend to do two axis's . I have been reading up on them but can't seem to find out which system would work the best .
I am looking for general and specific information on the various systems . Dan

danlb
01-19-2009, 01:48 PM
On a lathe that large you can use most of the designs.

The glass scale type are (arguably) the most accurate but bulky. I am in the process of adding a set to my mill. Got a 3 axis set from shars.com for the same price as a two axis set on ebay.

The ones based on the Chinese scales look like overgrown versions of the cheap digital calipers. They can be slimmer, but accuracy is reduced to .001 inch.

I saw some DROs for lathes that used three scales... X, Z and one for the
compound's topslide. The last one could be added to one othe first two.

The newall system uses ball bearings in a tube and a magnetic pickup. I have not discovered how accutrate they are.

The shooting star system uses a rack (toothed metal strip) with a meshing gear that spins an encoder. It can be accurate to .001 inch too. Swarf can be a concern, but most do fine with a simple aluminum cover.

My lathe is only a 7x10, so the room for mounting scales is limited. I'll figure out something. :)

Good luck with your search.

Dan

John Stevenson
01-19-2009, 01:53 PM
On a lathe you need the best you can get because of the diameter function,
Wind a thou on with a lathe and it takes two off, one from each side.

The cheap caliper type are useless as they are only good to 1 or 2 though which translates to 2 to 4 thou and to be honest you can get this from dials on a decent lathe.

.

Mcgyver
01-19-2009, 01:57 PM
The newall system uses ball bearings in a tube and a magnetic pickup. I have not discovered how accutrate they are.


pretty darn accurate, measured in millionths/meter per meter :eek:

http://www.newall.com/PDFs/download_linear_encoder_english_UK.pdf

most accurate and most durable, maybe also most expensive.

iirc the accuracy is not reliant on ball bearing accuracy, each scale is calibrated against some laser system at the factory. its all there though if you want to read more

http://www.newall.com/

pcarpenter
01-19-2009, 02:03 PM
Newall appears to have come out with a new DRO to compete with the < $800 mill DRO kits from others. This indeed claims to use a magnetic scale.

However, the original Spherosyn and Microsyn scales for use with the other line of readers uses steel balls in a stainless steel tube. My understanding is that it reads the changes in *capacitance* as the reader head crosses the balls. I would still think that this is much preferable than a magnetic design in an environment with lots of shards of magnetic material. However, I am not "dissing" the magenetic design because I know *nothing* about how they shield the scales.

Paul

Forrest Addy
01-19-2009, 02:32 PM
Most DRO's on the market are acurate and reliable to a point satisfactory to most home shop users. Lower end DRO's will be a bit less accurate and more bulky than the higher ens units. All this is generality. Most of the DRO's I've installed over the years are either no longer made (DRC, Ferrand) or expensive (Sony, Heidenheon).

I used a Sony on my lathe for the sole reason that it featured a magnetic encoded wire and a LDVT pickup. I had enough room in the cross slide nut channel in the carriage to tuck it inside. There is no scale scabbed on the side of the cross slide to get mashe against the tailstock. This was an expensive system laborious to install but worth it to me for my application.

There are many DRO systems out there. I would think is necessary to spend a month or more in spare time research to decide which is best for you even after collecting advice from people like us. I would advise against using low purchase proce as the first consideration.

danlb
01-19-2009, 02:52 PM
pretty darn accurate, measured in millionths/meter per meter :eek:




Thanks McGyver. I looked at a dozen (literally) PDFs from Newall's web site yesterday and did not stumble on that one. If I read it correctly, at 5 μm, it's on a par with the glass scales.



Dan