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sinbad
08-15-2003, 07:29 PM
What are the pros & cons of glass scale vs linear encoders. (Acu-rite vs Newall). I have an older Anilam 2 axis which has worked perfectly for years but I am in process of changing to a (new to me) mill without DRO. I need help understanding the differences. Price is very close so that eliminates that selection method. I want 3 axis on the (new to me) Mill. Thank you for the help.

wierdscience
08-15-2003, 08:46 PM
If you are talking about the Newall scales they are presicion steel balls in a stainless steel tube,damn near indestructable and no nothing will ever find its way inside of one.
Glass scales unless they have changed break easier than you would think,I don't know what everybody else thinks,but on this one my money would buy the Newall(no affiliation though)
I don't know just how much you use a dro,but have you considered Mitatoyo?there capacitance units are pretty good,between glass and hall units,but cheaper.

[This message has been edited by wierdscience (edited 08-15-2003).]

SGW
08-16-2003, 08:46 AM
Glass scales cane be made more accurately, I think. If the Newall has enough precision for your needs, I'd be tempted. One thing to watch out for: the overall length of the Newall Spherosyn scales is +10" over the measuring length, which can be a problem. On my milling machine, I've got a 30" table with 22" travel, so Newall's 24" scale would hang off the ends of the table by 2". I think most "big" mills wouldn't have that problem, but it's something to check.

Personally, I'd go with Acu-Rite, as I think their quality and support is outstanding. If installed properly, the alleged fragileness of the glass scales shouldn't be an issue. Untold numbers of them are in use with complete satisfaction. But the indestructible-ness of the Newall sure is appealing, too.

NSDesign
08-16-2003, 09:31 AM
Sinbad,

I have no experience with the newall products, but have heard good things. However, if you are willing to excercise care in mounting, the glass scales are generally more accurate. I work as a controls (electrical) engineer for a major machine tool manufacturer, and we used glass scales for all applications.

Please be aware that "magnascale" type units can be destroyed by strong magnetic fields - say like an indicator base.

Good luck,

Alan

sinbad
08-16-2003, 09:37 AM
Thanks for the info. Table length should not be a problem, However the X axis scale will need to be mounted on front of table because of horizontal spindle. Would this make Newell a better choice?

L Webb
08-16-2003, 01:04 PM
I have the Newall 2-axis C80 DRO on my Frejoth vertical mill. I bought it mainly for it's bolt hole pattern function and ease of use.
I am very happy with it. All the fixtures I have made with it have come out very accurate.
There are many opinions regarding the scales and accuracy. They seem to work just fine for what I am doing. I leave the resolution on .0005 to reduce the amount of time spent trying to nail the number.

I bought the unit about 15 months ago 2 weeks after it was introduced. I like it.

Les

SGW
08-16-2003, 02:23 PM
Acu-Rite sells what they call "backup spars," which are glorified aluminum angle with a special profile to hold the scale. The top leg of the angle projects out over the scale to protect it. They're required for Acu-Rite scales over 65" long, optional for others. Might be a good investment to protect against damage. The Acu-Rite web site has pictures of the setup.

A cheaper solution would be to get some 6063 1/4" x 1 1/2" x 1 1/2" aluminum angle and use that. (Get 6063 angle, not 6061; 6063 has parallel legs, 6061 has tapered legs.) You wouldn't have the supporting ridge under the scale that the "real" backup spars provide, but you'd have the protection over the top of the scales.


[This message has been edited by SGW (edited 08-16-2003).]