Glass Optical or Magnetic scales

Hi,

Does anyone have any experience with glass scales v magnetic scales. I am looking to fit a DRO Kit onto my new mill once I have finally decided what mill to purchase ,,,,,,see other post in Help....

In another life where I had money and a fully equipped workshop with Bridgeport Knee mill I never had any probs with Glass scales nor spindle distance to table......So should I only be considering magnetic scales or are the Glass Optical scales ok

Comments welcome

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I not so long ago fitted Easson DRO's and magnetic scales to my lathe and milling machines.

The main reason I chose the magnetic over the glass scales was down to them having a smaller physical profile. i.e. I did not lose very much movement on my machines. By the time one has put the protective covers onto glass scales even the slim ones can restrict movement a couple of inches. On my small machines I could not afford really to do this.

This loss is dependent upon the layout of the machine you have. On some milling machines. (e.g. SX3) you would not lose any movement even with full size scales if you positioned them correctly.

Magnetic scales are a sinch to fit. They can also be cut easily to any desired length and are by default already coolant and swarf proof. But cost more to buy. They do however become more cost effective the longer they get as the main cost is the head which is the same irrespective of length.

I know little about glass scales other than they do their job and have millions of happy punters worldwide. If I owned machines with more room and a different layout to them I would probably have gone down the glass scale route.

Regards, Nick

I don't have any DRO's on my machines at home but the ones on all the machines where I used to work were all magnetic. Bullet proof build and as said very compact.

Nick, worthy reply and much apreciated

I have glass scales on my Marlow mill and there is no reduction of travel on any of the axis, went with glass as they were part of the package I purchased at the time some 6 odd years ago and no problems. Even a house move did not cause any problems. Have no idea if magnetic would have been a better option but as far as size goes I think there is a slim glass scale that is on par with the magnetic ones.

Bob

There is standard, slim and micro. If you mean a micro glass scale the price would make you weep.

Even then they are not as small a profile when you have put a protective cover on one.

Edit :- Just checked. a micro is 16mm then plus whatever the cover is. A magnetic is 10mm

Nick

Edited By Nick_G on 29/05/2015 22:40:06

Hi Nick,

Fitted Eason glass scales to my SX3 mill and have not had any problems. 1µm accuracy scales were on sale, cheaper than the normal price for 5µm and cheaper than magnetic scales.

Previously had a set of cheap scales which failed.

Paul.

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Hi Paul,

The SX3 has loads of room for scales. It was top of my short list to buy before I purchased what I did.

Nick

Re BW Electronics - I have used these for the last 15 years and as John said, very easy to fit and adaptable. With the right 'clip' , you can unclip from one axis or machine to another. With simple pulleys, you can fit them such that the 'tape' runs at an angle to the readout, or fit to a rotary table etc. My comments GOOD.
BobH

I have fitted both glass and magnetic scales on different axes of two machines and both types have performed perfectly. I have used two 1 micron resolution magnetic scales so high resolution is available.

The slim physical size of the magnetic scales allowed me to fit one under the cross slide of a Myford Speed 10 lathe and the rock steady 1 micron resolution is a joy to use (photos of this in my album )

I previously had a set up with Chinese scales of the type used in digital callipers and they were a nightmare due to poor stability.

So both types are very good and it really comes down to cost and available space.

Doug

Whilst the pull wire sensors from BW electronics are excellent in their place, their resolution is only 2 thou, compared to 0.2 thou of glass and magnetic scales

I think like anything else you get what you pay, if you can only afford glass scales treat them carefully and they'll do the job. I guess there's a reason industrial machines have Magnetic scales though. I can't justify the cost of DRO's on my machines but if I really needed them I'd pay a little extra and get Magnetic scales. One thing I'd hate to lose though is the stops on my mill so fitting could be a challenge for me on the VMC.

.

Well I would imagine that would be temperature dependent on it's initial calibration.

As for cost. Well they can very cheaply cram over 2.5 billion transistors onto a tiny bit of silicon for a modest i7 processor. So I would imagine in comparison a glass scale would be the equivalent of measuring 100 yards by taking 100 strides.

Nick

Have used both for many years, my take use the glass where appropriate ie on lathe the X axis, mill on Y axis possibly vertical as well (Zo)

Magnetic 1 micron for anything else, especially lathe on cross slide. 5 micron will show up on repeatability as in threading, I get errors up to 0.04mm not good when doing .75mm pitch threads on high class products with no play.

Magnetic on mine are 25 x 7.29mm thick rather than C type 40mm thick. Further to that no masses of overhang needing circa 2" plus travel at either end plus having to go next size up. Imagine a tail stock with 4" travel, available size may be 6" plus 2x2" both ends, means unit would be 10" long.

Glass scales will need stripping down and cleaning at inopportune times once per year. Inside the scale its just a 45 degree glass inserted in to an extrusion, nothing more. Just a wipe with a rag.

Hi Frances,

I would not recommend the cheap DRO's (digital caliper type) as they are prone to failure. I replaced them 3 times on my mill. A total waste of money ! Save it to buy a set of good scales and you will not be sorry. The good DRO read-outs have many extra features, allowing you to easily find the centre between 2 points, drill hole PCD's, machine a radius (vertically and horizontally without a rotary table), store the position of multiple positions, and more. The best addition to my mill that I have bought, Also do a search for DRO's on this site. Lots of other posts.

Paul.

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... nothing more, except for the thousands of lines etched upon it.

MichaelG.

Frances, I recently fitted slimline magnetic scales to my X1L as an interim measure until I upgrade the mill. I can then transfer the X-axis scale on a larger machine. Fitting did require a fair bit on redesign of the mounting brackets to fit into the limited space on this small machine, and some loss of Y-axis travel. I have used scales and display from ems-international in Leicester. For the Z-axis I have the Arc digital readout bar. Overall its a great improvement on using the hand wheel scales - but cost more than the mill!

Thanks for the reference, 'Toolgrinding'

... For the convenience of others; here is a link.

They seem to have an excellent range of products !!

MichaelG.