Mill table DROs and way covers

March 2015

Counting turns of a handwheel is error-prone, inefficient and… dull. Wanting more spark in my life I decided to add DROs to the mill table.

I also installed some way covers at the same time as the scales – to prevent chips from collecting on the ways and also to protect the scales.

I have been using the DRO almost daily for a year and a half, and wonder how I ever managed without them.

Capacitive digital scales (abandonded)

I originally planned to use cheap(er) capacitive scales like the ones below, and build an Arduino-based display head. However, after MUCH sodding about and cursing I abandonded the capacitive scale approach and bought a DRO kit off eBay. For the gory detail of my attempts to build an Arduino-based reader see this page.

I did have a much more detailed write-up of installing the capacitive scales, however I had to switch to a DRO kit off eBay so this is a much shorter write-up.

ScalesDumped in the ‘too hard’ basket – I could not get a consistent reading from the heads.

DRO kit off eBay

I bought my kit from seller motor-mall. It arrived from China in just a week. The kit contained the multi-function display, and three linear scales.

There are many sellers offering the same or similar kits. Mine is made by ShenZhen HengXingXing Precision Instrument Co Ltd, and is the GCS series (GCS-900-3DB). Total cost in early 2016 was £250.

The display head comes with a number of functions. However, I only ever use the “1/2” function. I would probably use more but the English in the user manual is indecipherable. “Align the Goddess with the making part.” is a typical example. (I did my best with Mrs Naut as the Goddess but found that she is not adjustable.)

I paid a little extra and went for the version with 0.001mm resolution (instead of the standard 0.01mm). Not that I think I can machine to this level of accuracy, but to be able to detect slight changes – in the same way that the needle on an analogue dial may move around inside the dial’s smallest divisions. I am glad I went for the higher-resolution version, as I can now know when the gibs are loose, and get early warning of when things are not going to plan.

The head came with a variety of bracketry which made mounting it a doddle.

The only gripe I have is that the Y-axis in the head stopped working after about a month. I just disconnected the lead to the linear scale, and plugged it into the X-axis port on the back of the head. I did not follow this up with the seller…

The scales had solid mounting holes, and featured a yellow strip that neatly opened and closed around the link to the reading head. The heads have a mm or so of play in them perpendicular to travel, which made installing them easy.

X-axis

I decided to place the X-axis scales behind the table, out of the way of the gib adjusting screws and X-axis stops.

I installed the scale upside down – with the reading head at the bottom. The long part of the scale was bolted to the T-slot table, using a couple of spacers to match the distance of the reading head from the lower part of the table.

While I was at it I also installed way covers, made out of the plastic concertina part of an expanding file. I also added a piece of thin aluminium angle to shroud the scale from the top.

I took the top two parts of the table off and laid them upside-down on a sheet of plate glass, and then aligned and punched holes in both parts of the table to mount the scales. Behind the reading head and also the long part of the scale are spacers which give the necessary offset to each part of the scale.

X-axis scales installed, and after a year or so of use. You can see the thin aluminium shroud at the top, and the spacers pulling the scale out from the T-slot table. The plastic way covers work remarkably well, although after extensive use they could probably do with replacement… You can also see the Y-axis scale below.

Y-axis scales

I installed the y_axis scales on the right side of the table, away from the gib and locking screws. I made up a two-part bracket: one L-shaped part screwed to the middle section of the table, the other L-shaped partscrewed to the reading head. This two-part design made it easy to align everything and mark out the screw holes.

As I installed the scale right-way-up (with the reading head at the top), I felt I needed more protection for the scales than the yellow plastic strip that opens and closes around the head as it travels up and down the scale. I ended up milling a slot into a piece of aluminium angle, and using furry draught excluding strips which fill the slot when it is not occupied by the bracket connected to the reading head.

This furry stuff is great – I can see lots of uses for it. I got mine from The Hairy Worm, a family business who manufacture the stuff.

Top view showing the two-part bracket, the aluminium top cover with its milled slot. The bits of fur poking through the slot are the draught excluder. The arrangement works very well – only a few bits of swarf have gotten through the fur and they were easily dealt with by the yellow plastic strips on the scales.

Bottom view showing bracket connection to the reading head. The fur came with a self-adhesive strip: I stuck one side to the aluminium cover (seen in previous pic), and the other to the adjustable stub of aluminium angle that you can see in the photo above.

The front way covers: apologies for the quality of the pic, however you should be able to see how it all holds together. I used aluminium strips screwed to the center section of the table (on the right in the pic), with the other side screwed to the top of the leadscrew mounting block. The dial is now difficult (but not impossible) to read, however I have not found this to be an issue, as I now have DROs!

DROs in use

I have used this set-up for a year and a half, including some very messy jobs… Apart from the problem with the Y-axis on the display packing up, the DROs have proved more useful and robust than I could ever have hoped. In fact, I was so pleased I went a little DRO-mad and also added them to my lathe.

One thought on “Mill table DROs and way covers

  1. Robert

    Wow that looks like a classy DRO rig! And a very nice job installing on the Prazi. Seems like a bargain price too! DRO’s these days are must haves. Only trouble is after a while if the DRO stops working you’ll be lost as to how to use the mill / lathe in the “old way”!

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