The £10 Digital Readout

My Gate Mini Jig Borer came with Heidenhain digital readouts ("DRO's") on the X and Y axes. I thought it would be advantageous to also have one on the Z axis. A couple of years ago, I had purchased a Chinese digital caliper from Maplin Electronics. At the time of writing (1st October 2006) Maplin had a "special" on these calipers at only £9.99, so I thought I would have a go at using one for a DRO on the Z-Axis. A quick trawl around the internet revealed that quite a few people had already done this, so it looked good to go.

Specification

As the z-axis throw on the mini borer is approx 75mm, I can expect repeatability within half a thou and accuracy within 1 thou - plenty good enough for most model engineering uses. The following table shows you how I did it.

Click an image to view a larger version (opens in a new window)

Pictures	Description
	Here is the digital caliper as supplied. It comes in a foam lined plastic box with a spare LR44 battery. It is claimed by Maplin Electronics to be stainless steel - although I suspect it may be tool steel - whatever it is, it is VERY hard.
	Remove the sticker from the back - but please be aware that you invalidate your warranty at this point, so please make sure the caliper is working properly before you do this. Removal of the sticker is greatly aided by the use of a razor blade under the edge. Careful!
	Removal of the sticker leaves behind a very sticky adhesive residue. This came off as I worked with the caliper, but I suppose you could try nail poslish remover to get rid of it. Remove the 4 small screws from under the sticker (already removed for this photograph) and retain them for re-use later.
	The case holding the electronics can now be separated from the caliper. Don't be tempted to remove the PCB from the case to have a look - there are very fiddly bits inside.
	Remove the retainer from the end of the caliper - you do not need to retain any of these parts.
	Slide the 2 halves of the caliper apart. Watch out for a small brass leaf spring which will pop out as you separate the halves. You will need to retain the spring for later use.
	The depth measuring blade can be removed simply by fatiguing  it.
	Then you need to grind the caliper parts and drill mounting holes to suit your application. Don't attempt to cut the caliper parts with a hacksaw - you will simply blunt it. Drilling the holes was also a chore - in the end I used a centre drill to start off and then HSS drills of progressively larger sizes (ie removing only small amounts of material with each drill). Even so, I managed to blunt a couple of drills. I need to get my Stent Tool and Cutter Grinder finished so I can sharpen them!
	Drill suitable mounting holes on your mill, making sure they are accurately placed so that the caliper does not bind as the z-axis is moved.
	Attach to machine, test, adjust mountings if necessary and enjoy !