I have wanted digital readouts (DROs) on my mill for ages. It’s a bit hard to say what axis of a milling machine is most in need. The work being done is going to play a part in that decision. However on my mill the Z axis or up and down is a shocker. If you look at the first photo below showing the mill front on, the black hand-wheel on the left is the fine adjustment for height and used for milling operations. The scale is behind the wheel. The mark to read measurements off the scale/dial is on a small shiny plate you can see poking up at the right of the wheel. It’s all just about impossible to see.
As the photos show, I have hacked myself a DRO using a fairly long throw (25.4mm or 1 inch) digital dial indicator. Being digital, it has no dial so it’s really a ‘digital indicator’ (maybe a digimatic indicator.) ‘Digital dial indicator’, despite being an oxymoron, is unambiguous. Glad that’s clear now… Actual dial indicators are awesome, the slightest bump on the plunger causes the needle to spin wildly.
Digital dial indicators are cheap to buy on ebay or the other usual suspects (Ali Express etc.) at around $25 Australian and are decent quality. A review by AVE, complete with cussing and crudity and laughs, is available on YouTube – recommended viewing.
How does it work?
The top of the mill drops down towards the lower red section with the hand-wheel as the quill moves down (further obscuring the scale behind the wheel). This compresses the plunger on the dial indicator giving measurements down to 0.01mm.
Imagine that, I can drill a hole 17.01mm deep. Wow. I can also size parts by milling them with this same accuracy, also wow.
The full travel of the mill is 31mm, this is partly why the shiny aluminum part (milled to shape on the machine) is held on with magnets, if I forget it’s there it just slides out of the way. I hope the cast iron does not get too magnetised, but it’s out of the way and, lets be honest, this is a mill best used on softer metals anyway 🙂 Also, on the point of not being able to measure full travel in one stroke of the indicator, being a light mill it is best to not have the quill fully extended for precision work anyway to minimise flex. Finally, on this point, it is easy enough to move to say 20mm, slide the aluminum part down, reset the indicator to zero and start again from there. This is how I measured the full travel of the mill moments ago.
How did I make it?
The magnets are super-glued into flat bottomed holes that I made with a 10mm end mill (a ‘cutter’) that cuts in its centre (not all do). The magnets are ever so slightly recessed to protect them because they are quite brittle. I also used 12mm diameter end mill, for its length, to tidy up the roughly cut aluminium L shape. The side behind the length of the plunger in the photo was cut by the end of the cutter (which, on purpose, left the texture you can see). The dial indicator itself is attached to the mill with a screw that goes into a hole that I drilled with a battery drill and tapped. Swarf in the milling gearbox was not a problem because the gears were all about to be replaced (see my earlier post on rebuilding the gearbox) and I was cleaning everything.
Tangent: OK wordpress, it’s time we sorted out an Australian English spell checker. Hopefully there is a setting for it. Also, how could your dictionary not contain the word swarf? It is a favourite of mine and a handy way to describe the miscellaneous garbage produced by small children when they eat too (BTW).
What do I think about it?
The dial indicator DRO works well. It is easy to, using the fine feed, increase cut depth by .01mm increments. It is also so much neater and more accurate than hacks involving depth gauges based on digital vernier calipers. If I was starting again I would probably make it a little lighter. I did not know what size magnets I would use etc. but the extra weight is easily held by the three 10mm diameter magnets (they are strong ones) and it is solid.
My only complaint is that I could not use it while making the holes for the neodymium magnets…
UPDATE: I now lock the depth stop for the quill at around 22mm this makes sure I don’t bump the magnet block down and not notice. Honestly with a small mill the less quill extension the better anyway.
As always, a record of what I did. I am no engineer, this is not a ‘how to’ guide. Could this go wrong? Sure, if the aluminum thing falls off into a fly cutter it might take out an eye or send you reeling backwards onto your battle axe project.
Benjamin's Bench 