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Looking for advice a numpty at work has purchased 8 blocks they are probably mild steel but they are powder coated black. (I am hoping they are mild steel.)
They are meant to hold GC vials(Gas Chronograph) But the ones he ordered are for medical use. They have 28 10mm holes to hold 28 2ml sample vials. Our 2ml sample vials are 12mm in diameter.
So I need to open up the 10mm holes to 12mm.
The holes need to be precise.
How do I set up to find the centre of the holes. Ideally I would like them to be 11.9mm to start with the vials have to be a really close fit.
All the work will be done on a milling machine the blocks will be clocked in so they are running true to the cutting head.
I did point out to them that it would of been cheaper to go to a local machine shop with a drawing and let them do the work. But they are not happy to go outside of the Company. They obviously have to much money.

Techniques I've used in the past,

Find a bit of silver steel that fits the existing holes within tolerance. Put a bit of that into a collet chuck, use it to locate the hole on the mill/drill, clamp the workpiece. Change collet for the drill, and machine.. rinse and repeat.

Use a lever type dial gauge, again fit to collet chuck, in hole, rotate 180 degrees and move axis until dial is same measurement at each orientation, then repeat for next axis. Final check, rotate 360 deg, and check that deviation is within tol.

If I'm being really lazy, use a countersink bit, rotating backwards slowly to locate the part and clamp..

If I'm being fancy, I will calibrate the probe on the CNC and use the 3 point hole measuring cycle to get the centre, then bore out using an appropriate end mill.

Or last chance, does the original supplier offer a set of blocks with 12mm holes, will they accept returns as part exchange.

I'd be inclined if it is a simple matrix of holes, to work out the matrix dimensions, and then simply write a CNC program to bore out the holes and sod where the exact centres are. Simply program as if the block was solid, bore to 11.8 ish, and then do a finishing cut to get to 11.9.

I'm assuming your mills are manual only without probes?

Oh one I haven't used, is a coaxial bore gauge,

https://youtu.be/YoN_MSuqzE0?t=925

Never used one, but they look useful. https://www.arceurotrade.co.uk/Catalogu ... -Indicator

strangesam wrote: ↑Fri Dec 10, 2021 12:52 am Use a lever type dial gauge, again fit to collet chuck, in hole, rotate 180 degrees and move axis until dial is same measurement at each orientation, then repeat for next axis. Final check, rotate 360 deg, and check that deviation is within tol.

This is my usual method.

Alternatively you could use a manual edge finder. Not quite as accurate as the above method but works ok.

What will be teh cost of your time, plus further powder coating &c &c ? Would it not be cheaper to purchase a new set, or return the incorrect set for exchange?

Put a clock gauge in the mill collet or chuck (pref collet!_) & touch the sides of the holes in 3 places that gives you a triangle of measures - centre of a triangle is simple mafs.
then you check that by rotating the chuck - the clock should not move as it contacts the sides of the hole............ I spent about an hr... maybe more? getting that right once!

The inverse method put a slip gauge dowel rod in (beware getting it back out can be 'fun' ) use a clock to find the edge rotate till there is no clock motion.

Put a ball bearing in the hole thats bigger than the hole .... & use a clock gauge to find the top - thats the centre.

easiest way - ask the why requirement for the hole centre is x+/-Y -bowl till you get a sensible answer, then tolerance fit to that & reprog the robot arm!

centres of a hole if being milled is rarely better than 0.1mm or if drilled 0.2mm so use that to get 'close enough'?

Alpha 1, can you define 'precise'? Is the hole location on the block critical, or is it the diameter you are more concerned with? Easiest way, put the block on a piece of paper so that you don't scratch the fancy powder coat, lightly clamp the part to the bed of your mill, using another small piece of paper between the job and the clamp. Bolt a 'stop' to the table to prevent the part spinning on you, then start to drill a hole with a 11.9mm drill and let the part centre itself. Tighten the clamp a bit and continue to drill through. Without moving anything, swap the drill for a 12mm, then gently run it through again. Most importantly of all, don't drill a hole in the bed of your mill!

Before doing anything I'd find out if the blocks are machinable, if they aren't the job stops right there.

I use a co-axial indicator a fair bit and they are OK. However for volume I would look at a fixed gauge pin and see how I got on with it. Easy enough to machine and costs pence.

I have a co-axial indicator all though I have never used it seems like a good time to learn how to use it. The diameter and depth of the holes is the critical bit. Thanks for the input guys.