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Modifying Flex Shaft Handpiece Mandrel

Making an Adapter for Different Drill Shaft Sizes for the Handpiece

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Modifying flex shaft handpiece mandrel

A simple way to turn a rubber wheel mandrel into a drill bit extender or an adapter for different drill and burr shaft sizes such as dental drill bits to be used in your flex shaft motor handpiece.

Modifying flex shaft handpiece rubber wheel mandrel

Every now and then I have to drill a long hole through something with my hanging motor.
This is a real drag if the piece cannot be clamped into a drill press or a vice.
Just such a piece came across by bench the other day.
A long very delicate bone carving that had to have a 2 mm hole through.
One of those, that if it was broken, it would be irreparable and also had a bucket load of sentimental value attached to it.
So I modified a standard rubber wheel mandrel that I buy at the jewelry tool supplier.

Modifying flex shaft handpiece mandrel 1.5 mm screw

It's got a 1.5-ish mm screw that screws in to hold the rubber wheel.

Modifying flex shaft handpiece mandrel enlarge holes

So I ream it out using progressively larger ball frazers.

I do this on the bench using my hanging motor.

First 1.6 mm then 1.8 mm then 2.1 mm for a 2 mm drill.

Modifying flex shaft handpiece mandrel punch holes

Once it is reamed out, I file a flat on the ends and punch it.

Modifying flex shaft handpiece mandrel drill hole

I drill a 1.5 mm hole through both sides.

That is the correct size hole for a 2 mm tap.

I drill the hole right through so there is space for the tip of the tap to go deeper in.

Modifying flex shaft handpiece mandrel tap thread

Then I tap it.

Only one side needs be tapped.

Modifying flex shaft handpiece mandrel tapped hole

Tapped.

Modifying flex shaft handpiece mandrel brass screw

I used a brass screw because I had them.

I thought they might be a bit soft but they work fine.

Stainless steel would be better but they are a mission to make, so brass it is.

Modifying flex shaft handpiece mandrel short screw

The shortened screw.

Modifying flex shaft handpiece mandrel screw cut off

Then I trim the brass screw off and cut a slot in it with my piercing saw.

Then I use a cup burr to make it domed and smooth.

Modifying flex shaft handpiece mandrel shorten with cut-off wheel

I cut the mandrel shorter so the cone starts right up against the chuck.

I also made a flat section on the drill bit so that the lock screw holds the drill there.

I use a cut off disk for this.

That way the lock screw does not have to be tightened very, very tight

Modifying flex shaft handpiece mandrel fitted with drill bit

Drill bit fitted and locked.

Modifying flex shaft handpiece mandrel adapter for dental drill bits

My dentist gives me his old diamond burrs.
His blunt burrs are my sharp ones. These burrs have a shaft of 1.6mm
So I made a mandrel to fit those burrs as well.

Modifying flex shaft handpiece mandrel fitted in chuck

The mandrel cone right up against the chuck so there is minimum wobble.

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