In this context Always remove glow plugs from a warm/hot engine but NEVER fit them until the engine is cold ! The difference is staggering – a plug that was on the point of needing drilling out was removed with ease when the engine was hot !  Noel.

Like Noel, I always removed spark plugs on my car when the engine was hot, especially on alloy heads, for the very same reason. As he said, the difference is between an easy extraction or the fear of breaking something or stripping a thread. Always refitted when the engine had cooled down a bit.

As for parts being too small, I remember being told not to hold fuel injector plungers in my hand for too long, otherwise they would no longer fit back into the bore of the mating part until they had cooled down. Always seemed to take longer to cool down than to heat up.

Neil

PS. too hot for me in the shed to do any real work, 36 degrees.

That’s very neat Jason !  Noel.

It can be much worse in winter when a cold taper is inserted into a warm socket!

On 28 May 2026 at 06:25 DC31k Said:

On 27 May 2026 at 09:13 Bazyle Said:

Your big solid lathe got a bit cooler overnight but your screw on chuck was sitting on the bench in the sun since 6am. If you now screw it onto the spindle you will get a nice shrink fit.

It puzzles me a little when I read this.

If the chuck goes on and off the spindle when both are at the same temperature (i.e. clearance between parallel register and spindle nose is correct), why will a warm chuck cause a problem? The clearance will be increased; the fit on the threads will be looser.

It might be a problem if the spindle was a male taper and the chuck a female taper. Then in its warm state it would go onto the taper further than normal.

I cannot see how what you correctly describe for the tapered collet chuck has the same logical connection to a parallel-threaded spindle nose.

 

The flanks of the thread are an obtuse taper perhaps?

Rest easy Nigel Graham 2 & DC31k, the original post is complete fantasy! The colder lathe spindle will in fact get smaller in diameter the warmer chuck register bore will get bigger so if anything a looser fit but marginal? The mill spindle and collet chuck will get warmer at the same rate so no problem there either over what already exists in using a MT milling spindle taper. I’ve had my say folks, I’ve no more to add.

Tony

Hmm. There is clearance in the thread, which has been tightened. As the front flanks of the cooling chuck thread contract on the expanding back flanks of the warming spindle thread, the chuck will be drawn on tighter, but this will be less than the extent to which the cooling chuck contracts axially and the warming spindle expands axially, leaving less pressure, or even a clearance at the register contact face. Or not?

The register diameter is not going to come in to the matter.

The temperature differences between the chuck, register and thread on the spindle will be small, 30C at the most. This, with the transfer of heat, is very unlikely to give removal problems. I can see greater difficulties lifting a hot chuck off the bench. I trust you keep it well oiled!

This weather has wiped me out. Although slightly cooler, today has been the worst.

JA

Charles

……………… but I have oiled benches in my time.

JA

On 28 May 2026 at 22:38 Nigel Graham 2 Said:

Alecs –

No: if the chuck fits properly when at the same temperature, it will fit properly when both it and the mandrel have equalised from whatever their respective temperatures when put back together.

The only way a temperature difference might tighten the grip on the chuck is if a cold chuck is screwed tightly onto a hot mandrel, so the nose thread pulls the chuck backwards as the headstock cools.

The opposite to what is described: a hot chuck on a cool spindle.

That sounds about right.

Although, as pointed out above, will a temperature differential of 30C provide enough thermal expansion to cause sticking? I don’t know. I keep my spindle thread and collar well slathered in anti-seize goo so have never had a stuck chuck in any weather.

On 28 May 2026 at 23:41 alecs Said:

On 28 May 2026 at 22:38 Nigel Graham 2 Said:

Alecs –

No: if the chuck fits properly when at the same temperature, it will fit properly when both it and the mandrel have equalised from whatever their respective temperatures when put back together.

The only way a temperature difference might tighten the grip on the chuck is if a cold chuck is screwed tightly onto a hot mandrel, so the nose thread pulls the chuck backwards as the headstock cools.

The opposite to what is described: a hot chuck on a cool spindle.

That sounds about right.

Although, as pointed out above, will a temperature differential of 30C provide enough thermal expansion to cause sticking? I don’t know. I keep my spindle thread and collar well slathered in anti-seize goo so have never had a stuck chuck in any weather.

 

having done quite a lot of shrink fitting in my working life i will say 30c will make no differance

Probably the OP is concerned about the “Heat and Freeze” effect that we use when we do want an interference fit.With a 200C vs -18Ctempertaure difference, a 0.001″ interference assembled easily. But with everything at the same temperature, the fit is now permanent.

So a temperture difference of about 20C is unlikely tp present problems.

I would much more concerned about my Morse tapers.

But the sure fire way to be safe, if you are worried, is “Don’t do it!”

Howard