Leadscrew thread type.

[Taf_PembsParticipant @taf_pembs]

Hi All,

I don’t suppose anyone would know the thread type on the leadscrew on a Chester Super Lux X / Y ?

As there is only 1 deg difference between ACME and Trapezoidal and not having a gauge I cant tell. The pitch is so fine I’m not sure I would see the difference with a gauge anyway!

Being a RF45 clone type mill doesn’t really help me and all spare parts lists I can find for similar mills / copies doesn’t say.

I think I’m going to have to make at least a new X nut and would like to get a proper insert to do it rather than attempt to hand grind what would probably end up being an poor fitting one.

 

Cheers Ta!

[DC31kParticipant @dc31k]

The pragmatic approach is to grind your tool at 29 1/2 degrees, then it will be no worse than 1/2 degree off from whatever form the screw has.

If you want to go down the insert route, you will have no choice in the angle provided. If you buy a metric pitch insert, it will be 30 degrees; if you buy an ACME one it will be 29 degrees. You will not be able to buy a 5tpi insert ground at 30 degrees.

You could draw everything to scale and see the size of error this course of action would produce. Assess the significance of that error in the context of other likely sources of error including but not limited to the measuring equipment you have available, the machine on which the new screw is to be produced and the competence of the person driving the machine.

[Pete RimmerParticipant @peterimmer30576]

If you’re hand-grinding a tool and using a fish-tail I would not worry, just use a 30 degree fishtail because you’ll be hard-pressed to get it within 1 degree anyway. If you’re uing a tool and cutter grinder or D bit grinder go for the half-way as above.

[Taf_PembsParticipant @taf_pembs]

Thanks both…

However, having now engaged the brain slightly, ACME being imperial and Trapezoidal being metric means simply measuring the thread count for a given distance makes it easy.. all of which simply didn’t come into my head when I was standing there pondering it (note to self, must get them memory foam trainers).

Over 1 inch it is 10 tpi.. or could that be 2.5mm ?

Over 4 inches it’s about a thread out but over 100mm it is exactly 40 threads so must be 2.5mm pitch and Trapezoidal.

Simple when the grey matter is functioning a little – I need one of those AvE ” No Dumb Area” stickers !

Cheers again.

[David George 1Participant @davidgeorge1]

Hi Taf have alook on here,      https://www.shop-apt.co.uk/trapezoidal-tr-30-internal-threading-inserts.html

They also are very helpful on the phone.

David

[Taf_Pembs]

On Taf_Pembs Said:

However, having now engaged the brain slightly, ACME being imperial and Trapezoidal being metric means simply measuring the thread count for a given distance makes it easy.

You can also look at the graduations on the dials of the machine for further confirmation. If the handwheel dials are in metric, the feedscrew would also be metric.

What diameter is the screw for which you are to cut the nut? You need to make sure the insert plus bar is smaller diameter than the minor diameter of the thread.

[Taf_PembsParticipant @taf_pembs]

Thanks both, I’m still blaming the brain fart on the medication.. and DC, yes.. the fact that it is a metric machine should have hbeen a tiny little clue..!! Ah well…

Already shopping for suitable bar and insert.. it’s a 19mm screw so hopefully I can get away with a bar that will take 16IR inserts .. still looking at what is about.

Need to find a lump of bronze first that is big enough to make the thing with its protruding mounting’s but also affordable!

[Michael GilliganParticipant @michaelgilligan61133]

I’m not trying to be funny, Taf … but do bear in mind that 19mm is not a very “Metric System” diameter.

It wouldn’t be the first time that a manufacturer has used some weird cross-breed for their own convenience.

Good luck with whatever …

MichaelG.

[Taf_PembsParticipant @taf_pembs]

Thanks Michael, that was the kick up the bum I needed to go back up the workshop and measure it properly with a pen and paper instead of relying on a somewhat messed up organic grey computer at the moment..!

It is a 22mm screw.. (22.1 to be precise), minor ID 19mm.

Thread count in 4 inches 41.5 (near enough by eye)

Thread count in 100mm exactly 40 so 2.5mm pitch.

 

[Michael GilliganParticipant @michaelgilligan61133]

Excellent

MichaelG.

…

I have sent you a Personal Message, Taf

[Taf_PembsParticipant @taf_pembs]

Thanks for the help Michael, really appreciated..!

 

As for your comment above – “It wouldn’t be the first time that a manufacturer has used some weird cross-breed for their own convenience.” your not wrong there, now I’ve ordered an pair of 16IR2.5TR inserts I’ll put a pint on the fact that they used a 10Tpi ACME insert to cut a metric thread..!

I know it’s only a degree difference but it’s still wrong.. 🙂

It would be par for the course with everything else so far..

Cheers!

[Ady1Participant @ady1]

You can pour your own with a bit of babbit

Babbit pour – Drummond M leadscrew

Mine has done some seriously heavy use over the last 12 months, driving a 40KG milling table mounted on my lathe saddle up and down my lathe

[Taf_Pembs]

On Taf_Pembs Said:

I’ll put a pint on the fact that they used a 10Tpi ACME insert to cut a metric thread.

I think you should be OK.

It was common for British lathe manufacturers, living in an imperial world (didn’t Madonna sing a song of a similar title?), to cut their metric leadscrews to ACME thread form.

However, your machine, originating as it does from a metric-speaking country, should have the correct trapezoidal profile on its metric leadscrew.

Had it been an imperial version of the machine, its TPI leadscrew would stand some chance of being cut to a trapezoidal form.

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