Restoring old lathes, backlash in leadscrews

[John S]

Order a bit extra and flute it and get it cyanide hardened and use that for a tap.

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[irving2008]

Order a bit extra and flute it and get it cyanide hardened and use that for a tap.

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Interesting, I assume that would be OK for brass, being a lot softer (I dont suppose it would tap brass without hardening?)

Where and how much roughly?

[irving2008]

Hmmm..got a couple of 'approximate' quotes for hardening a 150mm length of 10mm - £80! and that depends on the actual steel used.

Maybe I need to learn how to do hardening at home... I have the book...

[John S]

Hmmm..got a couple of 'approximate' quotes for hardening a 150mm length of 10mm - £80! and that depends on the actual steel used.

Maybe I need to learn how to do hardening at home... I have the book...

Not easily done just by the heating and quenching as the screw will almost certainly be low carbon steel.
The only easy way to do this is by pack hardening in something like Kasenite which makes a mess of fine details like a tap, hence the reference to molten cyanide.

If you fancy going this route, buy an extra 150 to 200 mm length, send it up and I'll flute it and get it hardened in with the next batch of gear that goes over.
I'll make two, you get one back, I keep one for payment.

[irving2008]

Not easily done just by the heating and quenching as the screw will almost certainly be low carbon steel.
The only easy way to do this is by pack hardening in something like Kasenite which makes a mess of fine details like a tap, hence the reference to molten cyanide.

If you fancy going this route, buy an extra 150 to 200 mm length, send it up and I'll flute it and get it hardened in with the next batch of gear that goes over.
I'll make two, you get one back, I keep one for payment.

Now thats a deal John!

I was looking at Kasenite and similar stuff. It does say in the instructions that its ideal for one-off, low-use tools such as home made taps... but I can see that the fine detail might be problematic...

The company I talked to re cyanide hardening needed to know exactly what steel was being used and its exact composition else they couldnt harden it... I wonder if MD have that data? I'll email them...

[irving2008]

Found these guys...http://www.ondrives.com don't recall seeing them mentioned here before

They do 10x2 LH similar price to MD (£11.34 for 1m) and steel nuts in LH for £5.34 each. They advise steel nuts OK for hand operation and given the level of use I dont see this being a problem (comments?). The nut is 17mm sq and 15mm long so would easily fit inside a (brass?) carrier with a locking screw.

Is this a viable option?

[irving2008]

Ok, this is what I plan to do... the top shows the existing screw, very simple, very crude.

The lower two diagrams show the proposed 10x2G replacement, with a pair of 8x16x5 thrust bearings retained by a circlip and 12mm washer inboard and an M8X1.0 nut outboard to adjust endfloat. I'll probably extend the outboard shaft to allow me to fit a zeroable micrometre dial with a backing dial mounted on the bearing block.

Comments?

[John S]

Swap the screw to 20 tpi and use one of the C3 digital displays.
Instant imperial / metric change over, zero at any point and no counting turns ?

[irving2008]

Swap the screw to 20 tpi and use one of the C3 digital displays.
Instant imperial / metric change over, zero at any point and no counting turns ?

£75 is a tad outside my budget John. An adapted 6" vernier off eBay at £10 would be a cheaper DRO!