Hardening?

Hi All,

Being unhappy with the state of the cross slide on my Myford ML7 coupled with my preference to work metric I decided to make a metric version of the lead-screw and replace the mazak nut with a Phosphor Bronze one.

Whilst I can quite easily cut a 12mm x 2mm extenal ACME thread the nut would present a number of problems, not least of which would be the measurement - I know I could simply use the lead-screw to test it on an empirical basis but that is inherently unsatisfactory.

My idea is to cut the lead-screw (165mm) plus an extra length (70mm) which I can then flute and make into a tap. The length of 'FULL FORM' would be 15mm with 3mm at core dia., 45mm tapering and 7mm of 8mm square for the tap wrench.

Once the turning is complete and the 'tap' section separated from the lead-screw, the tap will need to be hardened of course (after fluting).

My only experience of hardening was some 45 years ago and entailed serious heat and cyanide baths amongst other similarly dangerous environs.

The material I already have on the workshop shelf is EN1a.

The questions are :-

  1. Am I wasting my time using EN1a?

  1. Can I harden EN1a in my workshop with access to only a blow-torch/5.6Kw Gas-Ring and a bucket of water?

  2. Should I use Silver Steel - with the possibility that the tap will not be 'exactly' the same size as the lead-screw (ie. machined as a separate component)

Bear in mind that it will only be needed to cut the one Pb Nut.

Thanks in anticipation.

JG

Reply to
JG
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JG,

EN1A being a low carbon mild steel will not harden by heating / quenching. As you are only making a 'one off' nut can I suggest that you case harden it. The process is fairly simple - you heat to cherry red and immerse in a powder (Casenite) then dunk in water. The Casenite is carbon rich and carbon is absorbed into the surface resulting in a hard out 'case'.

Stocked by GLR http://62.73.188.198/start.html but not under the name Casenite - search on 'hardening'

Andrew Mawson

Reply to
Andrew Mawson

What about an alternative aproach instead of hardening.

I seem to remember that there was an article in MEW recently about creating leadscrew nuts by casting (lead, or some sort of white metal I think) into a cavity using the leadscrew itself as the pattern.

Ian Phillips

Reply to
Ian Phillips

Since white metal has a fraction of the yield strength of phosphor bronze, you would either need a longer nut, or keep the loads down, or be prepared to replace it more often. I'd go for PB and case hardening mild steel or through-hardening a carbon steel (e.g. silver steel)

Reply to
OldScrawn

The Gingery book on making your own lathe has step-by-step details on doing this. My copy is packed away at the moment. GeoffH

Reply to
GeoffH

from "Andrew Mawson" contains these words:

Thanks Andrew (and others), I have eventually bitten the bullet and decided to go the Silver Steel route. The concept of casting in white metal is simply not attractive to me at all.

One of the main reasons is that the length of the tap that I can get out of the bar of EN1a would mean that there was no space for a shank, 10mm for a square and with only 45mm to get from core to full form there would be a relatively heavy 'cut' on each tooth.

Once it had to be a separate piece of material for the tap then the choice of silver steel was a foregone conclusion. So I am just going to trust that my skills (and the accuracy of the ML7) are adequate to produce two identical threads.

JG

Reply to
JG

[snip]> JG

Why go to all this length? Just give Myford a ring and order a new cross-slide screw and nut in whatever length and style you want!

They have both metric and Imperial, in short and long (for the extended slide) My original (on an ML7) was metric(which I loathe), and short. I obtained a long cross-slide s/h from a friend, and got an Imp long screw and nut from Myfords. Not expensive, and from stock, so why the hassle of cutting a square thread and making a nut, when they are available from stock?

Dave.

Reply to
speedy

from "speedy" contains these words:

It had occurred to me Dave but it is not just a matter of a switch to metric. I find the dial far too small and would also like the option to index the scale. If I buy from Myford I have to take their offering which is no real benefit.

The dial I have already made is 65mm Dia and beside the 200 divisions which are just over 1mm apart there is a separate ring which has 20 divisions marked 0 - 9 0 9 - 0 and this can be rotated to make 'relative' movement much more convenient.

In addition, my need to re-learn skills which have lain dormant for more that 40 years is being fed - not to mention the satisfaction of using the finished product :)

JG

Reply to
JG

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