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Which grade of steel required to make gears

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Clive Pearson14/06/2010 18:35:13
2 forum posts

I have damaged 3 of the gears on my Harrison L5 leadscrew gearbox.
Unable to locate any second hand spares I would like to attempt making them myself but am not sure which grade of steel would be best in terms of machineability and  hardness,
They dont appear to be hardened and file easily
KWIL14/06/2010 18:52:50
2955 forum posts
55 photos
EN8 machines well with sharp tooling.
Julie14/06/2010 19:31:21
24 forum posts
1 photos
Gears are usually made of EN32 or 24 these days, or EN58 (304) if stainless.
I made change gears for my Harrison M250, and I used EN32. (didn't case harden)
EN8 will be OK - it has a higher carbon content.
Any Carbon steel above 070M will be OK (EN3A, EN5/6, EN8..)
Jens Eirik Skogstad14/06/2010 19:41:13
346 forum posts
22 photos
Drill rod or as british man say silver steel. I has used hardened silver steel as gear cutting tool, works well.
But the change gears in the lathe are often made of cast iron. Some time in plastic, nylon as are found in the newer lathe from Asia.
I used the cast iron as material to a 25 teeth gear to my lathe when i maked a new after i lost the 25 teeth gear in my tool room. And later i maked the 127 teeth gear of aluminium to my lathe, no problem with load and abration. Lasted a lot of year.

Edited By Jens Eirik Skogstad on 14/06/2010 19:45:32

Edited By Jens Eirik Skogstad on 14/06/2010 19:48:25

KWIL15/06/2010 08:54:00
2955 forum posts
55 photos
EN8 suggested because it is generally available and if  you want to harden it, it through hardens rather nicely.
John Stevenson15/06/2010 08:58:16
5068 forum posts
3 photos
What model gearbox is it ? 3 speed or Norton ?
I know someone who converting a L5 to CNC so won't need the box but I'm not sure what's fitted to it.
John S.
macmarch15/06/2010 10:10:55
147 forum posts
1 photos
I would be a little wary of using EN3A as a gear material. This is a general purpose steel that is readily machinable, bendable, (fabrication duties) and suitable for welding. It does not have any gut strength in a shear application.
as you say en5/6 upwards will be fine.
Julie15/06/2010 22:00:28
24 forum posts
1 photos
The material chosen really depends upon the load and usage.
Given that the load is not generally severe  in a home type application such as this where the size may be physically driven rather than detail design based upon mechanical characteristics I would not get too wound up on the material.
Whichever option you go for in the commonly available materials EN3A - EN9 there are pros and cons
EN3A is a low carbon - about 80% the strength of EN8 - will wear in, easy to machine
EN5/6 Medium carbon - about 90% strength of EN8
EN8 - old choice for gears - can suffer fatigue
EN9 - Medium carbon - equal to EN8 less fatigue cracking
I would expect the load to be low, so any of the above should be suitable - however if you plan to heat treat then EN8 or 9 via induction hardening , EN32 via case harden etc...
There are some advantages to the low/med carbon as these will wear in if you are cutting with home made cutters on a small mill i.e. they will be more tolerant  - whereas if you cut low quality gear forms on high grade steel - this could cause more damage to the existing gears.
 Just my thoughts

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