Working hardened steel arbors and pivots

NigelW

Registered User
Jan 2, 2015
452
44
28
London and Kent
Country
I am currently struggling a little with the arbors and integral pinions I am making as part of the restoration of my early 18th C bracket clock.

I am making them from silver steel which I am hardening by taking them up to cherry red (after soaping and binding in iron wire) before plunging in brine, then tempering them by taking them up to a dark blue. Even after tempering the steel seems very hard. They can be cut with a carbide graver but I am fining them hard to work and clean up.

My questions are:

- Should I be using my pivot file on them? My file, which is several years old, seems to have lost a lot of its bite and they are expensive to replace

- I made the mistake of not deburring my pinions before hardening and am fining it difficult to remove the burrs. Diamond files are too large to get between the leaves - would a ceramic file do the trick? I fear that a fine needle file would just get blunted.

- I bought some pink coloured diamond abrasive paste (the middle one in Cousins' range, with 8 micron grit) but this seems too fine for the initial polishing of the pinions - should I be using a coarser grade, or something else?

Any tips would be much appreciated.
 

kinsler33

Registered User
Aug 17, 2014
3,705
507
113
74
Lancaster, Ohio, USA
Country
Region
Would carborundum dust (or even diamond dust, God forbid) mixed with a bit of oil and applied to a wood stick be of any help? I have no idea where anyone would get small quantities of these abrasives. Silicon carbide would likely work as well. In any event, abrasive powder and a wood stick is how the old-timers would have polished and de-burred this sort of thing. It sounds like you're doing very nice work.

Mark Kinsler
 

gmorse

NAWCC Member
Jan 7, 2011
12,380
2,060
113
Breamore, Hampshire, UK
Country
Region
Hi Nigel,

I think the best solution is to go back a couple of steps and anneal the work, then you can clean everything up and do the preliminary finishing before re-hardening and tempering. All you should need to do post tempering is to complete the polishing. With diamond polishing, depending on the initial finish from the cutting stages, you generally need several grades of increasing fineness, because if you go too fine too early you won't achieve a good finish; 25 micron is probably coarse enough to start with if your cutting tools are well finished, (Eternal Tools are another source for this stuff). A grey finish without cutting marks should be the basis for subsequent finer grades.

I've had pivot files for years and I can't remember the last time I used one.

Regards,

Graham
 

NigelW

Registered User
Jan 2, 2015
452
44
28
London and Kent
Country
Would carborundum dust (or even diamond dust, God forbid) mixed with a bit of oil and applied to a wood stick be of any help?
Thanks Mark. I found some oily grinding compound of unspecified origin at my clock club yesterday which I used with a wooden stick as you described and which had some effect. I tried Googling "valve grinding paste" have now ordered some 360 grit (extra fine) carbide paste - which would be at the coarse end of the spectrum for this work I think.
 

NigelW

Registered User
Jan 2, 2015
452
44
28
London and Kent
Country
Hi Nigel,

I think the best solution is to go back a couple of steps and anneal the work, then you can clean everything up and do the preliminary finishing before re-hardening and tempering. All you should need to do post tempering is to complete the polishing. With diamond polishing, depending on the initial finish from the cutting stages, you generally need several grades of increasing fineness, because if you go too fine too early you won't achieve a good finish; 25 micron is probably coarse enough to start with if your cutting tools are well finished, (Eternal Tools are another source for this stuff). A grey finish without cutting marks should be the basis for subsequent finer grades.

I've had pivot files for years and I can't remember the last time I used one.

Regards,

Graham
Thanks Graham. Very helpful advice, as always. I have only hardened two of my arbors so far and I think I may be able to rescue them without annealing and rehardening, but if not that would seem to be the right way forward.
 

John MacArthur

NAWCC Member
Feb 13, 2007
376
37
28
laplaza.org
You might try tempering them again, to the same temperature/color. I find that the second time brings them to a slightly less hard state, maybe somewhat more stable, and less likely to crack or break when you try straightening them or burnishing the pivots. If you have a way of keeping them at that temperature for a few minutes, that helps. For the polishing you should be able to find some carborundum paste that will do the trick. Good luck,
Johnny
 

shutterbug

Moderator
Staff member
NAWCC Member
Oct 19, 2005
46,395
1,851
113
North Carolina
Country
Region
It's a good lesson going forward: Don't harden until all clean-up work is done. Most good lessons come by experience.
 

kinsler33

Registered User
Aug 17, 2014
3,705
507
113
74
Lancaster, Ohio, USA
Country
Region
Note that valve grinding compound is generally available at your local auto parts store. It's good for a wide variety of abrasive needs, including glass grinding. I believe it's silicon carbide, which isn't quite diamond, but quite good nonetheless.

Diamond dust and (if I remember correctly) silicon carbide powder used to be used in watchmaking as a sort of Loctite for anchoring studs in holes. For all I know, it's still used that way.

M Kinsler
 

gmorse

NAWCC Member
Jan 7, 2011
12,380
2,060
113
Breamore, Hampshire, UK
Country
Region
Hi Mark,

...For all I know, it's still used that way...
I expect it is, but it's one of those old recipes that's discredited now. If the parts are properly made such contingencies aren't necessary.

Regards,

Graham
 

Forum statistics

Threads
165,351
Messages
1,439,170
Members
86,162
Latest member
Evocatas
Encyclopedia Pages
1,101
Total wiki contributions
2,873
Last edit
Weekly News 7/7/19 by Tom McIntyre