Stainless Steel Knife Point

This topic has 6 replies, 4 voices, and was last updated 14 May 2015 at 10:23 by Colin LLoyd.

Viewing 7 posts - 1 through 7 (of 7 total)

Author

Posts
13 May 2015 at 11:13 #189731
Colin LLoyd
Participant
@colinlloyd53450
Brian May's (Queen Guitarist) Red Special Guitar had a knife-point fulcrum for the tremolo arm movement. I'm making a replica of this guitar. The knife-point and fulcrum are specified as made from Stainless Steel. The Stainless Steel I have is totally non-magnetic and I believe that this steel cannot be heat-hardened. The knife-edge has a 30 deg angle and has to deal with guitar string base tensions of 18 lbs force (780 Newtons) that rise a little more when string bending. And there are 6 strings – although this may be irrelevant as I'm not sure whether the tension is to be totalled or just single at the 6 separate areas of contact. According to the chart I found, the Stainless Steel I have has a hardness of 150-180 (Brinell) and 80-90B (Rockwell) – whatever that means.

Would the knife-point be hard enough in its normal state to withstand these tensions when used in a rocking motion or should I go for a stainless steel that can be heat-hardened to a higher hardness?
Advert

13 May 2015 at 11:13 #7616
Colin LLoyd
Participant
@colinlloyd53450
13 May 2015 at 11:43 #189734
David Jupp
Participant
@davidjupp51506
Austenitc stainless steels (normally non-magnetic) are very prone to fretting and galling when in contact with like material, which I'd of thought might be an issue in a knife edge arrangement.

For that reason as much as stress levels, I'd suggest looking at a hardenable stainless, or maybe one of the fancy surface treatments available.

I know very little about guitars, so can't comment on your original question regarding stress level and material choice.

Edited By David Jupp on 13/05/2015 11:56:57
13 May 2015 at 12:37 #189739
Capstan Speaking
Participant
@capstanspeaking95294
That's about the same hardness as mild steel. It would wear rapidly, especially with wire wound strings.

Loading would be difficult to work out. The load pushing a string sideways would be different to the tension and both would increase rapidly as distortion increased.
13 May 2015 at 13:14 #189741
Colin LLoyd
Participant
@colinlloyd53450
Sorry guys, I forgot to mention that the knife edge is 55mm long (i.e. across the whole width of a normal guitar string array) and sits in a 90 degree V-shaped pocket again of 55mm width in another sheet of 10mm Stainless steel – so the tension is not at a single point. So I believe that the tension of 18 lbs force from each string is bearing on a 10mm width knife-point. As this is to allow a swinging motion, the knife-point can be rounded slightly to take the fine edge off. If there is further discussion I will try to attach a picture to my next post.
13 May 2015 at 16:49 #189756
Neil Wyatt
Moderator
@neilwyatt
Most guitars use a low-medium carbon steel, sometimes chrome plated. Wear I've seen on guitars is minimal. I have a locking micro-tune bridge and like many others it has two half-moon knife edges about 6mm radius that bear on two chromed pins, these must be taking the full tension over no more than a couple of mm of bearing surface maximum…

I'm sure standard stainless will be fine in the arrangement you describe.

Neil
14 May 2015 at 10:23 #189838
Colin LLoyd
Participant
@colinlloyd53450
Neil, my Burns Marquee has "The Point Classic" tremolo system where 2 chromed points rock in conical pockets that are also chromed. And I think its the toughness of the chrome plating that takes the strain and wear. Brian May and his dad when they made his guitar didn't have chrome plating facilities and would probably have used carbon-steel but went for stainless for its non-rusting and anti-magnetic properties.
Author

Posts