LF thoughts on this finger design please

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sleepingdog
Posts: 78
Joined: Tue Jan 17, 2017 7:57 am
Location: Almonte, Ontario, Canada

LF thoughts on this finger design please

Post by sleepingdog »

Hi folks.

After looking at lots of posts and pictures and diagrams on this forum, I've stolen a bunch of ideas and put together a CAD model of a finger assembly that I'm hoping I can get some feedback on before I prototype one.

Notes:
- Overall thickness is 10/32 plus I've put in a 1/32 spacer washer to give me 11/32 string spacing.
- Control finger will be brass. It overhangs the raise finger so that the raise finger will be hidden from view from above.
- Raise and lower finger plates will be 1/16" thick steel.
- I've put a small washer between the bearing and the lower finger so the bearing won't rub on the finger.
- There will be a slot in the brass control finger for the string to go into. It's not shown because I haven't figured out how to draw it yet in the cad system I'm using.
- Axle is 1/2" - thinking of using drill rod
- Tabs are (obviously) shown in the pre-bent position

Questions:
- Should the scissors be made from stainless? If regular steel, is rust a potential problem?
- How wide should the slot for the string be?
- What size holes do you normally use for pull rods? Figured I would just use steel welding rod for the pull rods.
- Is the spacer on the bearing required? If yes, is there a better way to achieve the goal of it not rubbing on the finger.

I would appreciate any and all feedback.

Thank you!

Dave
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Finger Assy - Back View.png
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Finger Assy - Top View.png
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Finger Assy - Home View.png
Finger Assy - Home View.png (146.87 KiB) Viewed 2177 times
maxi19
Posts: 365
Joined: Mon Oct 22, 2012 12:55 pm
Location: Milton Keynes, England

Re: LF thoughts on this finger design please

Post by maxi19 »

Hi Dave,

It will be a lot of work making that top finger but, it will keep you busy

Questions:
- Should the scissors be made from stainless? If regular steel, is rust a potential problem? Ans) I use mild steel and rust isn't a problem if you don't play under water
- How wide should the slot for the string be? Ans) I make the slot 2mm wide
- What size holes do you normally use for pull rods? Figured I would just use steel welding rod for the pull rods. Ans) I make the holes 3mm dia and use 2.4 mm stainless welding rods
- Is the spacer on the bearing required? If yes, is there a better way to achieve the goal of it not rubbing on the finger. Ans) I make and use PTFE washers.

Glad to help and have fun.

Ron Mc
sleepingdog
Posts: 78
Joined: Tue Jan 17, 2017 7:57 am
Location: Almonte, Ontario, Canada

Re: LF thoughts on this finger design please

Post by sleepingdog »

Thanks for the information, Ron. Really appreciate it.

Yes, that top finger will be a bit of work, but I have a milling machine and think I have a plan in my head that will work. I like a challenge - obviously I guess, or I wouldn't be trying to build a PSG :D .

It was some drawings that you posted on this forum that I was primarily referring to when laying out the fingers. I'm now looking at a drawing you posted for the key head. Very helpful. Thanks.
Dave
Storm Rosson
Posts: 191
Joined: Sat Jul 10, 2010 8:55 am
Location: Silver City, NM

Re: LF thoughts on this finger design please

Post by Storm Rosson »

Hi Dave, I would also use a ball or roller bearing on the fulcrum (top) part of the finger where the axle shaft goes thru ,also you can usually get the same bearing(s) with the inside race slightly wider than the outside race that will act as a spacer....Stormy ;)..PS. as somebody here mentioned in a post, Avid Racing Concepts (RC stuff) has the absolute best deal on mini bearings anywhere. Are those finger pix actual size?(J/K) hehehe
sleepingdog
Posts: 78
Joined: Tue Jan 17, 2017 7:57 am
Location: Almonte, Ontario, Canada

Re: LF thoughts on this finger design please

Post by sleepingdog »

Storm Rosson wrote:Hi Dave, I would also use a ball or roller bearing on the fulcrum (top) part of the finger where the axle shaft goes thru...Stormy ;)..PS. as somebody here mentioned in a post, Avid Racing Concepts (RC stuff) has the absolute best deal on mini bearings anywhere. Are those finger pix real size?
The pictures are just screen grabs so not to any particular scale. To give you an idea of the scale, the bearing I show on the lower finger plate is a R2ZZ which is 3/8" OD, 1/8" ID. The radius on the "top" of the brass finger 1". It is a 1/2" shaft (axle) that will go through it.

I did in fact order and receive 20 of the bearings from Avid Racing, based upon a post I found on this forum. Great price, even considering shipping across the border to Canada.

To be clear, you are saying to put a bearing between the 1/2" axle and the brass finger part, as on the following attachment?
Attachments
Finger Assy - Bearings.png
Finger Assy - Bearings.png (71.66 KiB) Viewed 2155 times
Dave
Storm Rosson
Posts: 191
Joined: Sat Jul 10, 2010 8:55 am
Location: Silver City, NM

Re: LF thoughts on this finger design please

Post by Storm Rosson »

Yes that is what I mean. Take a look at my post a couple lines down about my Super Pro finger upgrade...Stormy....I was just bein a wise-ass when I asked if the pics were actual scale doh!!... :mrgreen:the bearings on the lower finger part arre 9mm x 2.5mm..had to go metric as 3/8 was just a smidge to big. Your's is looking dam good tho. :D
sleepingdog
Posts: 78
Joined: Tue Jan 17, 2017 7:57 am
Location: Almonte, Ontario, Canada

Re: LF thoughts on this finger design please

Post by sleepingdog »

Re. scale joke, apologies Stormy. I guess I'm losing my sense of humour in my old age. :oops:

Just checked out that post. Interesting. What size bearing is the large one up top? I think I'd have to go down to a 3/8" shaft/axle if I was going to put a bearing in there. I'd still have the lower plate directly in contact with the shaft though. Do I need to worry about it as well? I see Fulawka puts an oilite bushing in his.

I was thinking the brass finger would be somewhat of a bearing (bushing) in and of itself.

Thanks for the feedback. I was worried when I posted that I'd just hear crickets, but you and Ron came through!
Dave
Storm Rosson
Posts: 191
Joined: Sat Jul 10, 2010 8:55 am
Location: Silver City, NM

Re: LF thoughts on this finger design please

Post by Storm Rosson »

ShoBud uses a 5/16 axle stock which is what I still have there, I left it stock as the idea was to make repairing an old worn finger not just a repair but an upgrade also. It's a fairly easy to do fix/upgrade so the old finger is way better than stock and shouldn't need any further repairs and is much smoother than stock. I would go to a 3/8 shaft if necessary cause the bearing precludes any wear/egg shaping of the axle hole in the finger. There have been some talk/rumours about hyterysis (sp) by using a bearing on the axle but ETS has a bearing there and debunked that theory. I gotta think that one reason older guitars didn't use ball/roller bearings much was the cost, modern production methods and cnc machinery have ,as we know, eliminated that factor....Stormy 8-) oh and a year or two ago, just before James Morehead got real sick, he sent me a pic of his new "super finger" design and it had bearings on the axle (so obviously the idea wasn't mine). I sure miss James we talked a lot about this kinda mods.. :cry: my bearing size is 5/16 ID x 1/2 OD.
maxi19
Posts: 365
Joined: Mon Oct 22, 2012 12:55 pm
Location: Milton Keynes, England

Re: LF thoughts on this finger design please

Post by maxi19 »

Hi Dave, if you are going for a fitted bearing as Storm suggests and it entails a slimmer shaft, you will have to use a 'comb' type housing in order to support the shaft along its length.

This is how I make my changer blocks.
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sleepingdog
Posts: 78
Joined: Tue Jan 17, 2017 7:57 am
Location: Almonte, Ontario, Canada

Re: LF thoughts on this finger design please

Post by sleepingdog »

Hmmm. That would really raise the milling complexity. Wondering if I might just go for a bearingless solution for my first go at this. I can always swap it out for a more complex/longer-lasting one in the future once I have more machining experience. Seems there have been a ton of instruments built without bearings there. I'll have to think on this some...

Thanks.
Dave
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