Blanton bell crank

[Bent]

Well here you go. I promised,in the other Blanton thread, to try and make a revamped Blanton type crank that would allow rods to run through the crank...rods going to other cranks in line with the crank in question.
Although it works, I will say that there are still things to be desired: One issue would be that the rod running thru to another crank is totally dependent on where the pull bracket is on the screw adjuster. A rod might run into it and there goes part of the idea.
Also, rods will still have to be bent to accommodate the adjuster offset.
- The adjuster is by no means the way I want it - I just made it for illustration
- The overall width is 1/2". Too wide actually when a desirable width is the same or less as the string spacing, which is 11/32" on a ten string.
- I think it was Allan who was interested in the way the bell crank fastens to the round cross rod, more specifically the strength of such a fastening method.
Mind you, I fastened this to a highly smooth, hard 303 stainless rod. Using a rod of milder steel or aluminum would greatly resist failure because of better bite for set screw. Anyway here are the numbers:

With the pulling length extended to max, the failure was at 13 lb (6 kg) (bell crank twists on axle due to set screw slippage).
With the pulling length shortened to just above the set screw hole (about 1" up from bottom in pic) the failure occurred at 26 lb (12 kg)

BlntCrnksetup1.jpg (30.23 KiB) Viewed 2336 times

BlntCrnksetup2.jpg (35.58 KiB) Viewed 2336 times

BlntCrnkRear.jpg (18.07 KiB) Viewed 2336 times

[Allan]

That shows the principle quite well Bent. It is indeed pretty much as I imagined it from the pics you posted before. Thanks for making the model. ( I still say you need to get into the CAD world though good buddy! )

Allan.....

[Bent]

Allan, Jesse is introducing me to Inventor slowly and gently. It is quite the program eh? I like the way you can activate the whole changer finger assembly and move it like for real and make sure no part hits the other. Awesome stuff!

[Eldon]

It seems to me that bell cranks with the split in the middle of the leg to allow the pull rod to go in between would give you less trouble because it is a straight pull. Other designs where you drill a hole and insert the pull rod would give you a sideways twisting of the crank making it a "poorer system??". I've seen pictures of both and the split appears more efficient to me. I hope I've used the right words to explain myself.

[Bent]

Eldon, technically you're right. A lot of steel builders use the sideways twisting type of crank. The Blanton one that i just adapted here has quite a sideways twist...almost a half inch. The fastening method onto the cross shaft is supposed to be strong enough to withstand that force.
Good or bad, I am starting to lean towards the bell crank made of 1/16" steel and has the 90 deg bend on the rod going into a hole of the same diam as the rod and retained by a spring clip. This has two advantages:Lends itself to placement of many holes (11? 14?)and thereby offering vastly finer pedal timing possbilities.
Also, with the material being so thin, it helps avoid having to bend rods to make things fit. Makes for a nicer undercarriage.

[Allan]

Allan, Jesse is introducing me to Inventor slowly and gently. It is quite the program eh? I like the way you can activate the whole changer finger assembly and move it like for real and make sure no part hits the other. Awesome stuff!

LOL, I was just having a wee laugh at your expense Bent. Truth is, I have no idea what 'Inventor' is. I use a really basic and simple CAD program for most of my drawings. It is called AutoSketch. The newer versions are not actually very good but the one I use is V2.3. It doesn't do animations. I do that in another program using the drawings from AutoSketch. (Animation Studio)
I am gonna go and look into Inventor however, I do like the sound of it.

Regards, Allan.....

[Georg]

That "rod-through" Blanton-variant isn't designed right, and takes up much too much space sideways.

1: the screw should be "in front" - towards the changer (same as on the original Blanton), so it doesn't take up sideways-space on its own.
2: the nut should be steadied against the bellcrank body, so it can't twist around at all even if there's no rod going through the hole.
3: only the "rod-puller with the hole" part on the nut should come out sideways, in such a way that the rod is kept close to the side of the bellcrank body. There should be only a slim millimeter passing-distance so a tube can be put on the rod as part of a pull-point.
4: depending on the strength in the material used, the bellcrank body should be made as slim as the adjustment-screw, except for at the very top and bottom where a) the adjustment-screw goes through and the bellcrank is clamped/screwed onto the axle.

This will result in a Blanton-variant that is almost as slim as the more regular "90º bent hook-up" ... one that will make optimal use of sideways space and let let rods to/from other bellcranks pass in line with its own pull-rod.


Which type of bellcrank that is "best" is not important, IMO. They all have "built-in" strong and weak characteristics.

Mechanical and "tuning" optimization is more important than "uniformity", so I'll probably use the "split" bellcrank that Eldon describes whenever/wherever it gets the job done, and put in a "90º bent hook-up" or a "Blanton-variant" where either of those will work better - allow for finer adjustment etc. Doesn't really matter which one is used where if they're all made to fit on the same axle-type/shape in the same PSG, and can be put in and taken out without removing the axle.

[Bent]

Georg,
Of course it's not designed right. It was just a prototype variant, shown how it can be done. Now you take this idea and improve on it. Make your own and show it off here. That way your contribution is a real one, instead of ending up just criticizing.
The nut , like I said was for illustration purposes only. It did, however, address your suggestion of offsetting the pull from the space for the passing thru rods.
4: Yes agreed

Looking forward to your variant of the same crank

Its all about contributing....

[Georg]

Bent, I'm not criticizing, at least not in the negative meaning of that word. I'm only trying to contribute in a constructive way - using words.

Sure, I can buy another copier - one that will cooperate with my PCs - and present drawings, or I may start using CAD/CAM again and present even nicer drawings or working prototypes - haven't used CAD/CAM for more than a decade.
As things are - for reasons that have nothing whatsoever to do with steel-building, I may never do either, and may never build, or even really play, a steel or any other instrument again in my life.
If you think that excludes me from contributing here in the way I can at the moment - with words, then just say so

[Bent]

Georg, Critique is A-ok. Criticizing is different and that's how your first line came across: Since you and I both knew that this "design" of mine was illustrative only, I felt it a bit harsh of you to say that things weren't designed right, because, of course they weren't and everybody knew that. I spent a few hours making my contribution, something that you, or any of us here have the opportunity to do as long as we have a digital camera, a file and other hand tools if they care to do it. If they don't care to do that, then maybe words should be weighed more carefully.

I said nothing about your method of contribution, just the seeming lack of it in this particular instance. I would be the last to suggest that your method of contribution should exclude you. I never said that either. Your participation on this and other steel sites is certainly of great value.

With all this said, I want to extend an apology to you for my flying off the handle over this. It's easy to misinterpret sometimes; when the only thing between us is the typed word on the PC screen.
Friends?