Sierra Bellcranks and 3D printing experiences

[Michael Whitmire]

Greetings all,

I thought I'd share a little project of mine that I just wrapped up. First time making PSG parts but no stranger to mills, lathes, and metalworking since I'm a fabricator by trade. Just too lazy most the time to do things like this! I'd rather be playing then making parts haha. But since I had a nice hole added to my foot at a slick boat ramp with a lovely 3/4" bolt sticking up randomly on the ramp in 2 feet of water... I had time and motivation to bust this out.

Anyways here's my Mill.

Mill.jpeg

I got this old girl for my other hobbies and other things. Mainly hotrodding and motorcycles. She's not the most precise and she's a bit worn. When I first got her, she got a full teardown and I had to clean all the ways, dress them up, and mess with the gibs a bit. It was stored outside under a tarp for many moons. If you're careful with her now, she'll hold a thousandth tolerance! Still runs off her original three phase motors! Everything was rehabbed. Anyways, back to the relevant parts to this forum.

Bellcranks.jpeg

Here are the finished bellcranks. Anyone who knows older Sierra steels, knows parts are like picking hen's teeth. Ignore the bad surface finish, my fly cutter needs resharpened and I was not into regrinding this time since these are for me and I'll hopefully be the only one looking at these, minus here.

Shavings 1.jpg

All the shavings from making seven of these. I'll gather them up later and clean the mill more later.

Bellcrank and 3D one.jpeg

And here's one of my 3D printed bellcranks at the bottom. For anyone wondering why 3D printed ones are not as common yet, I'll share my experiences trying to make this style to work.

Clamping is an issue with round rods. Near the end of my testing, I managed to get 80% (estimated) of my 3D printed ones to bite. The problem next is when you want to move them, they'll no longer bite again as the inside becomes flattened and smoothed too much. Plastic gripping stainless equals slippage. Trying to tighten them more to compensate does not improve the bite and leads to breaking eventually. And yes, they were printed 100% filled. When you do get the right bite, they're only good to a half tone raise/lower. Somewhere between maybe 3/4 to 7/8 of that move leads to it slipping and then it never bites right again.

I could see 3D printed working excellently on square or hex shafts, it's not the bite that matters, but the fact forces are now leading to compression. With correct and intentional printing practices, the Z layer wouldn't be a factor and filaments now a days are much better than they were years ago. But for round shaft steels, they just won't work.

Next is material. I've not tried any carbon fiber filaments as I do not want the risk of these fibers getting inhaled or embedded in myself. If you're not aware, CF filaments are fine enough to get lodged and not be removable by your body's natural processes. It's not as much as a concern on your skin as you shed and eventually, you'll shed those strands out. But they can and do become airborne during printing and possibly when handling. Once in the lungs, they can become trapped and create issues like asbestos. This is why all CF parts should be sealed by a clear coat or similar coating to prevent this. I choose not to use them as of now until further research is fully conducted, but the risk has been documented and slightly researched. So, use those at your own risk.

Anyways, first up is PLA. Very strong and easy to print. All these filaments have the grip issue, so I won't discuss that going forward. Playing outside leads to tuning stability. Inside it's not an issue, but outside temps in hot weather, you'll notice raises going flat and lowers going sharp. Every five minutes needs a tune up to compensate. Over time in a climate-controlled area you'll have creep set in depending on your playing. Parts were noted to have slowly shifted over time. If it's strictly an inside guitar, PLA would work fine and may need parts reprinted after maybe 2 years? Maybe longer depending on seat time.

PETG. Just no. It's impact resistant, but too flexible in anything reasonable for bellcranks. Changes will be inconsistent. Depends on how you hit pedals and levers. Unless you use the same force and speed every time, you'll probably notice it. Grip is horrible. Sorry I know I said I wouldn't mention that, but this stuff grips like 1% of the time enough to be useable. It's truly that bad for round shafts. Then you hit the other issues. Outside, no clue, never made it that far.

Nylon. Works but unless annealed and has absorbed moisture after printing, it's an issue. Playing aggressively leads to breakage. Better then PLA minus impacts of fast moving changes.

ABS/ASA. This is where I settled on, just ASA. (Difference mainly is ASA smells less and has more UV resistance then ABS.) Excellent impact resistance, heat doesn't really affect it, and creep is very minimal. Notice in the picture it's larger and the radius at the bottom. It's strong until it starts to flex. Once it flexes, very brittle and breakage happens. It'll give a smidge, but once that smidge happens it'll fail fast. Once I arrived at the appropriate dimensions, forced failures would happen ether at the Z layer or between all layers. Noticed I said forced failures, playing conditions arrived at this being a great design. Forced failures were at unreasonable playing conditions that I'm pretty sure would wreck your guitar other than the bellcrank. The downfall to this was grip on a round shaft!

In conclusion, it's why I went to making these out of aluminum on the mill. I think 3D printing can and will have a role, but in this scenario, aluminum is the superior choice.

Thanks for reading!
Mike

[Jon Jaffe]

Could you put a set screw that would engage the round shaft without putting to much stress on the moment arm of the bell crank?

[Michael Whitmire]

Could you put a set screw that would engage the round shaft without putting to much stress on the moment arm of the bell crank?

Perhaps. I did not try that. From experiences though, I don’t think it’d work without a flat being ground in the shaft. Similar to how I believe Franklin guitars are.

To note too, I used heat inserts for my Bellcranks. All the inserts were in tension so tightening made them want to dig into fresh material not affected by the heat.

If you wanted to try that route, I think it’d be best to make a pocket for a nut in the bellcrank. Then just add a line of code to pause the printer at the top of the pocket, insert the nut, and resume the print to encapsulate it. Heat inserts are great when you’re not pulling them the same way they went in. Otherwise they lack holding power in the plastic.

[Max Lee]

Those look sharp (figuratively and literally)! How many setups did these take and what would you estimate the per-piece machining time was? I always justify the cost of making parts myself by waiving the cost of tools and my time, lol.

I also am wary of long term exposure to 3d printing particulate matter.

Unfortunately, I think the current studies show that virtually all FDM printers/filaments tested release VOCs and microplastic particulate matter that can be inhaled[https://www.epa.gov/chemical-research/3 ... search-epa]. ABS being worse than PLA, PM-wise. Add onto that the teflon/PFOAs in the tri-flow lubricant folks on this forum like to use and I'm sure I've already got a credit cards worth of plastic floating around in my body .

That said, the dose makes the poison. I'm not sure the exposure to solvents, resins, cutting fluid, welding fumes, etc from fabrication do any less damage!

[Michael Whitmire]

Those look sharp (figuratively and literally)! How many setups did these take and what would you estimate the per-piece machining time was? I always justify the cost of making parts myself by waiving the cost of tools and my time, lol.

I also am wary of long term exposure to 3d printing particulate matter.

Unfortunately, I think the current studies show that virtually all FDM printers/filaments tested release VOCs and microplastic particulate matter that can be inhaled[https://www.epa.gov/chemical-research/3 ... search-epa]. ABS being worse than PLA, PM-wise. Add onto that the teflon/PFOAs in the tri-flow lubricant folks on this forum like to use and I'm sure I've already got a credit cards worth of plastic floating around in my body .

That said, the dose makes the poison. I'm not sure the exposure to solvents, resins, cutting fluid, welding fumes, etc from fabrication do any less damage!

Thanks for the compliments!

To do all seven, it had taken roughly a day of work. I'd say probably an hour and twenty a piece from aluminum flat bar to finished part. This factors in a lot of coffee breaks and other distractions. The bulk of time was setups. Each feature was it's own setup. I do not have a DRO on my mill so repeatable setups were done with the dials and a dial indicator.

With a DRO, I'd probably shave a lot of time off each one. Easily a third of it.

The microplastics and VOCs I'm honestly not as worried about. Drinking bottled water adds a bit of that to the body haha. The only thing I'm wary on is the carbon fiber strands in some filaments. The fibers are fine enough and easily get kicked up in the air from Carbon Fiber Filaments like PA612-CF, and being so fine your body can't reject them once in the lungs. They get stuck there permanently, and carbon fiber will do a number in the lungs. If I could clean it enough after printing to guarantee none of that, I'd probably use them and handle with a respirator until they're sealed for good.

They'll for sure do a number over time in the trades. It's why I always use a PAPR system or good old 3M respirator if the PAPR isn't working. Plus summer time, PAPR feels like AC on those hot days!

[Michael Whitmire]

Update today.

Yesterday evening I had pulled apart my Sierra. Then I got all the new bellcranks installed.

Undercarriage 1.jpeg

Undercarriage 2.jpeg

If you notice I had also recently made a vertical for this guitar. This was an 8x4 originally. Now it's an 8x5. I'm not sure if this is the original design for the Olympic series, I had copied the design off another Sierra of mine. But this is how the vertical is suppose to be on a later U14 Stafford Elegante. Works great still. Later on I'll grab a picture of the lever installed once I get it back together and set back up.

E9 side now has 5 pedals working it instead of 3. First pedal is now a "zero" pedal followed by standard ABC and then P5. C6th side is same as the guitar was made in 78 being I'm not a very good C6th player. Once I learn it more and better, I might add some changes there. But ABC being moved over 1 is more comfortable for me and P5 is easily reached without hitting the knees by accident.

Brass Tuning Caps.jpeg

Next was making the pull rods. I stuck to how the Sierra's were originally made. No mix and match or having multiple tuning keys for one guitar.

Pull Rods Complete.jpeg

Completed pull rods. Just like original. Made all the parts including the bushings. Also previously made the eccentric cam for the vertical as seen in the first two pictures.

Now today is the day where it all goes back together and readjusting all the pedals and throws. I also need to make a half stop then.

[Jim Palenscar]

The later versions of the bellcranks did have the two sides joined at the top so you could employ the use of a slot cutter which might lessen the amount of time.

[Michael Whitmire]

Final update.

All done and rods setup. Also excuse the dog hair. My big guy decided he had to help by laying right to where I was working. He's good moral support but messy with his coat!

Undercarriage Done 1.jpeg

Undercarriage Done 2.jpeg

So Sierra originally used aluminum bars with two holes drilled and two shaft collars to create pulls if you used up all your changer holes. The new pull would go in an adjacent opening in the changer but omit the nylon bushing from the tuning cap to the finger. The shaft collar would grab and activate a pull rod where you wanted your change and pull the rod only. That's why the open finger design on Sierra's is great. If the bellcrank bushing was contained or fixed, you would not be able to do this.

Since my changer is a 2R/2L, I came up with ether a nifty or bad idea depending on long term use. My vertical lowers 6 a whole tone and P5 now also does this too. But my zero pedal now also lowers 6 a half step. So 3 lowers in a 2 lower changer. Being my bellcranks are right in line, I did this for a tandem pull so string 5 and 7 do not get congested with rods if in the future I want to add changes to them.

Tandem Block.jpeg

I can adjust the slack between them by rotating the shaft collar. So far it works great being it's adjust up now. Later on I might knurl the shaft collar to make adjustments easier but if this works and requires little to no adjustments then I probably won't then. The nylon block is just a T basically. It can only slide up and down and fits inbetween the slot of the bellcrank.

Half Stop.jpeg

And here's my take on the half stop assembly as I've read in the tech manual somewhere. My Sierra's don't have one to copy, I cannot find any pictures of one, and I haven't managed to find a forum post detailing one.

It consists of a normal pullrod assembly omitting the nylon bushing for the finger and instead has a shaft collar that is not fastened tight so it can slide. The shaft collar is just big enough to hit the combs of the changer and not the fingers themselves. I bundled 3 springs to get some type of feel on it. On the bellcrank end, slot 3 is the normal whole tone lower and slot 4 is the half stop rod. I'm not impressed but it works like the manual says it should. An adjustable feel stop that is adjustable at the changer. I've never had a half stop, I adjusted it to where I just feel some type of resistance which puts string 2 close to D. Dropping to C# doesn't feel like much more is added. It's not definite for the feel. A quick tap to lower 2 to D and it would be easy to miss the feel of it and overshoot. Maybe stronger springs would help or maybe this is how they typically feel? Either way I'll probably mess with it more later then just train myself to where D is.

The later versions of the bellcranks did have the two sides joined at the top so you could employ the use of a slot cutter which might lessen the amount of time.

This guitar had the style you describe I believe, and I mimicked that. My Stafford model has the bellcranks with nothing joining at the top and they seem kinda flimsy to me without that small bit of material there.

Would chatter and protentional breaking of the part be an issue that way? I tried running the slots back and forth on the X axis. At a certain point the walls would get too flimsy and chatter and try to pull into the end mill for me. I ended up plunge milling the slots in mine which worked well. Hogging out the whole slot by plunge milling toke maybe a minute per one once I had the starts and stops setup going a third of the end mill diameter each plunge.

Also by chance did you get my email regarding used foot pedals for Sierras? I seen you replied by PM and I emailed you as requested. Even though I'm happy now with this setup, I'd like a spare pedal incase I want to make it an 9x5 with a true zero pedal.

[Jerry Overstreet]

That is some nice work there Michael. That all looks great. You are quite the craftsman. I wish all this had been around when I had My SE14. Would've saved me a lot of handmade stuff.

Concerning the half stop, you probably already know this, but the Sierra Technical manual is still archived with diagrams at www.steelguitar.com

[Barry Coker]

Nice work and well thought out.


Barry