Mild steel vs tool steel vs brass (with stainless balls)

Hi guys, I was just wondering if you had any thoughts about making sandwich plates out of brass, instead of mild steel? I understand that whatever material you use for the plates should be softer than the ball itself.

I imagine tool steel is used in conjunction with mild steel in single axis joints, no? I had a look at how julian clark does his single axis joints, and it appears to be a sort of ball joint hybrid design with an axis limiter plate on it.

The main reason I ask is: brass is soooo much easier to work with for me. It feels like a much more organic process shaping it, as I can do it easily with hand tools, as opposed to steel - which I have to use a mill for. (however, I do have access to a milling machine and lathe, I'm just not particularly good at using them).

Or does the brass wear out too fast?

My other concern with brass is stripping tapped threads on tensioners. Do you need a bolt system that goes through and into a steel nut on the other side? If this is the case, I guess mild steel may be a better option.

Is it possible to braze brass and stainless steel together?

Thanks in advance!

 

Harrie

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Brass will wear out faster than steel. But, that's not to say that it won't last long enough for animation purposes. The primary restriction that brass adds to an armature design is that it limits how small the joint can be. With a standard double ball joint I usually don't go much smaller than about a 3mm plate thickness. Small hinge joints can also present problems if the tongue is too thin which can cause the material to flex too much or even shear off from the bolt. So I imagine either mild or tool steel is used more often for hinge joints for that reason.

As for stripping threads, I have had it happen before, but it's usually not a huge concern. The main problem that I have had happen with brass threads is from brazing near any section of threads. I don't usually braze too hot, but with the really thin threads of m2 - m3 even at low temps I've had the brass warp/melt enough that threads become unusable and need to be re-tapped or tossed. I tend to prefer having a nut on the other side since it's not only stronger than the brass but also just allows for more material to be grabbed onto by the bolt.

Honestly, I don't see any problem with making entire armatures out of brass. I would suggest reading Sven Bonnichsen's blog posts about the brass armatures he's made. I don't remember a lot of the details of it now, but I remember that he often reports on the limits of materials and designs at times and has useful insight in general regarding armature designs/materials/etc.

And I believe it is possible to braze brass and stainless steel together. High strength (high silver content [in the 50-60% silver range]) silver solder is probably the best option for a good joint between the two.

Thanks Ethan! Will google his blog.

Just spent an hour on the phone with my dad, who is a mechanical engineer. I'm building my studio on his property next year and will have access to his workshop. He said he'd teach me how to mill and lathe, so a whole new world of possibilities just opened up.

We talked briefly about making single axis joints out of tool steel sandwiched in mild steel, so I assume this will be possible too.

I think I'll see if I can pick up a copy of "Stop-Motion Armature Machining" by Tom Brierton, as I'm starting to discover quite how deep this rabbit hole truly goes.

Here's Sven's blog: http://www.scarletstarstudios.com/blog/

I think if you search it for Armature you can find all of his armature posts. Or possibly just find one and click on an Armature tag under it, don't remember if it uses tags or not. 

Hmmm - nope, looks like the only relevant tag is Stopmo: http://www.scarletstarstudios.com/blog/archives/movies/stopmo/

Here's a link to a search for Armature: http://www.puddingbowl.org/MT/mt-search.cgi?IncludeBlogs=13&sea...

It's more to the point, but no pictures! 

Thanks man! That blog has a lot of good stuff on it. The ball drilling jig etc.

Been looking at a few other blogs too.

Hi Hendrikus, 

The first metal armature I made in the States used brass plates.  I had been taught to use bronze when I was an apprentice, but when I got home I couldn't any source for bronze in dimensions that worked (I still can't; I buy bronze sheets and have a shop cut them up for me).  It works, but, like aluminum, brass will "gall" over time, and the quality of the movement will be noticeably (and increasingly) poor. And yeah, it's softer then one would like.  There is a workaround, however; you can "tin" the contact areas (with pure tin) and use lubricant to improve things and get an acceptable result.  When you tin the plate areas, once the solder has flowed you simply tap the piece against something to shake off the excess, leaving a thin, conforming film.  Then, making a semi-dry lubricant from powdered graphite added to a little Vaseline, you can can add a little of the goop to the plates prior to assembly.  It should do the trick.  If you get a chance to use bronze, by all means do. 510 phosphor bronze; it'll change your life... ;)

Ted,

trikfx.com

P.S. Yeah, all copper alloys love steel.  That's what brazing with silver is all about; making those dissimilar metals play nice.

I've been using brass sandwich plates with steel ball bearings from the hardware store recently, brass is much easier to work and so far it hasn't bent and the threads have held up just fine. I could definitely imagine brass bending or striping under a really heavy puppet or really high tension but it hasn't given me any issues yet so I'd say it's definitely worth trying. 

I like brass and aluminium because I can cut them with my bandsaw, unlike steel.  But I use aluminium more often than brass, because it doesn't rot the latex that I usually use, and because it is lighter in weight.  You can cover the brass joints with cling wrap to keep the latex out, so that is not a deal breaker - in fact you want to keep the joints clear whatever you cast in.

I did find there was a problem with brass for very slim joints.  I had a character with thin arms and legs, that had been animated with a wire armature.  It was the main character in a series, and was due to be re-made.  A friend offered to make a jointed armature to fit my mould at a good price.  But the brass knee and elbow plates had to be ground down so fine, to fit in the mould, they couldn't hold tension.  His own characters were chunkier and he had thicker plates that were fine, but my character had been sculpted over armature wire and didn't have room for chunky joints. One knee broke when I had to tighten it again in the middle of the very first shot.  Then the other knee, and an elbow.  I never got a usable shot with it, and re-made the puppet with wire again.  The threads didn't strip, it was just the ball bending the brass plate out when the tension screws were tightened, and that was purely because there wasn't enough meat left on it by the time it fit into the mould.

Hi Nick!
I too had problems with brass giving out under tension (aside from the galling issues), but the 510 bronze I use is steel-like in its strength. To solve the rot problem, I spray the armature in a simple coating; Sprayon 322 silver vinyl coating; http://www.sprayon.com/product-categories/industrial-specialty-prod...
Cheap (6-7 bucks a can) and works great, if you ever have copper based alloys to deal with.

Best,

Ted

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