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Curta Calculator Scale Replica

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racer8412

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As a beginner to metalworking and machining I've taken on the challenge of creating a scale replice of an original type 1 Curta Calculator, I will be providing documentation, pictures, resources and tips along the way for anyone interested in the project or wanting to make their own. Solidworks part drawings https://drive.google.com/drive/folders/12UV_sGF0ronaqxmvK0PDOdtrl5kVPG28?usp=sharing not all drawings have been remade still working on the last few parts.
 
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Robo_Pi

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Fantastic. I'll definitely be following along. I'll try to build one along-side you if possible. I use Fusion 360 now so I'll see if I can open those solidworks drawings in Fusion 360. Thanks.
 

racer8412

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You can also use eDrawings in order to open them if necessary.
 

racer8412

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Most parts are made of aluminum, phosphor bronze, stainless steel, and nickel silver, the exact material is listed in german on most of the drawings. IMPORTANT: ALL MEASUREMENTS ARE IN METRIC
 
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racer8412

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Im also uploading the original part drawings in pdf form, they should appear soon in the drive repository.
 

Winegrower

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This is an unbelievably heroic undertaking. I have many times wished for one of these. This will be a fascinating thread...
 

Robo_Pi

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The following video is golden for anyone who is interested in how a Curta Calculator works.



 

Robo_Pi

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Done machining all the parts?

Good. Now assemble it,...

 

ch2co

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Best of luck to anyone who attempts this endeavor.
I stumbled upon a Curta type II at an estate sale and felt very guilty paying only $20 for it. Nobody knew what it was except for me who had been drooling over one ever since I worked for a surveyor back when I was 17. (Around 60 years ago). The condition of mine is perfect except for a tiny ding in the storage case. I still can’t see how someone in a German concentration camp could dream this thing up in his cell and then start manufacturing them soon after the war was over. They are AMAZING! And are now worth in the thousand plus plus dollar range. I will be watching your efforts as you proceed on this monumental task. Best of luck.

Chuck the grumpy old guy
 

ch2co

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Whoops, it’s a Type 1. Serial number shows that it was made in Oct. 1952. 4000 of them were manufactured in 1952.
Chuck the Grumpy Old Guy
 

Robo_Pi

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I'm emerald with envy Chuck. Can you post a photo of it and make me drool even more?
 

rgray

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I stumbled upon a Curta type II at an estate sale and felt very guilty paying only $20 for it.
I would give you a $100.00 for it just to make you feel better.LOL
 

ch2co

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I would give you a $100.00 for it just to make you feel better.LOL
I don’t feel quite that bad about the transaction. It would take about 15 times your offer before I would start thinking about it. But then maybe a little more.
Postage would be included though! :laughing:
 

Robo_Pi

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I'd like to have an old busted up junk one. Something I could take apart so I can look at the parts first hand. I wouldn't want to have pay much for it though.
 

ch2co

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This is ridiculous. I just finished reading Robo Pi’s
last message and turned back to what I was doing before this whole conversation began. And that was looking up Mahlers 7th Symphony because I never cared for it even though I love many of his other symphonies and a friend suggested reading an internet discussion that he thought was interesting and.......Anyhoo, I was presented with a YouTube page the top item of which was assembling a printed Curta Calculator! Weird! Here’s the address.


The thing is rather large and couldn’t really be called a handheld, but possibly interesting to some of you that have printers.

By the way, the first movement of Mahlers #7 just doesn’t please me. His Sym. 2 on the other hand is my favorite work in all of classical music. I’m now listening to another favorite musician, Tom Waits.
 

ttabbal

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I've thought about building a printed one. Then I got into metalworking...

That 2mm shaft sounds like a bear though. 4x upscale? :)
 

Robo_Pi

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Machining the parts for one that big would be a lot easier than trying to replicate the original size. The one we're hoping to build is next to impossible to build because of the microscopic size of the parts. But hopefully we'll give it a shot. We're going to need to be clever. No need for a Briidgeport mill on this project.
 

rwm

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I double-dog dare you....
Robert
 

Robo_Pi

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I double-dog dare you....
Robert
You'll have to double-dog dare Racer. I'm just a pain in the tailstock going along for the ride. :grin: :grin: :grin:
 

ttabbal

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I might have to cheat and use the CNC router for some bits. :D

Bridgeport and PM1127 here, neither lends itself to micro parts. Maybe I should use them to build a smaller lathe and mill... :D
 

Robo_Pi

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Maybe I should use them to build a smaller lathe and mill... :D
I've been thinking about this myself.

I might have to cheat and use the CNC router for some bits. :D
I confess that I've been thinking the same thing. Especially for the setting shafts part# 10061 it's begging for a CNC machine.

Like you, I thought of making my own micro mill. Then when I saw the setting shaft I instantly thought that I could automate this using an Arduino and stepper motors to control the micro mill.

Then I just realized that I will have built a CNC machine.

Can't blame us. Who wants to sit there a mill a thousand dimples when an Arduino would do it with no complaints. Then I could go work on my '47 Chevy while the Arduino drills the perfectly spaced dimples. :grin:
 

ch2co

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Yeah, but that takes all the fun out of it. :laughing:

I’m just too old to even think about taking on this complex of a project. I can see a LOT of time needed for this job. Kudos to any and every body who proceeds into this endeavor. Go get’em!
 

Robo_Pi

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Yeah, but that takes all the fun out of it. :laughing:
In that case when I get the setting shaft blanks cut to size I'll send them off to you for dimple drilling.

My donation to helping a grumpy old guy have some fun. :grin:
 

ttabbal

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Be careful, I tried to volunteer @mikey to make everyone's HSS tools and we ended up with a huge thread. And I ended up getting decent at grinding. :)

Maybe I should volunteer him for this too... I know he has a Sherline...
 

mikey

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Nope, don't even think about it. A Sherline is the right size for this and it is precise enough but you have to WANT to take this on and I DON"T! It would be an awesome project, though. :)
 

Robo_Pi

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We better quit. We're filling up Racer's project thread with silly chit-chat. :grin:

Just want to extend a gracious thanks to Chuck once again for sharing the beautiful photo of his awesome Curta.

Now everybody get back to work and find some dimples to drill or something.
 

rgray

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Swiss lathe parts for sure.
I've been following a few on auctions.
Every once and a while one sells in my price range.
I'm probably more worried about the learning curve to run one than anything.
 

Robo_Pi

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Racer has agreed to accept my proposition to be one of his mentors. I live in Pennsylvania, USA and he lives in Flordia, USA. So I won't be able to mentor him live on how to correctly operate any machines he might use. Hopefully he can find someone in person to help with that end of things.

What I am going to offer are lessons on how he might take on a project like this. My plan is to just start making some parts. He'll need to make all the parts eventually so it really doesn't matter which parts we start with. I've chosen some of the more difficult parts to start with.

Racer is under no obligation to actually follow my mentoring suggestions. He can also continue to seek other mentors and input from anyone else at any time. In fact, I encourage that. All of my mentoring will be suggestions only. So Racer is free to decline my suggestions at any time.

My first suggestion is to hold off on buying any machines or tooling for now. There is much that will need to be done before any actual parts will be made anyway. As I see this project there will also be two main categories of parts.

1. Larger parts that can actually be made on standard size machine shop equipment.
2. Micro parts that are going to need special techniques to make.

My proposal to begin is to consider a single part. We going to consider making the transmission gears. These are "micro parts" that will be extremely difficult to make. In fact, I think that making these transmission gears can be a real test of whether or not it's worth moving forward on this project.


Here are the parts.

Part #10038 Transmission Gear I (20 required)

10038 Transmission Gear I.JPG

Part #10053 Transmission Gear II (22 required)

10053 Transmission Gear II.JPG


This is a total of 42 gears. I don't know about anyone else, but I'm not going to sit around trying to machine out 42 micro gears by hand. :grin:

Not only this, but if I build one of these things I want to tool up to be able to make more than one of them.

So my proposal (and that's all it is at this time) is to make punch and dies to punch these gears out from sheet brass. Making the punch and dies will be the machine shop work. We are still going to need to machine these gears. Potentially four times. Once for the punch profile, once for the die profile, and we'll probably need to do this twice to make separate punch and dies for the above two gears.

What's the difference between part 10038 and 10053? Thickness. Period. I double checked this by laying the two drawings over each other. The drawings are identical in terms of gear profile. The only difference is that Gear I is 0.5 mm thick, and Gear II is 0.6 mm thick.

Because of these different thicknesses we may need to make special punch and dies for each gear.

This is where Racer comes in. :grin:

His mission, if he should decide to accept, is to design the punch and dies to punch out these gears. We need to have them designed before we even start machining anything.

So here's my proposed homework for Racer:


Assignment:

Download and read this 16 page booklet
Stamping Basics

If you have a printer print out the 16 pages and put them in a binder. You'll find this information useful for future operations. This will be a good place to keep all your notes and calculations as well.

Detailed Study:

Read on pages 2 - 3 the sections marked:
Punch Press
Simple Die
Compound Die

(You will need to design a compound die for this)

Read and take note of all the different types of Punch Operations
Page 7 - Stamping Terminology.
(for now we will only be using a "perforating" operation)

Read also on page 7 - Perforating

On page 8 copy the Perforating Pressure Formula information
.
(You'll need this to make your calculations)

On page 14 read
Shear Angles
(this will just give you some understanding of the different types of cutting edges a punch can have. You don't need to understand shear angles at this time. Just be aware that they are important)

When you're done with this we can move forward to the next stage which will be a second homework lesson concerning the design of punch and dies. You'll need to calculate punching pressures, and required clearances, etc.

Let me know when you have completed the above homework and I'll give you the next homework lesson.

Note to Racer: This all assumes, of course, that you agree with my proposal to punch out these gears. If you have another manufacturing process in mind, then you'll need another mentor. :grin:

Note to other Machinists: If you have a better idea of how to make these gears by all means chime in. I am in no way suggesting that my ideas are the only way to go, nor the best way forward. All I know is that I'm not about to sit down and try to machine out 43 micro gears individually. So this is my proposed solution. And just for the record I did think about cutting all the gears at once on a shaft, and then parting them off individually. The problem with that is the key in the center hole. You can't just drill a round hole through the stock. You need that triangular key. So it has already been suggested to me that after machining the rod and parting off the individual gears, I would still need to punch out the center hole. So why bother with double work? Why not just punch out the whole gear in one fell swoop and be done with it? The gears can then be deburred in a tumbler with the correct grit medium. That's my proposal. If you have a better idea that isn't CNC or Laser Cutting, by all means offer it up.


Second note to Racer: Don't worry about machining. You'll need to machine the punch and dies. So you'll be machining these micro parts. You'll have ample opportunity to be machining all sorts of things as a tool and die maker.
 
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