How to measure a part?

Machine Shop
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{EDIT}
update.
I meant EXTRAPOLATE, not DUPLICATE (words mean things, sorry.)
How it started:

goal
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How I measured:
Calipers vs. Scan.
Outcome- roughly the same, and seems to be in the +/- range of the original part.

image
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How it’s going:
I have a prototype of the cam profile ready to cut on the Shapeoko3.
The cam profile is cut to the outer tangent of the tool, while the inside is cut to the inner tangent of the tool.
I extended the length of the key slot to accommodate the radius of the tool, so the width of the slot is the same. The length of the slot will not matter to the machine.

carbidecreate
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I hope to cut/test in the next few days!

[[OLD POST]]
I’m looking for articles/videos showing how to accurately measure a cam so I can duplicate it(edit i meant ‘extrapolate a new cam profile from this existing profile’).

I have this one cam from a rare sewing machine. I would like to measure it and make my own cams.

I have digital calipers, but it seems if I move slightly, the measurement changes. So I’m looking for best practices when taking measurements on a piece of precise machining.

PXL_20230429_144402049
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Don’t use calipers (especially digital ones) for accurate measurements. Calipers are usually off by .001 (1 thousandth). You need to use a micrometer for an accurate reading.

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Amelia,

That is a complex part; machining one will be an involved task. I would look into making a mold of it and casting it. That should duplicate the intricate dimensions correctly within a few .001s. The center hole needs to be accurate. If the center hole is cast a wee bit small, it can be very accurately bored to the finished size required using a boring bar on the lathe or mill. The original piece was likely a cast part. At DMS the jewelry/small metals committee has members that do castings; some one within that group will be able to advise you on the feasibility of casting it.

Regards,
Bob

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As an aside; I’d love it if some of the Machine Shop people way smarter than me could come together and create a ‘how to measure stuff’ class or document some pointers to videos/educational materials on that topic.

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Amelia,

Here is a YouTube tutorial illustrating a casting technique; still the folks in jewelry/small metals may have a better method and the tools and supplies to support it.

Regards,
Bob

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I’ve only just started getting into machining, but what I’ve learned so far has made me a much more precise woodworker. It’s definitely a transferable skill.

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Amelia, My wife had a quilt finishing and embroidery business that she ran for 20+ years when she retired from IT. Her first sewing machine was a Kenmore sewing machine with 10 cams in 1972. Sewing machines in general do not hold thousands of an inch tolerance in fabric. Your cam has visible nicks in it so extreme accuracy in duplicating it is not needed. Casting is your best bet, just not casting metal in petrobond. Fins require a three part mold and are notoriously difficult to do unless you go to investment casting.
Make a silicone mold of the original, cast the new cam out of a wear resistant polyurethane and call it good. I wouldn’t even bother trying to place a metal wear ring in the reproduction. You aren’t going to use the cam thousands of times. Just cast duplicates. You might want to talk to folks in the Plastics Interest Group on how to degas the silicone and cast the polyurethane under pressure for best practices and results. Heck, you could sell duplicates and recoup some of your costs! :grin:
Best regards,
Jim

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If you would like, I could help show you Thursday evening during Tool Time.

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it’s a 1953 Phoenix 282 sewing machine by Baer & Rempel, this is decorative camstack #3.

Camstack #1 has the zigzag stitch, it will not zigzag without a cam.
So I wish to measure the hat, and create a cam hat so I can zigzag with the machine.

I’ve been using vector programs for a number of years from the graphic design side, so I have confidence in building a vector to cut the profile, but making sure that my initial measurements are correct is key.

Also, in general, I feel it’s a valuable skill for any maker, as @Jerry_Pirkle said.

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If you’re good in that arena, take some very careful photos and have a reference scale in the photo. You’ll come out with some very high accuracy drawings providing you get the photos taken completely perpendicular to the features you want to measure.

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Thinking out loud - wonder if…
3dFab has a scanner. Pretty high res as I recall, Setup includes a turn table and lighting(?). Scans result in a mesh files that can be used to create files for a 3d printer (or?). 3d print, check results, tweak files as needed. Paging @Evan_Lott.

You could machine this. Would need to be done in layers. Long learning curve. A bit of over kill, but…

Often the journey is far more rewarding than the end goal… :smirk:

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Another method is to use a photocopier, scan the cam profile* and import it into CAD (Fusion 360 or Solidworks), scale it, then trace around the image) to create the part.

  • If you scan an accurate scale (ruler), it will help when scaling in CAD.
    Message me if you have questions.
    Send a scan if you like, and I can model it for you.
    Here’s an example:
    https://youtu.be/QeshzlTaq5g
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I agree that casting is the best method, because the cam actually has three levels with three followers to control different actions in the machine. I have an early 1950s Necci that uses similar cams with three roller wheel followers. The zigzag may be simpler but accuracy is vital to keep from breaking the needles since in the needle has got to move up and over while the gripper is moving the fabric an exact distance.

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@AmeliaG can you bring the part into the solidworks class tomorrow night?

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This is an early experimental camstack.

It’s actually a stack of 4 different stitches with only one follower finger, which controls the x axis of movement. It doesn’t control the y axis (forward/backwards feed) at all.

My Elna has cams with feed and needle position control. But this one is older and doesn’t do that.

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I’ll absolutely bring it tomorrow.

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We studied cam design and modeling in watchmaking school. I can discuss the basics but I will run out of my depth very soon . There is some math related to lobe design and the related pitch of the lobes relative to the rotation, throw etc. There is a cam design plugin for solidworks that till do some math for you . Once you have a design we can machine a prototype of it out of delrin or nylon on the shakeypoo3 and measure it up. The completion here is that you don’t just want to duplicate the cam stack you have, but make a new cam for new functions . That will take some math .

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goal
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M1
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M2
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It seems like the a cam isn’t produced in quite the same method as a gear?
As it looks like special attention was paid to keep the length of each flat area the same, even when the radius changed.
Here’s how I was extrapolating the cam profile in Illustrator.
I’m working on learning solidworks and Carbide Create7 now.
I need to:
Verify my measurements,
Verify my methodology for creating the cam profile. And if those are correct, I should just need to deal with the offset to machine a test cam on the shapeoko3.
Gear Method
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To clarify: I transformed the line segments for the inner and outer circles, to maintain the 3.5mm width at the bisect point. The Roots are the same width as the Teeth.

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For those interested, casting in jewelry is only in bronze or sterling silver, and relatively small items. This might be too big for our flasks? Plus you would need a wax or resin model to cast from. So jewelry is not your best bet for this.

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You can scan anything you want on you phone (the app name escapes me atm) and then you can 3d print one. If not you can use solidworks and do whats called a top down design. I can help you if you need help on the solidworks part of things.

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