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Address various issues with Bernina B740 Sewing Machine
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epriestley
Dec 3 2022, 6:51 AM
Referenced Files
F11407481: Screen Shot 2022-12-02 at 11.13.04 PM.png
Dec 3 2022, 7:36 AM
F11407478: Screen Shot 2022-12-02 at 11.13.33 PM.png
Dec 3 2022, 7:36 AM
F11291992: Screen Shot 2022-11-03 at 4.23.07 PM.png
Dec 3 2022, 7:07 AM
F11407474: Screen Shot 2022-12-02 at 10.56.51 PM.png
Dec 3 2022, 7:07 AM
F11407472: 416466601.jpg
Dec 3 2022, 7:07 AM
F11407468: Screen Shot 2022-12-02 at 10.48.41 PM.png
Dec 3 2022, 6:51 AM
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Description

The Bernina B740 is a sewing machine that goes "whirrr" and sometimes "thunk thunk thunk thunk thunk". It can sew different kinds of truck and animals, including a turtle:

Screen Shot 2022-12-02 at 10.48.41 PM.png (460×1 px, 138 KB)

You can not order replacement parts for the B740.

Event Timeline

epriestley triaged this task as Normal priority.Dec 3 2022, 6:51 AM
epriestley created this task.

Turny Thing

See also T13689.

The B740 has a turny thing. It looks almost like this:

416466601.jpg (585×585 px, 18 KB)

The outside is perfectly smooth to make it difficult to turn. If you turn it too hard, oof:

Screen Shot 2022-12-02 at 10.56.51 PM.png (599×447 px, 428 KB)

This wheel appears to be sturdier and is easier to turn:

Screen Shot 2022-11-03 at 4.23.07 PM.png (671×1 px, 1 MB)

String Shelf

When sewing, you need a lot of different string. Bernina sells a Bernina String Shelf.

They do not list the price, but these shelves sell on eBay for about $100.

This is just a shelf for string and costs $100. It seems like it should be possible to build a shelf for string for more like $75 in materials and 40 hours of labor.

String Shelf Shelf

The sewing machine sits inside a Very Nice Table that I don't want to drive any screws into, so I started by making a String Shelf Shelf for the String Shelf to rest on. This is a sort of clamp that can squeeze a ~120mm strip of tabletop to the right of the machine:

Screen Shot 2022-12-02 at 11.13.33 PM.png (574×731 px, 171 KB)

The left part is printed twice. The actual shelf is a piece of plywood that goes between the left parts and the middle part, which I drove some M5 threaded inserts into. The final dimension of the plywood is 120mm x 130mm and I should probably just have printed this part instead of making four different sub-assemblies, but I haven't used heat-set inserts yet and I'm not sure if they're trustworthy or not.

Overcome with hubris, I hand-drilled the holes in the far end of the plywood to attach the clamping face and the bit wandered enough to throw the piece significantly out of square. I needed to reprint it anyway since the clamping action wasn't quite right, so I measured where the holes ended up and adjusted them in the model -- the one on the left went down 0.6mm, and the two on the right went up 0.5mm. Then I printed the asymmetrical "as-built" piece with the other adjustments. This felt horrible but worked well and fixed the squareness issue.

I put some of this CatTongue Grip Tape on the inner surfaces of the clamp and it seem to work pretty well: when you wiggle it, the table moves.

String Shelf Stick

I'm using 24" T-Track to create a vertical rail for string. It's bolted to the String Shelf Shelf on the bottom, and capped on the top since the aluminum corners can be a bit sharp/dangerous:

Screen Shot 2022-12-02 at 11.13.04 PM.png (802×636 px, 218 KB)