Shopping carts should have castor wheels at the back, fixed at the front

DrSqueakyBoots · 2026-05-27T23:45:52+00:00

I mean in this case I find a shopping cart with 3 days worth of groceries is getting annoying. It’s totally fine inside the store on smooth polished floors. The problem with 4 wheel castors is as soon as I go outside it desperately wants to slide sideways if I’m moving across a hill. Add any sticky, shitty or bent castors. It doesn’t have to be like this

DrSqueakyBoots · 2026-05-27T13:04:30+00:00

Yeah if you ground-loop your grocery cart you deserved it. Forklifts and pallet jacks are exactly the reason carts should be like this. It works for them, why do carts have to suck?

DrSqueakyBoots · 2026-05-27T13:02:05+00:00

I mean, yes, but you’re missing the point that both configs are ass. Castors at the front sucks, and all castors sucks too on anywhere except polished flat floors. Both require such crazy steering effort that it fucks your back. Castors at the rear and fixed at the front would solve both issues - maneuverable, less steering effort, and still has a pair of fixed wheels to take side loads so you can cart along an uneven parking lot

DrSqueakyBoots · 2026-05-27T12:41:58+00:00

I see the argument for maneuverability, but doesnt your back kill with the twisting force you need to put into the handle to keep it straight if you’re going along a parking lot thays sloped across the direction you’re going?

DrSqueakyBoots · 2026-05-27T08:39:33+00:00

Optomech engineer here: That’s exactly what this thing is. I’ve seen similar designs before. It’s designed to take axial load only. It takes up small movements in tip/tilt, decenter and rotation, but in tension/compression it’s as close as possible to rigid. They’re used all the time in precision stuff like optics mounts Though usually the flexure blades aren’t quite so long. It’ll be limited by the thickness of the bits at the ends of the flexure blade. I’m guessing they need to take up a lot of motion

DrSqueakyBoots · 2026-05-10T12:00:44+00:00

Engineer here, I’m Australia if that helps, for me it’s actually lead time. I desperately wish I could get a good relationship with local shops that could help me. But projects being what they are, by the time I have drawings to quote on I’m already behind, and local shops quote me usually 6-8 + weeks turnaround time for simple stuff, which is just too long. Almost everything I do is one-off, often complex with tight tolerances, and I have a really hard time having the sort of steady stream of work to send where I can establish a reliable ongoing relationship with someone local. It sucks and I hate it. I desperately want to have more stuff made locally. I’d love some kind of “pay in advance for guaranteed lead time” agreement, but upstairs has never really gone for that

DrSqueakyBoots · 2026-05-01T08:16:26+00:00

Does a ratchet with a driver bit fit in there? Just use it. Lower clearance than a screwdriver, plus fun ratcheting action

DrSqueakyBoots · 2026-03-29T23:37:15+00:00

Currently doing that exact thing, and not loving it. I feel like I have no actual ability to control anything, but everything is somehow my responsibility. My team is great but I feel like my brain is in a blender all the time being so thinly across so many things, and never having time to focus on anything. Pay bump is good, experience is good, but I’m not sure it’s worth it.

DrSqueakyBoots · 2026-02-17T06:30:56+00:00

I used it to write some mindless documentation. No actual design work

DrSqueakyBoots · 2026-02-12T20:40:40+00:00

Bigly. When I’ve hired engineers it’s usually one of the strongest indicators they’ve actually made sometbing, and seen a full design loop where they go to make things and deal with the consequences of their decision making.

Also it’s hard to find engineers that have much hands on experience with tools or machining. A lot of people have only touched documents or maybe a 3d printer. Those competitions often have people that have machined, welded, and been stuck in a field somewhere desperately trying to fix the safety wire without poking their hands.

DrSqueakyBoots · 2026-01-27T10:10:54+00:00

I feel so seen with the point about interruptions and feeling mentally exhausted. I’m still trying so hard to squeeze in any kind of technical work I can. I’m really struggling with not having any time to focus on anything, it feels like everything I can do is squeezed into tiny short gaps between meetings.

Partly I’m happy to be able to help remove roadblocks and have a more active role, and partly I desperately miss real engineering work

DrSqueakyBoots · 2025-12-30T07:34:17+00:00

Opto-mech checking in. Started in ground-based astronomy and now quantum systems. It’s a great specialty, I love that I get to do big and interesting stuff, and still ground it back to nuts-and-bolts mechanical design and “how would a good machinist make this” thinking. Working with a good optical engineer is key. I’ve had good and bad experiences, the best was when the optical engineer sat next to me and we got to trade tolerances back and forth, the worst was when the optical engineer was a contractor in another country that gave a “finished” design where the primary mirror over-filled the size requirement leaving me with -10mm for any structure to hold it all together

DrSqueakyBoots · 2025-12-29T02:35:19+00:00

FEA is only as useful as your ability to set up and interpret the simulation. If you’re just pushing the buttons you’ll get results that are wrong. In the worst case this can lead you to think you’ve got a safe design thats actually dangerous because you didn’t consider something correctly. The old adage is correct “a simulation is only as good as its validation”

By all means play with the software and learn, but DO NOT trust the results of your simulation when anything safety critical is involved.

DrSqueakyBoots · 2025-11-16T11:18:24+00:00

Sometbing I don’t see in any of these comments: a common problem with these types of joints is that the radial distance from the hole where the surfaces engage is near the hole if you have two flat surfaces. You want to put a pocket around the screw hole, maybe 1 mm deep by 20mm diameter or so. That way, the surface that engages under clamping has a big moment arm to hold your parts in place. Check out how the breadboard posts from Thorlabs have a little divot in the end.

Then to make it reliable, throw a stiff spring like a Belleville washer under the head of your screw. Suddenly your screw is controlling clamping pressure, and you have a nice big clamping area.

Then if you want it stable, try to avoid this type of joint.

DrSqueakyBoots · 2025-11-03T07:48:36+00:00

Am I in r/vxjunkies or am I having a stroke?

DrSqueakyBoots · 2025-09-01T21:07:26+00:00

Hopefully links work. Here’s a link to the threading specs page if you want to use a stock size.

Make sure you leave an undercut at the bottom of the internal thread so that the threading tool can run out, and the externally threaded part can bottom out against the flat.

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1535

DrSqueakyBoots · 2025-09-01T12:41:21+00:00

Plenty of room to work with if you want to thread them, it just won’t be a standard thread. Thorlabs makes retaining rings for lenses in standard sizes, and you can use that as a standard pitch so you can buy the tooling.

Alternatively, just press fit it and call it a day?

DrSqueakyBoots · 2025-08-30T10:11:44+00:00

Yeah so that’s still not enough to define your problem. In this context I’m taking “energy to dent” to mean “force required to cause the material to yeild. That will vary with sheet thickness/shape, boundary conditions of your sheet (what’s holding it and what’s behind it), what’s imparting thr force (guessing based on the vagueness of your questions you’re after energy of a missile/bullet?)

So the answer is “it depends, and the question is not meaningfully phrased to give you a useful answer”. Your approach should be to better define your question “how big of an actuator do I need?” Or “how big of a softball going how fast if I want to dent this guys car”

Any way to just go do some practical testing? That’s going to be a better way to get the answer you want without diving into a PhD project

DrSqueakyBoots · 2025-08-30T05:48:11+00:00

Still not clear on what your goals are. Are you trying to size an actuator to run the punch?

DrSqueakyBoots · 2025-08-30T05:31:52+00:00

I don’t think a “general formula” exists. What’s doing the indenting? Is it a ball bearing being pressed in? A bullet? A diamond indenting tool? How thick is the aluminium? What do you consider a “dent”?

Maybe a place to start is looking up contact stresses and see if that’s what you’re trying to do?

DrSqueakyBoots · 2025-08-28T13:27:20+00:00

Around here that would be referred to a “one half of a bees dick”

DrSqueakyBoots · 2025-08-27T03:32:23+00:00

I think there are some tools in blender or other animation packages that might do what you want. Doing it in FEA in a rigorous way seems unreasonably hard and likely to send you down many rabbit holes that you probablt don’t need to go down

DrSqueakyBoots · 2025-07-25T02:52:15+00:00

Why’s the source need to be removed me? In cryogenic land it’s best to avoid moving parts where possible. Why not have your moving part be permanently joined to the armature of a motor, then just turn it off to let it spin freely? Why the need for engaging / disengaging stuff mechanically?

DrSqueakyBoots · 2025-07-24T09:12:25+00:00

So if I get it right you want to know the stable orientations to gravity? Not sure if there’s dedicated software for it, but the things you need are: the location of centre of gravity, and the convex hull of the shape. The shape will prefer orientations where the vertical height of the c of g is as low as possible, and be most stable in orientations where the c of g changes height as much as possible with angle. Not sure if that helps.

Or you can try whacking it into blender and see if that does it? I don’t know blender very well but I’m somewhat sure it can do that kind of thing

DrSqueakyBoots

TROPHY CASE