Need some guidance for designing for 3D

[WobblyHand]

Since I started this thread, might as well ask here. I'd like to use some magnets to hold my ELS display box down to the lathe. My design now has 12.2mm diameter pockets for 12mm N52 magnets that are 2.8mm deep into the bottom wall of the box (really the side of the box). The magnets are allegedly 3mm thick. I was thinking of gluing them into the pockets and possibly putting a keeper steel plate across them inside the box. The magnets don't go through the box. The section under the magnet is 0.8mm, or 0.75mm depending on what layer thickness I use. (3 or four layers)
Is this sufficient? Is there another or better way to doing this?



Thanks for any insight on this. The four corner holes will have M3 brass inserts. I don't quite have enough room for inserts to hold the PCB down, without breakthrough. Can't lengthen them without running into a screw head on the PCB. If I redesign the PCB again, I'd fix that, but the PCB works, so there's little reason for a re-spin.

 

[jwmelvin]

Why so thick? I’d do two layers under the magnets (in PETG).

 

[WobblyHand]

Why so thick? I’d do two layers under the magnets (in PETG).

Not sure how strong this PLA stuff is. I'm new to 3D. Like less than a week new to it.

If this works, I'll leave it. Otherwise I need to rethink the magnet stuff. Standard cheap magnets are 12mm x 3mm. The wall thickness I made was 3.6mm. I wanted the magnet proud of the surface on the inside of the box to put a keeper plate across it. If I alternate the polarity of the magnets, it will increase the attractive force to the headstock. I've done that before.

In the next few days I will try printing with PETG. I have to get some hairspray for the platen. So far printing with PLA has be really easy and very close in dimension.

 

[hman]

Perhaps you could 3D print a "test plate," of the same thickness as the wall of your box, then try gluing in some magnets and attaching a keeper plate. Best wishes for a totally successful test!

 

[WobblyHand]

Perhaps you could 3D print a "test plate," of the same thickness as the wall of your box, then try gluing in some magnets and attaching a keeper plate. Best wishes for a totally successful test!

You are right. I should do that. Makes sense, too. Rev B fixes some blunders of mine.

Just a bit excited to have a new toy. Oh, wait, did I say that? A tool, yeah that's it.

 

[Huub Buis]

To fit a GX16 connector, your wall thickness should be 2 mm. Make a pocket or a M16x1 hole, 4 mm wall thickness.
I place magnets under a 0.5 mm layer PLA or PETG. The thinner the layer, the more magnetic strength.

 

[WobblyHand]

To fit a GX16 connector, your wall thickness should be 2 mm. Make a pocket or a M16x1 hole, 4 mm wall thickness.
I place magnets under a 0.5 mm layer PLA or PETG. The thinner the layer, the more magnetic strength.

I'm using 2.6mm wall for the GX16. The GX16 and GX12 connectors fit great, I have tested that.

Seems everyone is using a thinner layer for the magnets. Thanks for the recommendation.

 

[jwmelvin]

Not sure how strong this PLA stuff is. I'm new to 3D. Like less than a week new to it.
…
In the next few days I will try printing with PETG. I have to get some hairspray for the platen. So far printing with PLA has be really easy and very close in dimension.

When I first designed things, they were way stronger than required. I realized that you can get away with much less, especially when using infilled volume (like a fiber composite structure). I have also found that thin walls like you are doing can be quite thin. E.g., magnet pocket for bracket holding treadmill belt as chip shield, 0.4 mm; magnet pocket for hard-drive magnet mister base, 0.8 mm; end-mill drawer inserts, 0.55 mm; boring-bar box bottom, 2 mm. I’ve tried a variety. The 0.4 mm magnet pockets are plenty strong and allow strong magnet attraction.

Alternating poles and connecting the magnets improves the holding power? That’s good to know, thanks.

I use PETG because it’s not as brittle as PLA. Seems to print well too. I wipe the smooth PEI build plate with winded and let it evaporate; that seems to reduce the adhesion enough to make removal possible, though it’s still tenacious. I’ve heard hairspray is good but have not gotten around to trying it.

 

[WobblyHand]

When I first designed things, they were way stronger than required. I realized that you can get away with much less, especially when using infilled volume (like a fiber composite structure). I have also found that thin walls like you are doing can be quite thin. E.g., magnet pocket for bracket holding treadmill belt as chip shield, 0.4 mm; magnet pocket for hard-drive magnet mister base, 0. Mm; end-mill drawer inserts, 0.55 mm; boring-bar box bottom, 2 mm. I’ve tried a variety. The 0.4 mm magnet pockets are plenty strong and allow strong magnet attraction.

Alternating poles and connecting the magnets improves the holding power? That’s good to know, thanks.

I use PETG because it’s not as brittle as PLA. Seems to print well too. I wipe the smooth PEI build plate with winded and let it evaporate; that seems to reduce the adhesion enough to make removal possible, though it’s still tenacious. I’ve heard hairspray is good but have not gotten around to trying it.

The alternation of magnets seems to work quite well. I used that for my round LED spindle light for my mill. That light is on tight.

I need to get off my keister and go to the store and pick up some Aquanet scentless. Worth trying anyways for maybe $3. Probably do that tomorrow. Then I will try some PETG.

 

[WobblyHand]

Did a quick test of alternating magnets with and without keepers. Printed a test piece using the same geometry as in the box wall. Inserted magnets with alternating polarity.

Without keeper and 0.8mm plastic between magnet and weight 3 magnets cannot pick up 1.440 kg. The weight consists of two pieces of 1018 tied together with pipe cleaners.

With keeper (and 0.8mm plastic between magnet and weight) 3 magnets will pick up 2.484 kg. This is nearly double the pull. The weight is the same as above plus the cylinder of 1045 magnetically attached to the bottom of the 1018. For a keeper, I just used a piece of key stock that was a lathe tool model that I laid on top of the magnets.

My box will have 4 magnets with keeper. Hopefully this will have nearly 4/3 greater pull, or about 3.3 kg. Hopefully that will be enough.