Mixed Media tools: Foam stamps

It is easy to imagine what a moving object using electrical connections feels when passing through a strong magnetic field, The fan is moving faster with more amps so shows it more but any material that can transmit electrons will be perturbed some.

if you can loosely hold a screwdriver at a location the head might pass and can feel the pull then it is too much.

Better to make bed pins and hold things down that way. If you need to hold down an area you can hold down some scrap that covers the area needed.

Ohhhh ā€¦ something new to play with! I appreciate you sharing your process. Thank you!

3 Likes

Awesome technique and share!

Not sure if you have seen the holdown pins before, but if not, these might be the magic seatbelts youā€™ve been looking for! Theyā€™re pretty frigginā€™ amazing. Thereā€™s been several updated version and the ones with only one handle are my favorite.

2 Likes

I have some 3D printed ones. Do you just jam them into the waffle? is there a direction they fit nicely? I had trouble because the head/handle bit stuck up too far when holding down the foam (itā€™s pretty thick). Iā€™m going to print some with a flat top bit.

Are the ones you like in the free designs folder?

1 Like

Search for ā€œhoneycomb hold down pinsā€ and itā€™ll pop right up.

Thereā€™s usually one angle where theyā€™re loose, and one where theyā€™re tight - but two spots next to each other can be opposite angles.

1 Like

Yes, itā€™s @primal_healer version and hereā€™s the link to them. I used to break the other ones trying to get them out and I donā€™t have issues with these at all. And theyā€™re pretty intuitive because they only fit in my tray one way. I wonder if you could flatter the head a bit to get them under the head? :thinking:

2 Likes

Thanks, that is different from the one Iā€™m using.

1 Like

In his thread he says you can run it in the front, with the lid closed, but that you need a thin cord for the power. Not sure what thin is, but Iā€™ve seen some pretty thin cords on power supplies that I would expect to work.

1 Like

just so i understand, how big is the piece of foam you are cutting out the disk? and the magnets go on the edges (front?) to keep it in place and avoid the air assist, right?

in the cnc world they use masking tape and super glue. a layer of tape, super glue down the middle, then the second tape stuck to the board and sprayed with accelerator for quick curing. I have started using masking and double sided tape. less mess and easier to remove. maybe that would work.

1 Like

I have used paintersā€™ tape on the edge of stuff like the foam, then put a strip of scrap on the side of the tape thatā€™s on the honeycomb tray, and pin the scrap down with honeycomb pins.

If I ever cleaned my tray, the tape would probably just stick to it and I wouldnā€™t have to go to all the extra trouble. :stuck_out_tongue_winking_eye:

2 Likes

I donā€™t know why I felt the need to put on my weenie hat for this reply. But now Iā€™ve written it, seems a shame to delete it. So here it is FWIW. :slight_smile:

The motor is brushless, so the armature (wire windings) donā€™t rotate, the magnets do. The magnets inside the motor are the same rare-earth Neodymium as the magnets on the crumb tray. Theyā€™re smaller for sure, but theyā€™re a lot closer to the windings and that matters more. So the current induced in the motor by its own magnets is going to be much greater than the contribution from magnets on the crumb tray. IMO, I donā€™t think the crumb tray magnets can be inducing much if any current in the motor windings.

The problem I think, is that the fan uses a speed-regulated DC motor. I donā€™t think that thereā€™s anything particularly special about it. Just a typical brushless DC fan. But itā€™s a motor, and motor operation depends on magnetism, and external magnetic fields will affect the field inside the motor, which will negatively impact the motorā€™s performance. And if the motorā€™s speed is regulated, the motor controller will have to push the motor harder to maintain speed. Thatā€™ll make the motor run hotter and heat accelerates failure.

3 Likes

Actual experience tells a different story, A strong Magnet on the crumb tray will halt the motor when in range of the field and slow it down when in some distance. It took me a year and a dead Glowforge to figure that out, but once I did a whole lot of things made sense that had not before.

A brushless DC motor uses the motorā€™s ā€œback EMFā€ to determine the rotation of the magnets relative to the windings. That information is what controls the motorā€™s commutation circuit. When you put a rotating magnetic field inside a fixed magnetic field, the rotating field is skewed. That screws up the timing of the motor, which is why it runs slower. If the magnet is strong enough I could imagine it screwing up the motor to the point it canā€™t commutate correctly anymore and it stops spinning. But the controller thatā€™s driving the motor windings is probably still trying to spin the motor. Since the motor isnā€™t spinning, that is going to generate a lot of heat. A motorā€™s power dissipation is greatest when itā€™s stalled.

Iā€™m not saying a magnet doesnā€™t effect the motor, or that it canā€™t cause the motor to fail. Quite the opposite. Iā€™m only saying that itā€™s not extraneous current induced in the motorā€™s wires by those crumb tray magnets that is the cause of the problem. Itā€™s the effect the field has on the motorā€™s ability to function, which makes the motor run hotter, which ultimately causes it to fail.

1 Like

An easy experiment. Just put the magnet in the crumb tray and watch the fan stop every time it passes over the magnet. and spin up again when more than 6 inches away from the magnet, and then stop when coming the other way. Whatever the theory that is what happens. Not eventually but each time.

I have used paintersā€™ tape on the edge of stuff like the foam, then put a strip of scrap on the side of the tape thatā€™s on the honeycomb tray, and pin the scrap down with honeycomb pins.

Good idea.

Sorry I missed this because I was trying not to be tempted into the physics argument they were having.

I put the magnets on the corners of the uncut piece of foam. After I got the error about the fan speed I moved the image to the back of the 10 inch wide piece of foam and the magnets to the front. The stamp is 4x4 so the laser didnā€™t come closer than 5 inches to the magnets.

Iā€™ll just find another way to hold it down. The foam is light weight and will take to the air when the assist fan hits it, so it need pinning all the way around the edge. The honeycomb pins that I used had a sticking up bit (so you can pull them out) but since the foam is already pretty thick, these stuck up too high. Iā€™m going to 3d print myself some with flatter top bits.

Something I do for woodworking is a strip of masking down, then a strip of double stick tape and then a strip of masking, sticky side up. Easy to remove and should hold your foam. The other thing I was thinking was maybe some play-doh. Itā€™s malleable and dense enough it might hold it down.

2 Likes

Thanks! Playdoh sounds crumbly, but maybe museum putty would work. I think Iā€™ll try the tape. I have double sticky tape thatā€™s too tacky to use; your masking tape idea should take care of that.

Or silly putty

Wow slow reply here, sorry. Yes the Glowforge thought they door was closed, no problem. My power cord is pretty svelte, so I sneaked it in on the side of the lower door and it closed without issue.

2 Likes