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Vacuum table, small scale

This project may be complete at this point. It’s a three-layer vacuum table for the E1, with suction provided by a US standard shop vac. I have a comprehensive construction album showing the individual components. If there’s enough interest, I’ll post that deluge along with verbose comments regarding the construction and things I’d do differently.

In summary, it’s a frame of poplar, with a top layer of aluminum honeycomb sized exactly to the cutting limits of my A3 E1. Under that is ordinary window screen, aluminum, not plastic for obvious reasons and below that is a layer of 6 mm 0.25g airsoft pellets. The last layer is 3mm birch ply, again cut to the limits of the E1.

I discovered that it’s wise to secure the honeycomb before the other layers are added when the assembly is upside down. More than 3700 pellets take a long time to locate and vacuum up, then additional time is required to separate them from the trash in the vacuum canister.

The manifold connecting the frame to the shop vac is a 3d printed creation of my own doing, another learning experience. Fairly weak and fragile off the printer, but strong like bull after a single layer of 4 oz fiberglass and epoxy resin is applied. The white ring on the vacuum adapter is for lack of sanding the adapter to get a good bond but it hold together well. After all, it does suck, doesn’t it?

The manifold edge is sized to allow openings to be drilled under the honeycomb and screen while using the airsoft pellets to distribute the forces across the bed. If a single sheet of paper is placed at the manifold end, the vacuum transfers well to the zero-zero end.

Due to accidentally overheating my laser module, I am unable to test this in real life, but it works great in my imagination. I should be able to make a test in a few days if the postal service cooperates.

For US residents only, I’m willing to 3d print the manifold for anyone who wishes to duplicate and/or improve on my efforts. It would be ten bucks for the plastic and ten bucks for the shipping. No extra charge if you want the time-lapse of your part being made.

https://youtu.be/RuQnrNYKEHM

The video is a bit of misrepresentation, as there are now six spacers in the mouth of the manifold, to prevent collapse and I’ve managed to adjust temperatures and retractions to rid most of the stringing.

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Great idea Fred and thanks for sharing it.

This could also potentially help creating cleaner cuts because fumes would be drawn down and away through the vacuum table.

Everyone here at the Lab would certainly give a big thumbs up a detailed construction log. We really like seeing these mixed technologies being used.

By golly, you’re asking for trouble!

This dissertation may run several pages, as I’m going to include that which I would change should it be necessary to perform this project construction again.

First off, I cut the base 3mm plywood to perfectly match the cutting limitations of the laser, minus a few millimeters. This way I could ensure to get a perfectly sized and perfectly square rectangular piece of wood. A previous attempt with a table saw lacked the desired accuracy.

The plywood is not visible in the photo above, but it was used to mark and cut the 45 degree angles making up the frame. A power miter saw worked well and a manual version should do equally well for this task. In the photo above, the frame is glued together. The holes along the right side were drilled later. Wrong move on my part.

After cutting the plywood and the frame pieces, it would have been much smarter to use the router to create the outside gouge. I think there’s probably a better word for it.

I had originally attempted to create this gouge by using a Forstner bit and placing holes in a line, but that didn’t work well. Had I attempted this task prior to gluing it into a frame, it might have gone better. The router table and an unwieldy frame worked out okay in the end.

This gouge is 3mm from the bottom of the frame and is about 6mm wide/tall. The 3mm is for the base plywood panel thickness and the 6mm is the diameter of the airsoft pellets. I used a 1/4" router bit as I do not have as many metric tools as I’d like. You’ll find mixed dimensional references in this document. Next up is drilling 1/8" holes, staggered between top and bottom of the gouge. The gouge is about 1.5" deep, leaving 1/4" of inner frame for the 1/8" holes. Staggering them top and bottom means that none of the airsoft pellets are likely to become corks, which would be the case if the holes were centered in the gouge.

The aluminum honeycomb was already cut to size, as I was using it unadorned previously. It fit nearly perfectly inside the frame, with a little convincing at the edges required.

This is another thing I would change. I would cut a rabbet about 10-12 mm around the entire inside frame, 10 mm deep, to hold the honeycomb on a ledge. This would provide a greater area for gluing and securing the honeycomb to the frame and remove a number of complications I had to overcome to complete this project. This photo was taken with the frame on the bed of the E1, ensuring that it was a flat frame. The E1 has a double wall bed, with this type of honeycomb epoxied between. The frame panels were glued together while compressed on a machinist’s granite surface, certified to a thousandth of an inch or smalle flatness. I’m confident I don’t have a warp in either assembly.

If I were to cut a rabbet, I’d make several small passes and test fit for perfect flush fit of the honeycomb, then glue it in place. I neglected to do any gluing at all on the first attempt at construction.

 

This is Gorilla brand duct tape, wedged into the edge of the frame, pushed as securely as possible onto the honeycomb and creased into a corner along all four edges. Corners are difficult to seal and the twin rows of holes at the gouge were impossible to seal. The objective here was to fill the edge honeycomb cells with epoxy, bonding them to the faces of the frame. The aforementioned ledge rabbet would have solved ninety percent of this problem.

I had epoxy dripping everywhere. Oh, yeah, I saved a gigantic mess by using cheap silicone grilling mats under the frame. After the epoxy cured, it was a simple matter to peel off the drips and toss them in the bin. Thirty minute cure time meant a long time dripping and stuffing paper towels in places I could not seal, mostly the corners.

The photo above is the underside of the tape. It does not show clearly the gaps at the corners or the poorly sealed edge at the gouge end.

This shot above was the ideal result. The photo is of the wet uncured epoxy and was exactly what I was hoping to accomplish. Unfortunately, other portions of the edges are not quite as perfect, but I have sufficient bond around the perimeter to hold together, especially since I plan to transport it either flat in operational attitude or nearly vertical. I keep saying this, but the rabbet ledge or ledge rabbet is again superior to this method.

This photo shows the gloppy and blotchy and any other adjectives applied to the cured epoxy. It’s possible I could have either pushed the stuff out, or drilled it out, but I didn’t want to chance pulling the edges clear of the frame. It’s still going to suck in most of the cells and pull any mildly warped material flat over the entire surface.

The epoxy did a great job of filling in the 1/8" holes, so those had to be drilled out again. No big deal, as the epoxy drills as easily as a piece of plastic, which it mostly is.

With the frame upside down (honeycomb is the top), the aluminum/aluminium window screen is positioned, above and below:

My apologies for the not-so-good focus.

Sharp eyes may note sanding marks throughout the frame photos. 60 grit sand paper does quick work on dry epoxy. It’s important to have a flat surface for both the top and bottom.

The photo above is the initial dump of the recovered pellets. They are mostly cleaned after the trip through the shop vacuum and the operational status of the vacuum bed will only remove anything remaining. The screen is bowed upward a bit, which eventually is removed by the weight of the distributed pellets:

The photo above is after I added a couple hundred more pellets to the batch. They like to hop over the edge in an attempt to escape, but only one got away. His friends are all contained and secured.

The previously cut 3mm plywood fits perfectly, although it was necessary to shave away gobs of epoxy that reduced clearances from the corners and the sides. I applied high bond wood glue to the edges and wiggled it into place. I have some electric vehicle deep discharge/deep cycle batteries that weigh 72 pounds / 32 kg each. They kept the plywood nearly perfectly flat, although I worried for a bit about the strength of my double panel bed. The Workmate device provided additional support and peace of mind. It was necessary to sand a bit off one corner of the plywood to ensure it to be flush/flat on the bed when flipped.

I did not worry to make the joint to be air tight. With the amount of glue used, I expect that it is nearly so, but any leakage will pull the vacuum bed to the laser deck, to my benefit.

One can see the honeycomb, epoxy, window screening and airsoft pellets in this photo. Some of the honeycomb discoloration is likely the result of more than a few hours of cutting 3mm plywood in a concentrated area. I expect that the fumes condense on the honeycomb. With the vacuum aspect in use, that’s going to either be no longer a problem, or the pellets will begin to look pretty disgusting!

I sized this device to fit perfectly on the bed and be easily removed from the end. The manifold has plenty of clearance under the acrylic edge and the fiberglass coating provides necessary support for the hose.

It may seem mercenary for me to suggest that someone pay for me to make them a manifold. Okay, it is.

I’d love to make it rich doing 3d printing, but everybody and his brother has a 3d printer now. I’m only asking for materials and postage. No charge for the twelve hours it takes to print the thing!