Please Critique Yet Another Universal Vac Hold Down Design

[joelschuman]

I've got my new-to-me Desktop up and running. While I wait for my electrician's visit to add more circuits for Bot and vac(s), I've been working on universal vacuum hold down because none of the designs posted here meet all my reqts:

1. Unobstructed front access
2. Unobstructed feed-through for tiling longer parts
3. Preserve max Z travel
4. Vac hookup from rear
5. No irreversible alterations
6. Easy to cut, assemble, disassemble, and modify
7. Easy to swap out with original T-slot rig

The key to what I've sketched is to make use of the no-fly area to the left of the cutting volume. Please take a look and tell me if you spot anything unworkable or questionable.

Thanks,
Joel

[bleeth]

Could be on the right track but sooner or later that raised bump for the vac hose will get bit unless it is totally off the move pattern of your spindle.

[joelschuman]

Could be on the right track but sooner or later that raised bump for the vac hose will get bit unless it is totally off the move pattern of your spindle.

For sure. I need to measure where the collet nut and spindle are relative to the cut volume boundary with my lowest likely cut scenario. Then adjust the outlet block to be clear.

[Brady Watson]

You don't want to feed it from the top...Feed it from underneath, even if you have to use a few smaller tubes (1") to feed it. Emulate the bigger systems as much as you can.

-B

[joelschuman]

Brady,

Would you please explain why a top routing is bad? I'm not knowledgeable about fluid dynamics, but I have read that fewer sharp bends is better. This design has no bends at all from the edge of the plenum grid to the vac hose attachment. I've moved the outlet block further back as Dave suggested. Is there something else I'm missing?

Can you point me toward an image or drawing of the under table routing you recommend for the D2418?

Thanks,
Joel

[bob_dodd]

search forum Desktop vacuum or this http://www.shopbotblog.com/2006/11/a...own-potential/ for some ideas

[Brady Watson]

Brady,

Would you please explain why a top routing is bad? I'm not knowledgeable about fluid dynamics, but I have read that fewer sharp bends is better. This design has no bends at all from the edge of the plenum grid to the vac hose attachment. I've moved the outlet block further back as Dave suggested. Is there something else I'm missing?

Can you point me toward an image or drawing of the under table routing you recommend for the D2418?

Thanks,
Joel

Joel,
When you feed it from the top, there's always the issue of sealing the intake from where it feeds the plenum and bleeder. By feeding it from below, you avoid all of that & make things simpler and easier to seal. This is of course talking about a high CFM 'universal' vacuum system, like those run on large machines. It is way easier to do a pex fed high HG/low CFM setup from the top (or even the bottom) - depending on what you are cutting.

For a machine this small, with a shopvac-type vac source, you really only need one zone. You can feed the vacuum down from the top, between the last table extrusion (which is only 1.5 x 1.5) and pipe it over to the left or right side of the Y lead screw. From there you can pipe it up to the table by removing one of the 1.5x6" table extrusions and replace one with an 8020 1530 extrusion. You'll have a 3" gap in the middle of the table for piping up the vacuum.

For the top, to prevent too much loss of Z, I would use 1/2" material for the plenum & 1/2" ultralight for the bleeder. Set it up so you can still bolt down to the underlying extrusions from the top. You'll need to make islands around where the bolts go to act as a sealant to bleeding off vacuum. The vac grid itself doesn't have to be deeper than 3/16" or so...in fact, I doubt there's much to gain over the grid being deeper than 1/8" (even less). Seal all the edges and bottom of plenum for max performance.

1x3" AL rect tube is a great way to feed from front to back just like I did the BT48 system

Attached crude pic shows what I am talking about...




-B