Another Vacuum Hold-Down Thread...

This section is for useful tips and tricks for Aspire
Post Reply
Tailmaker
Vectric Wizard
Posts: 697
Joined: Sun Jun 16, 2013 4:40 am
Model of CNC Machine: Home Built 4-axis Router
Location: Fort Collins, CO

Another Vacuum Hold-Down Thread...

Post by Tailmaker »

I was asked on the latest vacuum related thread (started by neilgill) to provide more information about my extrusion channel vacuum conduit table. So I thought I start a new thread about that...
This method is mostly relevant for those with full surface t-slot extrusion tables. If you have only the typical spoilboard on the machine, you can safely ignore this thread. If you have individual t-slot rails embedded in the table, it may or may not be helpful.

I built my machine some 10 years ago, using a sturdy plywood torsion box a base for the table and mounted a surface of 1545 extrusions (1.5" tall x 4.5" wide with 3 slots each) on top of it, expecting that I would clamp material for most of my projects.
1545.jpg
Turned out that over time I used more and more vacuum hold down with pods like described in the other thread. But those had to be clamped or bolted to the table anyway which made for more effort than desirable and not always perfect horizontal clamping. That led me to the idea to use the t-slots themselves as vacuum conduit.

For this purpose I sealed the hairline gaps where the extrusions butt up to each other with CA glue. Then machined two plastic strips with nubs that fit exactly into the open ends of the t-slots. They are glued in, and one side has 3/8" holes for the middle slot of each extrusion to accommodate short pieces of rigid tubing as vacuum nipples. These nipples connect with air pressure hose to individual gas valves on top of my vacuum reservoir. That way, I can control vacuum separately for each of the extrusions. Although I have 6 of such connections, I use only 3 with a total width of 13.5" at this time. The rest of the table is still available for clamping. Also, I milled circular holes near the work surface ends into the extrusions to allow for t-bolts in the channel in spite of the closed channel ends.
DSC00307.JPG
DSC00311.JPG
IMG_4557.JPG
channelholes.jpg
Some more pictures to follow showing how I can use this setup:
Puzzle, Finger Joint, Maze and Guilloche freeware at https://fabrikisto.com/tailmaker-software/

Tailmaker
Vectric Wizard
Posts: 697
Joined: Sun Jun 16, 2013 4:40 am
Model of CNC Machine: Home Built 4-axis Router
Location: Fort Collins, CO

Re: Another Vacuum Hold-Down Thread...

Post by Tailmaker »

The active vacuum slots are covered with thin 4" wide aluminum flashing (from Home Depot roofing dept.) and held/sealed with electrical tape to the extrusion edges and with gaffer tape to the extrusion ends.
Flashing.jpg

Now I can punch a hole with an awl anywhere along the channel and slap a piece of material directly onto the table with a simple gasket. Unused holes from previous projects are covered with tape.
IMG_3433.JPG
Simple one-sided projects boards can be placed directly on the table with a gasket cut from non-slip drawer liner. I have a collection of such gaskets for re-use but often just cut a new one to size.
IMG_4553.JPG
Occasionally I still use pods, these are simple square pieces with gaskets on both sides. But they take a beating once in a while.
IMG_4555.JPG
Puzzle, Finger Joint, Maze and Guilloche freeware at https://fabrikisto.com/tailmaker-software/

Tailmaker
Vectric Wizard
Posts: 697
Joined: Sun Jun 16, 2013 4:40 am
Model of CNC Machine: Home Built 4-axis Router
Location: Fort Collins, CO

Re: Another Vacuum Hold-Down Thread...

Post by Tailmaker »

For double-sided projects or single sided ones with edge machining to the bottom, I use a disposable spoilboard of suitable size, i.e. some scrap plywood or old shelf board. That has a weatherstrip gasket on the bottom and another one on the top with a small hole to connect to the vacuum. Some examples below:
DSC00816.JPG
DSC00814.JPG
DSC00315.JPG
DSC00320.JPG
DSC01013.JPG
DSC01018.JPG
DSC01021.JPG
Puzzle, Finger Joint, Maze and Guilloche freeware at https://fabrikisto.com/tailmaker-software/

Tailmaker
Vectric Wizard
Posts: 697
Joined: Sun Jun 16, 2013 4:40 am
Model of CNC Machine: Home Built 4-axis Router
Location: Fort Collins, CO

Re: Another Vacuum Hold-Down Thread...

Post by Tailmaker »

Another use is mounting of my 4" machine vise for metal machining. That has a smooth glass/epoxy plate glued to its bottom and attaches with a gasket to the vacuum table without clamps or bolts. Surely not for heavy duty milling, but my machine could not do that, anyway.
DSC01035.JPG
Or, for rotary carving, I hold down the drive and the tailstock with vacuum, using aluminum bars in the open extrusion channels to align both pieces properly.
IMG_E3674.JPG
Finally, really odd-shaped blanks can be held down and machined without material loss, after glueing to a waste board with spray foam. The waste board again held down with vacuum. After machining, the foam can be broken loose easily.
LargeBlock.jpg

I hope the pictures give some ideas, even if not 100% applicable to all machines.
After all, I still use clamps and/or screws often, sometimes in combination with vacuum hold-down. Just depends on the job...
Puzzle, Finger Joint, Maze and Guilloche freeware at https://fabrikisto.com/tailmaker-software/

ctbjdm
Vectric Apprentice
Posts: 86
Joined: Sat May 13, 2017 11:45 pm
Model of CNC Machine: TBD

Re: Another Vacuum Hold-Down Thread...

Post by ctbjdm »

This is extremely clever, really well done. I might use this!

Bob T
Posts: 48
Joined: Fri Sep 23, 2011 9:01 pm
Model of CNC Machine: Shark HD 520

Re: Another Vacuum Hold-Down Thread...

Post by Bob T »

Hey Tailmaker, I may have missed it but what are you using for your vacuum source? Thanks Bob T

Tailmaker
Vectric Wizard
Posts: 697
Joined: Sun Jun 16, 2013 4:40 am
Model of CNC Machine: Home Built 4-axis Router
Location: Fort Collins, CO

Re: Another Vacuum Hold-Down Thread...

Post by Tailmaker »

Bob T wrote:
Mon Nov 14, 2022 9:57 pm
Hey Tailmaker, I may have missed it but what are you using for your vacuum source? Thanks Bob T
I am using one or two 1/2 hp Thomas or Thomas-style oil-less double piston pumps. Can be bought on eBay refurbished for $150-200, Amazon also has some offers new. These pumps are comparably quiet, use little power and can be run in the shop. Mind, they are only suitable for well-sealed applications and not at all for hold-down of large sheets with porous spoilboards. That needs much more power and noisy high volume pumps.

If the seal is good and the material not leaky, I use only one pump. If the vacuum gage shows low vacuum (usually some gasket or wood crack leakage), I may use both pumps.
IMG_4554.JPG
Puzzle, Finger Joint, Maze and Guilloche freeware at https://fabrikisto.com/tailmaker-software/

Post Reply