Hold down...non vac Qs. ...Noob alert

[baltic_birch]

My bot will be here in a few weeks.

I was trying to visualize if I need a vac hold down.

I make a lot of the same size parts from the same size stock.

I know when I use my handheld router to cutout parts with a template I just have clamps holding the board and template down. The part that gets cutout is loose after cutout.

Does this translate to the shopbot well?

For example:

Lets say I take a 4'x5' piece of 18mm Baltic Birch and clamp it down(clamps,cams etc)

Can I cut out a 11" x 30" rectangle out?
Will this work with the finished part NOT being held down with vac but using a 25 thou onionskin?

Could I through cut it like I do with my handheld?

I'll be using a router and multiple cut passes, with a 1/4 down spiral bit.


Just seeing if I really need a vac system of any type.

Thanks!!!!

[jsfrost]

Based on the experience of others, vacumes are a great hold down method.

Based on my own experience clamps, jigs or screws together with onionskins and tabs will reliably hold parts in place. To vac or not to vac depends initially on the projects you plan to cut and eventually on the projects that make your business work.

[donchapman]

Jump into vac hold down much sooner than I did.

I wasted much more time worrying about vac hold down than I've spent buiding and testing my system.

My ShopBot PR96 arrived seven years ago next month and I built my first vacuum hold down system just this past week.

I have about $300 and a few days time building and experimenting with my minimalist full table 4-zone system (about $170 for a Fein mini shopvac bought last March on Woodcraft's online closeout of the vac, the balance in 1.5" PVC pipe, valves, fittings, a sheet of 3/4" MDF, and some gasket material).

I generally followed the instructions and photos that came on a SB control software CD I received a couple of years ago, but without the expensive vacuum pump.

I screwed a 3/4" MDF board around the perimeter to my existing 3/4" MDF spoilboard, routed a 4 zone grid with a 1/4" instead of the recommended 1/2" upcut spiral bit using the SB vacuum grid program on the CD, attached 1.5" instead of 2" PVC pipe and valves under the table, attached the mini Fein shopvac, turned the vauum on and it firmly held a full sheet of 1/4" hardboard with all zones valves open, or a 2'x4' piece of 3/4, 1/2, and 1/4 inch MDF with one zone valve open.

I've experimented with filling the waffle iron like channels with strips of 1/4" x 1/2" closed cell foam or EPDM rubber insulation (cut from MD brand rubber garage door bottom) and been able to hold down pieces of SignFoam HDU, plywood, and MDF as small as 7" x 7" and then successfully routed small clock gears from the small HDU blank.

Yesterday I routed uke mold parts that filled most of a 2x4 foot piece of 3/4" MDF using a 1/4" upcut spiral bit leaving .02" skin on the bottom and only vacuum holding it over one of the four 2'x4' zones and it held firm and cut perfectly.

I haven't even glued the PVC, sealed the MDF vacuum grid with polyurethane or the edges with duct tape, or tried adding a second shopvac, or a spoilboard of Trupan ultralite fiber board.

I looked for Trupan locally and couldn't find any so I'm routing directly on the waffle grid, usually leaving a thin skin or some tabs.

If I'm leaving tabs rather than skin on the underside of the routed part and too much vacuum is being lost in the through cuts, I compensate with the minimalist method of slapping a piece of paper, laminate, tape, etc. over the already routed parts so the other parts can be finished with enough hold down.

I don't even know if my mini Fein vac wil be able to hold parts through the Trupan. If it won't, I'll add a second shopvac or I may just continue to make do without the Trupan spoilboard. The etchings left atop the waffle grid from thrucuts don't seem to matter anymore than they do on any other spoilboard. If I'm cutting small parts with an 1/8" bit I don't bother with dust collection, but I do use my dust collector when I'm producing a lot of dust as when I cut through or almost trough 3/4" MDF.


Could my vac table use improvement? Absolutely, but I've been so intimidated for so long by the high cost and complexity of vac table systems that I'm still in a bit of shock that my $300 system works at all and I'm not yet so much a vacuum purist that I can't add a clamp or screw for insurance against movement if necessary.

Somehow my minimalist system reminds me of a billboard I saw many years ago for a rot-gut wine: "Chicago Red gets the job done."

[fleinbach]

After using my shopbot for over three years now I finally got around to making my vacuum table. I too wish I had never waited so long. You can see my progress here http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=42554#POST42554

It works much nicer then placing screws, and no more risking a broken bit. Yes, I've broke a few.

I used to use tabs but know I leave a .02 skin which workes increadably well and to me is easier to deal with then tabs.


I am using a Fein vacuum for holddown and must admit, it works rather well. I draw 6 inches of vacuum with all valves closed. With a piece of 3/4" MDF covering one of the zones it drops to about 5 inches. I tried hooking up a second Fein vacuum and it did not seem to improve over using just one. According to the vacuum gauge readings were identical.

I do find that it will not pull down any warped material. As long as the material is flat t holds just great.

[patricktoomey]

The second vac will not really help with static pressure which is what the gauge is showing. It will help with airflow so you can hold a given pressure with more leaks. It will also help with holding down warped sheets. I have two vacs and sometimes I will use 2 to get a warped sheet flat and then turn one off to consever power. Most of the time though I leave them both run for insurance and to let me cut through the material in more places before losing pressure.

[harryball]

This vac setup is still working rather well for me

http://www.talkshopbot.com/forum/messages/28/15230.html?1162934598

I've had them running for hours at the time cutting. When I run bat house kits it takes a total 40 minutes to completely finish a sheet, they run the entire time. I've cut as many as 10 sheets of kits in one day.

If you cut sheets, don't wait, get some kind of vac going, you'll love it.


Robert

[jhicks]

I agree with the above posts and highly recommend early experimentation and testing but we waited 3 years and now only wonder why.
go for it, it may not be the 100% solution but it sure covers at least 90% and eliminates a lot of set up, clamp or fixture building, and overall is quite surprizing how well it does work.
See many earlier posts on sizes and styles of zone and manifold systems, then decide best layout for the work you plan to do.
Good luck

[baltic_birch]

Thanks Guys!!!!!!!

I plan on leaving onion skins all the time.

I now believe I don't need a spoilboard.

I had a dream of a 32 zone plenum last night LOL..
1sq ft each.

I may take the time to think that out.


Thanks again!!

[rob_bell]

a 32 zone plenum!...that's crazy talk!


8789

[geneb]

Ok, I give. How would you plumb that monster?


g.

[baltic_birch]

>a 32 zone plenum!...that's crazy talk!

Lol, show the underside!

I was thinking of using rubber plugs instead of valves for each unused zone, but who knows.

[rob_bell]

I have 6 valves and 2 Feins routed in such a way as to allow me to open/close many zone configurations. It's working pretty well.


8790

8791

[baltic_birch]

thanks for the photos!


I may put individual valves on each one as well as a few valves at the table side for master control.
I don't mind if I have to climb under the table to turn a few knobs every once in awhile.

Thanks!

[geneb]

Fantastic setup! I do have a couple of questions...

Is the grid made of individual pieces of stock or are they "notched" in order to make the grid from solid parts that run the length & width of the table?

Is the plenum itself made from MDF? If so, how do you keep the vac from sucking air "sideways" from adjacent(sp) sections?

tnx!

g.

[rob_bell]

The grid is notched strips glued to a base of mdf then each chamber was sealed with gesso ( it was handy ). Then the plenum layer which I routed in the radial channels so that the unsupported center of each chamber would still be strong. Lastly, not shown, is a layer of ultralight as my spoil/bleeder board. Performancewise the table has been magical.

In retrospect I'm not sure the chambers give me any real advantage - maybe a bit of buffering when there's leakage from a cut thru. I'm new at this too and it seemed like a good idea at the time. I do regret the thickness of the thing and now that I'm almost thru my first bleeder board I'm planning on milling the whole thing down as far as possible to get an inch or more back. As it is 3 1/2 inches is my max capacity above the table.

While there may be some side sucking due to the mdf plenum most of the force seems to follow the path of least resistance.

My favorite demo is to turn on chamber 1 only and wing a puck of material across the table from back to front as hard as I can. It stops dead on the chamber like in a cartoon.

-rob

[geneb]

Thanks for the quick reply Rob!

Hmm. Maybe you should consider a new game show! Guess the vac chamber!


g.

[baltic_birch]

Has anyone tried individual spoil boards w/sealed edges for each zone?

I'm wondering how much vac loss there is if you just use one zone with a master spoilboard.

Sure, it is sucking the part down directly over the selected zone..... but how much is getting sucked from the adjacent zone that is turned off?

I picture using a single zone in a master spoilboard similar to not sealing the edges on the master spoil board.... or am I nuts??

Thanks!

[Brady Watson]

I've made up seperate 'sealed' pods that could be called zones, due to their size. There isn't a marked difference between having a single board with multiple zones milled into it & side leakage between the zones. If you seal the grid before you attach the bleeder (or use a non-porous substrate like PVC to begin with) you won't notice leakage where the zones meet. Leakage thru the bleeder will be minimal.

Keep in mind with ALL of the multi-zone setups that various people have created, that they are primarily geared towards getting the most from a small vacuum pump, regen blower or Shopvac. It is not necessary to have more than 4 zones on a 4X8 for most applications dealing with sheet goods. Additional zones just help you to use more of what you've got to work with. Personally, I think that it would be more efficient (design time & cost) to just buy another shopvac (like a Fein) and increase the CFM of the vacuum source. This goes much further in terms of holding power when cutting all the way through than a gazillion zones.

When it comes to small parts, I have found that it is often more efficient to make an accessory vacuum plenum that you can screw down to the table top, and plug your vac source into. Then use replaceable 'masks' that direct the vacuum only under the parts to be cut, and a few places to hold the scrap from coming loose. I go into this in my latest Tips/Tricks on the SB site.

-B

[geneb]

Brady you make some good points here. While working on my F-15 project, I had numerous places where I worked with wood instead of metal for reasons of cost and tooling available. I discovered some very cool threaded inserts that will allow you to use a standard x32 threaded machine screw in regular wood. This would work really well for holding down the smaller sized individual vac pods. You could drill all the needed mounting holes in your SB table, thread these inserts in with a bit of glue on the outside and end up with a set of registerable locations for your portable vac hold down.

I need to think more on it, but I just go Brady's route of having portable vac pods. I was planning on building a vac table using David Buchsbaum's combination vac & t-track design. I think a hybrid version using the t-track in the table with portable 2x2 vac pods may be the ideal solution for me.

g.

[wayneo]

Hey Guys,
I have seen some vacuum pucks that you screw down to the table. Then I have seen some that suck themselves down (suck both top and bottom). Anyone used the ones that suck themselves down? How do you like them? Seems like they might be better/more universal?

Any pros, cons? I plan to make some and would like to know which way might be best.

Regards,

Wayneo

[billp]

You can't use a two sided puck on a porous table (MDF, Trupan, etc) unless you seal the table top completely.
You can't use a two sided puck if your table is torn up and you have a lot of cuts/grooves in your spoilboard
You can't trust a two sided puck if you have too much dust, or chips scattered on your table as it only takes one little chip to break your vacuum seal.

[wayneo]

OK, Thanks Bill, That is good information to know. I guess it would be good to have a variety of each, that way we are covered for any situation!

Have a Merry Christmas Folks!

Wayneo