Grooves in Vac Table

[bakerkr]

I'm beginning the process of building my vac table. I have 3/4" MDF bolted to the table, another piece of 3/4" MDF which will be the piece I cut the grooves into and yet another 3/4" piece of MDF to use as my spoilboard.

I'm using a Frued Lettering Bit (Bit #20-174) and plan to have a 2" border around the edge of the MDF and in between each zone. My question is how much distance should be between each set of grooves? I plan on cutting down into the MDF 1/2".

Thanks,
Kevin

[ron brown]

Kevin,

I don't think you have a workable solution from my read. I do not think a Fein, or any shopvac, will pull sufficient vacuum THROUGH a spoilboard. IF you have large vacuum pump you may be able to pull down sheet goods.

I don't have my Freud bit catalog handy, if i ever had one. You gave no indication of the power of your system and there is no information on what you want to hold. These things are somewhat critical to advise someone.

Until one understands exactly what is happening in a vacuum hold down SYSTEM it is difficult to visualize the problems.

Ron

[jhicks]

I heard from Allstar Adhesives that he discovered a material at or after the Ohio camp that he felt was perfect for vacuum table/ spoil boards but he hasnt sent me the details. Am also looking into a material from Vycom thats a closed cell expanded PVC. Lighter weight and apparently affordable. Supposed to be good sign stock as well. If anyone is aware of these or has tried them, please post your opinions. I'll do the same as I learn more.

[richards]

Ron,
The Fein Turbo III does a very credible job of pulling through a spoil board. I start with a 1/2-inch sheet of MDF and then surface both sides. The vacuum board under the spoil board is cut using the standard Shopbot 4-zone file.

Just yesterday I cut a bunch of sheets of particle board using that exact setup. Panels and doors are usually large enough to route in one pass without breaking vacuum. I use tabs on smaller parts to keeps things from moving.

Kevin,
I'm a little puzzled about your choice of using a 60-degree cutter. As far as I understand the whole vacuum concept, the grooves whould be as wide as is practically possible without causing either the spoil board or the material being cut to sag. (The 2-zone and 4-zone shopbot files are ready to use. If you need a different arrangement because of your exact setup, you might want to start with those files as a template and then modify them as necessary.)

[billp]

Mike/Kevin,
Maybe this is a good question to put to those who are of the engineering bent; I have also heard that a V groove makes more sense in a vacuum table as it is really the widest part of the groove that matters when holding things down. "Supposedly" the V groove acts somewhat like a Venturi and helps to maximize vacuum/air flow, while at the same time minimizing the AMOUNT of "air space" which has to be evacuated.
Of course I heard this AFTER I cut square grooved channels in my machine a few years back, but I'd be curious to hear if anyone has opinions (what am I saying,of COURSE there will be a bunch of opinions on this one...), or even better yet; facts based on science (as compared to the CNC equivalent of "urban legends"...).
I've spent much of this past year working on various vacuum techniques, and I think most people tend to UNDERestimate the capabilities of a well engineered, tightly gasketed, vacuum table/jig. I have a few "experiments"in the works which I hope will take things a few steps further. More to follow as things develop...

[gerald_d]

Bill, the word esoteric comes to mind....

May I suggest that the minutiae of channel shape be sidestepped in favour of focussing brainpower on the optimisation of the bleeder board porosity? It might be more fun to debate the channel shape because we can see and measure it, but the hard to see and measure porosity of the bleeder board will have a much bigger impact on the effectiveness of the system.

But, if you insist, the "maximising" of airflow is contrary to the princple of sealing leaks (minimising airflow) so that the pump develops more inches water/mercury. You want as little as possible resistance between the optimal bleeder and the pump - hence biggish plenum chambers. I can't see the advantage of minimising the airspace, except for reducing the time it takes for pump to develop full holding power. You want minimum airflow into the top of the bleeder, but the least resistance to airflow under the bleeder. The bleeding bleeder is the critical thing.

[btk]

Jerry,

I have been using Vycom PVC (AZEK) as a plenum for some time now (with a FEIN III) and feel it works great. Prior to this plenum, I used a piece of HDPE and have nearly identical hold down. After I moved my machine to a new location and damaged the HDPE I used a sheet of AZEK that I had on hand. The AZEK cost $135/sheet vs. the HPDE at over $300.

I use LDF as a spoil board.


I have cut some occasional signage with AZEK, however try to avoid in favor of Celtec or ColorCore due to the availability in a range of colors.



Brian

[paco]

I have tried V slots for my vacuum grids to see if I could ease table cleaning... I've gone back to straight/square slots because V ones we're not much easier to clean and further more they get smaller as table is being surfaced thus need to be re-routed often.

[gerald_d]

BTK, did you actually use "plastic" as a bleeder - ie. did you draw air through the plastic? If so, what type of holes did you have through the plastic?

[Brady Watson]

Gerald,
He is using PVC for the grid...and LDF for the bleeder (here he is calling it a spoilboard).

-Brady

[gerald_d]

Aha, after some googling I learn that LDF is not a plastic. *blush* (It is an unknown term around here)

[btk]

Yes, Brady, thanks for clearing that up.
When I call supply houses, no one knows what I am talking about by LDF (ask for Trupan).
I have seen LDF mentioned as spoil board many times on this forum, so did think to clarify,

By the way, if you do use the PVC as spoil board, two things to expect are (1) two cans full of PVC Shavings. (2) plasticy smell.

As a note, the Trupan also smells strange when being milled. I beleive that someone has pointed out that they use different wood (from south america).

However all being said, I think worth the extra expense (and odor).

Brian

[bakerkr]

I'm beginning to realize this forum doesn't provide much help. I simply asked if anyone had a RECOMMENDATION for the distance between the grooves, yet I get every comment dealing with everthing but the question I asked. All the extra "talking" makes following the posts in here almost impossible.

A few of you actually try and provide useful information and tips, but the vast majority of you just provide useless talk. For those that try to help, thanks, for those who respond to every question simply for the sake of responding thanks for nothing.

There is a difference between a personal opinion and a personal BELIEF.. Maybe a core group of us will start our own Shopbot forum where questions can be answered from people who want to share their experiences.

[gerald_d]

Somebody p---d in your cornflakes this morning?

[Brady Watson]

Kevin,
I can understand your point of view, however keep in mind that many of us, myself included, do not always look at the date on the top of the thread...and only look at the last one or 2 posts since it may be a new question in a similar thread.

To answer your question, the spacing works out pretty well at 1.5 to 2" or so squares. This will vary a little from machine to machine in order to eliminate a partial/non-similar square in the grid, if you follow me. In your SBParts folder there should be 2 files, S_Vac2.sbp & S_Vac4.sbp ~ One for 2 zones, one for 4-zones on a standard 48X96 machine. You can preview these to get ideas for your own setup.

After you have created your grid you MUST seal it with shellac, polyurethane or similar coating in order to retain your vacuum in the grid. The edges are very prone to leaking. After you seal it, machine it flat (just about .01" off ONLY) to clean up any raised hairs, and then coat again.

-Brady

[bob_lofthouse]

Kevin,

Try answering Ron's questions above...

Or simply put a 1/2 inch bit in...

Or read the following thread which you started.

http://www.talkshopbot.com/forum/messages/312/9944.html?1131160489#POST29095

[billp]

Kevin,
By all means see if you CAN create a better Forum than this one....OR use the search function above and see if your question has already been answered a few dozen times before.
You obviously DO have a LOT to learn.....

[mikejohn]

Gentlemen
This Forum has a huge number of very satisfied "members".
Once in a while somebody is going to come along who feels it should be designed just for their particular needs. I am truly amazed at the patience of many responders who, yet again, answer queries that have been answered many times before.
If people tried searching first, spent a little of their own time on the problem, then maybe the forum would be less cluttered.
I understand somebody asking a frequently asked question, and often find it more useful to point towards other threads than reply to the question.
"I'm beginning to realize this forum doesn't provide much help." That is strange, because I am turning out commericial products all the time, making money with the ShopBot, which I certainly could not have done without this forum.
Of course I am guilty to all the charges Kevin makes about "useless talkers"

.................Mike

[btk]

Kevin,

I know it is very hard to follow these complex and dynamic conversations, however here is a hint:

Try looking for the answers that say "Kevin" at the top. Those are for you. Then skip the ones that say "Jerry" or a different name other than yours, as those are most likely meant for other people.

However you are welcome to read the other ones too as this is a public forum and perhaps you can learn something new.


-Brian

P.S.
FYI, As an aside, you say in your post that "There is a difference between a personal opinion and a personal BELIEF.."
Actually according to the Thesaurus, a Belief is a direct synonym of "Opinion".
http://www.answers.com/opinion&r=67

[matt@summitgdc.com]

thats funny stuff. you must admit that there a a few regulars on the forum who are very helpful.
thats said, that is what makes the forum so beneficial to all.

everyone makes a good point in that the forum is what you want to make it. invaluable or frustrating, its up to you.

by the way, Mike and I have a suprisingly similar set-up for our vac systems. and a Fein III is very capable of holding sheets/pcs. in a production setting. I personally used a 1/2" bull nose cutter to cut my grid lay-out.