Hold down systems or methods

[elijah]

I am new in CNC routing, but I am planning to do hard wood carving in different sizes. I have serious doubts about vacuum hold down system - if I really need it? I was looking for the info on this forum about vacuum, but actually I didn't find the answer for myself. Is it really worth to buy vacuum keeping in mind that I will work with the wood, with small parts (as well as with large)? Is there other methods of convenient hold down the material? I would be thankful for any recommendations.

[ryan_slaback]

Predominantly I use small cams and blocks screwed to the spoilboard. I also use double stick tape for things like small nameplaes etc.

[harryball]

One method I used is to cut a profile out of MDF that will create a pocket for a plaque or part to fit in snuggly. Drop the part in that hole with a bit of 2 sided tape on the back and it's not going anywhere. I've even been able to do it without the tape on a snug fit.

If that doesn't make sense... think about cutting out a part from a sheet of material. The hole left in the board when you pull the part out is the width of the bit larger than the part you just cut out. I use an inside cut instead of outside to create a template pocket that will hold the part. I have to clean up the corners with a chisel for square inside corners.

If you repeat a part, like a name plate, this method does well. You can position the template on the table and secure it in the same place, then keep dropping in and carving names.

Robert

[Brady Watson]

Robert,
You can do what you want with carpet tape alone...the pocket is not necessary.

-Brady

[harryball]

Brady,
I tried taping the plaques down, but the carpet tape does not position the part on the table in the exact same place everytime. I was spending too much time placing the part. I carved 15 horse stall plaques with a drop in holder, after the first 3 I ran the rest with no tape at all and they did fine.

It's nice because I can bulk cut plaques and then use the same file I cut out the holding profile to place the lettering in the same place relative to 0,0 everytime. Drop, cut, pickup, drop, cut, pickup... finished up pretty quick.

For a larger barn sign I did just tape it down and cut the profile out last.

Robert

[Brady Watson]

Now I have a clearer picture of what you are doing. Sounds to me like your jig + vacuum would be a good combo without tape residue.

-B

[elijah]

Thank you Gentlemen, your advices very useful. If somebody has different methods with clamps, tapes etc, would be very interesting to know it. There was mentioned vacuum system - if somebody has experience with universal vacuum hold down system (if such exists at all), also would be interesting to know, because as far as I understood vacuum is very limited in it's application, it means not a universal thing. Keeping in mind its price, I feel that I am not ready to spend money for standard vacuum hold down, because I don't believe that it is worth.

[harryball]

EB,

I've seen a 39 HP vacuum hold down on a 5 x 10 CNC... the entire table surface sucks HARD. If anything, including a quarter, is laid on the surface, it stays where you put it. A sheet of paper is not recoverable while the vac is on. You'd have to scrap it off.

Yes, I think it is worth it if you have the production to drive it and you are cutting parts with flat bottoms. I simply can not afford one yet.

You also have to consider the power to drive it. As I understand, if you get a lower power unit the effect is not the same. Many here use shop vacs. I tried that method and it holds down a sheet of paper very well but it's not enough to hold a plaque in place nor is it enough to drive the entire table. I'm going to try and get a larger shop vac soon. I can see it would be useful in some applications even to have that kind of limited hold down.

However... a 39HP hold down on the full table... that's impressive... any part with a fairly flat bottom will not go anywhere once you drop it on the table.

Robert

[elijah]

Robert,

39HP is impressive of course, but I suppose that surface of the vacuum table, its design, matters a lot.

[Brady Watson]

You don't need anything more than a regular shopvac to hold your pieces and a little bit of ingenuity in PartWizard. The ability for vacuum to hold your part depends on how small it is, and how much of the vacuum's flow is leaking as a result of poor gasketing, open kerfs or other factors.

Do a search on here for vacuum. Take the concepts that already exist & just scale them to fit your application. Vacuum is not magic, although the 1st time you successfully use it in your shop, you will be hooked.

-Brady

[mikejohn]

If the material you are working with will not bend without tremendous force, and this can be as thin as 6m(1/4") or less for many hardwoods, then avoid vacuum. The main force when cutting is in x and y. For irregular shapes use some sort of pallet system to stop all x-y movement, for rectangular shapes simple blocks will do it.
using a downcut spiral and there is little up force. Minimum lateral clamping will hold the piece down enough. If possible, don't cut a blank first, use the waste material for hold down and cut out later, or cut out on the bot using tabs to stop movement.
I have a pallet with sliding stops in T-track. It is unusual to need more than 5 blocks to stop all lateral movement.
If you are cutting thin sheet material, that tends not to lie flat,use a vacuum, but still stop lateral movement with blocks. The only force needed then is to keep the material flat, a lot less than the 40kg (80lbs) of Shopbot lateral cutting force.
A well made pallet takes no time at all in changing material. Often, where parts are smaller than half the table size (which for me is the vast majority of time) I can change material at one end whilst the 'bot is cutting at the other. The Shopbot never stops.

And think what you are doing for the environment



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

[srwtlc]

Here's a setup that gets used on a daily basis. I have a couple of them if I want to run two at a time swapping out one blank while the other is cutting.

Pay no attention to that pathetic looking table top, it's past time to replace it!



7948

[joe]

Scott,

That a neet looking jig and wedge device. I bet it works too.

Joe

[trakwebster]

Has anyone used top & bottom clamps? Here are two examples --

http://store.thesawshop.com/catalogue/default.php?cPath=37

http://www.rockler.com/product.cfm?Offerings_ID=5331

Each is, apparently, a very long clamp functioning something like a pipe clamp though built much flatter. A pair of jaws facing downward clamps onto the ends (or sides) of your table, and then on the top face, another pair of jaws facing upwards holds the work.

The BlackJack clamps look really well made, but the website for the company (http://blackjackcompany.com) has been dead for the last several days.

In CNC Zone forum, there are some pix from a guy who is using them. The link is here --

http://www.cnczone.com/forums/showthread.php?t=23908

I would really like to track this down but have had no luck so far.

Has anybody here used them?

[myxpykalix]

I use the back to back clamps from rockler and they are great, just snap it down and go. I recommend them. I just tried the blackjack website and it works for me.

[trakwebster]

When I go to http://blackjackcompany.com I'm redirected to some other site, where I see the front page, but none of the links work. Maybe somebody is, very slowly, redoing a website, very clumsily. I've cleared the browser, and also used a different one. Other than a front page, no worko for me.

Thanks for the info on the Rockler clamps!

[dingwall]

Arthur, I use the flat type clamps. Instead of back to back, I use the singles bolted to a sheet of mdf that locates on a master fixture box.

They work very well for grabbing sheet stock, neck and body blanks. It helps to line the jaws with some PSA abrasive. The plastic jaws can be a little too slippery.

I got the idea from one of the long time members here.

[billp]

Arthur,
You can also find clamps like this at MLCS (www.mlcswoodworking.com (http://www.mlcswoodworking.com)) They now call them their "Red Boomer"clamps, and they come in sizes up to 50"wide (which fit across most tables nicely).

[trakwebster]

Hi, Bill Palumbo,

Right you are! I spoke today with Steve Siddel, whose company (WorkShop Supply in Ontario Canada) distributes the BlackJack clamps in Canada, and I confirmed that the MLCS 'Boomer' clamps are not only similar, but that they are actually the identical clamps under a different trade name. (Some accessories are slightly different.)

If I were in Canada I'd order from Steve's company (http://workshopsupply.com/blackjack), but they don't ship to the USA.

I've purchased from MCLS several times, and so I'll place an order with them instead. Thanks for the tip!

[mikek]

Woodcraft has Double Clamp Guides in 36" and 50" sizes that clamp to the table AND the item you are trying to hold. The new ones have more features than the 20 year old ones I have.

http://www.woodcraft.com/family.aspx?familyid=5819
7949

[mr_logan]

I made a new spoil board out of concrete foaming board ( 1 1/8" ) and drilled 3/8" holes over the entire surface to a 3/4" depth and 1 1/2" spacing. Then I cut up a couple of 3/8" fiber glass electric fence posts into 1 1/2" pieces to be used as pegs in the holes as needed. I placed a row of pegs along the bottom row and far left row to give me a known zero x and y each time I placed a peice for carving. I zeroed x and y to be at the intersection of the inside edge of the pegs. I hold the piece shug to the pegs with wedges and pegs. By using this system and a zzero plate I am able to remove one piece and install another in a very short time and make accurate cuts. I am having trouble getting my photos in a small enough format to send on this forum, but I would be able to email dirictly to anyone who wishes.

[trakwebster]

I think I've found yet another source for the 'double clamp' sold as BlackJack clamp in Canada and as Boomer Red from MLCS. A blue version of what appears to be the identical clamp is available through Amazon.com from the E. Emerson Tool Company and it's called the 'All In One' clamp.

As of today (9/23/06) it's about $10 cheaper than the red ones from MLCS, and Amazon has a $25 discount on orders over $150 as well.

These things come with t-rails built in, so I assume you can use any t-rail clamp, featherboard, stop blocks, etc.

[jseiler]

Even better, they have the ALLTOOLS coupon code discount + another 10% discount on hand tool accessories. With super saver shipping for four 36" clamps (I have a old pr32), I worked out to 159.76 - 25 - 15.98 = 118.78. Merry Christmas to me.


Thanks arthur for the heads up.

John

[steve4460]

Hi Guys

Check out these guys for hold down vacumm pucks
http://www.nemi.com/grid_table_fixturing.htm

[rhfurniture]

I like their grid plates - any idea how many $$? - or could self cut - maybe in plastic.

r.

[steve4460]

I would call the tool free number and get a price list . They have all kinds of cool stuff, even vacumm pumps etc.

[rhfurniture]

Unfortunately I'm UK, so tool free don't work. But I might email them.


r.

[gerald_d]

A playback (http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=2177#POST2177) from way back....wonder what that patent of Nemi says about grids...