Vacuum Hold Down

[John S.]

I have read a few of the posts regarding this issue, but now that I have a Bot and no hold down, I need to face the music.

I am cutting 1/2" starboard, basically a plastic cutting board material. I can get 15 repeated elliptical shapes that are 14"x20" on a 54 1/2"x 96" sheet.

I ordered a Fein turboIII vac from Northwest Tools and some gasket material from this place - http://www.allstaradhesives.com - (BTW these guys where really great about helping figure out what i needed.)

My plan is to plumb and gasket the 15 ellipses using the Fein for vacuum. My big question does anyone have a good guess as to if it will work or not? I tried one part (didn't cut though) with a reversed waffle pattern spoil board, fished some gasket material that didn't fit too well through the grid, and plugged in a 5hp QSP shop vac.

The little 4x7 area that I gasketed off held a piece down well enough that I could not pull it off, but I could move the material from side to side if I gave a good push. Could be the crappy gasket material and the fact that it didn't fit too well.

So... one piece was so so, but what of 15 pcs with a little more surface area, proper gasket material and a vac that pulls a little more water? Did I just blow several hundred dollars and add an expensive shop vac to my extensive collection?

Thanks,
John

[papadaveinwy]

John check to see that on your practice piece if the gasket is really above the spoilboard this will cause alot of proublem on sideways movement. When you get your real gasket material you should see a big difference. as those guys that helped you from Allstar more than likely told you too much compression is just as bad as not enough. your gasket needs to compress just the right amount so you have a good seal, too much and you don't seal because you are actually seting on the grid,and the foam is being sucked down more to let air in, not enough and you are set on the foam and will rock while the bot plunges,and cuts. you should have enough vac with the right material including a good grid material: some guys have proublems because they use too porous of a spoilboard for the grid. also remember that when you plumb it in you need to have a bleeder valve of some type or else you will burn up that new expensive vac. David in Wyoming

[gerald_d]

John, you are wasting your time and money trying to create a vacuum holding system for this job. See this post (http://www.talkshopbot.com/forum/messages/27/851.html?#POST4681) (which was repeated here (http://www.talkshopbot.com/forum/messages/29/892.html?#POST5711)). The "secret" is in the programming of the start position, direction and sequence. Think of slicing a loaf of bread - havn't we learnt to cut the first slice furthest away from the hand that is holding the loaf?

[gerald_d]

And you could get 17 out of sheet if you use a 1/2" cutter:


4719

The extra two ovals per sheet can pay off your Fein vacuum.

[gerald_d]

The same cutting logic, except that it is for tiny parts, is explained here (http://www.talkshopbot.com/forum/messages/30/1391.html?#POST8113).

[bill.young]

Hi John,

Gerald's probably right.. if you're only going to be cutting one sheet of these ovals and have to build a vacuum jig from scratch, then using vacuum might not be worth the trouble. Once you build a vacuum table, though, then it's pretty quick to get setup to do any particular job.

Holding with vacuum has a couple of advantages, though. Once you're setup it's quick and easy... no need to worry about putting in screws or placing and moving clamps while you're cutting. The second (and probably biggest) is that it holds the material down to the table, which not only helps when your workpiece is not very flat but also helps to eliminate chatter when you're cutting, giving a smoother edge.


I feel the key to holding things with vacuum (using low-powered vacuum sources like shop vacs at least), is to cut a mask that sits on top of your vac table. It concentrates the vacuum in the areas that you need it and lets you cut all the way through your material without losing vacuum. I use the cheapest material that I can find for masks; 1/8" luaun works well at $6 or so a sheet.


In this drawing the grey-shaded areas are the cutouts in the mask ( the circles hold the waste pieces), and the red lines will be the cut lines for your ovals. It only takes a couple of minutes of offsetting in a CAD program to create the mask and not too much longer to cut..they don't need a lot of detail.

After saying all this, I've cut a bunch of Starboard ( it makes great gears by the way) and there are a couple of reasons that it might not be the best material to try to hold with vacuum. First, it's very slick and slides around so you might have to use tabbing to keep the pieces from moving. In practice I've found that no matter how good your dust collection is, enough shavings get left in the kerf to keep things locked in place.

What might be the biggest problem is surface texture. If the Starboard that you're cutting is the kind with the textured surface then you might have problems holding it down...too many places for air to leak in.

Hope this helps,
Bill


4720

[gerald_d]

Bill, what have you got under the luaun mask? Bleeder top, plenum chamber, zoning and valves, and certainly not a small Fein Turbovac! John is trying to make do with his Turbovac and doesn't look like he has more money or time to throw at this.


He can test the following (at HIS risk):
1. Put 1/2" down spiral cutter in router.
2. Zero x,y at bottom left of table, with router tip slightly into spoilboard when z=0
3. Draw pencil marks to show where the clamps will be - from this drawing:


4721

4. Download, save, and air cut this file (http://www.scapenotes.com/Ovals.sbp). Check if everything is okay, judging by mark left in spoilboard.
5. If everything looks fine, throw plastic on table, put clamps in same place, cut. No clamps have to be moved.

(We normally work in millimeters, and the linked file is in inches, the ovals may have too rough an outline)

[kerrazy]

I have seen Bill's set up at ShopBot in NC, and it works great. The beauty of the Fien Turbo Vac III is that it constantly gets air from an external source to aid in cooling the unit down. This means, less trips to sears for new vacuums.

The masks actually will take the hit from the cutter, so it does not damage your bleeder board. Very effective for repetive cuts, as you create one mask and have it for ever, just throw your work on top and start cutting. just my canadian 2 cents worth which globaly is not worth much. [
]

[gerald_d]

And, if you have lots of sheets to cut, and don't like the plastic build-up that the down-cutter can leave, cut a deep groove in another spoilboard first. The chips move down into the groove.

[bill.young]

Hi Gerald,

I use a Sears shopvac for my vacuum. It was $100 or so when I bought it three years ago or so. The Fein would be a much better vac source...the Sears vacs ( and most others ) are cooled my air flowing through the hose so you should bleed a little air in to help keep it cool. In reality I rarely do, figuring if it lasts a couple of years I've got nothing to complain about.

Since I cut mostly full 4x8 sheets my whole tabletop is the plenum...just a series of grooves in the top sheet of ply with the hose connection coming from undeneath. It's decidely low-tech but will pull a warped sheet of 3/4" ply down firmly to the table top. I use masks when I can, but when I'm cutting something with scarfs that need a precise z-axis setting I just put the sheet directly on the table top and leave a little uncut to trim later with a utility knife.

You can see some pictures of my table at http://www.seasidesmallcraft.com/table.htm

Bill

[gerald_d]

Hi Dale, I didn't notice you slipping in there while I was typing.

Okay Bill, I'll come clean . . . . . . . we do have a vacuum setup! Also runs off a shopvac blower motor (we were too cheap to buy the whole shopvac, we only bought the motor as a spare part for US$25) and we have 8 pipe connections into the table (1.5" pipes). It does a great job of holding a buckled sheet down flat.

But, we never trusted the holding power, and always put on 2 or 3 clamps to make sure that the sheet doesn't slip around. Then, because we had clamps on, and the shopvac motor was noisy, we simply stopped switching on the vacuum.

These days we only use the vacuum to pull down a warped board, and the primary holding power always comes from clamps. (Only one clamp (so far)has a notch from a cutter hitting it).

The key to using clamps alone, is being able to program the cutting sequence and plunge positions of the whole sheet. This is the reason for our tricky love affair with Vector.

Two years ago we bought a huge vane vacuum pump and reckoned we will build a real vacuum system one day - but we have never found a job that desperately needs it. Because we do many odd jobs, it is really useful to have a table top that we don't feel sorry for. we are not shy to put bolts through it when a client brings an ugly railway sleeper for engraving.

My 16 cents South African = 2 cents USA

(Has anyone tried the file yet?)

[bill.young]

Well, since it's confession time, I've been know to use clamps myself, especially to hold partial sheets. My whole-table vac system is a pain if you're trying to hold small pieces of ply for one-off parts and don't want to cut a mask. And I'll agree it sure is noisy, especially with another one runing for dust collection

In reality I've found hold-down to be pretty job-specific. Since I cut mostly full sheets my vac system works best for me, but I've been known to use drywall screws. And a hot-glue gun. And an air-nailer with plastic brads. And double-stuck tape. And some methods that I'm embarassed to admit to in public (in case my insurance agent is reading this!)

Boy, confession IS good for your soul!

Bill

[gerald_d]

You see Bill, Sean does the programming at home in the evenings. And he better do it good, because his old man doesn't enjoy reports of broken cutters, nicked clamps/screws . . . . .

[bill.young]

"You see Bill, Sean does the programming at home in the evenings. "

AH-HA! Now we know who the REAL brains of the operation is!

Bill

[john@mindsightdesign.com]

Okay gents, thanks so much for all of the input. Gerald - Thanks for placing those extra 2 pieces! I have briefly read your post on the bread slicing thing, but still don't quite understand it. I will revisit it... many times. Did you put 1/4" spacing bewteen the the parts? I just got the Bot running last week and have cut only a few parts on it, and have had a little problem with keeping my tolerances, so I left a little extra room around my parts.

Do you have a program that nested those parts or did you do it manually? Also, thanks for the code, I will try it out. Because I am a newbie, I can only guess to copy and paste the code (the link provided only shows me code) to a text file and somehow bring it into the cutting software. The bad thing is that you guys are so helpfull, that I will not learn how to do it myself! But in no way am I complaining!

Bill - I am cutting ten sheets of the stuff. I do not have a plenum chamber type table. I was going to plumb each part directly through my table top into a gasketed spoil board. So you are using a shop vac for your vacuum? You think it will work for this job? Do you think I should make a plenum style table?

How do I post a images or exchange files in this forum?

John

[John S.]

Gerald-
"John is trying to make do with his Turbovac and doesn't look like he has more money or time to throw at this."

You are totally right! But if a little more time is nessary to do it a little better, a little midnight oil is available.

John

[srwtlc]

Hi John,

I had to cut 1300+ pieces of 1/2 Appleply (26 sheets of 4' x 8' 11 ply, dense/hard stuff) into 8" x 8" squares or diamonds (the grain ran from point to point). I made a special two layer vacuum surface out of 1/2" mdf and used some 1/4" foam backer rod in a 1/8" deep groove to create a vacuum area under each diamond. I used a 6hp 25 gallon ShopVac and it held the sheets very tight. At first I thought I would have to place tabs on the parts to keep them from sliding so I planned accordingly, but first tried cutting them without to see if each diamond would stay in place as it was cut free from the rest of the sheet(I needed to save as much time and labor as possible). To my surprise I was able to cut 53 diamonds from one sheet with no movement and nothing but sawdust and triangles from the outer edge left over (I was using a 1/2" compression spiral bit). 8 hours later I had 1300+ diamonds stacked up. I relate all this to say that if you have a need to do alot of the same part often and spend a little time/ingenuity, its nice to be able to put on that specialized vacuum jig and go. Otherwise, I, like Gerald, do so many different types of jobs that I rely heavily on screwing/clamping/wedging/camming for my part holding. My table could double as a sieve with all the screw holes in it.

Heh, Heh, I gotta say hi to Gerald my "Kindred Spirit" and fellow (closet) "Vector lover". Although I was a little hurt to hear your confession..... "You see Bill, Sean does the programming at home in the evenings."...... Hmmm, maybe I need to put on a second shift. Then again maybe not.

[gerald_d]

Hi Scott. Sean is my son (turned 21 this month) and he is the owner of the ShopBot. I bought it for him after he finished school so that he could start a practical career. He now occupies a corner of my company's metalwork shop, and hogs my computer at home at night. But you know how the story goes of fathers buying train sets for their sons......dad does most of the playing.


John, welcome to the family! At this stage of the game I would suggest that you concentrate on learning to use what you already have - and not consider buying any more hardware/software.

I did not add 1/4" between parts, but I think the closest that the parts are to each other is about 0.1" - that should be well within the tolerances of a badly running SB.

I nested them manually using a standard CAD program. Auto-nesting of ellipses is for expensive software only.

When you download my file (that is already a .sbp), tell your browser to Save it to a stiffy disk. Put that stiffy straight into your SB and run the file. BUT, SET YOUR SB ZEROS TO THE RIGHT PLACE FIRST - this file is for a 96 x 54.5 sheet and you don't want to hit the mechanical stops at the other end.

Posting images etc. is explained in the left-side blue block under Using this Forum - Format a Message.

[kfitzgerald@graphicmetalsinc.com]

Please help me out on this "bread-slicing" concept. It sounds fine if you can specify the part cutting sequence, as well as where your cuts start, but I have no control (that I know of) over those things. I am using AutoCAD LT 2002, TurboCad 7 Pro or Rhino to generate the dxf files, then bringing them in to Part Wizard. Do I need some special software to specify part cutting order and starting point?

Regards,

Kevin Fitz-Gerald
Project Manager

Graphic Metals, Inc.
P.O. Box 31
715 East Perry Street
Bryan, OH 43506
Voice 419-636-5757
Fax 419-636-6404

kfitzgerald@graphicmetalsinc.com (mailto:kfitzgerald@graphicmetalsinc.com)

[gerald_d]

Hi Kevin, we do it with a product called "Vector" that ShopBot used to supply with all SB's. Now they have replaced "Vector" with "Parts Wizard" and I hope that the facilities for changing sequence, direction and plunge point have been retained in "Parts Wizard". I would like to believe that all CAM programs offer these basic programming tools, but we only have personal experience of "Vector".

In the example of the ovals above, I spent most of the time in a CAD program (AutoCAD LT2000) to draw the ovals and do the nesting. Then I took the .dxf (of which you see the screen capture above) to "Vector" and literally 2 minutes later (no exaggeration) I had the .sbp code that I offered for downloading. (There has been no editting of the .sbp file after "Vector" produced it.)

[bjw]

Hi Kevin,

I think what is meant by "bread slicing" is that you should cut furthest away from your strongest holding spot on what ever you are cutting. Especially if you are cutting small parts.
I discovered this the hard way. We use a vacuum hold down system and the strongest holding power is in the center of the table. I ordered the cut in a linear progression from one side of the table to the other. What I found was the first row (on the outer right edge) cut very well, but when it got to the last row (far left) I lost allot of parts because they were not held in place.

I also use TurboCAD v7 (7.1)Professional and have Part Wizard. I have yet to find a way to control the cut sequence in PW. What I do is draw the tool path in TC useing colors for different depths and making sure to draw in the sequence I want to cut. Then convert to DXF and take it into SB, convert from there and break it into managable chunks with FE. I then do any other tweaking or editing in either notepad or wordpad. I find this method to allow me total control over the cutting routine.
So when it messes up it's totally my fault (but don't tell my company Pres.)

Hope this helps.

BJ Wilkinson
Kinderworks Corp.

[papadaveinwy]

Cutting Order in turbo cad is easy 1. Just Select all and Click on format 2. Send to front 3. Click anywhere on the screen Then on the Part you want to cut 1ST. 4. Click on format and send to back, It will cut in That order

Or you can do this: The f6 Key selects object in order of creation.When you press f6 the first object created in the drawing will be selected. if f6 is pressed repeatedly turbocad will select each object from the first to the last.When the last object is selected, selection will RESTART with the first object. If an object is already selected when f6 is hit the next object in order of creation will be selected. HOLD Shift key while pressing f6 to select a series of objects. The f7 key selects objects by reverse order of creation. Play with this and you will find more ways to do things. By using the f6 and the f7 together you can select any number of objects by their order of creation. You can determine which objects were created befor or after a selected object. David in Wyoming

[gerald_d]

The trick is to cut the furthest (from the clamp point) component first, but you must plunge nearest to the clamp point on each particular component.

Kevin & David, how would you control where the tool plunges for each oval? Take the top, right oval as an example; if you plunged at 3 o'clock, the oval would start coming loose when you come around to the start position.

And, if components have grain and sharp corners, you want to go anti-clockwise around the outside of a component. How do you non-CAM guys decide clockwise or anti-clockwise? I know that you could use a variation of the TurboCad "send_to_front" technique for each line segment, but even the simple ovals have ended up with over 2000 line segments and that is far too many to manipulate with that technique.

BJ, what is that FE that you speak of? Thanks for sharing your experience of cutting from the perimeter inwards with a vacuum system - I had never considered that.

[toys]

Gerald, FE is simply another way of accessing the editor from the shopbot software. It is the same as the UE command.

[papadaveinwy]

Gerald, I must confess I only was tell how to set your cutting order for Turbo Cad, I don't use that very offten at all. I use a program called VE Lxi master, it is designed to be used for vinyl Plotters; (Free when you buy one of those nasty little machines.)I can nest, change direction of cut, set the staring point. select the cuting order,it is a Cam program, it just dosen't give you z setings manipulation. but save as DXF then set that in the shopbot program I can do all this with about 4 easy clicks. If any thing is to complex for this program ( not very often) then I pull out the Inspire Pro program it does all the above plus is an engraving set up with ALL KINDS of STUFF. David in Wyoming

[gerald_d]

David, you are the third confessor in this thread
. I think that you confirm for us that a real CAM program is very valuable.

The question now is whether Parts Wizard allows you to control:
- parts sequence on a sheet
- the plunge point in each part
- the direction of travel around the part.
BJ mentions that he hasn't found this in Parts Wizard yet - can the Parts Wizard wizards tell us?

(BJ, you will be surprised to hear how few of the SB commands we actually use. We only know one F command and that is FP - our CAM program does all the rest.)

[gerald_d]

This thread has wandered off the original title of "Vacuum Hold Down" into the capabilities of CAM programs (Yes, you can shoot me for that!) and now we are talking Parts Wizard specifically. Therefore I created a new thread (http://www.talkshopbot.com/forum/messages/1038/1458.html?1048569736) at the correct topic of the Forum to continue the discussion of the specifics of Parts Wizard.

[Mayo]

I don't know about Parts Wizard but, Signlab 5 with the router module allows you to control parts sequence, plunge point, direction of travel and depth of cut, etc.

It also allows you to create an "array" of duplicates with settings for how many parts horizontally and vertically, or radially, and whether or not to rotate each part as they move away from the original.

The "array" feature also allows you to control the space between duplicates.

And the Shopbot driver saves the file as a Shopbot .sbp file, so there's no conversion or additional steps.

[gerald_d]

Here (http://www.talkshopbot.com/forum/messages/401/1469.html?1048874165) is how we do the programming in Vector.

[jeff]

Free Vacuum pumps

I just finished setting up my vacuum table using an old discarded air conditioner pump and it works like a charm. One could use a refrigerator pump also. So if you are looking for a cheap vacuum table that is really quiet give it a try.
Remember not to tip it over or all the oil will spill out(I bolted mine down to a small plywood sheet) and the very first time you turn it on, it will spatter a little oil so make sure its not anywhere that you cannot easily clean it up.

Cheers
Jeff

[brian]

Jeff,
I am anxious to see this set up that you are talking about. I'm a old junk man from way back and could probably find an old air conditioner pump. Post a picture if you could.

Thanks,

B.

[christopher@crasshomestead.net]

HELP!!
I am a toymaker. I primarily use my shopbot to cut parts for two of my products.
In the past I would use either brad nails or screws to hold the parts to the table, earlier this year I set up my vaccum table.
My hope was to not have to use the nails or screws again. I have tried several different setups and nothing seems to work quite
the way that I had hoped it would work. What I had in mind is this...
One of my products is cut from 1 1/2" by 9 1/2" pine and 3/4" by 11 1/2" pine. It take four separate runs to complete the project.
Each run requires a slightly different setup. My thought was to setup a template using a full sheet of MDF with stop blocks and
pre-drilled or cut-outs for the vaccum suction. But so far I cannot get a good enough seal to hold each part down after the router
comletes the cut. The vaccum has more than enough suction to hold a full sheet of MDF down to the table to where it is nearly
impossible to pull it up or push it from the vaccum table. I have tried using double stick tape, weather stipping, and a few other
items. Can anyone give me some othe ideas that might work.
I cut approximately 3 to 4 thousand of these parts a year and I need to streamline my operation badly.
By the way the parts are for rocking horses so, they are not small parts they range in size and shape.

Thanks
Chris
-Crass Homestead Collections.
-www.crasshomestead.net (you can see the horses here)

[gerald_d]

Chris, what are you using as a vacuum pump?

(Practically any old system will hold down a big sheet, but when you try and hold small pieces, you need something that can suck a lot harder than a shopvac)

[bill.young]

Hey Chris,

It sounds like a well thought-out system, but I wonder if the problem is the MDF...it's pretty porous so air (and holddown vacuum) is flowing through EVERYWHERE on the surface and not just through the cutouts. You might try sealing the MDF with a couple of coats of paint or polyurethane (including the edges) and see if that helps, or use plywood or something non-pourous instead. And a piece of thin gasket material around the bottom edge of the sheet of MDF might help stop leaks between it and your tabletop.

Oh yeah, if your table top and vacuum plenum are MDF, make sure you seal them as well including the underside...an amazing amount of vacuum can be lost there.

Hope this helps,
Bill

[coastalcarpentry@swfla.rr.com]

Gerald is right a shop vac does vary little for holding small parts. I used one for about six month then a found a used regenerative blower 7 hp. Works great for MDF. I have doors and drawer fronts 6” x 12” with no slip in the holding. When I need to hold a small piece of hard wood for milling I will place the wood for cutting and cover it with a plastic painters drop cloth turn the blower on and cut the plastic around the wood. With the drop cloth method I have held pieces 3” x 96” and cut out 2 ½” circles with no slip.

I bought the regenerative blower used for $450.00 a new one sells for about $ 1,200.00. After using the blower it and knowing how well it works the $ 1,200.00 for a new one is well worth the price.

[jay]

Ryan, I am not sure what you mean.

"I will place the wood for cutting and cover it with a plastic painters drop cloth turn the blower on and cut the plastic around the wood."

Do you mean you place the plastic over the wood then with the bit cut your parts through the plastic?

[coastalcarpentry@swfla.rr.com]

I cut the plastic with a knife the blower will suck and seal the plastic around the wood.

[kerrazy]

still not getting it?
Do you have a picture of this method?
Dale

[Ryan P]

No but i will take one.

[Ryan P]

I will not be able to take a picture until tomorrow. I will try to explain it better. The only way a vac system will work is to seal leaks or have a vac with high volume that can recover from any leaks. I set up a plenum Similar to what shopbot has for the four zone with out the shut of valves. For a bleeder board I use ½” trupan. The vacuum flows through the plenum then through the bleeder board. With this system I can hold down 2’x4’ pieces with out needing to seal the rest of the table. The air volume is high enough to recover from the leaks. If I need to cut any thing smaller I have to seal the leaks in the bleeder board. To do this I use plastic. All the plastic does is stop the air flow through the bleeder board. When I say cut the plastic I mean to fit the plastic around the piece to be cut to stop the leaks. I have also used the plastic as a vacuum clamp. Glue the wood put it on the table put a sheet of plastic over the glued wood turn the blower on. The blower pulls the plastic and the wood down tight to the table wait 30 to 40 min. for the glue to set.

To Christopher Crass your setup should work but I do agree with Bill Young. Try to use a sheet of masonite or some thing that is none pours.

[rgbrown@itexas.net]

Gee, I had been holding parts with less than 25 square inches using a $15 Surplus Center vacuum motor and "poly foam" caulk saving filler as a gasket.

My style mortising jig holds 4 - 3" X 24" pieces and cut 2 ~ 1-1/4" X 1/4" Mortices and a 1/4" slot for the door panels in each piece - with the same $15 motor.

I've held a bunch of parts with efficient vacuum rigs. I've held very small parts with a pump that could hold 25" of Mercury (Hg).

I didn't ever realize it was hard to do...

Ron

[Ryan P]

It is not hard do do. Any vacuum will hold a part that has no through cut but once you cut through you will have leaks and a $15.00 motor will not hold with out riging some sort of jig.

[rgbrown@itexas.net]

"a $15.00 motor will not hold with out riging some sort of jig."

Ryan,

I've been doing this for years. I use no "Jigs". almost all are held flat to the table. The "mortise jig" holds the pieces on the edge with NO "shear stops".

I am using "Surplus Center" Item# 16-1193-E.

When I say I've done something Ryan, it is fact. Pictures of my system have been posted on this forum in the past. I am more intelligent than to cut through a part I need to hold.

Yes, one can use a "high-dollar vacuum pump". And, with simple vacuum systems and a $15 pump, one can't afford the inefficiencies of a bleeder board and other things that can loose the energy created by inexpensive vacuum sources. Many of us have been holding part with "shop-vacs" long before ShopBot started selling vacuum systems. In fact, some of us were using vacuum systems to hold parts and laminate panels years before CNC machines became affordable. We understand flow, leaks and the necessity on nonporous or, probably more correct "semi-nonporous" materials. Under a vacuum of 10 to the minus 6 power Torr, copper starts to "leak". Those pumps, I have one, aren't $15 or even $1200.

Ron Brown

Diplomacy is the art of saying 'Nice doggie' until you can find a rock. - Will Rogers

[coastalcarpentry@swfla.rr.com]

Ron

I do not doubt you are holding your parts with out the use of jigs. As I said any vacuum will hold a part. I am sure you are more intelligent then to cut though. I have also used a shop vac and that worked but I did have to plan my cuts with two passes(I would cut most of the material out with the first pass leaving just a skin for the second pass) and as for small parts I could not cut through. With the blower I do not have to plan my cuts as well and cut with one pass. I am not saying your system does not work in fact I have probably read you previous posts and saw your pictures that have helped me in the past.

I am not saying nice dogie and I am not looking for rocks.

[jay_mack1@hotmail.com]

Ron,

Looked up that surplus center number, do you have a picture of that in use. I'd be interested in seeing how you use it.

By the way, surplus center, is located in Lincoln, Nebraska, less than an hour from here.

And you "children" play nice!

[coastalcarpentry@swfla.rr.com]

Picture of Rons system can be found here. http://www.talkshopbot.com/forum/messages/2/1641.html?#POST9648

I read this when it was posted and used a simular setup only used a shopvac. His motors probably run alot quiter.

Ron I never ment to imply that your system does not work. With the blower I now do not need to use any gasket to seal the grid.

[rgbrown@itexas.net]

Ryan,

I only needed to clarify you don't need expensive things to vacuum hold. There are certain principles that MUST be followed. There are advantages and disadvantages of the gasket systems. And, I'd almost take that bet on the blower. The cheap little blowers with NO shielding make a lot of racket.

[sales@vac-clamp.com]

Hello from Vac-Clamp,
I have been reading with interest the many ways that have been used to hold a workpiece to enable cutting a workpiece. It may well be worth your while to have a look at http://www.vac-clamp.com
We have a new clamp coming out in April (the VC4) which will sell for about USD$51.00 which may solve a number of issues.
All of the clamps are powered by compressed air. This means that they work by venturi effect. The venturi is within the unit itself so it is completely self contained. It also means that the clamps work independently of one another.
Any normal air compressor will power the clamps effectively, and the only part to wear out is the replaceable rubber seal.
Best Regards
Errol Weber
(Vac-Clamp)

[sales@vac-clamp.com]

Hello from Vac-Clamp,
I have been reading with interest the many ways that have been used to hold a workpiece to enable cutting a workpiece. It may well be worth your while to have a look at http://www.vac-clamp.com
We have a new clamp coming out in April (the VC4) which will sell for about USD$51.00 which may solve a number of issues.
All of the clamps are powered by compressed air. This means that they work by venturi effect. The venturi is within the unit itself so it is completely self contained. It also means that the clamps work independently of one another.
Any normal air compressor will power the clamps effectively, and the only part to wear out is the replaceable rubber seal.
Best Regards
Errol Weber
(Vac-Clamp)

[sales@vac-clamp.com]

Hello from Vac-Clamp,
I have been reading with interest the many ways that have been used to hold a workpiece to enable cutting a workpiece. It may well be worth your while to have a look at http://www.vac-clamp.com
We have a new clamp coming out in April (the VC4) which will sell for about USD$51.00 which may solve a number of issues.
All of the clamps are powered by compressed air. This means that they work by venturi effect. The venturi is within the unit itself so it is completely self contained. It also means that the clamps work independently of one another.
Any normal air compressor will power the clamps effectively, and the only part to wear out is the replaceable rubber seal.
Best Regards
Errol Weber
(Vac-Clamp)

[noah@noahsart.co.nz]

Hi all
Nearly all the problems I have ever had with cutting are due to having no proper hold down. I am beginning to realise that there is no substitute for a decent powerful vacuum.
Trouble is the cost.
I wonder if anyone has tried a bank of vacuum cleaner motors, I am thinking eight or twelve, under the table. If they are all pulling into the same plenum chamber will they combine pulling power? Or should they be connected in series?
It seems that a dozen of these are still far cheaper than a 7.5 hp pump. And you can always get more from that surplus place.
Simon

[gerald_d]

Bad news Simon - more motors don't hold any harder, unless you have huge leaks.

[ron brown]

Simon,

Make sure you have not restricted the flow of the vacuum and you have proper gaskets. My new table will have 2 of the ~120 cfm cheap vacuum motors to achieve hold-down of warped sheet goods then swich one off for holding. I am building large, home-made check-valves to keep the air from flowing back through the vacuum motor that is shut down.

When using low-powered motors, proper gasketing is neecssary. As Gerald stated, more motors won't help unless you are cutting through all the parts and loosing some vacuum there.

Ron

[garbob]

Hi Simon,

I haven't used large shop type vacs for vacuum hold down but I do use two in series for dust collection. From what I read, the mechanics of this are: if you use two identical vacuum systems in series you get 100% vacuum capicity from the first and fifty percent from the second and 25% from the third, etc. so as you add you lose overall, I found that two of the largest sears models really suck.

I have never used vacuum hold down becauase I never do the same job twice. It would seem to make sense to cut spoil boards for each job, but that's not economical unless you are doing many sheets.

I have always used double sided tape (http://www.intertapepolymer.com/)at about $7.50 per 100' roll, works great, no residue, but count on $8.00 cost per sheet. They will send samples, you'll be amazed!

Gary

[gerald_d]

Simon wanted a whole lot of motors in the same plenum chamber - that would have been a parallel arrangement, as opposed to the series arrangement described by Gary above.

As can be deduced from Gary's post, adding any amount of extra motors in series will never double the holding power of just one motor.

[garbob]

Hey I wasn't paying attention!

If I remember correctly if the same units are run in parallel there is no increase in vacuum pull but there is a proportionate increase in cubic feet per minute which helps in dust collection.

If you're curious you can find info on the net on the physics of this stuff including a design for a manometere that measures vacuum and velocity, I think. It's been a while since I built one and played with this. I have been so happy with the 2 sears thingees running into 0.3 micron filters that I haven't looked any further for more dust collection. The second unit never even gets the filter dirty!

Gary

[bleeth]

Since this is a vacuum story I'll post it here. Since I got my bot last year I've been using clamps and screws to hold down work and have been working on and off on setting up a vacuum system. I've been using vacuum for pressing veneers and other things(including large boat hull laminations for years and have fond memories of my bosses answer 25 years ago when I asked him "how does it work" Mike-do you know the answer? "It sucks". Over time I've set up my table with an eight zone grid of MDF and a 1 1/2" PVC system with valves hooked to the ubiquitous shop vac. The other day, looking at some of the stuff I was going to be getting into I decided to speed up the process, got out the spray pot and sealed up the mdf. I then threw a sheet of trupan on the table, turned on the vac, and ran the table leveling routine. Much to my surprise I noticed that as the program proceeded I was starting to get some ridges at the corners as the bot was changing directions after the first 6-10 passes. I stared down at this for a while and couldn't see any pattern to the tilt of the ridges. Walked away, scratched my head, turned around, and saw all four corners of my spoil/bleeder board turned up from the table. I love learning a new lesson and this one was: When you surface MDF it starts to act like a veneer job with no balancer. I guess I need a vacuum that sucks more. Mike: You can't get all the answers in advance. When it arrives, unpack it, put it together, try it out, tweak it, and learn learn learn. Like everything else worthwhile-the more we learn the more we realize what we don't know!!!
Dave