[wendtmk]

I've got a machine at the stage where I need to figure how I'm going to hold the work piece to the table. It's a rather unique machine, a Saw Beveler. My build diary sort of begins here: http://clarksclassicflyrodforum.yuku...l#reply-128173. The final stages of the build follow on over on the second page.

The "work piece" is a strip of bamboo, anywhere from about 2' long to around 5' long, 3/8" wide, and about 1/4" thick.

Typically, I see vacuum hold-down tables designed for work pieces that have a goodly amount of surface area, ie flat plates, MDF panels, etc.

Can I use vacuum to hold down a work piece like the bamboo strip, and if so, how would I go about figuring out how many holes per inch, diameter of holes, and anything else?

Thanks,
Mark

[wsa34]

Mark
It would really help to see the part so could give you a better idea how to do it. If you would like to use vacuum to hold the part I have found that .018 spaced at about .375 directly under the contact area will work. The bigger problem is the vacuum pump. A pump strong enough to hold your part can be as much as $2500 (Becker makes great pumps). Smaller pumps might work but I am kind of doubting it. The other way I would try is Roland makes a sticky sheet that you just press the part to it and it holds it tight. I have one and it worked pretty well if you’re not pushing the part to hard. It is used a lot for engraving type work. Stay away from a Pneumatic vacuum table as they use a ton of air. If cost is no object Datron makes a nice vacuum table. (See attached)
Hope this helps.
William

[ger21]

I don't think you'll be able to use vacuum on a thin part like that. For wood you usually use rubber seals, with a recessed chamber inside the seals. You just don't have enough room. If you tried to use just small holes, I think you'd get too much leakage.

I think some type of spring loaded travelling hold down roller might work, but not sure if you could integrate it into the machine design??

[wendtmk]

Mark
It would really help to see the part so could give you a better idea how to do it. If you would like to use vacuum to hold the part I have found that .018 spaced at about .375 directly under the contact area will work. The bigger problem is the vacuum pump. A pump strong enough to hold your part can be as much as $2500 (Becker makes great pumps). Smaller pumps might work but I am kind of doubting it. The other way I would try is Roland makes a sticky sheet that you just press the part to it and it holds it tight. I have one and it worked pretty well if you’re not pushing the part to hard. It is used a lot for engraving type work. Stay away from a Pneumatic vacuum table as they use a ton of air. If cost is no object Datron makes a nice vacuum table. (See attached)
Hope this helps.
William

William,

The part is basically a long skinny rectangle of wood. Don't really have any pictures of it yet, since the machine is not quite ready to start cutting yet, so I don't really have any pieces ready to run through the machine. I thought of the double sided sticky stuff, but when this thing is up and running, I'm planning on cutting several thousand of these strips per year, and not quite sure what the cost on that would be, or the time spent replacing that double sided tape for every strip.

Mark

[wendtmk]

I don't think you'll be able to use vacuum on a thin part like that. For wood you usually use rubber seals, with a recessed chamber inside the seals. You just don't have enough room. If you tried to use just small holes, I think you'd get too much leakage.

I think some type of spring loaded travelling hold down roller might work, but not sure if you could integrate it into the machine design??

Hi Gerry,

I'm trying to stay away from the travelling hold down, since I'd need one in front of the saws and one behind the saws, and I'd still need some kind of system in place to keep the strip from sliding lengthwise. If I have to go that route, I will but I'd rather find a way that doesn't require any more hardware on the moving gantry.

Mark

[stevespo]

Mark,

Even with your narrow pieces of bamboo, I suspect there is a way to hold them with vacuum. I've made a few fixtures with these two products (below) and had good results. One is a thin (1/16") foam gasket sheet that has adhesive on one side. You can apply it to a fixture and then rout thin channels or holes in it.

The other is a (self-stick) rubber material with an anti-slip surface. By combining the two, you can form an air tight seal on small parts and also help prevent them from twisting. A couple of alignment pins or positive stops would also help in that respect. I'll try and take a picture tomorrow, but you may find some examples on the website.

http://www.allstaradhesives.com/prod...d=SBC_CE_06_48
http://www.allstaradhesives.com/acce...s_zgrabber.php

I'm not sure I really understand the nuances of the application, but that is a cool looking machine you're working on.

Steve

[wendtmk]

Steve,

Thanks for the comments on the machine. It will cut a tapered bamboo "spline", which will be glued up typically with five other strips, to make a section of a bamboo fly fishing rod. I currently use a hand plane on each individual strip, taking about 45 minutes per strip to plane to the finished size. I'm working on two rods right now, where the tip top strip will have a flat to apex measurement of about .032" (when glued up, a flat to flat measurement of .064"). This machine will do the same thing in one pass, taking about 30 seconds... ;-)

Would I use both products at the same ime, or is it more likely to use one or the other?

Thanks,
Mark

[stevespo]

I use the two materials together. These pictures may help illustrate what I'm talking about. I cut a series of (connected) grooves in the surface of the fixture and then apply the 1/16" form gasketing material on top. They're connected to the air inlet on the side.

Drill holes or cut slots to open an air pathway. Then I surround the form with the 1/32" thick rubber (anti-slip) material. When you apply vacuum, the form will compress down to the level of the rubber and the rubber will help prevent parts from twisting or slipping under cutting forces.

This little fixture is used to hold pieces of scrap with pearl glued to them, for cutting inlay. The surface area is about 4 sq-in, and the holding power is quite good. Now, I'm not subjecting the materials to much in the way of cutting forces (small diameter bits), but it takes quite a bit of hand force to twist/move the blank. Very difficult to lift up. With a couple of small stops, it would be very solid.

I don't know if this is enough area for your application, with your parts being so narrow - but it might be worth investigating. You could call AllStarAdhesives and see if they may have some ideas as well.

I do understand the application a bit better. You're making tapered, beveled parts. Just saw a nice tutorial on fly rod making and it's a very cool process. Is there an advantage to the dual saw blades that an angled router bit wouldn't provide? I could imagine cutting those strips on my CNC with a 60 degree bevel bit and a fixture to hold the part. You'd then have the ability to make lots of other things on your CNC. I can see the appeal of a dedicated machine, but sometimes general purpose will get you there as well.

Just curious.

Steve

[CNCRouterm]

Have you considered "miter folding" a larger peice? Or, you could use "onion skin" machining techniques. Both are used in the CNC Routing industry frequently. Both are used in conjunction with flow through vacuum holding approaches. Frankly, for as small a part as described, I would reconsider a fixed clamp (assuming that you have to do ONE part at a time). If I were going to try what I think you are doing, I would be inclined to try to cut multiple parts from a blank that was big enough to reliably hold with vacuum, and I would likely use the onion skin approach regardless of miter folding considerations.

[stevespo]

Right - that's a great idea. Provided the blanks are wide enough you could use a single "V" bit and bevel and taper multiple pieces with a single setup. Possibly double, triple, your surface area.

Mark, I know this is not the direction you're headed, but we're just tossing out ideas here.

Steve

[wendtmk]

I don't know if this is enough area for your application, with your parts being so narrow - but it might be worth investigating. You could call AllStarAdhesives and see if they may have some ideas as well.

I do understand the application a bit better. You're making tapered, beveled parts. Just saw a nice tutorial on fly rod making and it's a very cool process. Is there an advantage to the dual saw blades that an angled router bit wouldn't provide? I could imagine cutting those strips on my CNC with a 60 degree bevel bit and a fixture to hold the part. You'd then have the ability to make lots of other things on your CNC. I can see the appeal of a dedicated machine, but sometimes general purpose will get you there as well.

Just curious.

Steve

I'll give AllStarAdhesives a call.

There's a long story behind this whole project. Being a bamboo rod maker makes one a bit of a traditionalist kinda nut to begin with. Back in the good old days, high end production rod makers like Leonard, Payne, and Dickerson used saw beveling machines to cut their splines from the strips too. They didn't have the advantage of using a computer to control the X and Z moments on the machine; they had to rely on a taper bar pulled through the machine at the same rate as the strip to raise or lower the cutting head so that the taper would be cut into the strip. This is my attempt at honoring tradition, while at the same time using modern techniques. The beauty of using a saw beveler rather than a router based cutter is a number of reasons: 1) peace and quiet... ;-), 2) don't need different cutters to cut splines for different rod geometries, ie 4 sided, 5 sided, 6 side, or even 8 sided rods - I just adjust the angle of each individual blade, 3) did I mention it's a lot quieter than a screaming router? ;-), 4) it keeps with the traditional method of cutting splines that the high end rod makers used, and 5) oh yeah, it's a hell of a lot quieter than a 25k rpm router...

I kind of like the idea of a single purpose machine, since it will do one thing rather well, and not a bunch of things okay. And it's a bit too late to change the design now. It's built already, and I've got way too much invested to make that major of a change.

The other problem is the part itself. Bamboo in it's natural form comes in a "tube". It takes quite a bit of strip prep, straightening, pressing the nodal areas so that they're flat and a number of other operations before they can be made into a rod section. The goal here is also keeping the dimensions of the tapered strip + or - .001" from the original taper itself. I can do this now manually with my hand plane and adjustable planing forms. It should be relatively easy for a machine to do that too. That's what makes the work holding a challenge here.

I'll have to dig through some of my old photos of the early machines and show you guys what the old masters did. Pretty neat stuff.

Mark

[skippy]

Surely you couldn't beat a carbon fibre rod with a bamboo veneer?
Ok guys, just joking..... By the way, nice projects and interesting reading!

[stevespo]

I completely understand the appeal and strategy of merging the old methods and new. That's something I'm always attempting to do with my own work. I was a dedicated hand tool user for many years, until the CS/ME/EE side of my brain exerted control and moved me towards robotics.

I've really come to appreciate the "general purpose" nature of a CNC router. It has the ability to replace (nearly) every template and jig in the shop. The speed, accuracy and repeatability can't be beat.

If noise is such a concern, an inexpensive (and still very accurate) VSD and spindle can run at high speeds and maintain very low noise levels. For the type of work you're doing, the dust collection is going to be louder than the spindle. Even a good quality router running at 12K RPM is really not so loud. Just another thing to consider.

Also, you can get V-bits with many different angles (or have them ground to spec). Swapping out a single bit is going to be much faster and accurate than adjusting 2 saw blades. I know that this type of efficiency is not really what you're after, but I'll mention it anyway.

Personally, I'm looking forward to seeing some video of your machine in action. Very cool.

Steve

[CNCRouterm]

Hello Steve,
No dissagreement on reducing the number of tools for a job! That said, my router is a lot quieter than my cabinet makers saw! Dust collector doesn't really count as it should be used for either, but when I include the vacuum pump, then it just depends on where you stand to decide which is more annoying. Now, using a HAND router, even when new it is noisy.
The noise generated by the cut is comparable, though I would say most materials cut with more noise generated on the table saw than the CNC router. I suppose it depends a lot on what saw is compared to what CNC router though.

[wendtmk]

Surely you couldn't beat a carbon fibre rod with a bamboo veneer?
Ok guys, just joking..... By the way, nice projects and interesting reading!

Good Lord! I'd never be caught dead fly fishing with a rod birthed from a test tube, designed by Monsanto, and marketed and sold by Tupperware!

Mark

[wendtmk]

Steve,

Nothing against routers, except for the noise. I really don't need another multi-purpose machine in the shop, rather need a single task oriented machine for what I want it to do. I have the lathe and milling machines for tackling the other projects... ;-)

Mark

[wendtmk]

Silly arsed question about vacuum pumps. Lets say I have two identical vacuum pumps ganged. Will that theoretically double my CFM? I realize vacuum pull in inches theoretically won't change, but will this effectively double my CFM?

Thanks,
Mark

[CNCRouterm]

Mark,
If ganged in parallel, and for a given pressure, then I would say yes, you would have XX cfm per pump. If you were to run them in series, then (depends a lot on what kind of pump) you would not see much if any difference in cfm, but the max Hg vacuum likely would draw down further than with just one. Up until the point where the pump closest to the atmosphere inlet over heated and siezes up, shredds vanes, or whatever it's failure mode exhibits.

I have a twin table, each is 63" x 63" and one 25hp Travaine liquid ring vacuum pump (around 350 cfm, max 27-28 Hg vac). For most jobs that I run, this works pretty well, though on occasion I wish I had gotten the 40hp version or twin 25s, one per table. I have heard of some operators who will run two 40s, one per table, piano makers I think.

There is actually a lot more to vacuum clamping than just horsepower. What needs prompt your question?

[wendtmk]

Eric,

I'm thinking of making a setup either like this one or something similar:
http://www.joewoodworker.com/veneering/EVS/concept.htm and I just happen to have two Gast vacuum pumps laying around that I think are 3 CFM units. I figured if I could gang them together, the evac process would be that much quicker, and since I have them already laying around, cheaper than buying a new pump with the higher CFM rating.

Mark

[CNCRouterm]

Ok Mark,
You may not need both, but the premise is sound. Have you conducted any simple experiments yet with the pumps and the application? Something like a seeing how long it takes one pump to draw down a vac bag of the size you anticipate using? The reservoir tanks will help with initial snap down. The first CNC I ever ran used a pair of 5 hp ganged rotary vane pumps. It was set up such that under high demand both would run, under low demand only 1, and they would alternate based on duty cycle.

For your project:

First off, you will want to determine if the pumps will pull enough vacuum to do the job, the volume will be secondary. If they don't pull enough vac, it is a moot point.

Secondly you may want to determine if you need one or two. Conduct an experiment or two to confirm both absolute pressure performance and practical volume capabilities (assuming that there is no data-plate, or you don't know how to interpret whatever data is available).

Opinion.

Unless the pumps are very low performance (in terms of absolute pressure capacity), I think that one pump will be enough for most projects smaller than 4' x 4', as long as you can tolerate a minute or two of marginal clamping force while it fully draws down.

Disclaimer.

The only vacuum bagging I have done is with my CNC router table and the attached 25 hp Travaini. Worked swell, but it of course meant the pump ran continuously during the process, and the router was not making any "router" revenue during the process.

Resources.

Lots of places, but Graingers or McMaster Carr come to mind quickly for things like tubing, fittings, vacuum gauges etc.