Any Vacuum Table gurus?

[jeff]

I'm having a vacuum issue, can someone take a look at my file and tell me what I'm not seeing?

The top plate is 3/8" aluminum tooling plate bolted down to the vacuum table and partitioned off with my gasket around the outer.

That's not the problem, when I put my part on top of this, I have zero vacuum holding power.

The part I need to cut is Garolite G10, but I've even tried another 3/8" tooling plate and it doesn't suck that down either.

Thanks!

XXX.MCX-5

[jeff]

A better visual of my top plate that I'm putting my part sheet on.

My sheet covers the entire top.

 

[Leigh @ Kodiak]

I'm far from a Guru, buit the first thing I would try is make a grid of vacuum channel inside your existing channel .

[jeff]

I'm far from a Guru, buit the first thing I would try is make a grid of vacuum channel inside your existing channel .

Do you think that 1 feeder groove coming from the hole isn't enough?

I can put more in, if that's the case.

[crazy^millman]

I'm far from a Guru, buit the first thing I would try is make a grid of vacuum channel inside your existing channel .

 

I have to agree with Leigh here. I am no guru either, but an internal grid to spread the vacuum over the area so the effective area of contact is spread more evenly is what I have done and seen done for years.

[jeff]

Thanks, I'll give that a whirl.

[Colin Gilchrist]

I'd start by making a small pocket where each vacuum port is. Not too big, maybe .500 dia x .250 deep. I'd recommend a grid of vacuum channels inside the vacuum profile, like others have mentioned. Go with .500 pitch between the channels, and mill them with a .125 diameter ball, .0625 deep. (full rad channel depth) That should give you enough vacuum at the fixture location.

 

Also, on your vacuum line going to the fixture, I'd recommend adding a chamber/cavity of some sort, to act as a reservoir for the vacuum, and to catch any coolant that might get past your gasket. In the past I've had a chamber welded up with 1/2" aluminum plate. I think we made them 12" square, by 18" deep. We tapped two 1/4" NPT fittings into the side. The one that leads to the fixture, we put about 4" down from the top, and the one that goes to the pump, we put about 2" down. That acts as a bit of a trap for any coolant...

[Colin Gilchrist]

Also, what does the "chamber" for the fixture plate look like on the back side? Your vacuum line on the fixture port looks tiny. Is that 1/4" OD plastic tubing? You'll want at least 1/4" ID, if not 3/8" ID to feed that thing. You've got that single tiny plastic line supplying vacuum, and that total vacuum gets divided by 12 at the fixture. So each fixture gets only a fraction of the available vacuum.

 

When I build a fixture like this, I put it together as a clam shell design. Top plate 1/2", bottom plate 1/2", and pocket almost the entire back side of the top plate .250 deep. Leave a 1" border around the outside, and make a gasket to fit the outside from some rubber sheet. On the bottom plate, pocket the top .375 deep, and leave a 1" border. Add 1/4-20 cap screws around the periphery to bolt it together (and provide clamping for the gasket).

 

If necessary, run two separate air lines (min 1/4" ID) from the fixture plate to the coolant trap...

[jeff]

I got it to work, for some reason I just had to wait a little longer for the vacuum to take effect.

[jeff]

Also, what does the "chamber" for the fixture plate look like on the back side? Your vacuum line on the fixture port looks tiny. Is that 1/4" OD plastic tubing? You'll want at least 1/4" ID, if not 3/8" ID to feed that thing. You've got that single tiny plastic line supplying vacuum, and that total vacuum gets divided by 12 at the fixture. So each fixture gets only a fraction of the available vacuum.

 

When I build a fixture like this, I put it together as a clam shell design. Top plate 1/2", bottom plate 1/2", and pocket almost the entire back side of the top plate .250 deep. Leave a 1" border around the outside, and make a gasket to fit the outside from some rubber sheet. On the bottom plate, pocket the top .375 deep, and leave a 1" border. Add 1/4-20 cap screws around the periphery to bolt it together (and provide clamping for the gasket).

 

If necessary, run two separate air lines (min 1/4" ID) from the fixture plate to the coolant trap...

This is what we're using.

It's my 2nd job ever using a Vac table, and my 1st one I had no issues with, this one just didn't want to be nice.

http://store.piersonworkholding.com/SmartVac-II-Starter-Package--135-x-20-Base_p_47.html

[Colin Gilchrist]

Hi Jeff,

 

That's perfect!

 

Is there any bow to the material? How rough is the surface? Sometimes those two things can have a great effect on how well a part will hold down. It can also take a small vacuum pump some time to evacuate the air in the lines, and build up a reservoir of vacuum. I typically put a 90 degree ball valve at the fixture, and turn the vacuum pump on with the valve closed, while I do the rest of my setup. That evacuates the coolant trap, and build up vacuum in the system. Then when I put the new part on the fixture and open the valve, it will take much less time to grab the part, and finish purging the rest of the air from the system...

[crazy^millman]

Might look at using a system that has an trap built into it. When you are using a central system it is important to have the system do all it should to protect the pump. I seen a company fill a 300 gallon tank not putting a trap process in place. I talked them into putting in a 100 gallon catch tank with a coil to allow the vacuum to go through with a automatic bleeder. After burning up their Vacuum 5 times they listened and didn't have a problem again. I have used cavities, but find they take way from the strength of my fixture. A tank or a reservoir have seem to be a better option than weakening the fixture to have it in it. Kind of what you do a full Hydraulic clamping system. You build as much volume into the fixture as possible, but the reservoir tanks always seems to be the way to keep a good balance in the system. Cool thing is they can help keep the system cleaner as well.

[jeff]

Hi Jeff,

 

That's perfect!

 

Is there any bow to the material? How rough is the surface? Sometimes those two things can have a great effect on how well a part will hold down. It can also take a small vacuum pump some time to evacuate the air in the lines, and build up a reservoir of vacuum. I typically put a 90 degree ball valve at the fixture, and turn the vacuum pump on with the valve closed, while I do the rest of my setup. That evacuates the coolant trap, and build up vacuum in the system. Then when I put the new part on the fixture and open the valve, it will take much less time to grab the part, and finish purging the rest of the air from the system...

The part is G10, and it's 1/8" thick. Pretty flexible.

After looking at it again, my main problem was that I wasn't pushing down on the material enough all over. It's so thin that I had to put 2 big weights on it to get the vacuum to seal.

1/8 x 13.5 x 20"

[Bob W.]

I'm a guru and even made a vacuum chuck that works in full 5-axis with unlimited B rotation.  Buy a vacuum switch (~$80 from McMaster) and wire it in series with your machine's E-stop.  Wire a relay (one of your spare M-codes) in parallel with the vacuum switch so when that M-code is used it opens the relay making the vacuum switch effective, no vacuum makes the machine alarm like E-stop has been activated.  On all of your vacuum programs put that M-code in the program header.  Trust me, the day will come when someone forgets to turn on the vacuum before hitting cycle start and this method will stop the machine dead in its tracks.  It will also stop the machine if vacuum is lost during machining.

[Bob W.]

Another thing that is important and it looks like it has been mentioned, is a channel inside the sealing gasket to allow air to be pulled by the vacuum.  These sealing channels are critical and they can be used pretty creatively as well.  The vacuum gasket applies lifting force to the part so if you are working on very thin, delicate features the gasket can cause you to break through if you are trying to seal that specific feature.  If you leave out the gasket and put a vacuum groove around the feature you CAN MACHINE THROUGH THE PART COMPLETELY and it will stay stuck down.  Remember, the material is pressed flat by air pressure and along with some coolant it will stay sealed as long as air isn't able to really get underneath it.  The groove, if correctly placed sucks away all air that begins to creep under the part very quickly so the part never has a chance to lift.  The fixture under the feature in question has to be flat with zero grooves, as does the part.  Kind of hard to explain but you can do some pretty crazy stuff with that technique.

[civiceg]

For such small parts, surface area kills you. I would have gotten closer to the oring for your outermost vacuum slot, leaving only a .03-.06 land between oring and vac groove. Then make an aggressively narrow grid pattern inside the outermost vacuum grove. G10 vacuum downs good. 

[civiceg]

 

The part is G10, and it's 1/8" thick. Pretty flexible.

After looking at it again, my main problem was that I wasn't pushing down on the material enough all over. It's so thin that I had to put 2 big weights on it to get the vacuum to seal.

1/8 x 13.5 x 20"

 

I used to do a lot of punched copper blanks on vac fixtures, when 246 blocks didn't do it, the size 12's would. 

[gms1]

If I were making it I would push that outer vacuum chanel closer to the oring groove (.125" max), create a grid centered on your feeder hole every 1/2" or so.

[Mike@Lustre]

nice to see some are getting the vacuum tables to work , we spent weeks trying to get our set-up to work and in the end ended up going to Chick double vices .

[Colin Gilchrist]

nice to see some are getting the vacuum tables to work , we spent weeks trying to get our set-up to work and in the end ended up going to Chick double vices .

 

Hi Mike,

 

You might consider bringing in someone to do some training if you guys were never able to get a vacuum setup working. Vacuum is such a great way to cut parts, especially if they are thin. Once you get the process down, and eliminate whatever issues you have been having, it is one of the best ways to extend your capabilities.

 

As Bob W. mentioned, it is possible to wire in vacuum switches into the process, and have your NC program check to be sure the part is being held down before machining commences.

 

In general, you need the following:

 

• A big enough vacuum pump for the application
• A fixture with enough support, and enough vacuum channels
• A sealing gasket around the outside periphery
• Adequate diameter of vacuum lines, especially if using multiple "stations"
• A vacuum reservoir and "catch can" for any coolant that leaks into the system.
• A vacuum gauge or switch that can either be visually checked, or programmatically verified. (this is really optional, but so handy to have...)
• When mounting a part to the fixture, press firmly (use weights if necessary), and allow a minute or two if necessary to evacuate the lines and reservoir. I find it helpful to have a on/off ball valve installed at the fixture location, to allow you to pre-purge the system (build up vacuum). That means you can load your part, press it down, and then open the valve. There will only be a small amount of air inside the fixture itself, so the vacuum will build up very quickly, and you won't need to hold/weigh the part down as long...

[crazy^millman]

Here is my latest Vacuum fixture work. I had to take an existing one and modify it for a Rev change and add the areas to the radius areas. Using a 1/4 ball endmill for the runners and keeping it at a 30 degree angle to the surface to eliminate Zero Surface speed at the tip. Nice to run 24000 rpms and 400 imp with a 2 flute ball endmill.

 

Pictured deleted to give space to upload files.

[Mike@Lustre]

 

Hi Mike,

 

You might consider bringing in someone to do some training if you guys were never able to get a vacuum setup working. Vacuum is such a great way to cut parts, especially if they are thin. Once you get the process down, and eliminate whatever issues you have been having, it is one of the best ways to extend your capabilities.

 

As Bob W. mentioned, it is possible to wire in vacuum switches into the process, and have your NC program check to be sure the part is being held down before machining commences.

 

In general, you need the following:

 

• A big enough vacuum pump for the application
• A fixture with enough support, and enough vacuum channels
• A sealing gasket around the outside periphery
• Adequate diameter of vacuum lines, especially if using multiple "stations"
• A vacuum reservoir and "catch can" for any coolant that leaks into the system.
• A vacuum gauge or switch that can either be visually checked, or programmatically verified. (this is really optional, but so handy to have...)
• When mounting a part to the fixture, press firmly (use weights if necessary), and allow a minute or two if necessary to evacuate the lines and reservoir. I find it helpful to have a on/off ball valve installed at the fixture location, to allow you to pre-purge the system (build up vacuum). That means you can load your part, press it down, and then open the valve. There will only be a small amount of air inside the fixture itself, so the vacuum will build up very quickly, and you won't need to hold/weigh the part down as long...

 

Hey Colin

 

Thanks for the tips and information , I will save the notes for later use should we go back to the vacuum set-up .

 

Truthfully the 3 double vice set-up has been KING for us , we just swap  the  vice tops and we run 6 different products with this set-up including the parts that where vacuum fixture only .

[SpacePilotPro]

Another thing that is important and it looks like it has been mentioned, is a channel inside the sealing gasket to allow air to be pulled by the vacuum.  These sealing channels are critical and they can be used pretty creatively as well.  The vacuum gasket applies lifting force to the part so if you are working on very thin, delicate features the gasket can cause you to break through if you are trying to seal that specific feature.  If you leave out the gasket and put a vacuum groove around the feature you CAN MACHINE THROUGH THE PART COMPLETELY and it will stay stuck down.  Remember, the material is pressed flat by air pressure and along with some coolant it will stay sealed as long as air isn't able to really get underneath it.  The groove, if correctly placed sucks away all air that begins to creep under the part very quickly so the part never has a chance to lift.  The fixture under the feature in question has to be flat with zero grooves, as does the part.  Kind of hard to explain but you can do some pretty crazy stuff with that technique.

 

If this were applied to his part....and his part had a hole in the center of it...one could use the same setup he has, but without gasket, and an additional groove around the hole feature to isolate it? The isolated hole feature would allow thru cutting then, correct?

[crazy^millman]

If this were applied to his part....and his part had a hole in the center of it...one could use the same setup he has, but without gasket, and an additional groove around the hole feature to isolate it? The isolated hole feature would allow thru cutting then, correct?

 

Correct if you look to the screen shots I put up there are 6 thru hols in that part with over 20 different bosses all have the o-ring groove adjusted to go around them.

[SpacePilotPro]

Correct if you look to the screen shots I put up there are 6 thru hols in that part with over 20 different bosses all have the o-ring groove adjusted to go around them.

 

Do you use a gasket with that fixture? Also...were you using just a 3 axis machine to put the grooves into the curved vacuum surfaces? That is a great looking fixture...lots going on with that one.